Seismic Volcanostratigraphy: The Key to Resolving the Jan Mayen Microcontinent and Iceland Plateau Rift Evolution

Volcanostratigraphic and igneous province mapping of the Jan Mayen microcontinent (JMMC) and Iceland Plateau Rift (IPR) region have provided new insight into the development of rift systems during breakup processes. The microcontinent's formation involved two breakup events associated with seven distinct tectono‐magmatic phases (∼63–21 Ma), resulting in a fan‐shaped JMMC‐IPR igneous domain. Primary structural trends and anomalous magmatic activity guided initial opening (∼63–56 Ma) along a SE‐NW trend from the European margin and along a WNW‐ESE trend from East Greenland. The eastern margin of the microcontinent formed during the first breakup (∼55–53 Ma), with voluminous subaerial volcanism and emplacement of multiple sets of SSW–NNE‐aligned seaward‐dipping reflector sequences. The more gradual, second breakup (∼52–23 Ma) consisted of four northwestward migrating IPR (I–IV) rift zones along the microcontinent's southern and western margins. IPR I and II (∼52–36 Ma) migrated obliquely into East Greenland, interlinked via segments of the Iceland‐Faroe Fracture Zone, in overlapping sub‐aerial and sub‐surface igneous formations. IPR III and IV (∼35–23 Ma) formed a wide igneous domain south and west of the microcontinent, accompanied by uplift, regional tilting, and erosion as the area moved closer to the Iceland hotspot. The proto‐Kolbeinsey Ridge formed at ∼22–21 Ma and connected to the Reykjanes Ridge via the Northwest Iceland Rift Zone, near the center of the hotspot. Eastward rift transfers, toward the proto‐Iceland hotspot, commenced at ∼15 Ma, marking the initiation of segmented rift zones comparable to present‐day Iceland.

To address the complex tectono-magmatic evolution of the JMMC and the Iceland Plateau Rift (IPR) region, we reviewed and interpreted seismic reflection and refraction data combined with gravity and magnetic anomaly data, multibeam bathymetric data, as well as stratigraphic, age and petrochemical data from borehole and seafloor samples.Of particular note in this review is the inclusion of expanded spread profiles (ESP) to better constrain the regional velocity interpretation.Our volcanostratigraphic model was constructed by comparison with igneous formations of the Mid-Norwegian margin (Vøring and Møre), the Faroe Islands, the Greenland-Iceland-Faroe Ridge Complex (GIFRC), and the north-eastern margin of the Blosseville Kyst of central East Greenland (Figures 1-3).Our model portrays igneous processes associated with the opening of the central Northeast Atlantic throughout the Cenozoic and complements previous palaeoenvironmental reconstructions by Blischke, Gaina, et al. (2017), Blischke et al. (2019).
The primary objective of this study is to describe volcanostratigraphy in context to the tectono-magmatic processes associated with the dual-breakup and formation of the JMMC in correlation to the comprehensive geological and geophysical data record.High-resolution kinematic reconstructions of the JMMC-IPR domain will provide new constraints on the gradual rift-transfer processes that separated the JMMC from East Greenland.We also address how pre-existing structural complexities and/or rift-hotspot/plume processes might have affected spreading obliquity and changes in rift transfer within the JMMC-IPR and GIFRC domains, thus contributing to the ongoing discussion on microcontinent formation (e.g., Gaina et al., 2003;Gaina & Whittaker, 2020;Müller et al., 2001;Nemčok et al., 2016).
Mayen Basin, the Jan Mayen Trough, and the Jan Mayen Southern Ridge Complex (Figure 1).The Jan Mayen Ridge is a well-defined, continuous, 70-80 km wide, flat-topped structural block, and bathymetric high.The highly eroded Lyngvi Ridge narrows southwards to ∼10 km width, where it is abruptly truncated.The Jan Mayen Basin is divided into a northern segment, west of the Jan Mayen Ridge, and a southern segment, west of the Lyngvi Ridge.The NNE-SSW-oriented Jan Mayen Trough widens toward the south-southwest and separates the Lyngvi Ridge from the Jan Mayen Southern Ridge Complex.The latter is composed of several ridges which locally protrude northwards into the Jan Mayen Trough but become indistinct to the south.The northern edge of the JMMC is bordered by the Jan Mayen Island volcanic complex, between the eastern and western segments of the Jan Mayen Fracture Zone (Svellingen & Pedersen, 2003).The eastern margin of the JMMC, which originally developed as the outermost part of the continental shelf of central East Greenland (73°N-68°N), is characterized by eastward-thickening Paleogene strata and basaltic lava flows that dip steeply toward the Norway Basin (e.g., Åkermoen, 1989;Blischke et al., 2019;Erlendsson, 2010;Gairaud et al., 1978;Gunnarsson et al., 1989;Peron-Pinvidic et al., 2012a, 2012b;Skogseid & Eldholm, 1987).The western margin of the JMMC developed by rifting within the Greenland continental shelf, in association with the Paleogene igneous province of the Blosseville Kyst and the Paleozoic-Mesozoic Jameson Land Basin (e.g., Blischke & Erlendsson, 2018;Larsen & Jakobsdóttir, 1988;Larsen et al., 1989Larsen et al., , 1999Larsen et al., , 2013)).
Volcanostratigraphic sections of the JMMC were compiled using seismic refraction and reflection data (Brandsdóttir et al., 2015;Breivik et al., 2012;Johansen et al., 1988;Kandilarov et al., 2012;Kodaira et al., 1998aKodaira et al., , 1998b;;Mjelde et al., 2002Mjelde et al., , 2007;;Olafsson & Gunnarsson, 1989) and shallow offshore boreholes, as well as information derived from previous analysis of the stratigraphic framework (Blischke, Gaina, et al., 2017;Blischke et al., 2019;Peron-Pinvidic et al., 2012a).In addition, ESP data from the ESP-5-L-DGO survey by Eldholm and Grue (1994) and IFP86 (ESP-121 to 128 on Figure 3) were analyzed using the travel-time-to-offset-ratio (e.g., Childs & Cooper, 1978) and the Vp velocity estimation methods of Diebold and Stoffa (1981).The resulting average ESP velocity values were correlated with the velocity facies domains of the JMMC to separate older Jan Mayen Ridge domains from igneous domains along the eastern breakup margin, within the Jan Mayen Basin, the Jan Mayen Trough, and the Jan Mayen Southern Ridge Complex (Figures 1, 3 and 4; Supplements 2, 6b in Supporting Information S1).Volcanostratigraphic interval velocity domains were defined for each velocity profile and tied to the interpretation of nearby seismic reflection profiles, providing a more robust definition of the structural setting, since velocity alone is not necessarily a definitive indication of the crustal type (Figure 4).

Seismic Volcanostratigraphy
The existing Cenozoic stratigraphic framework for the JMMC area (e.g., Blischke et al., 2019;Gunnarsson et al., 1989) was expanded by detailed chronostratigraphic appraisal of the igneous succession, based on seismic reflection, refraction, and potential field data interpretations.Our volcanostratigraphic characterization is based on methods developed by Hinz (1981), Symonds et al. (1998), Planke et al. (2000Planke et al. ( , 2015)), and Bischoff et al. (2019) with facies types and units identified by their shape, reflection patterns, and boundary reflection characteristics, within a chronological context.This approach facilitated mapping and identification of volcanic units, such as subaerial lava flow, SDR sequences, inner and outer SDR subsets, igneous centers, sill and dike complexes, volcanic vents, and axial rift zone structures Supplement 2,6,7 in Supporting Information S1).

Bathymetry
Our study included bathymetric data from two high-resolution multi-beam echo-sounder surveys conducted across the Jan Mayen Ridge and Jan Mayen Southern Ridge Complex in 2008 and 2010.Surveys A8-2008 and A11-2010 were acquired by the National Energy Authority of Iceland (Orkustofnun), the Norwegian Petroleum Directorate (NPD), and the Marine Research Institute of Iceland (HAFRO).In total, 10,500 km 2 of 50 × 50 m gridded bathymetric data was acquired with a depth range of 790-2,210 m (Blischke, Gaina, et al., 2017;Blischke et al., 2019;Helgadóttir, 2008;Helgadóttir & Reynisson, 2010).Data collected by the French Hydrographic and Oceanographic Office (SHOM) cruise NARVAL-2016 onboard R/V Beautemps-Beaupré in 2016 across the Jan Mayen Trough, Jan Mayen Southern Ridge Complex, and the Iceland Plateau Rift was also included (Figure 3; Supplement 1).The NARVAL survey acquired 35,000 km 2 of 50 × 50 m gridded bathymetric data, sub-bottom profiles, and magnetic data (Dupuy & Sogorb, 2017), providing important constraints on shallow structural trends and volcanic rift segments (Figure 1).
High-resolution multi-beam and ship-track bathymetry data were combined with satellite data and the international bathymetric chart of the Arctic Ocean (IBCAO) Version 3.0 with a 500 × 500 m resolution (Jakobsson et al., 2012).Bathymetry data were converted to two-way-travel time depth for comparison with seafloor depths obtained from seismic reflection lines (Figure 3).The compiled bathymetry data was used to delineate visible structural trends and igneous features at the seafloor.

New Petrology Data and Analysis
A total of 19 samples from DSDP sites 348 and 350 were analyzed at the universities of Iceland and Aarhus to better constrain interpretations of petrological composition for comparison to seismic reflection volcanic facies types (Supplement 5 in Supporting Information S1).At the University of Iceland, seven samples were analyzed for their major element compositions SiO 2 , Al 2 O 3 , FeO, MnO, MgO, CaO, Na 2 O, K 2 O, TiO 2 , and P 2 O 5 ) using inductively coupled plasma-optical emission spectroscopy (ICP-OES; SPECTRO CIROS) and methodologies similar to that described by Govindaraju and Mevelle (1987) and Halldórsson et al. (2008).The remaining 12 samples were powdered at Aarhus University (steel press and corundum mortar) and the compositions of whole-rock compositions were measured at Bureau Veritas Commodities Canada Ltd. by X-ray fluorescence (major elements) and by inductively coupled plasma-mass spectrometry (trace elements) as described by Tegner et al. (2019).

Chronology
Published geochronology data from offshore boreholes (DSDP Leg 38 sites 336,337,345,348 and 350) and onshore data (e.g., Ganerød et al., 2014;Kharin et al., 1976;L. M. Larsen et al., 2013L. M. Larsen et al., , 2014;;Talwani, Udintsev, & White, 1976;Talwani, Udintsev, & Shirshov, 1976;Talwani et al., 1976aTalwani et al., , 1976bTalwani et al., , 1976cTalwani et al., , 1976d, 1976e, 1976f, 1 976g, 1976h;, 1976e, 1976f, 1 976g, 1976h;Tegner et al., 2008) were reviewed.Large error margins and age ranges in K/Ar dating from DSDP Leg 38 boreholes 348 and 350 (Kharin et al., 1976) prompted resampling of these cores for Ar-Ar dating and geochemical analyses to constrain the timing of the ridge transition along the southern edge of the JMMC and the Iceland Plateau Rift.Middle Eocene basalts were sampled from core 350 located at the southeasternmost extent of the Jan Mayen Southern Ridge Complex, and lower Miocene basalts were sampled from core 348 located along the western igneous margin of the microcontinent (Figure 3; Supplements 2-5 and 6b in Supporting Information S1).Eight igneous rock samples were selected and described at the IODP core lab in Bremen (Germany), and thin sections were analyzed at the Iceland GeoSurvey's petrology lab.The whole-rock basalt samples were dated at the Oregon State University Argon Geochronology Laboratory (Supplement 3 in Supporting Information S1) through incremental heating in the 40 Ar/ 39 Ar Heine resistance furnace connected to the mass analyzer products (MAP) model 215-50 mass spectrometer.

Kinematic Modeling
Plate-tectonic reconstructions for the relative motion of JMMC with respect to its conjugate margins were obtained using the interactive fitting method of GPlates (https://www.gplates.org;see also Gaina, Nasuti, et al., 2017) and GIS visualization for each reconstruction stage (∼56-55 Ma; ∼55-49 Ma; and 33-21 Ma).To derive the relative motion of the JMMC tectonic block, the larger-scale kinematic reconstruction of Greenland, Eurasia, and the JMMC of Gaina, Nasuti et al. (2017) was used as a starting point, and local adjustments were derived by fitting the data on a GIS platform.The opening of the Norway Basin and the evolution of the AEgir Ridge system were based on the high-resolution magnetic data interpretation by Gernigon et al. (2015).Detailed kinematic reconstructions for the separate JMMC tectonic blocks were tied to the chronostratigraphic succession and best fit of the fault and block topography in chronologic order based on Blischke, Gaina, et al. (2017), Blischke et al. (2019).

The JMMC Seismic Volcanostratigraphy
Volcanostratigraphic units were defined on their chronological context, shape, and seismic reflection patterns, in line with methods developed by Larsen and Jakobsdóttir (1988); Symonds et al. (1998), andPlanke et al. (2000) for the NE-Atlantic region.
Figure 6.Key seismic reflection cross-sections of the JMMC igneous domains: (a) E-W profile from the Jan Mayen Island igneous complex (JMI), across the northern Jan Mayen Ridge (JMR) and into the East Jan Mayen Fracture Zone (EJMFZ); (b) ENE-WSW profile across the eastern flank of the Jan Mayen Ridge, the East Jan Mayen Fracture Zone and Eocene volcanic complex; (c) E-W profile from the southern Jan Mayen Ridge across the northern Jan Mayen Trough (JMT) and the Jan Mayen Southern Ridge Complex (SRC); and (d) N-S profile from the southern termination of Jan Mayen Southern Ridge Complex into the Iceland Plateau Rift (IPR) system.Bold red lines represent sill or dike intrusions, OBS seismic refraction profile legend as in Figures 1 and 3. (e) E-W seismic reflection profile (A-A´) across the Iceland Plateau Rifts, between the AEgir Ridge and proto-Kolbeinsey Ridge (PKR).Major sediment unconformities are delineated.The IPR-I and IPR-II rifts represent structurally segmented initial stages of the AEgir-Kolbeinsey rift transition, mostly intrusives within nascent axial rift segments, whereas IPR-III and IPR-IV represent more typical oceanic rift domains.Lower left: Magnetic intensity anomaly map from Nasuti and Olesen (2014) showing profile A-A´ in yellow and the KRISE reflection-refraction profile in red.Lower right: The KRISE crustal velocity structure (Brandsdóttir et al., 2015).Sediment-basement boundary (iso-velocity contour 4 km/s), upper-lower crustal boundary (iso-velocity contour 6.5 km/s), and iso-velocity contour 7 km/s are indicated with white, purple, and red lines, respectively.The IPR rifts are underlain by high-velocity lower crustal domes (275-425 km along profile).A marked increase in sediment and lower crustal thickness between OBS48 and OBS50 is attributed to the oldest part of the profile (i.e., west of magnetic anomaly C24).The 2D multi-channel seismic reflection data is based on the NPD 2011 survey, ICE02, 2009 reprocessed data set of the JM-85, and WI-JMR-08 surveys.Base map: Bouguer gravity (Haase & Ebbing, 2014), magnetic polarity chrons *1 Gaina, Nasuti, et al. (2017)

Landward Flows-Flood Basalts
Uniformly layered flow sections within the seismic records that underlie the inner SDR wedges or occur as a landward continuation from the SDR wedges onto the Jan Mayen Ridge segments are interpreted as early Eocene plateau basalts (Figures 5b and 5c; Supplement 2.5c in Supporting Information S1) These flow units display sheet-like and relatively smooth seismic reflections with high amplitudes that are assigned to subaerial and shallow marine inner flows as described by Abdelmalak et al. (2015) for the Vøring margin.These flood basalt reflections vary locally but are generally sub-parallel.Prograding seismic reflections, observed toward the northeast flank and eastern margin of the Jan Mayen Ridge, reflect lava and/or deltaic seismic units (Figures 6a-6c).Younger, late Oligocene to early Miocene flood basalt units form flat-lying marker horizon within the Jan Mayen Basin, Jan Mayen Trough, and south of the JMMC (Figure 5d; Supplements 2b, 2c, and 6e in Supporting Information S1).The flood basalts within the southern Jan Mayen Basin overlap older rift segments (Figure 5d), Oligocene sediments, and volcanic strata (Supplements 2c, 6e in Supporting Information S1).

Igneous and Volcanic Complexes
The outer high igneous centers are characterized by chaotic internal seismic reflection patterns and a strong top reflection.They appear as mounded or sloping shapes and can form circular features on magnetic and gravity datasets, especially along the north-eastern flank of the Jan Mayen Ridge (Figures 6a and 6b; Supplement 6a in Supporting Information S1) where an igneous center appears to have been active over a long-time-interval, apparently linked to a segment of the East Jan Mayen Fracture Zone (Figures 5a and 6b).This igneous complex is aligned with magnetic anomaly C24r (∼55 Ma) (Gaina, Nasuti, et al., 2017).
The Jan Mayen Island igneous complex is also characterized by homogenous and chaotic seismic reflection patterns, apparent deep-seated high-amplitude reflections, and young volcanic complexes that pierced through older igneous sequences (Figure 6a; Supplement 2 in Supporting Information S1).A younger volcanic center along the western boundary of the JMMC is clearly observed on seismic reflection and refraction data and possibly relates to the early Miocene proto-Kolbeinsey Ridge breakup margin (Figure 4b; Supplement 2 in Supporting Information S1).Other Neogene to Pleistocene volcanic centers along the northwestern margin intruded into an interpreted Eocene igneous section and form near-surface volcanic cone structures (Figure 6a).

Intrusives
Smaller-scale igneous intrusions, related to dikes and sills, are typically observed as local, often isolated, low frequency, high amplitude reflections that terminate abruptly, and are commonly connected to vent structures (Figures 5 and 6; Supplement 6 in Supporting Information S1).Their structural disposition ranges from semi-parallel to stratigraphic layering or along fault planes to discordant and crosscutting the strata as "smiley" shaped features, specifically along the JMMC eastern flank, the Jan Mayen Southern Ridge Complex (Figures 5a, 5b  and 6), the Jan Mayen Trough, and within the Jan Mayen Basin.

Volcanic Ridges-Axial Rift Zones
Volcanic ridges and axial rift zones characterize the Jan Mayen Southern Ridge Complex and Jan Mayen Trough regions, where they form up-doming structures of volcanic material close to fault or fracture zones.They are located mostly in the southern area of the Jan Mayen Southern Ridge Complex and along the northern end of the Jan Mayen Trough and are visible on seismic reflection and bathymetry data (Figures 1, 5b, 5c and 6b-6d).They appear both as centralized structures within the Jan Mayen Trough and along large fault zones that serve as conduits of rising magma, causing deformation and uplift of the overburden.A higher density of smaller-scale intrusions within nearby sedimentary strata appears to be associated with these conduits.

DSDP Leg 38 Site 348
DSDP Leg 38 site 348 is located within the oldest oceanic crust of the Kolbeinsey Ridge and serves as a control site west of the JMMC (Figure 1; Supplement 3a in Supporting Information S1).At site 348, 17.4 m of fractured but homogenous basalt section was penetrated at 526.6 m below the seafloor.Geochemical analysis by Kharin et al. (1976), Ridley et al. (1976), andMohr (1976) revealed abyssal tholeiites and dike or sill complexes.
Core resampling and thin-section analyses (Supplement 3a in Supporting Information S1) also showed finely crystalline olivine-tholeiite with volcanic glass (now replaced by smectite) close to the basalt/sediment contact, indicating that the intrusions penetrated the overlying sediments.The basalt is slightly porphyritic, with micro-phenocrysts of plagioclase and olivine, the latter now pseudomorphed and altered to iddingsite.Many plagioclase crystals exhibit skeletal growth and a "swallow-tail" morphology.Combined with the apparent glass content, this suggests that the basalt cooled rapidly (e.g., Lofgren, 1974).Clinopyroxene and opaque minerals are unaltered but exhibit dendritic or feather-like morphology deeper in the cored section, which is common for ocean floor basalts (e.g., Lofgren, 1983).The lowermost section consisted of fine-to medium-grained crystalline, aphyric olivine-tholeiite with large vesicles, possibly indicating rapid surface ascent as sills or dikes; a conclusion also reached by Kharin et al. (1976) and White and Schilling (1978), who argued that the absence of lava-flow characteristics, including pillow structures and glassy rims, did not support a submarine extrusion.
The K 2 O and Na 2 O content of DSDP site 348 basalts fall within the Mid-Ocean Ridge Basalt (MORB) field on the total-alkali-silica (TAS) classification diagram (Le Bas et al., 1989) (Figure 7a), along with samples from the AEgir-, Kolbeinsey-and Mohns ridges, as well as the Tjörnes Fracture Zone (TFZ; purple field in Figure 7a).TiO 2 ranges from 1.29 to 1.65 wt%, K 2 O from 0.02 to 0.08 wt%, and MgO between 6.02 and 8.25 wt%; values considerably lower than samples from the Jan Mayen Fracture Zone, Vesteris Seamount, and Vøring Plateau.Basalts from the Iceland Plateau Rift (DSDP site 350) and northern volcanic zone of Iceland are considerably higher in K 2 O and slightly higher in TiO 2 than site 348.

DSDP Leg 38 Site 350
The basalt section sampled at DSDP Leg 38 site 350, at the southern tip of the easternmost Jan Mayen Southern Ridge Complex (Figures 1, 7 and 8; Supplements 3b; 4 and 5 in Supporting Information S1), was recovered from an acoustically opaque layer between 362 and 388 m below the seafloor.The 26-m-thick section was initially described as a thick layer of highly altered tuff breccia with chlorite, zeolites, calcite, and doleritic basalt at its base (Kharin et al., 1976;Raschka et al., 1976;Ridley et al., 1976).The uppermost section consists of 95% basalt breccia with angular fragments of altered and phyric hyalobasalt (partly altered to palagonite) with plagioclase, pyroxene, and altered olivine crystals (Raschka et al., 1976).The deeper section at site 350 consists of very fresh, holocrystalline, fine-to medium-grained basalt, with rare plagioclase and pyroxene phenocrysts (2-5 mm), thin chlorite-calcite veins, and slickensides.The basalt has a homogenous appearance with various textures including micro-porphyritic, sub-ophitic, and trachytoid (Raschka et al., 1976).Core resampling and thin-section analyses (Supplement 3b in Supporting Information S1) showed that the basalt fragments have a thin chlorite-calcite-zeolite-smectite edging coated evenly on all sides.The breccia is cut by white-yellowish layered calcite veins with occasional pyrite occurrences.Geochemical analyses show elevated TiO 2 (2.09-3.09wt%), K 2 O (0.45-1.41 wt%), and slightly lower MgO (6.17-6.51wt%) relative to the samples of site 348 and typical MORBB rocks (Figures 7b and 7c).Interestingly, the altered samples from site 350 have compositions similar to geochemical trends for the Jan Mayen Fracture Zone, Jan Mayen Island igneous complex, northern Jan Mayen Ridge, and Vesteris seamount.
Reexamination of the deeper basalt section revealed a doleritic basalt intrusion with a distinct chilled margin against the basalt breccia, confirming the hypotheses of a younger intrusion, as observed in the seismic reflection data (Supplement 6b in Supporting Information S1).The stratigraphic unit that overlies the basalt breccia unit consists of turbiditic sedimentary rocks that are hydrothermally altered and lithified, indicative of contact-metamorphism by igneous activity after the emplacement of the turbidite section.
Analyses of the basalt intrusive samples show TiO 2 content between 2.34 and 2.75 wt%, a K 2 O of 0.27-0.37wt%, and MgO between 5.75 and 6.34 wt% (Figures 7b and 7c).The site 350 basalt intrusion is richer in plagioclase than typical MORB rocks of site 348 (Figure 7a), reflected by higher K 2 O and Na 2 O content on the total-alkali-silica (TAS) classification diagram.The samples fall within the same range as the Blosseville Kyst plateau basalts and overlap partly the Vøring margin ranges (Figure 7a; Supplements 3b in Supporting Information S1).With a higher concentration of titanium and potassium than typical MORB rocks, the intrusive section is geochemically analogous to present-day basalts from the Northern Volcanic Zone (NVZ) of Iceland and from the Vøring Plateau.

Dredged Seafloor Samples
Samples obtained during a dredging and gravity coring survey by Polteau et al. (2018) on the Jan Mayen Southern Ridge Complex were described as freshly broken, subaerially erupted, vesicular, and altered basalts, or brecciated volcaniclastic and dolerite basalt fragments.Two of the less altered samples are .06wt%) basalts based on the TAS classification (Le Bas et al., 1989) (Figure 7a, blue diamonds).However, they have different compositions based on their titanium and potassium content, one being closer to the MORB type, and the other to the Blosseville Kyst-Milne Land and Faroe Island Plateau basalt domains and syn-rift series (Figures 7b and 7c).

The Formation of the JMMC Igneous Provinces
Based on seismic-stratigraphic mapping, magnetic and gravity data, as well as geochemical analyses, seven distinct igneous phases have been identified within the JMMC region: pre-breakup and syn-breakup, followed by four Eocene-early Miocene rift propagation phases within the Iceland Plateau, a post-breakup phase, here referred to us a proto-Kolbeiney Ridge phase, and finally the initiation of spreading along the Kolbeinsey Ridge, as detailed below.

The Jan Mayen Ridge-Pre-Breakup Phase
The oldest igneous section of the Jan Mayen Ridge (stratigraphic unit JM-70, Figure 2) has been associated with pre-breakup volcanic activity during the late Paleocene and early Eocene (Blischke et al., 2019).Unit JM-70 underlies the inner SDR units along the eastern flank of the JMMC and onlaps the Jan Mayen igneous complex to the north (Figures 4 and 6; Supplement 2 in Supporting Information S1).On seismic reflection data, JM-70 is characterized by a laterally continuous succession of parallel-bedded seismic reflections, interpreted as stacked plateau-basaltic flows (Blischke et al., 2019).The parallel-bedded seismic reflections have been mapped across the Jan Mayen Ridge, Lyngvi Ridge, Jan Mayen Southern Ridge Complex, and partially along the eastern edge of the Jan Mayen Basin (Figures 9 and 10).The uppermost 0.5-1.0-s-thicksection of the sub-parallel, stratified lower Eocene pre-breakup basalts has a P-wave velocity between 3.8 km/s and 5.0 km/s based on seismic refraction data, similar to the flood basalts from ODP borehole 917A of Leg 152 from Southeast Greenland, where a P-wave velocity range between 2.5 and 5.5 km/s was recorded for brecciated and vesicular flow tops and 5-7 km/s for the central and lower part of the lavas (Planke & Cambray, 1998).Based on these values, the stratigraphic thickness of the lower Eocene basalt succession is about 1 km across the central Jan Mayen Ridge, increasing southward to approximately 3 km on the southernmost Lyngvi Ridge (dark gray layer in Figures 4b and 10b; Supplement 2a in Supporting Information S1).As the JMMC has subsequently been affected by major erosive events, the original stratigraphic thickness of this layer cannot be determined.The basalt succession is comparable in stratigraphic architecture to rocks exposed on the conjugate central East Greenland coast and imaged on offshore seismic reflection lines along the East Greenland continental margin (Blischke & Erlendsson, 2018;Blischke et al., 2020) (Figure 2a).Locally disrupted zones with chaotic seismic reflection patterns most likely represent smaller intrusive centers.These are embedded within the plateau basalt strata on the Lyngvi Ridge and on the northernmost segment of the Jan Mayen Southern Ridge Complex (Figures 6a-6c, 9, 10b; Supplement 2a, 2c in Supporting Information S1).These intrusions appear to be focused within the Jan Mayen and Lyngvi Ridge segments and do not deform the post-breakup formations and, thus, could be related to the pre-breakup volcanism as well.(Haase & Ebbing, 2014), the KRISE Line 7 seismic refraction data (Brandsdóttir et al., 2015), and boundary magnetic anomalies C24b (Gernigon et al., 2015) and C6c this study; and (b) the volcanic facies and provinces maps in order of emplacement: Early-Middle Eocene, Late Eocene-Oligocene, and Late Oligocene-Early Miocene igneous facies types and units, including intrusive and extrusive strata, plateau basalt equivalent, igneous centers, SDR, hyaloclastite volcanic strata, flood basalts.Abbreviations: AER-AEgir Ridge; CJMBFZ-Central Jan Mayen Basin Fracture Zone; CNBFZ-Central Norway Basin Fracture Zone; COB-Continent ocean boundary; EJMFZ-East Jan Mayen Fracture Zone segments; IFFZ-Iceland-Faroe Fracture Zone; IPR-Iceland Plateau Rift (segments I-IV); JMI-Jan Mayen Island complex; JMB-Jan Mayen Basin; JMBS-Jan Mayen Basin south; MCOB-Western margin continent-ocean boundary; JMR-Jan Mayen Ridge; JMT-Jan Mayen Trough; LYR-Lyngvi Ridge; MR-Mohns Ridge; SDR-Seaward dipping reflector sequences; SRCFZ-Jan Mayen Southern Ridge Complex Fracture Zone; SRC-Jan Mayen Southern Ridge Complex; SWJMBFZ-Southwest Jan Mayen Basin Fracture Zone; SWJMIP-Southwest Jan Mayen igneous province; TFZ-Tjörnes Fracture Zone; and WJMFZ-Western Jan Mayen Fracture Zone.

The JMMC Eastern Margin Igneous Domain-Syn-Breakup Phase
This syn-breakup igneous phase, stratigraphic unit JM-60, includes SDR units along the eastern flank of the JMMC, which discordantly overlies the plateau basalts of unit JM-70 (Blischke, Gaina, et al., 2017;Blischke et al., 2019) (Figures 2, 4-6, 9a, 10b; Supplements 2, 6, 7 in Supporting Information S1).The top surface of the unit (TSDR on Figure 2) is marked by high amplitude, continuous seismic reflections, providing a reliable correlation horizon across faults or graben structures that offset the SDR unit.Skogseid and Eldholm (1987) described a wide volcanic breakup margin that linked the JMMC across the eastern Jan Mayen Fracture Zone to the Vøring margin with distinct sets of SDR wedges forming along both margins during the breakup.Based on the dense grid of seismic reflection data, three sets of SDR units can be delineated along the northeastern margin of the JMMC close to the eastern Jan Mayen Fracture Zone.An igneous complex separates the innermost set from the two outer sets of SDR units (Figures 6a-6c, 9a, 10b) representing the outer highs of the volcanic breakup margin, as defined by Planke et al. (2000).This igneous complex is interpreted as a conjugate feature to the Vøring margin (e.g., Hinz, 1981;Mutter et al., 1982;Skogseid & Eldholm, 1987;Planke et al., 2000) across the eastern Jan Mayen Fracture Zone as indicated by plate tectonic reconstructions (Figures 11a and 12).
The inner (and older) SDR units onlap westward onto the Jan Mayen Ridge and Jan Mayen Southern Ridge Complex, where they unconformably pinch out onto the plateau basalts of unit JM-70 (Figures 2, 6, 9a).The inner SDR units exhibit a parallel bedded, eastward prograding seismic reflection pattern, with localized hummocky to lenticular patterns that tend to be thinner (<1.5 km).The inner SDR are up to 4 km in stratigraphic thickness and are related to the landward, subaerial lava flows (Figures 6a, 9a and 10b; Supplements 2 and 6 in Supporting Information S1) (see e.g., comparison in Hinz, 1981;Mutter et al., 1982;Planke et al., 2000).The transition between the inner SDR wedge and the outer high is commonly parallel to the interpreted continent-ocean boundary zone and limits the eastward extent of the Jan Mayen Ridge and Jan Mayen Southern Ridge Complex domains (e.g., Figures 6a-6c; Supplement 2 in Supporting Information S1).
Previously, the eastern Jan Mayen Ridge volcanic margin has been mapped as a continuous feature (e.g., Gaina et al., 2009, Skogseid & Eldholm, 1987, or Peron-Pinvidic et al., 2012a).The data presented here, however, suggests that the margin is segmented and made up of distinct igneous complexes that are related to the inner SDR set, outer high complexes, and one or two outer SDR sets (Figures 9a, 10b and 11a).The igneous complexes along the eastern margin are characterized by chaotic seismic reflection patterns that probably represent shallow sill and dike systems (Figures 6,9a,10b,11; Supplement 6 in Supporting Information S1).A faulted igneous complex is tied to a segment of the eastern Jan Mayen Fracture Zone (Figure 6b), where deposits from several volcanic episodes are stacked vertically rather than in a typical seaward progression as in Figures 6a and 6c.Some of these complexes appear semi-circular and have possibly formed volcanic cone structures in a shallow marine environment, as they are covered by prograding seismic reflection units possibly related to hyaloclastite and volcanoclastic depositional patterns (Figure 10b; Supplement 6 in Supporting Information S1).
The outer highs of the primary volcanic margin have been correlated with the early Eocene polarity chron C24 magnetic anomaly (Figures 6a, 6b and 10a), previously defined as polarity chron C24B (56-53 Ma) by (Skogseid & Eldholm, 1987); or C24r (∼55 Ma) by Gaina et al. (2009) and Gernigon et al. (2015).The oldest continuous magnetic anomaly in this region is C24n3n (∼53,4 Ma) (Gaina et al., 2009;Gernigon et al., 2015) (Figures 6a-6c).Anomalies C24 and C24n3n lie parallel to the two outer SDR units (Figures 6a-6c), which represent younger events since they onlap onto the inner SDR units.The eastward prograding outer SDR units appear to stack on top of each other, within a distinct and longer-lived volcanic system that developed at the termination of one of the eastern Jan Mayen Fracture Zone segments (Figures 6b, 9a and 10b).SDR wedges disappear south of the central Norway Basin Fracture Zone (CNBFZ) and are recognizable only across the northernmost two ridges of the Jan Mayen Southern Ridge Complex (Figures 6c, 9a and 10b).
volcanism during the formation of the early Eocene volcanic margin along the northern Jan Mayen Ridge domain, and intrusive complexes within the Jan Mayen Basin (Figure 6a).
The seafloor samples recovered from the Jan Mayen Southern Ridge Complex were placed in a stratigraphically consistent order along the available dredge profile.These samples have an estimated age range between 59 and 47 Ma (Polteau et al., 2012(Polteau et al., , 2018)), which correlates to the plateau and SDR basalts (see Jan Mayen Trough flanks on Figure 6c).Their geochemical composition is, however, different from the main SDR's lower series basalts on the Vøring margin, as well as the lower basalt and plateau basalt series on the Blosseville Kyst (Figure 7a).The Jan Mayen Southern Ridge Complex samples are located within the uppermost part of the plateau and SDR basalts series and are best placed within the syn-breakup igneous strata, where we tentatively assign an age range estimate of ∼55-52 Ma (early Eocene) within the SDR sequence JM-60.This later-stage early Eocene volcanism was coincident with the formation of the JMMC eastern flank volcanic margin and SDR units, possibly correlating with the Prinsen of Wales Bjerge formation (54-53 Ma) of the Blosseville Kyst (L.M. Larsen & Watt, 1985; L. M. Larsen et al., 1989Larsen et al., , 2013) ) and the intrusive phase (56-54 Ma) described by Tegner et al. (2008) just south of the Kangerlussuaq Fjord and southwest of the JMMC.Based on this correlation, it appears probable that the SDR formations originally reached across the southern extent of the JMMC domain toward central East Greenland, which has since been subjected to several magmatic and erosive events resulting in the removal of approximately 2-3 km volcanic section (Blischke et al., 2019;Japsen et al., 2014;Mathiesen et al., 2000) (Figures 4, 11a, and 12).

Eocene Rift Propagation, the Iceland Plateau Rift I-IPR-I
A second phase of breakup igneous activity occurred coevally with seismic unit JM-50; early to mid-Eocene igneous rocks are preserved overlying the outer high igneous complexes of the primary eastern JMMC volcanic margin and the inner SDR units of stratigraphic unit JM-60 (Figures 2,5c,6,9a,and 10).This phase of igneous activity appears to represent a period of enhanced volcanism with post-SDR lava flows, volcaniclastic extrusions, sill and dike intrusion along the entire JMMC eastern flank, around the Jan Mayen Southern Ridge Complex ridges, and the southeastern JMMC margin, forming the Iceland Plateau Rift I (IPR-I) domain (Figure 10).
The IPR-I rift extrusives overlay the Jan Mayen Southern Ridge Complex blocks and are best observed within the southernmost two ridges, along a volcanic margin that is estimated to have been active during the early Eocene from 52 to ∼50 Ma (lower JM-50 unit; Figures 2, 6d, 9a, and 10).The IPR-I igneous phase included dike and sill intrusions associated with small-scale faulting within the blocks of the Jan Mayen Ridge and Jan Mayen Southern Ridge Complex as well as the extrusion of lava flows, possibly interlayered with volcaniclastic flows (e.g., Figures 5c, 6b, and 6d; Supplement 6a-iii & 6a-iv, 6b in Supporting Information S1).The IPR-I domain (Figure 9) is characterized by high-amplitude irregular seismic reflection patterns that dip toward the AEgir Ridge domain with an increase in seismic velocities from 4.8 to 5.5 km/s in the basaltic strata (Figures 5c and 6d; Supplement 6a-ii, 6b in Supporting Information S1).This succession of the Jan Mayen Southern Ridge Complex volcanic margin overlies the JM-60 SDR unit and the JM-70 plateau basalts.Moreover, the original eastern breakup margin is buried and obscured by the IPR-I volcanic units (Figures 6d, 9a and 10; Supplement 6b in Supporting Information S1).The IPR-I volcanic rocks may be the source of the magnetic anomalies that closely align with the very southeastern edge of the JMMC-IPR domains that are parallel to the initial AEgir Ridge axis (Figure 10a).Geochemically the basalt breccia of IPR-I in site 350 shows similar MgO versus TiO 2 (wt%) and MgO versus K 2 O (wt%) trends to samples from the Jan Mayen Fracture Zone and Jan Mayen igneous complex (Figure 7).
The IPR-II rift was accompanied by normal and transpressional faulting by oblique extension and by widespread dike and sill emplacements, parallel to small-scale lava flows in the adjacent graben areas (Figures 5c,6d,6e,9a,10b).West of site 350, a segment of the IPR-II rift is visible in gravity and magnetic data which show structural trends aligned with the faulted graben structure, fault-parallel dikes, and shallow sills (Figures 5c and 10; Supplements 6b & 6e, 7 in Supporting Information S1).
The mid-Eocene unconformity is dated to ∼43 ± 3 Ma based on seafloor samples recovered from the northwestern Jan Mayen Ridge (Sandstå et al., 2012), the Jan Mayen Southern Ridge Complex (Polteau et al., 2018;Talwani et al., 1976b), and seismic chronostratigraphic mapping (Blischke et al., 2019).Sills and small intrusions observed on seismic reflection data have deformed or uplifted sediments around the unconformity (ME on Figures 2 and 6d).The IPR-II volcanism was originally considered to have an age range between 50 and 33 Ma (mid-to late Eocene) based on K-Ar dating of samples from site 350 (Kharin et al., 1976).However, based on the paleontological record of the overlying sediments, Raschka et al. (1976) proposed that the basalts were most likely emplaced no later than 40-44 Ma.New 40 Ar-39 Ar dates range from 49.28 ± 0.3 Ma to 44.05 ± 0.21 Ma consistent with this latter interpretation, suggesting that the volcanic activity is chronologically similar in age to the intrusions described by Tegner et al. (2008) for the Kangerlussuaq Fjord area (50-47 Ma) and coincident with the emplacement of the Igtertivâ Formation at Kap Dalton (∼49-43 Ma) (L.M. Larsen et al., 2013).All three areas were thus volcanically active during the early to mid-Eocene (Figure 11b).
The intrusive section of IPR-II is geochemically similar to MORB and the Blosseville Kyst plateau basalts (Figure 6a).The MgO versus TiO 2 (wt%) and MgO versus K 2 O (wt%) of the sill intrusion shows a good correlation with the Igtertivâ formation of the Blosseville Kyst, as well as recent volcanic rocks within the Northern Volcanic Zone of Iceland and the Faroe Island syn-breakup series compositions (Figures 6b and 6c).

Rift Transfer and the Magmatic Incursion of the Iceland Plateau Rift III (IPR-III)
A gradual westward rift transfer within the Iceland plateau occurred between the late Eocene and late Oligocene, forming the Iceland Plateau Rift III (IPR-III), which is coeval with seismic units JM-35 to JM-20 (Figures 1, 2, 5b, 5d, 6c, 6e, 9b; Supplements 2, 6a & c in Supporting Information S1).The IPR-III phase strongly affected the Jan Mayen Trough and the southwestern Jan Mayen igneous province (Figure 9b) with increased faulting and igneous activity.
The IPR-III phase affected a much wider area than IPR-II, with substantial sill and dike emplacements and the formation of volcanic ridges within the Jan Mayen Trough extending into the late Oligocene (Figures 5b-5d and 6c, and 9b).The volcanic ridges within the Jan Mayen Trough and between the Jan Mayen Southern Ridge Complex blocks are oriented in an N-S direction, parallel to Bouguer gravity and magnetic lineaments and appear to coincide with the formation of fault-bounded pre-IPR-III fault blocks (Figures 9b and 10; Supplement 7b in Supporting Information S1).This implies extensive igneous activity extending from the Iceland-Faroe Ridge into the Jan Mayen Southern Ridge Complex, the Jan Mayen Trough, and into the southernmost extent of the Lyngvi Ridge region that is associated with the rift relocation along the southern margin of the JMMC (Figures 5b, 6c, 6e, 9b, and 10; Supplement 6a-viii in Supporting Information S1).The record of this activity is clearly observed at the intersection of the Jan Mayen Trough and the Jan Mayen Southern Ridge Complex fracture zone (SRCFZ on Figures 1, 5b, and 6c) as a northward rift propagation.

Correlating Key Unconformities and Igneous Features
Both the mid-Oligocene and top Paleogene unconformities (Figures 2, 5b, 5d, and 6c; Supplements 2, 6b, 6c in Supporting Information S1) are characterized by distinctive flat-topped topography across the main Jan Mayen Ridge as well as the highest parts of the Jan Mayen Southern Ridge Complex.The mid-Oligocene unconformity has been deformed by subsequent faulting and intrusive activity.It is overlain by extrusive volcanics located below the top Paleogene unconformity.The Jan Mayen Trough and the southern end of the Lyngvi Ridge show an increased prevalence of intrusive complexes that appear to expand into the JMMC domain, separating the Jan Mayen Southern Ridge Complex from the main ridge and thus forming the Jan Mayen Trough and southwestern Jan Mayen igneous province (Figures 8c, 9b and 10).
Volcanic ash layers present within late Eocene to late Oligocene (∼43-30 Ma ±4 Ma) sediments at DSDP Leg 38 sites 346, 347, and 349 signal volcanic and phreatic activity affecting the entire area.In contrast, ash layers are absent in the Oligocene sediments of site 350 (Sylvester, 1975(Sylvester, , 1978;;Talwani, Udintsev, & White, 1976;Talwani, Udintsev, & Shirshov, 1976;Talwani et al., 1976aTalwani et al., , 1976bTalwani et al., , 1976e, 1978)).This suggests that site 350 was further away from later Oligocene volcanic and phreatic activity and coincided with igneous activity south of the Kangerlussuaq Fjord at 37-35 Ma southwest of the JMMC-IPR area (Tegner et al., 2008).An east-to-west shift of igneous activity across the JMMC-IPR area can be observed by tracing the seismic horizons related to extrusive and intrusive areas that appear connected to flood basalt events.The oldest flood basalt marker horizon "F-Marker 3" (Figure 2) and "IPR-II intrusions & extrusives" (Figure 9) lie within the late Eocene to the mid-Oligocene interval.A further subsequent flood basalt event, referred to as "F-Marker 2," occurs within the mid-to late Oligocene stratigraphic succession (Figure 2) and forms the Jan Mayen Trough-IPR-III rift domain (Figure 9b; Supplement 6d-viii, 6c in Supporting Information S1).

F-Marker 3 -IPR-II Intrusions & Extrusives
Horizon "F-Marker 3" is observed over approximately 1250 km 2 and appears related to the mid-Oligocene unconformity within the Jan Mayen Southern Ridge Complex region, overlying the early-mid Eocene strata within the Jan Mayen Southern Ridge Complex, IPR-I, and IPR-II domains (Figures 2 and 9b).On seismic profiles, F-Marker 3 is characterized by a relatively flat-lying hummocky to irregular seismic reflection that locally infills smaller graben areas that are connected to a series of small intrusive features.These grabens contain up to 2.5 km of stratigraphic infill material, including igneous rocks (Figure 5c).Late Eocene to mid-Oligocene faulting, smaller-scale intrusions, and vents are observed within the faulted, southernmost Jan Mayen Southern Ridge Complex, IPR-I, and IPR-II domains.

F-Marker 2-Jan Mayen Trough-IPR-III Rift Domain
The mid-to late Oligocene sub-aerial extrusive and intrusive features of the horizon "F-Marker-2" (Figures 2, 5b, and 9b; Supplement 6a-viii in Supporting Information S1) are manifested as strong seismic reflections covering an area of approximately 8,100 km 2 and are well defined within the Jan Mayen Trough.Thus, a variable stratigraphic thickness estimate of up to 990 m for the IPR-III flood basalts is postulated within the Jan Mayen Trough domain (Figure 9b).The flood basalts of the Jan Mayen Trough-IPR-III rifting domain terminate against the rotated fault blocks and structural highs of the Lyngvi Ridge, the Jan Mayen Southern Ridge Complex western margin, and faulted blocks within the Jan Mayen Trough (Figures 5b and 5d).Little seismic energy appears to penetrate this horizon and deeper structures and strata are not well imaged.The partly irregular and hummocky structure of F-Marker 2 is possibly related to extrusions emplaced sub-aqueously, or perhaps into thin, unconsolidated wet sediments.

The Western Igneous Margin, and IPR-IV to the Kolbeinsey Ridge Transition (Proto-KR)
The last rift-transfer phase is associated with the Iceland Plateau Rift system IV (IPR-IV) at the southwestern limit of the visible Jan Mayen Ridge segments.The formation of this igneous domain represents the last rift transfer phase between central East Greenland and the JMMC during the late Oligocene and early Miocene (Figure 2), forming the western margin of the microcontinent.Its western boundary is marked by the first clear magnetic polarity chron , which is tied to DSDP Leg 38 site 348 (Figures 6e, 9b and 11c).The IPR-IV domain is characterized by dike and sill emplacements, igneous complexes, and regionally extensive flood basalts identifiable on seismic reflection data (Figures 4b and 5d; Supplements 6a-vii, 6b in Supporting Information S1).The IPR-IV domain represents the direct conjugate to the central East Greenland margin along the Blosseville Kyst shelf.Rifting leading to breakup is estimated to have been active from ∼25 to 24 Ma (e.g., Blischke, Gaina, et al., 2017;Blischke et al., 2018;Talwani & Eldholm, 1977) (Figures 1, 4, 9b, and 11c; Supplement 7 in Supporting Information S1).The flood basalts associated with this phase of volcanism are marked by a distinct seismic horizon, "F-Marker 1" (Figure 2), that corresponds to seismic unit JM-15 and onlaps onto the JMMC structures and older igneous domains (Figures 4b and 5d; Supplement 2b, 2c in Supporting Information S1).

Tectonic Evolution of the Jan Mayen Basin
The northern and southern segments of the Jan Mayen Basin that form part of the JMMC's western breakup margin are different in structure, crustal thickness, and igneous character.The entire western flank of the JMMC is strongly faulted into several westward-rotated fault blocks along segments that have partly slid into the basin, forming half-graben and small graben structures.Most of the faults and tilted features are overprinted by intrusive rocks (Blischke, Gaina, et al., 2017;Blischke et al., 2019).The basin is bounded to the south by the SW-NE aligned southwestern Jan Mayen Basin Fracture Zone, which has the same orientation as the younger Spar Fracture Zone on the Kolbeinsey Ridge (Figures 1b, 1c, 10b, and 11c).The southwestern edge of the Jan Mayen Basin is reconfigurable to a large igneous center located offshore the central Blosseville Kyst, active ∼33-22 Ma (Figure 11c).
The deep Jan Mayen Basin appears to have formed gradually along the WNW-ESE-striking central Jan Mayen Basin Fracture Zone from the mid-Eocene to the early Miocene, and along the NW-SE-striking normal fault system of the Jan Mayen Ridge margin (Figures 9b,10b,11c,and 12), that is, opposite the N-S-to NE-SW-striking normal fault systems south of the central Jan Mayen Basin Fracture Zone.Seismic refraction data indicate that crustal thickness varies from 6 to 12 km within the basin (Blischke, Gaina, et al., 2017;Blischke et al., 2019;Kodaira et al., 1998a;Olafsson & Gunnarsson, 1989) (Figure 1; Supplements 6b, 7 in Supporting Information S1).Thinned crust with seismic velocities >6.8 km/s (Figures 1 and 4b; Supplement 2b-c), reflect crustal extension and subsidence.In addition, the southern Jan Mayen Basin segment is characterized by different Bouguer gravity anomaly values (>150 mGAL) than the northern segment (<150 mGAL).The proto-Kolbeinsey Ridge is oriented parallel to magnetic anomaly C6c within the southern Jan Mayen Basin segment (Figures 1b  and 10a; Supplement 2b, 2c in Supporting Information S1).
The F-Marker 1 horizon is interpreted as an early Miocene flood basalt marking the top of seismic-stratigraphic unit JM-15 (Figures 2, 5d, and 9b; Supplements 6a-vii, 6b in Supporting Information S1).It is characterized by a flat-lying high-amplitude reflection in seismic data with an aerial extent of approximately 9,400 km 2 within the low areas of the Jan Mayen Basin.Subsequent faulting in response to continued extension later offsets what is interpreted as an initially continuous set of lava flows.The basalt layer is approximately 300-500 m thick based on refraction data (Supplement 6b in Supporting Information S1).Thickness estimates increase up to ∼1.2 km near inferred igneous centers, which are likely source areas for the flood basalts, as fissure or axial rift segments are not observed in this region (Figures 4b and 9b).

The Initiation of the Kolbeinsey Ridge (Proto-KR)
Initial igneous complexes of the Kolbeinsey Ridge appear to be associated with wedge-shaped sections of SDR sequences along the western edge of the Jan Mayen Basin, and a conjugate sequence along the eastern edge of the Liverpool Land Basin (Figure 4).The seismic reflection data imply an overlap of highly thinned JMMC crust within the Jan Mayen Basin, onto Late Oligocene to Early Miocene SDR sequences from the initial volcanic complexes within the proto-Kolbeinsey domain (Figures 4 and 10).Based on the higher-resolution post-2011 seismic reflection data the SDR units appear to be consistent across the central Jan Mayen Basin, just south of the central Jan Mayen Basin Fracture Zone (Figures 9b and 10).The SDR units form a relatively wide zone (40-50 km) adjacent to the first clear magnetic spreading anomaly, C6c.Combined with the conjugate central East Greenland margin, a wide and complex volcanic transition zone formed along the Eocene-Miocene breakup margin, prior to full seafloor spreading along the Kolbeinsey Ridge.

The Post-Breakup Neogene-Quaternary Phase
After the Kolbeinsey Ridge was established, an oceanic domain formed west of the JMMC and igneous activity decreased significantly within the microcontinent (Figures 10 and 11c), except around the Jan Mayen igneous complex and western Jan Mayen Fracture Zone northwest of the JMMC.The record of Neogene volcanic activity is observed in DSDP and ODP cores within the JMMC as interbedded volcanic ash and tuff layers within the deep-marine sediments (Blischke, Gaina et al., 2017;Sandstå et al., 2012Sandstå et al., , 2013;;Talwani, Udintsev, & White, 1976;Talwani, Udintsev, & Shirshov, 1976;Talwani et al., 1976aTalwani et al., , 1976bTalwani et al., , 1976e, 1978)).Seafloor basalt samples of the northern Jan Mayen Ridge show similar geochemical trends as the Jan Mayen Fracture Zone and Jan Mayen igneous complex (Figure 8), though no age data are available.However, samples from the northwesternmost breakup margin have an age range from 13.2 to 0.1 Ma (e.g., Campsie et al., 1990;Davis & McIntosh, 1996;Fitch, 1964;Mertz et al., 2004).

JMMC Igneous Provinces-Summary
The reconstructed tectonic evolution of the JMMC-IPR domain consists of seven distinct local to regional tectono-magmatic phases (Figures 11 and 12) that can be summarized as follows: 1.An initial breakup phase characterized by anomalous magmatic activity that followed an SW-NE opening trend along WNW-ESE-striking pre-existing fracture zones south and west of the JMMC, here inferred as an oblique opening of the Geikie Plateau into the central Jan Mayen Ridge domain (∼63-56 Ma); 2. Formation of multiple SDR sets along the JMMC eastern igneous margin during syn-breakup in the early Eocene.Segments of SSW-NNE-striking SDR units propagated northwards as a precursor to the formation of the AEgir Ridge spreading system, which opened along the NW-SE-striking eastern Jan Mayen Fracture Zone, central Norway Basin Fracture Zone, and Jan Mayen Southern Ridge Fracture Zone segments (∼55-53 Ma). 3. Activation of the Iceland Plateau Rift (IPR-I) along the eastern JMMC breakup margin, and the southernmost part of the AEgir Ridge system (∼52-50 Ma) represented by flood basalts, intrusive complexes, volcanic breccia, and volanoclastic sequences.4. Activation of the IPR-II segment in association with an SW-NE-aligned magmatic event between the GIFRC and the JMMC.The IPR-II rift intersected the IPR-I segment and the southernmost Jan Mayen Southern Ridge Complex contemporaneously with the AEgir Ridge.Volcanism within these axial rift segments by intrusions and flood basalts (∼49-36 Ma). 5. Activation of the IPR-III rift domain, during an SW-to-NE magmatic incursion into the southern margin of the JMMC, severing the Jan Mayen Southern Ridge Complex from the main Jan Mayen Ridge (Lyngvi Ridge) forming the Jan Mayen Trough and volcanic ridges within the Jan Mayen Southern Ridge Complex domain (∼35-24 Ma). 6.The final breakup of the JMMC, along the IPR-IV segment and formation of the western JMMC igneous margin (∼24-23 Ma). 7. Initiation of the Kolbeinsey Ridge along the proto-KR segment and the western Jan Mayen Fracture Zone segments (∼22-21 Ma).

Pre-Breakup Setting
Pre-and primary breakup igneous units west and southeast of the JMMC-IPR (Figures 11a and 12) are contemporaneous with the lower basalt sections of their conjugate margins.The lower basalt sections along the central East Greenland margin range in age from ∼63 Ma to 56 Ma (e.g., L. M. Larsen et al., 1989;Pedersen et al., 1997), whereas the conjugate pre-breakup lower basalts of the Faroe Island Basalt Group (FIBG) range from ∼61 to 56 Ma (e.g., Mudge, 2015;Ólavsdóttir et al., 2019).Rocks from these conjugate areas are of alkaline and felsicto-mafic compositions, suggesting contamination with continental crust (Kokfelt & Árting, 2014;L. M. Larsen et al., 1999;Meyer et al., 2009;Parson et al., 1989;Tegner et al., 1998).The seismic reflection characteristics and velocity structure of these lower basalt sections are broadly comparable to the JMMC-IPR region (Figures 4b  and 8; Supplements 2, 6a-6i in Supporting Information S1).Prior to breakup, the Faroe Plateau and the Faroe Islands were located south-southwest of the JMMC domain (Figures 11a and 14).The Lopra and Beinisvørð formations, which are part of the Faroe Island Basalt Group, have pre-breakup age ranges from 60.94 ± 2.1 Ma to 55.9 ± 1.1 Ma (e.g., Árting et al., 2014;Horni et al., 2017).These formations consist of a mixture of intrusives, lavas, volcanoclastic, and hyaloclastite units.Thick hyaloclastite units have been drilled on the Faroe shelf into the deepest levels of the pre-breakup Faroe Island Basalt Group, but an accurate definition of its base is missing (Ólavsdóttir et al., 2019).The pre-breakup Base Palaeogene unconformity (BPU) is marked as a strong seismic reflection beneath the Jan Mayen and Lyngvi ridges; however, it is marked by an irregular and locally faulted erosion surface across the Jan Mayen Southern Ridge Complex and the Jan Mayen Basin, where truncated Mesozoic strata is inferred to be overlain predominantly by pre-breakup plateau basalts (e.g., Blischke et al., 2019) (Figures 4b and 6; Supplement 2 in Supporting Information S1).
We interpret the JM-70 plateau basalt section to be equivalent to the Blosseville Kyst basalts, as the JMMC-PR area was located ∼50 km east of onshore East Greenland (Figure 11a).The plateau basalt section appears to increase in stratigraphic thickness toward the south, including the Jan Mayen Southern Ridge Complex (Figures 6  and 11a).Similarly, Brooks (2011) described a northeast-to-southwest increase in plateau basalt thickness from Jameson Land basin through Scoresby Sund and the Blosseville Kyst toward the Kangerlussuaq basin.The inland and northern areas show regional onlap onto structural highs with subsequent erosion estimated to have removed 2-3 km of basaltic stratigraphy in central East Greenland (L.M. Larsen et al., 1999Larsen et al., , 2014;;Mathiesen et al., 2000;Passey, 2009;Passey & Hitchen., 2011;Passey & Jolley, 2009).This magnitude of denudation has been related to several phases of uplift and erosion events for the central East Greenland area (Figure 12).In particular, Eocene-Oligocene uplift and erosion resulted in the formation of the Upper Planation Surface that was accompanied by faulting and intrusion of magmatic bodies with extensive mass wasting on the East Greenland shelf (e.g., Bonow & Japsen, 2021;Bonow et al., 2014;Japsen et al., 2014Japsen et al., , 2021)).The marked north-to-south increase in thickness of the pre-breakup lower series and plateau basalt sections of the Blosseville Kyst, from 'absent' to up to 6-7 km suggests a deep-seated source located at the intersection of the Blosseville Kyst and the proto-Iceland-Faroe Fracture Zone (Figure 11a).Furthermore, large deep-seated igneous sources appear to be located close to the Scoresby Sund and Geikie plateau as distinct magnetic anomalies are present adjacent to the southern end of the Jameson Land Basin, and alongside extensive intrusive systems within the sedimentary basins of Jameson Land, Liverpool Land and the continental margin of the Blosseville Kyst (Figure 11a; Supplement 8 in Supporting Information S1) (e.g., Blischke & Erlendsson, 2018;Eide et al., 2021;Franke et al., 2019;Guarnieri et al., 2016).
Kinematic reconstructions show how the JMMC area was conjugated with central East Greenland (Figure 11a).Pre-breakup structural trends in the Jameson Land Basin match those inferred from the JMMC.Several igneous centers along the eastern flank of the JMMC, arranged slightly en-echelon and narrowing southward might have formed along the initial breakup margin prior to the formation of syn-breakup SDR units.This igneous activity is likely to have been contemporaneous with underplating suggested beneath the Jan Mayen igneous complex by Kandilarov et al. (2012) and deep intrusions along major Jan Mayen fault segments (Blischke et al., 2019), as observed on seismic reflection, gravity, and magnetic anomaly data (e.g., Figures 5a and 6b).The higher-velocity lower crust of the eastern JMMC margin is mostly located oceanward, close to the projected microcontinent-ocean boundary, and within an oceanic crust domain (horizons R1 and R2 on Figures 4b and 6; Supplement 2 in Supporting Information S1).The initial opening was from north to south within a regional NE-SW spreading direction.Two inferred dextral fracture zones (proto CNBFZ and SRCFZ) separated individual spreading segments (Figures 11a and 11b).The dextral proto-Jan Mayen Fracture Zone opened at a ∼60° angle to the northeastern margin of the JMMC, lending further support to an overall right-lateral oblique rift opening along the northern boundary of the JMMC during the initial breakup.The JMFZ was the regional transfer element between the Norwegian and East Greenland margins (Figures 10 and 11a).The Norwegian Basin opened south of the NW-SE striking JMFZ, in response to gradual subsidence along the eastern JMMC margin (Figures 11a Abbreviations: EJMFZ -Eastern Jan Mayen Fracture Zone; GIFRC -Greenland-Iceland-Faroe Ridge complex; IFFZ -Iceland-Faroe Fracture Zone; IPR -Iceland Plateau Rift; JMFZ -Jan Mayen Fracture Zone; JMMC -Jan Mayen microcontinent; SRCFZ -Jan Mayen Southern Ridge Complex Fracture Zone; and TWT -Two-way travel time.and 11b).In contrast to subsidence within the Norway Basin, the Vøring Plateau and Transform Margin remained bathymetrically elevated during early Eocene.The breakup unconformity of the top volcanic units there has been dated at ∼55 Ma (Figure 12) (e.g., Berndt et al., 2001;Hjelstuen et al., 1997Hjelstuen et al., , 1999;;Polteau et al., 2020), supporting the existence of a transpressional region north of the Jan Mayen Fracture Zone.
The Traill Ø volcanic igneous province (Figure 11b) and Vøring margin were linked through the Jan Mayen Fracture Zone and northernmost JMMC (Figures 11a and 11b).The SW-NE-striking Geikie Plateau (Figure 11a) appears to align parallel to the magnetic trend observed at the Traill Ø-Vøring igneous complex (Figure 11b) but is offset by the proto-Jan Mayen Fracture Zone.The Vøring margin is interpreted to contain a high-velocity lower crustal body that was generated by magmatic underplating, possibly associated with magma leaking along a large-scale fracture zone (e.g., Abdelmalak, et al., 2016;Gernigon et al., 2019Gernigon et al., , 2021)).Similar observations have been reported for the Jameson Land Basin and Scoresby Sund area by Eide et al. (2021) in East Greenland.
Several NE-SW-striking magnetic lineaments aligned parallel to presumably contemporaneously active onshore igneous centers, southwest of the Blosseville Kyst (Figure 11a) may mark the area of the initial breakup between East Greenland and the Faroe Islands, generating the oldest segment of the GIR and the Iceland-Faroe Fracture Zone.These events would also have affected the southernmost part of the JMMC, an area that is presently unresolved due to sparse seismic data coverage.Our reconstructions leave open the possibility that the southernmost limit of the JMMC may well lie beneath the northeast Iceland shelf or is, in part, embedded into the Iceland-Faroe Ridge.Based on refraction measurements, the western Iceland-Faroe Ridge and Eastern Iceland areas comprise up of 30-35 km thick Iceland-type crust (Smallwood et al., 1999;Staples et al., 1997).The reconstructed Iceland-Faroe Fracture Zone domain aligns with the Kangerlussuaq area, across to the Faroe Islands platform and Fugloy ridge, and into the Møre margin.(Blischke, 2020;Gaina, Nasuti, et al., 2017).Magnetic anomaly data background from magnetic Nasuti and Olesen (2014).

Syn-Breakup Setting
The syn-breakup-to-drift phase was dominated by the formation of SDR units and oceanic crust along the AEgir ridge at the initiation of the Norway Basin (Figure 11b).A wide igneous area with thick SDR units lies along the East Greenland Traill Ø margin, north of the Jan Mayen Fracture Zone.The primary breakup margin along the eastern flank of the JMMC is aligned with distinct igneous complexes, represented by onlapping, inner SDR sets within polarity chron C24r (∼55 Ma).The oldest magnetic polarity chron within the Norway Basin is C24n.3n(∼53.4Ma, based on the timescale of Gradstein et al. (2012)), associated with the outer SDR units (e.g., Gaina et al., 2009;Gernigon et al., 2015;Skogseid & Eldholm, 1987) (Figures 6a-6c).The outer SDR units can therefore be considered as a direct conjugate to the early Ypresian (55-52 Ma) syn-breakup volcanic rocks that have been sampled along the Vøring margin and have been mapped on seismic reflection data for the East Greenland Traill Ø margin (e.g., Franke et al., 2019;Geissler et al., 2017;Gernigon et al., 2015;Horni et al., 2017;Planke & Eldholm, 1994;Polteau et al., 2020) (Figures 11b and 12).
Thickness variations within the JMMC-SDR units most probably represent fluctuations in the focus of volcanic activity within the central volcanic systems along the eastern JMMC breakup margin, and segmented separation of the microcontinent from the Norway Basin and an apparent decrease of SDR unit wides toward the Southern Ridge Complex (Figures 9a,10b,11b,and 12).The southernmost blocks of the Jan Mayen Southern Ridge Complex are overlain by a younger early-to mid-Eocene volcanic margin, which obscures underlying igneous strata (Figures 5c and 6d; Supplement 2c in Supporting Information S1).Seismic reflection data from the underlying lava units exhibit amplitudes and semi-parallel reflection characteristics of classic SDR units and landward flow units.Thus, the early-to mid-Eocene igneous margin of the Jan Mayen Southern Ridge Complex region is synchronous with the formation of the southern AEgir Ridge, conjugate to the southern Møre Basin and the Fugloy Ridge (Figure 11b).
The wide igneous SDR margin between Greenland and the Faroe Island, extends northeast along the Fugloy Ridge and the southern Møre margin (Figure 11b), indicating a clear asymmetry in the early opening of the Norway Basin.Norcliffe et al. (2019) suggest that asymmetric SDR units form preferentially above a waning thermal anomaly in the mantle or due to variations in the pre-rift lithospheric structure.This latter possibility is clearly appropriate for the eastern JMMC, implying that the structural setting that facilitated rift transfer systems was already established prior to rifting.These rifting processes appear to coincide with a change in spreading direction of the Northeast Atlantic system, that is, a regional rather than a localized event (Gaina, Nasuti, et al., 2017) (Figure 12).Anomalously thick SDR sections along the southeasternmost Jan Mayen Southern Ridge Complex region most likely represent overlapping of different axial rift segments similar to those that have been observed south of the Iceland Faroe Ridge (e.g., Blischke et al., 2016;Erlendsson & Blischke, 2013;Hjartarson et al., 2017).
The wider and partially stacked SDR units of the northeast JMMC margin narrow southwards, reflecting opening from north to south within the Norway Basin at the initiation of the AEgir Ridge (Figure 11b).In contrast, SDR units between East Greenland and the Faroe Islands narrow northwards, to the Southern Ridge Complex and the Bosseville Kyst.These opposite rift opening directions during breakup were accommodated by a rift transfer along the southern JMMC and the activation of the Iceland Plateau Rifts, which gradually sheared the microcontinent from the East Greenland margin.

Rift-Transfer Within the Iceland Plateau
The timing of this early to mid-Eocene IPR rift transfer corresponds with an overall change in spreading direction, accompanied by decreased seafloor spreading rates within the NE Atlantic (Gaina, Nasuti, et al., 2017) (Figure 12).As no major tectonic events occurred during this time, this rift re-organization is most likely related to large-scale magmatic processes, which generated a regional uplift and development of the mid-Eocene unconformity (Figure 12) (Blischke et al., 2019).The IPR is petrographically similar to the Igtertivâ Formation and appears to be part of the same rift system; its higher-than-typical MORB TiO 2 and K 2 O contents may also be indicative of a mantle anomaly influence (Figure 8).The substantially increased magmatic activity in the N-Atlantic region affected the adjacent rift systems, including the Reykjanes Ridge and the asymmetric AEgir Ridge.The IPR rift transfer was contemporaneous with regional volcanism from mid-to late Eocene (approximately 43-40 Ma) along the northern margin of the JMMC, eastern Jan Mayen Fracture Zone, Jan Mayen Island, Traill Ø igneous province, and within the Iceland-Faroe Ridge (e.g., Blischke et al., 2019;Gaina et al., 2009;Geissler et al., 2017).Individual IPR segments align with the projected orientation of rift segments from the Reykjanes ridge across the GIFRC in an SSW-NNE direction at ∼54-49 Ma (Figure 11b), albeit offset by segments of the Iceland-Faroe Fracture Zone.Parallel, subaerial, rift systems formed south of the JMMC, connected by short fracture zone segments, including a failed axial rift system across the Iceland-Faroe Ridge (∼49-40 Ma; Figures 11b and 11c).
The two-rift transfer phases (IPR I-II) accommodated the oblique spreading system of the AEgir ridge that intersected the southernmost JMMC domain and the northern IFR (Figures 10,11b,11c,12,and 14).The oldest continuous magnetic anomaly, chron C21 (late Ypresian-early Lutetian, ∼48-46 Ma) (Blischke, Gaina, et al., 2017;Ellis & Stoker, 2014;Gaina et al., 2009), formed after the emplacement of IPR-I and overlapped that volcanic succession (∼52-50 Ma).In turn, the IPR-I appears to overlap the syn-breakup JMMC and SDR units (Figures 6d and 11b  , 5b, 6c, 9b, 11c, and 12), synchronously with decreased spreading rate along the southern AEgir Ridge (Gaina, Nasuti, et al., 2017;Gernigon et al., 2015).The IPR-III period is characterized by massive magmatic intrusions, emplacement of volcanic ridges, dikes, and flood basalts, extending into the IPR-IV phase and the early stages of Kolbeinsey Ridge formation.The intrusions appear related to an S-N-aligned magnetic and Bouguer gravity anomaly trend within the Jan Mayen Trough, the northern Jan Mayen Southern Ridge Complex, and the southwest Jan Mayen igneous complex immediately south of the Lyngvi Ridge.Thus, supporting the interpretation of a rift system that segmented and propagated into the southern extent of the JMMC.
The final JMMC breakup phase (∼24-23 Ma) occurred along the southwestern and western flank of the microcontinent, where evidence for increased volcanic activity is preserved, including the emplacement of igneous complexes within the IPR-IV region, increased dike and sill emplacement, extrusive flood basalts, and the western SDR margin (Figures 4b,9b,10,and 11c; Supplements 2, 6 in Supporting Information S1).The formation of a distinct igneous margin along the western JMMC instigated full separation from central East Greenland along the proto-Kolbeinsey ridge by magnetic anomaly C6c (23.3-22.5 Ma) that was linked to the Mohns Ridge via the western Jan Mayen Fracture Zone to the east (Figures 1, 6a, 10b, and 11c).To the west, the western Jan Mayen Fracture Zone was partially inverted during the Mid-Oligocene, which was accompanied by the intrusion of a syenite pluton and dikes at around 30 Ma (Blischke et al., 2019;Geissler et al., 2017;Parsons et al., 2017) (Figure 12).
Global plate-motion reorganizations are believed to have triggered changes in spreading rates and directions in the NE Atlantic, around 33 Ma, when the relative motion between Greenland and the Eurasian plates changed from NNW-SSE to a WNW-ESE direction (Gaina et al., 2009).Around 35 Ma, the Western Mediterranean-Alpine area changed from subduction to a collision mode that pushed the Adriatic plate into the European margin (Le Breton et al., 2021), coinciding with a change in plate motion of the Eurasian plate from SSE-NNW to WSW-ENE (∼40-33 Ma) (Gaina et al., 2009;Gaina, Nasuti et al., 2017).These events coincided with major erosional events across the central NE Atlantic region as well as to changes in spreading directions associated with the final rift transfer of IPR-III and IPR-IV (Figure 12).Thus, the mid-Alpine Pyrenean orogeny occurred at the same time as this final phase of the Northeast Atlantic opening, placing the NW European plate margin between the active ocean spreading ridges and the orogenic belt (Figures 11c and 12) (e.g., Lundin & Doré, 2002;Ritchie et al., 2008).This process may have enabled a rearrangement of active spreading centers within the Northeast Atlantic region, which caused reactivation and compression along the southeastern JMMC domain, generating inversion structures within the Jan Mayen Southern Ridge Complex highs and within the Iceland-Faroe Ridge area (Blischke et al., 2019;Gaina et al., 2009).Furthermore, the center of the Iceland plume hotspot track was located offshore Greenland underneath the western segment of the GIFRC, the Greenland-Iceland Ridge, in the proximity of the JMMC around 30 Ma (Figure 11c), indicating that a mantle impingement may have caused the eastward regional tilt of the GIFRC, which corresponds to a collapse of the JMMC's eastern flank that triggered massive slumping (Blischke et al., 2019;Gaina, Nasuti et al., 2017;Stärz et al., 2017) (Supplement 6b, 6c in Supporting Information S1).

Tectono-Magmatic Evolution of the JMMC
The JMMC displays many of the characteristics of microcontinents as described by Müller et al. (2001), Nemčok et al. (2016), and Gaina and Whittaker (2020), such as inherited lithospheric heterogeneities, wrench tectonics, and oblique rifts.Highly oblique spreading ridges have been recognized globally in relation to slow, intermediate, and super-fast spreading centers.They are assumed to be related to reorganizations of plate boundaries and magmatic overpressure, causing spreading obliquity generally up to ∼10° and in a few cases even up to 30°-40°, as can be observed for the Mohn's Ridge just north of the JMMC (e.g., Dauteuil & Brun, 1993;Zhang et al., 2018).
The IPR spreading centers formed in a southeast-to-northwest direction simultaneously with southward cessation of spreading along the AEgir Ridge.The IPR rifts sheared the JMMC from East Greenland in four stages (IPR-I to IPR-IV; Figures 11 and 12).IPR blocks are separated by graben and half-graben structures and intersecting rift segments.This heterogeneity appears to reach far into the JMMC and is especially apparent within the Jan Mayen Southern Ridge Complex, where IPR-II rifting intersects the IPR-I domain and abrupt thinning is observed (Figures 1, 6, 9 and 10; Supplement 7 in Supporting Information S1).
The present-day oblique rift systems form microplates affected by strike-slip and crustal deformation processes, as observed in outcrops (e.g., Einarsson, 2008;Einarsson et al., 2020;Karson et al., 2018Karson et al., , 2019)).Similar relationships are observed on seismic reflection data within the Jan Mayen Southern Ridge Complex, where the overall right-lateral opening of the Southern Ridge Complex Fracture Zone and Southern Ridge Complex includes left-lateral compensating or block-rotating strike-slip elements (Figure 13b) (Blischke, 2020).
The orientation of rift opening, and therefore the obliquity of a given rift segment changes through time and location along a rift zone, just as for the JMMC-IPR structural fabric (Figures 12 and 13).This can be solved by calculating spreading-time directions from the finite rotation of each tectonic segment within a kinematic reconstruction (e.g., Gaina, 2014;Gaina, Nasuti, et al., 2017).Thus, for each given tectonic block within such a reconstruction, the opening direction could, in turn, reflect a unique stress-field orientation (Figure 13).
The reconstructed time ∼49 Ma was constrained using the northern AEgir Ridge, the southern AEgir Ridge, and the northernmost tip of the Reykjanes Ridge, to assess if the calculated opening direction and its associated potential overall horizontal stress-field fits the documented fault and fracture zone patterns (Figure 13).All three locations vary in the opening direction and sense of shear within dextral or sinistral oblique rift segments (Figure 13) and reflect the orientation of normal fault sets, block fault rotation-related strike-slip faulting, or overall fracture zone orientations.These zones represent wide fracture zones that impact entire structural domains.Extinct rift segments are "frozen" in place and are rotated out of their original position by younger rifting episodes.

The Iceland Plume
Large tectonic elements have been suggested as the primary reason for the complex breakup history and rift formation along the GIFRC (e.g., Foulger et al., 2020;Gernigon et al., 2012;Higgins & Leslie, 2008;Ritchie et al., 2011) and as a primary mechanism of magmatially inflated and stretched continental crust forming a hybrid continental-oceanic lithosphere along the GIFRC (Foulger et al., 2020(Foulger et al., , 2021)).Seismic tomography, spectral analysis of magnetic data, Bouguer gravity anomaly, and thermal models have illuminated the hotspot track beneath Greenland, Jan Mayen, and Iceland in higher detail (e.g., Bjarnason, 2008;Martos et al., 2018;Mordret, 2018;Wolfe et al., 1997;or Toyokuni et al., 2020aor Toyokuni et al., , 2020b)).Modeled hotspot track segments aligned with anomalous areas on Bouguer gravity, magnetic anomaly, and seismic refraction data along the GIFRC (e.g., Mordret, 2018;or Toyokuni et al., 2020aor Toyokuni et al., , 2020b)), around the Eggvin Bank and the western Jan Mayen Fracture Zone, which have been interpreted as thick heterogeneous crust along the northern JMMC and the Jan Mayen igneous complex (Tan et al., 2017, 2018) (Figures 1, 9b, 10, and11c).These observations all confirm previous models of a large mantle anomaly with a regional impact in the Blosseville Kyst, JMR-SRC, and GIR-IFR areas (Figure 11).An area where underlying structural complexity most certainly existed prior to the breakup, between central East Greenland and the Faroe Plateau (Figure 11a).However, this region may contain thin slivers of highly stretched and intruded continental crust, as observed within the ridge segments of the Jan Mayen Southern Ridge Complex and inferred within the Iceland-Faroe Ridge (Figure 11).

Petrologic Provenance
Asymmetric rift development and transfer across Iceland serves as an important example of a hotspot-ridge interaction system for the GIFRC as well, both geodynamical and geochemically.Iceland-type basalts, as in the case of the Northern Volcanic Zone, have a wide variation that could be linked to changes in mantle source composition or variation in mantle melting conditions, such as plume temperature, reflecting heterogeneities in the Icelandic mantle that are described as a large-scale regional magmatic source that produced the Northern Volcanic Zone sub-alkaline tholeiite basalts (e.g., Chauvel & Hémond, 2000;Fitton et al., 1997;Kokfelt et al., 2006;Thirlwall et al., 2004).The early influence of the Iceland plume in the JMMC-IPR domain formation can be inferred by comparing to the geochemical compositions of the Northern Volcanic Zone basalts that are similar to the IPR-II core samples and the Igtertivâ Formation for East Greenland in terms of MgO/K 2 O (wt%) and MgO/TiO 2 (wt%) contents (Figure 7).However, geochemical composition variations can relate to potential crustal assimilation of slivers of continental crust from the outermost breakup margins not just within the JMMC (Figure 11c).In order to answer the question of which of the two interpretations is more applicable, drill samples for each IPR phase would be required to compare those to the onshore outcrop analogs and spars borehole record in the region, which is targeted for future research (e.g., Larsen, Blischke, Halldórsson, et al., 2021;Larsen, Blischke, Brandsdóttir, et al., 2021).Similarly, seafloor sampling along the eastern scarp of Lyngvi Ridge and the western scarp of the Jan Mayen Southern Ridge Complex has given strong indications that East Greenland continental fragments of Late Permian-Early Triassic to Early Cretaceous ages underlie the JMMC (e.g., Polteau et al., 2018;Sandstå et al., 2012) (Figure 3).

Mid-Oceanic Ridge Asymmetry
V-shaped ridges flanking the Reykjanes Ridge are commonly attributed to the pulsing of the Iceland mantle plume from around 35 Ma, at a frequency of 3 to 8 m.y.(e.g., Parnell-Turner et al., 2014;White et al., 1995).The initiation of pulsing coincides with the formation of IPR-III and the separation of the JMMC from the central East Greenland margin.Whereas some of the inferred plume-pulsing events south of the GIFRC correlate with changes in spreading directions Gaina, Nasuti, et al. (2017), they are inconsistent with the chronology outlined for rifting events north of the GIFRC.Major unconformities around the JMMC are associated with regional tectonic and magmatic events that do not correlate with the plume-pulsing events along the Reykjanes Ridge.Instead, they are associated with gradual rift transfer of an oceanic spreading system from the AEgir Ridge to the Kolbeinsey Ridge via the four phases of the Iceland Plateau Rift system, which was likely influenced by the Iceland mantle anomaly from IPR-III onwards.

Structural Inheritance Within the North-Atlantic
At the time of the breakup, the Jan Mayen Ridge and Jan Mayen Basin were juxtaposed to the Blosseville Kyst and Scoresby Sund areas in East Greenland.Fault trends and the SW-NE-striking magnetic anomaly interpreted across the Geikie plateau appear to terminate against the JMMC (Figures 11a and 14; Supplement 8 in Supporting Information S1).This is interpreted as indirect evidence for intrusive complexes located within pre-breakup sediments just north of Kap Brewster at the mouth of the Scoresby Sund and observed on seismic reflection data throughout the Jameson Land Basin (e.g., Blischke & Erlendsson, 2018;Eide et al., 2021) (Figure 11a).The Geikie plateau structures have distinct magnetic trends associated with pre-breakup and breakup lava flows that cover the area.There is no clear geochemical evidence at the surface to link these lava flows to specific feeder dike systems (e.g., L. M. Larsen et al., 1989;Pedersen et al., 1997).However, the magnetic anomalies across the Geikie plateau might represent deep-seated faults that served as pathways for upwelling magma.These structural features align with the modeled hot-spot track estimates for heat flux >70 mW/m 2 (Martos et al., 2018) (55-50 Ma on Figure 14).The right-stepping alignment of these magnetic anomalies and potential fracture systems would correspond to a left-lateral opening of that area, as proposed by Guarnieri (2015) for the GIFRC and northward into the Scoresby Sund area, thus linking the tectonic fabric to the magmatic emplacement processes during the initial breakup phase (Figures 12 and 14; Supplement 8 in Supporting Information S1).
Large tectonic elements, such as the main Caledonian thrust belt, the Archean terrane, fracture zones crossing into the Fugloy Ridge, or the Moine Thrust Fault (e.g., Foulger et al., 2020;Gernigon et al., 2012;Higgins & Leslie, 2008;Ritchie et al., 2011) (Figure 14), appear to connect East Greenland with the European margin via a broad sinistral shear zone.Anomalous magnetic anomaly patterns, potential fracture zones, and structural lineaments continue across the GIFRC (Figure 14) indicating pre-rift lithospheric structures that appear to connect to the large tectonic elements.Two primary structural trends formed during the syn-breakup phase: a WNW-to-ESE trend across the main GIFRC, and an NW-to-SE trend forming the Iceland Plateau and the proto-eastern Jan Mayen Fracture Zone, north of the GIFRC.The Iceland Plateau and GIFRC structural trends were reactivated during later rift phases, gradually extending the Iceland-Faroe Fracture Zone along the northern edge of the GIFRC and the JMMC fracture zone systems throughout the formation of the AEgir Ridge and Iceland Plateau rifts (Figures 11b,11c,12,13,and 14).The Iceland-Faroe Fracture Zone linked adjoining rift systems, the AEgir Ridge, and subsequently the IPR from the northeast and the Reykjanes Ridge from the southwest (Figure 14).
The initial settings of the proposed fracture zones (55 Ma on Figure 14) display two primary structural trends that appear to have guided the opening of this area; a SE-NW trend that links the JMMC to the European margin, and a WNW-ESE trend linking the JMMC to East Greenland.The structural setting and overall rift and oblique rift systems appear to guide the breakup (55-47 Ma on Figure 14), with the AEgir and Reykjanes ridges "turning" westward toward East Greenland that might be linked structurally or toward a proposed hot-spot track (Martos et al., 2018).From the Late Eocene and Early Oligocene (∼35 Ma on Figure 14), the hot-spot is northwest of the main rift system IPR-III; there was a substantial increase of volcanic intrusives and extrusives in the region; and a west-to-east tilting of the GIFRC.Separating the JMMCR-IPR domain from the East Greenland shelf (∼24-21 Ma on Figure 14), the IPR-IV rift merged with the proto-Kolbeinsey Ridge in southward continuation with the NW Iceland Rift Zone and Reykjanes Ridge, whilst located just above the hotspot center.By ∼15 Ma, the plate boundary within the Iceland region had shifted eastwards as the hotspot moved east of the rift zone (e.g., Harðarson et al., 1997Harðarson et al., , 2008) ) requiring an oblique SE-to-NW rift transition similar to the IPR.Thus, the Snaefellsnes-Húnaflói Rift Zone (∼15-7 Ma) was linked to the Kolbeinsey Ridge via a transfer system west of the Iceland-Faroe Fracture Zone (∼15 Ma on Figure 14).The interaction of the GIFRC and IPR rift segments with the center of the hotspot, instigated the formation of complex rift, rift-flank, and fracture zone systems (e.g., IPR, Iceland-Faroe Fracture Zone, Snaefellsnes-Húnaflói Rift Zone, and the Tjörnes Fracture Zone on Figure 14) from the second JMMC breakup to present day.

Conclusions
Detailed volcanostratigraphic mapping based on geological, geophysical, and petrological data have provided a new kinematic model for the opening of the central NE-Atlantic.The Jan Mayen microcontinent developed through seven tectono-magmatic phases over a period of ∼40 million years (∼63-21 Ma).The Cenozoic evolution of the NE-Atlantic region is a prolonged history of continental breakup and seafloor spreading, highlighting the complexity of rift evolution interconnected to a hotspot region from breakup to the present.
Initial breakup within the N-Atlantic (∼63-56 Ma) was accompanied by enhanced igneous activity that was linked to preexisting structural features.Primary fracture zones accommodated the opening of the JMMC region along a SE-NW trend at the European margin and a WNW-ESE trend in East Greenland.Microcontinent formation was accomplished by oblique opening within two fan-shaped domains: Initial breakup, from NNE-SSW along the segmented northeastern JMMC igneous margin, forming thick, overlapping sets of SSW-NNE-aligned igneous sections (SDR; ∼55-53 Ma), prior to the activation of rifting at the AEgir Ridge and opening of the Norway Basin (∼55-26 Ma).Second breakup, from SE-NW through rift transfer along the western JMMC igneous margin, within four Iceland Plateau Rift systems (IPR-I to IPR-IV).The overlapping and propagating IPR rift segments, interlinked via fracture zones, gradually separated the JMMC from East Greenland, over a period of ∼25 million years (∼52-23 Ma).
The Iceland Plateau Rift domain links the Iceland-Faroe Ridge with East Greenland's central Blosseville Kyst, through both tectonics and geochemistry.The overlapping IPR rift systems contributed to vertical accretion of lava flows that resulted in an anomalous thick igneous crust in this region.Direct Iceland hotspot-rift interaction most likely coincided with IPR phase III (∼35-24 Ma), and substantial increase in intrusives and extrusives in the region, and a west to east tilt of the JMMC, Iceland Plateau Rift, and Greenland-Iceland Ridge domains.Full separation occurred during IPR phase IV (∼24-23 Ma), during which the Reykjanes Ridge and the proto-Kolbeinsey Ridge connected via the NW Iceland Rift Zone, near the center of the hotspot (∼22-21 Ma).
Oblique rift transitions continued within the proto-Iceland region, as the hotspot migrated eastward.The NW Iceland Rift Zone (∼21-15 Ma) and the Snaefellnes-Húnaflói Rift Zone (∼15-7 Ma) are likely to have connected the Reykjanes and Kolbeinsey ridges through fracture zones at this time, progressively generating plate boundary structures observed in Iceland today.

Figure 8 .
Figure 8. 40 Ar/ 39 Ar radiometric age determinations of samples from boreholes DSDP Leg 38 sites 350 and 348, (a) radiometric diagram and description of samples from core 16 of DSDP Leg 38 site 350, and (b) radiometric diagram and description of samples from core 32 of DSDP Leg 38 site 348.Abbreviations: DSDP, Deep Sea Drilling Program.

Figure 13 .
Figure13.Comparison of the mapped oblique rift zones and fracture/transfer zone systems for the greater JMMC-IPR region to present-day: (a) reconstructed early Eocene (∼49 Ma) reconstruction along the northern AEgir Ridge and EJMFZ, along the southern AEgir Ridge associated with cessation of spreading and increase in IPR-II rift activity, the IPR-II-IFFZ, and the northernmost extent of the Reykjanes Ridge; (b) Opening and rifting of the Jan Mayen Southern Ridge Complex in comparison to the apparent opening fabric of the EJMFZ and the IPR-II-Iceland-Faroe Fracture Zone system (IFFZ) (modified afterBlischke et al., 2021Blischke et al.,  , 2017.  .Abbreviations: EJMFZ -Eastern Jan Mayen Fracture Zone; GIFRC -Greenland-Iceland-Faroe Ridge complex; IFFZ -Iceland-Faroe Fracture Zone; IPR -Iceland Plateau Rift; JMFZ -Jan Mayen Fracture Zone; JMMC -Jan Mayen microcontinent; SRCFZ -Jan Mayen Southern Ridge Complex Fracture Zone; and TWT -Two-way travel time.
). Segment IPR-II on the other hand intersected IPR-I and the underlying early Eocene margin, most likely between ∼49 and 44 Ma.The IPR-II correlates chronologically and geochemically with the Igtertivâ formation (∼49-43 Ma) of Kap Dalton and the central Blosseville Kyst area.Thus, the overall southeast-to-northwest oriented Iceland Plateau Rift system, extending from the northern IFR into the southeastern part of the JMMC, constitutes the tectono-magmatic connection between the Iceland-Faroe Ridge and the Blosseville Kyst areas.6.1.4.Final Breakup Along the Western JMMCBreakup along the western margin of the JMMC commenced initially with a westward transfer of IPR-III activity into the central graben of the Jan Mayen Trough during the Oligocene (∼35-25 Ma; Figures 1