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In recent years, unexpected continental crust in areas presumed to be purely oceanic in nature has been discovered, indicated by the presence of Paleozoic zircons in rock samples. Notable examples include the Rio Grande Rise, Mauritius, and potentially also the Comoros islands, which have all previously been interpreted as mantle plume edifices. Iceland is also often interpreted as a hotspot of mantle plume origin, however the presence of a deep seated consistent thermal anomaly with depth has long been challenged, with implications for the wider regional geodynamic evolution. Previous reports of Mesozoic and Paleozoic zircons from Iceland may allude to the presence of continental material at depth, although these are sometimes suggested to be the result of contamination. Nonetheless, geochemical evidence from erupted material at Öræfajökull may indicate a continental contribution to melts beneath SE Iceland, and the nearby Jan Mayen microcontinent readily demonstrates the ability of continental material to make its way to the ocean interior, coincident with hotspot volcanism. Furthermore, continental material in the NE Atlantic Ocean is perhaps more common than previously thought, with recent work suggesting that substantial components of the Greenland-Iceland-Faeroes region may be continental in nature. Here, we test the hypothesis that the basaltic upper crust of Iceland is underlain by older continental crust. To do this, we have undertaken extensive, targeted sampling of Icelandic rocks and sediments using robust collection approaches to eliminate the possibility of contamination. Over a 3-week period in summer 2022, we collected samples from across the entirety of Iceland. We sampled both intrusive and extrusive rocks with a wide range of ages (both felsic and mafic, but with an emphasis on felsic rocks), as well as river sediments from above 250 m elevation (to avoid potential contamination from Greenland glacial debris). Zircons will be separated from these samples using contamination-safe approaches, and then U-Pb and Hf isotopic age analysis will be completed. The results from this preliminary study will be used to guide further sampling in summer 2023, allowing evaluation of the competing hypothesises for the origin of Iceland.

Polyphase deformation on passive margins, including fault reactivation, has been documented globally. These processes form complex structures that can be integral to petroleum systems and can provide essential constraints on the kinematic and structural evolution of rifts and passive margins. In some cases, inversion structures can also be used as global markers for far-field stress changes and help us to understand how plate tectonics operates on Earth. Despite the importance of reactivated faults, their identification, extent mapping, controls on kinematic evolution, and knowledge of interaction within fault populations are often poorly constrained. As such, there is need for detailed investigations of such structures, including their relationship with halokinesis, which can lead to complex and sometimes misleading structural observations.We present a new structural interpretation of the Penobscot 3D seismic reflection survey, and associated relay ramp, imaged offshore Nova Scotia, Canada, down to ~3.5 s TWT, constrained by two exploration wells. The relay ramp comprises two dominant faults that dip approximately SSE and are associated with smaller antithetic and synthetic faults. The wider fault population is dominated by ~ENE-WSW striking normal faults that dip both NNW and SSE. The two major normal faults display evidence for reverse deformation in their lower portions (below ~2.5 s TWT), which manifests as anticlinal folding and reverse offsets. However, in their upper portions the faults display normal offset. Smaller faults tend to only affect the uppermost strata and do not show evidence of reactivation. Analysis of fault throw demonstrates that movement on the two main faults was coupled during both the reverse and normal deformation intervals. Through our structural analysis and previous regional interpretations of widespread salt kinesis, we determine that the observed style of deformation likely occurred due to normal (extensional) reactivation of reverse faults that had initially formed due to halokinesis of underlying salt. The timing of salt movement broadly corresponds to documented times of kinematic reorganisation on many Atlantic margins, and thus salt kinesis may have been in response to this. The kinematic dichotomy with depth along the two dominant faults is important to document as this style of polyphase reactivation may go unrecognised where seismic data does not image the full depth of a structure. Therefore, reactivation may be more widespread than previously thought if only uppermost parts of structures have been imaged. The interpretation of salt as an important contributor to kinematic reactivation of faults is crucial as it likely provides a mechanism to explain inversion at many other locations globally.

The disintegration of Pangea north of the Charlie Gibbs fracture zone led to the formation of the NE Atlantic and Arctic Oceans. Both these oceans are exceptionally complex in terms of diversity of the structures they contain and the sequence of events leading to their formation. Recent, extensive work by cross-disciplinary international groups has cast a great deal of new light on the structure and evolution of both oceans. Both have experienced fan-shaped oceanic-type spreading and ridge growth by linear propagation. Both contain shallow, linear bathymetric highs which comprise substantially or almost wholly, continental crust. There are also regions of continental crust, some hyper-extended, capped with lavas. Much of the NE Atlantic Ocean is floored by oceanic crust produced by classical, albeit piecemeal, oceanic spreading. The spreading rate is low and dwindles to ultra-low on the Gakkel Ridge in the Eurasia Basin of the Arctic Ocean. The Gakkel Ridge is flanked by linear, oceanic-like magnetic anomalies although it is not entirely clear whether these represent fully oceanic crust formation or whether some residual stretched continental crust remains beneath this region. The same may be true of the extinct Canada Basin spreading axis in the Amerasia Basin. Likewise, the nature and location of the continent-ocean transition in the NE Atlantic is currently under discussion and it has recently been proposed that the oldest linear magnetic anomalies, closest to the continental edges, characterize some form of magma-injected continental crust. A similar structure has been recently proposed for the Greenland-Iceland-Faroe Ridge and the Alpha-Mendeleev Rise. What is currently unclear is the extents, in both oceans, of the three kinds of crust – true continental crust including microcontinents, magma-injected continental crust, and fully oceanic crust. There is furthermore likely a structural and geological continuum between these types. Classical linear magnetic anomalies are discontinuous between sections of the spreading ridge, raising the question of whether continuous fully oceanic crust connects these sections. In our presentation we will summarize what is known geologically and tectonically about both oceans, compare and contrast them, and outline their evolution. We will discuss the extents of the three types of crust and explore the implications for the history and mechanisms of ocean formation and the origins and extents of flood basalts. Of particular interest also is the control of pre-existing structure on the style of breakup.

The inversion of rift-related faults on passive margins through kinematic reactivation is documented globally. Such structures form an integral part in petroleum systems, provide essential constraints on the kinematic and structural evolution of rifts and passive margins, and can be used as global markers for far-field stresses. Despite the importance of inverted normal faults, the controls on their kinematic evolution, as well as existence and interactions within fault populations are often poorly constrained. Here, we present new structural interpretation and kinematic modelling of an inverted relay ramp structure located offshore Nova Scotia, Canada. This structure is imaged on the Penobscot 3D seismic reflection survey down to ~3.5 s TWTT, and is constrained by two exploration wells. We map two major normal faults that display evidence for inversion in their lower portions (reverse faulting and low-amplitude folding), below ~2.5 s TWTT, though retain a normal offset in upper sections. The wider fault population is dominated by ~ENE-WSW striking normal faults that dip both north and south, while both of the two major faults dip approximately south and are associated with antithetic and synthetic faults. This kinematic dichotomy along the major faults is important as inversion such as this may go unrecognised if seismic data does not image the full depth of a structure. To accommodate such depth-dependent inversion, if both horizons co-existed during inversion, a reduction in volume of the sedimentary package is required between the normal and reverse segments of the fault. In this study, we explore possible kinematic mechanisms to explain inversion structure and the mechanisms accommodating the volumetric changes/ or mass movements required using fault restoration and strain modelling. Our results favour a poly-phase deformation history that can be reconciled with other inversion structures on related passive-margin segments, suggesting these could be widespread processes.

Recent advances in knowledge have led to the recognition of continental crust beneath the Comoros islands offshore East Africa and conflicting fracture zone patterns in isolated regions of the Indian ocean. Furthermore, whilst the presence of continental crust within the Davis Straight has been known for some time, its origin remains debated.Here, using gravity lineament analysis, plate kinematic modelling, seismic reflection interpretations, and 3D crustal thickness inversions (constrained by a new composite sedimentary thickness dataset), we investigate the origin of microcontinents and proto-subduction events in the Western Somali Basin, Indian Ocean, and the Labrador Sea. We find the role of plate motion changes, which induce transpression along active transform faults, play a critical role in the cleaving of the Comoros microcontinent and inducing previously poorly understood plate convergence and missing crustal sections along the Chain and Owen ridges. Furthermore, the temporal and spatial patterns of thrust and normal faulting in the Davis Straight indicates an analogous mechanism emplaced continental crust in this region, suggesting a generic and predictable mechanism may be applicable to the production of this type of microcontinent around the globe. The Davis Straight proto microcontinent (i.e., incompletely rifted microcontinent) began development during the 53 Ma spreading axis reorientation and ceased separation at 33 Ma, when the basin became extinct. We postulate that the extinction of ocean spreading in the Labrador Sea, and possibly also the Western Somali Basin, may have been influenced by increasing transpression across long-offset fracture zones and suggest further study of this phenomenon.

The breakup of Pangaea was accompanied by extensive, episodic, magmatic activity. Several Large Igneous Provinces (LIPs) formed, such as the Central Atlantic Magmatic Province (CAMP) and the North Atlantic Igneous Province (NAIP). Here, we review the chronology of Pangaea breakup and related large-scale magmatism. We review the Triassic formation of the Central Atlantic Ocean, the breakup between East and West Gondwana in the Middle Jurassic, the Early Cretaceous opening of the South Atlantic, the Cretaceous separation of India from Antarctica, and finally the formation of the North Atlantic in the Mesozoic-Cenozoic. We demonstrate that throughout the dispersal of Pangaea, major volcanism typically occurs distal from the locus of rift initiation and initial oceanic crust accretion. There is no location where extension propagates away from a newly formed LIP. Instead, LIPs are coincident with major lithosphere-scale shear movements, aborted rifts and splinters of continental crust rifted far out into the oceanic domain. These observations suggest that a fundamental reappraisal of the causes and consequences of breakup-related LIPs is in order.

The opening of the North Atlantic region was one of the most important geodynamic events that shaped the present day passive margins of Europe, Greenland and North America. Although well-studied, much remains to be understood about the evolution of the North Atlantic, including the role of the Jan Mayen microplate complex. Geophysical data provide an image of the crustal structure of this microplate and enable a detailed reconstruction of the rifting and spreading history. However, the mechanisms that cause the separation of microplates between conjugate margins are still poorly understood. We assemble recent models of rifting and passive margin formation in the North Atlantic and discuss possible scenarios that may have led to the formation of the Jan Mayen microplate complex. This event was probably triggered by regional plate tectonic reorganizations rejuvenating inherited structures. The axis of rifting and continental break-up and the width of the Jan Mayen microplate complex were controlled by old Caledonian fossil subduction/suture zones. Its length is related to east–west-oriented deformation and fracture zones, possibly linked to rheological heterogeneities inherited from the pre-existing Precambrian terrane boundaries.

Accurate reconstructions of the dispersal of supercontinent blocks are essential for testing continental breakup models. Here, we provide a new plate tectonic reconstruction of the opening of the Western Somali Basin during the breakup of East and West Gondwana. The model is constrained by a new comprehensive set of spreading lineaments, detected in this heavily sedimented basin using a novel technique based on directional derivatives of free-air gravity anomalies. Vertical gravity gradient and free-air gravity anomaly maps also enable the detection of extinct mid-ocean ridge segments, which can be directly compared to several previous ocean magnetic anomaly interpretations of the Western Somali Basin. The best matching interpretations have basin symmetry around the M0 anomaly; these are then used to temporally constrain our plate tectonic reconstruction. The reconstruction supports a tight fit for Gondwana fragments prior to breakup, and predicts that the continent-ocean transform margin lies along the Rovuma Basin, not along the Davie Fracture Zone (DFZ) as commonly thought. According to our reconstruction, the DFZ represents a major ocean-ocean fracture zone formed by the coalescence of several smaller fracture zones during evolving plate motions as Madagascar drifted southwards, and offshore Tanzania is an obliquely rifted, rather than transform, margin. New seismic reflection evidence for oceanic crust inboard of the DFZ strongly supports these conclusions. Our results provide important new constraints on the still enigmatic driving mechanism of continental rifting, the nature of the lithosphere in the Western Somali Basin, and its resource potential.

The onshore exposures adjacent to modern, offshore passive continental margins may preserve evidence of deformation from the pre-, syn-, and post-rift phases of continental breakup that allow us to investigate the processes associated with and controlling rifting and breakup. Here, we characterize onshore brittle deformation and pre-rift basement metamorphic mineral fabric from onshore Labrador in Eastern Canada in the Palaeoproterozoic Aillik Domain of the Makkovik Province. Stress inversion (1) was applied to these data and then compared to (2) numerical models of hybrid slip and dilation tendency, (3) independent calculations of the regional geopotential stress field, and (4) analyses of palaeo-stress in proximal regions from previous work. The stress inversion shows well-constrained extensional deformation perpendicular to the passive margin, likely related to pre-breakup rifting in the proto-Labrador Sea. Hybrid slip and dilatation analysis indicates that inherited basement structures were likely oriented in a favorable orientation to be reactivated during rifting. Reconstructed geopotential stresses illuminate changes of the ambient stress field over time and confirm the present paleo-stress estimates. The new results and numerical models provide a consistent picture of the late Mesozoic-Cenozoic lithospheric stress field evolution in the Labrador Sea region. The proto-Labrador Sea region was characterized by a persistent E&ndash, W (coast-perpendicular) extensional stress regime, which we interpret as the pre-breakup continental rifting that finally led to continental breakup. Later, the ridge push of the Labrador Sea spreading ridge maintained this general direction of extension. We see indications for anti-clockwise rotation of the direction of extension along some of the passive margins. However, extreme persistent N&ndash, S-oriented extension as indicated by studies further north in West Greenland cannot be confirmed.

The Labrador Sea is a small (∼900 km wide) ocean basin separating southwest Greenland from Labrador, Canada. It opened following a series of rifting events that began as early as the Late Triassic or Jurassic, culminating in a brief period of seafloor spreading commencing by polarity chron 27 (C27; Danian) and ending by C13 (Eocene-Oligocene boundary). Rift-related magmatism has been documented on both conjugate margins of the Labrador Sea. In southwest Greenland this magmatism formed a major coast-parallel dike swarm as well as other smaller dikes and intrusions. Evidence for rift-related magmatism on the conjugate Labrador margin is limited to igneous lithologies found in deep offshore exploration wells, mostly belonging to the Alexis Formation, along with a postulated Early Cretaceous nephelinite dike swarm (ca. 142 Ma) that crops out onshore, near Makkovik, Labrador. Our field observations of this Early Cretaceous nephelinite suite lead us to conclude that the early rift-related magmatism exposed around Makkovik is volumetrically and spatially limited compared to the contemporaneous magmatism on the conjugate southwest Greenland margin. This asymmetry in the spatial extent of the exposed onshore magmatism is consistent with other observations of asymmetry between the conjugate margins of the Labrador Sea, including the total sediment thickness in offshore basins, the crustal structure, and the bathymetric profile of the shelf width. We propose that the magmatic and structural asymmetry observed between these two conjugate margins is consistent with an early rifting phase dominated by simple shear rather than pure shear deformation. In such a setting Labrador would be the lower plate margin to the southwest Greenland upper plate.