ABSTRACT The Tanquary High is a positive tectonic feature that was identified on the southern margin of the far northeastern portion of Sverdrup Basin. A sequence stratigraphic analysis of the Triassic succession of northern Ellesmere Island, involving 27 measured sections and one well section, has allowed the geometry and evolution of the high in the Triassic to be elucidated. The Triassic succession occurs within five second-order sequences, and each sequence boundary reflects the occurrence of a tectonic episode that included basin margin uplift and basinward movement of the shoreline. The Tanquary High was uplifted during these tectonic episodes, which occurred in the latest Permian, latest Early Triassic, latest Middle Triassic, latest Carnian, and latest Norian. Each sequence is truncated toward the crest of the high where Rhaetian strata now overlie Cambrian strata. Isopach and facies data for each sequence reveal that, at the times of maximum uplift of the Tanquary High, the subaerially exposed part of the high extended 100–150 km down its northwest-trending axis and up to 150–200 km down each flank. Rapid subsidence completed each tectonic episode and initiated the development of a new sequence. The Tanquary High was completely drowned at these times. It is hypothesized that the tectonic episodes were generated by changes in horizontal stress fields driven by plate tectonic reorganizations. The facies and isopach maps of the latest Triassic to early Early Jurassic (Rhaetian-Sinemurian) second-order sequence demonstrate that the Tanquary High ceased to exist following the first order, latest Norian sequence boundary. A complete reversal of source areas and the initiation of the Amerasia rift basin coincided with the demise of the Tanquary High.

Abstract This book is the final product of the Circum-Arctic Lithosphere Evolution (CALE) project. The project’s ultimate goal is to link the onshore and offshore geology in order to develop a self-consistent set of constraints for the opening of the Amerasia Basin. The circum-Arctic is divided into seven regions, each with its own research team; the teams included geophysicists and geologists working together to integrate geological and geophysical data, from onshore to offshore. This work is summarized in the 18 papers contained in this volume.

Abstract This paper synthesizes the framework and geological evolution of the Arctic Alaska–Chukotka microplate (AACM), from its origin as part of the continental platform fringing Baltica and Laurentia to its southward motion during the formation of the Amerasia Basin (Arctic Ocean) and its progressive modification as part of the dynamic northern palaeo-Pacific margin. A synthesis of the available data refines the crustal identity, limits and history of the AACM and, together with regional geological constraints, provides a tectonic framework to aid in its pre-Cretaceous restoration. Recently published seismic reflection data and interpretations, integrated with regional geological constraints, provide the basis for a new crustal transect (the Circum-Arctic Lithosphere Evolution (‘CALE’) Transect C) linking the Amerasia Basin and the Pacific margin along two paths that span 5100 km from the Lomonosov Ridge (near the North Pole), across the Amerasia Basin, Chukchi Sea and Bering Sea, and ending at the subducting Pacific plate margin in the Aleutian Islands. We propose a new plate tectonic model in which the AACM originated as part of a re-entrant in the palaeo-Pacific margin and moved to its present position during slab-related magmatism and the southward retreat of palaeo-Pacific subduction, largely coeval with the rifting and formation of the Amerasia Basin in its wake. Supplementary material: Supplementary material Plate 1 (herein referred to as Sup. Pl. 1) comprises Plate 1 and its included figures, which are an integral part of this paper. Plate 1 contains regional reflection-seismic-based cross sections and supporting material that collectively constitute CALE Transects C1 and C2 and form an important part of our contribution. Plate 1 is referred to in the text as Sup. Pl. 1, Transects C1 and C2 as Plate 1A and 1B, and plate figures as fig. P1.1, fig. P1.2, etc.). Supplementary material 2 contains previously unpublished geochronologic data on detrital zircon suites and igneous rocks. Supplementary material are available at https://doi.org/10.6084/m9.figshare.c.3826813

Abstract The tectonomagmatic evolution of eastern Chukotka, NE Russia, is important for refining the onset of Pacific plate subduction, understanding the development of the Amerasia Basin, and constraining Arctic tectonic reconstructions. Field mapping and strategic sample collection provide relative age constraints on subduction-related continental arc magmatism in eastern Chukotka. Ion microprobe U–Pb zircon ages provide absolute constraints and identify five magmatic episodes ( c. 134, 122, 105, 94 and 85 Ma) separated by three periods of uplift and erosion ( c. 122–105, 94–85 and post-85 Ma). Volcanic rocks in the region are less contaminated than their plutonic equivalents which record greater crustal assimilation. These data, combined with xenocrystic zircons, reflect the self-assimilation of a continental arc during its evolution. Proto-Pacific subduction initiated by c. 121 Ma and arc development occurred over c. 35–50 myr. Crustal growth was simultaneous with regional exhumation and crustal thinning across the Bering Strait region. Ocean–continent subduction in eastern Chukotka ended at c. 85 Ma. The timing of events in the region is roughly synchronous with the inferred opening of the Amerasia Basin. Simultaneous arc magmatism, extension and development of the Amerasia Basin within a back-arc basin setting best explain these coeval tectonic events. Supplementary material: Includes SIMS U–Pb and geochemistry data tables, detailed geological map and geochemical figures which are available at https://doi.org/10.6084/m9.figshare.c.3784565

Abstract The New Siberian Islands are affected by a number of Mesozoic tectonic events. The oldest event (D1a) is characterized by NW-directed thrusting within the South Anyui Suture Zone combined with north–south-trending sinistral strike-slip in the foreland during the Early Cretaceous. This compressional deformation was followed by dextral transpression along north–south-trending faults, which resulted in NE–SW shortening in the Kotelny Fold Zone (D1b). The dextral deformation can be related to a north–south-trending boundary fault zone west of the New Siberian Islands, which probably represented the Laptev Sea segment of the Amerasia Basin Transform Fault in pre-Aptian–Albian times. The presence of a transform fault west of the islands may be an explanation for the long and narrow sliver of continental lithosphere of the Lomonosov Ridge and the sudden termination of the South Anyui Suture Zone against the present Laptev Sea Rift System. The intrusion of magmatic rocks 114 myr ago was followed by NW–SE-trending sinistral strike-slip faults of unknown origin (D2). In the Late Cretaceous–Paleocene, east–west extension (D3) west of the New Siberian Islands initiated the development of the Laptev Sea Rift System, which continues until today and is largely related to the development of the Eurasian Basin.

Abstract This paper considers the lithospheric structure and evolution of the wider Barents–Kara Sea region based on the compilation and integration of geophysical and geological data. Regional transects are constructed at both crustal and lithospheric scales based on the available data and a regional three-dimensional model. The transects, which extend onshore and into the deep oceanic basins, are used to link deep and shallow structures and processes, as well as to link offshore and onshore areas. The study area has been affected by numerous orogenic events in the Precambrian–Cambrian (Timanian), Silurian–Devonian (Caledonian), latest Devonian–earliest Carboniferous (Ellesmerian–svalbardian), Carboniferous–Permian (Uralian), Late Triassic (Taimyr, Pai Khoi and Novaya Zemlya) and Palaeogene (Spitsbergen–Eurekan). It has also been affected by at least three episodes of regional-scale magmatism, the so-called large igneous provinces: the Siberian Traps (Permian–Triassic transition), the High Arctic Large Igneous Province (Early Cretaceous) and the North Atlantic (Paleocene–Eocene transition). Additional magmatic events occurred in parts of the study area in Devonian and Late Cretaceous times. Within this geological framework, we integrate basin development with regional tectonic events and summarize the stages in basin evolution. We further discuss the timing, causes and implications of basin evolution. Fault activity is related to regional stress regimes and the reactivation of pre-existing basement structures. Regional uplift/subsidence events are discussed in a source-to-sink context and are related to their regional tectonic and palaeogeographical settings.

Abstract We perform an integrated analysis of magnetic anomalies, multichannel seismic and wide-angle seismic data across an Early Cretaceous continental large igneous province in the northern Barents Sea region. Our data show that the high-frequency and high-amplitude magnetic anomalies in this region are spatially correlated with dykes and sills observed onshore. The dykes are grouped into two conjugate swarms striking oblique to the northern Barents Sea passive margin in the regions of eastern Svalbard and Franz Josef Land, respectively. The multichannel seismic data east of Svalbard and south of Franz Josef Land indicate the presence of sills at different stratigraphic levels. The most abundant population of sills is observed in the Triassic successions of the East Barents Sea Basin. We observe near-vertical seismic column-like anomalies that cut across the entire sedimentary cover. We interpret these structures as magmatic feeder channels or dykes. In addition, the compressional seismic velocity model locally indicates near-vertical, positive finger-shaped velocity anomalies (10–15 km wide) that extend to mid-crustal depths (15–20 km) and possibly deeper. The crustal structure does not include magmatic underplating and shows no regional crustal thinning, suggesting a localized (dyking, channelized flow) rather than a pervasive mode of magma emplacement. We suggest that most of the crustal extension was taken up by brittle–plastic dilatation in shear bands. We interpret the geometry of dykes in the horizontal plane in terms of the palaeo-stress regime using a model of a thick elastoplastic plate containing a circular hole (at the plume location) and subject to combined pure shear and pressure loads. The geometry of dykes in the northern Barents Sea and Arctic Canada can be predicted by the pattern of dilatant plastic shear bands obtained in our numerical experiments assuming boundary conditions consistent with a combination of extension in the Amerasia Basin sub-parallel to the northern Barents Sea margin and a mild compression nearly orthogonal to the margin. The approach has implications for palaeo-stress analysis using the geometry of dyke swarms. Supplementary material: Details on traveltime tomography model: Resolution tests, traveltime information and ray coverage are available at https://doi.org/10.6084/m9.figshare.c.3783542

Abstract Transform-margin development around the Arctic Ocean is a predictable geometric outcome of multi-stage spreading of a small, confined ocean under radically changing plate vectors. Recognition of several transform-margin stages in the development of the Arctic Ocean enables predictions to be made regarding tectonic styles and petroleum systems. The De Geer margin, connecting the Eurasia Basin (the younger Arctic Ocean) and the NE Atlantic during the Cenozoic, is the best known example. It is dextral, multi-component, features transtension and transpression, is implicated in microcontinent release, and thus bears close comparison with the Equatorial Shear Zone. In the older Arctic Ocean, the Amerasia Basin, Early Cretaceous counterclockwise rotation around a pole in the Canadian Mackenzie Delta was accommodated by a terminal transform. We argue on geometric grounds that this dislocation may have occurred at the Canada Basin margin rather than along the more distal Lomonosov Ridge, and review evidence that elements of the old transform margin were detached by the Makarov–Podvodnikov opening and accommodated within the Alpha–Mendeleev Ridge. More controversial is the proposal of transform along the Laptev–East Siberian margin. We regard an element of transform motion as the best solution to accommodating Eurasia and Makarov–Podvodnikov Basin opening, and have incorporated it into a three-stage plate kinematic model for Cretaceous–Cenozoic Arctic Ocean opening, involving the Canada Basin rotational opening at 125–80 Ma, the Makarov–Povodnikov Basin opening at 80–60 Ma normal to the previous motion and a Eurasia Basin stage from 55 Ma to present. We suggest that all three opening phases were accompanied by transform motion, with the right-lateral sense being dominant. The limited data along the Laptev–East Siberian margin are consistent with transform-margin geometry and kinematic indicators, and these ideas will be tested as more data become available over less explored parts of the Arctic, such as the Laptev–East Siberia–Chukchi margin.