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The Cryogenian 'Sturtian' snowball Earth glaciation (c. 717–658 Ma) likely had a major role in shaping continental landscapes and biotic radiations of the late Neoproterozoic Era. However, an incomplete sedimentary record and inadequate syn-glacial age constraints make Cryogenian studies challenging. We present detrital zircon U–Pb ages for >2000 zircons from 11 sandstone samples taken at <200 m stratigraphic resolution throughout the Port Askaig Formation, a c. 1.1 km thick glaciogenic succession within the Dalradian Supergroup of Scotland and Ireland. Eight new maximum depositional age constraints, including a key constraint on deglaciation (<662.7 ± 7.8 Ma), support lithostratigraphic and stable isotope evidence that suggests the Port Askaig Formation preserves a relatively complete record of the global 'Sturtian' glaciation. An increasing contribution from Archean and Paleoproterozoic detritus to the sandstones through the lower c. 500 m of the Port Askaig Formation likely reflects the progressive glacial unroofing of the previously buried Lewisian Gneiss terrane. Archean and Paleoproterozoic grains then become scarce in the uppermost c. 300 m of the formation, which we attribute to glacial modification of the Laurentian continental margin landscape during the waning stage of 'Sturtian' glaciation. The disruption to sediment transport pathways caused by this modification, and evidenced by the detrital zircon data, points to partially warm-based 'Sturtian' ice sheets that were, to some degree, dynamic. [ABSTRACT FROM AUTHOR]

The External Ligurian Units are regarded as representative of the ocean continent transition between the Ligure‒Piemontese oceanic basin and the hyperextended Adria continental margin. The remnants of this transition are preserved as slide blocks embedded in a sedimentary mélange. This mélange sedimented during the Santonian to Campanian in the rear of the accretionary wedge that developed during the east-dipping subduction of the oceanic lithosphere below Adria. The main characteristic of this mélange is the occurrence of slide blocks of subcontinental mantle, lower continental crust, granitoids, gabbro, basalt and sedimentary rocks in a sedimentary matrix. In this paper, we provide petrographic observations coupled with U‒Pb zircon ages and δ 18O zircon isotopes of the slide blocks of felsic granulites and granitoids. U‒Pb data indicate ages ranging from Neoproterozoic to Late Triassic. δ 18O isotopes help to define the source of the magma of granitoids and felsic granulites, which was the continental crust. Overall, the collected data indicate that the slide blocks from sedimentary mélanges can be regarded as true archives that are able to provide useful constraints about the geodynamic history of the source area of these deposits. Supplementary material: The dataset related to the U–Pb and ∂18O analysisis available at https://doi.org/10.6084/m9.figshare.c.6922535 Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists [ABSTRACT FROM AUTHOR]

Ophiolite obduction, the process during which part of the oceanic crust overlaps the continental margin, presents a challenge in geodynamic reconstructions of lithospheric processes. The difference in buoyancy between the dense oceanic crust and the relatively buoyant continental crust makes obduction of the oceanic crust difficult, if not impossible, if we only consider the buoyancy forces. The initial configuration of the oceanic basins must have specific thermal and geometric constraints to overcome the difficulties posed by the negative buoyancy. Here, we present a systematic investigation of the geometric and geodynamic parameters controlling the process of ophiolite emplacement. We show which parameters are the most important during ophiolite emplacement and the optimum geometries favouring this emplacement. We focus on 'Tethyan' ophiolites, which are characterized by a relatively small inferred basin size and are commonly found in the Mediterranean region. Based on a combination of parameters, we identify the configurations most susceptible to ophiolite obduction. Our models, in agreement with the geological data, show that to achieve ophiolite obduction, the obducted lithosphere must be young and the length of the ocean–continent transition zone must be relatively sharp. Supplementary material: Supplementary figures S1–S5, that are mentioned in the main text, are available at https://doi.org/10.6084/m9.figshare.c.6922526 Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists [ABSTRACT FROM AUTHOR]

The fault locations and orientation of the Zabargad Transform Fault Zone, also called the Zabargad Fracture Zone (ZFZ), have previously only been delineated by satellite-based geophysical data, causing intense debate over the last few decades. Newly recognized geomorphological features identified in bathymetric and LiDAR data from the NE Red Sea margin present the first ground evidence for the northern extent of the ZFZ. The features are aligned over 84 km, starting from the Mabahiss Deep, near the spreading axis, and continuing to the shallow Saudi Arabian shelf along the northern termination of the Al Wajh carbonate platform. Analysis of the seafloor morphology reveals three geomorphic terrains: (1) a deeply incised canyon feeding into the Mabahiss Deep, which is characterized by dozens of amphitheatre-shaped scarps; (2) a 22 km wide head-scarp that follows the edge of the Al Wajh platform; and (3) multiple fault scars and graben-like structures on the shallow shelf. We interpret these morphological features as deformation indicators associated with the deformation processes in the ZFZ and postulate that they represent the northern end of the ZFZ. In addition, the fault zone delineates the NW margin of the Al Wajh carbonate platform and most likely continues to shape it. This paper gives new insights into the interaction between fracture zones and continental margins and their role in the morphogenesis of the seafloor. [ABSTRACT FROM AUTHOR]

The Indo-Myanmar Ranges make up an enigmatic mountain belt occupying a complex tectonic zone in western Myanmar, extending from the northern continuation of the active Sunda–Andaman arc into the eastern Himalayan Syntaxis. The Indo-Myanmar Ranges are part of an accretionary forearc basin–arc complex that includes the Central Myanmar Basin and the Wuntho–Popa Arc to the east. New biostratigraphic, petrological and detrital zircon U–Pb age data are presented and used to test and refine the divergent tectonic models that have been proposed for western Myanmar. These data suggest that: (1) the Upper Triassic Pane Chaung Formation was originally deposited adjacent to the NE Indian continental margin within northern Gondwana during the Late Triassic; and (2) the Upper Cretaceous–Paleogene rocks of the Indo-Myanmar Ranges were mainly derived from the Wuntho–Popa Arc and Inner Belt, with a subordinate input from a crustal source, potentially from the Naga metamorphic-type Paleozoic basement. The Kalemyo Ophiolite has an Early Cretaceous age similar to the ages of ophiolites in the Indus–Yarlung Tsangpo Suture Zone, south Tibet and Nagaland, reinforcing the hypothesis that they were once part of the same Neotethyan ocean floor. Supplementary material: Sample locality details, detailed methodologies and geochemical data are available at https://doi.org/10.6084/m9.figshare.c.6487105 [ABSTRACT FROM AUTHOR]

The Sindong Group (Aptian–Albian), distributed in southeastern Korea, is a fluvio-lacustrine sequence deposited in the NE–SW-trending Nakdong Trough formed in an active continental margin. Sediments were derived from the Yeongnam Massif located west and NW of the Nakdong Trough, where Early Jurassic arc magmatism began in the southern part of the Korean Peninsula. We report mineral chemistry of detrital chromian spinels of first-cycle origin occurring as an accessory mineral in arkose to feldspathic litharenites of the Sindong Group. Chromian spinel grains have Cr/(Cr + Al) atomic ratio between 0.36 and 0.94, Mg/(Mg + Fe2+) atomic ratio between 0.12 and 0.74, Fe3+/(Fe3+ + Al + Cr) value mostly <0.1, and <0.2 wt% TiO2; these values are consistent with spinel composition of forearc mantle peridotites, but are different from spinel composition of ultramafic rocks exposed in the southern Korean Peninsula. The results of this study indicate that forearc mantle peridotite or serpentinite was present in the Yeongnam Massif, and its tectonic emplacement is interpreted to have occurred by protrusion through the NE–SW-trending strike-slip fault zone developed in Middle Jurassic–Early Cretaceous time in the Yeongnam Massif and along the border with the adjacent tectonic province to the NW as a result of oblique convergence. Supplementary material: Locations of sandstone samples and compositions of spinels are available at https://doi.org/10.6084/m9.figshare.c.6004354 [ABSTRACT FROM AUTHOR]

The Nambour Basin provides the easternmost record of Jurassic sedimentation for Australia. U–Pb detrital zircon age spectra constrain basin infill as Early–Middle Jurassic (c. 195–163 Ma). Early Jurassic samples are dominated by 650–500 Ma detrital zircon sourced from the Lachlan Orogen of southeastern Australia. Distal Jurassic upland associated with this orogen was generated by epeiric uplift. Sediment sourced from it was transported northwards and eastwards into the Nambour Basin as corroborated by basinal paleocurrent data. In contrast, Devonian to Triassic detrital zircon from the New England Orogen, which abuts the Nambour Basin margin, are scarce. Topographic relief across this orogen generated by the Permo-Triassic (c. 260–230 Ma) Hunter Bowen Orogeny, had been largely eliminated by the Early Jurassic. Dominant Jurassic detrital zircon for one sample of this age, combined with related paleocurrent data and the absence of a Jurassic zircon source in eastern Australia, reflects an easterly Jurassic igneous assemblage now located on submerged northern Zealandia. The detrital zircon data presented herein constrains tectonic interpretations proposed for Jurassic east Gondwana, continental margin sedimentary assemblages in New Caledonia and New Zealand. Documentation of continental epeiric uplift from detrital zircon age data obtained from basin fill has potential yet to be explored. Supplementary material: Tables S1 and S2 are available at https://doi.org/10.6084/m9.figshare.c.5988017 [ABSTRACT FROM AUTHOR]

The architecture of canyon-fills can provide a valuable record of the link between tectonics, sedimentation and depositional processes in submarine settings. We investigated the role of plate tectonics in the initiation and evolution of submarine canyons. We demonstrate that events at the plate tectonic scale (i.e. continental break-up and shortening) have a first-order influence on the initiation and development of submarine canyons. The Late Cretaceous (c. 65 Ma) separation of Australia and Antarctica initially resulted in extensional fault systems, which then formed a steep stair-shaped palaeoseabed. Subsequently, the Late Miocene (c. 5 Ma) collision of Australia and Eurasia resulted in substantial uplift and exhumation on the SE Australian continental margin. These tectonic events led to elevated seismicity, which ultimately gave rise to gravity-driven processes (i.e. turbidity currents and mass wasting processes) and formed the base of the canyon. The inherited stair-shaped topography then facilitated further gravity-driven processes that established a mature sediment conduit extending from the shallow marine shelf to the abyssal plain. We suggest that the stratigraphic architecture of canyons can be used as an archive to record tectonic movements. Moreover, the factors that precondition and trigger gravity-driven processes can induce canyon initiation and facilitate canyon development. Supplementary material: A PDF file containing all the clean, uninterpreted seismic sections is available at https://doi.org/10.6084/m9.figshare.c.5937760 [ABSTRACT FROM AUTHOR]

New structural data from a mid-crustal segment in the Eastern Sierras Pampeanas, coupled with geochronological methods and P–T estimates, reveal polyphase contractional deformation and metamorphism during the Famatinian Orogeny over a long period of time. Peaks of metamorphic monazite and zircon ages are recorded at c. 500 Ma, between 484 and 465 Ma and at c. 440 Ma. Between 484 and 465 Ma the region attained high-temperature (HT) low-pressure (LP) conditions that resulted in widespread partial melting (peak at c. 470 Ma). A contractional phase occurred during this event, as suggested by syn-anatectic structures, as well as folding at subsolidus conditions. Renewed contraction under subsolidus conditions is evidenced by reverse ductile shearing and folding at c. 440 Ma. Thrusting along the La Chilca Shear Zone caused metamorphic inversion. The consistent orientation of folds in the Quebrada del Molle Metamorphic Complex, El Portezuelo Metamorphic–Igneous Complex and the La Chilca Shear Zone as well as WSW-directed thrusting at the later shear zone indicate uniform WSW–ENE-directed shortening. This late deformation records the Ocloyic tectonic phase and brought the Famatinian Orogeny to an end in the Late Ordovician to Early Silurian. Supplementary material: Analytical methods, methods and description of the calculated P–T pseudosection diagrams, bulk compositions, and electron microprobe, U–Pb and 40Ar–39Ar data are available at https://doi.org/10.6084/m9.figshare.c.4697189 [ABSTRACT FROM AUTHOR]

Elevated topography is evident across the continental margins of the Atlantic. The Cumberland Peninsula, Baffin Island, formed as the result of rifting along the Labrador–Baffin margins in the late Mesozoic and is dominated by low-relief high-elevation topography. Apatite fission-track (AFT) analysis of the landscape previously concluded that the area has experienced a differential protracted cooling regime since the Devonian; however, defined periods of cooling and the direct causes of exhumation were unresolved. This work combines the original AFT data with 98 apatite new (U–Th)/He (AHe) ages from 16 samples and applies the newly developed 'broken crystals' technique to provide a greater number of thermal constraints for thermal history modelling to better constrain the topographic evolution. The spatial distribution of AFT and AHe ages implies that exhumation has been significant toward the SE (Labrador) coastline, and results of thermal modelling outline three notable periods of cooling: in the pre-rift stage (460–200 Ma), from synrift stage to present (120–0 Ma) and within the post-rift stage (30–0 Ma). Pre-rift cooling is interpreted as the result of exhumation of Laurentia and synrift cooling as the result of rift-flank uplift to the SE and differential erosion of landscape, whereas the final post-rift period is probably an artefact of the modelling process. These results suggest that the source of the Cumberland Peninsula's modern-day elevated topography is uplift during rifting in the Cretaceous and the isostatic compensation following continuous Mesozoic and Cenozoic differential erosion. This work highlights how interaction of rift tectonics and isostasy can be the principal source for modern elevated continental margins, and also provides insight into the pre-rift exhumational history of central Laurentia. Supplementary material: Thermal histories are available at: https://doi.org/10.6084/m9.figshare.c.4528409 [ABSTRACT FROM AUTHOR]

Zircons from Late Triassic deep-water sandstone turbidites of the Mamonia Complex (west Cyprus) have prominent Ediacaran–Cryogenian and Tonian–Stenian age populations, with smaller populations at c. 2.0 and 2.7–2.5 Ga, but only minor concordant Paleozoic zircons. Late Jurassic–Early Cretaceous deep-water gravity-deposited sandstone, also from the Mamonia Complex, has a greater proportion of Ediacaran–Cryogenian and Tonian–Stenian zircons, but less abundant Paleoproterozoic, Archean and Paleozoic zircons. Similar zircon populations characterize an Early Cretaceous shallow-marine sandstone block in the Moni Melange (southern Cyprus). The dominant Ediacaran–Cryogenian and Tonian–Stenian zircon populations originated in the NE Africa/Arabian–Nubian Shield (north Gondwana). However, they were probably recycled from Paleozoic sandstones within Anatolia following South Neotethyan rifting, which also gave rise to sparse Permian–Triassic zircons. Paleozoic zircons reflect Variscan magmatism within Anatolia. Both Late Cretaceous and overlying Eocene sandstone turbidites in the Kyrenia Range (north Cyprus) contain prominent Ediacaran–Cryogenian populations, together with small Archean, Tonian, Carboniferous and Late Cretaceous populations, with additional Triassic zircons in the Eocene sample. Late Cretaceous zircons dominate an overlying Late Miocene sandstone turbidite, together with minor Ediacaran–Cryogenian, Eocene and Miocene populations. The Late Cretaceous zircons record continental margin arc and/or ophiolite-related magmatism, whereas the Eocene and Miocene zircons represent collision-related magmatism, both located in southern Turkey. Supplementary materials: Detailed zircon U–Pb geochronological data and supplementary figures are available at https://doi.org/10.6084/m9.figshare.c.4483736 [ABSTRACT FROM AUTHOR]

We present field, chemical and U–Pb age data for metamafic–ultramafic bodies of the Triassic rift-related Therma–Volvi–Gomati (TVG) complex of the Serbo-Macedonian Massif (SMM) in the northern Aegean region. The TVG rocks record igneous textures overprinted by Alpine metamorphism and deformation. The high-Ti Volvi body was transformed into amphibolites, which also rim the low-Ti Gomati and Nea Roda bodies. The compositions are compatible with normal (N-) and enriched (E-) mid-ocean ridge basalt (MORB) and weak ocean island basalt (OIB) signatures of the high-Ti rocks, whereas the low-Ti rocks are depleted with respect to MORB, suggesting melt extraction from a mantle source. U–Pb geochronology reveals Triassic crystallization of the Volvi body at 240 Ma. Ordovician to Carboniferous xenocrystic zircons were found in the Stratoni body of the TVG complex, which were sampled from the SMM basement. The Triassic Arnea rift-related metagranite intrudes the Volvi body. Comparison of the compositions of the Volvi body and the Arnea metagranite of the SMM with Triassic metagranite of the Rhodope Massif (RM) supports the presence of a regional bimodal rift suite. The location of the TVG complex at the SMM–RM margin of Eurasia confirms its origin as a Middle Triassic rift suite, and its nature as a continental margin ophiolite representing an ocean–continent transition of the propagating Neotethys. Supplementary material: Whole-rock chemical analyses and U–Pb geochronology analytical results data tables are available at https://doi.org/10.6084/m9.figshare.c.4087022 Thematic collection: This article is part of the 'Tethyan ophiolites and Tethyan seaways collection' available at: https://www.lyellcollection.org/cc/tethyan-ophiolites-and-tethyan-seaways [ABSTRACT FROM AUTHOR]

Two Cenozoic magmatic cycles occurred in Sardinia separated by a 5 myr gap: Oligo-Miocene subduction-related calc-alkaline magmatism associated with Sardinia migrating from the European continental margin to its current location, and Plio-Pleistocene intraplate alkaline magmatism associated with the opening of the southern Tyrrhenian basin. Based on an integration of new and published geochemical data on the Cenozoic volcanic rocks of Sardinia, and regional tectonics, we propose that a northward propagating slab tear formed south of Sardinia at the end of the Oligo-Miocene cycle. This was responsible for the transition from subduction-controlled calc-alkaline to extension-controlled mildly alkaline to peralkaline magmatism in the Sulcis area (SW Sardinia), and for the end of the Oligo-Miocene magmatism. The inflow of hotter material from the European Asthenospheric Reservoir (EAR) through the slab window could have produced the minor EAR-type alkaline lavas that erupted at the end of the Oligo-Miocene cycle and at the beginning of the Plio-Pleistocene cycle. The dominant younger Plio-Pleistocene lavas with EMI-type compositions probably formed from decompression melting of a shallower lithospheric mantle with little influence from the EAR-forming event. [ABSTRACT FROM AUTHOR]

Paleozoic continental margin strata in the western Foreland Belt of the Canadian Cordillera are characterized in part by alkaline volcanic sequences, carbonatite intrusions, coarse clastic sedimentary units, and erosional unconformities. These strata also contain a record of mid-Paleozoic contractional deformation unseen in coeval passive margin strata in the eastern Foreland Belt. In order to test potential genetic links between Paleozoic alkaline igneous activity, active margin sedimentation, and deformation in thewestern Foreland Belt, and better understand their implications for the evolution of the Foreland Belt as a whole, we have undertaken a detailed mapping and structural study of the Aley carbonatite intrusion and its host strata in the western Foreland Belt of NE British Columbia. Our work demonstrates that carbonatite emplacement was coeval with a Late Devonian contractional nappe-forming tectonic event. Interpreting tectonism as associated with continental collision along a long-lived active margin provides the best explanation for our structural and stratigraphic observations, and suggests that the western Foreland Belt is far-travelled and exotic relative to coeval passive margin strata in the eastern Foreland Belt. Deformed alkaline-carbonatite intrusions that characterize continental suture zones in Africa may provide an analogue for the Aley carbonatite and correlative alkaline-carbonatite complexes in the western Foreland Belt. [ABSTRACT FROM AUTHOR]

The thick sedimentary cover (=18 km) along the Eastern Continental Margin of India (ECMI) and over the Bay of Bengal has hindered understanding of the mechanisms of rifting that operated on the eastern Indian and Bangladesh margins. Analysis of multichannel seismic reflection data, together with 3D gravity inversion and 2D gravity forward modelling, illuminates basement configuration, crustal thickness and Moho topography, thereby revealing the modes of rift evolution and the location of the continent-ocean boundary (COB) along these margins. The basement, particularly in the shelf and slope regions of eastern peninsular India, is traversed by nearly coast-perpendicular graben, and their seaward continuity is delineated up to 125 km from the coastline. Three different types of continental margin are present along the ECMI: (1) sheared rift on the southern segment of the ECMI, up to 14° N latitude (offshore the Southern Granulite Terrain); (2) hyper-extended rift in the central segment between 14° N and 17° N (offshore the Dharwar Craton); and (3) hypo-extended rift on the northern segment between 17° N and 20° N (offshore the Eastern Ghats Mobile Belt). The graben terminations, crustal thickness and Moho topography of both the ECMI and offshore Bengal Basin clearly suggest that the COB runs nearly parallel to the coastline of peninsular India, but takes an orthogonal turn offshore in the Bengal Basin and connects the palaeo-continental shelf and the Rajmahal-Sylhet Line onshore in the Bengal Basin. Crustal thickness (8-10 km) and depth to the Moho discontinuity (=28 km) beneath the Bangladesh margin are unusual because the crustal thickness increased through interaction of the Kerguelen plume with the existing oceanic lithosphere. The Moho deepened largely due to the load of the Bengal Fan sediments. The absence of rifted crustal blocks on the Bangladesh margin and the continuity of the COB into the onshore Bengal Basin together imply that the present Bangladesh region was under marine conditions at least until the beginning of Bengal Fan sedimentation (i.e. no less than 23 Ma). [ABSTRACT FROM AUTHOR]

The Plio-Quaternary magmatism in the Tyrrhenian Sea area exhibits wide compositional variations, which cover almost entirely those observed for volcanic rocks worldwide. Some volcanoes (Etna, Iblei, Sardinia, etc.) range from tholeiitic to Na-alkaline, and display elemental and isotope signatures typical of FOZO and EM-1 ocean-island basalts (OIB). Other volcanoes (Aeolian Arc, Italian peninsula) range from calc-alkaline-shoshonitic to K-alkaline, exhibit typical 'subduction- related' trace element signatures (low Ta-Nb, high Rb-Cs-LREE), and show a large range of radiogenic isotope ratios, from mantle-like in the Aeolian Arc to crustal-like in central Italy. Geochemical data suggest that OIB-type magmatism originated in lithosphere-asthenosphere sources that were unaffected by recent subduction. In contrast, subduction-related magmas come from mantle sources that underwent Eocene to present mixing with various amounts and types of subducted crustal components. Fluxing of the mantle wedge by water-rich fluids from a mid-ocean ridge basalt-type slab occurred in the southern Tyrrhenian Sea, whereas interaction between peridotite and various types of sediments occurred in central Italy. These contrasting styles of mantle contaminations relate to the nature (oceanic or continental) of the foreland, slab geometry and pre-metasomatic mantle compositions, which vary greatly along the Apennine arc and are the reason for the formation of the wide variety of orogenic magmas in Italy. [ABSTRACT FROM AUTHOR]

Since the 1970s, the largest oil and gas reservoirs have been discovered in the Permian-Early Triassic formations in Saudi Arabia. Thus, this time period is important for the discovery of new oil reserves in Iran. The Arabian passive continental margin has undergone lithospheric extension during the Permian-Triassic, which led to the formation of the Neo-Tethys. The aim of this paper is to describe the development of the continental rift basin in the Zagros region based on the tectono-sedimentological evolution. We have studied well-log data to specify the distribution of synrift deposits in the Zagros and have related this information to the modelling. Environmental changes indicated by various sedimentary sequences, from a siliciclastic basin to a carbonate platform setting, are described. The Cambrian Hormuz salt, which overlies the metamorphosed Precambrian basement, becomes effective as a basal detachment layer influencing the style of overburden deformation during the Permian-Triassic extension event. We have investigated the formation of various structures linked to the presence or absence of the Hormuz layer by analogue modelling and relating these structures to the Late Palaeozoic sedimentation. Based on results of the analogue modelling, we argue that the basal detachment layer (Hormuz series) has contributed to the various structural styles of the extensional basin development in the Fars domain and the Lorestan domain. [ABSTRACT FROM AUTHOR]

Submarine slope failures are a widespread, hazardous phenomenon on continental margins. The prevailing opinion links large submarine landslides along the glaciated NW European continental margins to overpressure generated by the alternation of rapidly deposited glacigenic and hemipelagic material. Here, we report a newly discovered large landslide complex off NW Svalbard. It differs from all known large slides off NW Europe, as the available data rule out that this slope failure resulted from rapid glacigenic deposition. This suggests that processes such as contour currents, tectonic faulting, and overpressure build-up related to the gas hydrate system must be considered for hazard assessment. [ABSTRACT FROM AUTHOR]

Palaeozoic-Mesozoic brittle normal faults onshore along the SW Barents Sea passive margin off northern Norway give valuable insight into fault and fluid flow processes from the lower brittle crust. Microstructural evidence suggests that Late Permian-Early Triassic faulting took place during multiple phases, with initial fault movement at minimum P-T conditions of c. 300 °C and c. 240 MPa (c. 10 km depth), followed by later fault movement at minimum P-T conditions of c. 275 °C and c. 220 MPa (c. 8.5 km depth). The study shows that pore pressures locally reached lithostatic levels (240 MPa) during faulting and that faulting came to a halt during early (deep) stages of rifting along the margin. Fault permeability has been controlled by healing and precipitation processes through time, which have sealed off the core zone and eventually the damage zones after faulting. A minimum average exhumation rate of c. 40 m Ma-1 since the Late Permian is estimated. It implies that the debated Late Cenozoic uplift of the margin may be explained by increased erosion rates in the coastal regions owing to climate detoriation, which caused subsequent isostatic recalibration and uplift of the marginal crust. The studied faults may be used as analogues of basement-involved fault complexes offshore, revealing details about the offshore nature of faulting, including past and present basement and fault zone permeability. [ABSTRACT FROM AUTHOR]

The only place where Neogene-Quaternary rocks crop out for the entire Tuscan Archipelago in the Northern Tyrrhenian Sea is the island of Pianosa. In particular, the Miocene deposits record the depositional and tectonic evolution of the Northern Tyrrhenian region during this time period. These deposits are subdivided into two successions separated by a low-angle unconformity. The older, middle Burdigalian succession represents a calciturbidite shallow marine system, whereas the younger late Tortonian-early Messinian succession comprises a continental alluvial system that evolves upwards into a lagoonal-marginal marine environment. Here we present sedimentological, palaeontological and petrographical data that support a new stratigraphic and palaeogeographical framework for reconstructing the opening of the Northern Tyrrhenian back-arc basin. The early Miocene succession records a pre-rift marine depositional phase followed by a late Burdigalian-Langhian erosional phase. This was followed by a period of synrift continental-marginal deposition, as recorded by the late Miocene succession, terminated by an important phase of uplift, probably induced by the start of magmatic activity in the Tuscan Archipelago area. [ABSTRACT FROM AUTHOR]

Radiometric dating by the 40Ar-39Ar incremental heating method was carried out on lavas, sills, dykes, and a central intrusion from NE Greenland. Eighteen samples gave acceptable crystallization ages. Lavas of both Lower and Upper Plateau Lava Series gave ages in the range 55.5-53.5 Ma and cannot be constrained to better than 56-53 Ma. Sills and dykes from Traill Ø to Shannon, with compositions fairly similar to those of the lavas, gave ages of 55.1-51.3 Ma, contemporaneous with and slightly younger than the lavas. Alkaline lavas on inland nunataks have ages of 53-50 Ma, and the Kap Broer Ruys intrusive centre has an age of 48.7 ± 0.5 Ma. An alkaline sill on Hvalrosø is much younger at 20.3 ± 0.1 Ma. There are no pre-breakup lavas onshore NE Greenland. We surmise that the hot mantle of the Iceland plume arrived and melted extensively beneath the northern basins only at the time of breakup around 55 Ma. Post-breakup intrusive events in NE Greenland coincided with plate-tectonic events such as reorganization, uplift and opening in the north. The Hvalrosø sill represents a local small melting event that may be related to coeval opening of the Lena Trough. [ABSTRACT FROM AUTHOR]

Evolution of slab geometry beneath the North Island, New Zealand, has been investigated using a combination of published arc-type volcanic ages and earthquake locations in the subducting Pacific plate. Arc-front volcanoes migrated SE by 150 km in the last 8 myr subparallel to the present active arc. Migration of the arc is interpreted to mainly reflect slab rollback along the Tonga-Kermadec subduction system changing to fixed hinge slab steepening beneath the central North Island. The strike of the Pacific plate beneath the North Island, imaged by Benioff zone seismicity (50-200 km) and positive mantle velocity anomalies (200-600 km), is parallel to the NE-SW trend of arc-front volcanism. Arc parallelism since 16 Ma indicates that the strike of the subducting plate beneath the North Island was constant over this time interval, in contrast to clockwise vertical-axis rotations of =50° of the overriding plate over the same period along the eastern and southern Hikurangi margin. Acceleration of arc-front migration rates (from c. 4 to c. 18 mm a-1), eruption of high-Mg# andesites, increasing eruption frequency and size, and uplift of the overriding plate indicate an increase in the hydration, temperature and size of the mantle wedge beneath the central North Island from c. 7 Ma. [ABSTRACT FROM AUTHOR]

Examples of epigenetic hematite mineralization located at the margins of the East Irish Sea Basin have been sampled for palaeomagnetic investigation to establish the timing of ore formation. Samples collected from 10 sites in Cumbria are dominated by hematite of near-pure composition and characterized by dual polarity and, in part, dual component magnetizations that yield palaeopoles (nine sites) between 50°N, 130°E and 50°N, 150°E. In contrast, samples recovered from seven sites on the Isle of Man have more varied mineralogical compositions that include ferromagnets with lower unblocking temperatures. Manx hematite mineralization also exhibits dual polarity, but magnetizations yield steeper inclinations with palaeopoles lying between 55°N, 130°E and 70°N, 150°E. Steeper directions probably reflect minor tilting of the Manx block following hematite emplacement. Correlation of poles with the European apparent polar wander path indicates that these ore deposits formed during the Middle Triassic. Results show that hematite mineralization sited at the margins of the East Irish Sea Basin is essentially contemporaneous and establishes, for the first time, an underlying temporal relationship between these geographically dispersed ore bodies. Dating places the mineralization within a broader extensional geotectonic regime associated with the early rifting of Pangaea in the North Atlantic. The context implies a causal link between crustal extension, development of ore-forming fluids within the evolving East Irish Sea Basin, and subsequent migration of fluids to basin margins where iron was precipitated as hematite. [ABSTRACT FROM AUTHOR]

Early Ordovician collision of the Lough Nafooey Arc (part of the Baie Verte Oceanic Tract) with the passive continental margin of Laurentia peaked at c. 475 Ma in Scotland and Ireland and was followed by subduction polarity reversal. We examined Upper Ordovician–Silurian sedimentary rocks from western Ireland to see whether collision was followed by renewed arc magmatism. Despite the scarcity of dated igneous intrusions between the Grampian (c. 470 Ma) and Acadian (c. 420 Ma) orogenies in Ireland, detrital zircons show a continuity of activity peaking at 480–440 Ma, implying no hiatus in regional magmatism. Differences in zircon U–Pb age spectra highlight the isolation of basins in the southern Killary Harbour area from those north of the South Mayo Trough. These latter rocks were largely derived by erosion from Moine and Upper Dalradian sources. By contrast, the Killary Harbour Basin shows a decreasing influence from the Dalradian after c. 436 Ma and an increasing influence of contemporaneous magmatic zircons. These were transported from sources along-strike from the present NE, probably at the southern end of the Scandian Mountains in SE Greenland. The western Irish basins formed as pull-apart basins in a forearc setting and are analogous to Cenozoic pull-apart basins in Sumatra. Supplementary material: U-Pb zircon analytical data is available at a decreasing influence from the Dalradian after c. 436 Ma and an increasing influence of contemporaneous https://doi.org/10.6084/m9.figshare.c.5209849 [ABSTRACT FROM AUTHOR]

The Chile Trench of the convergent continental margin of Central Chile is a sediment-filled basin that stretches over 1500 km in a north-south direction. The sediment fill reflects latitudinal variations in climate as well as in the morphology and geology of Chile, but also of sediment transport processes to the trench and within the trench. We try to untangle these signals by calculating the total volume and the latitudinal volume distribution of trench sediments and by relating this distribution to a number of factors that affect this pattern. The volume calculation is based on a model geometry of the top of the subducting oceanic plate that is buried beneath trench sediments and the sea floor as measured by swath bathymetry. We obtain the model geometry of the subducting plate by interpolating between depth-converted seismic reflection profiles that cross the trench. The total volume of the trench fill between 32 and 46°S is calculated to be 46000 ± 500 km³. The resulting latitudinal volume distribution is best explained by a sedimentation model that alternates between (1) glacial phases of high sediment flux from Southern Chile combined with active latitudinal sediment transport within the trench and (2) interglacial phases over which sediment input is dominated by local factors. [ABSTRACT FROM AUTHOR]

The origin and age of topography along the west Greenland margin is a matter of continued debate. Evidence for tectonically driven Neogene uplift has been argued from interpretations of offshore seismic surveys, onshore fission-track data and inferred episodes of cooling. Here, analysis of seismic reflection profiles and 1D modelling of exploration wells along the Greenland margin of Davis Strait demonstrate that the data are consistent with a model of ancient continental topography affected by late Cretaceous-early Palaeocene rifting followed by thermal subsidence where offshore Neogene tectonic uplift is not required. This interpretation for the offshore evolution of the west Greenland margin has implications for the adjacent onshore evolution and for other continental margins developed throughout the Atlantic-Arctic rift system. [ABSTRACT FROM AUTHOR]

Regionally constrained 3D gravity inversion results on the Orphan Basin-Flemish Cap and the Irish Atlantic conjugate continental margins are compared to investigate crustal structure, early rifting history and geological evolution of this part of the North Atlantic. The full-crustal density anomaly distributions provide some of the first depth images of how rifted structures compare along and across these conjugate margins. Broad similarities in crustal structure are identified with some noticeable differences, linked to rifting and crustal stretching processes. Extreme crustal thinning (stretching factors >3.5) is indicated beneath much of the southern Porcupine Basin, the western half of West Orphan Basin, the eastern half of Jeanne d'Arc Basin, the southeastern half of East Orphan Basin and in pockets beneath Rockall Basin. This appears to have resulted in the serpentinization (and possible exhumation) of mantle lithosphere on the Irish Atlantic and Flemish Cap margins but not beneath Orphan Basin. A simple evolution model is proposed for the early stages of rifting between the margins. It is suggested that ancient orogenic sutures played an important role in controlling the northward migration of rifting and the rotation and displacement of Flemish Cap out of Orphan Basin. [ABSTRACT FROM AUTHOR]

The beginning of the Mesozoic, the Early Triassic, is characterized by several ecological perturbations following the end-Permian mass extinction. They are reflected in multiple C-isotope excursions coupled with climatic changes. Here we present palynological data from two accurately dated sections from the North Indian Margin (Pakistan and South Tibet). The climate of the Early Triassic was controlled by persistent monsoon circulation. The spore/pollen ratios, used as a proxy for humidity changes, indicate several significant climatic changes coinciding with C-isotope excursions. Comparison with published climate model simulations reveals that the climatic shifts were induced by orbital forcing and probably represent eccentricity cycles. Humidity peaks indicate an insolation forced shift of the intertropical convergence zone towards the North Indian Margin. Comparison with palynological data from Norway and other proxies reveal that the profound climatic change from humid to drier climate across the Smithian-Spathian boundary represents a global event, which affected southern and northern mid-latitudes and coincided with major ammonoid and conodont extinction events. This implies that increased greenhouse gas concentrations owing to recurring volcanic pulses increased the climate system sensitivity, resulting in climatic changes in distant parts of the world. Our data strongly support a link between C-isotope excursions, climatic changes and biotic responses. [ABSTRACT FROM AUTHOR]

An extensive grid of 2D seismic reflection data imaging the non-volcanic continental margin of SW Iberia is used to investigate the post-rift compressional evolution in the transition zone between continental and oceanic crust. Tectonic compression affected the margin almost continuously since the latest Cretaceous, but was predominantly focused during the mid-Eocene and the late Oligocene-mid-Miocene. The detailed interpretation of post-rift structures and their adjacent strata shows that crustal shortening in the various sectors of the margin is neither synchronous nor similar in style. Main post-rift structures include: (1) thick-skinned transpressional deformation on the distal margin; (2) localized basin shortening on the outer proximal margin; (3) limited reverse faulting and inversion on the inner proximal margin. The location and magnitude of crustal shortening are dependent on the inherited syn-rift geometry, the existence of evaporite (or clay-rich) detachments at depth, the rheological behaviour of previously extended continental crust and the position of the ocean-continent transition zone. The mechanisms of compression are mainly dominated by plate collision associated with the southeastern migration of the Iberian microplate during the Alpine orogeny and with recent westward convergence with the oceanic domain. [ABSTRACT FROM AUTHOR]

Three Pleistocene giant slope failures are observed in high-resolution bathymetric and seismic reflection data off Southern Chile, two of which extend across the full width of the continental slope from the shelf break to the trench. With mobilized volumes between 253 km³ and 472 km³, these slides are among the largest submarine landslides documented at active continental margins so far. Deposits of each of the slides are imaged as chaotic sequences in seismic reflection lines buried beneath well-stratified sediments in the Chile Trench. The ages of the three slides are about 0.25, 0.41 and >0.56 Ma. The main preconditioning factor for the slope instabilities seems to be local uplift of the continental slope that results in peculiarly high slope angles of up to 30°. Uplift of the marine and continental forearc of the study area is the result of shortening across upper plate faults and therefore a long-term continuous process. Slope instability seems to be an iterative process and failure is likely to recur. [ABSTRACT FROM AUTHOR]

Current models for the Palaeogene-aged continental break-up in the North Atlantic invoke a NW- SE extension vector throughout the rift-to-drift process, accommodated by margin-parallel normal faults, and margin-oblique (strike-slip) transfer zones. However, Palaeogene and younger faults in the Faroe Islands provide evidence for a progressive anticlockwise rotation in extension vectors immediately prior to and following North Atlantic break-up. Six deformation stages are recognized: (1) east-west to NE-SWextension, accommodated by dip-slip north-south- and NW-SE-trending faults; (2) continued NE-SW extension accommodated by NW-SE- and NNE-SSW-oriented dykes; (3) north-south extension accommodated by ENE-WSW and ESE-WNW conjugate dykes; (4) crustal extrusion involving both east-west shortening and further north-south extension along ENE-WSW (dextral) and ESE-WNW (sinistral) conjugate strike-slip faults; (5) during the final stages of rifting, the regional extension vector became NW-SE and was accommodated predominantly by slip along NE-SW dextral oblique-slip faults; (6) pre-existing structures were locally reactivated as tensional and extensional-shear features, characterized by the entrainment of clastic material along fault planes. The present study reveals a distinct period of margin-parallel extension immediately prior to break-up that is not accounted for by existing models, illustrating the importance of conducting field-based studies to validate otherwise widely accepted margin-scale models worldwide. [ABSTRACT FROM AUTHOR]

We present a regional, crustal-scale, 3D structural model of the Norwegian continental margin integrating sedimentary and crustal layers from the continental and the oceanic domain. The model includes six sedimentary units, underlain on the continental side by a thinned crystalline crust and a lower-crustal high-velocity body. In the oceanic domain, three crustal layers (2AB, 3A and 3B), thickened at the continent-ocean transition (COT), are modelled below the post-breakup deposits. Two major rift phases with different rift axes (Late Jurassic--Early Cretaceous and Late Cretaceous--Early Tertiary) have caused post-Jurassic subsidence and post-depositional deformation of the pre-Cretaceous units. The modelled COT suggests that the pre-breakup rifting event was related to differential stretching focused at the outer margin and that breakup took place in a 'base-up' magmatic process as a continuation of underplating. For the earlier rift event, stretching was distributed over the entire margin and led to accumulation of up to 12 km of Cretaceous deposits. The large sediment thickness of the Cretaceous units requires deep-water conditions and abundant sediment supply and thus coeval offshore subsidence and onshore uplift. All layers indicate a sinistral offset along the Jan Mayen Fracture Zone and its continentward continuation. [ABSTRACT FROM AUTHOR]

We report four late Palaeozoic zircon sensitive high-resolution ion microprobe (SHRIMP) U-Pb ages for granitic plutons from the Inner Mongolia Palaeo-uplift on the northern margin of the North China block. These cast a new light on the poorly understood tectonic history of the northern margin of the North China block and the Central Asian Orogenic Belt during the late Palaeozoic. The plutons have for a long time been considered to belong to the early Precambrian basement of the North China block. Our new SHRIMP U-Pb zircon dating of four plutons at Longhua, Daguangding, Boluonuo and Hushiha has yielded intrusive ages of 311 ± 2 Ma, 324 ± 6 Ma, 302 ± 4 Ma and 310 ± 5 Ma, respectively. Geochemical data suggest that these granitoids have a calc-alkaline, subduction-related I-type signature, indicating the existence of an Andean-style continental arc along the northern margin of the North China block during the late Palaeozoic. Our results also indicate that the Palaeo-Asian Ocean still existed during latest Carboniferous-earliest Permian time, and that the final collision between the southern Mongolia composite terranes and the North China block occurred later than c. 290 Ma. We suggest that the northern margin of the North China block was an active continental margin and the Inner Mongolia Palaeo-uplift is a deeply exhumed mid-crustal 'root' of a late Palaeozoic Andean-style continental arc. [ABSTRACT FROM AUTHOR]

The lithospheric structure across the Møre Margin has been studied by integrating regional elevation, gravity, geoid and heat-flow data together with available seismic and geological data. Our results show that the Moho depth varies from 42 km beneath the Caledonides to 20-15 km beneath the basin and to 13-16 km in the oceanic domain. The lithosphere thins in a step-like manner from 160 km inland to 60-80 km in the oceanic domain. A comparison with the Vøring Margin reveals that both margins have similar crustal and lithospheric structures. Major dissimilarities are: (1) the volume of underplating beneath the ocean-continent boundary; (2) the lithospheric thickness beneath the Caledonian Front; (3) the lithospheric thickness beneath the distal parts of the margins. The heat transfer across the Vøring Transform Margin, the secular variation of lithospheric thickness with age, and the jump of the Aegir spreading ridge are responsible for these differences. [ABSTRACT FROM AUTHOR]

The North Atlantic continental margins have been subject to widespread exhumation, although the timing, magnitude and causes of this uplift and erosion are debated. Exhumation is thought to be most severe across the Irish Sea basin system (Western UK), and recent years have seen an increasing emphasis on the role of Palaeogene underplating as the primary mechanism of uplift. We present a study of palaeothermal and compaction data from the Mochras borehole (NW Wales). Located near the presumed locus of exhumation, Mochras penetrated thick successions of Lower Jurassic and Oligo-Miocene sediments. Our results indicate that both these successions experienced considerably deeper burial prior to early Cretaceous and Neogene exhumation, respectively. Apatite fission-track analysis (AFTA) and vitrinite reflectance data from the borehole reveal evidence for exhumation-related cooling episodes beginning during the Cretaceous (150-80 Ma) and Cenozoic (50-0 Ma). Regional AFTA results and stratigraphic constraints refine the timing estimates to the early Cretaceous (120-115 Ma) and Neogene (20-0 Ma). Estimates of exhumation magnitudes during these episodes based on palaeothermal and compaction data are c. 2.5 km and c. 1.5 km, respectively. Palaeothermal data provide no evidence for elevated Palaeogene palaeotemperatures indicative of deeper burial, and thus question the basis of Palaeogene exhumation. [ABSTRACT FROM AUTHOR]

Presents a correspondence regarding the study on the northwestern Tethys Himalaya stratigraphic successions and the implications for the obduction of a section of oceanic lithosphere on top of the Indian passive continental margin. Examination of the Zangla margin; Correlation of Spontang Ophiolite with Oman Ophiolite; Thickness of the kangi-La formation.

The FAST deep seismic reflection profile traverses the whole width of the Faroe--Shetland Trough. The principal target of the profile was the structure of the crust beneath the Faroe basalts. In this region, bright reflections are seen from between 7 and 9 km depth beneath the basalts, dipping westwards in the opposite direction to the dip of the basalts and reflections within the basalts. These sub-basalt reflections are regarded as originating from near top basement. The Moho has not been imaged beneath the basalts, possibly because of the absence of any impedance contrast at the base of the crust. The profile shows that the basement of the Faroe--Shetland Trough thins to c. 10 km beneath the centre of the trough. Thinning of the crystalline basement is probably the result of more than one phase of extension, the most recent of which occurred in the mid- to late Cretaceous. Extension appears to have been concentrated on a series of east-dipping normal faults cutting through the basement. These faults may have originated during a Precambrian rifting event. It is suggested that opening of the NE Atlantic occurred to the west of the Faroe Islands, as Mesozoic rifting in the Faroe--Shetland Trough had strengthened the lithosphere in this region. [ABSTRACT FROM AUTHOR]

Detailed geological field mapping has allowed the restoration of two full stratigraphic sections through the highly deformed Mesozoic and Early Tertiary fold and thrust belt of the north Indian continental margin. The two sections, which are representative of a proximal and a distal facies on the margin, have been backstripped using standard techniques. Profiles of the tectonic subsidence and uplift through the precollisional history of the margin have been constructed and compared with the predictions of simple thermal and mechanical models. The pre-collisional history can be explained by a thermal model with an initial age of rifting of 270 Ma and a stretching factor, β, of c. 1.2. This model accounts for the general exponential decrease in the backstripped tectonic subsidence. The model fails, however, to completely explain the subsidence and uplift history of the margin since the late Cretaceous. The history during this time is characterized by uplift at the most proximal location and an increase in subsidence at the most distal location. We attribute these differential vertical movements to flexural loading of the north Indian margin by obduction of the Spontang ophiolite. The best fit model is one in which a 70 km wide wedge-shaped load, tapering from 10 to 0 km thick, is emplaced on rifted lithosphere with an elastic thickness, Te, of 5-10 km. These results, which are in accord with the late Cretaceous timing of obduction and the structure of the Spontang ophiolite, provide new constraints on the Te structure of extended continental lithosphere 120-150 Ma after a rifting event. [ABSTRACT FROM AUTHOR]

Emplacement of the southern Urals accretionary complex onto the East European Craton involved off-scraping of shallow marine limestones from the continental margin and their underplating to the base of the accretionary complex during the final stages of arc-continent collision. These limestones underwent localized ductile to semi-brittle deformation at upper-crustal levels, at temperatures close to 200 °C. Field observations, macroscopic fabric elements and crystallographic preferred orientations indicate a heterogeneous distribution of the deformation. Measurements from twinned calcite grains indicate that peak differential stress conditions during deformation attained c. 230 ± 40 MPa. These differential stress conditions are further supported by the small size of both recrystallized and twinned calcite grains. Twinning and intracrystalline slip were the major contributors to the bulk deformation and lattice preferred orientation (LPO) formation. LPO evolved with progressive strain, from an initial constrictional fabric that is consistent with the macroscopic mineral lineation as the dominant macroscopic fabric element to a c- axis maximum normal to foliation as the rock underwent dynamic recrystallization and grain refinement during progressive simple shear. [ABSTRACT FROM AUTHOR]