Evolution Of Continental Margin Research Articles

Tectonic evolution of the Early Paleozoic proto-East Asian continental margin: Inference from Paleozoic metamorphic rocks in the South Kitakami belt, northeast Japan

To constrain the incipient Pacific-type orogeny and tectonic processes in the Early Paleozoic proto-East Asian continental margin, the Motai–Matsugadaira–Yamagami (MMY) metamorphic rocks in the South Kitakami belt, northeast Japan were investigated. They are divided into two different types: amphibolite-facies rocks associated with serpentinite and blueschist-facies rocks associated with pelitic and psammitic schists. Three geochemical groups are identified from the MMY metamorphic rocks. Groups 1 and 2 resemble geochemical characteristics of mid-ocean ridge basalt and continental arc rocks, respectively. Group 3 exhibits considerable depletion of highly incompatible elements, which is caused by the high degree of partial melting of a hot mantle plume. The zircon U–Pb ages of Group 1 indicate that the protoliths experienced amphibolite-facies metamorphism soon after their formation in the Early Ordovician. Group 2 exhibits a coeval zircon U–Pb age with Group 1. The age distribution of detrital zircons in the MMY psammitic schists shows a peak of 500–400 Ma, the presence of Archean to Neoproterozoic zircons, and the youngest Late Devonian zircon. The following model is proposed for the tectonic evolution of the proto-East Asian continental margin: (1) the formation of an arc in the eastern margin of the South China craton in the Cambrian to Ordovician; (2) the subduction of a spreading axis and an oceanic plateau at the same time as the continental arc formation; (3) the consumption and subduction of arc materials by tectonic erosion; and (4) the formation of the Carboniferous accretionary complex and high-pressure metamorphic rocks under steady oceanic plate subduction. The proposed tectonic evolution model may also be applicable to equivalent Early Paleozoic rocks in southwest Japan.

Mesozoic to Cenozoic tectonic evolution in the central Bohai Bay Basin, East China

The Mesozoic and Cenozoic tectonic evolutionary history of the East Asian continental margin has been the focus of many researchers because of the overprinting of multiple tectonic domains. Previous studies have suggested that the westward subduction of the Paleo-Pacific Plate and the Pacific Plate resulted in the deconstruction of the North China Craton and controlled the formation of the related basins on the continental margin of East Asia. However, controversy remains regarding the tectonic transition processes and mechanisms that occurred from the Mesozoic to the Cenozoic. Since the Mesozoic, the Bohai Bay Basin on the eastern margin of the North China Craton of East China has been influenced by multiple tectonic domains of the Paleo-Tethys, Paleo-Pacific, and Pacific oceans, and there are complete records of these tectonic transition processes. The Bozhong Depression is a subbasin in the Bohai Bay Basin, which is a crucial area for researching the tectonic evolution of the Bohai Bay Basin throughout the Mesozoic−Cenozoic and the regional tectonic evolution of the eastern continental margin of China. Based on 3-D seismic data, logging core data, and a balanced cross section in the Bozhong area, combined with data from the apatite fission-track inversion model, we reconstructed the tectonic evolutionary history of central Bohai Bay Basin and established a three-cycle and eight-stage tectonic model of the central Bohai Bay Basin during the Mesozoic−Cenozoic. The three cycles are the Indosinian, the Yanshinian, and the Himalayan. (1) The Indosinian was marked by two stages. During the early Indosinian, NW-trending thrust faults were formed due to the collision and northward subduction of the South China Block underneath the North China Block. In the late Indosinian, the tectonic stress in the central Bohai Bay Basin shifted from compression to extension. Consequently, the thrust faults reversed, leading to the deposition of Early−Middle Jurassic strata. (2) The Yanshanian cycle comprises three main phases. Early Yanshanian transpressional shearing led to the formation of a NE/NNE-trending, left-lateral strike-slip fault due to NWW-directed subduction of the Paleo-Pacific Plate. Middle Yanshanian transtensional shearing was driven by Paleo-Pacific Plate rollback and resulted in regional extension and the negative inversion of previous compressive faults. Late Yanshanian compression gave rise to the basin reversion, which resulted from an increased subduction speed of the Paleo-Pacific Plate and a transition from a high angle to a low angle. (3) The Himalayan cycle was marked by three phases. During the early Paleogene, the region was characterized mainly by extension, and NE-trending, right-lateral strike-slip normal faults began to form. This coincided with a decrease in the Pacific Plate’s subduction speed. In the late Paleogene, the subduction rate of the Pacific Plate increased, resulting in the change of the central Bohai Bay Basin from an extensional environment to one marked by regional differential compression. In the Neogene, regional thermal subsidence and depression sedimentation occurred, which were probably induced by the increasing subduction speed and rollback of the Pacific Plate. The Bozhong Depression has experienced multiple stages of tectonic evolution, which indicates the concurrent and superimposed effects and transition of multiple tectonic domains.

The role of ice-sheet dynamics in the Miocene-Pliocene depositional systems of the Ross Sea, Antarctica

The dynamics of the Antarctic ice sheet (AIS) have profound implications for the evolution of the Antarctic continental margin, global ocean currents, and climate changes. Marine sediments from the Antarctic continental margins recorded the history of the advance and retreat of the AIS. In this study, we present an integrated analysis of the sedimentary characteristics of the Early Miocene to Late Miocene of the Ross Sea by using 2D seismic reflection data and cores from International Ocean Discovery Program (IODP) Expedition 374 Sites U1521, U1522, and U1524. The characteristics of the seismic facies and sediments show that the expansion and grounding of the ice sheets across the continental shelf significantly influenced the depositional processes, leading to increased glacial erosion, the formation of prograding wedges, mass transport deposits (MTDs), and mixed (turbidite-contourite) depositional systems since the Early Miocene. The seaward migration of the continental shelf edge and the steepening of the continental slope were mainly influenced by the glaciation of extreme expansion of the AIS. Marked increases in the prograding wedge and MTD are associated with extensive sediment reworking and deposition at the grounding zones and along the continental slope as a result of ice sheet expansion. The development of the mixed (turbidite-contourite) depositional systems was the result of extensive sediment reworking and deposition by gravity flows and bottom currents on the continental slope and the rise. This research provides new insights into the complexity of the ice sheet and the sensibility of marginal sediments in responding to the past climate changes in Antarctica.

Geodynamic Settings of Late Paleozoic–Early Mesozoic Granitoid Magmatism at the Arctic Continental Margins: Insights from New Geochronological and Geochemical Data from the Taimyr Peninsula

Despite significant progress in Arctic geological studies, a number of principal questions concerning the Paleozoic collisional events remain unanswered. Therefore, the Taimyr Peninsula, representing the only outcropped high Arctic region where magmatic complexes, formed by Hercynian collision between the Siberian Craton and the Kara Block, are well exposed, is crucially important. In this paper we report new geochemical and geochronological data for intrusions in the poorly studied northeastern part of the Taimyr Peninsula. The obtained results in combination with published data show that supra-subduction magmatism at the southern active margin of the Kara Block continued from ca. 345 to 285 Ma (Early Carboniferous to Early Permian), and was followed by a post-collisional magmatic pulse that affected the whole Taimyr across terrane boundaries at ca. 280 Ma in the Early Permian. After cessation of the post-collisional magmatism at ca. 265 Ma, the Taimyr experienced extension, and voluminous magmatic series associated with a Siberian mantle plume were formed between 251 and 228 Ma during the Triassic. The studied post-collisional and plume-related intrusions of the Northeastern Taimyr are generally classified as evolved high-K I-type granites with adakitic affinity. The latter is a regional feature because the majority of the analyzed plume-related granitoids are geochemically similar to high potassium continental adakites. It is suggested that the adakitic geochemical characteristics of the plume-related granitoids resulted from melting of hydrated mafic lower crustal protoliths and were controlled by the source lithology. Comparison of the new results with data available for adjacent areas allows for correlation of terranes on a regional scale and sheds light on the evolution of the Arctic continental margins in general. In the Early–Middle Paleozoic, the Kara Block was part of a continental terrane that formed at the northern edge of Baltica as a result of Neoproterozoic Timanian orogeny. In the Early Carboniferous, the southern margin of Kara turned into an active margin, while its inferred continuation in the eastern Uralian margin of Baltica remained a passive margin until the Early Permian. This discrepancy can be explained by dextral displacement of Kara relative to Baltica that took place in the Early Carboniferous and was later accommodated by the formation of the Taimyr collisional belt in the course of the Early Permian collision between Kara and Siberia. After collision, the Taimyr was incorporated into the northern Eurasian margin as an uplifted block that experienced surface erosion and supplied clastic material in surrounding basins.

Synrift and post-rift thermal evolution of rifted margins: a re-evaluation of classic models of extension

Abstract The thermal evolution of continental rifted margins is key to understanding margin subsidence and hydrocarbon prospectivity. Observed heat-flow values, however, do not always comply with classic rifting models. Here, we use 2D numerical models to investigate the relationship between rifting, sedimentation and thermal history of margins. We find that during the synrift, the basement heat-flow and temperature are not only controlled by extension factor, but also by synrift sediment thickness and the evolution of deformation. As this progressively focuses oceanward, the proximal sectors thermally relax, while the distal sectors experience peak temperatures. In the post-rift, the lithosphere under the hyperextended margins does not return to its original state, at least for c. 100 Myr after break-up. Instead, it mimics that of the adjacent oceanic plate, which is thinner than the original continental plate. This results in heat-flow increasing oceanward at post-rift stages, when classic rifting theory predicts complete thermal relaxation. Our models also predict slightly increased heat-flows in the adjacent oceanic crust, potentially extending hydrocarbon plays into distal margins and oceanic crust, previously discarded as immature. Finally, our models indicate that commonly used temperature approximations to calculate heat-flow during rifting may strongly differ from those occurring in nature.

Lateral changes of crustal extension and passive margin type along the Brazilian southeastern margin

For the last half century, studies based on an increasing, diverse data set, have focused on passive continental margin evolution, as a result of a sequence of tectonic processes that occur in crustal scale and in the geological time. Where extensive subsurface data exists, two distinct endmembers of continental margin architectures were first described along specific margins of the North Atlantic: 1) wide continent-ocean transitions or hyper-extended; 2) narrow continent-ocean transitions or hypo-extended. The lateral transition between these endmember margins, which can occur laterally in short distances, is still not fully understood. The same two endmember margin types are observed across passive margins around the world and notably along the South Atlantic margin. In an area known for controversial interpretations about the crustal nature and the limits of thinned continental crust, this investigation integrates crustal thickness, seismic interpretation, and facies analyses across ∼150,000 km of seismic data along the Brazilian southeastern margin. This study has implications for those investigating the crustal geometry variations for basin analysis and results impact hydrocarbon assessments for the southeastern margin of Brazil. We resume continental margin analyses, in a critical moment as hydrocarbon exploration advances from the continental slope to ultra-deep waters. Results indicate a marked change from a narrow, hypo-extended, sub-aerial, Iceland-like, plume-related volcanic crust in the Pelotas Basin, to a hyper-extended, Iberia-like, magma-rich crust in the Santos Basin, which is separated by a pronounced oceanic transform-fault zone. Dextral movement along this NW-oriented fault zone accommodated differential extensional rates between the hypo- and the hyper-extended margins. Lateral variations in magmatic content within these margin types are interpreted as result from the interaction with mantellic plumes. Margin architecture can locally be affected by pre-existing fault zones and be later modified by oceanic transform faults. The interactions between crustal extensional rates, crustal rheology, mantle underplating, and volcanic material exhumed through mantle-derived plumes, are the key controls for the evolution of continental margins. Tectonic framework classification proposed in this study presents an alternative, original model for continental passive margins evolution.

Jurassic-Paleogene spreading history of the northern Indian Ocean as a constraint on the evolution of the north Australia continental margin

The spreading history of the northern Indian Ocean is re-examined with the aim of interpreting the late Mesozoic-Paleogene evolution of the northern Australian continental margin in eastern Indonesia and Timor-Leste. The earliest seafloor spreading (‘Argo phase’) developed between approximately 155-131Ma (Kimmeridgian, Late Jurassic to Valanginian, Early Cretaceous). A clockwise pole of rotation relative to Australia (‘Argo pole’) is interpreted at 7°09’S, 133°07’E, a present-day location near the Tanimbar islands in eastern Indonesia. A second ‘Gascoyne’ phase of spreading, between 131-100Ma (late Early Cretaceous), had an interpreted clockwise rotation pole at 3°40’N, 125°00’E, a present-day location between the islands of Mindanao (southern Philippines) and Sulawesi (eastern Indonesia). A third ‘Wharton’ phase of spreading, commencing at the beginning of the Late Cretaceous (~100Ma) had a more distant pole (clockwise pole at 5°S, 171°E: Jacob et al., 2014), although more local rotations are interpreted for the Greater Sula Spur continental terrane, about a pole estimated at 9°24’S, 134°40’E, close to the earlier Argo pole.The motions of two continental terranes are inferred from the spreading history. The Argoland Terrane, which is identified in this study as eastern Sundaland (Borneo and Java), would not have entirely detached from Australia before the mid Cretaceous due to the relatively proximal locations of the Argo and Gascoyne rotation poles. In this scenario Argoland could not have collided with Eurasia in the Cretaceous, as suggested by several previous studies. The Greater Sula Spur Terrane (several continental fragments in present-day eastern Indonesia), is repositioned in the initial reconstructions immediately north of Timor, and did not move northward to its late Paleogene (pre-Neogene collision) location until the Wharton phase of rifting that commenced in the Late Cretaceous. This northward motion of the Greater Sula Spur was accommodated by the development of a narrow oceanic basin (the Banda Embayment).The reconstructions suggest that the Argoland and Greater Sula Spur continental terranes formed a continuous crustal connection between SE Asia and northern Australia throughout the late Mesozoic and early Paleogene, and that the Indian Ocean developed entirely within the body of the disrupting Gondwanaland supercontinent, rather than linking eastwards into the Pacific Ocean.

Magnetic field map of the Wilhelm Archipelago shelf zone, West Antarctica

The Antarctic Digital Magnetic Anomaly Project is an international research effort to construct a magnetic map of the continent based on ground, satellite, marine, and aeromagnetic surveys. This paper reports the magnetic mapping of the shelf zone in the SE part of the Wilhelm Archipelago, West Antarctica, based on magnetic surveys conducted with Zodiac boats. A spectacular feature of this area is the strong magnetic anomaly of the Antarctic Peninsula (AP) batholith, which was the product of subduction-related Mesozoic–Cenozoic arc magmatism on the former margin of Western Gondwana. We constructed and analyzed a detailed magnetic map of magnetic field anomalies using field observations of rock exposures on the islands and magnetic properties of rocks from laboratory data. The oldest volcanic rocks of Jurassic to Lower Cretaceous age relate to N-NE trending bands of negative magnetic field. The largest feature in the study area is an Upper Cretaceous/Paleogene granodiorite complex that produces a positive magnetic anomaly. Many smaller anomalies are also present over gabbroid bodies of Cretaceous age. Two-dimensional magnetic modeling shows that heterogeneities in the upper crust may have magnetic susceptibilities in the range of 0.005–0.13 SI. Magnetic field anomalies also delineate an orthogonal system of tectonic faults, including the main NE fault along the Penola Strait (sub-parallel to the AP coastline) and four intersecting faults. These fault systems may be associated with different stages of continental margin evolution along the Antarctic Peninsula.

The cryptic stratigraphic record of the syn‐ to post‐rift transition in the offshore Campos Basin, SE Brazil

AbstractRift basins typically comprise three main tectono‐stratigraphic stages; pre‐, syn‐ and post‐rift. The syn‐rift stage is often characterised by the deposition of asymmetric wedges of growth strata that record differential subsidence caused by active normal faulting. The subsequent post‐rift stage is defined by long‐wavelength subsidence driven by lithospheric cooling and is typified by the deposition of broadly tabular stratal packages that drape any rift‐related relief. The stratigraphic contact between syn‐ and post‐rift rocks is often thought to be represented by an erosional unconformity. However, the late syn‐rift to early post‐rift stratigraphic record is commonly far more complex since (i) the associated tectonic transition is not instantaneous; (ii) net subsidence may be punctuated by transient periods of uplift; and (iii) strain often migrates oceanward during rifting until continental breakup is achieved with crustal rupture. Previous publications on the Eastern Brazilian marginal basins have not historically used the tripartite scheme outlined above, with the post–pre‐rift interval instead being subdivided into rift, sag and passive margin tectono‐stratigraphic stages. In addition, the sag stage has been previously described as late syn‐rift, early post‐rift or as a transition between the two, with the passive margin stage being equivalent to the classically defined post‐rift, drift stage. Two (rather than one) erosional unconformities are also identified within the rift‐to‐sag succession. In this work, we use 2D and 3D seismic reflection and borehole data to discuss the expression of and controls on the syn‐ to post‐rift transition in the shallow and deep water domains of the south‐central Campos Basin, south‐east Brazil. We identified three seismic–stratigraphic sequences bounded by unconformities, named lower and upper pre‐salt and salt. The lower pre‐salt interval is characterised by wedge‐shaped packages of reflections that thicken towards graben and half‐graben‐bounding normal faults. This stage ends with the development of an angular unconformity, inferred to form as a result of the onset of the oceanward migration of deformation. The upper pre‐salt is typically defined by packages of subparallel and relatively continuous reflections that are broadly lenticular and thin towards fault‐bound basement highs, but that locally contain packages that thicken against faults. The pre‐salt to salt contact is defined by an erosional unconformity that is largely restricted to basement highs, and which is inferred to have formed due to base‐level fall and uplift associated with local fault reactivation, resulting in the formation of channels of possible fluvial origin. Based on its geometries and seismic facies, we conclude that the lower pre‐salt interval is syn‐rifting and syn‐tectonic, deposited during active continental extension and upper crustal faulting affecting the entire evolving margin, whereas the overlying upper pre‐salt is syn‐rifting and post‐tectonic in the Campos Basin, deposited when extension and faulting had migrated seaward to the future location of the spreading centre. The results of our study support the arising notion that the syn‐rift sequence does not only display syn‐tectonic sedimentary packages, and thus the tripartite tectono‐stratigraphic model for rift development is too simplistic and cannot be applied when assessing rifts in the context of the regional development of continental margins.

Ediacaran and Cambrian Volcanogenic and Sedimentary Complexes of Southern Ulutau (Central Kazakhstan): Structure, Substantiation of Age and Setting of Formation

The article presents the results of studying and substantiating the age of the Ediacaran volcanogenic-sedimentary and Cambrian sedimentary strata isolated for the first time within the southern part of the Ulutau terrane (Southern Ulutau) in the west of Central Kazakhstan. Age Estimates (SHRIMP II) obtained 594 ± 3, 594 ± 5, 600 ± 2 Ma for effusive and tufogenic rocks, as well as their isotope-geochemical characteristics, are the first evidence of the manifestation of Ediacaran suprasubduction magmatism in the paleozoics of Kazakhstan and the Northern Tien Shan. The data obtained indicate the participation of the Ulutau terrane at the end of the Precambrian in the structure of the volcanic-plutonic belt, fragments of which are also Neoproterozoic blocks within Southwestern Kazakhstan (the Zeltava and Chui‒Kendyktas terranes) of the Southern Tien Shan and the Karakum‒Tajik terrane. The formation of the Ediacaran suprasubduction belt may be a continuation of the evolution of the Neoproterozoic active continental margin that arose in the Tonian period on the northwestern margin of the supercontinent Rodinia.

Post-rift magmatism controlled by detachment faults in a microplate, northwestern South China Sea

Post-rift magmatism along continental margins is usually focused on highly stretched basins or aborted rifts. Adjacent microplates with relatively thick lithosphere are not expected to exhibit intense post-rift magmatism. This study identifies 20 mounded structures and associated pathways using two-dimensional, multichannel seismic data and ocean bottom seismometer (OBS) data across the southeastern Xisha Massif of the northwestern South China Sea. This massif is a relatively thick (>20 km) region of crust that forms a microplate between two rift branches. The mounded structures are interpreted as volcanoes, based on their seismic reflections and morphological characteristics. Detachment faults that extend into the middle crust captured the magma and provided pathways for vertical migration. During the rise of magma into the sedimentary stratum, detachment faults still served as the main channels of magmatic migration. The rigidity differences between the basement and the overlying sediments, as well as the stress field, facilitated subordinate pathways for magmatic migration, particularly at the depocenters and flanks of half-grabens. Consequently, larger volcanoes are present above the basement highs, while smaller volcanoes are located in the centers of half-grabens. This study provides criteria for identifying submarine mounded structures of different origins that are applicable beyond the study area. Moreover, this study highlights that detachment faults play a key role in the volcanic systems of the relatively rigid microplates of heterogeneous crustal structure. It also promotes our understanding of post-rift magmatism and the dynamic evolution of continental margins, and the results could be applicable to other areas with similar geological settings.

Crustal structure beneath the Jiamusi Block and the Nadanhada Terrane from seismic and magnetotelluric studies: Implications for the subduction of the Pacific Plate

The Nadanhada terrane is considered to accrete to the eastern end of the Jiamusi Block during the Pacific Plate subduction. Constraints on the deep structure of the Nadanhada terrane and Jiamusi Block are essential to study the evolution, transformation and current activity of the eastern Asian continental margin. To reconstruct the accretion processes, two magnetotelluric sounding sections and a seismic reflection section were conducted in the eastern part of Jiamusi Block, the middle, and the southern end of the Nadanhada terrane respectively. Geophysical data revealed resistant stable structures and west-dipping discontinuous reflections with a thickness of around 15 km in the upper crust of Jiamusi Block. In contrast, the lower crust of the Jiamusi block exhibited high conductivity and short sub-horizontal reflections that suggest upwelling of mantle material under Pacific Plate subduction. Moreover, the low resistivity zone observed connecting the shallow crust with the upper mantle in the Tongjiang-Yuejinshan fault was interpreted as the boundary line between the Jiamusi block and Nadanhada terrane. The Nadanhada terrane can be subdivided into the Yuejinshan and Raohe complexes based on their distinct geophysical features. The Yuejinshan Complex is characterized by irregular bodies with high resistivity and short arc reflections with a thickness of about 10 km. In contrast, the Raohe Complex displays high-resistivity blocks and west-dipping thrust nappe strong reflections with a thickness of about 5 km. Additionally, the high-conductivity layer located between the Raohe Complex and the underlying basement is believed to be the detachment zone. Since the Cretaceous, the continuous subduction of the Pacific Plate has caused magmatism that has led to the high conductivity crust. The observation of low-resistivity channels and arcuate reflections within the crust supports the notion of upwelling of mantle-derived materials brought about by the subduction of the Pacific Plate in the Cenozoic era.

Protolith origin of the Lanling high-pressure metamorphic terrane in central Qiangtang, Tibet, reveals the subduction of the Permian–Triassic ocean island and abyssal submarine fan in the Paleo-Tethys Ocean

Unraveling the protolith origin of high-pressure and low-temperature (HP-LT) metamorphic rocks is the key to understanding the tectonic evolution of active continental margins. A comprehensive study, including field observations, geochemical analyses and zircon U-Pb geochronological dating, was conducted on the Lanling HP-LT terrane to determine its protolith origin and the presubduction paleogeography of the Paleo-Tethys Ocean. The metabasites can be divided into two geochemical groups: Group A samples exhibit low TiO2 values (1.15–1.81 wt%) and subalkaline basalt affinity with rare earth element (REE) distribution patterns and trace element abundances similar to enriched mid-ocean ridge basalts (E-MORB); Group B samples have higher TiO2 values (2.75–3.32 wt%) and show alkaline basalt affinity and ocean island basalt (OIB) geochemical signatures. Lanling metabasites are likely derived from a long-depleted mantle source combined with crustal contamination based on the following evidence: (1) positive εNd(t) values (+4.8 to +5.6) and a scattered distribution of Isr(t) values (0.704684 to 0.710999), (2) abundant Precambrian zircon grains, and (3) a volcanic arc trend in the tectonic discrimination diagram. Zircon U–Pb dating yields a timing of ca. 272–241 Ma for the protolith age of the Lanling eclogites. The protoliths of the OIB- and E-MORB-type metabasites in Lanling are postulated to be ocean island magmatites and basaltic crust of the Paleo-Tethys Ocean, respectively. Moreover, the Lanling quartzose schists contain only ancient detrital zircons with ages of >500 Ma and show protolith lithostratigraphy and provenance similar to those of the late Paleozoic clastic flysch in the South Qiangtang block (SQB). Based on the above observations and other geological evidence, a hypothetical model of the Permian–Triassic ocean island and adjacent abyssal submarine fan in the Paleo-Tethys Ocean is proposed to explain the protolith origin of the Lanling HP-LT terrane and the presubduction paleogeography in central Qiangtang.

Constraining the tectonic evolution of rifted continental margins by U–Pb calcite dating

We employ U–Pb calcite dating of structurally-controlled fracture fills within crystalline Caledonian basement in western Norway to reveal subtle large-scale tectonic events that affected this rifted continental margin. The ages (15 in total) fall into four distinct groups with ages mainly ranging from latest Cretaceous to Pleistocene. (1) The three oldest (Triassic-Jurassic) ages refine the complex faulting history of a reactivated fault strand originated from the Caledonian collapse and broadly correlate with known rifting events offshore. (2) Two ages of ca. 90–80 Ma relate to lithospheric stretching and normal fault reactivation of a major ENE-WSW trending late Caledonian shear zone. (3) We correlate five ages between ca. 70 and 60 Ma with far-field effects and dynamic uplift related to the proto-Iceland mantle plume, the effect and extent of which is highly debated. (4) The five youngest ages (< 50 Ma) from distinct NE–SW trending faults are interpreted to represent several episodes of post-breakup fracture dilation, indicating a long-lived Cenozoic deformation history. Our new U–Pb data combined with structural and isotopic data show that much larger tracts of the uplifted continental margin of western Norway have been affected by far-field tectonic stresses than previously anticipated, with deformation continuing into the late Cenozoic.

Controls on the morphology of closely spaced submarine canyons incising the continental slope of the northern South China Sea

Submarine canyons are key elements in source-to-sink systems that are commonly developed along continental margins. They act as major conduits transferring sediment and pollutants from continental shelves to deep-water basins, and control the general morphology and evolution of continental margins. This work uses multibeam bathymetric and high-resolution (two- and three-dimensional) seismic data to investigate the main factors controlling the morphology of the Shenhu Canyon System in the northern South China Sea, as well as its detailed morphological character. The Shenhu Canyon System consists of nineteen (19) submarine canyons whose morphologies vary from southwest to northeast along the continental slope. Canyons (C1–C10) in the southwest show greater incision depths, and steeper thalwegs and walls, when compared to their counterparts to the northeast (C11–C17). The southwest canyons are located close to the shelf edge, where the upper continental slope is relatively steep and multiple landslides are imaged. We show that the thalwegs and walls of the southwest canyons were more actively eroded by sediment flows, with respect to the northeast canyons, making them deeper and steeper. Hence, submarine canyons in the southwest, with a more linear geometry, are now directly connected to the Pearl River Canyon. In parallel, seafloor fault scarps act as barriers for sediment transported to the heads of the northeast canyons. This research highlights how sediment supply, sediment pathways, and seafloor scarps can influence submarine canyon morphology along continental slopes. It contributes to a better understanding of the factors controlling canyon morphology worldwide.

Thermochronometry constraints on south West Greenland passive continental margin development

Passive continental margins (PCMs) represent the interface between the marine and terrestrial realms. However, topographic evolution of PCMs is often difficult to decipher due to paucity of the preserved geological record. Here, we report uranium-thorium-helium ((U-Th)/He) analysis of the Precambrian crystalline basement from southern West Greenland that help constrain the process of rifting between Greenland and North America and contributes to the debate about the West Greenland PCM development. The majority of zircon (U-Th)/He dates (220-580 Ma) imply several kilometres of burial of the basement by Paleozoic (and potentially Mesozoic) sediments. Apatite (U-Th)/He dates (80-230 Ma) record thermal processes associated with extensional tectonism starting in the Late Triassic and passive margin formation in the Early Cretaceous. Our data provide no evidence of thermal activity during Cenozoic times, suggesting that the thermal effects of Paleogene rifting and break-up were negligible and the magnitude of Cenozoic erosion was <3.5 km in the study area.

Cryogenian A-type Granites of the Yenisei Ridge – Indicators of Tectonic Transformation in the Southwestern Margin of the Siberian Craton

Abstract —We document the evolution of A-type granitoid magmatism during the Cryogenian tectonic transformation of the Yenisei Ridge from a postcollisional mode to the early stage of development of an active continental margin. We illustrate the A-type granitoid magmatism evolution in a model for the emplacement and cooling of the intrusions of the Strelka pluton, reflecting the final stage of magmatism during the formation of the postcollisional Glushikha complex (719–702 Ma). These processes took place at the same time as the formation of mantle, mantle-crustal and crustal rocks of the Tatarka complex (711–683 Ma), including the Yagodka pluton A-type granites (711–705 Ma) during the early stage of active continental margin development. During this period of tectonic transition, both convergent events involved the continuous formation of felsic intrusions corresponding to oxidized A-type granites.

Extensional structures of the Nan′an Basin in the rifting tip of the South China Sea: Implication for tectonic evolution of the southwestern continental margin

Nanan Basin is a giant hydrocarbon basin, but its tectonic division scheme and associated fault systems has not been well understood. Based on newly acquired seismic data from the southwestern margin of the South China Sea, this study analysed the structural units, tectonic feature and geodynamics of the sedimentary basin. The new data suggests that the Nanan Basin is a rift basin oriented in the NE-SW direction, rather than a pull-apart basin induced by strike-slip faults along the western margin. The basin is a continuation of the rifts in the southwest South China Sea since the Late Cretaceous. It continued rifting until the middle Miocene, even though oceanic crust occurred in the southwest subbasin. However, it had no transfer surface at the end of spreading, where it was characterized by a late middle Miocene unconformity (reflector T3). The Nanan Basin can be divided into eight structural units by a series of NE-striking faults. This study provides evidences to confirm the relative importance and interplay between regional strike-slips and orthogonal displacement during basin development and deformation. The NE-SW-striking dominant rift basin indicates that the geodynamic drivers of tectonic evolution in the western margin of the South China Sea did not have a large strike-slip mechanism. Therefore, we conclude that a large strike-slip fault system did not exist in the western margin of the South China Sea.

CAGE19-3 Cruise Report: Calypso giant piston coring in the Atlantic-Arctic gateway – Investigation of continental margin development and effect of tectonic stress on methane release

CAGE 19-3 cruise with RV “Kronprins Haakon” to the Atlantic-Arctic gateway region is organized and funded through the Tromsø Forskningsstiftelse (TFS) and Research Council of Norway (RCN) supported SEAMSTRESS project and the Center of Excellence "CAGE – Centre for Arctic Gas Hydrate, Environment and Climate" at UiT-The Arctic University of Norway in Tromsø. SEAMSTRESS focuses on studies of the effect of tectonic stress on methane release at Arctic continental margins while CAGE studies the amount of methane hydrate and magnitude of methane release in Arctic Ocean environments on time scales from the Neogene to the present. CAGE 19-3 cruise is directed to the Atlantic-Arctic gateway region to provide necessary field data for these objectives. From previous cruises, we have identified key localities which will be main targets for this cruise. The cruise may be known as: CAGE19_3

Crustal evolution of the Laurentian continental margin from the Paleo- through Mesoproterozic: A zircon U–Pb and Hf transect through the western Grenville Province, Ontario, Canada

The Great Proterozoic Accretionary Orogeny along the southern and southeastern margin of Laurentia is arguably the first long-lived, modern-style active plate margin on Earth, representing significant crustal growth and reworking. Here, we present new detrital zircon U–Pb and Hf data, along with zircon and monazite metamorphic ages, from tectonic domains in the southwestern Grenville Province that represent depositional basins formed and reworked during a series of events between 2.2 and 1.2 Ga. As such, the data allow a glimpse into the evolution and assembly of this extensive margin. The Nepewassi domain contains Archean basement overlain by mature sandstone characterized by near-unimodal, ca. 2.7–2.6 Ga detrital zircon peaks and likely correlative with Superior Province basement and its Huronian cover. The Nepewassi domain underwent both Archean (ca. 2.65 Ga) and Killarnean (ca. 1.76 Ga) metamorphism. In addition, all units preserve evidence of Grenvillian high-grade metamorphism between ca. 1.05 and 0.99 Ga. The structurally highest parts of the Nepewassi domain also contain younger sedimentary rocks that received detritus from Killarnean sources, with evolved Hf isotopic compositions indicative of reworked Archean crust. Sedimentary rocks in the Tomiko domain preserve detrital zircon of Penokean and Killarnean age (1.9–1.7 Ga) with evolved Hf compositions, along with Labradorian (1.7–1.6 Ga) grains of more juvenile composition. Detrital zircon from the Kiosk domain yield Penokean through Labradorian ages, with Hf compositions ranging from evolved to juvenile. In contrast to the sedimentary rocks found in these Laurentia-derived parautochthonous domains, similar rocks from younger, more allochthonous units, including the Shawanaga and basal Parry Sound domain, dominantly contain zircon ranging from Pinwarian (ca. 1.45 Ga) through ca. 1.20 Ga that show exclusively juvenile isotopic compositions. The data show that sedimentary basins received detritus from nearby active sources as well as from the nearby Superior continent, and that successively younger sources and basins became increasingly less influenced by continental input as the margin grew wider. The data add to a growing database of similar data from other parts of this several thousand-kilometer-long margin that seemingly displayed little along-strike variation in overall evolution, implying the existence of a vast, Pacific-scale ocean.