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ABSTRACT Present day submarine canyons are active conduits for the transfer of large volumes of sediment, carbon and pollutants from continents to oceans. However, the evolution of submarine canyons over geological timescales remains poorly understood due to their erosional nature and low preservation potential. The Late Cretaceous Punta Baja Formation represents a well‐preserved submarine canyon‐fill that evolved on a tectonically‐active ocean‐facing margin. Exposures provide kilometre‐scale continuous strike and dip sections of the 120 m thick and 1.2 km wide feature. An inherited tectonic fabric influenced the location and orientation of canyon incision into fluvial bedrock. The stratigraphic evolution of the Punta Baja submarine canyon is reconstructed from incision to fill, which shows that it remained an active sediment conduit throughout the time represented by the preserved fill. The depositional architecture of the north–south oriented erosionally confined canyon‐fill is asymmetrical, with sub‐vertically stacked channel‐fills to the west, and an overbank confined by the canyon margin to the east. Sedimentary process interactions led to depositional patterns that are considered distinct to submarine canyon fills. Dynamic topography generated by mass‐wasting processes captured sediment and drove knickpoint development, an autogenic mechanism that modifies sediment delivery to the ocean floor. Widespread upstream dipping surfaces in channel‐fills are interpreted as the stratigraphic expression of upstream migrating supercritical‐flow bedforms, which played an important role in sediment storage and transport in the canyon. The steep relief and internal topography of canyons leads to complicated and characteristic confined overbank flow behaviour and depositional patterns. This study provides insight into how processes that are observed in modern canyons are selectively preserved through the lifetime of the canyon and construct or destroy stratigraphy on geological timescales. [ABSTRACT FROM AUTHOR]

The Clarke River Shear Zone marks the boundary between the Thomson and Mossman orogens in the northeastern Tasmanides. To better understand the kinematic history of this east-northeast-trending shear zone, and its role during the tectonic history of eastern Gondwana, we investigated rock deformation along a segment of the Clarke River Shear Zone. Based on field observations, interpretation of aeromagnetic data and microstructural analysis, we show that the Clarke River Shear Zone experienced at least three phases of reactivation. Gently plunging stretching lineation and kinematic indicators, such as steeply plunging asymmetric folds and asymmetric porphyroclasts, correspond to an early phase of sinistral strike-slip ductile shearing. Subsequent general dextral shear deformation is suggested based on the presence of S-tectonites, symmetric porphyroclasts and kinematic indicators with dominant dextral and subordinate sinistral shear senses. This phase, which occurred under amphibolite-facies metamorphic conditions, was contemporaneous with the emplacement of the Craigie Tonalite, for which we obtained a new zircon U–Pb crystallisation age of 410.3 ± 1 Ma. A later reactivation phase along the Clarke River Shear Zone, under brittle conditions, is indicated by the presence of cataclasite zones and chlorite–epidote alteration. Based on our findings, and regional information on the tectono-magmatic evolution of northeastern Queensland, we suggest that the Clarke River Shear Zone was possibly a sinistral transform fault during the Silurian. During the Devonian, it is possible that deformation along the Clarke River Shear Zone was related to the transition between the non-retreating subduction zone in the north, and the highly mobile (retreating) plate boundary farther south. However, the dextral kinematic component associated with this deformation is not fully explained. Brittle deformation, likely associated with dextral transpression during the Carboniferous, marked the last stage of activity along the Clarke River Shear Zone. The Clarke River Shear Zone records three phases of reactivation during the Silurian–Carboniferous. Ductile dextral general shear deformation along the Clarke River Shear Zone occurred at ca 410 Ma, based on zircon U–Pb dating of a syn-tectonic intrusion. The Clarke River Shear Zone likely accommodated subduction segmentation during the Silurian–Devonian. [ABSTRACT FROM AUTHOR]

The continental crust of Iran is dominated by abundant calc-alkaline and alkaline plutonic and volcanic rocks and by rifted basins filled with mostly terrigenous sedimentary rocks that formed at a Late Ediacaran to Cambrian extensional convergent plate margin along the northern margin of Gondwana. Here we present new zircon U–Pb age, geochemical, and isotopic data from plutonic (granite-granodiorite) and metamorphic (gneiss) rocks in the Kariznou region of NE Iran to provide insights into the nature of the Cadomian convergent margin of Iran. Geochemical data indicate calc-alkaline signatures, characterized by strong depletions in Nb, Ta, P, and Ti and arc-like trace element patterns. New zircon U–Pb ages show that calc-alkaline granitoids and granitic gneiss formed at ~564 to 537 Ma and 538 Ma, respectively. Bulk rock Sr-Nd isotopic data of calc-alkaline rocks have εNd(t) = –5.42 to −5.53 and −6.93 to −7.43 for granite and gneiss, respectively. The gneisses show stronger interaction with and/or re-melting of older continental crust than do granitic rocks. We interpret Kariznou magmatic rocks as forming in association with strong extension accompanied by crustal assimilation. Extension initiated ~570 Ma with the deposition of Late Ediacaran sediments, and magmatism began at 545–535 Ma, generating calc-alkaline magmas. The tectonomagmatic evolution of the Kariznou region encapsulates the prolonged transition of Cadomian Iran from a strongly extensional convergent margin, possibly as a result of oblique oceanic subduction and slab roll-back of the subducting Proto-Tethys oceanic lithosphere, culminating in the formation of an Early Palaeozoic passive margin on the northern side of Gondwana. [ABSTRACT FROM AUTHOR]

Tectonic deformation and associated submarine slope failures modify seafloor relief, influencing sediment dispersal patterns and the resulting depositional architecture of deep-water systems. The exhumed Middle Eocene strata of the Banastón deep-water system in the Aínsa depocentre, Spain, allow the interplay between submarine slope confined systems, mass flow deposits, and syn-depositional compressional tectonics to be investigated. This study focuses on the Banastón II sub-unit, interpreted as deposits of low-sinuosity and narrow (2-3 km wide) channel-belts confined laterally by tectonically-controlled, fine-grained slopes. The studied succession (111 m-thick) is exposed along a 1.5 km long SE-NW trending depositional dip section and is documented here by facies analysis and physical correlation of 10 measured sections. Results show a stratigraphic evolution in which the channel axes migrated to the southwest, away from a growing structure in the northeastern part of the Aínsa depocentre. Uplift of this structure promoted the breaching of confining channel walls and slope material with mass failures and the development of sand-rich crevasse scour-fills and crevasse lobes. We show that crevasse deposits form an important component of overbank succession. These crevasse lobes are characterized by structureless thick and medium beds that form < 5 m thick packages in proximal parts and thin abruptly over 1 km across strike (NE) and along downdip (NW) into structured thin beds, similar to the heterolithic dominated overbank deposits. Although the development of crevasse lobes has been observed in multiple deep-water systems in ancient and modern systems, this study documents, for the first time, crevasse lobe development on the active compressional margin of a foreland basin rather than on the opposing, more stable and gentler inactive margin. We discuss the mechanism for forming these crevasse deposits, which exploited the accommodation generated by submarine landslides derived from the tectonically-active compressional margin.

Hydrocarbon seeps are common manifestations of gas leakage from the seafloor. However, the fate of methane seepage within the gas hydrate stability zone at active margins is poorly constrained. This study presents a 40‐thousand‐year record of hydrocarbon seepage archived by a ∼5‐m long core composed of authigenic carbonate from the Yam Seep area, Four‐Way Closure Ridge off SW Taiwan. Different carbonate microfacies could be distinguished: Consolidated microcrystalline aragonite representing lithified host sediments intercalated by pure aragonite present in 10–50 cm thick intervals in the core. These aragonite intervals are interpreted as having precipitated within former fractures in the host rock. High resolution U‐Th dating of these aragonites is interpreted to record the minimum age of the opening of these fractures. The chronology of aragonite precipitation throughout the core suggests a record of continuous seepage from ∼41 to 2 ka that fluctuated in intensity over this time period. The chronology of putative fracturing events and observed carbonate precipitation suggest (a) an active period of fracturing and seepage from ∼37 to 27 ka, (b) a more quiescent period from ∼27 to 16 ka, followed by (c) another active period from ∼16 to 12 ka. A schematic model illustrates the evolution of carbonate formation within the core influenced by faulting, fracturing, erosion, gas hydrate accumulation, and aragonite precipitation and provides a unique 40,000‐year‐old record of methane seepage and crucial insights into the dynamics of long‐term seepage systems at active margins. Key Points: A 40‐thousand‐year history of hydrocarbon seepage at an active margin accretionary ridge off SW TaiwanUranium‐Thorium dating of authigenic carbonate reveals alternating periods of seepage activity and quiescenceDating of fracture boundaries provides evidence for episodes of tectonic and seepage activities [ABSTRACT FROM AUTHOR]

Hemipelagites are widespread fine‐grained sediments found from shelf margin to deep‐water environments, and they are considered to have been formed as background sedimentation by vertical settling and slow lateral advection of clastic and biogenic fine‐grained particles. Downflow variation in hemipelagic sedimentation, however, is not yet clearly understood, and was investigated in the lower Pleistocene Kiwada and Takamizo formations in the Kazusa forearc basin on the Boso Peninsula, Japan. Mapping of three tephra key beds enabled detailed correlation of two hemipelagite beds over a distance of ca 30 km from shelf‐margin to basin‐plain environments. The sedimentation rates decreased gradually in the downslope direction, but increased locally in response to turbidite sedimentation. This downslope variation indicates that hemipelagic sedimentation is not necessarily constant and varies in response to progradation and retrogradation of deep‐water depositional systems, as well as additional input of fine‐grained sediments from turbidity currents. In contrast, the grain size, magnetic susceptibility, clay‐mineral composition, total organic carbon contents relative to total nitrogen contents (carbon/nitrogen), and δ13C values of organic carbon do not exhibit distinct downslope variation. This downslope consistency indicates that hemipelagites document temporal perturbations of geological and palaeoclimatic conditions in hinterlands, regardless of spatial and temporal variations in deep‐water depositional environments. The concentrations of total organic carbon, total nitrogen and five biomarkers were lower values in turbiditic mudstones and hemipelagites that formed above a turbidite bed than in those of the other hemipelagites. This variation suggests that an additional supply of fine‐grained sediments from turbidity currents likely diluted the organic matter in the hemipelagites. In addition, hemipelagites for which deposition was affected by turbidity currents exhibit slightly lower δ13C values, and may also document an additional contribution of terrestrial organic matter from turbidity currents. [ABSTRACT FROM AUTHOR]

Abstract Hydrocarbon seeps are common manifestations of gas leakage from the seafloor. However, the fate of methane seepage within the gas hydrate stability zone at active margins is poorly constrained. This study presents a 40‐thousand‐year record of hydrocarbon seepage archived by a ∼5‐m long core composed of authigenic carbonate from the Yam Seep area, Four‐Way Closure Ridge off SW Taiwan. Different carbonate microfacies could be distinguished: Consolidated microcrystalline aragonite representing lithified host sediments intercalated by pure aragonite present in 10–50 cm thick intervals in the core. These aragonite intervals are interpreted as having precipitated within former fractures in the host rock. High resolution U‐Th dating of these aragonites is interpreted to record the minimum age of the opening of these fractures. The chronology of aragonite precipitation throughout the core suggests a record of continuous seepage from ∼41 to 2 ka that fluctuated in intensity over this time period. The chronology of putative fracturing events and observed carbonate precipitation suggest (a) an active period of fracturing and seepage from ∼37 to 27 ka, (b) a more quiescent period from ∼27 to 16 ka, followed by (c) another active period from ∼16 to 12 ka. A schematic model illustrates the evolution of carbonate formation within the core influenced by faulting, fracturing, erosion, gas hydrate accumulation, and aragonite precipitation and provides a unique 40,000‐year‐old record of methane seepage and crucial insights into the dynamics of long‐term seepage systems at active margins.

The Devonian Terra Australis accretionary orogen along the proto-Andes is characterized south of 33°S by the eastward accretion of the Chilenia and Chaitenia terranes. From the middle Silurian to the early Carboniferous the evolution north of 33°S, in the southern central Andes, is enigmatic, and herein called the Silurian-Devonian lull. This lull is notable for the absence of magmatism, metamorphism and deformation while mature siliciclastic detritus accumulated in marginal basins governed by depositional and not by tectonic controls. Detrital zircon age spectra uniformly display a marked scarcity of Silurian and Devonian ages. No evidence of a Devonian active margin system has been put forward so far. Newly discovered volcanic arc lavas in the Devonian-early Carboniferous Compléjo Epimetamórfico Chañaral (CEMC) of northern Chile give evidence of Devonian to early Carboniferous intermediate arc magmatism in this area for the first time. The CEMC also includes mafic volcanic rocks as syndepositional intercalations and as tectonic accretions. They predominantly have E-MORB and OIB characteristics and very likely formed at an extensional volcanic rifted margin environment. The veiled presence of scarce arc magmatism during the Silurian-Devonian lull might be taken as evidence of flat-slab subduction. However, present-day flat-slab regimes produce strongly telescoped mountain belts with high topography and relief. The absence of any deformation during the lull attests against this interpretation. Assuming an extension of Chilenia into northern Chile is unlikely because of different stratigraphies and the absence of ophiolitic sutures. The Silurian-Devonian lull may be explained as a magmatic lull between the flare-ups of the Famatinian and Gondwanide orogenies (Cambrian-Ordovician and Carboniferous-Triassic, respectively) the latter of which is attributed to rapid trenchward migration of the volcanic axis. Magmatic lulls are characterized by less than 25% of magma production relative to flare-ups and occur at times of slow landward migration of an arc system. [ABSTRACT FROM AUTHOR]

Based on scanning electron microscopy (SEM) images, we studied the microtextures of quartz grains recovered from the Boca del Cielo and Chocohuital beach sediments in the Chiapas state, Mexico. Microtextures of mechanical, chemical, and mechanical/chemical origins were identified. Quartz grains in both beaches were sub-angular to sub-rounded in shape, indicating high energy, short transport, and nearby source. The microtextures of mechanical origin like percussion marks, conchoidal fractures, and V-shaped marks were abundant in the Chocohuital beach, which revealed high energy subaqueous beach environment. Large-scale conchoidal fractures are characteristic of crystalline rocks, and abrasion features are due to energetic grain-to-grain collision during eolian transport. However, quartz grains in the Boca del Cielo beach were dominated with microtextures of chemical origin such as adhered particles, solution pits, and crystal overgrowth, and are abundant with trapped diatoms, which indicated the diagenetic processes in a silica saturated environment. Two diatoms Navicula incertata and Cyclotella bodanica of 15-μm size are identified in Boca del Cielo quartz grains. [ABSTRACT FROM AUTHOR]

A database-informed metastudy of 294 globally distributed submarine canyons has been conducted with the aim of elucidating the role of tectonic setting on submarine-canyon geomorphology. To achieve this, data from seafloor and subsurface studies derived from 136 peer-reviewed publications and from open-source worldwide bathymetry datasets have been statistically analyzed. In particular, relationships between margin type (active vs. passive) or plate-boundary type (convergent vs. transform vs. complex) have been assessed for key morphometric parameters of submarine canyons, including: streamwise length, maximum and average width and depth, canyon sinuosity, average canyon thalweg gradient, and maximum canyon sidewall steepness. In addition, possible scaling relationships between canyon morphometric parameters and characteristics of the associated terrestrial catchment, continental shelf and slope, and of the broader physiographic setting for canyons along both active and passive margins have been evaluated. The following principal findings arise: 1) overall canyon geomorphology is not markedly different across tectonic settings; 2) slope failure might be more important in passive-margin canyons compared to active ones, possibly due to seismic strengthening in the latter; 3) some aspects of canyon geomorphology scale with attributes of the source-to-sink system and environmental setting, but the strength and sign in scaling might differ between active and passive margins, suggesting that the extent to which canyon geomorphology can be predicted depends on the tectonic setting. Insights from our analysis augment and improve conceptual, experimental and numerical models of slope systems at the scale of individual canyons and source-to-sink systems, and increase our understanding of the complex role played by tectonic setting in shaping deep-water systems.

The precise timing of subduction initiation of the Paleo-Asian Ocean (PAO) in the northern margin of the North China Craton (NCC) remains controversial. In this study, we have conducted zircon U Pb dating, whole-rock major and trace elements, and zircon Hf isotope analyses on metadacites and metamorphic greywackes from the Changde volcano-sedimentary rocks, feldspar quartz sandstones and argillaceous siltstones from the Luquantun Formation and the Sidao sedimentary rocks in central-eastern Jilin Province (NE China), to constrain the initial closure of the PAO. We obtained Early Carboniferous zircon U Pb ages (345 ± 2 Ma and 351 ± 7 Ma) from the Changde volcano-sedimentary rocks. The metadacites are characterized by the enrichment in light rare earth elements and large ion lithophile elements, depletion in heavy rare earth elements and high field strength elements, and rare earth element ratios similar to those of the continental crust, indicating that these rocks originated from crustal melting. The metadacites exhibit affinity with the peraluminous A-type granite, with high zircon ε Hf (t) values (+3.46 − +12.21) and T DM2 of 1132–571 Ma, suggesting that they formed in a post-collisional extensional setting. Detrital zircon U Pb ages from the Luquantun Formation and Sidao sedimentary rocks constrain their maximum depositional ages to the Late Carboniferous (319 ± 5 Ma) and Early Permian (284 ± 4 Ma), respectively. Most detrital zircons have age peaks at 1800 Ma with negative zircon ε Hf (t) values, and 2500 Ma with positive zircon ε Hf (t) values, suggesting that the Carboniferous–Early Permian sediments from these two formations were mainly sourced from the NCC. Moreover, the chemical index of alteration, index of compositional variability, and plagioclase index of alteration values suggest that the sediments of the Changde volcano-sedimentary rocks originated from a mafic igneous source with a low degree of weathering and a sedimentary recycling history, while the samples from the Luquantun Formation and Sidao sedimentary rocks were sourced from an intermediate-felsic igneous rock with a moderate to intense degree of weathering and mainly influenced by source composition. The crystallization age curves and summary plots of detrital zircons indicate that the Early Carboniferous metamorphic greywackes from the Changde Formation were mainly deposited in a passive margin, while the Carboniferous–Early Permian sediments of the Luquantun Formation and Sidao sedimentary rocks were mainly deposited in an active margin. We suggest that the tectonic transition from passive to active margin occurred at ∼333 Ma, marking subduction initiation in the PAO close to the northern margin of the NCC. [Display omitted] • The Carboniferous–Early Permian sediments in central-eastern Jilin Province (NE China) are mainly sourced from the NCC. • During the Carboniferous, the eastern part of the northern margin of the NCC transitioned from passive to active. • The precise subduction initiation of the PAO occurred at approximately 333 ± 5 Ma along the northern margin of the NCC. [ABSTRACT FROM AUTHOR]

Early Miocene limestones from the Wairarapa region of New Zealand were deposited on thrust-bounded margins of trench-slope basins, and consist of two superposed stratal units, namely units A and B, interpreted as forced regressive and forced transgressive foralgal and rhodolith-bearing deposits, respectively. Unit A is floored by a regressive surface of marine erosion cut into shelfal to bathyal siliciclastic successions, and is overlain across a transgressive surface of erosion by Unit B. A drowning surface abruptly places the latter deposits in contact with deeper hemipelagites and turbidites. The succession is explainable within a tectono-eustatic based framework as follows: (1) Structurally controlled rapid relative sea-level fall, (i.e. sea-bed rise), from upper bathyal to shelfal depths promoted development of regressive ('lowstand') mixed carbonate–siliciclastic deposits. Continuation of seabed rise resulted in deposition of pure carbonate sediments, which are represented by channel-fill rhodolithic rudstones; (2) early stage of relative sea-level rise (i.e. seabed drowning) caused emplacement of transgressive glauconitic limestones, consisting of either foralgal deposits, or incised rhodolithic limestones; (3) continued relative sea-level rise terminated carbonate production. The present study documents carbonate production and termination in a tectonically active and confined intra-slope setting, reflected in the development and distribution of unusual forced regressive, and transgressive rhodolithic-heterozoan carbonates. [ABSTRACT FROM AUTHOR]

Continental shelves generally supply large-scale mass-wasting events. Yet, the origin and significance of shelf-derived mass-transport deposits (MTDs) for the tectonostratigraphic evolution of subduction complexes and their trench-slope basins have not been extensively studied. Here, we present high-resolution, outcrop-scale insights on both the nature of the reworked sediments, and their mechanisms of development and emplacement along tectonically active margins, by examining the Middle Miocene shelf-derived MTDs outcropping in the exhumed southern portion of the Hikurangi subduction margin. Results show that periods of repeated tectonic activity (thrust propagation, uplift) in such compressional settings not only affect and control the development of shelfal environments but also drive the recurrent generation and destruction of oversteepened slopes, which in turn, favour the destabilisation and collapses of the shelves and their substratum. Here, these events produced both large-scale, shelf-derived sediment mass-failures and local debris flows, which eventually broke down into a series of coalescing, erosive, genetically linked surging flows downslope. The associated MTDs have a regional footprint, being deposited across several trench-slope basins. Recognition of tectonic activity as another causal mechanism for large-scale shelf failure (in addition to sea-level changes, high-sedimentation fluxes) has implications for both stratigraphic predictions and understanding the tectonostratigraphic evolution of deep-marine fold-and-thrust belts. [ABSTRACT FROM AUTHOR]

We report new results of a comprehensive study into Carboniferous – Early Permian granite magmatism of the northern Taimyr Peninsula, Russia (southern part of the Kara Terrane). U-Pb zircon ages (SHRIMP and LA–ICP–MS) represent the crystallization ages of these intrusions and range from ca. 344.5 to 288.4 Ma, defining the onset of granite magmatism during the Early Carboniferous (Visean; ca. 344 Ma) and its termination in the Early Permian (Artinskian; ca. 288 Ma). Ar-Ar dating of micas and amphiboles indicates that Late Palaeozoic tectonic activity in northern Taimyr ceased during the Middle Permian (Roadian; ca. 272 Ma). Rb/Sr and Sm/Nd isotopic data from the same intrusions, show initial (87Sr/86Sr)i ratios of between 0.70288 and 0.71027, with εNd(t) values range between −3.3 and +3.1. The combined geochemical and isotopic compositions of the granites describe an affinity to peraluminous I-type granites, probably formed in an Andean-type active continental margin setting. Our new geochemical, isotopic, and geochronological data indicate the existence of a long-lived (ca. 56 Myr) Andean-type active continental margin along the southern edge of the Kara Terrane during the Late Palaeozoic. Furthermore, our study reveals a causal relationship between Late Palaeozoic magmatism across northern Taimyr and closure of the Uralian Ocean. [ABSTRACT FROM AUTHOR]

The northernmost part of the Australian continent is exposed in a basement high in the Bird's Head Peninsula at the NW tip of New Guinea. This basement consists of Silurian–Devonian turbidites that were regionally metamorphosed in the lower greenschist facies. Along its eastern margin, the basement high is intruded by numerous granitoid bodies and records a second, higher‐grade metamorphic overprint. We present the first detailed study of metamorphic rocks from this eastern part of the basement high, supported by field and petrographic observations, bulk rock and mineral chemistry, and phase equilibria modelling. Lower‐grade basement rocks include chlorite‐mica schists, slates, silt‐, and sandstones, which give way to andalusite‐ and cordierite‐bearing pelites and psammites, interspersed with layers of quartzite. The dominating pelitic phase assemblage is biotite+white mica±andalusite±cordierite+plagioclase+quartz+ilmenite; incipient sillimanite (fibrolite) is present in some rocks and replaces andalusite in baked margins around the numerous dykes and sills. Other rock types include metasedimentary migmatites, metacarbonates and calcsilicate concretions, rare metavolcanics, and kyanite‐bearing segregation veins. Metamorphism is of regional extent and often unrelated to granitoid intrusions. Our observations support the previous notion of an increase in peak metamorphic temperature from west to east. Microstructural relations suggest two phases of metamorphism, which are tentatively correlated with two phases of magmatic activity in the Devonian–Carboniferous and the Permian–Triassic. Based on petrographic observations and phase equilibria modelling, we propose that during the Permian–Triassic, metamorphism proceeded under high temperature/low pressure (HT/LP) or Abukuma‐type conditions along a narrow, counter‐clockwise P–T–t path with peak metamorphic conditions of the amphibolite facies (~520–650°C and ~2–4 kbar), potentially in an active continental margin setting. While much less evidence is available, similar metamorphic conditions are proposed for the Devonian–Carboniferous metamorphic event. [ABSTRACT FROM AUTHOR]

The late Eocene–early Oligocene Keasey Formation in Northwestern Oregon contains a unique fauna of deep-water (>200 m) marine bivalves preserved in sparsely fossiliferous massive tuffaceous siltstone as well as in several distinctive cold-seep limestone bodies and carbonate layers. The Keasey gastropod fauna has been described previously, but this treatment of the anomalodesmatan bivalves is the first systematic account for any portion of the bivalve fauna. Cenozoic evolutionary radiation and history of anomalodesmatans is less well known than their deep Paleozoic and Mesozoic history. Because internal relationships are not well resolved, ranked classification is not used above the family level, while recognizing that these rare and unusual bivalves do represent a monophyletic assemblage nested within the basal heterodonts. Six species in four anomalodesmatan families in the Keasey Formation shed new light on the Cenozoic history of the group as well as the Eocene appearance of precursors of the living deep-water fauna of the northeastern Pacific. The families represented are Pandoridae, Thraciidae, Periplomatidae, and Cuspidariidae. The new species are Pandora eocapsella, Thracia keaseyensis, Cardiomya anaticepsella, and Cardiomya pavascotti. Aperiploma? n. sp. is described in open nomenclature pending discovery of additional and more complete material. Although shells are frequently crushed and the exterior shell layers are often poorly preserved, the interior nacre is distinctive, well-preserved and useful for recognizing fragments in the field. Characteristic anomalodesmatan granules are well preserved on many specimens of the new thraciid, and the fine-grained matrix at some localities preserves shell features on external molds where no original shell material remains. High-resolution images of uncoated shell encourage greater attention to collection of fragments and imperfect specimens in the fine-grained deep-water facies on the active margin of the Pacific.

This paper is focused on the relationship between plate‐ and plume‐tectonic processes during the formation of Neoproterozoic and Vendian‐Paleozoic island‐arc systems and active continental margins in the interaction zone of the Siberian continent and Paleoasian Ocean (PAO). In this study, we use our own materials collected in the long‐term research of the Central Asian Orogenic Belt (CAOB) and the published models showing convection in the asthenosphere and mantle, subduction‐related and plume magmatism at the Cenozoic active margins of the Western Pacific and California types. It is clearly shown that subduction‐related magmatism of the Paleoasian Ocean active margins should not be considered separately from plume magmatism. These interrelated processes played a major role in the CAOB formation. Based on the reconstructed Neoproterozoic, Vendian – Early and Middle Paleozoic paleogeodynamic features, 25 island‐arc systems of PAO are characterized. These island arcs are related to the occurrence of more than 30 plume magmatism areas. At the active margin of the Siberian continent, there are numerous fields of intraplate magmatism in riftogeneous structures. Such fields of various scales not related to subduction zones, especially at the final Late Paleozoic stage. All the major stages of the CAOB development, including the Cambrian‐ Ordovician collision stage, are clearly correlated with plume magmatism. Considering a revealed combination of the island arcs and the plume magmatism areas, there are grounds to suggest that the development of the entire Neoproterozoic‐ Paleozoic region of Central Asia was related to the activity of mantle plumes.

Reconstructions of the plate tectonic history of a continental margin are rarely unique. Comments on my recent contribution point out statements that the commentators considered confusing and misleading. The comments essentially focus on the significance, or not, of the Chilenia terrane and coeval magmatism in Argentina and to the south of the area which is the focus of my contribution. I offer here a perspective on this issue. [ABSTRACT FROM AUTHOR]

Vendian and Permian–Triassic plagiogranite magmatism is distinguished for the Ust-Belsky and Algansky terranes of West Koryak fold system. The U‒Pb zircon ages from Vendian and Permian–Triassic plagiogranites are 556 ± 3 Ma (SIMS), 538 ± 7 Ma (LA–ICP–MS) and 235 ± 2 Ma (SIMS), respectively. It is revealed that Vendian and Permian–Triassic plagiogranites are mainly low-K and low-Al. Sr‒Nd isotopy and rare earth element patterns make it possible to suggest their formation as partial melting of primarily mantle substrate or fractional crystallization of the basic magma. Vendian plagiogranites formed within active margin in ensimatic island arc simultaneously with deposition of the lower part of the volcano-sedimentary complex of Otrozhninskaya sheet. We suggest that the Permian–Triassic plagiogranites were formed within the limits of the Ust-Belsky segment of the Koni-Taigonos arc during partial melting of melanocratic ophiolite material built up as fragments in the accretionary structure of that arc or by fractional crystallization of basic magmas melted from a similar substrate. [ABSTRACT FROM AUTHOR]

By comparison with igneous rock assemblages of well-exposed modern magmatic arcs and their typical calc-alkaline, magnesian, I-type signatures, many deeply eroded magmatic arcs have been characterized worldwide, unraveling ancient plate margins. Since the 1980's, different assemblages of Ediacaran to Cambrian magmatic rocks have been systematically mapped and characterized according to their distinctive petrographic, structural, lithochemical, geochronologic, and isotopic features, allowing to establish the pre-collisional, collisional, and post-collisional stages of the Araçuaí orogen (SE Brazil). Among them, the tonalitic-granodioritic batholiths and stocks with calc-alkaline, magnesian, I-type signatures, rich in dioritic to mafic enclaves, and related metavolcano-sedimentary successions compose a magmatic arc formed in the early Ediacaran, the Rio Doce magmatic arc. Extending for more than 1000 km along the Araçuaí-Ribeira Orogenic System (AROS), the Rio Doce arc shows a hybrid isotopic signature and crustal inheritance, compatible with modern magmatic arcs built on continental active margins. We present new field, petrographic, and lithochemical studies, coupled with U–Pb (LA-ICPMS) geochronology and isotopic (in-zircon Lu–Hf and whole-rock Sm–Nd) analysis, unraveling the least evolved isotopic signatures ever found for tonalitic-granodioritic plutons of the Rio Doce magmatic arc, and a comprehensive data comparison with modern magmatic arcs. The studied Santa Tereza and Jequitibá suites comprise tonalitic-granodioritic and Opx-bearing charnockitic rocks, with calcic-to-alkali-calcic-magnesian I-type signature, associated with gabbroic rocks. Zircon U–Pb data yielded Concordia ages of 612 ± 3 Ma (Santa Tereza) and 594 ± 3 Ma (Jequitibá) for magmatic crystallization, and 580 ± 5 Ma to 571 ± 3 Ma for metamorphic recrystallization, with associated εNd (612Ma) values from −0.06 to −7.05 (T DM model ages: 1.4–2.04 Ga), and εNd (594Ma) values from −6.67 to −8.8 (T DM model ages: 1.64–1.87 Ga). The zircon εHf (t) (+2.3 to −4.8) and Hf T DM model ages (1.33–1.65 Ga) assigned a moderately juvenile to evolved signature for the Santa Tereza suite, while the Jequitibá suite (εHf (t) : −1.7 to −36.4; T DM model ages: 1.33–3.21 Ga) shows a more evolved signature. Altogether, data from the Rio Doce arc are similar to typical continental-margin magmatic arcs with the involvement of mantle melts and/or melting of juvenile crust, suggesting a westward slab retreat during ocean-floor subduction within the Araçuaí confined orogen. • From rock assemblages to chemical signatures: keystones for arc definition. • Comparing chemical footprints from ancient and modern magmatic arcs. • The easternmost expression of arc magmatism in the Araçuaí Orogen. • The least evolved magmatism yet found in the Rio Doce Arc. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Detrital zircon ages constrain transition from Cadomian orogen to passive margin. • This transition spanned about 50 M.y. • Curved geometry of the West African margin and subduction zone played a key role. • The transition was driven by oblique ridge–trench interaction. • Slab pull of the Iapetus Ocean followed. Abstract The Avalonian–Cadomian belt formed as a collage of accretionary complexes, island arcs, and sedimentary basins along the northern margin of Gondwana during the Neoproterozoic times. One of the enigmatic issues is how and when this active margin evolved to a passive margin in the southern realms of the Rheic Ocean during late Cambrian to early Ordovician. This issue is addressed here using U–Pb detrital zircon dating of key stratigraphic sections in the Teplá–Barrandian unit, Bohemian Massif. The new ages constrain the base of the Davle volcanic arc to 608 ± 6 Ma, 591 ± 6 Ma, and 590 ± 4 Ma and its termination to 563 ± 7 Ma. The lower part of the overlying Příbram–Jince continental basin was deposited between 512 ± 5 and 511 ± 3 Ma. These brackets define a time span of about 50 M.y. for the geodynamic transition from Cadomian subduction, accretion, and arc magmatism to a passive margin and lithospheric extension. In our model, a major role is assigned to a presumably curved geometry of the adjacent West African continental margin, which consisted of the outboard Armorican–Saxothuringian portion at an angle to the inboard Iberian–Barrandian portion. We suggest that during oblique subduction, ridge–trench collision and slab break-off occurred in the former at ca. 540 Ma, while subduction/accretion continued in the latter and was terminated by a major pulse of sediment accretion at around 527 Ma and ridge subduction at ca. 524–520 Ma. Finally, the tectonic regime in the Cadomian arc and accreted upper crust switched to extension associated with crustal remelting to produce intraplate magmatism and development of continental basins with short-lived marine transgressions between ca. 512 Ma and ca. 488 Ma. The continued extension led to rifting and basaltic volcanism, directly linked to the diachronous opening of the Rheic Ocean. We conclude that the prolonged transition from active to passive margin in the Cadomian belt was driven two principal geodynamic causes: first by oblique oceanic subduction and ridge–trench interactions, bearing many similarities to modern Cordilleran-type active margins, and then by the far-field slab-pull force of the subducting Iapetus Ocean. [ABSTRACT FROM AUTHOR]

Data on the petrography, geochemistry, and isotopic geochronology of granites from the northern part of the Taimyr Peninsula are considered. The Early-Middle Carboniferous age of these rocks has been established (U-Pb, SIMS). Judging by the results of 40Ar/39Ar dating, the rocks underwent metamorphism in the Middle Permian. In geochemical and isotopic composition, the granitic rocks have much in common with evolved I-type granites. This makes it possible to specify a suprasubduction marginal continental formation setting. The existence of an active Carboniferous margin along the southern edge of the Kara Block (in presentday coordinates) corroborates the close relationship of the studied region with the continent of Baltia. [ABSTRACT FROM AUTHOR]

The West Gondwana orogen, represented in NE Brazil by Santa Quitéria continental magmatic arc and ultrahigh-pressure metamafic rocks of a suture zone, have amphibolite and coesite-bearing retro-eclogite in both margins of the magmatic arc. This research reports and discuss the geochemical and geochronological data (U–Pb and Lu–Hf in zircon and Sm–Nd whole-rock) of amphibolite and retro-eclogite from the eastern margin of a continental magmatic arc. The Santa Quitéria Complex and metasedimentary Ceará Complex hosted these rocks. The Santa Quitéria amphibolites shows evident fractionation of REE. Nb–Ta–Ce anomalies evidence magma generated in a subduction zone with contribution and recycling of crustal sedimentary material, corroborate for slightly negative εNd (−1.56) and Paleoproterozoic NdTDM value (1.80 Ga). Isotopic Lu–Hf in zircon data indicates positive εHf (+5.00 to +7.78) and Neoproterozoic model ages (HfTDM from 0.97 to 0.86 Ga) (t = 637 ± 34 Ma - sample TJF5-258) indicate their extraction from the mantle. For the amphibolite samples from the Ceará Complex, the elemental distribution suggest that these rocks place them among oceanic basalts of enriched segments of mid-ocean ridges (E-MORB) and oceanic island basalts (OIB) – intra-oceanic arc basalts (IOAB). U–Pb zircon data of Ceará Complex amphibolite points to crystallization at ca. 670 Ma (674 ± 9 Ma, sample TJJV-07) and two metamorphic events around 640 Ma (644 ± 9 Ma) and 600 Ma (591 ± 5 Ma) related to the continental collision. Positive εNd values (+1.66 to +4.16) and model ages (NdTDM from 1.26 to 1.00 Ga) suggest a protolith crystallized from juvenile material of mantle source. Our data support that the eastern edge of the Santa Quitéria magmatic arc constitutes an active margin with subduction of the Cryogenian oceanic crust. [Display omitted] • U–Pb zircon ages of metamafic rocks from the West Gondwana orogen in NE Brazil. • Geochemical of Neoproterozoic metamafic rocks from an active margin setting of West Gondwana. • Evidence of Neoproterozoic oceanic crust in the active margin of the West Gondwana orogen. [ABSTRACT FROM AUTHOR]

Geological complexity, progressive tectonic overprint and prevailing submarine location of subduction margins generally hinder investigating the early stages of development of their oldest trench-slope basins, witnesses of subduction initiation and early history. Along the eastern North Island of New Zealand, the inner portion of the Hikurangi subduction wedge is emerged, thereby offering a unique opportunity to examine, at outcrop-scale, the tectonostratigraphic evolution of a trench-slope basin (Castlepoint trench-slope basin) that was linked to the onset of subduction. We present new occurrences of lowermost Miocene gravity-driven systems, suggesting a more intricate depositional framework to the ones previously inferred during this key period. Results show that the early stages of development of a trench-slope basin coeval with the birth of a subduction margin may deviate from traditional models either comprising (1) sustainable sediment sources connected to the basin very early in the history of the margin and (2) a sedimentation-deformation feedback mechanism promoting the long-term development of an aggradational turbidite system downslope. Analysis of the mass-transport deposits (MTDs) also revealed that the outboard migration of deformation was discontinuous and uneven along the margin during the earliest Miocene. Two major tectonic events, separated by a period of reduced tectonic activity, were recorded at the inboard border of the Castlepoint trench-slope basin, each resulting in seaward motion, oversteepening and frontal denudation of a thrust sheet. Each thrust sheet provided contrasting failed material and morphometric characteristics to the associated deposits, thereby allowing us to discriminate the nature of the nappe and related controls responsible for shedding each MTD as well as refine the timing of nappe emplacement along this part of the margin. Overall, this study draws new insights on the early structural evolution and stratigraphic infill during the birth of subduction zones, insights which may, in turn, help improve understandings of active margin settings. • Thrust fault growth can result in a vertical partitioning of mass-wasting processes at its front (mass movement then flow). • MTDs can record denudation of their source by progressively incorporating clasts in reverse stratigraphic order. • Overpressure at the sole of nappes may favor preservation of underthrust deposits preventing significant tectonic reworking. • Early stages of trench-slope basin fill coeval with the birth of a subduction margin can deviate from classical models. • Outboard migration of deformation during the earliest Miocene was discontinuous and uneven along the Hikurangi Margin. [ABSTRACT FROM AUTHOR]

Large amounts of gas hydrate are present in marine sediments offshore Taitao Peninsula, near the Chile Triple Junction. Here, marine sediments on the forearc contain carbon that is converted to methane in a regime of very high heat flow and intense rock deformation above the downgoing oceanic spreading ridge separating the Nazca and Antarctic plates. This regime enables vigorous fluid migration. Here, we present an analysis of the spatial distribution, concentration, estimate of gas-phases (gas hydrate and free gas) and geothermal gradients in the accretionary prism, and forearc sediments offshore Taitao (45.5°–47° S). Velocity analysis of Seismic Profile RC2901-751 indicates gas hydrate concentration values

The Southern Brasília Orogen is the result of Ediacaran continental collision between the active margin of the Paranapanema paleocontinent and the passive margin of the São Francisco paleocontinent. The active margin was deformed into the Socorro-Guaxupé Nappe and the associated Embu Domain. This paper presents new U–Pb zircon data and geothermobarometric estimates that allow to reconstruct the metamorphic evolution in these upper plate units. A pre-collisional metamorphism M1 with an age peak in metamorphic rims of zircon grains in the range 680–630 Ma is related to the development of the Socorro-Guaxupé magmatic arc with batholiths dated in a similar time span, 690 - 630 Ma. This metamorphism reached medium pressure granulite facies, now exposed by the tilted uplift and erosion due to the collision. Another peak is detected in metamorphic rims of zircon grains, in the range 630–590 Ma, labeled M2, related to the collision and corresponds to the main metamorphism in the lower plate and accretionary wedge-like nappe stack, underlying the Socorro-Guaxupé Nappe. This nappe stack was affected by greenschist facies metamorphism in the autochthonous underlying craton, grading to high pressure granulite facies in the upper nappe, with local occurrences of retroeclogite lenses. In the Socorro-Guaxupé Nappe and Embu Domain this main metamorphism (M2) is characterized by three metamorphic zones decreasing in grade with distance from the suture: a granulite facies orthopyroxene bearing zone; a high temperature amphibolite facies zone and a lower amphibolite facies zone. Geothermobarometric results in mineral associations related to M2 show temperatures decreasing from about 770 °C to ∼620 °C and pressures decreasing from about 9 kbar close to the suture to about 5 kbar in the southern and western parts of the studied region. On the upper Paranapanema plate, relative to the Socorro-Guaxupé Nappe and Embu Domain units, at the base of the plate, an older metamorphism (M1) is verified with temperatures between 960 and 890 °C and pressures between 11 and 9 kbar, reequilibrated at approximately 700 °C with a pressure of about 9 kbar (M2, continental collision). For this reason, it can be assumed that the rim of the Paranapanema plate was exhumed during the continental collision, since the temperature and pressure of the metamorphic peak determined during the continental collision are lower than those determined for the pre-collisional magmatic arc metamorphism. • Active margin in the Paranapanema Paleocontinent. • Metamorphism related to magmatic arc stage. • Exhumation of the upper plate during the Brasilia Meridional continental collision. • Arc metamorphism superimposed by collisional metamorphism of lesser degree. [ABSTRACT FROM AUTHOR]

The Taiwan area, where the Philippine Sea Plate collides with Eurasia, is one of the most seismically active areas in the world and has been consequently struck repeatedly by destructive earthquakes. To better constrain the occurrence of large earthquakes, we have conducted two cruises in 2012 and 2013 from which five piston, gravity and box-cores were retrieved from selected sites in targeted areas that contain continuous and accurate turbidite deposition offshore eastern Taiwan. Forty-seven turbidite layers deposited between 675 BC and 2012 AD have been described in the cores with facies varying from silty clay to coarse sand. We modeled each turbidite layer using the sedimentation rate deduced from radiocarbon age measurements performed on planktonic foraminifers. Precise dating based on 210 Pb– 137 Cs chronology provided ages for the XXth century turbidites. Coring sites' locations, biotic association within turbidites beds and seismic calibration over the instrumental period, suggest that earthquakes are the most likely triggering mechanisms of turbidity currents over the last 2700 years. Calibration of correlations between turbidites and instrumental earthquakes allowed us to determine the minimum magnitude of recorded events (M w = 6.8) and the maximum distance between the epicenter and the slope failure. Turbidites' synchroneity between cores has been tested but results showed that this criterion cannot be used in our study area because of the high level of seismicity, i.e., a M > 6.8 earthquake recurrence interval much smaller than the uncertainty on radiocarbon ages. The excellent accuracy of dating allows correlating all the turbidites deposited since 1920 with instrumental earthquakes. For each core, we established a return time ranging between 112 and 147 years for the period pre-1900 and ~ 27 and 34 years for the period post-1900. The discrepancy between pre-1900 and post-1900 recurrence either suggests, that slope stability varies, with higher slope instability after 1900 possibly due to increased sediment delivery by rivers. [ABSTRACT FROM AUTHOR]

The Hikurangi Margin, east of the North Island of New Zealand, is known to contain significant deposits of gas hydrates. This has been demonstrated by several multidisciplinary studies in the area since 2005. These studies indicate that hydrates in the region are primarily located beneath thrust ridges that enable focused fluid flow, and that the hydrates are associated with free gas. In 2009–2010, a seismic dataset consisting of 2766 km of 2D seismic data was collected in the undrilled Pegasus Basin, which has been accumulating sediments since the early Cretaceous. Bottom-simulating reflections (BSRs) are abundant in the data, and they are accompanied by other features that indicate the presence of free gas and concentrated accumulations of gas hydrate. We present results from a detailed qualitative analysis of the data that has made use of automated high-density velocity analysis to highlight features related to the hydrate system in the Pegasus Basin. Two scenarios are presented that constitute contrasting mechanisms for gas-charged fluids to breach the base of the gas hydrate stability zone. The first mechanism is the vertical migration of fluids across layers, where flow pathways do not appear to be influenced by stratigraphic layers or geological structures. The second mechanism is non-vertical fluid migration that follows specific strata that crosscut the BSR. One of the most intriguing features observed is a presumed gas chimney within the regional gas hydrate stability zone that is surrounded by a triangular (in 2D) region of low reflectivity, approximately 8 km wide, interpreted to be the result of acoustic blanking. This chimney structure is cored by a ∼200-m-wide low-velocity zone (interpreted to contain free gas) flanked by high-velocity bands that are 200–400 m wide (interpreted to contain concentrated hydrate deposits). [ABSTRACT FROM AUTHOR]

The uplift of the coastal cordillera of central Ecuador is a likely consequence of the subduction of the Carnegie Ridge, a 400-km-long and 2-km-high topographic asperity. This study aims at analyzing the impact of the subduction of the Carnegie Ridge on the continental shelf sedimentation during the Quaternary. We interpret high-resolution (50–450 Hz frequency) multi-channel (72 channels) and single-channel (Sparker) seismic data, piston cores, sediment profiles (3.5 kHz), and high-resolution multibeam bathymetry acquired during the ATACAMES cruise with the RV L’Atalante in 2012. In the La Plata Island–Cabo San Lorenzo Peninsula region, the results show a full and detailed record of the last ten Quaternary sedimentary sequences deposited in intra-shelf basins, at and -just seaward of the shelf break. These 100-ka-scale sequences are tied to piston core data, to well-dated Quaternary onshore exposures and to a flight of coastal marine terraces on Cabo San Lorenzo Peninsula and La Plata Island. These sequences correlate with the global ice volume and deep marine temperature changes (d18O) for the last 0.7 Ma, which points to a strict climatic control on depositional sequence development and preservation. However, the subsidence of the continental shelf acoustic basement, estimated by the stepwise backstripping of the sedimentary record, exhibits a complex deformation pattern with uplifting and subsiding regions. Deep marine seismic data, currently under processing, show evidence for a subducted seamount beneath La Plata Island and GPS data indicate an important interplate coupling in the same area with the potential to generate a Mw 7–7.5 earthquake. The pattern of the continental shelf deformation is consistent with the shape of this seamount. We tested the hypothesis of a link between the margin deformation and the subduction of the seamount, by comparing a stepwise subduction of the seamount to the palinspastic restoration of the deformation of the continental shelf for the last 1 Ma. This comparison shows that the collision probably started c.500 ka ago, together with the syntectonic sedimentation, and drastically slowed down by c.50 ka, with the sealing of most of the deformation on the shelf. [ABSTRACT FROM AUTHOR]

The South Limón fold-and-thrust belt, in the back-arc area of southern Costa Rica, is characterized by a 90° curvature of the strike of the thrust planes and is therefore a natural laboratory for the analysis of curved orogens. The analysis of curved fold-and-thrust belts is a challenge because of the varying structural orientations within the belt. Based on seismic reflection lines, we created a 3-D subsurface model containing three major thrust faults and three stratigraphic horizons. 3-D kinematic retro-deformation modeling was carried out to analyze the spatial evolution of the fold-and-thrust belt. The maximum amount of displacement on each of the faults is (from hinterland to foreland); thrust 1: 800 m; thrust 2: 600 m; thrust 3: 250 m. The model was restored sequentially to its pre-deformational state. The strain history of the stratigraphic horizons in the model was calculated at every step. This shows that the internal strain pattern has an abrupt change at the orogenic bend. Contractional strain occurs in the forelimbs of the hanging-wall anticlines, while a zone of dilative strain spreads from the anticline crests to the backlimbs. The modeling shows that a NNE-directed transport direction best explains the structural evolution of the bend. This would require a left-lateral strike-slip zone in the North to compensate for the movement and thereby decoupling the South Limón fold-and-thrust belt from northern Costa Rica. Therefore, our modeling supports the presence of the Trans-Isthmic fault system, at least during the Plio-Pleistocene. [ABSTRACT FROM AUTHOR]

Recent sedimentary facies and processes along the offshore slope of east Taiwan are investigated using a large set of geophysical and sedimentological data. The Taiwan orogen is often considered as one of the most tectonically active regions in the world and also suffers important climatic activity with an average of four typhoons per year. We have mapped in details the morphosedimentary features and characterized the sedimentary facies along offshore eastern Taiwan. There, we show that the slope is driven by a variety of erosional processes from mass wasting to turbidity current. Mass movements such as slides or mass transport deposits (MTDs) are ubiquitous and affect the whole east coast off Taiwan. Detailed core investigations, such as grain size analysis, chemical and mineralogical composition, revealed that turbidite facies range from thin fine-grained turbidites to thick massive turbidite facies. The detailed analysis of turbidite beds allow us to discuss the controlling factors of turbidity current generation. Turbidity currents represent an important sedimentary process that governs the slope morphology off east Taiwan. Triggering mechanisms likely range from slope instabilities related to earthquakes shaking to failure relative to climatic-controlled pulses of sediment supply. We propose that at least two end-members are characteristics in our turbidite records in term of controlling factor: 1) Turbidity currents likely generated by tectonic activity and earthquakes shaking in particular; and 2) Turbidity currents likely generated by climatic activity such as typhoon-induced floods. [ABSTRACT FROM AUTHOR]

The interactions between the sand-rich Orinoco turbidite system and the compressional structures of the Barbados prism have been active since Eocene time as illustrated by the study of outcrops onshore Barbados Island. Because of strong morphologic and tectonic control, the present-day Orinoco turbiditic pattern system does not exhibit a classic fan geometry. The sea-floor geometry between the slope of the front of the Barbados prism and the slope of the South-American margin induces the convergence of the turbidite channels toward the abyssal plain, at the front of the accretionary prism. Whereas in most passive margins the turbidite systems are organized upstream to downstream as canyon, channel-levee and lobes, here, due to the tectonic control, it is organized as channel-levee, canyons and channelized lobes. At the edge of the Orinoco platform, the system has multiple sources with several distributaries and downstream the channel courses are complex with frequent convergences or divergences. While erosion processes are almost absent on the highly subsiding Orinoco platform and in the upper part of the turbidite system, they develop mostly between 2000 and 4000 m of water depth, above the Barbados prism. In the abyssal plain, the main turbiditic channel develops toward the east and connects with the Vidal mid-Atlantic channel. The sediments transported in this channel are filling elongated basins linked with fracture zones (notably the Barracuda Basin), and finally end their course in the Puerto-Rico trench. The turbidite sediments above the accretionary prism and in the abyssal plain are mostly coarse sandy deposits covered by recent pelagic planktonic-rich sediments. Stratigraphic modelling suggests that during the last glacial event, the main depocentres were located in the abyssal plain and that, during the Holocene eustatic rise, a large accommodation space formed on the shelf confining sedimentation mostly on the Orinoco platform. [ABSTRACT FROM AUTHOR]

The study area is northwest part of Sanandaj-Sirjan or Esfandegha-Marivan zone in the northwest of Iran. The oldest rocks which are limestone, sandstone, tuff, and lava belong to the Jurassic which have deformed during the Late Cimmerian orogeny. This complex is unconformably overlain by Cretaceous volcano sedimentary. The dominantly Cretaceous outcrops are limestone, shale, tuff, and basic to intermediate volcanic rocks. The Jurassic complex was locally metamorphosed by granitoid intrusions during the Cretaceous. Geochemical interpretations show some differences in magmatic activity in the Jurassic and Cretaceous periods. Furthermore, the chemical composition confirms the alkaline to calc alkaline trend for these two major groups. In petro-tectonic diagrams, they plot in the extensional and active margin tectonic regime. The existence of a few hundred meters of Jurassic lava with interbeded sediments, which have deformed in the Late Cimmerian orogeny infer the simultaneous existence of extension and subsidence during the Jurassic and so a compression regime in the late Jurassic (Late Cimmerian). Based on our findings, this area shows sporadically occurring extension and compression tectonic regimes over the subduction zone in the Jurassic and Cretaceous such as Cordilleran belt. [ABSTRACT FROM AUTHOR]

Exposures of Triassic-Jurassic volcanic sequences in northeastern Mexico suggest that they developed along an active continental margin. Other sequences in support of such a tectonic environment are exposed in Durango, Zacatecas, San Luis Potosí, Nuevo León and Tamaulipas, where siliciclastic flysch sediments to the west and an older metamorphic continental block to the east underlie the volcanics. It is proposed that these Triassic to Jurassic volcanic rocks and associated redbeds from middle to northeastern Mexico are genetically related to a Jurassic active continental margin. The red beds of easternmost Mexico are either associated with rifting related to the break-up of Pangea, or preferably to a back-arc basin and to the younger transgressive Callovian to Oxfordian sequence, beginning with redbeds and associated to the basin evolution of the Gulf of Mexico and an eastern passive continental margin.

The cored sediments sampled by R/V Marion Dufrense in the active margin off southwestern Taiwan on the east side of the Manila Trench are mostly muds consisting mainly of quartz, feldspar, illite, chlorite + kaolinite with a trace amount of montmorillonite. The cored sediments have higher Fe, Ti, Cr, Cs, Li, Ni, and V but lower Ca, Na, Mn, Hf, Nb, Sr, Ta, U and Zr contents when compared with the upper continental crust (UCC, Taylor and McLennan, 1985). The Eu/Eu* ratios of the sediments averaging 0.69 indicate that the recycling effect on the Eu anomaly may be minor and the contribution of mafic source rock was unimportant, which can also be depicted in the La-Th-Sc plot (Cullers, 1994) showing a 'mixed origin' close to the felsic end member. The chemistry of the cored sediment can be explained by a mixing model designed by Ho and Chen (1996) with four end members i.e., greywacke, shale, quartzite and limestone, which are widely distributed in the Cenozoic formations of southern Taiwan with greywacke as the dominant contributor followed by shale. [ABSTRACT FROM AUTHOR]

Abstract: Paleoseismic studies seek to characterise the signature of pre-historical earthquakes by deriving quantitative information from the geological record such as the source, magnitude and recurrence of moderate to large earthquakes. In this study, we provide a ∼16,000 yr-long paleo-earthquake record of the 200 km-long northern Hikurangi Margin, New Zealand, using cm-thick deep-sea turbidites identified in sediment cores. Cores were collected in strategic locations across the margin within three distinct morphological re-entrants – the Poverty, Ruatoria and Matakaoa re-entrants. The turbidite facies vary from muddy to sandy with evidence for rare hyperpycnites interbedded with hemipelagites and tephra. We use the Oxal probabilistic software to model the age of each turbidite, using the sedimentation rate of hemipelagite deduced from well-dated tephra layers and radiocarbon ages measurements on planktonic foraminifera. Turbidites are correlated from one core to the other using similarity in sedimentary facies, petrophysical properties and ages. Results show that 46 turbidites are synchronous along the entire margin. Amongst them 41 are interpreted as originating from the upper continental slope in response to earthquake-triggered slope failures between 390 ± 170 to 16,450 ± 310 yr BP. Using well-established empirical relationships that combine peak ground acceleration, magnitude and location of earthquakes, we calculate that synchronous slope failures were triggered by the rupture of 3 of the 26 known active faults in the region, each capable of generating M w 7.3 to 8.4 earthquakes – two are crustal reverse faults and one is the subduction interface. The 41 M w ≥ 7.3 earthquakes occurred at an average recurrence interval of ∼400 yr over the last ∼16,000 yr. Among them, twenty are interpreted as subduction interface earthquakes that occurred at an average recurrence interval of ∼800 yr, with alternating periods of high activity and low return times (305–610 yr) and quiescence periods with high return times (1480–2650 yr). Based on turbidite paleoseismology, we propose that subduction interface earthquakes were of lower magnitude during active periods (M w > 7.5) than during quiescence periods (M w ≥ 8.2). [Copyright &y& Elsevier]