Cenozoic Tectonic History Research Articles

Cretaceous Crust in the Scotia Sea: Missing Pieces in a Geological Puzzle?

AbstractThe interplay between regional tectonics and the development of a major ocean gateway between the Pacific and the Atlantic Ocean has resulted in numerous paleogeographic reconstruction studies that describe the Cenozoic tectonic history of the Scotia Sea region. Despite the multitude of published tectonic reconstructions and the variety of geological and geophysical data available from the Scotia Sea, the geological history remains ambiguous. We present a comparative paleogeographic analysis of previously published tectonic reconstructions to identify agreements and conflicts between these reconstructions. We propose an alternative model to explain the Cenozoic evolution of the Scotia Sea region. The paleogeographic comparison shows that most reconstructions agree on the tectonic evolution of the South Scotia Ridge and the East Scotia Ridge. Major differences between the reconstructions are the role of the westward subducting plate below the South Sandwich plate, and the age and origin of the Central Scotia Sea. Tectonic reconstructions assume that the Central Scotia Sea is either part of a Cenozoic back‐arc basin, or a captured piece of Cretaceous oceanic crust. We propose a new alternative tectonic reconstruction that brings these two prevailing hypotheses elegantly together. Here, we identified new geographical blocks consisting of thinned continental or Cretaceous oceanic fragments that originate from the Paleo‐Pacific Weddell Sea gateway from high‐resolution bathymetry. These fragments are now part of the Central Scotia Sea and have been affected by early back‐arc tectonic activity of the South Sandwich subduction zone, leading locally to the formation of Cenozoic‐aged crust in the Central Scotia Sea.

Revised chronology of the middle−upper Cenozoic succession in the Tuotuohe Basin, central-northern Tibetan Plateau, and its paleoelevation implications

Currently, the climatic implications associated with the Cenozoic tectonic history and growth mechanisms of the Tibetan Plateau lack consensus and remain controversial. This is due in part to chronological uncertainties and few paleoelevation records distributed in the central to northern Tibetan Plateau, which we address here with the development of a robust chronology (using magnetostratigraphy, biostratigraphy, detrital zircons, and regional radiochronologic dating) and a paleoelevation reconstruction for the Tuotuohe Basin (central-northern Tibet). We refined the age of the Tuotuohe Formation (37−33 Ma), Yaxicuo Formation (33−23.6 Ma), and Wudaoliang Formation (23.6−19.7 Ma). We estimated early Oligocene (ca. 29 Ma) paleotemperatures of the Tuotuohe Basin from 11 °C to 16.1 °C, which correspond to paleoelevations of 2.9 km (±0.4 km) when the relative humidity is 64% and 2.5 km (±0.5 km) when this value is 75%, using various methods including ostracod assemblages, gastropods, charophytes, branched glycerol dialkyl glycerol tetraether analysis, regional empirical formulas, and climate model simulation. Paleoelevation data and existing geological evidence in the vicinity indicate that late Eocene to late Oligocene uplift was associated with upper-crustal shortening. Since the middle Miocene, uplift has been associated with convective removal of lithospheric mantle and/or lower-crustal flow beneath the Hoh Xil Basin.

Double arc–continent collision record in the latest Mesozoic–Cenozoic tectonic history of the Himalayan–Tibetan orogenic belt in western Pakistan

Our recent field investigations in western Pakistan have revealed that serpentinized peridotites here are crosscut by numerous intrusions of gabbro and tonalite. New zircon U–Pb dating of these plutons indicates Late Cretaceous–Early Eocene ages of their crystallization. They have arc-like geochemical signatures and constitute the middle crust of an island arc complex. Together with their extrusive counterparts they form the RasKoh island arc (RIA), defined for the first time in this study. The RIA and the Chagai continental arc to the north represent the manifestations of two separate subduction-zone systems within Neotethys, developed between India and Eurasia. We posit that this Neotethyan domain contained two oceanic plates. Subduction of the leading plate beneath Eurasia generated the Jurassic–Late Oligocene Chagai continental arc, and the northward subduction of the trailing plate resulted in the development of the Late Cretaceous–Oligocene, ensimatic RasKoh arc. Arrival of the Indian subcontinent at the latitude of the RasKoh arc in the earliest Miocene caused the emplacement of the RasKoh arc onto India via oblique arc–continent collision. The subsequent collision of this composite Indian plate with Eurasia resulted in extensive deformation of Late Cretaceous flysch deposits and the ophiolitic arc basement. Supplementary material: Rock compositions and analytical results are available at https://doi.org/10.6084/m9.figshare.c.6795686 Thematic collection: This article is part of the Ophiolites, melanges and blueschists collection available at: https://www.lyellcollection.org/topic/collections/ophiolites-melanges-and-blueschists

Global back-arc extension due to trench-parallel mid-ocean ridge subduction

Subduction of young seafloors straddling mid-ocean ridges (MOR) is an inevitable consequence of plate tectonics. Surprisingly, this process correlates globally with prolonged back-arc extension when the MOR is largely trench-parallel. We investigate the underlying mechanism by analyzing the East China Sea Basin (ECSB) whose Cenozoic tectonic history consists of three syn-rift stages with the rift center progressively migrating oceanward. Global geodynamic models satisfying the past subduction history and present-day mantle structures successfully reproduce the lithospheric stress states of the evolving ECSB. We show that segmented removal of the Mesozoic Izanagi slab due to subduction of the young seafloor initiated Paleocene rifting within the western ECSB. Detachment of the former slab facilitated a strong landward mantle wind driven by the large pressure gradient across the slab. The resulting mantle traction pushed the thickened upper plate landward while entraining the young seafloors behind to slowly subduct, a process causing long-lasting Eocene extension of the central ECSB. The waning mantle wind after 30 Ma reduced basal traction and upper plate extension. A final phase of ECSB extension since the late Miocene formed the Okinawa Trough, when the subducting plate became old enough to trigger slab retreat. A similar dynamic scenario is also predicted in other circum-Pacific margins. We conclude that this enduring back-arc extension during MOR subduction represents an important mechanism for continental evolution during the closure of major ocean basins.

Mesozoic–Cenozoic multistage tectonic evolution of the Pamir: Detrital fission‐track constraints from the Tajik Basin

AbstractKnowledge of the tectonic history of the Pamir contributes to our understanding of both the evolution of collisional orogenic belts as well as factors controlling Central Asian aridification. It is, however, not easy to decipher the Mesozoic–Cenozoic tectonics of the Pamir due to extensive Neogene deformation in an orogen that remains largely understudied. This study reports detrital apatite and zircon fission‐track (FT) ages from both the eastern Tajik Basin sedimentary rocks and Pamir modern river sands. These FT data, supported by vitrinite reflectance and zircon and apatite U–Pb double dating, suggest that the majority of the FT ages are unreset and record exhumation stages of the Pamir, which has served as the source terrane of the Tajik Basin since the Cretaceous. Furthermore, we combine the new data with a compilation of published detrital apatite and zircon FT data from both the Tajik Basin sedimentary rocks and Pamir modern river sands, to explore the Mesozoic–Cenozoic tectonic history of Pamir. Deconvolved FT Peak Ages document two major Mesozoic exhumation events associated with the Late Triassic–Early Jurassic Cimmerian orogeny that reflects accretion of the Pamir terranes, as well as the Early–early Late Cretaceous deformation associated with the northward subduction of the Neo‐Tethys Ocean beneath Pamir. The compiled data also show significant Late Eocene–Neogene exhumation associated with the ongoing formation of the Pamir, which peaks at ca. 36, 25, 14 and 7 Ma.

Asthenospheric flow through the Izanagi-Pacific slab window and its influence on dynamic topography and intraplate volcanism in East Asia

The tectonics of East Asia are notoriously complex. Consisting of an intricate patchwork of microplates and accreted terranes, even the Cenozoic tectonic history of the region remains controversial, and many differing reconstructions have been proposed. While the exact kinematics remain poorly constrained, it is generally accepted that East Asia has been characterised by a long history of subduction and downwelling. However, numerous geological observations, at a first glance, appear to lie in stark contrast to this history. For example, seismically slow anomalies in the uppermost mantle are extensive in this region and coincide spatially with widespread intraplate volcanism since the latest Paleogene, which is seemingly at odds with the cold upper mantle and downwelling flow expected from a history of subduction. Here, we propose a solution to this paradox, in which hot asthenospheric material flows through the slab window opened by the subduction of the Izanagi-Pacific ridge during the early Cenozoic, passing from the Pacific domain into East Asia. To investigate this hypothesis, we compare several independent geological observations to the asthenospheric flow predicted by a suite of recently published global mantle circulation models. The timing and location of intraplate volcanism is compared with the predicted distribution of this hot material through time, while observations linked to uplift and erosion are compared to the changes in dynamic topography that it induces. These include the widespread late Eocene–Oligocene sedimentary hiatus in far eastern China and the regional erosion of the South China Block since the Miocene inferred from Apatite Fission Track Thermochronology studies. The westward influx of hot asthenospheric material is a robust feature in the models, being predicted regardless of the implemented Cenozoic tectonic reconstruction. However, we find that a small Philippine Sea Plate that overrides a marginal “vanished ocean” during the late Cenozoic provides an optimal fit to the geological observations considered. Flow of hot asthenospheric material through gaps in subduction has the potential to significantly affect the geodynamic and geologic history of backarc and hinterland regions, and might have been a recurring phenomenon throughout Earth’s history. However, further research will be required in order to establish this.

Deciphering the Late Paleozoic–Cenozoic Tectonic History of the Inner Central Andes Forearc: An Update From the Salar de Punta Negra Basin of Northern Chile

We integrated new and existing geological, geochronological, thermochronological, and two-dimensional (2D) seismic data from the Salar de Punta Negra Basin to define the Late Paleozoic–Cenozoic tectonic evolution of the inner Andean forearc of northern Chile more precisely. Our results indicate that this region experienced early Late Paleozoic–Mesozoic crustal extension, creating several basement half-graben structures bounded by east- and west-dipping master faults. These extensional basins were filled by Upper Permian to Jurassic volcanic and sedimentary (continental and marine) syn-rift deposits. The genesis of these structures is related to the early breakup of the western Gondwana continent and the development of the large Tarapacá Basin in northern Chile and southern Perú. Subsequently, Late Cretaceous to Paleocene contraction occurred, which led to the tectonic inversion of the pre-existing rift system and the uplift of the Paleozoic–Mesozoic syn-rift deposits. Seismic data show that Upper Cretaceous and Paleocene synorogenic deposits accumulated along and over inversion anticlines, recording the initial contraction and marking the change from an extensional to a contractional tectonic setting. During the final episodes of basin inversion, crustal shortening was accommodated by the Eocene to recent basement reverse faulting accompanied by the rapid exhumation of basement pre-rift blocks, which served as the principal sources for the sediments that filled the pre-Andean basins during the Late Cenozoic. Finally, the exhumed basement pre-rift blocks and the reverse faults compartmentalized the contractional intermontane basins, which constitute the main low topographic relief of the inner forearc of northern Chile.

Inversion of bedrock channel profiles in the Daqing Shan in Inner Mongolia, northern China: Implications for late Cenozoic tectonic history in the Hetao Basin and the Yellow River evolution

Many studies indicate the Hetao Basin in Inner Mongolia, northern China, controlled the erosion base level of the upper Yellow River before 1.5 Ma. The late Cenozoic extensional rifting in the Hetao Basin in response to the northeastward growth of the Tibetan Plateau may be an plausible mechanism that initiated the headward erosional signal along the Yellow River at the northeastern margin of Tibetan Plateau ~1.8 Ma ago. However, little attention has been paid to establish the relationship between the late Cenozoic tectonic evolution in the Hetao Basin and integration of the upper Yellow River. In this paper, we explore the tectonic mechanism that can drive headward erosion along the Yellow River and the timescales over which it occurred by reconstructing the late Cenozoic tectonic history in the Hetao Basin. We applied linear inversion of bedrock channel profiles and late Cenozoic sedimentary strata in the Daqing Shan to explore the late Cenozoic tectonic evolution in the Hetao Basin. Results show that the accelerated vertical slip between the Daqing Shan and the Hetao Basin initiated at 2.8 ± 0.8 Ma, and the average relative uplift rate was 0.18 ± 0.04 mm/yr since 2.8 Ma. The lowering of erosion base level in the Hetao Basin since 2.8 ± 0.8 Ma produced a headward erosional signal along the Yellow River that initiated fluvial incision at the northeastern margin of the Tibetan Plateau ~1.8 Ma ago. That indicates the accelerated extensional rifting in the Hetao Basin has been responsible for the integration of the upper Yellow River since the late Pliocene. Our study improved understanding how the Yellow River responds to the late Cenozoic rifting around the Ordos Block, as well as the northeastward growth of the Tibetan Plateau. Meanwhile, these tectonic processes were also linked together by the Yellow River evolution.

Cenozoic structural history of the Gippsland Basin: Early Oligocene onset for compressional tectonics in SE Australia

Abstract The Gippsland Basin contains some of the largest hydrocarbon accumulations in Australia, and has been in production since the 1920's. These hydrocarbons are trapped by large growth anticlines offshore, in reservoirs of the Cretaceous to Eocene-aged Latrobe Group. Despite the obvious importance of these growth anticlines, the timing of their formation, and the overall Cenozoic tectonic history of the basin is not well understood. Here, we present a detailed growth strata analysis of the faults and anticlines within the Cenozoic sediments of the Gippsland Basin. This indicates two major phases of tectonism in the basin: 1. Late Cretaceous to Eocene extension, and 2. Oligocene to Holocene compression. Detailed analysis of the extensional phase indicates the development of numerous normal growth faults, which display an overall reduction in the magnitude of extension from the Late Cretaceous to the Eocene, commonly terminating at the top of the Latrobe Group. The shift to compressional tectonism occurred at approximately the Eocene-Oligocene boundary (~34 Ma). A major and widespread episode of compression then occurred, with evidence of growth on anticlines and reverse faults beginning in the early Oligocene. This previously unrecognized early Oligocene event produced significant growth (20–50% total growth) of the major anticlines which host hydrocarbon accumulations. The early Oligocene event represents the first phase of the compressional tectonic regime that continues to the present day in SE Australia. It appears likely that this Oligocene event affected other basins in SE Australia and probably contributed to uplift of the Eastern Highlands. The underlying tectonic cause for this Oligocene compressional regime is enigmatic and may be related to far field tectonic processes. A second pulse of compressional tectonism and anticline growth occurred during the mid-Miocene and is generally more significant in the onshore regions of the basin. The youngest phase of compressional tectonism beginning in the Late Miocene (~10 Ma) is also more intense in onshore regions and is marked by an unconformity that is widespread in SE Australia.

Evidence of a common source component for east Australian Cenozoic mafic magmatism

Eastern Australia includes Cenozoic mafic volcanic provinces that are commonly divided into age-progressive and non-age-progressive groups. The former group is typically ascribed to the Cenozoic northward motion of Australia over fixed thermal anomalies in the mantle (i.e., “hotspots”), while the latter group is traditionally attributed to the opening of the Tasman and Coral Seas, though more recent interpretations have linked its formation to edge-driven convection or other processes. However, the initial criteria used to define the groups based on morphological and lithological features are neither robust nor consistently able to be applied to individual provinces. Despite their importance in the Cenozoic tectonic history of eastern Australia and, more broadly, the SW Pacific, geochemical distinctions between the two groups have been underexplored. Based on examination of an extensive database of new and previous major element, trace element, and radiogenic isotope data and principal component analysisfrom key volcanic exposures in Queensland and New South Wales, we find no systematic geochemical differences between the two groups. Both age-progressive and non-age-progressive Cenozoic mafic volcanic rocks in eastern Australia have an EM1-like source signature that could have originated in the asthenosphere and interacted with SCLM upon ascent. Our work underpins the necessity of understanding the magma generation mechanisms and the geodynamic context of individual volcanoes across eastern Australia.

Structural evolution of central Death Valley, California, using new thermochronometry of the Badwater turtleback

AbstractThe Badwater turtleback, Copper Canyon turtleback, and Mormon Point turtleback are three anomalously smooth, ∼2-km-high basement structures in the Black Mountains of Death Valley, California. Their structural evolution is linked to the Cenozoic tectonic history of the region. To explore their evolution, we apply (U-Th)/He, Ar/Ar, and U-Pb analyses, with multi-domain diffusion modeling to 10 samples from the Badwater turtleback. The cooling history of the Badwater turtleback is used as a proxy for its exhumation history as it uplifted from warmer depths.We find slow (<2 °C/m.y.) cooling from ca. 32 to 6 Ma, followed by rapid (120–140 °C/m.y.) cooling from ca. 6 to 4.5 Ma, and finally moderate (30–120 °C/m.y.) cooling occurred from ca. 4.5 Ma until the present. When these data are added to previously published cooling paths of the Copper Canyon turtleback and Mormon Point turtleback, a northwest cooling pattern is broadly evident, consistent with a top-to-NW removal of the hanging wall along a detachment fault. We propose a six-phase tectonic history. Post-orogenic collapse and erosion dominated from ca. 32 to 16 Ma. At 16–14 Ma, a detachment fault formed with a breakaway south and east of the Black Mountains, with normal faults in the hanging wall. Moderate extension continued from 14 to 8 Ma causing exhumation of the turtlebacks through the brittle-ductile transition. Dextral transtension at 7–6 Ma produced a pull-apart basin across the Black Mountains with rapid extension. The locus of deformation transferred to the Panamint and Owens Valley fault systems from 4.5 to 3.5 Ma, slowing extension in the Black Mountains until present.

Nature and genesis of potassic high Ba[sbnd]Sr granitoids associated with syn-convergent extension in NW Turkey

The Cenozoic post collisional magmatism in NW Turkey produced several granitic emplacements during the Eocene and Late Oligocene-Early Miocene. Both Eocene and Late Oligocene-Early Miocene plutons are represented by high BaSr granitoids. We document here whole-rock chemical and Sr–Nd–Pb-O isotopic compositions of the Solarya plutonic association (SPA) with the age of 21 Ma (Lower Miocene) to evaluate the nature and genesis of potassic, high BaSr granites. SPA is one of the major plutons representing the Late Oligocene- Early Miocene high BaSr granitoids. The SPA consists of three coeval granitic members (K-Feldspar megacrystalline granodiorite, microgranite-granodiorite and haplogranite) with associated mafic microgranular enclaves (MME) and mafic dikes of gabbroic diorite to diorite in composition. Along the southern contact of the pluton, hypabyssal rocks having quartz diorite and granodiorite composition were injected into the ring fault system coeval with SPA. Hypabyssal rocks (HA) display similar mineralogical, geochemical and isotopic characteristics with SPA which indicate that HA and SPA are temporally and spatially related. K-Feldspar megacrystalline granodiorite, microgranite-granodiorite and haplogranite display high K-calcalkaline affinity whereas the mafic dikes and MME's present mid-alkaline and shoshonitic character. SPA presents Ba values between 710 and 1505 ppm and Sr values between 305 and 706 ppm. They display low Y, Yb and HREE contents and an insignificant negative Eu anomaly, which are typical geochemical signatures of high BaSr granitoids.SPA has initial 87Sr/86Sr values of 0.70702–0.70805 and 143Nd/144Nd values vary from 0.51235 to 0.51250. They display ƐNd values of −4.9 and −2.05. 207Pb/204Pb and 206Pb/204Pb isotopic values range between 15.68 and 15.73 and 18.75 to 18.88, respectively. Quartz and whole rock δ 18O isotopic values vary from 8 to 10.6. These similar Sr-Nd-Pb and O isotopic features of MME/mafic dikes and host granodiorites points out to a common igneous precursor for the magma source. All these major-trace element and isotopic compositions of SPA suggest an enriched mantle (EMII) or sub-continental lithospheric mantle source for their parental magma. Bulk mixing model between ƐNd and 87Sr/86Sr isotopic data suggests that, the crustal contribution to the enriched mantle source is about 30–45%.Regarding the Cenozoic tectonic history of NW Anatolia, the inferred mantle source and magma evolution suggest that the melt generation to produce high BaSr granitic magmatism was most probably the result of syn-convergent extension.

Deepwater sedimentation and Cenozoic deformation in the Southern New Caledonia Trough (Northern Zealandia, SW Pacific)

Abstract The New Caledonia Trough (NCT) is a 2000–3000 m deep bathymetric feature that extends 2500 km from Taranaki, New Zealand, to the western margin of New Caledonia (Northern Zealandia, SW Pacific). The underlying sedimentary basin originates from Cretaceous extension, but underwent a significant Eocene tectonic event that shaped its present physiography. We present an analysis of the basin based on multibeam data, seismic profiles and rock samples collected on the TAN1312 and TAN1409 Expeditions onboard R/V Tangaroa, combined with legacy data. We focus on the southern part of the basin, where new data reveal a link between compressive deformation of Paleocene strata and their potential reworking into the basin. On the western basin side, Upper Cretaceous to Paleocene strata were deformed by local reverse faults and folds that created a sub-circular bathymetric ridge and seabed exposure. This folded unit (seismic Unit 2) is sharply overlain by a restricted interval imaged as chaotic high-amplitude reflections that are interpreted as syntectonic mass-transport deposits due to slope oversteepening (seismic Unit 1b). This unit is stratigraphically below the main basin onlap surface and seismic mapping revealed that it rapidly thins away from the mouth of a present day submarine canyon imaged on the western slope of the basin, and that is diverted by exposures of Unit 2 deformed strata. Deformed and syntectonic intervals are in turn overlain by a flat-lying unit (seismic Unit 1a) we interpret as reflecting a passive basin fill. Our new data provide insight into an extensive deep-water basin that is remote from terrigenous sediment sources, and new constraints on its Cenozoic tectonic history. Stratigraphic ages are constrained by seismic ties to Taranaki basin petroleum wells and biostratigraphic dating of dredged samples. This specific site has particular significance for understanding tectonic events in the southwest Pacific. Indeed, our observations show that deformation is younger than the Paleocene and is envisaged to be a local expression of a widespread Cenozoic compressive event (called “TECTA”, Tectonic Event of the Cenozoic in the Tasman Area), which affected the region after the Mesozoic rifting. On a regional perspective, this study provides new insights on the evolution of the submerged Zealandia continent and associated geodynamic processes such as Gondwana break-up and initiation of the Tonga-Kermadec subduction.

Three-dimensional structural model of the Qaidam basin: Implications for crustal shortening and growth of the northeast Tibet

AbstractThe Qaidam basin, bounded by the Altyn Tagh fault in the north, is located in the northeast of the Tibet plateau, and it has important implications for understanding the history and mechanism of Tibetan plateau formation during the Cenozoic Indo-Eurasia collision. In this study, we constructed the main geological structures and surfaces in three dimensions through the interpolation of regularly spaced 2D seismic sections, constrained by wells data and surface geology of the Qaidam basin in northeast Tibet. Meanwhile the Cenozoic tectonic history of the Qaidam basin was reconstructed and the uplift mechanism of the Tibetan plateau was discussed. This study presents the subsurface data in conjunction with observations and analysis of the stratigraphic and sedimentary evolution. The Cenozoic deformation history of the Qaidam basin shows geologic synchroneity with uplifting history of the Tibet Plateau. It is therefore proposed that the deformation and uplifting in the south and north edges of the Tibet Plateau was almost synchronous. The total shortening and shortening rate during Cenozoic reached 25.5 km and 11.2% respectively across the Qaidam basin, indicating that the loss of the left-lateral strike slip rates of the Altyn Tagh fault has been structurally transformed into local crustal thickening across NW-trending folds and thrust faults. Meanwhile there is an about 11° vertical component along the strike-slip Altyn Tagh fault, the block oblique slip shows one more growth mechanism of the northeast Tibet.

Cretaceous–Cenozoic tectonic history of the Jiaojia Fault and gold mineralization in the Jiaodong Peninsula, China: constraints from zircon U–Pb, illite K–Ar, and apatite fission track thermochronometry

The Jiaojia Fault (JJF) in the Jiaodong area of eastern China is an important NNE-trending structure that is subsidiary to the regional Tancheng–Lujiang (Tan-Lu) Fault Zone, and hosts >1200 t of gold reserves contained in disseminated and stockwork ore, dominantly in the footwall of the fault. We present new zircon U–Pb, apatite fission track, and illite K–Ar data along the JJF and have delineated its tectonic history focusing on its formation and reactivation. Zircon U–Pb dating shows that the Shangzhuang granite is a composite body with ages between 132 ± 1 and 127 ± 1 Ma. Illite K–Ar ages for the fault’s gouge range from 83 ± 2 to 68 ± 2 Ma, and the measured apatite fission track ages for ores are between 55 and 21 Ma. Previous zircon U–Pb geochronology and structural studies suggest that the JJF was originally activated in the Jurassic during 160–150 Ma as a sinistral fault. The JJF was a normal fault in the Early Cretaceous due to NW–SE orientated tension and NE–SW compression, which lasted from 135 to 120 Ma. This was followed by sinistral strike–slip faulting due to NW–SE compression and NE–SW tension during 120–110 Ma, and it changed to normal displacement at ca. 110 Ma. Our apatite fission track data analysis and thermal modeling of representative samples suggest that there was a subsequent dextral reactivation of the fault at ca. 55 Ma. Previous age data of ca. 130–110 Ma for gold mineralization along the JJF coincides with the Early Cretaceous magmatism and is coeval with the transition from normal faulting to sinistral strike–slip faulting of the JJF in Early Cretaceous, which is interpreted to be due to changing direction of the subducting Pacific Plate.

Neogene marine isotopic evolution and the erosion of Lesser Himalayan strata: Implications for Cenozoic tectonic history

An extensive, northward deepening blanket of Neoproterozoic and Cambrian sedimentary rocks once extended from the Himalayan margin far onto the Indian craton. Cambrian deposits of this “upper Lesser Himalayan” succession, which include deposits of the “outer” Lesser Himalaya tectonic unit, are enriched in radiogenic 187Os. They make up part of a proximal marine facies belt that extends onto the craton and along strike from India to Pakistan. By contrast, age-equivalent facies in the Tethyan Himalaya are more distal in nature. Neoproterozoic to Cambrian strata of the upper Lesser Himalayan succession are now missing in much of the Lesser Himalaya, with their erosion exposing older Precambrian Lesser Himalayan strata. We suggest that exhumation and weathering of the upper Lesser Himalaya and related strata caused dramatic changes in the 187Os/188Os and 87Sr/86Sr Neogene record of seawater starting at ∼16 Ma. First-order estimates for the volume of upper Himalayan strata, as well as the volume of all LH rock eroded since this time, and geochemical box modeling, support this idea. Exhumation at 16 Ma is a fundamental event in the evolution of the Himalayan orogeny and the geochemical evolution of the oceans, and will be a critical part of the construction of future models of Himalayan thrust belt evolution.

Cenozoic tectonic history of the South Georgia microcontinent and potential as a barrier to Pacific-Atlantic through flow

Cenozoic opening of the central Scotia Sea involved the tectonic translation of crustal blocks to form the North Scotia Ridge, which today is a major topographic constriction to the flow of the deep Antarctic Circumpolar Current that keeps Antarctica thermally isolated from warmer ocean waters. How this ridge developed and whether it was a topographic barrier in the past are unknown. To address this we investigated the Cenozoic history of the South Georgia microcontinental block, the exposed part of the ridge. Detrital zircon U-Pb geochronology data confirm that the Cretaceous succession of turbidites exposed on South Georgia was stratigraphically connected to the Rocas Verdes backarc basin, part of the South America plate. Apatite thermochronometry results show that South Georgia had remained connected to South America until ca. 45–40 Ma; both record a distinct rapid cooling event at that time. Subsequent separation from South America was accompanied by kilometer-scale reburial until inversion ca. 10 Ma, coeval with the cessation of spreading at the West Scotia Ridge and collision between the South Georgia block and the Northeast Georgia Rise. Our results show that the South Georgia microcontinental block could not have been an emergent feature from ca. 40 Ma until 10 Ma.

Middle to Late Cenozoic tectonic events in south and central Palawan (Philippines) and their implications to the evolution of the south-eastern margin of South China Sea: Evidence from onshore structural and offshore seismic data

Using recently gathered onland structural and 2D/3D offshore seismic data in south and central Palawan (Philippines), this paper presents a new perspective in unraveling the Cenozoic tectonic history of the southeastern margin of the South China Sea. South and central Palawan are dominated by Mesozoic ophiolites (Palawan Ophiolite), distinct from the primarily continental composition of the north. These ophiolites are emplaced over syn-rift Eocene turbidites (Panas Formation) along thrust structures best preserved in the ophiolite–turbidite contact as well as within the ophiolites. Thrusting is sealed by Early Miocene (∼20 Ma) sediments of the Pagasa Formation (Isugod Formation onland), constraining the younger limit of ophiolite emplacement at end Late Oligocene (∼23 Ma). The onset of ophiolite emplacement at end Eocene is constrained by thrust-related metamorphism of the Eocene turbidites, and post-emplacement underthrusting of Late Oligocene – Early Miocene Nido Limestone. This carbonate underthrusting at end Early Miocene (∼16 Ma) is marked by the deformation of a seismic unit corresponding to the earliest members of the Early – Middle Miocene Pagasa Formation. Within this formation, a tectonic wedge was built within Middle Miocene (from ∼16 Ma to ∼12 Ma), forming a thrust-fold belt called the Pagasa Wedge. Wedge deformation is truncated by the regionally-observed Middle Miocene Unconformity (MMU ∼12 Ma). A localized, post-kinematic extension affects thrust-fold structures, the MMU, and Late Miocene to Early Pliocene carbonates (e.g. Tabon Limestone). This structural set-up suggests a continuous convergent regime affecting the southeastern margin of the South China Sea between end Eocene to end Middle Miocene. The ensuing structures including juxtaposed carbonates, turbidites and shallow marine clastics within thrust-fold belts have become ideal environments for hydrocarbon generation and accumulation. Best developed in the Northwest Borneo Trough area, the intensity of thrust-fold deformation decreases towards the northeast into offshore southwest Palawan.

Jurassic to Cenozoic tectonics of the Zagros Orogen in northwestern Iran

The Zagros Mountains of Iran formed by continental collision from closure of the Neo-Tethyan Ocean. The Zagros Orogen underlying the mountain range reflects a much longer history with the Pan-African basement and Phanerozoic successions. New mapping, radiometric ages, and stratigraphic analyses have enabled advances in our understanding of the Jurassic to Cenozoic tectonic history. The northwestern Zagros Orogen consists of three belts: (1) the Zagros Fold and Thrust Belt, divided into the outer Zagros Simply Folded Belt and the inner High Zagros Belt; (2) the Zagros Suture Zone including radiolarite, ophiolite, and Bisotun limestone thrust sheets; and (3) the Sanandaj–Sirjan Zone, which contains abundant metamorphic rocks. Late Cretaceous ophiolites of the Kermanshah region are part of the outer ophiolite belt of the Zagros Orogen and have formed in passive margin and supra-subduction zone settings. Major events include early Mesozoic rifting, Jurassic subduction followed by a more cryptic interval of subduction in the Cretaceous, multiple ophiolite emplacement on the Arabian margin in the Late Cretaceous to Eocene, and collision of central Iran and the Arabian margin in the Oligocene with final closure of the shallow Tethyan seaway in the mid-Miocene. A Middle to Late Jurassic plutonic belt, the Qorveh–Aligodarz Plutonic Belt, formed a magmatic arc with subdued topography related to a moderately NE-dipping subduction zone under the Sanandaj–Sirjan Zone. An Early Cretaceous unconformity reflects limited uplift followed by widespread marine deposition with intercalated volcanic rocks in the Sanandaj region. Subduction continued with a low-lying arc that underwent trenchward advance. In the Late Cretaceous to Oligocene interval, the Neo-Tethyan Ocean closed with ophiolite obduction over the Arabian Peninsula margin and major shortening affected the Sanandaj–Sirjan Zone with uplift and plutonism. Much of the forearc of the Jurassic to Cretaceous arc system has been lost by tectonic erosion along a low-angle Eocene subduction zone prior to collision. Flattening of the subducting slab in the Late Cretaceous and Palaeogene explains the inland retreat of the arc to central Iran. Continental collision initiated in the Oligocene but the Tethyan seaway remained open until the mid-Miocene.

Unionidae (Bivalvia; Palaeoheterodonta) from the Palaeogene of northern Vietnam: exploring the origins of the modern East Asian freshwater bivalve fauna

Eocene/Oligocene sediments deposited in two Cenozoic pull-apart basins in northern Vietnam, i.e. the Na Duong and Cao Bang basins, yield several rich and well-preserved assemblages of unionid bivalves. This study outlines the taxonomy of the Unionidae from these communities, and all taxa are described and illustrated in detail. As far as we are aware, this is the first comprehensive treatment of Cenozoic Unionidae from South-East Asia. Eight of the nine taxa are described as new to science. Four species – Cuneopsis quangi sp. nov., Cristaria mothanica sp. nov., Cristaria falcatocostata sp. nov. and Lamprotula hungi sp. nov. – can be confidently assigned to modern genera. The generic position of the remaining species is equivocal (?Nodularia cunhatia sp. nov., ?Cuneopsis sp., ?Lanceolaria sp., ?Lamprotula sp.) or remains tentative (Anodontini sp.). The phyletic relationships of the fossil taxa to modern species are discussed and interpreted in light of the Cenozoic tectonic history of South-East Asia and the intimately associated evolution of drainage systems. The results confirm a close relationship of the fossil unionids to the modern mussel fauna of the Yangtze, Pearl and Red River catchment areas. Moreover, the fossils from Cao Bang and Na Duong are among the earliest confirmed records of all genera identified, and thus document an important, early stage in the development of the modern East and South-East Asian bivalve faunas. http://zoobank.org/urn:lsid:zoobank.org:pub:D52F10F0-1AFF-4EFD-B724-692E982143E4