Late Mesozoic Era Research Articles

Electrical structures in the central part of the North China Craton and their implications for the mechanism of Craton destruction

The North China Craton is a stable cratonic block that emerged in the Paleozoic era. During the late Mesozoic era, lithospheric stretching and thinning, as well as volcanic activities, caused extensive destruction of the craton. In this study, we conducted a magnetotelluric profile within the North China Craton, covering the western (Ordos Block), middle (Taihangshan Uplift), and eastern (North China Plain) segments of the craton. The electrical structure along the profile was obtained. Our analysis revealed that the Huoshan fault and the piedmont fault of the Taihangshan are large-scale high- and low-resistivity boundaries, which traverse the entire crust. These two faults divide the three major secondary blocks within the North China Craton. The crust of the Taihangshan Uplift is characterized by a layered high-resistivity body, while the lower and middle crust exhibits widespread high conductivity layer. The crustal-scale structures of the North China Plain and the Ordos Block on both sides are dominated by stable layered resistivity structures. This indicates that the lithospheric destruction near the profile may have mainly concentrated beneath the central Taihangshan Uplift. The seismogenic environment of the 1303 Hongtong earthquake may have been controlled by multiple factors. The upwelling of mantle-derived materials in the lower and middle crust beneath the Taihangshan Uplift caused the extension of the Shanxi Graben fault system where the Linfen Graben is located. The main controlling factor of this earthquake is the southeastward sliding of the Huoshan fault. We speculate that the destruction process beneath the central Taihangshan Uplift of the North China Craton exhibited a bottom-up process, and the thermo-mechanical-chemical erosion mechanism may have dominated the destruction of craton.

Post-extinction recovery of the Phanerozoic oceans and biodiversity hotspots

The fossil record of marine invertebrates has long fuelled the debate as to whether or not there are limits to global diversity in the sea1–5. Ecological theory states that, as diversity grows and ecological niches are filled, the strengthening of biological interactions imposes limits on diversity6,7. However, the extent to which biological interactions have constrained the growth of diversity over evolutionary time remains an open question1–5,8–11. Here we present a regional diversification model that reproduces the main Phanerozoic eon trends in the global diversity of marine invertebrates after imposing mass extinctions. We find that the dynamics of global diversity are best described by a diversification model that operates widely within the exponential growth regime of a logistic function. A spatially resolved analysis of the ratio of diversity to carrying capacity reveals that less than 2% of the global flooded continental area throughout the Phanerozoic exhibits diversity levels approaching ecological saturation. We attribute the overall increase in global diversity during the Late Mesozoic and Cenozoic eras to the development of diversity hotspots under prolonged conditions of Earth system stability and maximum continental fragmentation. We call this the ‘diversity hotspots hypothesis’, which we propose as a non-mutually exclusive alternative to the hypothesis that the Mesozoic marine revolution led this macroevolutionary trend12,13.

Discovery of Late Mesozoic volcanic seamounts at the ocean-continent transition zone in the Northeastern margin of South China Sea and its tectonic implication

The Northern South China Sea (SCS) margin experienced the switch from Andean-type active subduction to passive extension during late Mesozoic era. However, the mechanism of cessation of paleo-Pacific subduction in the SCS region is unclear, and the location of suture zone between paleo-Pacific plate and South China block is obscure. In this study, we report new 40Ar/39Ar ages and whole-rock Hf isotopes of basalts from two poorly studied volcanic seamounts (namely, Puyuan and Beipo) at the ocean-continent transition zone in the Northeastern SCS margin, with an emphasis on the existence of exotic, buoyant oceanic plateau and its geodynamic effect on subduction cessation. Results indicate that the OIB-type Puyuan and E-MORB-type Beipo volcanic seamounts were erupted at 154.1 Ma and 93.2 Ma, respectively. Whole-rock trace element, Sr-Nd-Pb-Hf isotopic compositions, and subduction polarity point out that these samples were oceanic intraplate basalts formed within the paleo-Pacific plate, independent of the coeval, Late Mesozoic paleo-Pacific subduction system in the region. The ages and geochemical data of the two volcanic seamounts, combined with geochemical data of Late Mesozoic Pacific oceanic plateaus and seismic data of the Northeastern SCS margin, show that there may exist a Late Mesozoic exotic, buoyant oceanic plateau in the region. The collision between the oceanic plateau and the South China block could lead to the cessation of paleo-Pacific plate subduction, and changes in tectonic regime during the Late Cretaceous era (ca. 100–65 Ma). The pre-existing, Late Mesozoic suture zone has been well constrained by the remnant oceanic plateau and continental arc, and may play a key role in the formation of Cenozoic rifting tectonic units in the region.

Structural geometry and kinematics of thrust belts between the Dabashan and eastern Sichuan Basin, South China block: Constraints from (U-Th)/He dating and seismic data

Abstract The relationship between the North and South China blocks, particularly their spatial-temporal framework and evolutionary history, has been widely debated. We conducted a comprehensive study of the structural geometry and kinematics of the thrust belts in the intersection zone between the Dabashan and eastern Sichuan Basin based on seismic data, drilling data, field investigation data, and zircon and apatite (U-Th)/He thermochronology data. These data sets provide important insights into the relationship between the North and South China blocks during the post-orogenic process. Due to the detachments, the strata of the eastern Sichuan Basin can be divided into four structural intervals characterized by duplex structures and fault-related fold structures. Balanced restoration indicates the vertical differences are represented by the shortening ratio of the upper structural interval of ∼6%, that of the middle ∼10%, and that of the lower ∼7%. Besides, the shortening ratios indicate an increasing tendency of the deformation intensity from the west to the east. The (U-Th)/He dating results suggest two age ranges, i.e., from 180 Ma to 130 Ma and from 50 Ma to 20 Ma, respectively. These age data sets also imply a younger tendency westward. The intersection zone may have experienced the following stages since the late Mesozoic era: (1) the stable continental sedimentation stage from the Late Triassic to the Late Jurassic epochs; (2) the continuous thrust stage from the Late Jurassic to the early Paleogene epochs, which is associated with the subduction of the Paleo-Pacific Ocean; and (3) the uplift and denudation stage as a whole caused by the uplift of the Tibetan Plateau since the Paleogene period.

Taxonomic notes on Eustrophinae from the mid-Cretaceous Burmese amber, with description of a new species (Coleoptera, Tetratomidae)

A new polypore fungus beetle species Allostrophus Hsiao, Ślipinski, Yu, Deng and Pang embedded in Upper Cretaceous Burmese amber (Cenomanian, ca. 99 Ma) is described: A. yangi sp. nov.; this new species can be differentiated from its only congener based on its antennomere 11 and fusiform, elongate body. Morphological characters preserved in the inclusion compared to A. cretaceus Hsiao, Ślipinski, Yu, Deng and Pang provide further data for completing the definition of Allostrophus. This new discovery highlights the species diversity of fungivorous beetles during the Cretaceous period, adding evidence that the formerly hypothesized co-diversification between fungus-feeding coleopterans and their food resources originated in the late Mesozoic Era.

Southward propagation of Nazca subduction along the Andes.

The Andean margin is the plate-tectonic paradigm for long-lived, continuous subduction, yet its geology since the late Mesozoic era (the past 100 million years or so) has been far from steady state. The episodic deformation and magmatism have been attributed to cyclic changes in the dip angle of the subducting slab, slab break-off and the penetration of the slab into the lower mantle; the role of plate tectonics remains unclear, owing to the extensive subduction of the Nazca-Farallon plate (which has resulted in more than 5,500 kilometres of lithosphere being lost to the mantle). Here, using tomographic data, we recreate the plate-tectonic geometry of the subducted Nazca slab, which enables us to reconstruct Andean plate tectonics since the late Mesozoic. Our model suggests that the current phase of Nazca subduction began at the northern Andes (5°S) during the late Cretaceous period (around 80 million years ago) and propagated southwards, reaching the southern Andes (40°S) by the early Cenozoic era (around 55 million year ago). Thus, contrary to the current paradigm, Nazca subduction has not been fully continuous since the Mesozoic but instead included episodic divergent phases. In addition, we find that foredeep sedimentation and the initiation of Andean compression are both linked to interactions between the Nazca slab and the lower mantle, consistent with previous modelling.

Allostrophus cretaceus gen. et sp. nov.: A new polypore fungus beetle (Coleoptera, Tetratomidae) from the Cretaceous Myanmar amber

A new species and genus of polypore fungus beetle, Allostrophus cretaceus gen. et sp. nov., is described and illustrated, representing the third documented occurrence of Tetratomidae from Burmese amber (Cenomanian, ca. 99 Ma, Upper Cretaceous). This fossil species can be placed in the extant subfamily Eustrophinae based on the following combination of characters: small-sized, oblong-oval body, narrowed posteriorly; clubbed antennomeres; semicircular pronotum, with two weakly developed subbasal impressions; scutellum without light-colored pubescence and each elytron with traces of eight striae. Morphological characters preserved in the inclusion support the previously proposed high diversity of antennal morphology during the early evolution of eustrophines and suggest the potential fungivory of this extinct species. The new discovery sheds lights on the paleodiversity of mycophagous beetles during the Cretaceous period, strengthening the formerly hypothesized diversification of mushrooms in the late Mesozoic Era.

A middle Triassic extensional event in the Hainan Island: Geochronologic and geochemical evidence from igneous rocks from Dazhou Island

Hainan Island lies at the southern tip of the South China block that was affected by the opening and closure of the paleo-Tethys from Paleozoic to Mesozoic and subsequently by the subduction of the paleo- Pacific plate beneath the Euroasian plate since the late Mesozoic era. This study presents zircon U-Pb ages and geochemistry of granites and basic diabase veins in Dazhou Island located 5 km southeast of Hainan Island. The age for granites is 237.2 Ma (MSWD = 0.14, n = 14), suggesting that they were emplaced in the late middle Triassic and are products of magmatic-tectonic episodes during the closure of paleo-Tethys. The granites belong to the shoshonitic magmatic series and are metaluminous I-type granites. They are systematically depleted in Ba, Nb, Sr, P, and Ti, and have variable ranges of initial 87Sr/86Sr ratios (0.71005 ~ 0.71110), but relatively constant eNd(t) values (–6.4~–6.8). The two-stage depleted mantle Nd model ages (TDM2 = 1531–1562 Ma) for these granites suggest that they may have originated from partial melting of the lower crust with a crustal residence age of early Middle Proterozoic Era. The zircon U-Pb ages for diabase veins can be divided into three groups. The age for Group I is 236.8 Ma (n = 4), which represents the crystallization age of the veins and somewhat younger than the accompanying granites. The ages for Group II and III are 1767 Ma (n = 6) and 2432 Ma (n = 3), respectively. These suggest that the veins have inherited some old zircons that possibly represent old geological events in the Hainan Islands. The diabase also belongs to the shoshonitic magmatic series and has arc-like trace element characteristics. The veins have high 87Sr/86Sr and low 143Nd/144Nd ratios, which suggest that they may have originated from an enriched mantle II type source or a mantle source metasomatized by aqueous fluids released from previously subducted slab. The new ages obtained for the Dazhou igneous rocks in the present study are similar to those for the Qiongzhong batholith in the Hainan Island, which implies that the Hainan Island had also regionally experienced a middle Triassic extension event after the Indosinian Orogeny.

Petrology and geochemistry of Early Cretaceous A-type granitoids and late Mesozoic mafic dikes and their relationship to adakitic intrusions in the lower Yangtze River belt, Southeast China

ABSTRACTThe relationship among magmatism, large-scale metallogenesis of Southeast China, and subduction of the Pacific plate has long been debated. The lower Yangtze River belt (LYRB) in the northeastern edge of Southeast China is characterized by intense late Mesozoic magmatism and associated polymetallic mineralization such as copper, gold, iron, tungsten, molybdenum, etc. The copper-related adakitic rocks (148–130 Ma) in this belt are the oldest episode of magmatism and intruded as small intermediate-acid intrusive bodies. The Huayuangong granitoids (HYG), located in the southern part of this belt, however, are copper-barren. Three granitoid samples from this pluton give zircon U–Pb ages of 126.4 ± 1.6 Ma, 125.9 ± 1.9 Ma, and 126.2 ± 1.2 Ma, respectively. The HYG has A-type affinity with metaluminous to weakly peraluminous, high FeOT/(FeOT+MgO) ratios, and high Zr+Nb+Ce+Yb contents. Meanwhile, 10 late Mesozoic mafic samples from the LYRB exhibit similar trace element characteristics to those of ‘continental arc andesite’ (CAA) and suggest an enriched lithospheric mantle source with depletion in high field strength elements (e.g. Nb, Ta, Zr, Hf, and Ti) and enrichment of large ion lithophile elements (e.g. Rb, Th, U, and Pb). Although the HYG exhibits similar Sr–Nd isotope composition with the mafic dikes, distinct whole-rock Pb isotope ratios imply that the granitoids and mafic magmas originated from heterogeneous mantle sources. Compared with coeval Baijuhuajian A-type rocks that are exposed along the Jiang–Shao fault of Southeast China, the HYG shows enriched Hf isotope ratios of zircon with εHf(t) values ranging from −4.8 to −11.1. In the Yb/Ta versus Y/Nb diagram, being different from the major asthenospheric mantle-origin Baijuhuajian pluton, a large range of and high Y/Nb ratios as well as high Zr contents of the HYG pluton suggest a magmatic source of mixing between the asthenospheric and enriched crustal component in the LYRB. Compared with early-stage copper-related adakitic rocks (148–130 Ma) with subduction-related affinities and high oxygen fugacity, the copper-barren HYG has with-plate A-type affinities and lower oxygen fugacity. Summarizing, the production of early-stage (i.e. subduction related) adakitic rocks followed by late-stage A-type granitoids in the LYRB is ascribed to the rollback of the Palaeo-Pacific plate beneath Southeast China and associated with asthenospheric upwelling and lithospheric thinning during the late Mesozoic era.

Two episodes of structural fractures and their stress field modeling in the Ordos Block, northern China

The importance of the Ordos Block, which is surrounded by different Chinese continental blocks, is well documented, but the development of the structural fractures and the stress fields within the Late Mesozoic and Cenozoic eras in this stable block (dips of the Mesozoic and Cenozoic strata are less than 3°) have been poorly studied. In this paper, two dominant groups of structural fractures with NW to EW and NNE to ENE trends are identified through field measurements and imaging log observations. The maximum principal compressive stress magnitudes and stress trajectories are calculated employing 2D finite element models (2D-FEM). Based on the displacement fields, the rotation of the Ordos Block and comparisons between the measured and the calculated stresses, it can be deduced that there are two episodes of fracture formation in the Ordos Block. The calculated orientations of maximum compressive stress in the Late Mesozoic and the Cenozoic eras are found to be WNW and NE respectively, which imply that the NW to EW trending structural fractures were developed in a Late Mesozoic stress field whereas the NNE to ENE ones were developed in a Cenozoic stress field in the block. The change in stress fields may have resulted in the change in tectonic setting from the northwestward subduction of the Izanagi Plate in the Late Mesozoic to the collision between the Indian Plate and the Eurasian Plate in the Cenozoic. The change in the Mesozoic and Cenozoic stress fields is of great significance to the further fracture prediction in fractured reservoirs, basin analyses in the Ordos Basin and research on the geodynamics of the North China Craton.

Wear biomechanics in the slicing dentition of the giant horned dinosaur Triceratops.

Herbivorous reptiles rarely evolve occluding dentitions that allow for the mastication (chewing) of plant matter. Conversely, most herbivorous mammals have occluding teeth with complex tissue architectures that self-wear to complex morphologies for orally processing plants. Dinosaurs stand out among reptiles in that several lineages acquired the capacity to masticate. In particular, the horned ceratopsian dinosaurs, among the most successful Late Cretaceous dinosaurian lineages, evolved slicing dentitions for the exploitation of tough, bulky plant matter. We show how Triceratops, a 9-m-long ceratopsian, and its relatives evolved teeth that wore during feeding to create fullers (recessed central regions on cutting blades) on the chewing surfaces. This unique morphology served to reduce friction during feeding. It was achieved through the evolution of a complex suite of osseous dental tissues rivaling the complexity of mammalian dentitions. Tribological (wear) properties of the tissues are preserved in ~66-million-year-old teeth, allowing the creation of a sophisticated three-dimensional biomechanical wear model that reveals how the complexes synergistically wore to create these implements. These findings, along with similar discoveries in hadrosaurids (duck-billed dinosaurs), suggest that tissue-mediated changes in dental morphology may have played a major role in the remarkable ecological diversification of these clades and perhaps other dinosaurian clades capable of mastication.

Possible links between long-term geomagnetic variations and whole-mantle convection processes

The Earth's internal magnetic field varies on timescales of months to billions of years. The field is generated by convection in the liquid outer core, which in turn is influenced by the heat flowing from the core into the base of the overlying mantle. Much of the magnetic field's variation is thought to be stochastic, but over very long timescales, this variability may be related to changes in heat flow associated with mantle convection processes. Over the past 500 Myr, correlations between palaeomagnetic behaviour and surface processes were particularly striking during the middle to late Mesozoic era, beginning about 180 Myr ago. Simulations of the geodynamo suggest that transitions from periods of rapid polarity reversals to periods of prolonged stability — such as occurred between the Middle Jurassic and Middle Cretaceous periods — may have been triggered by a decrease in core-mantle boundary heat flow either globally or in equatorial regions. This decrease in heat flow could have been linked to reduced mantle-plume-head production at the core-mantle boundary, an episode of true polar wander, or a combination of the two.

Widespread late Cenozoic increase in erosion rates across the interior of eastern Tibet constrained by detrital low‐temperature thermochronometry

New detrital low‐temperature thermochronometry provides estimates of long‐term erosion rates and the timing of initiation of river incision from across the interior of the Tibetan Plateau. We use the erosion history of this region to evaluate proposed models of orogenic development as well as regional climatic events. Erosion histories of the externally drained portion of the east‐central Tibetan Plateau are recorded in modern river sands from major rivers across a transect that spans >750 km and covers a region with no published thermochronometric ages. Individual grains from eight catchments were analyzed for apatite (U‐Th)/He and fission track thermochronometry. A wide distribution in ages that, in most cases, spans the entire Cenozoic and Late Mesozoic eras requires a long period of slow or no erosion with a relative increase in erosion rate toward the present. We apply a recently developed methodology for inversion of detrital thermochronometric data for three specified erosion scenarios: constant erosion rate, two‐stage erosion history, and three‐stage erosion history. Modeling results suggest that rates increase by at least an order of magnitude between 11 and 4 Ma following a period of slow erosion across the studied catchments. Synchroneity in accelerated erosion across the whole of the Tibetan Plateau rather than a spatial or temporal progression challenges the widely held notion that the plateau evolved as a steep, northward‐propagating topographic front, or that south to north precipitation gradients exert a primary control on erosion rates. Instead, we suggest that accelerated river incision late in the orogen's history relates to regional‐scale uplift that occurred in concert with eastern expansion of the plateau.

Geological comparative studies of Japan arc system and Kyushu-Palau arc

Based on the published data of structure geology, geochronology, petrology and isotope geochemistry, the authors of this paper have conducted studies on the tectonic evolution history of Japan arc system and Kyushu-Palau ridge (KPR). The studies show that the initial Japan arc system was resulted from the subduction of ancient Pacific plate beneath Eurasian Plate in Permian. It was part of an Andean-type continental volcanic arc which occurred in the offshore in the east of Asian during late Mesozoic era. The formation of tertiary back-arc basin (Japan Sea) resulted in the fundamental tectonic framework of the present arc system. Since Quaternary the system has been lying at E-W compression tectonic setting due to the eastward subduction of Amur Plate. It is expected that Japan arc system will be juxtaposed with Asian continent, which is similar to the present Taiwan arc system. The origin of Philippine Sea Plate (PSP) is still in debate. Some studies argued that it is a trapped oceanic crust segment, while the others insisted that it is a back-arc basin accompanied with ancient IBM arc. However, it is all agreed that the tectonic evolution of PSP started since 50 Ma, i.e., PSP has drifted from the site around equator at 50 Ma to the present site, and the subduction of PSP along Nankai trough-Ryukyu Trench beneath the Japan arc system during 6–2 Ma led to the formation of the present Ryukyu arc system. Of the PSP, the KPR has been found with the oldest rocks formed at 38 Ma. Combining with its geochemical characteristics of oceanic arc tholeiite, it is suggested that KPR is an intraoceanic volcanic arc, more specifically, a relic arc (i.e., rear arc of the ancient IBM) after rifting of ancient IBM. In addition, Amami-Daito province is of arc tectonic affinity, but has been affected by mantle plume. Therefore, based on their respective tectonic evolution history and geochemical characteristics of rock samples, it is inferred that there is no genetic relationship between Japan arc system and KPR. It is noted that rocks reflecting continental crust basement feature have been collected on the northern tip of KPR, which may be related to the process of KPR accreting on Japan arc, but the arc-continent accretion process are still at initial stage of modern continental crust accretion model. However, due to the scarcity of data of the northern tip of KPR, crustal structure of this location and its adjacent Nankai trough need to be further constrained by geophysical studies in the future.

Late Mesozoic‐Cenozoic exhumation history of the Lesser Hinggan Mountains, NE China, revealed by fission track thermochronology

AbstractThis study uses zircon and apatite fission‐track (FT) analyses to reveal the exhumation history of the granitoid samples collected from the Lesser Hinggan Mountains, northeast China. A southeast to northwest transect across the Lesser Hinggan Mountains yielded zircon FT ages between 89.8 ± 5.7 and 100.4 ± 8.6 Ma, and apatite FT ages between 50.6 ± 13.8 and 74.3 ± 4.5 Ma with mean track lengths between 11.7 ± 2.0 and 12.8 ± 1.7 µm. FT results and modelling identify three stages in sample cooling history spanning the late Mesozoic and Cenozoic eras. Stage one records rapid cooling from the closure temperature of zircon FT to the high temperature part of the apatite FT partial annealing zone (∼210–110 °C) during ca. 95 to 65 Ma. Stage two records a period of relative slow cooling (∼110–60 °C) taking place between ca. 65 and 20 Ma, suggesting that the granitoids had been exhumed to the depth of ∼1−2 km. Final stage cooling (60–20 °C) occurred since the Miocene at an accelerated rate bringing the sampled rocks to the Earth's surface. The maximum exhumation is more than 5 km under a steady‐state geothermal gradient of 35 °C/km. Integrated with the tectonic setting, this exhumation is possibly led by the Pacific Plate subduction combined with intracontinental orogeny associated with asthenospheric upwelling. Copyright © 2010 John Wiley & Sons, Ltd.

Basement configuration of on-land Kutch basin from seismic refraction studies and modeling of first arrival travel time skips

The Kutch basin is one of the three (Narmada, Cambay and Kutch) major marginal rift basins that are close to each other in mid-western part of the Indian subcontinent. The seismic refraction and wide-angle reflection data were acquired and a first order velocity structure of the Kutch sedimentary basin along Jakhau–Mandvi, Mandvi–Mundra, Mundra–Adesar and Hamirpur–Halvad profiles is derived. The travel time skip phenomenon has been noticed in the travel time plots and record sections indicating presence of low velocity sediments. Derived two-dimensional velocity–depth models revealed a Mesozoic sedimentary sequence sandwiched between Trap and Limestone layers, in some of the profiles. Two thick low velocity layers (that corresponds early to late Mesozoic era) have been identified. These are dipping towards Mandvi along Jakhau–Mandvi profile. The early Mesozoic layer that is thinning towards southeast is completely missing in Mandvi–Mundra profile. It is also noticed that the early Mesozoic Bhuj formation exists in the northern parts of the Mundra–Adesar and Hamirpur–Halvad profiles, where it directly overlies the granitic basement. The derived velocity–depth model suggests that the basement is about 3 km deep near Jakhau and reaches a depth of about 6 km near Mandvi. The layered structure may correspond to the Tertiary, Trap, Late Mesozoic sediments and Mesozoic limestone. The velocity–depth model obtained in Kutch is very similar to earlier derived model for Jamnagar and Dwarka sub-basins of northwestern Saurashtra peninsula suggesting probable continuity/linkage between southern on-land Kutch and, across the Gulf of Kutch to Saurashtra peninunsula. We also conclude that the evolution of Kutch basin, as a peri-cratonic rift basin, is essentially controlled by the four (F1–F4) faults inferred from obvious abrupt changes in layer thickness/velocity along the seismic refraction profiles.

Zircon U-Pb SHRIMP ages of the Taiping (calc-alkaline)-Huangshan (alkaline) composite intrusion: Constraints on Mesozoic lithospheric thinning of the southeastern Yangtze Craton, China

The Taiping-Huangshan composite intrusion is a unique complex with characteristics changing from calc-alkaline (Taiping intrusion) to alkaline (Huangshan intrusion). Huangshan intrusion samples show a spectacular tetrad effect in their REE distribution patterns as well as non-CHARAC (charge-and-radius-controlled) trace element behavior, indicating a highly evolved late-stage magma component. This composite intrusion provides a rare opportunity to investigate the variance of tectonic setting and lithospheric thinning of the southeastern Yangtze Craton in late Mesozoic era. Zircon SHRIMP U-Pb analyses yield an emplacement age of 140.6±1.2 Ma for the Taiping intrusion, and ages of 127.7±1.3, 125.7±1.4, 125.1±1.5, and 125.2±5.5 Ma for four samples from the Huangshan intrusion respectively. The ages for four different phases of the Huangshan intrusion agree within their small analytical errors, indicating that the emplacement was in a short time. The Taiping and Huangshan intrusions are intimately associated, but there is about 15 Ma interval between their intrusion, and the magma characters change from calc-alkaline to alkaline without transition. This probably corresponds to lithospheric thinning of the southeastern Yangtze Craton. This event possibly happened from about 141 Ma (the emplacement age of the Taiping intrusion), to 128 Ma (start of emplacement of the Huangshan intrusion). The thinning mechanism is dominantly delamination.

A lamprey from the Devonian period of South Africa

Lampreys are the most scientifically accessible of the remaining jawless vertebrates, but their evolutionary history is obscure. In contrast to the rich fossil record of armoured jawless fishes, all of which date from the Devonian period and earlier, only two Palaeozoic lampreys have been recorded, both from the Carboniferous period. In addition to these, the recent report of an exquisitely preserved Lower Cretaceous example demonstrates that anatomically modern lampreys were present by the late Mesozoic era. Here we report a marine/estuarine fossil lamprey from the Famennian (Late Devonian) of South Africa, the identity of which is established easily because many of the key specializations of modern forms are already in place. These specializations include the first evidence of a large oral disc, the first direct evidence of circumoral teeth and a well preserved branchial basket. This small agnathan, Priscomyzon riniensis gen. et sp. nov., is not only more conventionally lamprey-like than other Palaeozoic examples, but is also some 35 million years older. This finding is evidence that agnathans close to modern lampreys had evolved before the end of the Devonian period. In this light, lampreys as a whole appear all the more remarkable: ancient specialists that have persisted as such and survived a subsequent 360 million years.

Tectono‐thermal modelling of sedimentary basins with episodic extension and inversion, a case history of the Jiyang Basin, North China

AbstractA two‐dimensional kinematic model is presented for superimposed basins. It is based on a finite‐element algorithm in the Lagrangian system, which incorporates different stages of lithosphere stretching and shortening to simulate alternating extension and inversion. The Jiyang Basin, developed in the North China, is a superimposed basin comprising four proto‐type basins separated by several unconformities. Four‐phase extension and two‐phase inversion have developed in this basin since the Late Mesozoic era. The thermal history of the basin is modelled based on a seismic cross‐section across the basin. Tectonic subsidence (or uplift) histories from backstripping serve as the objective functions, and crustal thickness, as well as heat flow, provides additional constraints. Effects of different Mesozoic erosion on the thermal history are discussed. Modelling results show that the thermal history of the Jiyang Basin since the Late Mesozoic can be divided into six stages, including four phases of heating accompanied by following thermal attenuation, and two phases of cooling with following thermal recovery. The model also implies a variant pattern of thermal regime in the basin. In the deepest centres of the depressions, the maximum heat flow occurred during the Late Mesozoic, but in the slopes of the depressions, the maximum heat flow appeared in the Cenozoic era.

Tectonic-stratigraphic division and blind fold structures in Nansha Waters, South China Sea

Extensive multiple-channel reflection seismic data have been collected in the Nansha (Spratley Islands) Waters, the southern margin of the South China Sea. Stratigraphic correlation is shown with focus on a comprehensive geophysiXcal survey line run from offshore NW Sabah to offshore SE Vietnam. According to the varying tectono-stratigraphy from southeast to northwest, five tectonic belts can be determined, i.e. the Palawan-Borneo Nappe, Nansha Trough, Nanwei-Liyue Compressive Belt, Zheng'he Extensional Belt and the Circum-Southwest Subbasin Belt. In the Palawan-Borneo Nappe, Neogene-Quaternary deposits were highly upthrust northwestwards, resulting in a series of moderately to tightly folded anticlines separated by open synclines. The Nansha Trough was a narrow, deep-water belt filled with thick, undisturbed Neogene-Quaternary deposits. The Nanwei-Liyue Compressive Belt was dominated by strongly folded paleo-anticlines overlain by an undeformed sedimentary cap with a pronounced hiatus of Paleogene sediments. The Zheng'he Extensional Belt consisted of a rugged topography and Paleogene half-grabens bounded by listic faults. The major extensional faults were reactivated to cut through the overlying Neogene-Quaternary deposits. Over the Circum-Southwest Subbasin Belt, Neogene-Quaternary deposits draped on the largely subsided fault blocks related to the Late Oligocene–Mid-Miocene seafloor spreading. Based on the regional stratigraphic correlation, the prominent paleo-anticlines found within the Nanwei-Liyue Compressive Belt are deduced to consist of mainly Mesozoic marine sediments that were compressed in the Late Mesozoic Era. Therefore, the Nansha Microcontinent Block is shown to be a collision complex assembled during Late Mesozoic Era.