Lithosphere In China Research Articles

Reworking of Yangtze crust into the mantle lithosphere of the North China Craton along the Dabie–East Qinling Orogen: Evidence from the Early Cretaceous volcanic rocks

Abstract Mineral chemistry, zircon U-Pb geochronology, and elemental and Sr-Nd-Pb-Hf-O isotopic data for the Early Cretaceous volcanic rocks from the Dabie and East Qinling orogens of China constrain the reworking history of the Yangtze crustal materials in the North China lithosphere. These data provide new insights into the recycling of the deepsubducted crustal materials into the mantle and the transformation process from continental subduction to collision. Our data show that the Early Cretaceous volcanic rocks are characterized by shoshonitic and high-K calc-alkaline basaltic trachyandesite, trachyandesite, and trachyte. They synchronously erupted at ca. 135–120 Ma, and have zircon in situ εHf(t) values ranging from −29.0 to −17.2, and δ18O values from 4.89‰ to 6.84‰. These samples share similar “crust-like” geochemical signatures, whole-rock enrichment in the large-ion lithophile elements, depletion in high field strength elements (Nb/La = 0.12–0.38), highly enriched Sr-Nd isotopic compositions, as well as (206Pb/204Pb)i = 15.97–17.59, (207Pb/204Pb)i = 15.33–15.54, and (208Pb/204Pb)i = 36.87–38.59. The εNd(t) values range from −24.4 to −15.6, −21.8 to −13.1, and −16.8 to −10.9 for the eastern and western North Huaiyang belts of the Dabie Orogen and the East Qinling Orogen, respectively. Such geochemical similarities suggest that the northward deep-subduction of Yangtze crustal materials have been reworked into the North China Craton enriched lithospheric mantle. The spatial pattern of the Early Cretaceous volcanic rocks suggests that the Yangtze subduction extended northward beyond the southern margin of the North China Craton and ran into its interior. The surface and deep lithospheric boundaries are decoupled between the Yangtze Block and North China Craton. The Early Cretaceous igneous rocks in the Dabie–East Qinling Orogen were induced in response to the post-collisional unrooting of the Triassic over-thickened lithosphere coupling.

USTClitho2.0: Updated Unified Seismic Tomography Models for Continental China Lithosphere from Joint Inversion of Body-Wave Arrival Times and Surface-Wave Dispersion Data

Abstract Xin et al. (2019) presented 3D seismic velocity models (VP and VS) of crust and uppermost mantle of continental China using seismic body-wave travel-time tomography, which are referred to as Unified Seismic Tomography Models for Continental China Lithosphere 1.0 (USTClitho1.0). Compared with previous models of continental China, the VP and VS models of USTClitho1.0 have the highest spatial resolution of 0.5°–1.0° in the horizontal direction and are useful for better understanding the complex tectonics of continental China. Although USTClitho1.0 is implicitly constrained by surface-wave data by using the VS model from surface-wave tomography and the converted VP model as initial models for body-wave travel-time tomography, the predicted surface-wave dispersion curves from USTClitho1.0 do not fit the observed data well. Here, we present updated 3D VP and VS models of the continental China lithosphere (USTClitho2.0) by joint inversion of body-wave arrival times and surface-wave dispersion data. Compared with the previous joint inversion scheme of Zhang et al. (2014), similar to Fang et al. (2016), it is further improved by including the sensitivity of surface-wave dispersion data to VP in the new joint inversion system. As a result, the shallow VP structure is also better imaged. In addition, the new joint inversion scheme considers the large topography variations between the eastern and western parts of China. Thus, USTClitho2.0 better resolves the upper-crustal structure of the Tibetan plateau. Compared with USTClitho1.0, USTClitho2.0 fits both body-wave arrival times and surface-wave dispersion data. Thus, the new velocity models are more accurate and can serve as a better reference model for regional-scale tomography and geodynamic studies in continental China.

Curie point depths in Northeast China and their geothermal implications for the Songliao Basin

This work integrates processing and interpretation of the combined geomagnetic anomaly model of NGDC-720-V3.1 to better constrain thermal structures of the Northeast China lithosphere, which shows intensive extension and active volcanism during the Mesozoic and Cenozoic. Numerical tests demonstrate that magnetic anomalies calculated at 20 km altitude can be used for accurate Curie depth estimation. Averaged Curie depths using a 3D fractal exponent of 3.0 vary from ∼13±2.0 to 33±4.1 km with a mean of ∼22±2.4 km in Northeast China. With temperature-dependent thermal conductivity models constrained by incorporated surface heat flow and Curie depths in different geological blocks, the thermal lithospheric thicknesses are estimated mostly between 45 and 90 km based on 1D steady-state thermal conduction equation. Beneath the Songliao Basin, the Moho temperatures are abnormally high, ranging from ca. 700 to 1000 °C, and the mantle contributes about 65% of the total surface heat flow. The shallow Curie points and thermal lithosphere-asthenosphere boundary, together with high Moho temperatures and mantle heat flow, support abnormally high geotherms in the Songliao Basin, originated from hot upper mantle upwelling triggered likely by lithospheric delamination.

Mesozoic mafic magmatism in North China: Implications for thinning and destruction of cratonic lithosphere

The North China Craton (NCC) has been thinned from >200 km to in its eastern part. The ancient subcontinental lithospheric mantle (SCLM) has been replaced by the juvenile SCLM in the Meoszoic. During this period, the NCC was destructed as indicated by extensive magmatism in the Early Cretaceous. While there is a consensus on the thinning and destruction of cratonic lithosphere in North China, it has been hotly debated about the mechanism of cartonic destruction. This study attempts to provide a resolution to current debates in the view of Mesozoic mafic magmatism in North China. We made a compilation of geochemical data available for Mesozoic mafic igneous rocks in the NCC. The results indicate that these mafic igneous rocks can be categorized into two series, manifesting a dramatic change in the nature of mantle sources at ~121 Ma. Mafic igneous rocks emplaced at this age start to show both oceanic island basalts (OIB)-like trace element distribution patterns and depleted to weakly enriched Sr-Nd isotope compositions. In contrast, mafic igneous rocks emplaced before and after this age exhibit both island arc basalts (IAB)-like trace element distribution patterns and enriched Sr-Nd isotope compositions. This difference indicates a geochemical mutation in the SCLM of North China at ~121 Ma. Although mafic magmatism also took place in the Late Triassic, it was related to exhumation of the deeply subducted South China continental crust because the subduction of Paleo-Pacific slab was not operated at that time. Paleo-Pacific slab started to subduct beneath the eastern margin of Eruasian continent since the Jurrasic. The subducting slab and its overlying SCLM wedge were coupled in the Jurassic, and slab dehydration resulted in hydration and weakening of the cratonic mantle. The mantle sources of ancient IAB-like mafic igneous rocks are a kind of ultramafic metasomatites that were generated by reaction of the cratonic mantle wedge peridotite not only with aqueous solutions derived from dehydration of the subducting Paleo-Pacific oceanic crust in the Jurassic but also with hydrous melts derived from partial melting of the subducting South China continental crust in the Triassic. On the other hand, the mantle sources of juvenile OIB-like mafic igneous rocks are also a kind of ultramafic metasomatites that were generated by reaction of the asthenospheric mantle underneath the North China lithosphere with hydrous felsic melts derived from partial melting of the subducting Paleo-Pacific oceanic crust. The subducting Paleo-Pacific slab became rollback at ~144 Ma. Afterwards the SCLM base was heated by laterally filled asthenospheric mantle, leading to thinning of the hydrated and weakened cratonic mantle. There was extensive bimodal magmatism at 130 to 120 Ma, marking intensive destruction of the cratonic lithosphere. Not only the ultramafic metasomatites in the lower part of the cratonic mantle wedge underwent partial melting to produce mafic igneous rocks showing negative e Nd( t ) values, depletion in Nb and Ta but enrichment in Pb, but also the lower continent crust overlying the cratonic mantle wedge was heated for extensive felsic magmatism. At the same time, the rollback slab surface was heated by the laterally filled asthenospheric mantle, resulting in partial melting of the previously dehydrated rocks beyond rutile stability on the slab surface. This produce still hydrous felsic melts, which metasomatized the overlying asthenospheric mantle peridotite to generate the ultramafic metasomatites that show positive e Nd( t ) values, no depletion or even enrichment in Nb and Ta but depletion in Pb. Partial melting of such metasomatites started at ~121 Ma, giving rise to the mafic igneous rocks with juvenile OIB-like geochemical signatures. In this context, the age of ~121 Ma may terminate replacement of the ancient SCLM by the juvenile SCLM in North China. Paleo-Pacific slab was not subducted to the mantle transition zone in the Mesozoic as revealed by modern seismic tomography, and it was subducted at a low angle since the Jurassic, like the subduction of Nazca Plate beneath American continent. This flat subduction would not only chemically metasomatize the cratonic mantle but also physically erode the cratonic mantle. Therefore, the interaction between Paleo-Pacific slab and the cratonic mantle is the first-order geodynamic mechanism for the thinning and destruction of cratonic lithosphere in North China.

Constraints on upper mantle Vp/Vs ratio variations beneath eastern North China from receiver function tomography

To detect the thinning, modification, and replacement of the basement of the lithosphere is a key step in understanding the destruction mechanism of the North China lithosphere. The difference of the basement of the lithosphere is mainly displayed by the variation of the peridotite composition and its physical state. Vp/Vs ratio (hereafter referred to as velocity ratio) is more sensitive to this change than Vp or Vs alone. By means of the strong dependence of the travel-time of the wave converted at the 410-km discontinuity (P410s) observed in the receiver function (RF) on the velocity ratio in the upper mantle, we developed a new mapping method to constrain the velocity ratio between the Moho and 410-km discontinuity. Using the RFs extracted from 246 broadband stations beneath the North China Craton (NCC), we obtained a high-resolution velocity ratio image of the upper mantle. The abnormal velocity ratio indicates a strong lateral variation of the mineral composition in the upper mantle beneath North China. Two low-velocity-ratio patches are imaged at the top of the upper mantle and the 410km depth, respectively. The former may be related to the orthopyroxene enrichment in the lithospheric mantle, and the latter may reflect the stagnant Pacific slab in the mantle transition zone (MTZ). A prominent high-velocity-ratio anomaly is also imaged in the upper mantle beneath the Shaanxi–Shanxi rift system in the central NCC, with the highest anomaly reaching 10%. We speculate that the high velocity ratio of upper mantle is related to convective flow due to slab dehydration in the MTZ. The dehydration of the retained slab in the MTZ results in partial melting and upwelling of upper mantle materials. Such convective flow and their melting are closely related to the Cenozoic basalt eruption in the northern section of the Shaanxi–Shanxi rift system.

Discussion on the Special Lithosphere Type in Eastern China

In this paper, the authors proposed that there is a special type of thin lithosphere, with continental crust (about 35 km thick) and oceanic mantle (about 40 km thick) in eastern China. The characteristics of eastern China lithosphere is so special, it is different to most of continental lithosphere of globe. To detail research the characteristics and evolution of eastern Asian lithosphere is important, which will be helpful to develop the theory of global plate tectonics. This paper will expound the thickness change, tectonic characteristics and transformation period of lithosphere type, and to discuss its mechanism.

Mesozoic tectonic evolution of the Daba Shan Thrust Belt in the southern Qinling orogen, central China: Constraints from surface geology and reflection seismology

The Daba Shan Thrust Belt is located along the southern margin of the Qinling orogen that separates the north China block in the north from the south China block in the south. Despite decades of research, the total magnitude of shortening accommodated by continent-continent convergence across the Qinling orogen after Triassic ocean closure between north and south China remains poorly constrained. The lack of knowledge on the shortening magnitude in turn limits our ability to test a wide array of tectonic models for the development of the Qinling orogen and thus the convergence history between north and south China. In order to address this issue, we construct a balanced cross section and develop a new kinematic model for the evolution of the Daba Shan Thrust Belt. This work was accomplished by integrating (1) surface geologic mapping, (2) detailed kinematic analysis of key structures, (3) existing geochronologic and thermochronological data, and (4) a recently obtained lithospheric-scale seismic reflection profile. Restoration of the cross section indicates that the minimum shortening strain increases northward from ~10% in the foreland to >45% in the thrust belt interior. The estimated amount of upper crustal shortening across the Daba Shan Thrust Belt is >130 km, which is sufficient to allow the inferred mafic lower crust of the subducted south China lithosphere to have experienced eclogite phase transition. Thus, our work supports that the development of the Daba Shan Thrust Belt may have been driven by slab pull of the subducted mafic lower crust at the leading edge of the down-plunging south China continental lithosphere.

Structural control and genesis of the Oligocene Zhenyuan orogenic gold deposit, SW China

The Zhenyuan gold deposit with >50t gold reserve is located within the Jinshajiang–Ailaoshan suture zone that formed through the closure of Paleo-Tethyan ocean in late-Permian. This suture separates the Simao and South China blocks. A west-dipping high velocity zone down to ca. 250km beneath the Simao block in the seismic tomography suggests that the South China lithosphere was underthrust westward. The NNW-trending Ailaoshan–Red River shear zone is situated to the east of Ailaoshan suture. The shearing in this belt, generally following a regional mantle upwelling and crust extension event, was initiated at 32Ma and culminated at ca. 27Ma. This shearing was induced by the lateral extrusion and large clockwise rotation of the Simao block during the India–Eurasia continental collision and the underthrusting of South China block. The Zhenyuan ore deposit consists of the Donggualin and Laowangzhai orebody clusters. The Donggualin orebodies are controlled by the NW-striking shear faults, whereas most orebodies in the Laowangzhai are dominated by NE- and ENE-striking transcompressional faults. It is observed that the NE- and ENE-striking faults are crosscut by the NW-striking faults. It is deduced that the former were primarily formed as nearly NS-trending faults during the regional extension or initial shearing stage at ca. 32Ma. The primary faults were then re-oriented to the current strike concomitant with the rotation of the Simao block, and further cut by the NW-trending shear faults, which are subsidiary to the Ailaoshan–Red River shear zone. The rock types in the ore deposit including slate, meta-sandstone, limestone, lamprophyre, and meta-mafic to ultramafic units, which were all mineralized by the infiltration of ore-bearing fluids into extensional fractures. The low temperature ore mineral assemblage (pyrite–stibnite–arsenopyrite), enriched element association, and ranges of S and Pb isotopic compositions in the two ore clusters are broadly similar, indicating that the mineralization is contemporary despite the different formation times of ore-controlling structures. The 206Pb/204Pb, 207Pb/204Pb, and 208Pb/204Pb values of hydrothermal pyrite are close to those of the lower crust. Pyrite δ34S values show a wide range with a peak near 0 per mil. The S and Pb isotopic compositions, together with previously published H–O–He–Ar isotopic data, suggest that the ore fluid is mainly metamorphic. The data also suggest the input of mantle volatiles, consistent with mantle upwelling. The control of the shear zones on mineralization favors the interpretation that the Ar–Ar isochron age ~27Ma of phlogopite in the mineralized lamprophyre represents the mineralization age. This mineralization age implies that the South China block had started westward underthrusting before ~27Ma. The Zhenyuan ore deposit is considered to be an orogenic type, formed in a transitional stage from mantle upwelling to continental underthrust. The continental underthrusting drove the release of gold-charged metamorphic fluids and formation of the Zhenyuan ore deposit.

Progress in deep lithospheric exploration of the continental China: A review of the SinoProbe

The SinoProbe, deep exploration in China, is a multidisciplinary earth science research program that aims at revealing the composition, structure and evolution of the continental lithosphere in China. The SinoProbe (2008–2012) has successfully conducted research and field experiments on determining the crustal and mantle structures using new deep seismic and magnetotelluric (MT) exploration. This has allowed the accumulation of new exciting data that have significantly accelerated China's development on deep lithospheric exploration. The new data also led to new understandings on the Mesozoic and Cenozoic geological evolution of the continental China. The main results of the SinoProbe so far include (1) a collection of ca.6000 km long seismic reflection profile data, (2) a nation-wide geochemical baseline, (3) a nation-wide 4° × 4° MT array and regional 1° × 1° MT arrays in the North China and the Qinghai–Tibet Plateau, (4) three dimensional (3-D) exploration of ore districts in the eastern China, (5) several continental scientific drilling holes, (6) regional in-situ stress monitoring networks, (7) geodynamic modeling of the lithosphere underneath the continental China, and (8) instrumentation development for deep exploration in China, etc. For the first time, the SinoProbe has obtained deep seismic reflection evidence for the Moho surface below the thick crust of the central Qinghai–Tibet Plateau. It also reveals dipping fabrics in the lithospheric mantle beneath the northeastern China. The preliminary results from MT array observation of the SinoProbe show an abnormal electric-conductivity structure of the lithosphere beneath the Ordos basin, providing important evidence for the evolution mechanism of the North China craton (NCC). Generally, the SinoProbe has conducted successfully during its initial phase (2008–2012), which has settled a foundation for the next phase of the SinoProbe in the future. • We summary achievement and development carried out by SinoProbe in 2008 to 2012. • SinoProbe is a major program on deep exploration in continental China. • SinoProbe helps to reveal structure and composition of China's lithosphere. • SinoProbe has significantly accelerated China's development on deep exploration.

The genesis of tectono-magmatism in eastern China

The tectono-magmatism in eastern China is a hotspot for the researches, and many hypotheses of that were discussed. There is a middle crust with solid, low velocity and high conductivity in eastern China, which is impossible to form “convection magmatic layer”. The subduction and compression of oceanic plate induced to the lateral pressure for the eastern China lithosphere in the condition of increasing pressure and decreasing temperature, it is also impossible to form an extensively melting magma layer. In South China, the granitic zone migrates from west to east, their evolution cannot be explained by plate subduction. The original magmatic reservoirs are controlled by main faults and spheres, which occurred the tectonic detachment and formed in the process of decreasing pressure and increasing temperature. The magma only originates in very small part of lithosphere. The tectono-magmatism and tectonic detachment of eastern China lithosphere during the Jurassic and the Cretaceous are concentrate mainly near the intersections between the regional faults and middle crust or the Moho discontinuity, and then magma intrudes or erupts along faults. The tectono-magmatism of Cenozoic originates near the intersections between the regional high-angle normal faults and the bottom of lithosphere. Obviously, the different penetration depth of faults induces a different kind of magmatism.

The principal characteristics of the lithosphere of China

The lithospheric structure of China and its adjacent area is very complex and is marked by several prominent characteristics. Firstly, China’s continental crust is thick in the west but thins to the east, and thick in the south but thins to the north. Secondly, the continental crust of the Qinghai–Tibet Plateau has an average thickness of 60–65 km with a maximum thickness of 80 km, whereas in eastern China the average thickness is 30–35 km, with a minimum thickness of only 5 km in the center of the South China Sea. The average thickness of continental crust in China is 47.6 km, which greatly exceeds the global average thickness of 39.2 km. Thirdly, as with the crust, the lithosphere of China and its adjacent areas shows a general pattern of thicker in the west and south, and thinner in the east and north. The lithosphere of the Qinghai–Tibet Plateau and northwestern China has an average thickness of 165 km, with a maximum thickness of 180–200 km in the central and eastern parts of the Tarim Basin, Pamir, and Changdu areas. In contrast, the vast areas to the east of the Da Hinggan Ling–Taihang–Wuling Mountains, including the marginal seas, are characterized by lithospheric thicknesses of only 50–85 km. Fourthly, in western China the lithosphere and asthenosphere behave as a “layered structure”, reflecting their dynamic background of plate collision and convergence. The lithosphere and asthenosphere in eastern China display a “block mosaic structure”, where the lithosphere is thin and the asthenosphere is very thick, a pattern reflecting the consequences of crustal extension and an upsurge of asthenospheric materials. The latter is responsible for a huge low velocity anomaly at a depth of 85–250 km beneath East Asia and the western Pacific Ocean. Finally, in China there is an age structure of “older in the upper layers and younger in the lower layers” between both the upper and lower crusts and between the crust and the lithospheric mantle.

Development of an Ionospheric Numerical Assimilation Nowcast and Forecast System Based on Gauss‐Markov Kalman Filter–an Observation System Simulation Experiment taking Example for China and Its Surrounding Area

AbstractIn this paper, we constructed an ionospheric data assimilation system based on Gauss‐Markov Kalman filter and gave some test results. We chose some ionosphere stations (including meridional project stations, China lithosphere deformation GPS network, part of IGS stations) in China and its surrounding areas as the observational system to do the simulation experiment. The International Reference Model (IRI) is chosen to be the background model, while NeQuick model output is taken to be the observations. Our assimilation results show that it can get good estimation of ionosphere electron density by ingesting the observed slant TEC data into the model by Kalman filter. It illustrates that our assimilation algorithm is feasible and the selected parameters are reasonable. We also obtained reasonable short‐time forecast results by Gauss‐Markov assumption.

Thermal history, geodynamics, and current thermal activity of lithosphere in China

The tectonic framework of China includes major and smaller-scale units that differ in age and in style of tectonomagmatic activity, the latter being related to the thermal history of the lithosphere. Heat flow in the area varies from 25 to 150 mW/m 2 or higher, with an average of 58±11 mW/m 2. It is high in active faults, rifts, and other structures of extension (or sometimes compression) subject to heating from rising lithospheric and mantle plumes. The current thermal activity in the region is controlled by the Pacific subduction beneath Eurasia in eastern China and mainly by the lateral strain and rotation of the Ordos block associated with the India–Eurasia interaction in central and western China.

System of Crust-Mantle Ductile Shear Zone in the Continental Lithosphere in China

On the basis of the tectonic analysis of many seismic sounding profiles, there are two fracture systems in the continental lithosphere of China, which are obviously different but closely interrelated. One is the shallow fracture system composed of brittle shear zones mainly in upper crust, and the other is the deep fracture system composed of crust-mantle ductile shear zone which penetrate the Moho discontinuity. Combined with the structural characteristics of seismic wave velocity, the petrology and geochemistry of deep tectonic and the crust-mantle ductile shear zones can be divided into five types: the trench subduction zone at the border of continental lithosphere, collision suture in continental lithosphere, compressive crust-mantle ductile shear zone, extensional ductile shear zone, and strike-slip ductile shear zone in the crust and the mantle. Therefore, it is considered that the continental lithosphere in China is a bidirectional development model, development from the surface to the deep crust and from the crust-mantle transition zone to the mid-upper crust. The crust-mantle ductile shear zone is the channel for gas and fluids of inorganic origin, as well as the seismic activity area. The research of the crust-mantle ductile shear zone is of great academic value and realistic significance.

Post-collisional, potassic monzonite–minette complex (Shahewan) in the Qinling Mountains (central China): 40Ar/ 39Ar thermochronology, petrogenesis, and implications for the dynamic setting of the Qinling orogen

The nondeformed, postcollisional Shahewan monzonite–minette complex in the North Qinling orogenic belt, central China, is composed of potassic monzonites and mafic minette dykes. The monzonites and minette dykes were coevally intruded as evidenced by a zircon U–Pb age of 211 ± 2 Ma for the monzonites and a 40Ar/ 39Ar age of 209.0 ± 1.4 Ma on the biotite from the minette dykes. These dates also indicate that the Shahewan complex postdated shortly the cessation of convergent deformation in the Qinling orogenic belt. The K-feldspar 40Ar/ 39Ar MDD modeling result combined with the zircon U–Pb age reveals a rapid average cooling history (11.5 °C/Ma) for the complex from 211 to 150 Ma, implying a fast exhumation within a short period of time. The minettes take features of ultrapotassic rocks. Their geochemical characteristics, such as high MgO (Mg# up to 80), low TiO 2 (0.38–0.62 wt.%) and FeO (2.52–3.42 wt.%), enrichment in LILEs and LREEs, and depletion in HFSE, together with primitive initial 87Sr/ 86Sr ratios (0.70444–0.70562) and slightly negative ε Nd( t) (−3.4 to −2.5), suggest that they were derived from an enriched refractory lithospheric mantle. The monzonites have the similar geochemical (incompatible element enrichment, Nb, Ta, Ti depletion) and isotopic (initial 87Sr/ 86Sr: 0.70513–0.70646; ε Nd( t): −0.5 to −3.6) imprints, indicating they were derived from a common source. The dynamic setting in which the Shahewan complex formed is discussed. The Shahewan complex formed most likely in a postcollisional extensional setting. Its formation requires a high enough temperature to partially melt an enriched, refractory mantle source. Considerable uplift is necessitated for the rapid exhumation. These may be explained by convective mantle thinning or slab-breakoff mechanisms. The enrichment features in the lithospheric mantle source can be interpreted by injection of small percentage (<1%) partial melts from the convective mantle, or by addition of the metamorphic fluids from the subducted South China lithosphere.

Age and Composition of Peridotites:Implications for the Lithospheric Thinning Accompanying with Mantle Replacement Beneath the Eastern North China Craton

Olivine-Mg # values and diopside-REE patterns of mantle peridotites from the North China were systematically compared. In situ LAM-MC-ICPMS Re-Os isotopes of sulfides in the Hannuoba peridotitic xenoliths are also reported. Based on these data, the lithospheric thinning mechanism beneath the eastern North China Craton during Mesozoic-Cenozoic times was discussed. The results show that in situ analysis, relative to the whole-rock Re-Os results, is advanced to open out the lithospheric deep processes in detail, and that the existence of thermal events in Mesoproterozoic (1.4 Ga) and in Neoproterozoic (0.7–0.8 Ga) within the subcontinental lithospheric mantle (SCLM) beneath the North China Craton. The coexistence of the lithospheric mantle including refractory, transitional and fertile affinity cannot be well interpreted by the mechanism of lithospheric delamination. On the other hand, simple melt-peridotite interaction is also difficult to interpret abundant diopside with LREE-depletion patterns in the Cenozoic lithospheric mantle, that is, it is irreversible of the transitions of the cratonic mantle with complex evolution history to the “oceanic” one with simpler history. The complex processes including the lateral spreading (extension), melt-rock interaction, asthenospheric erosion and mantle replacement, therefore, must be involved during the lithospheric thinning beneath the North China Craton. These processes may include: 1) the northward subduction and subsequent collision of the Yangtze Craton in Early Mesozoic would result in the North China lithospheric mantle experienced metasomatism or modification (melt-rock interaction) by fluids/melts derived from the subducted Yangtze continent, lithospheric mantle extension and asthenospheric erosion; 2) asthenospheric upwelling related to the subduction of the Kula and the Pacific Plates during Late Mesozoic-Paleogene, erodes the remaining lithospheric mantle (including those modified and newly accreted ones) and results in the huge thinning of North China lithosphere; and 3) asthenospheric cooling in Neogene would slightly lowers the boundary between the lithosphere and asthenosphere, create newly accreted lithospheric mantle and achieve a thinning lithosphere as a whole. The fertile peridotite xenoliths in the Fuxian basalts erupted at 100 Ma indicate that the early mantle replacement beneath the eastern North China Craton took partly place before the time.

North China and South China collision: Insights from analogue modeling

Abstract The North China–South China collision during early Mesozoic time formed the Dabie–Sulu ultrahigh pressure (UHP) metamorphic belt in eastern China, the largest UHP metamorphic belt on Earth. However, no consensus exists about the dynamics of this continental collision. In order to get insights into this process, a series of four analogue models was performed. The experiments used layers of silicone putty and sand mixtures to reproduce the rheological characteristics of four-layer continental lithospheres and two-layer oceanic lithospheres. Based on existing constraints, the models reproduced a thick and cool North China block and a relatively thinner and warmer South China block. The shape of these different blocks was varied in different experiments in order to reproduce the main geometrical boundary conditions suggested in previous models. It is suggested here that, under present knowledge of North–South China lithosphere strengths prior to the collision, South China could not have penetrated into North China. Detachment of South China upper crust from lower crust was not observed throughout the experiments. A model that North China as a rectangular promontory penetrated South China approximately normal to the future Tanlu fault zone was advocated here.

Dynamics of the Present‐Day Crustal Movement in the China Mainland

AbstractWe employ the finite element method to perform modeling for the crustal and lithospheric movement in the China mainland and its neighboring areas. In the modeling we use a viscous sheet (Newtonian and non‐Newtonian) to simulate the continental lithosphere. By solving the force balance equations, we obtain the velocity field of China continental crust with respect to Eurasia plate and compare them with the recent Global Positioning System (GPS) measurements. Our result shows that the primary driving force source accounting for the crustal movement in this region is from the collision between the India and Eurasia plates as well as the huge gravity potential energy of the Qinghai‐Xizang plateau. In comparison, the contribution from the former is larger than the latter. The result also indicates that the media of the China lithosphere has a strong heterogeneity of rheology, which results in its block‐division feature of the present‐day crustal velocity field.

The thermal state and composition of the lithospheric mantle beneath the Leizhou Peninsula, South China

Two localities on the Leizhou Peninsula, southern China (Yingfengling and Tianyang basaltic volcanoes) yield a wide variety of mantle-derived xenoliths including Cr-diopside series mantle wall rocks and two distinct types of Al-augite series pyroxenites. Metapyroxenites have re-equilibrated granoblastic microstructures whereas pyroxenites with igneous microstructures have not thermally equilibrated to the mantle conditions. An abundant suite of megacrysts and megacrystic aggregates (including garnet, plagioclase, clinopyroxene, ilmenite and apatite) is interpreted as the pegmatitic equivalents of the igneous pyroxenite suite. Layered spinel lherzolite/spinel websterite xenoliths were formed by metamorphic differentiation caused by mantle deformation, inferred to be related to lithospheric thinning. Some metapyroxenites have garnet websterite assemblages that allow calculation of their mantle equilibration temperatures and pressures and the construction of the first xenolith geotherm for the southernmost China lithosphere. Heat flow data measured at the surface in this region yield model conductive geotherms (using average crustal conductivity values) that are consistent with the xenolith geotherm for the mantle. The calculated mean surface heat flux is 110 mW/m 2. This high heat flux and the high geotherm are consistent with young lithospheric thinning in southern China, and with recent tomography results showing shallow low-velocity zones in this region. The xenolith geotherm allows the construction of a lithospheric rock type section for the Leizhou region; it shows that the crust–mantle boundary lies at about 30 km, consistent with seismic data, and that the lithosphere–asthenosphere boundary lies at about 100 km.

Dynamics of the India‐Eurasia collision zone

We present simple new dynamic calculations of a vertically averaged deviatoric stress field (over a depth average of 100 km) for Asia from geodetic, geologic, topographic, and seismic data. A first estimate of the minimum absolute magnitudes and directions of vertically averaged deviatoric stress is obtained by solving force balance equations for deviatoric stresses associated with gravitational potential energy differences within the lithosphere plus a first‐order contribution of deviatoric stresses associated with stress boundary conditions. This initial estimate of the vertically averaged deviatoric stress field is obtained independent of assumptions about the rheology of the lithosphere. Absolute magnitudes of vertically averaged deviatoric stresses vary between 5 and 40 MPa. Assuming bulk viscous behavior for the lithosphere, the magnitudes of deviatoric stresses, together with the magnitudes of strain rates inferred from Quaternary fault slip rate and GPS data, yield vertically averaged effective viscosities for Tibet of 0.5–5×1022 Pa s, compared with 1–2.5×1023 Pa s in more rigid areas elsewhere in the region. A forward modeling method that solves force balance equations using velocity boundary conditions allows us to refine our estimates of the vertically averaged effective viscosity distribution and deviatoric stress field. The total vertically averaged deviatoric stress and effective viscosity field are consistent with a weak lower crust in Tibet; they are consistent with some eastward motion of Tibet and south China lithosphere relative to Eurasia; and they confirm that gravitational potential energy differences have a profound effect on the spatially varying style and magnitude of strain rate around the Tibetan Plateau. Our results for the vertically averaged deviatoric stress argue for a large portion of the strength of the lithosphere to reside within the seismogenic upper crust to get deviatoric stress magnitudes there to be as high as 100–300 MPa (in accord with laboratory and theoretical friction experiments indicating that stress drops in earthquakes are small fractions of the total deviatoric stress).