The Lithosphere Structure and its Implication for Different Metallogenic Belts beneath the Eastern South China Block

The South China Block(SCB)was formed through the Neoproterozoic amalgamation of the Yangtze Block(YB),the Cathaysia Block(CB),and the accreted components of the Jiangnan orogenic belt(JNO),it is bounded by the Jiangshan–Shaoxing–Pingxiang fault(JSPF)and the Jiujiang–Shitai–Jishou fault(JSJF)(Yao et al.,2019).The SCB has undergone a series of complex geological events,including Paleozoic orogeny,Mesozoic collisions with the North China Craton(NCC)and the Indochina Block,as well as the intracontinental orogeny,leading to extensive lithospheric modifications and magmatic activities(Zhang H J et al.,2023;Fig.1).

深大断裂之郯庐断裂

郯庐断裂带是中国东部规模最大的一条岩石圈断裂带,也是中国东部最重要的一条中、新生代岩浆、成矿和构造活动带。不能很好地认识郯庐断裂,就不能很好地认识中国东部中生代的构造演化,也就不能很好地理解欧亚大陆的当今格局。本文从我们近年来对郯庐断裂带沿线中生代岩浆岩的研究成果出发,以任纪舜先生主编的《国际亚洲地质图》为指导思想,提出郯庐断裂的大型走滑启动应与早白垩世(~143 Ma)洋底高原与欧亚大陆的碰撞有关。郯庐断裂这一切割岩石圈深度的大型断裂是导致华北克拉通发生破坏的关键因素,为深部幔源物质的上涌提供了通道。郯庐断裂带两侧有规律地成群成带分布金矿等多金属矿产,多形成于郯庐断裂大型挤压走滑后(~123 Ma)的伸展背景。

Analysis of Error Caused by Replacing Spherical Shell with an Elastic Plate Model in Studying Bending Deformation of the Lithosphere

To study the bending deformation of the lithosphere, the simplification of replacing a spherical shell by a plate model is usually made. Based on the differential equations for the bending of plates and shallow spherical shells, an expression for the error caused by such a simplification is derived in this paper. The effect of model sizes on the error is discussed. It is proved that if we replace the shallow spherical shell by a plate model to solve the bending deformation of lithospheric plate, a large error will be caused. In contrast, if we use a plate on an elastic foundation instead, an approximate solution closer to that of spherical shell can be obtained. In such a way, the error can be reduced effectively and the actual geological condition can be modeled more closely.

高温高压下石榴斜长角闪岩的热物理性质研究及其对岩石圈热结构的约束

高温高压下矿物和岩石的热导率与热扩散系数可以为地质过程的热演化历史模拟提供数据支撑,同时也是建立稳定状态下的深部圈层热结构的必要参数.本文选取下地壳中具备较高代表性的石榴斜长角闪岩,利用基于六面顶压机上的瞬态平面热源法测试系统,测量了其在0.5~1.5 GPa、300~973 K下的热导率与热扩散系数,结果发现热导率和热扩散系数随温度增加而降低,随压力增加而升高,温度对热导率和热扩散系数的影响远大于压力的影响.在固定压力下,热导率和热扩散系数随温度的变化最大可达40%,在固定温度下,压力对热导率和热扩散系数的影响最大可达23%.利用实验获得的数据,结合前人的高温高压数据与热岩石圈模型参数,计算了不同地表热流下华北克拉通不同区域的热岩石圈厚度范围.

重震联合反演青藏高原岩石圈密度结构

本文联合重力和面波相速度数据反演了青藏高原岩石圈的密度模型,揭示了密度异常分布特征,并对密度异常的成因进行了讨论.模拟实验结果表明,面波相速度反演结果的横向分辨率在青藏高原东部达到1°,中部达到1.5°,西部低于2°,而重震联合反演结果的分辨率在青藏高原中西部均能达到1°;在波速异常和密度异常特征存在显著差异的情况下,重震联合反演的结果比面波相速度单独反演的结果更接近真实的密度模型.基于重震联合反演揭示的密度模型表明:(1)青藏高原中下地壳呈现显著的低密度、低VS异常,表明发生了部分熔融且存在地壳流通道.(2)青藏高原岩石圈地幔整体呈现高密度、低VS异常,表明上地幔可能发生了部分熔融和底侵作用.(3)班公湖—怒江缝合带和龙木错—双湖缝合带的岩石圈地幔呈现低密度、低VS异常,这可能是岩石圈地幔中橄榄岩的水合作用造成的;昆仑断裂带的低密度、低VS异常则支持该区域软流圈上涌的构造学说.(4)云贵高原、四川盆地和鄂尔多斯地体的岩石圈地幔呈现低密度、高VS异常,符合克拉通型岩石圈地幔特征.

Thermal State and Strength of the Lithosphere Beneath the Chinese Mainland

The temperature distributions of the lithosphere underneath the mainland of China were estimated by applying local isostatic equilibrium-constrained geothermal calculations. Maps of the lateral temperature variation at depths of 40, 70, and 100 km are presented for the whole Chinese continent, with the thermal thickness of the lithosphere is calculated. Lithospheric roots of 160-200 km thickness underlie Tarim and the Upper Yangtze Korean platform. In general, the Tibetan plateau lithospheres, whereas thinner thermal lithospheres platform, but are absent beneath the entire Sino- and fold belts to the north have warm but thick have been identified in northern Tibet and central Tian Shan around Issyk-Kul Lake. The warm and soft lithosphere in the Tibetan plateau and Tian Shan are caused by uniform north-south shortening, which may represent a snapshot of the early stage of convective thinning of the convergent lithosphere. However, the lithospheric thinning beneath northeastern China might be related to volatile infiltration by dehydration of the deeply subducting Pacific slab during the Cenozoic. Dry and wet upper mantle rheology display ＂jelly sandwich＂ and ＂cr^me brfil^e＂ pictures, respectively, demonstrating the mechanical behaviour of the Chinese lithosphere outside the Tibetan plateau. Considering a more geologically evident wet-mantle rheology, the ＂creme brulee＂ model can approximate the lithospheric rheology for the most earthquake-prone regions on the Chinese mainland.

Multi-layer Tectonic Model for Intraplate Deformation and Plastic-Flow Network in the Asian Continental Lithosphere

In a large area of the east—central Asian continent there is a unified seismic network system composed of two families of large—seismic belts that intersect conjugately. Such a seismic network in the middle—upper crust is actually a response to the plastic flow network in the lower lithosphere including the lower crust and lithospheric mantle. The existence of the unified plastic flow system confirms that the driving force for intraplate tectonic deformation results mainly from the compression of the India plate, while the long-range transmission of the force is carried out chiefly by means of plastic flow. The plastic flow network has a control over the intraplate tectonic deformation.

Azimuthal anisotropy in lithosphere on the Chinese mainland from observations of SKS at CDSN

The shear wave splitting in SKS are investigated from all available teleseismic data recorded at the broad band stations of China Digital Seismograph Network. The polarization direction of fast S wave of anisotropy and the time delay of slow S wave are determined. Detectable shear wave splitting was found at eight analysed stations of CDSN. Time delay ranges from 0. 7 s to 1. 7 s. The previous work show that the shear wave splitting of SKS which propagate through the mantle is due to the anisotropy in upper mantle. The anisotropy in upper mantle can be interpreted by the strain-induced lattice dominant orientation of mantle minerals. The thickness of the anisotropic layer responsible for SKS wave splitting, which is estimated from time delay, corresponds generally to the thickness of lithosphere beneath Chinese mainland, which is estimated from depth of the high conductivity layer and the low velocity layer in the upper mantle. In most stations, the polarization direction of fast S wave obtained in this study are generally close to these predicted by the deformation of intraplate blocks as a whole. However, there is obvious difference between the two directions at some stations. This suggests that the causes of this well observed phenomenon are clearly complex. In order to interpret the shear wave splitting of mantle shear wave, more high-quality observation and more additional information about the strain in the mantle will be needed.

A comparative study of seismic tomography models of the Chinese continental lithosphere

The Chinese mainland is subject to complicated plate interactions that give rise to its complex structure and tectonics. While several seismic velocity models have been developed for the Chinese mainland, apparent discrepancies exist and, so far, little effort has been made to evaluate their reliability and consistency. Such evaluations are important not only for the application and interpretation of model results but also for future model improvement. To address this problem, here we compare five published shear-wave velocity models with a focus on model consistency. The five models were derived from different datasets and methods (i.e., body waves, surface waves from earthquakes, surface waves from noise interferometry, and full waves) and interpolated into uniform horizontal grids (0.5° × 0.5°) with vertical sampling points at 5 km, 10 km, and then 20 km intervals to a depth of 160 km below the surface, from which we constructed an averaged model (AM) as a common reference for comparative study. We compare both the absolute velocity values and perturbation patterns of these models. Our comparisons show that the models have large (> 4%) differences in absolute values, and these differences are independent of data coverage and model resolution. The perturbation patterns of the models also show large differences, although some of the models show a high degree of consistency within certain depth ranges. The observed inconsistencies may reflect limited model resolution but, more importantly, systematic differences in the datasets and methods employed. Thus, despite several seismic models being published for this region, there is significant room for improvement. In particular, the inconsistencies in both data and methodologies need to be resolved in future research. Finally, we constructed a merged model (ChinaM-S1.0) that incorporates the more robust features of the five published models. As the existing models are constrained by different datasets and methods, the merged model serves as a new type of reference model that incorporates the common features from the joint datasets and methods for the shear-wave velocity structure of the Chinese mainland lithosphere.

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 adja- cent 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 kin, 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 kin. 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.

Piecemeal Delamination of Thickened Lithosphere Triggered Pulsed Magmatism and Mineralization during Late Mesozoic Intracontinental Orogeny in East Asia

The East Asia continent is characterized by a mosaic architecture with various composing blocks,such as the North and South China blocks,which had been collaged in Late Permian to Triassic in response to the break-up of Pangea.In the Late Mesozoic.

The westward drift of the lithosphere:A tidal ratchet?

Is the westerly rotation of the lithosphere an ephemeral accidental recent phenomenon or is it a stable process of Earth's geodynamics? The reason why the tidal drag has been questioned as the mechanism determining the lithospheric shift relative to the underlying mantle is the apparent too high viscosity of the asthenosphere. However, plate boundaries asymmetries are a robust indication of the 'westerly'decoupling of the entire Earth's outer lithospheric shell and new studies support lower viscosities in the low-velocity layer(LVZ) atop the asthenosphere. Since the solid Earth tide oscillation is longer in one side relative to the other due to the contemporaneous Moon's revolution, we demonstrate that a non-linear rheological behavior is expected in the lithosphere mantle interplay. This may provide a sort of ratchet favoring lowering of the LVZ viscosity under shear, allowing decoupling in the LVZ and triggering the westerly motion of the lithosphere relative to the mantle.

Effective elastic thickness of the lithosphere from joint inversion in western China and its implications

The western China lies in the convergence zone between Eurasian and Indian plates.It is an ideal place to study the lithosphere dynamics and tectonic evolutions on the continental Earth.The lithospheric strength is a key factor in controlling the lithosphere dynamics and deformations.The effective elastic thickness(T_(e))of the lithosphere can be used to address the lithospheric strength.Previous researchers only used one of the admittance or coherence methods to investigate the T_(e) in the western China.Moreover,most of them ignored the internal loads of the lithosphere during the T_(e) calculation,which can produce large biases in the T_(e) estimations.To provide more reliable T_(e) estimations,we used a new joint inversion method that integrated both admittance and coherence techniques to compute the T_(e) in this study,with the WGM2012 gravity data,the ETOPO1 topographic data,and the Moho depths from the CRUST1.0 model.The internal loads are considered and investigated using the load ratio(F).Our results show that the joint inversion method can yield reliable T_(e) and F values.Based on the analysis of T_(e) and F distributions,we suggest(1)the northern Tibetan Plateau could be the front edge of the plate collision of Eurasian and Indian plates;(2)the southern and part of central Tibetan Plateau have a strong lithospheric mantle related to the rigid underthrusting Indian plate;(3)the southeastern Tibetan Plateau may be experiencing the delamination of lithosphere and upwelling of asthenosphere.

Deep scientific drilling results from Koyna and Killari earthquake regions reveal why Indian shield lithosphere is unusual, thin and warm

The nature of crustal and lithospheric mantle evolution of the Archean shields as well as their subsequent deformation due to recent plate motions and sustained intraplate geodynamic activity, has been a subject of considerable interest. In view of this, about three decades ago, a new idea was put forward suggesting that out of all shield terrains, the Indian shield has an extremely thin lithosphere（w100 km,compared to 250e350 km, elsewhere）, apart from being warm, non-rigid, sheared and deformed. As expected, it met with scepticism by heat flow and the emerging seismic tomographic study groups, who on the contrary suggested that the Indian shield has a cool crust, besides a coherent and thick lithosphere（as much as 300e400 km） like any other shield. However, recently obtained integrated geological and geophysical findings from deep scientific drillings in 1993 Killari（M w： 6.3） and 1967 Koyna（M w： 6.3）earthquake zones, as well as newly acquired geophysical data over other parts of Indian shield terrain,have provided a totally new insight to this debate. Beneath Killari, the basement was found consisting of high density, high velocity mid crustal amphibolite to granulite facies rocks due to exhumation of the deeper crustal layers and sustained granitic upper crustal erosion. Similar type of basement appears to be present in Koyna region too, which is characterized by considerably high upper crustal temperatures.Since, such type of crust is depleted in radiogenic elements, it resulted into lowering of heat flow at the surface, increase in heat flow contribution from the mantle, and upwarping of the lithosphereasthenosphere boundary. Consequently, the Indian shield lithosphere has become unusually thin and warm. This study highlights the need of an integrated geological, geochemical and geophysical approach in order to accurately determine deep crust-mantle thermal regime in continental areas.

HETEROGENEITY OF THE LITHOSPHERE IN TIBETAN PLATEAU ON THE CONSTRAINTS OF MAGMATISM

Many evidences including those from magmatism and igneous rocks strongly support the heterogeneity of lithosphere in Tibetan plateau.By estimation, volcanic and plutonic rocks occupy an area of 300000km\+2, equaling to 10% of total area of the Tibetan Plateau. Temporal and spatial distribution of igneous rocks in the Tibetan Plateau is very inhomogeneous (Mo et al., 1998). Temporarily, most of plutonic and volcanic rocks, which occurred in 60% of total area of igneous rocks in the plateau, formed in the period of 65～45Ma. Spatially, 80% of igneous rocks in the plateau concentrated in the Gangdise—Nyainqentanglha region formed a huge complex granite\|volcanic belt. Petrotectonic assemblage and type of igneous rocks also vary from district to district. While Himalayas (especially High\|Himalayan region) were characterized by well development of muscovite\|bearing granites with no high\|potassium volcanic rocks and other volcanic contemporaries, North Tibet (Qiangtang region) by highly potassic volcanic rock series without muscovite\|bearing granites. Besides wide\|spreading calc\|alkaline igneous rocks, however, both highly potassic volcanic rocks and muscovite\|bearing granites developed in the central portion of Gangdise\|Nyainqentanglha region. It was lack of igneous activities in the Pamirs. Mantle\|derived nodules and their hosted rocks have been found only on northern and eastern margins of the plateau so far. All mentioned above, combined with other evidences from geophysics, geochemistry and structural geology, give us a hint to understand the heterogeneity of the lithosphere in its structure, thermal state and evolution processes underneath Tibetan plateau.

Comparison of mantle lithosphere beneath early Triassic kimberlite fields in Siberian craton reconstructed from deep-seated xenocrysts

Mantle xenocrysts from early Triassic kimberlite pipes from Kharamai, Ary-Mastakh and Kuranakh fields in the Anabar shield of Siberia revealing similar compositional trends were studied to estimate the superplume influence on the subcratonic lithosphere mantle （SCLM）. Pressure-temperature （PT） reconstructions using monomineral thermobarometry for 5 phases show division of the SCLM beneath the Kharamai field into 6 units： pyroxenitic Fe-rich （1-2 GPa） and Mg-rich （2-3 GPa） layers; middle with two levels of Gar-Sp pyroxenites at - 3 and 4-5 GPa; Gar-dunite-harzburgites - 4.5-6.5 GPa subjected to llm-Px vein metasomatism; and a Mg-rich dunite lower part. In the Anabar shield （Ary-Mastakh, Dyuken and Kuranakh fields） mantle lithosphere is composed of three large units divided into two parts： upper part with amphiboles and phlogopite; two levels of pyroxenites and eclogites at 3 and 4 GPa, and a lower part composed of refertilized dunites. Diagrams showing P-Fe#Gar clusters for garnets and omphacites illustrate the differences between SCLM of these localities. Differences of Triassic SCLM from Devonian SCLM are in simple layering; abundance of Na-Cr-amphiboles and metasomatism in the upper SCLM part, thick pyroxenite-eclogite layer and lower part depletion, heated from SCLM base to 5.0 GPa. Kharamai mantle clinopyroxenes represent three geochemical types： （1） harzburgitic with inclined linear REE, HFSE troughs and elevated Th, U; （2） lherzolitic or pyroxenitic with round TRE patterns and decreasing incompatible elements; （3） eclogitic with Eu troughs, Pb peak and high LILE content. Calculated parental melts for garnets with humped REE patterns suggest dissolution of former Cpx and depression means Cpx and garnets extraction. Clinopyroxenes from Ary-Mastakh fields show less in- dined REE patterns with HMREE troughs and an increase of incompatible elements. Clinopyroxenes from Kuranakh field show flatter spoon-like REE patterns and peaks in Ba, U, Pb and St, similar to those in ophiolitic harzburgites. The PT diagrams for the mantle sections show high temperature gradients in the uppermost SCLM accompanied by an increase of P-Fe#OI upward and slightly reduced thickness of the mantle keel of the Siberian craton, resulting from the influence of the Permian-Triassic superplume, but with no signs of delamination.

The effect of altimetry data in estimating the elastic thickness of the lithosphere in the western Pacific Ocean

The elastic thickness of the lithosphere(Te)is a key parameter used to describe the strength of the lithosphere.It is usually estimated by a spectral analysis between gravity and topography.In previous research on the estimation of Te,altimetry data were used on both the gravity data and topography data,which could lead to deviations.The study described in this paper analyzed the effects of using gravity anomalies derived from different data sources on the estimation of Te,Taking the western Pacific region as an example,this study analyzed the impact of the repeated presence of altimetry satellite data on the calculation of the effective elastic thickness and found that if gravity anomalies and topography model both contain altimetry satellite data,they systematically overestimate effective elasticity.For a uniform area,the difference in Te can reach up to 30%.For a Te distribution,the difference can reach up to about16%.After eliminating this effect,the effective elastic thickness of the western Pacific region was found to be 10 km,and the statistical results of the effective elastic thickness distribution showed that the effective elastic thickness of the lithosphere in most areas of the western Pacific is about 12 km.The paper shows the importance of choosing the appropriate gravity model in evaluating the elastic thickness of lithosphere in the oceans.A figure of Te at seamounts with loading ages demonstrates that Te in the western Pacific is generally distributed within the 100-300℃isotherm depth and does not increase with loading age.

A Thickness Gauge for the Lithosphere Based on Ce/Yb and Sm/Yb of Mantle–Derived Magmatic Rocks

A new method for determining the partial melting depth of mantle-derived magma and lithospheric thickness in continental regions is derived from REE geochemistry. This effective technique uses variations in the Ce/Yb and Sm/Yb ratios found in mainly volcanic rocks in continental China. The ratios change with the depth of origin consistent with the correlation between lithospheric thickness and the Ce/Yb and Sm/Yb ratios found in oceanic basalt. These ratios increase exponentially with the depth of origin, the lithospheric thickness, of a wide variety of Cenozoic volcanic basalt and Paleozoic kimberlite in the North China Craton, northeastern China continent and vicinity. This functional relationship with depth is shown in a plot of the ratios that forms a concordia curve, which is closely expressed by formulas using 8–degree polynomials. These provide a more accurate gage in measuring the lithospheric thickness than the traditional geophysical methods. When applied to volcanic rock of different ages it also reveals how the thickness has changed over time and thus, greatly aids the understanding of the tectonic history. Relations between the COcontent, mineral reactions and pressure in the upper asthenosphere beneath the base of the lithosphere appears to affect the proportions of REE in partial melts and brings about a close correlation between lithospheric thickness and the Ce/Yb and Sm/Yb ratios in mantle–derived magmatic rock. This thickness gauge, for both continental and oceanic lithosphere, provides a new approach in analyzing the lithospheric thickness in different tectonic settings and geologic times.

Mineralogy, Geochemistry and Palaeomagnetism of Mafic Dykes from Kumaun Lesser Himalaya: Implication on Petrogenesis, Tectonic Setting and Timing of Mafic Magmatism in Northern Part of Indian Lithosphere

Occurrence of mafic dykes in Himalaya has been intriguing and debated since long because of its difficulty to ascent and emplacement through a thickened crust.Mafic dykes in Kumaun Lesser Himalaya(KLH)of central Indian

The latest geodynamics in Asia:Synthesis of data on volcanic evolution,lithosphere motion,and mantle velocities in the Baikal-Mongolian region

From a synthesis of data on volcanic evolution,movement of the lithosphere,and mantle velocities in the Baikal-Mongolian region,we propose a comprehensive model for deep dynamics of Asia that assumes an important role of the Gobi,Baikal,and North Transbaikal transition-layer melting anomalies.This layer was distorted by lower-mantle fluxes at the beginning of the latest geodynamic stage（i.e.in the early late Cretaceous） due to avalanches of slab material that were stagnated beneath the closed fragments of the Solonker,Ural-Mongolian paleoceans and Mongol-Okhotsk Gulf of Paleo-Pacific.At the latest geodynamic stage,Asia was involved in east-southeast movement,and the Pacific plate moved in the opposite direction with subduction under Asia.The weakened upper mantle region of the Gobi melting anomaly provided a counterflow connected with rollback in the Japan Sea area.These dynamics resulted in the formation of the Honshu-Korea flexure of the Pacific slab.A similar weakened upper mantle region of the North Transbaikal melting anomaly was associated with the formation of the Hokkaido-Amur flexure of the Pacific slab,formed due to progressive pull-down of the slab material into the transition layer in the direction of the Pacific plate and Asia convergence.The early—middle Miocene structural reorganization of the mantle processes in Asia resulted in the development of upper mantle low-velocity domains associated with the development of rifts and orogens.We propose that extension at the Baikal Rift was caused by deviator flowing mantle material,initiated under the moving lithosphere in the Baikal melting anomaly.Contraction at the Hangay orogen was created by facilitation of the tectonic stress transfer from the Indo-Asian interaction zone due to the low-viscosity mantle in the Gobi melting anomaly.