Subducting slabs transport carbon to deep mantle depths and release it into the overlying mantle wedge and lithospheric mantle through multiple mechanisms,including mechanical removal via diapirism,metamorphic decarbo...Subducting slabs transport carbon to deep mantle depths and release it into the overlying mantle wedge and lithospheric mantle through multiple mechanisms,including mechanical removal via diapirism,metamorphic decarbonization,carbonate dissolution and parting melting.Identifying the dominant carbon recycling mechanism responsible for carbonation of subcontinental lithospheric mantle(SCLM)remains challenging,yet it is critical for understanding the genesis of post-collisional carbonatites and associated rare earth element deposits.To address this issue,we investigate the Li isotopic systematics of typical post-collisional carbonatite-alkalic complexes from Mianning-Dechang(MD),Southeast Xizang.Our results show that the less-evolved magmas(lamprophyres)have mantle-like or slightly lowerδ^(7)Li values(0.3‰–3.6‰)with limited variability,contrasting sharply with the widerδ^(7)Li range observed in associated carbonatites and syenites.We interpret this dichotomy as reflecting distinct processes:while the variable and anomalousδ^(7)Li values in differentiated rocks(carbonatites and syenites)were caused by late-stage magmatic-hydrothermal processes(including biotite fractionation,fluid exsolution and hydrothermal alteration),the lamprophyres retain the primary Li isotopic signature of their mantle source.Together with their arc-like trace element and EM1-EM2-type Sr-Nd-Pb isotopic signatures,such mantle-like or slightly lowerδ^(7)Li values of the lamprophyres preclude carbon derivation from high-δ^(7)Li reservoirs(altered oceanic crust,serpentinites)and recycling of sedimentary carbon through metamorphic decarbonization or dissolution.Instead,these features indicate that the carbon was predominantly transported into the mantle source via partial melting of subducted carbonate-bearing sediments.This study demonstrates that Li isotopes can serve as a tracer for identifying the mechanism of carbon recycling in collision zones.展开更多
In the author list,the corresponding author indicator(*)was inadvertently omitted from HOU Zengqian’s name.This has now been corrected to:“HOU Zengqian¹,*”.The online version of this article was corrected.
A subducted continental slab is sometimes torn during collision,yet the exact impact of slab-tearing on the overlying lithosphere remains unclear.Here,we image the structure and architecture of the Asian lithosphere a...A subducted continental slab is sometimes torn during collision,yet the exact impact of slab-tearing on the overlying lithosphere remains unclear.Here,we image the structure and architecture of the Asian lithosphere above the Indian slab in the eastern Tibetan Plateau using multiscale seismic tomography models and zircon Hf isotopic mapping,respectively.Our mantle V_(p)model shows that a large low-velocity anomaly extends laterally beneath the thinned Asian lithosphere above the tear zone roughly along the 26°N.The V_(s)images,magmatic records and Hf isotopic mapping indicate that this low-velocity anomaly recorded an asthenosphere flow eastward along the tear zone,which thermally eroded and refertilized the overlying Asian lithosphere,leading to the lithospheric melting,thinning and root delaminating.The vertical tear also generated a tectonic weak zone with associated Cenozoic potassic and carbonatitic magma suites.We argue that such a hot lithosphere discontinuity provided a reasonable mechanism for the abrupt change of crust thickness and the transformation of crust-mantle deformation from coupling to decoupling across the tear zone.展开更多
The lithospheric magnetic field is an important component of the geomagnetic field,and the oceanic lithosphere exhibits distinct characteristics.Because of its formation mechanisms,evolutionary history,and geomagnetic...The lithospheric magnetic field is an important component of the geomagnetic field,and the oceanic lithosphere exhibits distinct characteristics.Because of its formation mechanisms,evolutionary history,and geomagnetic field polarity reversals,the oceanic lithosphere has significant remanent magnetization,which causes magnetic anomaly stripes parallel to the mid-ocean ridges.However,it is difficult to construct a high-resolution lithospheric magnetic field model in oceanic regions with relatively sparse data or no data.Using forward calculated lithospheric magnetic field data based on an oceanic remanent magnetization(ORM) model with physical and geological foundations as a supplement is a feasible approach.We first collect the latest available oceanic crust age grid,plate motion model,geomagnetic polarity timescale,and oceanic lithosphere thermal structure.Combining the assumptions that the paleo geomagnetic field is a geocentric axial dipole field and that the normal oceanic crust moves only in the horizontal direction,we construct a vertically integrated ORM model of the normal oceanic crust with a known age,including the intensity,inclination,and declination.Both the ORM model and the global induced magnetization(GIM) model are then scaled from two aspects between their forward calculated results and the lithospheric magnetic field model LCS-1.One aspect is the difference in their spherical harmonic power spectra,and the other is the misfit between the grid data over the oceans.We last compare the forward calculated lithospheric magnetic anomaly from the scaled ORM and GIM models with the Macao Science Satellite-1(MSS-1) observed data.The comparison results show that the magnetic anomalies over the normal oceanic crust regions at satellite altitude are mainly contributed by the high-intensity remanent magnetization corresponding to the Cretaceous magnetic quiet period.In these regions,the predicted and observed anomalies show good consistency in spatial distribution,whereas their amplitude differences vary across regions.This result suggests that regional ORM construction should be attempted in future work to address these amplitude discrepancies.展开更多
As a means of quantitative interpretation,forward calculations of the global lithospheric magnetic field in the Spherical Harmonic(SH)domain have been widely used to reveal geophysical,lithological,and geothermal vari...As a means of quantitative interpretation,forward calculations of the global lithospheric magnetic field in the Spherical Harmonic(SH)domain have been widely used to reveal geophysical,lithological,and geothermal variations in the lithosphere.Traditional approaches either do not consider the non-axial dipolar terms of the inducing field and its radial variation or do so by means of complicated formulae.Moreover,existing methods treat the magnetic lithosphere either as an infinitesimally thin layer or as a radially uniform spherical shell of constant thickness.Here,we present alternative forward formulae that account for an arbitrarily high maximum degree of the inducing field and for a magnetic lithosphere of variable thickness.Our simulations based on these formulae suggest that the satellite magnetic anomaly field is sensitive to the non-axial dipolar terms of the inducing field but not to its radial variation.Therefore,in forward and inverse calculations of satellite magnetic anomaly data,the non-axial dipolar terms of the inducing field should not be ignored.Furthermore,our results show that the satellite magnetic anomaly field is sensitive to variability in the lateral thickness of the magnetized shell.In particular,we show that for a given vertically integrated susceptibility distribution,underestimating the thickness of the magnetic layer overestimates the induced magnetic field.This discovery bridges the greatest part of the alleged gap between the susceptibility values measured from rock samples and the susceptibility values required to match the observed magnetic field signal.We expect the formulae and conclusions of this study to be a valuable tool for the quantitative interpretation of the Earth's global lithospheric magnetic field,through an inverse or forward modelling approach.展开更多
Geodynamic processes following the Indo-Eurasian plate collision remain a key research focus,and the Jinshajiang-Red River tectonic zone(JRTZ),situated along this collision boundary,provides critical insights into pos...Geodynamic processes following the Indo-Eurasian plate collision remain a key research focus,and the Jinshajiang-Red River tectonic zone(JRTZ),situated along this collision boundary,provides critical insights into post-collision tectonic evolution.In this study,we identify a lithological assemblage in the JRTZ,including amphibolite,granite gneiss,and migmatite.These rocks exhibit contrasting geochemical signatures,reflecting multiple source regions:asthenospheric mantle,lithospheric mantle,mafic lower and upper crust.Specifically,amphibolite(28.5 Ma)formed through the partial melting of OIB-like mantle source,whereas S-type granite gneiss(28.2 Ma)originated from the dehydration melting of metamorphosed sedimentary rocks.Amphibole monzonite(28.9 Ma)records the mixing of ancient crustal material with mantle-derived components,while migmatite(37.9 Ma)resulted from deep melting processes of metasedimentary rocks under shear conditions.We propose that the ongoing Indo-Eurasian convergence progressively thickened the crust,ultimately driving large-scale lithospheric delamination between the Eocene and Oligocene.This delamination triggered asthenospheric upwelling,which provided the thermal input required for widespread melting.This lithospheric delamination event started around 38-37 Ma and lasted at least until 28 Ma.展开更多
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 Jiangs...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).展开更多
Beijing,China,16-18 November,2011 An“International Symposium on Deep Exploration into the Lithosphere”(ISDEL),hosted and sponsored by the Chinese Academy of Geological Sciences(CAGS),and national program SinoProbe–...Beijing,China,16-18 November,2011 An“International Symposium on Deep Exploration into the Lithosphere”(ISDEL),hosted and sponsored by the Chinese Academy of Geological Sciences(CAGS),and national program SinoProbe–Deep Exploration in China,co-sponsored by the Incorporated Research Institutions for Seismology(IRIS),International Continental Scientific Drilling Program(ICDP)and International Lithosphere Program(ILP)was held in Beijing,from 16 to 18 November,2011(Fig.1).展开更多
This paper shows that the catastrophe of lithosphere asthenosphere system (LAS) is developed for the Yanshanian metallogenic belt in the East China. Two types of Yanshanian disturbed LAS and metallogenesis in the Eas...This paper shows that the catastrophe of lithosphere asthenosphere system (LAS) is developed for the Yanshanian metallogenic belt in the East China. Two types of Yanshanian disturbed LAS and metallogenesis in the East China are recognized: great lithosphere thinning and thickening in the compressional orogenic environment, and the related Andes type and Hercyn type metallogenesis, respectively. Great amount of the juvenile and hot mantle materials and the reactivated hot lower crustal materials replaced, heated and injected into the cold lithosphere and crust are believed to be a fundamental source and a basic deep environment for the Yanshanian metallogenic explosion. Reactivated and active discontinuities on the lithosphere scale are considered to be the main ore storing space of the metallogenic zone. Large magma tectonic metallogenic system is necessary for the formation of large cluster area of ore deposit. The eastern China is believed to have large potential for prospecting of ore deposits in terms of the metallogenic environment.展开更多
The Beijing SHRIMP Center,in association with the International Precambrian Research Center of China and SinoProbe,Deep Exploration in China,organized an international meeting on“Precambrian Evolution and Deep Explor...The Beijing SHRIMP Center,in association with the International Precambrian Research Center of China and SinoProbe,Deep Exploration in China,organized an international meeting on“Precambrian Evolution and Deep Exploration of the Continental Lithosphere”on 7-9 October 2013 in the Loong Palace Hotel and Resort,Changping,Beijing.The meeting celebrated the opening of the new SHRIMP Laboratory Building in the Life Science Park of Beijing(Fig.1)and commemorated 30 years of collaborative Precambrian Research in China that began in 1983 with a now famous international meeting held at the Temple of the Sleeping Buddah.展开更多
Application of reliable thermobarometer on garnet-bearing mantle xenoliths and granulite xenoliths entrained by Cenozoic basalts in eastern China reveals two main types of geotherm. The first type, as exampled by Hann...Application of reliable thermobarometer on garnet-bearing mantle xenoliths and granulite xenoliths entrained by Cenozoic basalts in eastern China reveals two main types of geotherm. The first type, as exampled by Hannuoba （汉若坝）, Mingxi （明溪） and probably Northeast China, is characterized by constant slope of data in the P-T space. The second type, as exampled by the high geotherms of Niishan （女山） and probably Xinchang （新昌）, is characterized by variable slopes, with the samples with pressure 〈2 MPa defining a slow slope, whereas the samples with pressure 〉2 MPa define a virtually vertical slope. The different slopes in the second type of geotherm may correspond to different heat transfer mechanisms, with conductive transfer for the shallow upper mantle and advective transfer for the deep mantle. This observed transition in thermal transfer mechanism is consistent with theoretical modeling. The two types of geotherm are not mutually exclusive, because the second type may characterize the thermal state of whole lithospheric section including both mechanical boundary layer （MBL） and thermal boundary layer （TBL）, while the first type may only depict the MBL. The variable geotherms for different regions are indicative of a heterogeneous lithospheric structure in eastern China. （a） Eastern North China craton （NCC） is characterized by a second-type geotherm, corresponding to a thin lithosphere （-70 km）. Comparison of the equilibrium temperatures of spinel peridotites with this geotherm constrains the depth to Moho in eastern North China craton to be 30 kin. In contrast, western NCC （Hannuoba： the first-type geotherm） possesses a relatively low thermal gradient, indicative of a thick lithosphere （〉90-100 km） and a thick crust-mantle transition zone. The dramatic change in crustal and mantle structure across the DTGL （Daxing＇anling （大兴安岭）- Talhangshan （太行山） gravity lineament） is consistent with recent seismic studies. （b） There is a decrease in thermal gradient and in lithospheric thickness from the coast （Xinchang： the second-type geotherm） to the inland （Mingxi： the first-type geotherm） in South China （from -80 km to 〉90 kin）, which is collaborated with westward variation in basalt geochemistry. （c） The weak convex-upward pattern of the geo- therm in Qilin （麒麟） and Leizhou （雷州） Peninsula is peculiar, probably reflecting a transitional feature between conductive and advective heat transfer. It may result from impregnation of mantle plume on the base of the lithosphere. These new results not only provide a basic framework for the ongoing 4-D lithosphere mapping project in eastern China, but also yield important implications for deep processes that operated over the past.展开更多
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 a...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.展开更多
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 c...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.展开更多
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 an...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.展开更多
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 dis...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.展开更多
Late Mesozoic magmatism in southeastern China has been widely considered to be related to the subduction of the Paleo-Pacific Plate.However,it remains controversial whether mafic rocks are derived from the lithosphere...Late Mesozoic magmatism in southeastern China has been widely considered to be related to the subduction of the Paleo-Pacific Plate.However,it remains controversial whether mafic rocks are derived from the lithosphere or the asthenosphere.Here we present a comprehensive study on mafic dikes from Fujian Province in southeastern China,aiming to understand their source.Two types of mafic rocks have been recognized based on their trace-element features.Type-Ⅰrocks show arc-like trace-elemental characteristics,while type-Ⅱrocks are distinguished by their relatively flat patterns in primitive-mantle-normalized trace-element diagram.Despite such differences between two types of rocks,these mafic dikes show two trends in the plots of^(87)Sr/^(86)Sr(i)versus La/Nb,which can be explained by the influences of crustal contamination and melt-lithospheric mantle interaction,respectively.^(87)Sr/^(86)Sr(i),La/Nb,Sr/Y and Zr/Y ratios of type-I rocks are significantly correlated to the thickness of the underlying lithosphere,and the signals of lithosphere are clearer with increasing lithospheric thickness.This highlights the important influences of melt-lithosphere interaction during their formation.Such observations also indicate that these mafic rocks are more likely to have been originated from the asthenosphere rather than the lithospheric mantle.展开更多
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 i...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.展开更多
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 determinin...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.展开更多
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 t...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.展开更多
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 co...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.展开更多
基金funded by the National Natural Science Foundation of China(42263006)Open Fund from the Jiangxi Province,China(Grant No.20224ACB203011 and 2020101003)East China University of Technology(DHYC-202401 and 1410000874).
文摘Subducting slabs transport carbon to deep mantle depths and release it into the overlying mantle wedge and lithospheric mantle through multiple mechanisms,including mechanical removal via diapirism,metamorphic decarbonization,carbonate dissolution and parting melting.Identifying the dominant carbon recycling mechanism responsible for carbonation of subcontinental lithospheric mantle(SCLM)remains challenging,yet it is critical for understanding the genesis of post-collisional carbonatites and associated rare earth element deposits.To address this issue,we investigate the Li isotopic systematics of typical post-collisional carbonatite-alkalic complexes from Mianning-Dechang(MD),Southeast Xizang.Our results show that the less-evolved magmas(lamprophyres)have mantle-like or slightly lowerδ^(7)Li values(0.3‰–3.6‰)with limited variability,contrasting sharply with the widerδ^(7)Li range observed in associated carbonatites and syenites.We interpret this dichotomy as reflecting distinct processes:while the variable and anomalousδ^(7)Li values in differentiated rocks(carbonatites and syenites)were caused by late-stage magmatic-hydrothermal processes(including biotite fractionation,fluid exsolution and hydrothermal alteration),the lamprophyres retain the primary Li isotopic signature of their mantle source.Together with their arc-like trace element and EM1-EM2-type Sr-Nd-Pb isotopic signatures,such mantle-like or slightly lowerδ^(7)Li values of the lamprophyres preclude carbon derivation from high-δ^(7)Li reservoirs(altered oceanic crust,serpentinites)and recycling of sedimentary carbon through metamorphic decarbonization or dissolution.Instead,these features indicate that the carbon was predominantly transported into the mantle source via partial melting of subducted carbonate-bearing sediments.This study demonstrates that Li isotopes can serve as a tracer for identifying the mechanism of carbon recycling in collision zones.
文摘In the author list,the corresponding author indicator(*)was inadvertently omitted from HOU Zengqian’s name.This has now been corrected to:“HOU Zengqian¹,*”.The online version of this article was corrected.
基金supported by the National Natural Science Foundation of China(92462304)National Key Technologies R&D Program(2022YFF0800903)。
文摘A subducted continental slab is sometimes torn during collision,yet the exact impact of slab-tearing on the overlying lithosphere remains unclear.Here,we image the structure and architecture of the Asian lithosphere above the Indian slab in the eastern Tibetan Plateau using multiscale seismic tomography models and zircon Hf isotopic mapping,respectively.Our mantle V_(p)model shows that a large low-velocity anomaly extends laterally beneath the thinned Asian lithosphere above the tear zone roughly along the 26°N.The V_(s)images,magmatic records and Hf isotopic mapping indicate that this low-velocity anomaly recorded an asthenosphere flow eastward along the tear zone,which thermally eroded and refertilized the overlying Asian lithosphere,leading to the lithospheric melting,thinning and root delaminating.The vertical tear also generated a tectonic weak zone with associated Cenozoic potassic and carbonatitic magma suites.We argue that such a hot lithosphere discontinuity provided a reasonable mechanism for the abrupt change of crust thickness and the transformation of crust-mantle deformation from coupling to decoupling across the tear zone.
基金supported by the National Natural Science Foundation of China (41804067, 42174090, 42250101, and 42250103)the Science Research Project of the Hebei Education Department (BJK2024107)+3 种基金the Hebei Natural Science Foundation (D2022403044)the Opening Fund of the Key Laboratory of Geological Survey and Evaluation of the Ministry of Education (GLAB2023ZR02)the MOST Special Fund from the State Key Laboratory of Geological Processes and Mineral Resources (MSFGPMR2022-4)the Excellent Young Scientist Fund of Hebei GEO University (YQ202403)。
文摘The lithospheric magnetic field is an important component of the geomagnetic field,and the oceanic lithosphere exhibits distinct characteristics.Because of its formation mechanisms,evolutionary history,and geomagnetic field polarity reversals,the oceanic lithosphere has significant remanent magnetization,which causes magnetic anomaly stripes parallel to the mid-ocean ridges.However,it is difficult to construct a high-resolution lithospheric magnetic field model in oceanic regions with relatively sparse data or no data.Using forward calculated lithospheric magnetic field data based on an oceanic remanent magnetization(ORM) model with physical and geological foundations as a supplement is a feasible approach.We first collect the latest available oceanic crust age grid,plate motion model,geomagnetic polarity timescale,and oceanic lithosphere thermal structure.Combining the assumptions that the paleo geomagnetic field is a geocentric axial dipole field and that the normal oceanic crust moves only in the horizontal direction,we construct a vertically integrated ORM model of the normal oceanic crust with a known age,including the intensity,inclination,and declination.Both the ORM model and the global induced magnetization(GIM) model are then scaled from two aspects between their forward calculated results and the lithospheric magnetic field model LCS-1.One aspect is the difference in their spherical harmonic power spectra,and the other is the misfit between the grid data over the oceans.We last compare the forward calculated lithospheric magnetic anomaly from the scaled ORM and GIM models with the Macao Science Satellite-1(MSS-1) observed data.The comparison results show that the magnetic anomalies over the normal oceanic crust regions at satellite altitude are mainly contributed by the high-intensity remanent magnetization corresponding to the Cretaceous magnetic quiet period.In these regions,the predicted and observed anomalies show good consistency in spatial distribution,whereas their amplitude differences vary across regions.This result suggests that regional ORM construction should be attempted in future work to address these amplitude discrepancies.
基金supported by the National Natural Science Foundation of China(Grant Nos.42250103 and 42174090)the Opening Fund of Key Laboratory of Geological Survey and Evaluation of Ministry of Education(Grant No.GLAB2023ZR02)the Ministry of Science and Technology(MOST)Special Fund from the State Key Laboratory of Geological Processes and Mineral Resources(Grant No.MSFGPMR2022-4)。
文摘As a means of quantitative interpretation,forward calculations of the global lithospheric magnetic field in the Spherical Harmonic(SH)domain have been widely used to reveal geophysical,lithological,and geothermal variations in the lithosphere.Traditional approaches either do not consider the non-axial dipolar terms of the inducing field and its radial variation or do so by means of complicated formulae.Moreover,existing methods treat the magnetic lithosphere either as an infinitesimally thin layer or as a radially uniform spherical shell of constant thickness.Here,we present alternative forward formulae that account for an arbitrarily high maximum degree of the inducing field and for a magnetic lithosphere of variable thickness.Our simulations based on these formulae suggest that the satellite magnetic anomaly field is sensitive to the non-axial dipolar terms of the inducing field but not to its radial variation.Therefore,in forward and inverse calculations of satellite magnetic anomaly data,the non-axial dipolar terms of the inducing field should not be ignored.Furthermore,our results show that the satellite magnetic anomaly field is sensitive to variability in the lateral thickness of the magnetized shell.In particular,we show that for a given vertically integrated susceptibility distribution,underestimating the thickness of the magnetic layer overestimates the induced magnetic field.This discovery bridges the greatest part of the alleged gap between the susceptibility values measured from rock samples and the susceptibility values required to match the observed magnetic field signal.We expect the formulae and conclusions of this study to be a valuable tool for the quantitative interpretation of the Earth's global lithospheric magnetic field,through an inverse or forward modelling approach.
基金supported by the National Natural Science Foundation of China(Grant No.42472181)the National Key Research and Development Program of China(Grant No.2021YFA0719000)CNPC Innovation Fund(Grant No.2021DQ02-0103).
文摘Geodynamic processes following the Indo-Eurasian plate collision remain a key research focus,and the Jinshajiang-Red River tectonic zone(JRTZ),situated along this collision boundary,provides critical insights into post-collision tectonic evolution.In this study,we identify a lithological assemblage in the JRTZ,including amphibolite,granite gneiss,and migmatite.These rocks exhibit contrasting geochemical signatures,reflecting multiple source regions:asthenospheric mantle,lithospheric mantle,mafic lower and upper crust.Specifically,amphibolite(28.5 Ma)formed through the partial melting of OIB-like mantle source,whereas S-type granite gneiss(28.2 Ma)originated from the dehydration melting of metamorphosed sedimentary rocks.Amphibole monzonite(28.9 Ma)records the mixing of ancient crustal material with mantle-derived components,while migmatite(37.9 Ma)resulted from deep melting processes of metasedimentary rocks under shear conditions.We propose that the ongoing Indo-Eurasian convergence progressively thickened the crust,ultimately driving large-scale lithospheric delamination between the Eocene and Oligocene.This delamination triggered asthenospheric upwelling,which provided the thermal input required for widespread melting.This lithospheric delamination event started around 38-37 Ma and lasted at least until 28 Ma.
基金jointly sponsored by the Sinoprobe Laboratory of Chinese Academy of Geological Sciences(Grant No.JKYQN202303)National Natural Science Foundation of China(Grant No.U2344220)the China Geology Survey Project(Grant Nos.DD20230008,DD20240079)。
文摘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).
文摘Beijing,China,16-18 November,2011 An“International Symposium on Deep Exploration into the Lithosphere”(ISDEL),hosted and sponsored by the Chinese Academy of Geological Sciences(CAGS),and national program SinoProbe–Deep Exploration in China,co-sponsored by the Incorporated Research Institutions for Seismology(IRIS),International Continental Scientific Drilling Program(ICDP)and International Lithosphere Program(ILP)was held in Beijing,from 16 to 18 November,2011(Fig.1).
文摘This paper shows that the catastrophe of lithosphere asthenosphere system (LAS) is developed for the Yanshanian metallogenic belt in the East China. Two types of Yanshanian disturbed LAS and metallogenesis in the East China are recognized: great lithosphere thinning and thickening in the compressional orogenic environment, and the related Andes type and Hercyn type metallogenesis, respectively. Great amount of the juvenile and hot mantle materials and the reactivated hot lower crustal materials replaced, heated and injected into the cold lithosphere and crust are believed to be a fundamental source and a basic deep environment for the Yanshanian metallogenic explosion. Reactivated and active discontinuities on the lithosphere scale are considered to be the main ore storing space of the metallogenic zone. Large magma tectonic metallogenic system is necessary for the formation of large cluster area of ore deposit. The eastern China is believed to have large potential for prospecting of ore deposits in terms of the metallogenic environment.
文摘The Beijing SHRIMP Center,in association with the International Precambrian Research Center of China and SinoProbe,Deep Exploration in China,organized an international meeting on“Precambrian Evolution and Deep Exploration of the Continental Lithosphere”on 7-9 October 2013 in the Loong Palace Hotel and Resort,Changping,Beijing.The meeting celebrated the opening of the new SHRIMP Laboratory Building in the Life Science Park of Beijing(Fig.1)and commemorated 30 years of collaborative Precambrian Research in China that began in 1983 with a now famous international meeting held at the Temple of the Sleeping Buddah.
基金supported by the Knowledge Inno-vation Project of the Chinese Academy of Sciences (No. KZCX2-YW-Q08-3-6)the National Natural Science Founda-tion of China (Nos. 90714001, 40773015)the CAS/SAFEA International Partnership Program for Creative Research Teams (No. KZCX2-YW-Q04-06)
文摘Application of reliable thermobarometer on garnet-bearing mantle xenoliths and granulite xenoliths entrained by Cenozoic basalts in eastern China reveals two main types of geotherm. The first type, as exampled by Hannuoba （汉若坝）, Mingxi （明溪） and probably Northeast China, is characterized by constant slope of data in the P-T space. The second type, as exampled by the high geotherms of Niishan （女山） and probably Xinchang （新昌）, is characterized by variable slopes, with the samples with pressure 〈2 MPa defining a slow slope, whereas the samples with pressure 〉2 MPa define a virtually vertical slope. The different slopes in the second type of geotherm may correspond to different heat transfer mechanisms, with conductive transfer for the shallow upper mantle and advective transfer for the deep mantle. This observed transition in thermal transfer mechanism is consistent with theoretical modeling. The two types of geotherm are not mutually exclusive, because the second type may characterize the thermal state of whole lithospheric section including both mechanical boundary layer （MBL） and thermal boundary layer （TBL）, while the first type may only depict the MBL. The variable geotherms for different regions are indicative of a heterogeneous lithospheric structure in eastern China. （a） Eastern North China craton （NCC） is characterized by a second-type geotherm, corresponding to a thin lithosphere （-70 km）. Comparison of the equilibrium temperatures of spinel peridotites with this geotherm constrains the depth to Moho in eastern North China craton to be 30 kin. In contrast, western NCC （Hannuoba： the first-type geotherm） possesses a relatively low thermal gradient, indicative of a thick lithosphere （〉90-100 km） and a thick crust-mantle transition zone. The dramatic change in crustal and mantle structure across the DTGL （Daxing＇anling （大兴安岭）- Talhangshan （太行山） gravity lineament） is consistent with recent seismic studies. （b） There is a decrease in thermal gradient and in lithospheric thickness from the coast （Xinchang： the second-type geotherm） to the inland （Mingxi： the first-type geotherm） in South China （from -80 km to 〉90 kin）, which is collaborated with westward variation in basalt geochemistry. （c） The weak convex-upward pattern of the geo- therm in Qilin （麒麟） and Leizhou （雷州） Peninsula is peculiar, probably reflecting a transitional feature between conductive and advective heat transfer. It may result from impregnation of mantle plume on the base of the lithosphere. These new results not only provide a basic framework for the ongoing 4-D lithosphere mapping project in eastern China, but also yield important implications for deep processes that operated over the past.
基金supported by the 973 Research Project(Grant no. 2008CB425704) from the Ministry of Science and Technology,PRCthe National Natural Science Foundation of China(Grant nos 40572128,40376013,40104003)the Fundamental Research Funds for the Central Universities(Grant nos 2010ZD15 and 2010ZY23)
文摘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.
基金This project (No. 49070196) is funded by the National Science Foundation of China.
文摘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.
文摘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.
基金supportedby the Special Fund of the Instituteof Geophysics,China Earthquake Administration(Grant No.DQJB21B32)the National Natural Science Foundation of China(No.U1939204).
文摘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.
基金financially supported by the National Natural Science Foundation of China(Nos.41672048,41802045)the State Key Laboratory for Mineral Deposits ResearchNanjing University(No.ZZKT-201908)。
文摘Late Mesozoic magmatism in southeastern China has been widely considered to be related to the subduction of the Paleo-Pacific Plate.However,it remains controversial whether mafic rocks are derived from the lithosphere or the asthenosphere.Here we present a comprehensive study on mafic dikes from Fujian Province in southeastern China,aiming to understand their source.Two types of mafic rocks have been recognized based on their trace-element features.Type-Ⅰrocks show arc-like trace-elemental characteristics,while type-Ⅱrocks are distinguished by their relatively flat patterns in primitive-mantle-normalized trace-element diagram.Despite such differences between two types of rocks,these mafic dikes show two trends in the plots of^(87)Sr/^(86)Sr(i)versus La/Nb,which can be explained by the influences of crustal contamination and melt-lithospheric mantle interaction,respectively.^(87)Sr/^(86)Sr(i),La/Nb,Sr/Y and Zr/Y ratios of type-I rocks are significantly correlated to the thickness of the underlying lithosphere,and the signals of lithosphere are clearer with increasing lithospheric thickness.This highlights the important influences of melt-lithosphere interaction during their formation.Such observations also indicate that these mafic rocks are more likely to have been originated from the asthenosphere rather than the lithospheric mantle.
文摘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.
文摘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.
文摘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.
文摘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.
