Structure of the Upper Mantle and Transition Zone Beneath the South China Block Imaged by Finite Frequency Tomography

We applied the finite frequency tomography method to S wave data recorded by 350 broadband stations beneath the South China Block（SCB） and its surroundings from earthquakes occurring between July 2007 and July 2010,to better understand upper mantle deformation.Differential travel-times in the pair of stations with appropriate weighting for each station are used in the inversion.Our results are consistent with previous tomography that show a high velocity anomaly beneath the Sichuan basin and a high velocity anomaly in the transition zone beneath the Yangtze Craton.However,the resolution of mantle heterogeneity provides new insight into the tectonic framework of subduction of Burmese lithosphere in the west part of the study region and subduction of oceanic lithosphere in the east.In the subduction realm,west of 107°E,a significant fast S-wave anomaly is located on the southeast of Sichuan Basin.East of 107°E,and two narrow and discontinuous fast S-wave anomalies occur at a depth of 400-600 km beneath the middle of the South China block overlain by the pronounced low S-wave anomalies at a depth of 100 and 400 km.If the fast anomalies located in the mantle transition zone represent stagnant slabs,their fragmented nature may suggest that they could be produced by different episodes of subduction beneath western Pacific island and the above slow velocity anomaly may associated with the back-arc regions of ongoing subduction.In addition,tomography also reveals an anomalously high S-wave velocity continental root extends eastward to a depth 400 km beneath the eastern Sichuan Basin.This anomaly may be related to eastern extrusion of Indian lithosphere associated with the collision of India and Eurasia.Moreover,our results also show large slow anomalies beneath the Red River fault region connected to deeper anomalies beneath the South China Fold Belt and South China Sea.AH these observations are consistent with the scenario that the South China block has been built by both of subduction of Paleopacific plate and eastward subduction of Burma microplate.

Depositional Age, Provenance Characteristics and Tectonic Setting of the Ailaoshan Group in the Southwestern South China Block

The depositional and metamorphic ages and provenances of the Ailaoshan(ALS) Group in the Ailaoshan-Red River(ALS-RR) shear zone, southwestern South China Block(SCB), were investigated to constrain the tectonic history of the southwestern SCB. In this study, we use petrology, geochemical analysis, zircon cathodoluminescence imaging and UPb geochronology to analyse samples of quartzite, garnet-bearing two-mica schist and metapelite. The age spectra of detrital zircon grains from these metasediments show two dominant age peaks at 550–424 Ma and 876–730 Ma and two subordinate peaks at 970–955 Ma and ~2450 Ma. The youngest peak, corresponding to the early Palaeozoic, accounts for more than 20% of the total dates and constrains the deposition of the ALS Group to the Palaeozoic rather than the Palaeoproterozoic as traditionally thought. Moreover, two peaks of metamorphic ages corresponding to the Permo-Triassic and Cenozoic were also identified, and these ages document the tectonothermal events associated with the Indosinian collision between the Indochina Block and the SCB and the Himalayan collision between the Indian and Asian plates. Geochemical data suggest that the provenances of the ALS Group were dominated by continental arc and recycled metasedimentary rocks. The comparison of probability density distribution plots of the detrital zircon U-Pb age data indicates that the Neoproterozoic detritus in the ALS Group was probably derived from the arc-related Neoproterozoic intrusive bodies in the northwestern and southwestern SCB. Furthermore, the early Palaeozoic detritus might have been sourced from eroded early Palaeozoic strata and magmatic plutons in Cathaysia and volcanic rocks in the western Indochina Block.

Two-episode Tectono-thermal Events of the Heyuan Fault in Late Cretaceous and Oligocene and their Tectonic Implications, Southernmost South China Block

The Heyuan Fault, is one of the main NE-trending faults in the southernmost South China Block and is close to the northernmost South China Sea to the south. The fault features multi-stage deformation and controlled the formation of late Cretaceous to Cenozoic basins. Based on detailed field investigations and comprehensive geochronological research, including zircon U-Pb, Rb-Sr isochron, zircon U-Th-He dating, two episodic tectono-thermal events are recognized. The first occurred during ~79 Ma to 66 Ma, which is characterized by large-scale quartz-fluid emplacement. The other occurred at ~34 Ma, which features the eruption of a set of basalts. The two events show a changing on material source from siliceous hydrotherm to basalt magma, supporting obvious lithospheric thinning of the southernmost South China Block, which shed light on the geological evolution and the interaction mechanisms between the SCB and the northern South China Sea since the Late Cretaceous.

The Silurian A-Type Granites in Northeastern Guangxi,South China Block:New Evidence of Transition from Compression to Post-orogenic Extension of the Kwangsian Orogen

Objective More and more evidence suggests that the Kwangsian orogen is probably an intraplate orogen, which is one of the few examples of intraplate orogenesis worldwide. However, the initiation time, size and scope of the Kwangsian orogeny have not been determined yet. This study analyzed the Silurian A-type granites in northeastern Guangxi, South China Block, which may provide new evidence for the transition from compression to post- orogenic extension of the Kwangsian orogen.

Triassic magmatism in the eastern part of the South China Block： Geochronological and petrogenetic constraints from Indosinian granites

The granitic dykes in the Badu Group, Zhejiang Province, South China provide important insights on tectonic setting and crustal evolution of the South China Block （SCB） and the Indochina Block during Triassic. Here we report LA-ICP-MS U-Pb data of granitic rocks from the Hucun and Kengkou which show early Triassic ages of 242 ± 2 and 232 ± 3 Ma, respectively, representing their timing of emplacement. The dyke rocks are enriched in K, AI, LREE, Rb, Th, U, and Pb, and are depleted in Nb, Ta, St, and Ti. The rocks are characterized by highly fractionated REE patterns with （La/Yb）N ratios of 28.46 -38.07 with strong negative Eu anomalies （Eu/Eu＊ = 0,65-0.73）. In situ Hf isotopic analyses of zircons from the Hucun granite yielded CHf（t） values of -13.9 to -6.4 and two-stage depleted mantle Hf model ages of 1.68-2.15 Ga, which indicate that the magma was formed by partial melting of the Paleo- proterozoic metasedimentary protoliths in the Cathaysia Block. The zircons from the Kengkou granite have eHf（t） values ranging from -40.7 to 31.5 and yield two-stage depleted mantle Hf model ages of 0.99 -2.49 Ga, indicating magma origin from a mixed source. The Hucun and Kengkou dykes, together with the Triassic A-type granites in SE China were probably generated during magmatism associated with crust-mantle decoupling along the convergent plate boundary between SCB and the Indochina Block.

Paleomagnetism of Cretaceous Red beds from Eastern Part of South China Block

We performed on paleomagnetic investigation of the Upper Cretaceous red sandstones collected from Fujiau and Guangdong provinces. Significant characteristic directions were isolated by principal comPonent analysis from 22 of 25 and 9 of 14 sampling sites iu Fujian and Guangdong,respectively. Maximum concentration of global mean directions every province is achieved at 70 %and complete (100 % ) untilting for Fujian and Guangdong, respectively. We regarded these mean directions as the Late Cretaceous paleomagnetic directions and calculated virtual geomagnetic poles (VGPs); Fujian, Lat. /Lon. = 79. 4°N/210. 3°E (α95= 5. 1°) and Guangdong, Lat. /Lon. = 80. 1°N/193. 4°E (α95=8. 0°). These two VGPs are nearly equal to each other and to a mean VGP from Sichuan Province reported previously. This observation suggests no relative movement among three regions, Fujian, Guangdong and Sichuan, since the Late Cretaceous. Two VGPs from this study are significantly different from previously reported VGPs from the same regions. Further systematic paleomagnetic works are needed to clarify this difference of VGP Positions.

The Lithospheric Structure in the South China Block from Receiver Function: Implications for the Source of Mineral System

The South China block(SC),composed of Cathaysia(CA),Jiangnan Orogenic belt(JNB),and Yangtze block(YB),is one of the most important poly-metallic metallogenic provinces in the world(Zhang et al.,2013),containing of four famous major Mesozoic metallogenic belts,involving the Middle-Lower Yangtze Fe-Cu-Au metallogenic belt(MYMB).

The Earlier Spreading of South China Sea Basin due to the Late Mesozoic to Early Cenozoic Extension of South China Block: Structural Styles and Chronological Evidence from the Dulong-Song Chay Metamorphic Dome, Southwest China

To understand the forming and tectonic evolution of the South China Sea basin, new data of the structural styles and geochronology were obtained from the Dulong-Song Chay dome, southeastern Yunnan and northern Vietnam. The structural styles were acquired through field investigation and geo-chronological dating was carried out using zircon SHRIMP Ⅱ U-P and argon isotopic analyses. The South China Sea basin extension occurred firstly at Late Mesozoic to Early Cenozoic, and then at Late Oligocene to Middle Miocene （32-17 Ma）. The second stage of extension formed immediately after the first stage, and both extensions have a consistent forming mechanism. New structural analysis and geo-chronological data do not support the models of ＂backarc spreading＂ and ＂strike-slip faults producing the extension＂. Then what mechanism resulted in the extension of South China Sea basin？ The data indicate that at least two episodes of major extensional tectonics, i.e. , the D1 deformation at 237-228 Ma resulted in the rising and exhumation of the dome, and D2 deformation at 86-78 Ma overprinted and redeformed the dome. Of them, the D2 shows a consistent forming time, extensional direction and tectonic regime among Dulong-Song Chay dome, South China block and the northern margin of the South China Sea basin. Regional geology has proved that the northern margin of the South China Sea basin belongs to the South China block, therefore, we interpreted that the Late Mesozoic to Early Cenozoic extensional tectonics occurred in the northern margin of the South China Sea basin due to the intraplate deformation of the South China block, while the Ailaoshan-Red River sinistral slip strengthened the Cenozoic extension in the South China Sea basin.

Cretaceous Deepwater Lacustrine Dedimentary Sequences from the Northernmost South China Block, Qingdao, China

A sequence of terrigenous siliciclastic rocks crop out at Baxiandun, Qingdao, near the Mesozoic collisional boundary between North China block （NCB） and South China block （SCB）. These low-grade metamorphosed siliciclastic rocks are dominated by greywacke with shale, man- ganiferous fine-grained sandstone, arkose and conglomerate layers. There are two basic interpreta- tions about the formation of these rocks. One considered that this sequence was formed within NCB, and is part of the Cretaceous Laiyang Group and Qingshan Group fluvial facies and volcanic debris facies, as shown on the Shandong Regional Geological Map. Another opinion suggested that these rocks represent turbidity depositional systems in the slope and the basin facies was mainly deposited in Ordovician. Based on field observation, petrological analysis, and most importantly, geochemical results in this study, the sedimentary strata at Baxiandun Section mainly consist of siltstone, sand- stone and mudstone lithologies. They are dominated by deepwater debris and turbidity deposits in the slope and base of a lake. The U-Pb detrital zircon dating of the rocks at the Baxiandun Section indicates that the source rocks are very complex and their ages are varied from Archean to Early Cretaceous. The youngest age of the terrigenous detritus could represent the age of the sedimentary strata. Therefore, we infer that the sedimentary rocks belong to Early Cretaceous deepwater lacus- trine sedimentary sequences and have multiple sources origined from the erosion of the Sulu UHP orogen and South China block margin.

Crustal thickness and composition in the South China Block:Constraints from earthquake receiver function

Crustal thickness and composition are closely related to geology and tectonic evolution of the region.Studying the differences in the crustal thickness and composition of the South China Block(SCB)is important to gain a comprehensive understanding of multi-phase amalgamation,breakup,reworking,and regional geodynamic processes.In this study,teleseismic data from 135 high-density portable broadband stations from Sino Probe were processed using Common Conversion Point(CCP)stacking and H-κstacking methods.The Moho depth and P-wave and S-wave velocity ratio(V_(p)/V_(s))were studied.Our results revealed several insights about the tectonic processes in the SCB.First,the crustal structure and V_(p)/V_(s)ratios of the Cathaysia Block,Jiangnan Orogenic Belt,and Yangtze Block were significantly different.The average depth of the Moho in the Cathaysia Block was approximately 31 km,and the V_(p)/V_(s)ratios increased from the inland area(1.66)to the coastal area(1.78),indicating the oceanward increase of mafic proportion in the lower crust,which is related to the influence of the Paleo-Pacific Plate westward subduction.Second,the crustal thickness of Jiangnan Orogenic Belt deepens from east ca.31 to the west ca.42 km and the V_(p)/V_(s)ratios varied from 1.75 to 1.64,illustrating a relatively felsic crust,which could have been related to the Mesozoic upper crustal thickening under compression followed by the lower crust removal under the extensional background.Third,the average crustal thickness of the Yangtze Block was 42 km,and the V_(p)/V_(s)ratios ranged from 1.64 to 1.84,presenting a positive correlation between the Moho depth and the V_(p)/V_(s)ratio,which is explained by the relatively thick mafic lower crust.Based on the variations in the crustal structure and V_(p)/V_(s)ratios of the profile,we inferred that the central part of the Jiangnan Orogenic Belt was bounded by the Jiangshan-Shaoxing-Hengyang in the east and the Jiujiang-Shitai-Jishou in the west.The small-scale Moho depth undulations at the intersection of the Cathaysia Block and the Jiangnan Orogenic Belt could be related to the Mesozoic compression-extension geodynamic transformation.

Different accretion and diagenetic patterns within the fabrics of the Permian–Triassic boundary microbialites on the Leye isolated carbonate platform, South China Block

A comprehensive study on the accretion and diagenesis of the Permian–Triassic boundary microbialites is conducive to a better understanding of the ecological community after the end-Permian mass extinction. Here we studied the special microbialite sequences at the Tianba section of Leye isolated carbonate platform, South China Block. The microbialites are shown as small columnar stromatolites, stromatolitic thrombolites, spotted thrombolites,and domical digitate thrombolites in an ascending order. Thin section analyses, coupled with cathodoluminescence photos and oxygen isotopic data, reveal that all types of microbially-mediated laminae/clots are partly recrystallized.Layers of the Polybessurus-like fossils commonly occur in the recrystallized fabrics of stromatolitic laminae. However,the Polybessurus-like fossils are rare in quantity and generally fragmentary and structureless in stromatolitic clots and spotted clots. Such taphonomic features are likely interpreted as the early decomposition by heterotrophic bacteria in an oxygen-depleted microenvironment caused by rapid accumulations of organic matter in the calm water.More enrichments of ~(13)C in the laminae of stromatolite and in the clots of stromatolitic thrombolite and spotted thrombolite than in adjacent interstitial matrixes signify the photosynthesis-dominated isotopic fractionation during the growth of microbial communities. Rare calcimicrobial structures but many calcite crystal fans were found in the ~(13)C-depleted digitate clots. These phenomena indicate that seawater on the carbonate platform was ~(12)C-enriched and supersaturated, accelerating carbonate precipitations and decompositions of organic matter within the microbial community. Different preservations of the Polybessurus-like fossil revealed the complicated microbiallydominated sedimentation and post-depositional diagenesis in the abnormal seawater after the catastrophe.

Discussion on the Neoproterozoic glaciations in the South China Block and their related paleolatitudes

The Kaigas, Sturtian, Marinoan, and Gaskiers glaciations are widely recognized in Neoproterozoic. However, in the South China Block only the Jiangkou (Sturtian) and Nantuo (Marinoan) are symbolized by sedimentary records. The Kaigas, recorded by isotopic and chemical proxies, exhibited likely the nature of cold paleoclimate with local mountain glaciation. The correlation of the Doushantuo Formation with the Gaskiers is indicated by the carbon isotope excursion and the dated age from the interval, however the South China Block was then under non-glacial weather. With no paleomagnetic data, the position of the South China Block during the Sturtian glaciation cannot be determined. The paleolatitudes of the South China Block during the Kaigas and Nantuo glaciations are intermediate, even though the Nantuo was once rendered erratically deduced equatorial. In fact, the paleolatitudes of the South China Block during the Neoproterozoic glaciations are all likely at about 30°―40°.

Rayleigh wave phase velocities of South China block and its adjacent areas

Using records of continuous seismic waveforms from 609 broadband seismic stations in the South China Block and its adjacent areas in 2010–2012, empirical Green's functions of surface waves were obtained from cross-correlation functions of ambient noise data between these stations. High quality phase velocity dispersion curves of Rayleigh waves were obtained using time-frequency analysis. These interstation dispersion curves were then inverted to build Rayleigh wave phase velocity maps at periods of 6–50 s. The results of phase velocity maps indicate that phase velocities at 6–10 s periods are correlated with the geological features in the upper crust. Major basins and small-scale grabens and basins display slow velocity anomalies; while most of the orogenic belts and the fold belts display high velocity anomalies. With the gravity gradient zone along Taihang Mountain to Wuling Mountain as the boundary for the phase velocity maps at period of 20–30 s, the western area mainly displays low velocity anomalies, while the eastern side shows high velocity anomalies. Phase velocities in the eastern South China Block south to the Qinling-Dabie orogenic belt is higher than that in the eastern North China Block to the north, which is possibly due to the differences of tectonic mechanisms between the North China Craton and the South China Block. The phase velocities at periods of40–50 s are possibly related to the lateral variations of the velocity structure in the lower crust and upper mantle: The low-velocity anomalies in the eastern part of the Tibetan Plateau are caused by the thick crust; while the Sichuan Basin and the southern part of the Ordos Basin display distinct high-velocity anomalies, reflecting the stable features of the lithosphere in these blocks. The lateral variation pattern of phase velocities in the southern part of the South China Block is not consistent with the surface trace of the block boundary in the eastern Yunnan Province and its vicinities. The phase velocities in the Sichuan Basin are overall slow at short periods and gradually increase with period from the central part to the edge of the basin, indicating the features of shallower basement in the center and overall stable lithospheric mantle of the basin. The middle and upper crust of the southern Ordos Basin in the North China Block is heterogeneous, while in lower crust and the uppermost mantle the phase velocities mainly exhibit high anomalies. High-velocity anomalies are widespread at the middle of the Qinling-Dabie orogenic belt, as well as the areas in southeastern Guangxi with Caledonian granite explosion, but its detailed mechanism is still unclear.

Petrogenesis and Geodynamic Implications of Late Jurassic Diorite Porphyry in the Neoproterozoic Ophiolitic Mélange of NE Jiangxi (South China)

Mesozoic magmatism is widespread in the eastern South China Block and has a close genetic relationship with intensive polymetallic mineralization. However, proper tectonic driver remains elusive to reconcile the broad intracontinental magmatic province. This study presents integrated zircon U-Pb dating, Hf isotopes and whole-rock geochemistry of the Xiwan dioritic porphyry in the NE Jiangxi ophiolitic mélange. Zircon U-Pb dating by SIMS and LA-ICP-MS methods yielded an emplacement age of ～160 Ma for the Xiwan diorite, confirming its inclusion into the Mesozoic magmatic province in SE China, instead of a component of the Neoproterozoic ophiolitic mélange genetically. The dioritic rocks have low Si02(58.08 wt%-59.15 wt%), and high NaO(5.00 wt%-5.21 wt%) and MgO(4.60 wt%-5.24 wt%) contents with low TFeO/MgO ratios(1.02-1.09). They show an adakitic geochemical affinity but exhibit relatively low Sr/Y ratios(24.8-31.1) and high Y contents(14.6-18.3 ppm) compared to the Dexing adakitic porphyries. In addition, the Xiwan diorites have moderately evolved zircon Hf isotopic compositions(ε(t)=-6.1--0.1; T=1597-1219 Ma). These elemental and isotopic signatures suggest that the Xiwan diorite formed through partial melting of a remnant arc lower crust(i.e., early Neoproterozoic mafic arc-related rocks) in response to the underplating of coeval mafic magmas. In conjunction with the temporal-spatial distribution and complex geochemical characteristics of the Mesozoic magmatism, our case study attests to the feasibility of a flat-slab subduction model in developing the broad intracontinental magmatic province in SE China. The flat-slab delamination tends to trigger an asthenospheric upwelling and thus results in extensive partial melting of the overlying lithospheric mantle and lower crustal materials in an extensional setting during the Mesozoic.

A New Species of Amsassia from the Ordovician of Korea and South China:Paleobiological and Paleogeographical Significance

A new species of the probable calcareous alga Amsassia, A. koreanensis, is recognized from the Duwibong Formation （Middle Ordovician, Darriwilian） of the Taebaeksan Basin in mid-eastern Korea. This is the first report of the genus from the Korean Peninsula, expanding its geographical range to the eastern Sino-Korean Block. The new species also occurs in the Xiazhen Formation （Upper Ordovician, Katian） at Zhuzhai in the South China Block. Amsassia koreanensis is the smallest species of this modular genus, having a maximum module diameter of 0.28 ram. Module increase is by bipartite, tripartite and quadripartite types of longitudinal axial fission, but unlike other species of the genus, quadripartite fission is common. The types of fission are comparable to those in some Tetradiida （now Prismostylales, florideophycean rhodophyte algae）, although the processes of fission are different. The distribution of A. koreanensis further strengthens the biogeographical connection between the Sino-Korean and South China blocks, suggesting that these two paleocontinents were located closer together during the Middle to Late Ordovician than previously speculated.

Characteristics and Tectonic Significance of the Gravity Field in South China

Based on gravity data processed with the matched filter, depth continuation and horizontal gradient we obtained the spatial distribution of the gravity field and made analyses of the tectonic framework of South China. Then, inversion was conducted for the depth to study the depth variation of the boundary between the crust and upper mantle, namely the Mohorovicic discontinuity (Moho). The results demonstrate that the Moho depth in South China ranges from 30 to 40 km, and the crust thins from west to east, 27-29 km under the continent margin and shallow sea. We think it possible that the Tanlu fault crosses the Yangtze River and extends southwards along the Ganjiang and Wuchuan-Sihui faults to the South China Sea, and that there is an E-W hidden structural belt along 24.5°-26°.

华南中生代陆内成矿作用

陆内成矿机制是全球性科学难题。华南陆块中生代成矿大爆发,成矿作用远离活动大陆边缘,形成西部金锑铅锌低温成矿省和东部钨锡多金属高温成矿省,是研究陆内成矿的理想场所。因为空间上的分离,两个成矿省长期被认为是互为独立的体系。研究发现,西部低温成矿(230~200 Ma、160~130 Ma)与东部高温成矿时代一致并显示类似的地球化学指纹,印支期陆内造山和燕山期软流圈上涌是其共有成矿驱动机制,两个成矿省是具有成因联系的整体,共同构成面状展布的巨型多金属陆内成矿区;成矿后华南从西向东剥蚀程度的增强控制了目前近地表矿西部低温、东部高温的空间分布格局,低温成矿省东部区域的深部可能存在高温钨锡多金属矿床。在此基础上,建立了定位于陆内岩石圈先存薄弱区、陆壳供给矿源、高低温矿并重、成矿面状展布从而明显区别于板块边缘成矿机制的华南陆内成矿新理论。

华南地区地幔过渡带结构及其动力学意义

华南地区同时受特提斯构造域和太平洋构造域影响,是研究板块相互作用的最佳场所之一.为研究华南地区深部动力学过程,本文基于国家固定台网30°N以南的宽频带台站数据,利用接收函数方法开展了华南地区地幔过渡带结构研究,并结合已有地质、地球物理资料,讨论了华南地区深部构造单元划分及其浅部构造响应.研究结果表明:(1)扬子克拉通下方地幔过渡带结构接近全球平均水平,相对稳定;(2)海南岛地区地幔过渡带厚度偏薄,且410-km和660-km界面分别显著下沉和上升,可能与海南地幔柱密切相关;(3)太平洋构造域和特提斯构造域深部构造边界显著,青藏高原东南缘主要受特提斯构造域影响,其地幔过渡带中可能残留有拆沉的岩石圈板片;(4)雪峰山以东地区的地幔过渡带主要受太平洋构造域影响,但南北也存在局部差异,南部华夏地块下方可能不存在滞留板片,太平洋板块的俯冲、后撤与东南沿海地区地壳减薄和大规模出露的中-新生代岩浆岩密切相关.

扬子陆块西北缘早新元古代俯冲增生过程的岩浆记录

华南早新元古代俯冲相关岩浆作用记录为揭示罗迪尼亚超大陆边缘陆块的聚合及增生过程提供了重要制约。本文聚焦华南扬子陆块西北缘出露的早新元古代岩浆作用记录,总结梳理了其年代学框架、地球化学特征以及同位素特征,查明了其源区性质和岩石学成因、并探讨了不同阶段岩浆记录所对应的构造环境。结果表明,扬子陆块西北缘约1.0~0.9 Ga岩石具有与新生岛弧岩浆类似的微量元素特征,强不相容元素的含量略低于大陆弧,并且具有亏损的Sr-Nd-Hf同位素组成和略低于地幔值的锆石δ~(18)O值,这些特征指示约1.0~0.9 Ga岩浆岩最有可能形成于洋内弧环境。相比之下,约0.9~0.83 Ga岩浆岩具有与平均上地壳类似的微量元素特征,富集强不相容元素和轻稀土元素,亏损高场强元素,并且具有富集的SrNd-Hf同位素组成,锆石δ^(18)O值与地幔值相当或略高,指示其可能形成于大陆弧环境。此外,镁铁质岩石全岩Nd和锆石Hf同位素随年龄的长期变化趋势揭示了地幔源区性质周期性地富集和亏损,这可能是由于俯冲带间歇性地前进和后撤引起的挤压–伸展构造体制的不断交替所致。本文结果为扬子陆块西北缘新元古代早期的构造演化历史和俯冲增生动力学机制提供了制约。

基于背景噪声反演华南块体岩石圈三维S波速度结构

利用背景噪声方法,对布设在华南块体及其周边区域数个流动地震台阵中共704个地震台站的连续数据进行分析,反演得到华南岩石圈的三维S波速度结构。结果表明,地表附近S波速度结构与华南块体的地表构造高度相关,低速异常区集中在四川盆地和江汉盆地等沉积层较厚的区域。江南造山带的中上地壳呈现明显的高速异常,该高速异常即为华夏块体与扬子块体的分界区域。华夏块体中地壳低速异常区与该区域广泛分布的中生代花岗岩对应较好。华南上地幔岩石圈的东部与西部存在显著的速度差异,西部呈现显著的高速异常,反映西部四川盆地底部稳固的克拉通结构;上地幔的低速异常揭示华南东部岩石圈因太平洋板块俯冲的影响而明显减薄(<70km)。推测华夏块体以琼州海峡为中心的上地幔显著低速区可能对应海南地幔柱的热物质上涌。