Late mesozoic A-Type granitoids in se China and paleo-pacific plate subduction and slab rollback北大核心CSCD

This study has reviewed the distribution and pedogenesis of late Mesozoic A-Type granitoids in SE China. These A-Type granitoids belong to four belts ( S Jiangxi-SW Fujian belt, Xiang-Gui-Yue belt, Can-Hang belt and coastal belt) due to their temporal-spatial distribution. Based on the comparative analysis of chronology, geochemistry and magmatic association, this study has discussed the formation of A-Type granitoids and the subduction and slab rollback process of paleo-Pacific plate beneath SE China.     

Rock associations and their spatial-Temporal variations of the early mesozoic igneous rocks in the NE Asia: Constraints on the initial subduction timing of the paleo-pacific plate北大核心CSCD

This paper summarizes rook associations and spatial-Temporal variations of the early Mesozoic igneous rocks in the NE Asia, with the aim of revealing the initial subduction timing of the Paleo-Pacific Plate beneath the Eurasia, and the relationships between the early Mesozoic magmatisms and the Paleo-Asian tectonic system, Mongol-Okhotsk tectonic system, and amalgamation of the Yangtze and North China cratons. Dating results indicate that the early Mesozoic magmatisms in the NE Asia can be subdivided into three stages, i.e., Early-Middle Triassic, Late Triassic, and Early Jurassic. The early Mesozoic calc-Alkaline magmatisms within the Erguna Massif reveal southward subduction of the Mongol-Okhotsk oceanic plate. The Triassic alkaline and bimodal magmatisms within the northern margin of the North China Craton indicate an extensional environment related to the final closure of the Paleo-Asian Ocean. The Late Triassic A-Type rhyo- lites and bimodal magmatisms, together with the Late Triassic stable sedimentary rocks, in eastern Heilongjiang-Jilin provinces, reveal an extensional environment and passive continental margin setting, whereas the Early Jurassic calc-Alkaline magmatisms and its compositional variations, together with the coeval accretionary complex, reveal the onset of the Paleo- Pacific plate beneath the Euirasian continent.     

Crctaccous magmatism in NE China and adjacent areas and its relationship with the paleo-pacific plate subduction北大核心CSCD

This paper briefly reviewed the tectonic evolution history of the Paleo-Pacific Plate and tectonic regimes of NE China and adjacent areas. It also summarized the spatial and temporal association and petrogenesis of Cretaceous igneous rocks, proposing its relationship with Paleo-Pacific Plate subduction. The Erguna, Xing'an, Songliao, and Jiamusi blocks of NE China have significant igneous activities in 145-88 Ma, characterized by a spatial and temporal eastward migration and an association of I-And A-Type granites and asthenosphere-derived basaltic rocks, with minor OlB-Type basalts after ~ 88 Ma. The Cretaceous magmatism in the Wandashan-Sikhote-Alin and Vanbian area is also characterized by eastward migration but an association of intermediate to acidic rocks including high-Mg andesites, adakites, and I -And S-Type granites. Cretaceous magmatism in Erguna-Xing'an-Songliao-Jiangmusi and Wandashan-Sikhote-Alin-Yanbian areas was thought to be formed in back-Arc( intra-plate) and continental arc settings, respectively, and was controlled by roll-back of the Paleo- Pacific Plate. The Early Cretaceous continental arc accompanied with back-Arc extension was most likely to result from subduction of old oceanic lithosphere, which rarely occurred in the modem earth. The Late Cretaceous continental arc at NE China, characterized by back-Arc compression, was similar to the present Chilean continental margin.     

Petrogcncsis and gcodynaniics of late mesozoic granitoids in SE China: Tectonic model involving repeated slab-Advance-re treat of the paleo-pacific plate北大核心CSCD

During late Mesozoic times, extensive magmatism took place in SE China, forming widespread granitoids. Recently, we identify a series of Early Jurassic mafic rocks and A-Type granites in southern Jiangxi and western Fujian provinces. The Early Jurassic A-Type granites occur as a NE-Trending belt. By integrated previously published data, we find that there are other three A-Type granite belts in SE China, i.e., the Lite Jurassic, Early Cretaceous, and Late Cretaceous A-Type granite belts, respectively, all of which are NE-Trending, parallel to the present coastline. The Lite Jurassic belt is located further inland, to the west of the Early Jurassic belt, whereas the Early Cretaceous belt almost overlaps the Early Jurassic belt and the Lite Cretaceous belt is located at the coastal area of SE China. Integrated these observations, we propose a repeated slab-Advance-retreat model for the late Mesozoic magmatie evolution of SE China.     

Mesozoic subduction of the paleo-pacific plate along the eastern margin of the Xing-Meng orogenic belt北大核心CSCD

The eastern pari of the Xing-Meng Orogenic Belt( XMOB )consists of the Lesser Xing'an-Zhangguangcai Range Orogenic belt, the Bureya-Jiamusi-khanka Block and the Sikhote-Alin accretionary belt. This area is located between the Paleo-Asian oceanic and Paleo-Pacific tectonic regimes. Recent researches imply that the Paleo-Pacific subduction might have begun since early Permian and influenced the both sides of the Mudanjiang Fault during Triassic, which generated a N-S trending magmatic belt and accretionary complexes, such as the Heilongjiang Complex. In Late Jurassic to Early Cretaceous, some tectono st rati graph ic terranes were produced in Sikhote-Alin, which were then dismembered and migrated northwards in late Early Cretaceous by sinistral strike-slip faults. The continental margin parallel transportion weakened subduction-related magmatism in NE China which was under an extensional setting. However, in Lite Cretaceous, the Paleo-Pacific subduction was re-Activated in the eastern XMOB, which contributed to the magmatism in Sikhote-Alin.     

Revisiting the tectonic evolution of South China: interaction between the Rodinia superplume and plate subduction?

New field observations and zircon U‐Pb age data, combined with previous studies, are employed here to evaluate the process of assembly of the Yangtze and Cathaysia Blocks. We show that the process started from the west prior to 1.0 Ga and migrated eastward with the final amalgamation along the suture at around 830–820 Ma. During the period of 850–820 Ma, both the mantle plume which possibly started at 850 Ma and the north‐directed plate subduction along the southern margin of the Yangtze Block controlled the formation and closure of a back‐arc basin along the middle to eastern segment of the Yangtze Block, as well as the diverse and complex magmatic activities. The closure of the back‐arc basin and almost synchronous rift basin overlying the folded “basement” sequence mark the termination of subduction when the Rodinia plume exerted a dominant control on the evolution of the middle to late Neoproterozoic basin and the related magmatic pulses.     

Geological records of the pacific plate subduction in the northeast asian continental margin; An overview北大核心CSCD

The Paleo-Pacific Ocean was originated from the Panthalassa, which was a vast global ocean surrounding the Pangea Supercontinent. With the breakup of the Pangea and the closure of the Paleo-Tethyan Ocean, the Paleo-Pacific, Atlantic, Arctic and Indian Oceanic plates were in turn formed. About 190 Ma, the Pacific Plate was initially generated at the junction of the oceanic rift among the Izanagi, Karallon and Pheonix plates. Although most geologists considered a coherent genetic relationship between Meso-Cenozoic tectonic evolution of NE Asian continental margin and subduction of the Pacific Plate, there still exist some key problems. The main issues include; ( I ) the formation, motion trait and evolution paths of the Pacific Plate, especially the Izanagi Plate which subducted beneath the NE Asian continental margin at least since early Jurassic; ( 2) the beginning time of the Pacific Plate subduction; (3) the identification of subduction-related magmatisni; and(4) physical conditions of subduction processes. Based on the recent research progress of the above issues, this paper synthesizes that the subduction of the Paleo-Pacific Plate( or Izanagi Plate) beneath the NE Asian continent started in the early Jurassic. The subduction zone was gradually migrated eastward and constituted anarchipelagic oceanic framework with the involvement of old microblocks or foreign massifs.     

The genesis of pyroclasts and the mechanism of submarine eruption of Naozhou Island in Guangdong,South ChinaSCIEI北大核心CSCD

水下火山喷发作用机制不同于陆地环境喷发,随着水参与程度的变化,喷发机制趋向复杂。本文以雷琼火山群的湛江硇洲岛作为研究对象,聚焦浅海火山产物的判断依据和水下火山喷发机制。硇洲岛是我国最大的第四纪火山岛,其上的那晏湾剖面保留了完整的火山喷发堆积序列。在那晏湾剖面的凝灰岩中,主要有三类火山成因的大粒径原生碎屑(2-5mm):塑变熔岩碎屑、碎玄玻璃及玄武玻璃,推断为不同程度水-岩浆相互作用的产物,根据水的参与程度大致排序为:碎玄玻璃>玄武玻璃>塑变熔岩碎屑。通过对硇洲岛水-火山作用机制研究,发现水-岩浆混合质量比(Mwater/Mmelt)是控制爆炸强度和火山碎屑粒度的关键因素。火山喷发序列分析表明,硇洲岛的喷发过程总体可分为三期,早期是冰岛苏特塞式喷发的浅水环境蒸汽爆炸与“火喷泉”喷发;中期过渡转为“火喷泉”喷发,伴随陆上的射汽岩浆喷发;最终以岩浆溢流式喷发结束。     

Petrogenesis of Late Ordovician intrusive rocks in the West Kunlun orogenic belt: Constraints on the subduction process of the Proto-Tethys OceanSCIEI北大核心CSCD

西昆仑造山带发育有大量的早古生代岩浆岩,它们的形成与原特提斯洋俯冲-碰撞密切相关,然而,对于这些岩浆岩的岩石成因和形成的构造背景仍然存在较大的争议。本文对西昆仑造山带早古生代阿喀孜二长岩和赛图拉石英闪长岩岩体开展了详细的矿物学、锆石U-Pb年代学、全岩地球化学和Sr-Nd-Hf-O同位素研究,以探讨这些侵入岩的岩浆源区与成因,揭示原特提斯洋在这一时期的构造演化过程。这两个岩体的LA-ICP-MS锆石U-Pb年龄分别为456±2Ma和452±2Ma,指示它们形成于晚奥陶世。阿喀孜二长岩具有富碱(K_(2)O+Na_(2)O=10.5%~11.8%)、富钾(K_(2)O/Na_(2)O=1.20~1.44)特征,相对低MgO(0.89%~0.97%)、TiO_(2)(0.42%~0.45%)含量,富集Rb、Th、U等大离子亲石元素,且具有较高的全岩锆饱和温度(T_(Zr)=814~862℃),属于钾质碱性岩石。该岩体具有较高的(^(87)Sr/^(86)Sr)_(i)值(0.72057~0.72186),负的全岩ε_(Nd)(t)值(-5.1~-4.5)和负的锆石ε_(Hf)(t)值(-7.6~-3.4),以及较高的锆石δ^(18) O值(5.39‰~7.94‰),表明其源区可能为伸展环境下古老基性下地壳部分熔融。赛图拉石英闪长岩SiO_(2)含量为56.8%~58.6%,全碱(Na_(2)O+K_(2)O)含量为5.75%~6.39%,具有较低的铝饱和指数(A/CNK=0.85~0.89),相对高的MgO含量(2.93%~3.41%)以及Mg^(#)值(~45),为高钾钙碱性系列岩石。它们富集大离子亲石元素(Rb、Ba、Th)和亏损高场强元素(Nb、Ta、Ti),且具有微弱的Eu异常(δEu=0.72~0.77),类似于俯冲带岩浆岩地球化学特征。这些石英闪长岩具有相对高的(^(87)Sr/^(86)Sr)_(i)比值(0.71317~0.71322),负的全岩ε_(Nd)(t)值(-5.6~-5.1)和负的锆石ε_(Hf)(t)值(-7.8~-2.9),与同时期来源于富集地幔的基性岩同位素特征相似,表明赛图拉石英闪长岩岩浆可能是由俯冲板片流体交代的富集地幔楔部分熔融形成,并在岩浆演化的过程中经历了橄榄石、辉石、角闪石、磷灰石和Fe-Ti氧化物等矿物的分离结晶作用。结合同位素和数字模拟计算(Rhyolite-MELTS)结果表明,赛图拉石英闪长岩可能由塔里木克拉通南缘玄武质岩浆的分离结晶而成。综合前人研究,本文提出晚奥陶世阿喀孜二长岩和赛图拉石英闪长岩形成于原特提斯洋向北俯冲相关的活动大陆边缘环境,该时期原特提斯洋板片回撤,诱发软流圈地幔的上涌,从而产生了大量的弧岩浆岩。     

The Characteristics and Genetic Mechanism of Igneous Topazites in South China

Igneous topazites found recently in South China are closely associated with F-rich granites in time and space. They have a typical igneous porphyritic texture. The phenocrysts are topaz and quartz, while the groundmass consists mainly of prismatic or acicular topaz microlites and anhedral quartz. Compared with granites, topazites are rich in SiO2 (65.06%-81.12% ) and Al2O3 (13.01%-18.09%) but poor in MgO and Na2O and strongly peraluminous with A/NKC = 3.204-37.313. Geochemically, the rocks are evidently depleted in Sr and Ba, but enriched in Sn, W, Nb and F. The concentrations of Sn and partial W in the topazites are 1-2 orders of magnitude higher than the average of acid rocks. The F-riched granites related to the topazites in the area usually have much higher ISr (0.7103-0.7460) and δ18OQ‰ (9.5-14.24), but lower INdCT) (-4.8- 9.4). It suggests that the topazite is similar to S-type granites in genesis. Hydroxylated silicate melt inclusions, consisting of several grains of quartz and aqueous fluids,     

Types and Distribution of Geological Hazards in the South China Sea

Various types of geological hazards exist in the South China Sea. In dynamics sense, they can be categorized into 5 principal genetic types related to effects of hydraulic dynamics, gaseous activity, soil mechanics, gravity and tectonism, respectively. Integrated analyses indicate that the geological hazards associated with volcanoes, earthquakes and fractures are mainly distributed in tectonically active regions, whereas those resulting from mudflows, landslides and diapirs are usually concentrated in the region of slope, that shallow gas, high pressure gas pockets and soft intercalations are major potential geological hazards in the inner shelf, and that strong hydraulic dynamics, especially storm tide, is one of the major causes of geological hazards in the littoral areas. The geological hazards that occurred in the South China Sea are also characterized by periodicity, succession and, to a certain extent, unpredictability in addition to regionalization.     

Analysis of water vapor characteristics in snowstorm process on the northern slope of Tianshan Mountains北大核心CSCD

Based on the daily precipitation data of 16 national meteorological observation stations on the north⁃ ern slope of Tianshan Mountains from 2000 to 2020（September to April the following year）,28 blizzard weath⁃ er processes were screened out. Then NCEP/NCAR reanalysis data and HYSPLIT model were used to simulate backward tracking of the water vapor during the snowstorm,analysis of the circulation background of the snow⁃ storm process on the northern slope of the Tianshan Mountains,as well as the main sources and transport of wa⁃ ter vapor and its contribution to the snowstorm. The research showed that the snowstorm area in the northern slope of the Tianshan Mountains was located on the right side of the axis of the southwest jet at 300 hPa high,the southwest airflow in front of the West Siberia trough at 500 hPa,the front convergence of the exit area of the southwest jet at low level at 700 hPa,and the convergence area of water vapor flux divergence and the overlap near the ground cold front area. The water vapor affecting the blizzard on the northern slope of the Tianshan Mountains mainly came from the Mediterranean Sea,the Black Sea and its vicinity,Southwest Asia,Central Asia,the Atlantic Ocean and its coasts,as well as the 850 hPa water vapor in Europe and northern Xinjiang. The water vapor from North America and other places had a relatively small contribution to the blizzard;after each water vapor source reaches the key area with the westerly airflow,under suitable circulation conditions. It mainly entered the blizzard area along the westward（southwest）and the northwest paths. But there were some differences between the layers. Based on the above characteristics,the structure of the source and transport of wa⁃ ter vapor in the snowstorm process on the northern slope of the Tianshan Mountains was established and the char⁃ acteristics of vapor transport at various heights were revealed. © 2023 The Author(s).     

Composition characteristics and significance of spinel in the kinibcrlite from No. 30 Pipe in the wafangdian area. China北大核心CSCD

The spinel coexisting with diamonds is often used as indicator mineral to evaluate the diamond-bearing potentiality of the kimberlite. In order to figure out the characteristics of spinels in the No. 30 kimberlite pipe, this paper has carried out detailed morphological observation and electron probe analysis on the spinels. The results show that spinels are elliptical and sub-Angular grains, with large particle diameter( 5(H)-1000 μm). A small amount of spinels shows erosional embay men t shape. With high contents of Cr2O3( up to 66. 56% ) and MgO ( 8. 88% - 16. 68% ) , and low TiO2, contents (mostly相似文献   

The Permian mafic intrusive events in the northwestern margin of the Tarim Basin and their tectonic significanceSCIEI北大核心CSCD

塔里木大火成岩省是我国境内发现的两个重要的二叠纪大火成省之一,不仅有大规模的溢流相玄武岩喷发,还有复杂多样的侵入岩及其组合。以往的研究主要集中在二叠系等显生宙地层发育区,对于前寒武系等古老层系中是否存在二叠纪岩浆侵入未引起重视。本文通过野外地质调查,在阿克苏地区前寒武系中识别出数条侵入南华系的基性岩墙和较大规模侵入震旦系的基性岩床。岩墙、岩床与围岩之间均显示出典型的侵入接触关系,包括岩体内部结晶粗、边部结晶细的淬冷边结构、岩床顶底面显著的切层现象以及包裹围岩团块等;显微镜下观察表明,辉绿岩具有典型的辉绿结构和嵌晶含长结构。锆石U-Pb年代学结果表明,侵入下震旦统的辉绿岩岩床和侵入南华系的辉绿岩岩墙的侵位时代在误差范围内基本一致,约为290Ma。岩石地球化学特征表明,辉绿岩岩床具有与洋岛玄武岩(OIB)相似的稀土及微量元素配分模式,结合Sr-Nb-Pb同位素测试结果,认为它们来源于碳酸盐化的富集型岩石圈地幔部分熔融,而辉绿岩岩墙具有Nb、Ta、Zr、Hf等负异常的地球化学特征,可能来自曾被俯冲相关流体/熔体交代的岩石圈地幔源区。本文的早二叠世辉绿岩岩床和岩墙的形成时代、岩浆源区和岩浆演化...     

Comparative analysis of the cold surge characteristics over China before and after 2000北大核心CSCD

Based on the daily minimum temperature data in China from 1961 to 2018, using n-order polynomial fitting, sliding t-test, empirical Orthogonal Function analysis, Morlet wavelet transform and other methods, this paper reveals the temporal and spatial distribution characteristics of the number of cold surge (CS) day, CS frequency and CS intensity by time and region. The results are as follows. On a national level, the number of CS day, CS frequency, and CS intensity decreased from 1962 to 2000. Specifically, the trend of every element of CS has changed from a previous decrease trend to an increase trend, and the inflection point was around 2000. The CS activity occurred more frequently, became more strengthen, and last for longer time after 2000. There are obvious spatial differences in the number of CS days, CS frequency, CS intensity and their changing trends in China. The number of CS days and CS frequency reach the maximum value in northeast China and northern Inner Mongolia. Meanwhile, the CS intensity value is low in the southeast China and high in the northwest China, with the exception of southern Xinjiang. The changes in the number of CS day and the CS frequency are mainly manifested as the “Northeast, Southwest Reverse Pattern”, the CS intensity is mainly manifested as the “Uniform Change Pattern”. The number of CS day, CS frequency, and CS intensity did not change significantly after, but a significant transition point was detected in 1980. On a regional scale, from 1962 to 2018, the number of CS day, frequency and intensity of cold surge in all regions showed a decreasing trend, while they increased after 2000. In the northern and northeastern of China, mean of three elements of cold surge increased after 2000. The transition year was different in different regions. The transition year of three elements of cold surge in Northeast China were the earliest. Mean value of the number of CS day, CS frequency, and CS intensity have an oscillation period of 3~5 years in total China and all regions. In addition, the periodic oscillations of the number of CS day and CS frequency in all regions are basically the consistent. © 2022 Science Press (China).     

Petrogenesis and geological implications of the ca.2520Ma gabbroic intrusions in Wutai Mountain of the North China CratoSCIEI北大核心CSCD

本次研究从华北克拉通五台地区基底中识别出一套-25亿年的基性侵入体(主要为岩株)。其中,龙王堂岩株出露面积约5km2,侵入新太古界五台群台怀亚群,岩石类型主要为粗粒辉长岩。一条北东向基性岩墙侵入该岩株,岩墙边部发育明显的冷凝边,岩性为中粒辉长岩。LA-ICP-MS锆石U-Pb同位素年代学分析显示龙王堂粗粒辉长岩岩株形成时代为新太古代晚期(-2520Ma),中粒辉长岩岩墙形成时代为晚三叠世(-230Ma)。锆石原位Lu-Hf同位素分析显示龙王堂岩株具有正的εHf(t)值(4.75-7.95,峰值为6.3),其亏损地幔Hf模式年龄与岩浆年龄接近(tDM=2.64-2.53Ga),指示龙王堂粗粒辉长岩的原始岩浆来自于亏损地幔端元。全岩主微量元素地球化学分析显示龙王堂粗粒辉长岩表现出与洋岛玄武岩(OIB)相似的地球化学特征,并经历了橄榄石和单斜辉石等的结晶分异。结合前人研究成果,本文认为龙王堂新太古代晚期辉长岩岩株与区域上绿岩带(五台群)及同时期花岗侵入体形成时代接近,可能共同指示早期地幔直接分异形成陆壳物质的过程。这可能与俯冲构造体制不同,而与地幔柱作用产生的岩浆特征更为相似。     

The feature and tectonic setting of Dongqiao podiform chromitite in the central segment of the Bangong Lake-Nujiang suture zone in TibetSCIEI北大核心CSCD

早侏罗世东巧蛇绿岩位于班公湖-怒江缝合带(班怒带)东段,蕴含较为丰富的豆荚状铬铁矿资源。东巧地幔橄榄岩主体由方辉橄榄岩组成,铬铁矿赋存在其内部的纯橄岩脉中。方辉橄榄岩和纯橄岩均显示出弧前橄榄岩的特征。方辉橄榄岩中橄榄石的Fo值为89.8~92.2,斜方辉石的和单斜辉石的Mg^(#)值分别变化于89.7~92.0和92.7~95.1,铬尖晶石的Cr^(#)值(Cr^(#)=100×Cr/(Cr+Al))为60.8~75.9;纯橄岩中橄榄石的Fo值为91.7~92.5,斜方辉石Mg^(#)值变化于91.7~92.1,单斜辉石的Mg^(#)值变化于94.0~94.6,铬尖晶石的Cr^(#)值为69.0~83.1。铬铁矿主要呈致密块状和浸染状构造,其中铬尖晶石的矿物包裹体有橄榄石、斜方辉石、单斜辉石、角闪石和铂族矿物等。矿石中的铬尖晶石与橄榄岩中的铬尖晶石相比,具有较高的Cr^(#)值(72.5~86.9)和Mg^(#)值(52.8~70.5),较低的Al_(2)O_(3)(6.25%~13.6%)、TiO_(2)(0.06%~0.16%)和Zn(518×10^(-6)~714×10^(-6)),属于高铬型铬铁矿,平衡熔体与玻安质熔体有亲缘性。方辉橄榄岩中铂族元素(PGE)总含量(14.01×10^(-9)~32.81×10^(-9))近似于原始地幔,IPGE(Os、Ir和Ru)/PPGE(Rh、Pt和Pd)的比值均大于1;纯橄岩的PGE总量(13.36×10^(-9)~16.08×10^(-9))略低于原始地幔,IPGE和PPGE富集程度近似;铬铁矿的铂族元素总量(108.4×10^(-9)~645.7×10^(-9))远远高于原始地幔和地幔橄榄岩中PGE的含量,且IPGE以及Rh相对原始地幔富集,而Pt和Pd相对亏损,具明显右倾特征的配分模式,指示东巧地幔橄榄岩和铬铁矿形成过程经历了熔体抽取和交代作用。通过与全球典型豆荚状铬铁矿矿床的特征对比,认为班怒带的蛇绿岩应该有良好的铬铁矿成矿背景。     

Provenance and tectonic setting of the Gudongjing Group in Beishan OrogenSCIEI北大核心CSCD

增生造山带中陆源碎屑岩物源区特征的研究可为解剖造山带结构甚至大陆地壳的形成和演化提供关键证据。北山造山带中部的古硐井群被认为是前寒武纪稳定沉积盖层,是北山造山带存在微陆块的重要依据。本文围绕古硐井群的物源区特征,进行了碎屑颗粒和重矿物统计、全岩主微量元素地球化学分析、碎屑锆石U-Pb年代学和Hf同位素测试。古硐井群碎屑岩的碎屑颗粒多呈棱角状,主要为石英、长石,同时含大量硅质岩碎屑和一定数量的火山岩碎屑;重矿物组成以褐铁矿、锆石、白钛石、尖晶石为主,角闪石、电气石、辉石次之,暗示物源区可能存在蛇绿岩、增生杂岩。全岩主量元素以高硅、高铝、富碱、低锰为特征,结合REE、Cr、Co、Sc和Th等惰性元素含量特征共同指示了长英质的物源区。最年轻的碎屑锆石年龄为443.9±13Ma,表明古硐井群最大沉积时限为晚奥陶世。碎屑锆石的年龄高度集中于470Ma附近,且该区间锆石ε_Hf(t)值多为正值,指示物源区存在大量新生地壳物质。本文推测古硐井群可能形成于增生楔楔顶盆地;研究结果支持北山造山带是古生代持续增生造山的产物这一认识。     

Transport process of radionuclides in the East China Sea

Settling particles were collected from six stations at the Okinawa Trough and the East China Sea continental margin. Activities of U, Th, Pu isotopes and ^210Pb were determined for the particles to elucidate their transport processes. Surface sediment samples were also analyzed for their isotopes. There was a tendency for ^210Pb activities to increase almost linearly with depth from 72 m on the continental shelf edge to 1019 m in the Okinawa Trough. Increasing ^210Pb activities in settling particles with depth on the continental margin may be attributable to enhanced ^210Pb scavenging by particles and removal near the front. There also was a clear tendency for total mass fluxes and the radionuclide fluxes to increase with depth, with an especially large increase near the bottom. The ratio of the observed ^210Pb flux to the ^210Pb deficiency flux in the near-bottom traps ranged between 8.9 and 46. These high values show a strong ^210Pb excess which would be attributable to large advective import to the near-bottom and resuspended particles that have settled through the water column but have not been incorporated into the sediments. High variability of radionuclide fluxes occurred in very short time periods. Activities of ^238U, ^232Th, ^230Th, ^228Th, ^210Pb and ^239Pu＋^240Pu in settling particles were significantly higher than those in the underlying surface sediments.     

Late Permian to Early Triassic subduction and retreating of the Paleopacific slab: Constraints from continental arc magmatism in Hainan IslandSCIEI北大核心CSCD

海南岛大规模二叠-三叠纪侵入岩的形成是与古特提斯洋有关,还是与古太平洋俯冲闭合有关还存在巨大争议。本文对琼中金波两处辉绿岩脉及其围岩花岗岩的研究显示,露头1辉绿岩脉的锆石U-Pb年龄为245.4±3.8Ma,TiO_(2)含量(1.07%~1.18%)低,而MgO(8.60%~9.41%)和Mg^(#)值(62.31~65.02)较高,为钙碱性系列,球粒陨石和原始地幔标准化配分曲线中具有明显的Eu、Nb、Ta、Ti和Ba负异常,以及显著Th、U、Zr、Rb和Pb等正异常,(^(87)Sr/^(86)Sr)_(i)=0.707138~0.712797,(^(143) Nd/^(144)Nd)_(i)=0.511884~0.511965,ε_(Nd)(t)值为-7.01~-8.58,指示其形成于大陆岛弧环境。相比之下,露头2辉绿岩锆石U-Pb年龄为242.8±3.1Ma,但其TiO_(2)(2.65%~3.06%)含量较高,而MgO(4.24%~5.39%)和Mg^(#)值(40.09~45.86)较低,具有Eu、Rb、Pb、Nb、Ta和Ti弱正异常和Th负异常,(^(87)Sr/^(86)Sr)_(i)=0.690244~0.717031,(^(143) Nd/^(144)Nd)_(i)=0.512886~0.512915,ε_(Nd)(t)值为+6.41~+7.93,具有板内玄武岩的特征,指示其形成于板内裂解环境。辉绿岩脉围岩二长花岗岩的锆石U-Pb年龄为255.3±3.0Ma和255.7±3.2Ma,含少量角闪石和黑云母,具有较高的SiO_(2)(71.62%~73.72%)、Na_(2)O+K_(2)O(6.60%~9.17%)和Al_(2)O_(3)(平均14.88%)含量,A/CNK值(0.97~1.03)较低,亏损Nb、Ta、Ti、Sr和Ba,富集Rb、Th、U和Pb,为高分异I型岛弧花岗岩。总的来看,二长花岗岩和辉绿岩形成于大陆岛弧挤压向伸展过渡的构造环境。对比二叠-三叠纪侵入岩体的走向、碰撞前-同碰撞-碰撞后岩浆岩的时代以及榴辉岩的变质年龄等,发现海南岛侵入岩与哀牢山-松马造山带明显不同,而与日本和朝鲜半岛的岛弧岩浆岩类似,由此我们认为海南岛大规模晚二叠-早三叠世岩浆岩为古太平洋板片向欧亚板块俯冲后撤的产物,后撤过程受到古特提斯俯冲板片的影响。