Tracing a late Mesozoic magmatic arc along the Southeast Asian margin from the granitoids drilled from the northern South China Sea

Abstract

The granitoid suites encountered by drilling in the northern South China Sea (SCS) remain important for understanding the evolution of the late Mesozoic Southeast Asian continental margin. They comprise a range of rock types including diorite, tonalite, granodiorite, monzogranite and syenogranite with SiO₂ spanning 56.4–76.8%. Newly acquired secondary ion mass spectrometry (SIMS) U–Pb ages of samples from 14 boreholes indicate two key magmatic episodes: Late Jurassic (161.6–148.2 Ma) and Early Cretaceous (136.5–101.7 Ma). Jurassic magmatism probably began in late Middle Jurassic time, documented by the dates of inherited zircons. The granitoids are dominated by metaluminous to weakly peraluminous I-type granites, are transitional between magnesian and ferroan, and encompass calc-alkaline, high-K calc-alkaline, and shoshonitic series. The geochemical signatures suggest that these granitoids were mostly generated in a normal continental arc environment. Notable features of the I-type samples are well-defined negative Nb–Ta–Ti anomalies typical of arc-related magmas. Taken together, the late Mesozoic arc granites of the SCS, the accretionary wedge of the Palawan terrane to the southeast, and the zone of lithospheric extension north of the SCS throughout Southeast China, define a southeast-to-northwest trench-arc-backarc architecture for the late Mesozoic Southeast Asian continental margin whose geodynamic setting is related to subduction of the Palaeo-Pacific slab beneath the Asian continent. Two key subduction episodes are recognized, one in Late Jurassic and the other in Early Cretaceous time.     

晚中生代东亚多板块汇聚与大陆构造体系的发展

东亚大陆原型形成于三叠纪印支造山运动旋回,其周邻环绕的三大洋（古太平洋、蒙古-鄂霍茨克洋、中特提斯洋）于早侏罗世初期几乎同时向东亚大陆俯冲,开启了东亚多板块汇聚历史。文章通过总结东亚大陆晚中生代构造变形和构造岩浆事件的新近研究成果,简述了东亚多板块汇聚产生的三个陆缘汇聚构造系统（北部蒙古-鄂霍次克碰撞造山带、东部与俯冲有关的增生造山系统、西南部班公湖-怒江缝合构造带）、陆内汇聚构造变形体系和大陆伸展构造体系。在此基础上,重新构建了东亚多板块汇聚大陆构造-岩浆演化的时间框架,将其划分为三个阶段:早侏罗世（200~170 Ma）周邻大洋板块初始俯冲阶段和陆缘裂解事件,中晚侏罗世-早白垩世早期（170~135 Ma）周邻陆缘碰撞造山或俯冲增生造山作用、陆内再生造山作用和汇聚构造体系的形成;中晚白垩世（135~80 Ma）大陆岩石圈的减薄作用和大陆伸展构造体系的发育。研究认为,晚中生代东亚多板块汇聚在时空上的有序演化和深浅构造的复合叠加,不仅产生了东亚大陆复杂的陆缘和陆内构造体系,同时控制了中国东部燕山期爆发式岩浆-成矿作用,也使东亚构造地貌发生东西翘变,早期陆缘汇聚产生的东部高原因晚期大陆岩石圈的减薄和伸展而垮塌。东亚大陆构造体系的形成和演化与联合古大陆的裂解同步,晚中生代东亚多板块汇聚完成了从东亚到欧亚大陆的演替,以东亚大陆为核心的多板块汇聚格局一直延续至新生代,可能成为未来超大陆形成的起点。      

Tectonic nature of the NE Asian continental margin during the Late Jurassic–Early Cretaceous: constraints from the geochronology and geochemistry of igneous rocks in the NE North China Craton

ABSTRACT

This paper presents geochronological, geochemical, and zircon Hf–O isotope data for late Mesozoic intrusive rocks from the northeastern North China Craton (NCC), with the aim of constraining the late Mesozoic tectonic nature of the NE Asian continental margin. U–Pb zircon data indicate that the Late Mesozoic magmatism in the northeastern NCC can be subdivided into two stages: Late Jurassic (161 ? 156 Ma) and Early Cretaceous (125 ? 120 Ma). Late Jurassic magmatism consists mainly of monzogranites. These monzogranites display high Sr/Y ratios and the tetrad effect in their REE, respectively, and have negative ε_Hf(t) values (?22.6 to ?15.8). The former indicates that the primary magma was generated by partial melting of thickened NCC lower crust, the latter suggests that the monzogranites were crystallized from highly fractionated magma, with the primary magma derived from partial melting of lower continental crust. Combined with the spatial distribution and rock associations of the Late Jurassic granitoids, we conclude that the Late Jurassic magmatism in the eastern NCC formed in a compressional environment related to oblique subduction of the Paleo-Pacific Plate beneath the Eurasia. The Early Cretaceous magmatism consists mainly of granitoids and quartz diorites. The quartz diorites formed by mixing of melts derived from the mantle and lower crust. The coeval granitoids are classified as high-K calc-alkaline and metaluminous to weakly peraluminous series. Some of the granitoids are similar to A-type granites. The granitoid ε_Hf(t) values and T_DM2 range from ?14.3 to ?1.4 and 2089 to 1274 Ma, respectively. These values indicate that their primary magma was derived from partial melting of lower crustal material of the NCC, but with a contribution of mantle-derived material. We therefore conclude that Early Cretaceous magmatism in the northeastern NCC occurred in an extensional environment related to westward subduction of the Paleo-Pacific Plate beneath Eurasia.     

东亚大地构造发展的重要转折

本文根据现实主义原则和现代地质学理论,分析综合了东亚构造地质、古地磁、古生物地理、地质年代学等方面的一些最新研究成果,提出东亚古亚洲洋构造系和古特堤斯构造系向环太平洋主动陆缘的转变最终出现在中侏罗世,著名的燕山运动正是这一重要构造转折的产物。     

燕山运动和中国大陆晚中生代的活化

燕山运动可分为2类:一是印支期拼合大陆外侧的新特提斯洋消减及嗣后的碰撞引起的内硅镁质的造山运动,形成滇藏、东南沿海、苏鲁和蒙古-鄂霍次克造山带;二是拼合大陆内部因古缝合线或古深断裂活化发生的内硅铝质的(陆内的)造山运动,前者如川黔湘-鄂南、湘赣闽和阴山-燕山褶皱-冲断系,后者如川南-滇东和中扬子褶皱-冲断系及江南冲断-推覆带.文章剖析了中国大陆晚中生代活化的时空特征,指出陆内造山带及冲断带的发育受制于东亚燕山期山系的形成,简述了研究构造-岩浆活化对内生矿产和油气资源评价的指导意义.     

中国东北地区中生代构造体制的转变:来自火山岩时空分布与岩石组合的制约

东北地区中生代经历了蒙古-鄂霍茨克构造体系向太平洋构造体系的转换,形成了不同期次火山活动。本文归纳总结了露头区与覆盖区中生代火山岩的年代学、空间分布、岩石组合以及地球化学特征,揭示了两个构造域的时空分布范围。该区火山岩锆石U-Pb年龄统计结果表明中生代存在五期火山活动:早-中侏罗世(190~160Ma)、晚侏罗世(160~145Ma)、早白垩世早期(145~120Ma)、早白垩世晚期(120~100Ma)、晚白垩世早期(100~90Ma)。早-中侏罗世火山岩分布较少,火山岩仅分布在大兴安岭西部满洲里地区和东部张广才岭以及南侧辽宁北票-朝阳地区,火山岩属于高钾钙碱性系列,为蒙古-鄂霍茨克海闭合和法拉隆板块双俯冲作用的产物。晚侏罗世东北地区火山活动明显增强,主要分布在大兴安岭地区,张广才岭以及小兴安岭也有少量分布。西部大兴安岭地区以粗面安山岩、粗面岩为主,属于同碰撞造山成因,为蒙古-鄂霍茨克海闭合造山环境产物。东部以中酸性、酸性岩为主,为法拉隆板块背离欧亚大陆,岩石圈伸展引起的壳源物质熔融产物。早白垩世早期火山活动最为强烈,火山岩主要分布在大兴安岭地区。岩性以高钾钙碱性系列的粗面玄武安山岩、粗面安山岩、安山岩、粗面岩为主,为蒙古-鄂霍茨克海闭合造山后伸展环境产物。早白垩世晚期火山岩主要分布在松辽盆地内部。火山岩以中酸性岩为主,属于中钾-高钾钙碱性系列,为伊泽奈崎板块俯冲引起的弧后拉张,软流圈上涌导致年轻地壳熔融的产物。晚白垩世早期火山岩仅分布在小兴安岭及吉林、黑龙江省东部地区。火山岩为一套玄武岩、玄武安山岩、安山岩和英安岩组合,属于中钾钙碱性系列,是伊泽奈崎-库拉板块高角度俯冲的大陆边缘岩浆活动产物。东北地区中生代不同期次火山岩记录了蒙古-鄂霍茨克构造域向太平洋构造域转换过程及其时空影响范围。     

中国大地构造演化与金矿成矿作用

本文讨论了中国大地构造演化对金矿成矿作用的制约。认为中国华北克拉通化时间较晚,变形变质作用强烈,显生宙又遭受多次板块运动的叠加改造,有利于前寒武纪金矿的形成和保存。显生宙以来在中国古陆块周边发生了四次大的板块碰撞或俯冲造山运动,即塔里木－华北克拉通北缘及其以北地区的海西期造山运动;昆仑－祁连－秦岭地区的海西－印支期造山运动;西南地区印支－喜山期的喜马拉雅造山运动,东部大兴安岭－太行山－豫西－鄂西＝     

Petrogenesis of Early Cretaceous low-Mg adakitic rocks along the southernmost margin of the North China Craton: implications for late Mesozoic crustal evolution

This article reports systematic zircon U–Pb dating, whole-rock geochemistry, and Sr–Nd isotopic data for the Early Cretaceous Jialou granitoids along the southernmost margin of the North China Craton (NCC), adjacent to the Tongbai Orogen. These results will provide significant constrains on the crustal evolution of the southern margin of the NCC. Zircon U–Pb analyses, using laser ablation–multicollector–inductively coupled plasma–mass spectrometry, indicate that the Jialou granitoids were emplaced at ~130 Ma. The granitoids have high SiO₂, K₂O, Al₂O₃, Sr, and Ba contents, high Sr/Y and (La/Yb)N ratios, and low concentrations of MgO, Y, and heavy rare earth elements, indicating a low-Mg adakitic affinity. They have relatively high initial ⁸⁷Sr/⁸⁶Sr ratios (0.707464–0.708190) and negative εNd(t) values (–11.8 to –15.2), similar to those of the Palaeoproterozoic lower crust in the NCC. These geochemical and isotopic features indicate that the Jialou low-Mg adakitic rocks were derived by partial melting of mafic Palaeoproterozoic lower crust of the NCC at >50 km depth, leaving behind a garnet amphibolite residue. The petrogenesis of the Jialou low-Mg adakitic rocks, plus the petrogenesis of Mesozoic granitoids and lower crustal xenoliths entrained in the Late Jurassic Xinyang volcaniclastic diatreme, suggests that the continental crust along the southern margin of the NCC was thickened during the Middle Jurassic to Early Cretaceous, but thinned after 130 Ma. We propose that crustal thickening was caused by a late Middle Jurassic to Early Cretaceous intra-continental orogeny, rather than continent–continent collision between the NCC and the Yangtze Craton. We also suggest that crustal thinning and Early Cretaceous magmatism were related to subduction of the palaeo-Pacific plate, rather than post-orogenic collapse of the Qinling–Tongbai–Dabie Orogen.     

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.     

华南中生代同熔系列花岗岩类的Nd-Sr同位素特征及成因讨论

本文讨论了华南20个同熔系列花岗岩类的Nd-Sr同位素组成。根据样品的同位素组成及其在￠Nd-T,(87Sr/86Sr)i-T和￠Nd-￠Sr图上的分布特征,认为这些同熔系列花岗岩类是华南上地壳端员和亏损地幔端员按一定比例混合的产物。利用简单二元混合方程计算了这些花岗岩体的壳幔混合比例。根据产出的大地构造环境和物质来源,华南同熔系列花岗岩类可划分为三种类型:大陆边缘型,大陆内部型和断裂拗陷带型。     

Spatial–temporal relationships of Mesozoic volcanic rocks in NE China: Constraints on tectonic overprinting and transformations between multiple tectonic regimes

LA-ICP-MS zircon U–Pb ages and geochemical data are presented for the Mesozoic volcanic rocks in northeast China, with the aim of determining the tectonic settings of the volcanism and constraining the timing of the overprinting and transformations between the Paleo-Asian Ocean, Mongol–Okhotsk, and circum-Pacific tectonic regimes. The new ages, together with other available age data from the literature, indicate that Mesozoic volcanism in NE China can be subdivided into six episodes: Late Triassic (228–201 Ma), Early–Middle Jurassic (190–173 Ma), Middle–Late Jurassic (166–155 Ma), early Early Cretaceous (145–138 Ma), late Early Cretaceous (133–106 Ma), and Late Cretaceous (97–88 Ma). The Late Triassic volcanic rocks occur in the Lesser Xing’an–Zhangguangcai Ranges, where the volcanic rocks are bimodal, and in the eastern Heilongjiang–Jilin provinces where the volcanics are A-type rhyolites, implying that they formed in an extensional environment after the final closure of the Paleo-Asian Ocean. The Early–Middle Jurassic (190–173 Ma) volcanic rocks, both in the Erguna Massif and the eastern Heilongjiang–Jilin provinces, belong chemically to the calc-alkaline series, implying an active continental margin setting. The volcanics in the Erguna Massif are related to the subduction of the Mongol–Okhotsk oceanic plate beneath the Massif, and those in the eastern Jilin–Heilongjiang provinces are related to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent. The coeval bimodal volcanic rocks in the Lesser Xing’an–Zhangguangcai Ranges were probably formed under an extensional environment similar to a backarc setting of double-direction subduction. Volcanic rocks of Middle–Late Jurassic (155–166 Ma) and early Early Cretaceous (145–138 Ma) age only occur in the Great Xing’an Range and the northern Hebei and western Liaoning provinces (limited to the west of the Songliao Basin), and they belong chemically to high-K calc-alkaline series and A-type rhyolites, respectively. Combined with the regional unconformity and thrust structures in the northern Hebei and western Liaoning provinces, we conclude that these volcanics formed during a collapse or delamination of a thickened continental crust related to the evolution of the Mongol–Okhotsk suture belt. The late Early Cretaceous volcanic rocks, widely distributed in NE China, belong chemically to a low- to medium-K calc-alkaline series in the eastern Heilongjiang–Jilin provinces (i.e., the Eurasian continental margin), and to a bimodal volcanic rock association within both the Songliao Basin and the Great Xing’an Range. The volcanics in the eastern Heilongjiang–Jilin provinces formed in an active continental margin setting related to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent, and the bimodal volcanics formed under an extensional environment related either to a backarc setting or to delamination of a thickened crust, or both. Late Cretaceous volcanics, limited to the eastern Heilongjiang–Jilin provinces and the eastern North China Craton (NCC), consist of calc-alkaline rocks in the eastern Heilongjiang–Jilin provinces and alkaline basalts in the eastern NCC, suggesting that the former originated during subduction of the Paleo-Pacific Plate beneath the Eurasian continent, whereas the latter formed in an extensional environment similar to a backarc setting. Taking all this into account, we conclude that (1) the transformation from the Paleo-Asian Ocean regime to the circum-Pacific tectonic regime happened during the Late Triassic to Early Jurassic; (2) the effect of the Mongol–Okhotsk suture belt on NE China was mainly in the Early Jurassic, Middle–Late Jurassic, and early Early Cretaceous; and (3) the late Early Cretaceous and Late Cretaceous volcanics can be attributed to the subduction of the Paleo-Pacific Plate beneath the Eurasian continent.     

下扬子独立地块与中生代改造型残留盆地

下扬子地块在古纬度、火山岩和花岗岩时空发育、区域成矿专属性、沉积建造和构造变形等方面具独特性,与扬子地块有显著差异,是一个晚古生代——中生代早期的独立地块。受燕山期苏鲁板间造山作用影响,下扬子地块直至燕山中期才“楔入”在印支期已拼合的扬子与华北地块,从而演化成独特的下扬子改造型残留叠合盆地。这种改造型叠合盆地的基本特点是:晚印支-早燕山同造山期前陆盆地沉积层和上叠的中燕山期陆相沉积层遭受大量剥蚀,并与古生-中生界海相沉积层一起被卷入强烈的多期次的燕山造山运动,晚白垩世——古近纪又强烈反转成为断陷盆地,形成鲜明的上部地壳的双层结构。这是造成下扬子地区海相古生-中生界油气地质勘探高复杂性、高难度性和高风险性的根本原因,也造就了下扬子区海相烃源岩的二次生烃和晚期成藏的优势。     

似新华夏式伸展盆海系的基本特征及其形成演化的力学机制

晚中生代(白垩纪)以来,中国东部及西太平洋大陆边缘发育一系列NNE、NE乃至NEE向(与纬向构造联合)的巨型右行张扭性断陷(地堑、半地堑)在平面上组成平行雁列的多字型构造,其深部发育同走向的上地幔隆起和基底拆离,地表常出现变质核杂岩和大型低缓倾角的伸展剥离断层,它主要是东亚及西太平洋大陆边缘陆缘扩张的产物,其地球动力学过程为晚燕山期以来的后造山期的大陆隆升和水平侧向伸展以及晚白垩世末一早第三纪、45Ma以来的印度板块与欧亚板块碰撞所产生的碰撞效应。      

俄罗斯远东地区晚中生代花岗岩类的时空分布 及其地质意义

在俄罗斯远东地区晚中生代花岗岩类年龄和相关地球化学数据的基础上,初步建立了该区晚中生代花岗岩类的年代学格架：大致以145Ma为界,分为侏罗纪(178~151Ma)和早白垩世(142~122Ma)2期。侏罗纪的花岗岩类主要为花岗岩－花岗闪长岩－石英二长岩组合,总体上为准铝质—强过铝质高钾钙碱性系列;早白垩世的花岗岩类主要为花岗岩－石英闪长岩－石英二长岩组合,主要为过铝质钙碱性—高钾钙碱性系列—钾玄岩系列。2期花岗岩稀土元素配分曲线均呈右倾型,重稀土元素曲线较平坦,都富集大离子亲石元素(如U、K)和轻稀土元素。与中国东北地区晚中生代花岗岩类对比,中国东北地区总体以兴安岭为中心,中间为早白垩世的花岗岩类,两侧为侏罗纪花岗岩类对称分布。境内外的侏罗纪花岗岩类构造背景不同,其分布与鄂霍次克洋和太平洋板块的俯冲有关,早白垩世花岗岩类可能形成于鄂霍次克带挤压造山后的伸展垮塌和太平洋板块的俯冲弧后伸展阶段。     

东北亚南区中—新生代大地构造轮廓

东北亚南区是西太平洋构造带、北美大陆板块(或鄂霍次克板块)与中亚造山带、中朝、扬子板块等交汇部位,在泛大陆(Pangaea)拼合、裂解的宏观背景下中—新生代以来经历了多次构造事件的叠加,构造面貌比较复杂。包括朝鲜半岛在内,许多中—小型陆块的构造归属长期以来一直存在着争议,笔者根据近年来SHRIMP测年信息、生物古地理和相邻构造带的延伸,认为朝鲜半岛、日本飞驒—隐歧地块古生代应该归属于中朝板块;萨哈林岛—日本北海道归属于北美板块;布列亚—佳木斯—兴凯地块古生代归属于西伯利亚板块。20世纪80年代以来绝大多数学者都把本区中生代以来的构造发展同西太平洋壳向东北亚大陆的俯冲联系在一起,然而近年相当多学者从东亚大陆本身的陆-陆碰撞-挤出-扩张来寻求晚中生代以来地壳-岩石圈减薄的地球动力学原因。本区经历了晚海西—印支期古亚洲洋消亡和晚燕山期(晚侏罗—早白垩世)南北大陆的陆-陆碰撞汇聚两个时期,使中亚造山带扩展到中朝板块北缘的阴山—燕山地区,使地壳增厚,形成与现今青藏高原类似的高原地貌;早白垩世晚期—古近纪本区地壳-岩石圈减薄,出现大规模伸展型盆-山结构,郯—庐断裂北延,出现左行走滑错移,东部陆缘俯冲增生、太平洋板块运动转向,引起的挤压变形,以及古近纪晚期大面积准平原化,黑龙江、吉林古近纪隆起边缘断陷盆地中的许多重、贵金属砂矿矿床也多半形成在此期;新近纪本区地壳-岩石圈进一步减薄,大陆裂谷扩展为东亚—西太平洋裂谷带,形成NNE向伸展型盆-山结构,日本海打开,西太平洋岛弧形成,早更新世末初步形成地形阶梯,晚更新世以后才形成了控制着地热与水系分布的现今地貌格架。     

浅议沂沭断裂系及其邻区金矿成矿作用演化

沂沭断裂系在晚侏罗世－早白垩世早期期间的挤压作用造成了胶东地区钙碱性岩浆的侵入，同时形成了相应的金矿化。早白垩世期间沂沭断裂系及其邻区进入拉张应力环境，在形成胶莱走滑拉分盆地的过程中，于盆地边缘产生层滑动断层带，造成层间滑动角砾岩型金矿的形成。燕山中期板块俯冲运动和地幔上涌等因素引起的区域性拉张作用使沂沭断裂继续向下深切张裂，向裂谷性质演化，造成沂南、临沂等地区较大规模中性偏碱性次火山岩型小岩体的侵入和火山喷发，在火山机构内或围绕次火山岩小岩体形成与中性偏碱性次火山岩有关的次火山岩型金矿化。沂沭断裂系及其邻区中生代构造岩浆活动与其相应金矿的形成均是与古太平洋各板块与欧亚大陆板块间的相互作用的结果。     

华南花岗岩物源成因特征与陆壳演化

华南不同时代的花岗岩按物质来源及成因可划分为:幔源(分异)系列:幔-壳混源(同熔)系列;壳源改造(重熔)系列和幔-壳混源碱性系列等四个不同的系列,简要阐述了划分四类系列的岩石学、地球化学的依据。侧重根据Sm-Nd、Rb-Sr同位素成分,以二元混合模型计算了花岗岩源区物质组成中,上壳和亏损地幔组份各占的比例。在此基础上探讨了不同物源成因系列花岗岩形成与华南陆壳演化的内在联系:东安、雪峰旋回褶皱系阶段花岗岩物源成因类型比较多样,有幔源(分异)系列、不成熟壳源、成熟壳源改造(重熔)系列等;加里东,海西期以陆壳改造(重熔)系列为主;印支、燕山期活化区(地洼)阶段,在地幔活化激发下,中国东部陆缘形成幔—壳混源(同熔)系列花岗岩和相应的火山岩;但沿内部断裂带,在壳下地幔热传输及构造作用下引起陆壳重熔,形成属于壳源改造(重熔)系列花岗岩。同位素的研究证明了:地洼阶段的构造-岩浆活动主要动力是来自壳下地幔的活化。     

东南大陆边缘早侏罗世火成岩特征及其构造意义

东南大陆边缘早侏罗世火成岩主要呈双峰式火山岩、基性超基性杂岩体及A型花岗岩等形态产出。本文运用岩石学探针技术,通过早侏罗世火成岩岩石学与地球化学研究,并与晚中生代火成岩作对比,提出早侏罗世火成岩的形成与南岭东段近EW向张性断裂活动有关,标志着印支挤压造山的结束;之后东南大陆进入晚中生代NE向活动大陆边缘俯冲造山阶段,经历了挤压造山—剪切拉张过程,并在晚白垩世末期进入又一轮后造山拉张裂解阶段,即中生代时东南大陆边缘经历了早中生代(三叠纪—早侏罗世)和晚中生代(中侏罗世—晚白垩世)两期造山事件,其中早侏罗世的区域拉张作用是特提斯构造域向滨太平洋构造域转换的前奏,构造域转换可能始于中侏罗世(165Ma)。     

中生代东亚大陆边缘构造演化

摘　要　根据东亚陆缘增生带生物古地理、放射虫时代研究的进展并结合同位素年代及东亚 地区火山活动、构造演化探讨了中生代东亚大陆与古太平洋板块之间的运动学关系及俯冲带 后退特征。中、晚三叠世那丹哈达岭、美浓等地体还位于北纬１２°以内及赤道附近,晚侏罗世 到达中高纬度。东亚活动大陆边缘开始于中侏罗世末,在此之前属转换大陆边缘。洋壳板块 向大陆下俯冲之后,由于地体拼贴引起俯冲带快速、长距离后退。     

Changes of Late Mesozoic Tectonic Regimes around the Ordos Basin (North China) and their Geodynamic Implications

A synthesis is given in this paper on late Mesozoic deformation pattern in the zones around the Ordos Basin based on lithostratigraphic and structural analyses. A relative chronology of the late Mesozoic tectonic stress evolution was established from the field analyses of fault kinematics and constrained by stratigraphic contact relationships. The results show alternation of tectonic compressional and extensional regimes. The Ordos Basin and its surroundings were in weak N-S to NNE-SSW extension during the Early to Middle Jurassic, which reactivated E-W-trending basement fractures. The tectonic regime changed to a multi-directional compressional one during the Late Jurassic, which resulted in crustal shortening deformation along the marginal zones of the Ordos Basin. Then it changed to an extensional one during the Early Cretaceous, which rifted the western, northwestern and southeastern margins of the Ordos Basin. A NW-SE compression occurred during the Late Cretaceous and caused the termination of sedimentation and uplift of the Ordos Basin. This phased evolution of the late Mesozoic tectonic stress regimes and associated deformation pattern around the Ordos Basin best records the changes in regional geodynamic settings in East Asia, from the Early to Middle Jurassic post-orogenic extension following the Triassic collision between the North and South China Blocks, to the Late Jurassic multi-directional compressions produced by synchronous convergence of the three plates (the Siberian Plate to the north, Paleo-Pacific Plate to the east and Lhasa Block to the west) towards the East Asian continent. Early Cretaceous extension might be the response to collapse and lithospheric thinning of the North China Craton.