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1.
The eastern segment of Central Asian Orogenic Belt underwent not only a long evolution history related to the Paleo-Asian Ocean during Paleozoic but also the tectonic overprinting by the westward subduction of Paleo-Pacific Ocean crust during Mesozoic. When the subduction of Paleo-Pacific Ocean crust started has been long debated issue for understanding the tectonic evolution of the eastern Asian continental margin. The eastern margin of the Jimusi Block (Wandashan Terrane) preserved complete records for the accretionary process of the westward subduction of Paleo-Pacific Ocean crust. Comprising the Yuejinshan Complex and Raohe Accretionary Complex (RAC), the Wandashan Terrane is located in the eastern margin of Jiamusi Block, NE China, and is considered to be an accretionary wedge of the westward subducting oceanic crust. To reconstruct the marginal accretion processes of the Jiamusi Block, the structural deformation of the Wandashan Terrane was investigated in the field and the geochronology of the Dalingqiao and Yongfuqiao formations were studied, which were formed syn-and-post RAC accretion respectively. The Yuejinshan and Raohe complexes were discontinuously accreted to the eastern margin of the Jiamusi Block. Contrary to the previous consideration of the Late Triassic to Early Jurassic, this study suggests that the Yuejianshan Complex in southwest Wandashan Terrane probably accreted from Late Carboniferous to Middle Permian, which was driven by unknown oceanic crust subduction existing to the east (present position) of the Jiamusi Block at that time. The siltstones of the Dalingqiao Fm. yield the youngest zircon U-Pb age of 142 ± 2 Ma, indicating the emplacement of the RAC not earlier than the Late Jurassic. Thus, the RAC might start to accrete from the Jurassic and emplace during 142–131 Ma, resulted from the Paleo-Pacific subduction which started from the Late Triassic to Early Jurassic.  相似文献   

2.
吉林-黑龙江东部地区的中生代增生杂岩,主要由吉林-黑龙江高压变质带和那丹哈达增生杂岩(或那丹哈达地体)组成。它们将为古亚洲洋与环太平洋构造域的转换作用,大洋板块地层(OPS)层序重建,特别是古太平洋板块向欧亚大陆的俯冲历史提供重要的科学依据。吉林-黑龙江高压带分布在佳木斯-兴凯与松辽地块之间的具有高压变质带性质的缝合带,新的地质年代学研究表明其形成时代为210~180Ma,表明晚三叠-早侏罗世为南北向古亚洲洋关闭和西向俯冲增生开始的关键时期。那丹哈达增生杂岩则发育在佳木斯-兴凯地块东侧,并具体分为西部的跃进山杂岩和东部的饶河杂岩。新近发表的数据显示,跃进山杂岩就位时代为210~180Ma,这与佳木斯-兴凯地块西缘的吉黑高压带形成时代相似。而饶河杂岩就位时代为晚侏罗-早白垩世,最晚期就位的时代为早白垩世(137~130Ma)。因此,吉黑东部地区的中生代增生杂岩为古太平洋向欧亚大陆中生代的俯冲过程提供了关键的信息。  相似文献   

3.
那丹哈达地体是中国境内唯一保存的古太平洋板块俯冲-增生的直接记录,包括跃进山杂岩和饶河增生杂岩。跃进山杂岩出露于那丹哈达地体的西缘,属于地体早期阶段的增生产物,对揭示古太平洋板块的俯冲-增生历史以及古亚洲洋构造域、泛大洋和古太平洋构造域之间的转换过程具有重要意义。本文通过野外地质调查明确了跃进山杂岩是一套构造混杂岩,主要由硅质岩、石英片岩、大理岩、二云母片岩、石英-云母片岩、变玄武岩、辉长岩、纯橄榄岩、异剥橄榄岩和单斜辉石岩组成。LA-MC-ICPMS锆石年代学测试结果表明变玄武岩原岩和辉长岩的形成时代分别为303±2Ma和278±2Ma,此外前人报道了跃进山杂岩中最年轻的玄武岩形成于232±5Ma,这些年代学研究成果限定了镁铁质-超镁铁质岩形成于303~232Ma。大量地球化学研究数据证实了跃进山杂岩中的玄武岩为洋中脊玄武岩(MORB)和洋岛玄武岩(OIB)。糜棱岩化绿泥石-绢云母板岩的绢云母^(40)Ar/^(39)Ar测试结果为193±1Ma,根据跃进山杂岩中最年轻的原岩时代为~220Ma,本文限定了跃进山杂岩的最终就位时代为220~193Ma。结合中国东北地区中生代增生杂岩及佳木斯地块和松辽地块东缘晚古生代至中生代的岩浆弧,本文揭示了中国东北地区古亚洲洋和泛大洋构造域向古太平洋构造域的转换发生在晚三叠世至早侏罗世。  相似文献   

4.
佳木斯地块位于中亚造山带东段,是我国东北地区一个重要的大地构造单元,古生代以来经历了复杂的多构造体系叠合的演化过程。本文在总结近二十年已报导的相关研究成果基础上,结合笔者近年工作,探讨了佳木斯地块的基底属性和来源,重塑了佳木斯地块西缘碰撞拼贴,以及东缘俯冲-增生的构造演化过程。研究表明,佳木斯地块具有亲冈瓦纳大陆的构造属性,裂离后经历了长距离的北漂。与松辽地块先后两次拼合,首次发生于中志留世(~425Ma),在晚二叠世前后(~250Ma)沿原缝合带位置发生裂解,拉张出新的有限洋盆(牡丹江洋),并于侏罗纪(185~145Ma)与松辽地块沿牡丹江-依兰构造带再次碰撞拼贴,形成了高压变质的黑龙江增生杂岩带。而佳木斯地块东缘受晚石炭世-晚三叠世(305~250Ma)泛大洋的俯冲-增生事件影响,形成了跃进山增生杂岩,随后于中侏罗世-早白垩世(165~128Ma)在古太平洋板块的西向俯冲作用下,形成了饶河增生杂岩。因此,佳木斯地块的构造演化既涉及了晚古生代古亚洲洋构造域的消亡,又经历了中生代古太平洋构造域的叠加与改造,而黑龙江杂岩的形成标志着古太平洋构造体制与古亚洲洋构造体制的转换始于晚三叠世(~210Ma)。  相似文献   

5.
The Late Jurassic–Early Cretaceous Wandashan accretionary complex (AC) in NE China is a key region for constraining the subduction and accretion of the Palaeo-Pacific Ocean; however, the protoliths and structure of the region remain poorly understood, resulting in debates regarding crustal growth mechanisms and subduction-related accretionary processes in Northeast China. In this contribution, we integrate detailed field observations, ocean plate stratigraphy (OPS) reconstruction, and associated geological data to determine the structure and tectonic evolution of the Wandashan AC. The Wandashan AC formed through the progressive incorporation of OPS units along an oceanic trench. The observed OPS comprises, in ascending order, Permian basalt and limestone, Middle Triassic–Early Jurassic chert, Middle Jurassic siliceous shale and mudstone, and Late Jurassic–Early Cretaceous turbidite. Numerous NNE–SSW-striking thrust faults have segmented the OPS into a series of bedding-parallel tectonic slices that were successively thrust over the Jiamusi massif along a basal thrust (the Yuejinshan Fault), producing a large-scale imbricate thrust system. The Wandashan AC underwent oceanward accretion via multiple deformational processes. The OPS units were detached and rearranged along or within a decollement through offscraping, underplating, thrusting, and duplexing. The units were then emplaced over the Jiamusi massif along the basal thrust. The timing of accretion and thrusting is constrained to the latest Middle Jurassic to earliest Early Cretaceous (ca. 167–131 Ma). Reconstructed accretion-related structural lines within the Wandashan AC trend dominantly NE–SW, close to the direction of Jurassic extension at the eastern Asian continental margin. Large-scale left-lateral strike-slip movement on the Dunmi Fault during the late Early Cretaceous resulted in the folding of structural lines within the Wandashan AC, producing their present-day westward-convex orientation.  相似文献   

6.
台湾造山带是中新世晚期以来相邻菲律宾海板块往北西方向移动,导致北吕宋岛弧系统及弧前增生楔与欧亚大陆边缘斜碰撞形成的。目前该造山带仍在活动,虽然规模很小,但形成了多数大型碰撞造山带中的所有构造单元,是研究年轻造山系统的理想野外实验室,为理解西太平洋弧-陆碰撞过程和边缘海演化提供了一个独特的窗口。本文总结了二十一世纪以来对台湾造山带的诸多研究进展,讨论了其构造单元划分及演化过程。我们将台湾造山带重新划分为6个构造单元,由西至东分依次为:(1)西部前陆盆地;(2)中央山脉褶皱逆冲带;(3)太鲁阁带;(4)玉里-利吉蛇绿混杂岩带;(5)纵谷磨拉石盆地;(6)海岸山脉岛弧系统。其中,西部前陆盆地为6.5Ma以来伴随台湾造山带的隆升剥蚀形成沉积盆地。中央山脉褶皱逆冲带为新生代(57~5.3Ma)欧亚大陆东缘伸展盆地沉积物由于弧-陆碰撞受褶皱、逆冲及变质作用改造形成的。太鲁阁带是造山带中的古老陆块,主要记录中生代古太平洋俯冲在欧亚大陆活动边缘形成的岩浆、沉积和变质岩作用。玉里-利吉蛇绿混杂岩带和海岸山脉岛弧系统分别为中新世中期(~18Ma)以来南中国海板块向菲律宾海板块之下俯冲形成的岛弧和弧前增生楔,其中玉里混杂岩中有典型低温高压变质作用记录,变质年龄为11~9Ma;岛弧火山作用的主要时限为9.2~4.2Ma。纵谷磨拉石盆地记录1.1Ma以来的山间盆地沉积。台湾造山带的构造演化可划分为4个阶段:(a)古太平洋板块俯冲与欧亚大陆边缘增生阶段(200~60Ma);(b)欧亚大陆东缘伸展和南中国海扩张阶段(60~18Ma);(c)南中国海俯冲阶段(18~4Ma);(d)弧-陆碰撞阶段(<6Ma)。台湾弧-陆碰撞造山带是一个特殊案例,其弧-陆碰撞并不伴随着弧-陆之间的洋盆消亡,而是由于北吕宋岛弧及弧前增生楔伴随菲律宾海板块运动向西北方走滑,仰冲到欧亚大陆边缘,形成现今的台湾造山带。  相似文献   

7.
深入研究了跃进山岩系的物质组成与构造特点,确认其为佳木斯地体东缘晚古生代—中生代的增生杂岩,探讨了该杂岩形成与演化的构造作用过程。  相似文献   

8.
本文系统总结了东北亚陆缘晚古生代和中生代增生杂岩的构成与形成时代,并结合同时代火成岩组合及其时空变异以及沉积建造组合,重塑了西太平洋板块俯冲带的演变历史.结果表明:①位于佳木斯地块东缘的跃进山杂岩代表了二叠纪俯冲带,它是古亚洲洋构造体制的产物;②侏罗纪增生杂岩代表了侏罗纪俯冲带,与陆缘同期钙碱性火成岩组合以及含煤建造一...  相似文献   

9.
那丹哈达增生杂岩为中国东部古太平洋板块俯冲最为可靠的地质记录之一,对限定古大洋板块的西向俯冲具有重要意义。跃进山杂岩位于那丹哈达增生杂岩的增生前锋位置,发育典型的增生杂岩组合。其中变玄武岩类多呈构造透镜体状与硅质岩、片理化泥岩和片岩相伴产出,部分可见变余枕状构造。本文对位于研究区北部勤得利和南部东方红地区的3件变玄武岩样品进行了同位素年代学和地球化学研究。变玄武岩样品中含有数量不等的锆石,多呈自形-半自形,条带结构,结合其较高Th/U比值(0.15~2.4),暗示其具有典型的基性岩岩浆锆石特征。锆石LA-ICP-MS U-Pb年代学证据显示跃进山杂岩中的变玄武岩形成于270±2 Ma~279±4 Ma,表明其原岩形成时代应为早二叠世。地球化学分析显示,跃进山杂岩南、北地区的地球化学组成略有不同,北部勤得利地区的变玄武岩具有富Na2O,贫Mg O,轻度富集轻稀土元素,富集大离子亲石元素Sr和Ba,亏损高场强元素Nb等特征,南部东方红地区变玄武岩具有贫Na2O、K2O和Mg O,亏损轻稀土元素和富集大离子亲石元素Rb、Sr等特征,结合构造判别图解,北部勤得利地区变玄武岩形成于消减带或俯冲带(SSZ)构造背景下,而南部东方红地区变玄武岩显示为N-MORB型,形成于大洋中脊(MOR)环境。结合前人资料及北部勤得利地区岩石的年代学与地球化学研究确定了佳木斯地块与那丹哈达地体之间的缝合线的具体位置为勤得利-二龙山-尖山子乡—线,并对该岩浆岩演化的动力学背景进行了初步分析。  相似文献   

10.
跃进山铜金矿床是完达山活动带的典型矿床,位于密山—敦化深断裂北侧。本文对含矿花岗斑岩开展了锆石LA-ICP-MS U-Pb测年、主量和微量元素的研究,厘定岩体的形成时代,探讨了成矿构造背景。结果表明与成矿密切相关的花岗斑岩的年龄为(109.17±0.91)Ma。它们为过铝质钙碱性系列岩石,富集Rb、Ba、La、Nd、Hf等元素,亏损Nb、Sr、P、Ti等元素,具俯冲带岩浆岩的基本特征,这些暗示它们形成于岛弧或活动大陆边缘环境。结合岩体的地球化学特征和完达山成矿带的构造岩浆演化,认为该矿床形成于岛弧构造背景,其形成与中生代太平洋的俯冲及早白垩世晚期东亚东部岩浆活动陆缘迁移、构造单元转化有关。  相似文献   

11.
Geochronological, geochemical, and structural studies of magmatic and metamorphic complexes within the Kyrgyz North Tianshan (NTS) revealed an extensive area of early Palaeozoic magmatism with an age range of 540–475 Ma. During the first episode at 540–510 Ma, magmatism likely occurred in an intraplate setting within the NTS microcontinent and in an oceanic arc setting within the Kyrgyz-Terskey zone in the south. During the second episode at 500–475 Ma, the entire NTS represented an arc system. These two phases of magmatism were separated by an episode of accretionary tectonics of uncertain nature, which led to obduction of ophiolites from the Kyrgyz-Terskey zone onto the microcontinent. The occurrence of zircon xenocrysts and predominantly negative whole-rock ɛNd(t) values and ɛHf(t) values of magmatic zircons suggest a continental setting and melting of Precambrian continental sources with minor contributions of Palaeozoic juvenile melts in the generation of the magmatic rocks. The late Cambrian to Early Ordovician 500–475 Ma arc evolved mainly on Mesoproterozoic continental crust in the north and partly on oceanic crust in the south. Arc magmatism was accompanied by spreading in a back-arc basin in the south, where supra-subduction ophiolitic gabbros yielded ages of 496 to 479 Ma. The relative position of the arc and active back-arc basin implies that the subduction zone was located north of the arc, dipping to the south. Variably intense metamorphism and deformation in the NTS reflect an Early Ordovician orogenic event at 480–475 Ma, resulting from closure of the Djalair-Naiman ophiolite trough and collision of the Djel'tau microcontinent with the northern margin of NTS. Comparison of geological patterns and episodes of arc magmatism in the NTS and Chinese Central Tianshan indicate that these crustal units constituted a single early Palaeozoic arc and were separated from the Tarim Craton by an oceanic basin since the Neoproterozoic.  相似文献   

12.
增生型造山带形成于活动大陆边缘,以宽阔且延伸稳定的增生杂岩为代表,在大洋板块向大陆板块发生缓慢而复杂的俯冲、碰撞过程中,大洋板块、火山岛弧、海山、大陆碎块等沿逐渐后退的海沟拼贴,仰冲板块前端发生刮削作用、底垫作用和构造剥蚀等作用,使得洋壳物质在海沟内壁增生,具体表现为增生杂岩的形成、垂向和侧向的生长,最终实现陆壳的横向生长。陆陆碰撞期间,加入俯冲通道的被动陆缘也将遭受类似的构造作用,从而形成规模较大的陆缘增生杂岩。因此,造山带增生杂岩的物质组成与结构、形成机制和演化过程对解剖洋陆转换过程中的复杂地球动力学过程具有极为关键的作用。西藏南羌塘增生杂岩是近年来通过走廊性地质填图以及多学科交叉工作得到的研究认识。然而,该增生杂岩的物质组成和结构等关键内容还未得到系统的研究,严重阻碍了对其形成机制和演化过程的理解。因此,本文以时空演化为主线,解剖杂岩物质组成和结构,结合俯冲期和同碰撞期大地构造单元,洞察南羌塘增生杂岩的形成演化过程。本次研究显示:(1)南羌塘增生杂岩具有俯冲杂岩在下、褶皱-冲断带在上的双层结构,二者间为大规模的拆离断层系统;(2)俯冲杂岩内不只含有洋板块地层单元,还含有大量的南羌塘被动陆缘物质;(3)褶皱-冲断带虽主要由被动陆缘物质变形改造而来,也含有属于洋板块地层系统的海山和洋内岛弧等物质。结合同俯冲期弧前盆地和楔顶盆地、同碰撞期晚三叠世岩浆的时空分布,高压变质岩的形成与折返时限,南羌塘增生杂岩内的双层结构应主要是陆陆碰撞过程中被动陆缘俯冲的结果,少量形成于大洋俯冲期间的俯冲反向过程中。本文提出的陆缘俯冲导致南羌塘增生杂岩双层结构的研究认识,对理解南羌塘地壳结构、中生代盆地基底形成演化具有较为重要的意义。  相似文献   

13.
大洋或弧后洋盆俯冲增生是大陆地壳增长的主导地质作用.重建大陆中消亡的洋地层岩石组合序列是当代大陆动力学和地学研究的重大前沿.洋壳消减杂岩带的厘定是洋板块地质构造重建乃至全球大地构造研究之纲,是理解区域大地构造形成演化及动力学的核心.俯冲增生杂岩带的基本特征:(1)俯冲增生杂岩带物质组成的共性是:以强烈构造变形洋底沉积的硅质岩-硅泥质岩-粉砂岩、凝灰岩;弧-沟浊积岩等为基质;以洋岛-海山灰岩-玄武岩及塌积砾岩,洋内弧残留岩块,超镁铁质蛇绿岩、绿片岩、蓝片岩等为岩块.(2)变形样式:同斜倒转冲断叠瓦构造、增生柱前缘重力滑动构造以及泥质岩的底辟构造;增生楔前缘变形和增生形式受控于大洋或弧后洋盆的规模和洋壳的俯冲速度,也取决于陆缘碎屑供给量及洋底沉积厚度和岩性.(3)宽度和厚度:厚常达几千米,宽达几十公里至数百公里,延长上千公里,是洋壳俯冲消亡过程洋盆地层系统及陆缘沉积物加积的结果.(4)形成机制:是大陆碰撞前大洋(或弧后洋盆)岩石圈俯冲消减的产物.结合带中的早期俯冲增生杂岩带往往卷入晚期的构造混杂作用.  相似文献   

14.
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.  相似文献   

15.
黑龙江省饶河县石场一带分布的跃进山杂岩为一套富含晚三叠世化石的海陆交互相沉积地层.砾岩样品中的LA-ICP-MS锆石U-Pb测年结果显示,样品中的碎屑锆石年龄谱具有4组年龄,分别为800 Ma以上、500 Ma、251~284 Ma和219~222 Ma.前三者与佳木斯地块中的热事件年龄完全一致,表明其沉积物源主要来自佳木斯地块;后者为砾岩最小年龄组,大致可将这组最小年龄视为这套砾岩的沉积时代下限,与西侧松辽地块东缘的张广才岭地区广泛分布的210~228 Ma的晚三叠世早期花岗岩基本一致,说明具有最小年龄组的碎屑锆石可能来自松辽地块东部.碎屑锆石年龄及其源区特征表明,在晚三叠世之前,跃进山增生杂岩已经就位在佳木斯地块东缘,并成为佳木斯地块东部大陆边缘的一部分.  相似文献   

16.
黑龙江省饶河县石场一带分布的跃进山杂岩为一套富含晚三叠世化石的海陆交互相沉积地层.砾岩样品中的LA-ICP-MS锆石U-Pb测年结果显示,样品中的碎屑锆石年龄谱具有4组年龄,分别为800 Ma以上、500 Ma、251~284 Ma和219~222 Ma.前三者与佳木斯地块中的热事件年龄完全一致,表明其沉积物源主要来自佳木斯地块;后者为砾岩最小年龄组,大致可将这组最小年龄视为这套砾岩的沉积时代下限,与西侧松辽地块东缘的张广才岭地区广泛分布的210~228 Ma的晚三叠世早期花岗岩基本一致,说明具有最小年龄组的碎屑锆石可能来自松辽地块东部.碎屑锆石年龄及其源区特征表明,在晚三叠世之前,跃进山增生杂岩已经就位在佳木斯地块东缘,并成为佳木斯地块东部大陆边缘的一部分.  相似文献   

17.
黑龙江东部饶河境内的层状燧石是中生代完达山造山带蛇绿混杂岩的重要组成部分,这些层状燧石的构造意义成为人们关注的热点。对完达山造山带饶河三叠纪大佳河组层状燧石280余块定向手标本开展深入的古地磁研究,结果表明这些层状燧石遭受不同程度的重磁化,重磁化的时间推测为晚侏罗世中期—早白垩世之间。说明对黑龙江东部晚侏罗世—早白垩世存在太平洋板块俯冲的响应。本区重磁化的机制是太平洋板块向西俯冲导致的地体增生、拼贴过程中的造山带流体造成的区域性重磁化现象。  相似文献   

18.
东海陆架盆地处于欧亚板块东南缘,其构造演化、动力学机制转换同太平洋板块与欧亚板块碰撞及印度-澳大利亚板块远程推挤效应有关。中生代以来,该盆地形成和演化过程受到古太平洋板块多期俯冲及多构造体系的叠加改造,地质构造和地球物理场复杂,盆地演化及动力学过程等一直是争论的焦点。本文利用最新调查资料,通过构造物理模拟实验、构造解析和平衡地质复原剖面等方法,结合区域构造背景,系统分析了东海陆架盆地中生代演化过程,探讨了其构造动力学转换过程。研究认为东海陆架盆地自中生代以来经历了晚三叠世前的被动大陆边缘和晚三叠世-中侏罗世活动大陆边缘挤压坳陷型盆地阶段,挤压应力来源于伊泽奈崎板块向欧亚大陆板块的低角度俯冲;早白垩世晚期-晚白垩世活动陆缘伸展断陷型盆地阶段,应力来源于太平洋板块向欧亚大陆板块俯冲后撤导致的岩石圈减薄作用;古近纪为弧后伸展断陷型盆地阶段。同时认为东海陆架盆地古特提斯构造域向古太平洋构造域转换的时间应该发生在中三叠世末期,古太平洋板块低角度俯冲和俯冲后撤代表华南中生代深部地质过程。  相似文献   

19.
张魁武  邵济安 《岩石学报》1997,13(2):168-172
跃进山群出露位于佳木斯地块和那丹哈达地体之间,是完达山造山带的组成部分。它由大陆斜坡相沉积物、大洋中脊型玄武岩和洋岛型玄武岩组成,其中有镁铁-超镁铁质岩块体。它不是一个地层单位,而是与活动大陆边缘板块俯冲作用有关的蛇绿混杂岩  相似文献   

20.
北祁连榴辉岩相变沉积岩的特征及其构造意义   总被引:1,自引:0,他引:1  
李金平  张建新  于胜尧  孙刚 《地质学报》2009,83(11):1667-1686
在北祁连造山带中,出露典型的高压/低温变质岩石,前人对其中的低温榴辉岩已做过较多的研究,但对其中的变沉积岩研究涉及很少.本文展示了榴辉岩相变质沉积岩的岩石学、地球化学、锆石U-Pb年代学和Hf同位素方面的一些新的研究结果.变沉积岩含有榴辉岩相的矿物组合,峰期温压条件为t= 450~520℃,p=1.9~2.3 GPa,与相邻榴辉岩的温压条件一致.地球化学显示这些岩石的原岩为不成熟的沉积岩,可能形成于大陆边缘或大陆岛弧环境.变沉积岩中的碎屑锆石U-Pb年龄主要集中在1800 Ma左右和540~600 Ma之间,结合锆石Hf同位素特征,表明其原岩的碎屑来源既有周缘陆块的前寒武纪变质基底物质,又有新元古代-早古生代新生洋壳或增生物质.同时,这些数据也表明北祁连早古生代洋壳俯冲过程中发生了活动大陆边缘的构造剥蚀作用,即形成于上盘的沉积物(弧前盆地或增生楔)被构造作用运移到俯冲带中,并俯冲到60~70km深处,遭受榴辉岩相变质作用,然后折返到地表.  相似文献   

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