| 古太平洋板块俯冲-增生时限：饶河增生杂岩的地球化学和年代学制约 |
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| 引用本文： | 韩伟,周建波.古太平洋板块俯冲-增生时限：饶河增生杂岩的地球化学和年代学制约[J].岩石学报,2020,36(3):703-725. |
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| 作者姓名： | 韩伟 周建波 |
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| 作者单位： | 吉林大学地球科学学院, 长春 130061,吉林大学地球科学学院, 长春 130061 |
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| 基金项目： | 本文受国家重点研发项目（2017YFC0601304）和国家自然科学基金项目（41730210）联合资助. |
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| 摘 要： | 饶河杂岩作为那丹哈达增生杂岩的主体,是古太平洋板块西向俯冲的直接证据。饶河增生杂岩组成与增生过程的研究对限定古太平洋板块向欧亚大陆的俯冲与增生过程具有重要的指示意义。本文在野外地质调查和饶河大岱地区大比例尺填图基础上,明确了饶河杂岩主要由枕状玄武岩、辉长岩以及大洋板块沉积地层(OPS)组成,这些岩石均呈构造透镜体状分布在海沟沉积物中,并被中生代花岗质岩脉所穿切,因此为限定饶河增生杂岩的组成、增生和就位时代提供了关键制约。地球化学数据表明玄武岩具有洋岛玄武岩(OIB)的地球化学属性。LA-ICPMS锆石测试结果表明该地区玄武岩和辉长岩的形成时代分别为166±2Ma和214±5Ma,限定了饶河杂岩中镁铁质-超镁铁质岩石的形成时代为晚三叠世至中侏罗世。结合该区粉砂质泥岩和砂岩的沉积时代下限分别为167±3Ma和133±4Ma,表明饶河杂岩的增生时代为167～133Ma,此外样品的碎屑年龄信息表明基质的物源为邻近的佳木斯地块和中亚造山带东段,其中前寒武的碎屑年龄在中国东北的多个陆块均有出现,可能源于早前存在的前寒武纪基底。本文测得侵入饶河杂岩的2个二长花岗岩形成年龄分别为126±1Ma和105±2Ma,表明饶河杂岩中的花岗岩脉主要形成于两个阶段,其中较老的花岗岩侵入体进一步限定了饶河杂岩的最终就位时代为133Ma至126Ma,表明古太平洋板块在中侏罗世至早白垩世存在西向俯冲-增生作用,为古太平洋板块的构造演化提供了重要的制约。
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| 关 键 词： | 饶河增生杂岩 锆石U-Pb年龄 增生时代和就位时代 古太平洋板块俯冲 |
| 收稿时间： | 2019/8/30 0:00:00 |
| 修稿时间： | 2019/11/19 0:00:00 |
Paleo-Pacific subduction-accretion: Geochemical and geochronology constraints from the Raohe accretionary complex, NE China |
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| HAN Wei and ZHOU JianBo.Paleo-Pacific subduction-accretion: Geochemical and geochronology constraints from the Raohe accretionary complex, NE China[J].Acta Petrologica Sinica,2020,36(3):703-725. |
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| Authors: | HAN Wei and ZHOU JianBo |
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| Institution: | College of Earth Sciences, Jilin University, Changchun 130061, China and College of Earth Sciences, Jilin University, Changchun 130061, China |
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| Abstract: | The Raohe Complex forms the main part of the Nadanhada accretionary complex resulted from the westward subduction of Paleo-Pacific plate. The rocks assemblage and accretion process of the Raohe Complex will provide new constraints for subduction-accretion process of Paleo-Pacific plate beneath the Eurasia. Based on field geological investigation and large-scale geological map of Dadai area, we define that the Raohe Complex consists of pillow lava, cumulate gabbro, oceanic plate stratigraphy (OPS), which form tectonic lenses distributing in the trench sedimentation, indicating its nature of tectonic mélange, in addition, the Raohe Complex was intruded by granitic plutons, these evidence can provide important constraints for the rocks assemblage, accretion and final emplacement timing of the Raohe Complex. Geochemical data show that the Raohe basalts have ocean island basalts (OIB) affinities. LA-ICPMS zircon U-Pb data define the formation ages of the basalt and gabbro are 166±2Ma and 214±5Ma, respectively, thus, there is a range in the formation age for the mafic-ultramafic from the Late Triassic to Middle Jurassic. A silty mudstone sample has maximum depositional age of 167±3Ma, different from the sandstone sample (133±4Ma), which indicates the accretion timing of the Raohe Complex is from 167Ma to 133Ma, and their detrital ages can all be related to the Jiamusi Block and eastern segment of the Central Asian Orogenic Belt (CAOB), based on the Precambrian detrital and inherited ages occurring in the several adjacent blocks, we consider there might be Precambrian basement in NE China. In addition, we obtained forming ages of 126±1Ma and 105±2Ma from two monzonitic granite samples, indicating that the granitic plutons formed at two stages, the older age of 126±1Ma, together with an age of 133±4Ma from a sandstone sample, constrains the final emplacement of the Raohe Complex between 133Ma and 126Ma. These evidences verify the westward subduction-accretion of the Paleo-Pacific plate between Middle Jurassic and Early Cretaceous, and provide important constraints for the tectonic evolution of Paleo-Pacific plate. |
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| Keywords: | Raohe Complex Zircon U-Pb dating Accretion and emplacement timing Subduction of Paleo-Pacific plate |
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