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吉尔吉斯南天山阿特巴西增生杂岩结构-构造解析及其意义
桑苗
学位类型博士
导师肖文交
2017-05-01
学位授予单位中国科学院大学
学位授予地点新疆乌鲁木齐
学位专业工学博士
关键词阿特巴西增生杂岩 双重构造 高压变质岩 斜向挤出 大洋板块地层学 南天山 吉尔吉斯斯 Atbashi Accretionary Complex Duplexes Hp/uhp Rocks Oblique Extrusion Ocean Plate Stratigraphy South Tianshan Kyrgyzstan.
摘要古增生杂岩的解剖对理解增生造山带的构造过程具有重要意义。然而,由于古增生杂岩具有复杂的物质成分且经历了强烈变形,因此对古老造山带中增生杂岩的识别与解剖具有挑战性,其难点在于野外岩块-基质形成的时限及相互关系、构造背景厘定等诸多方面。本文通过对吉尔吉斯南天山阿特巴西增生杂岩系统的构造、年代学和地球化学研究,分析了中亚造山带西部的构造演化、大洋板块地层形成和增生时序。吉尔吉斯南天山阿特巴西增生杂岩位于中亚造山带南部关键的大地构造位置,分别以北部的阿特巴西-伊内尔切克-南那拉提断裂和南部的穆兹杜克-北塔里木断裂分隔伊犁-中天山岛弧和塔里木克拉通,记录了塔里木克拉通与伊犁-中天山岛弧的拼贴历史。具有高压/超高压变质岩和蛇绿岩混杂带出露的阿特巴西增生杂岩是解剖南天山增生杂岩最好的天然实验室之一,对解决国际学术界关于中亚造山带南部最终拼贴时空格局具有重要的理论意义。通过详细的大比例尺地质填图与构造解析、室内综合研究,取得以下主要创新成果与认识:(1)阿特巴西增生杂岩可分为 4 个构造单元,即北部蛇绿混杂岩单元、高压/超高压变质岩组合单元、层序-混杂岩组合单元和南部蛇绿混杂岩单元。构造单元中大量发育岩块-基质的混杂特征,主体构造样式表现为逆冲-褶皱推覆体、双重构造和叠瓦扇构造。(2)高压/超高压变质岩组合夹于一个由北部右行转换挤压体系和南部左行转换伸展体系形成的复杂双重构造中,表明高压/超高压变质岩的折返具有平行于岛弧、朝西南斜向挤出的复杂三维(3D)形态。(3)榴辉岩和基性岩具有 N-MORB 和 OIB 性质,其中西部以具有 OIB 性质的海山/洋底高原/洋底高原环境为主,东部以具有 N-MORB 的正常洋壳为主。(4)榴辉岩等高压变质岩最小变质年龄为 217Ma-221Ma,基性岩的最小锆石年龄为 214Ma-248Ma。(5)变质沉积物的碎屑锆石年龄范围集中于 470-500Ma 之间,主体记录伊犁-中天山岛弧活动特征,表明沉积物源自位于俯冲上盘的伊犁-中天山岛弧。(6)获得4个构造单元中沉积物碎屑锆石的最小年龄分别为264Ma,223Ma,350Ma 和 303Ma,表明构造变形至少发生于这些时代之后。(7)确定古生代-早中生代增生楔大洋板块地层学特征,提出南天山洋整体向北俯冲,俯冲板片结构沿走向上存在西部海山/洋底高原较多、东部正常洋壳的差异性;南天山洋俯冲可能持续至晚二叠至晚三叠世,期间高压/超高压变质杂岩于晚三叠世哈萨克斯坦山弯构造南翼(伊犁-中天山岛弧)向东运动期间,朝西南斜向挤出。(8)讨论了信息技术在高寒山区岛弧增生楔构造填图中的辅助作用。这些成果具有重要理论意义,有助于解决长期针对南天山洋俯冲极性和最终闭合时间的重大争议问题,并示范了通过野外大比例尺构造填图、使用大洋板块地层学来解决古老造山带增生楔构造解析难点的关键作用。
其他摘要Anatomy of an ancient accretionary complex has great significance for better understanding tectonic processes of accretionary orogens. However, due to its complicated compositions and strong deformation, identification and anatomy of an accretionary complex of ancient orogens are challenging. The difficulty lies in several aspects such as defining the time framework for block-in-matrix in the field and their relationship and tectonic settings. By means of a thorough structural,geochronological and geochemical study of a fossil accretionary complex in the Atbashi Ridge, South Tianshan (Kyrgyzstan), this paper analyzes the evolution and ocean plate stratigraphy of the western Central Asian Orogenic Belt (CAOB). The Atbashi accretionary complex (ATAC), South Tianshan (Kyrgyzstan), is located in an important tectonic position of the southern CAOB, separating the Ili-Central Tianshan Arc from the Tarim Craton to the south. The ATAC is bounded by the Muzduk-North Tarim Fault to the south and the Atbashi–Inylchek–South Nalati Fault to the north, which records the assembled history of the Tarim Craton and Yili-Tianshan Arc. The ATAC that conatins HP/UHP metamorphic rocks and ophiolite mélanges is one of the best nature laboratories for the anatomy of a fossil accretionary complex in the South Tianshan, which is of great significance to solve the final collage with spatial-temporal tectonics of southern CAOB. Through large-scale geolocical mapping and structural analysis, together with laboratory comprehensice study, the main innovative conclusions were obtained as follows: (1) The architecture of the Atbashi accretionary complex is subdivided into the following four lithotectonic units, North Ophiolitic Mélange,High-pressure/Ultra-high-pressure Metamorphic Assemblage, Coherent & Incoherent Mélange, and South Ophiolitic Mélange. Within these units well develloped mélanges with ―block-in-matrix‖ structure, and the major structural patterns are thrust-fold nappes, duplexes & imbricate fans. (2) The HP/UHP Metamorphic Assemblage is situated in a complicated duplex formed by a northerly dextral transpression system and southerly sinistral transtension system. The two major shear systems suggest that the exhumation of HP/UHP Complex have a complicated 3-D style with an arc-parallel feature, which extruded obliquely southwestwards. (3) The eclogites and basic rocks have signatures of N-MORB and OIB,indicating a complicated paleogeography, the western part of which is characterized by OIB, and the eastern part, by the normal oceanic crust with N-MORB type. (4) The youngest metamorphic ages of HP rocks are 217-221Ma, and the youngest zircon ages of basic rocks from 214Ma to 248Ma. (5) The major peaks of detrital zircon ages for meta-sediments are focused at 470-500 Ma, which is in an accordance with the magmatic activities of the Ili-Central Tianshan Arc, demonstrating a provenance from the Ili-Central Tianshan Arc to the north. (6) The isotopic ages of the youngest components for meta-sediments of the four units are 264Ma, 223Ma, 350Ma, 303Ma, indicating the structural deformation generated after these times. (7) The features of oceanic plate stratigraphy (OPS) in the ATAC suggest a general northward subduction of the South Tianshan Ocean during Paleozoic to Early Mesozoic, and the paleogeography of subduction slab varied along its strike with more seamountains/oceanic plateaus in the western part and normal oceanic crust in the eastern part. (8) The subsidiary function of geographic information technology is found to be effective in geology mapping for mountainous accretionary complexes.These results have great significance, which help to resolve the long-standing controversy regarding the subduction polarity and the timing of the final closure of the South Tianshan Ocean, and demonstrate a pivotal role in solving the difficulties in anatomy accretionary complex of an ancient orogeny through large-scale field mapping and OPS study
学科领域地球探测与信息技术
语种中文
文献类型学位论文
条目标识符http://ir.xjlas.org/handle/365004/14789
专题研究系统_荒漠环境研究室
作者单位中国科学院新疆生态与地理研究所
推荐引用方式
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桑苗. 吉尔吉斯南天山阿特巴西增生杂岩结构-构造解析及其意义[D]. 新疆乌鲁木齐. 中国科学院大学,2017.
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