附件2
论文中英文摘要格式
作者姓名：王博
论文题目：西天山伊犁地块古生代地球动力学演化
作者简介：王博，男，19xx年1月出生，20xx年9月师从于南京大学舒良树教授，于20xx年12月获博士学位。
中 文 摘 要
伊犁是位于西天山南、北两支之间的一个三角形区域，其主要部分向西延伸到哈萨克斯坦境内，属于一个具有元古代结晶基底的大陆微地块，在西天山古生代构造演化中发挥着重要的作用。前人的研究表明，西天山造山带由多个地块经过多期俯冲、碰撞作用形成，传统的大地构造划分将其分为北天山、中天山和南天山。本文通过构造地质学、地球化学、地质年代学和古地磁学综合研究，重新定义了部分构造单元及其边界，提出了一个新的西天山古生代动力学演化模式。
伊犁地块一直被认为是中天山板块的一部分，前寒武纪构造基底出露在其南、北两缘，早古生代地层主要由被动大陆边缘台地相和浅海相沉积岩组成，主要分布在伊犁地块北缘。石炭纪火山岩和海西中期侵入岩广泛分布在伊犁盆地边缘，它们的岩石学和地球化学特征表明：1）火山岩主要包括安山岩、流纹岩和少量玄武质安山岩，侵入岩主要由辉长岩、闪长岩、花岗闪长岩和花岗岩组成，火山岩和侵入岩均属于钙碱性系列；2）火山岩和侵入岩均表现为Nb-Ta负异常，与俯冲作用形成的岩浆岩类似；3）在高场强元素判别图中，火山岩全部投在大陆岛弧区域，与板内和洋中脊岩浆作用无关，侵入岩则全部投在岛弧花岗岩或同碰撞花岗岩区域。另外，Rb-Sr和Sm-Nd同位素研究显示，这些火山岩和侵入岩源自一个亏损的地幔岩浆库，并经受了明显的上地壳或陆源沉积岩的混染作用。考虑到伊犁地区石炭纪岩浆岩与碎屑沉积岩的紧密伴生关系，本论文认为该岩浆岩系列代表一个大陆岩浆岛弧，形成于活动大陆边缘环境。系统的锆石U-Pb ICPMS测年表明，伊犁地块晚古生代岩浆岩形成于389-301Ma，即中泥盆世晚期-石炭纪末，其中岩浆活动的高峰期为360-310Ma。
伊犁地块北缘边界由北天山晚石炭世浊积岩和巴音沟-莫托沙拉沟蛇绿混杂岩带组成。浊积岩和蛇绿岩的地层学、岩石学和几何学特征表明，它们构成一个俯冲增生杂岩体，是北天山洋盆俯冲缝合的产物。蛇绿混杂岩的构造特征显示，镁铁岩和超镁铁岩经历了洋壳内部的变形、洋底再沉积和洋壳俯冲过程中的构造变形作用。硅质岩中放射虫和牙形刺化石的时代指示北天山洋盆至少存在于晚泥盆世-早石炭世。蛇绿混杂岩中包含浊积岩块体，并被早二叠世岩脉侵入，指示构造事件发生在晚石炭世-早二叠世之间。上述地质事实表明，北天山洋盆从晚泥盆世开始向南俯冲，形成伊犁晚古生代大陆岩浆岛弧，最终于石炭纪末闭合。由于新生代陆内俯冲作用使蛇绿混杂岩再次发生变形并逆冲推覆在准噶尔盆地之上，因此，代表洋壳俯冲的真正缝合带已被新生代推覆体所掩盖。在北天山后峡及博格达地区，石炭系火山岩
由粗玄岩、安山岩和英安流纹岩组成，其地球化学特征与伊犁岛弧火山岩一致，因而代表北天山岛弧。鉴于伊犁岛弧与北天山岛弧以及北天山俯冲杂岩在时、空上的匹配关系，可以推测北天山缝合带向东可能延伸到后峡-博格达山以北，但这一推论仍需要进一步的研究来检验。
伊犁地块南部边界是一个复杂的变形、变质带，带内分布有高压变质岩、蛇绿混杂岩、前寒武纪结晶基底和古生代侵入岩。沿科克苏河剖面的运动学研究发现，在元古代花岗片麻岩、古生代辉长岩及其南侧的角闪岩和高压变质岩中发育有缓倾面理和南北向倾滑线理，运动学标志指示从南向北的剪切推覆作用；在退变质的绿片岩相石英岩中还发现了向南滑脱的运动学标志，代表一期伸展作用。对退变质的蓝片岩和绿片岩相石英岩中白云母进行了40Ar/39Ar定年，获得年龄为330-315Ma，反映高压变质岩的折返年龄；结合前人的研究结果，高压（超高压）变质作用的时代应该早于345Ma。同时，长阿吾孜-穹库什太蛇绿混杂岩向东经那拉提延伸到干沟-米什沟蛇绿混杂岩带，其中蛇绿岩时代均为奥陶纪-志留纪；干沟-米什沟蛇绿混杂岩带的变形运动学与科克苏高压变质岩带变形特征完全一致。在科克苏高压变质带-长阿吾孜-干沟蛇绿混杂岩带以南，出露有奥陶纪-志留纪钙碱性火山-沉积岩系和元古代片麻岩，且被石炭纪碎屑岩不整合覆盖，本文将其称为具有前寒武纪基底的中天山地块。因此，科克苏高压变质带-长阿吾孜-干沟蛇绿混杂岩带代表一个洋壳（天山洋）在奥陶纪-志留纪向南俯冲，形成中天山岛弧，最终在晚泥盆-早石炭世缝合碰撞。
在中天山地块南缘的阿合奇-乌什-黑英山一带，蛇绿混杂岩中辉长岩岩块锆石U-Pb年龄为392Ma，而片理化硅质岩基质中放射虫时代为晚泥盆-早石炭世。库勒湖地区条带状硅质岩的发育指示中天山南缘在早-中泥盆世期间由碳酸盐斜坡沉积转变为半深海沉积。这些地质证据表明，在中天山和塔里木之间曾经出现过一个边缘海盆地。变形运动学研究表明，蛇绿混杂岩从南向北推覆在韧性变形的志留系火山碎屑岩和泥盆系碳酸盐岩之上。鉴于下石炭统不整合覆盖在蛇绿混杂岩之上，因此，蛇绿混杂岩的推覆就位与韧性变形发生在早石炭世之前。同时代、同变形特征的蛇绿混杂岩和类似的石炭系不整合关系也可以在库勒湖、乌瓦门、榆树沟和库米什地区观察到。因此，本文把阿合奇至库米什一带的蛇绿混杂岩定义为南天山蛇绿混杂岩带，但不同于前人关于该带是从北向南的构造推覆体的认识，本文认为该蛇绿混杂岩带是天山地区最南部的一条构造缝合带。
伊犁地块的南、北缘边界在二叠纪期间经受了走滑作用的强烈改造。在伊犁北缘，北天山断裂使石炭纪浊积岩的南部发生了韧性变形，以垂直面理和近水平线理为特征。运动学研究表明，北天山断裂为一个右旋韧性剪切带，糜棱岩化变质泥岩的40Ar/39Ar全岩年龄为285-245Ma, 与前人在天山主断裂获得的变形时代（280-250Ma）基本一致。伊犁南缘现今被菁布拉克-那拉提断裂所限，并向东延伸与中天山南缘断裂相连。在科克苏河、拉尔墩达坂和桑树园子一带观察到的运动学特征表明，该断裂系也是一个右旋韧性剪切带，其中糜棱岩变形白云母40Ar/39Ar为280-252Ma。二叠纪右旋韧性剪切带附近广泛分布有钾长花岗岩和长英质火山岩。其中花岗岩发育明显的同构造变形组构特征，其锆石U-Pb ICPMS年龄为294-252Ma。这些岩浆岩具有高钾钙碱性、碱性或过度系列岩浆岩的地球化学特征，指示它们可能源于受到交代的地幔岩石圈和上隆的软流圈。根据前人的研究，软流圈的上隆可能受控于东西向拉张作用引发的岩石圈减薄作用。本文认为，在南北向构造为主的西天山，东西向拉张作用只有与后碰撞阶段大型走滑作用有关。另外，晚二叠世红色砾岩沉积在整个天山地区普遍发育，并与下伏地层角度不整合接触。以上地质现象表明，天山造山作用至少在晚石炭世末-早二叠世结束。
本文对伊犁地块及其邻区奥陶-二叠纪地层进行了古地磁学研究。从 61 个采点中采集了 500 多个砂岩、灰岩和火山岩岩芯。岩石磁学和剩磁清洗实验均显示，这些样品中主要的剩 磁载体为磁铁矿和赤铁矿。经过剩磁方向分析、可靠性判断和剩磁年龄讨论，最后只从昭苏、 新源和巩留地区的样品中，计算得出伊犁地块晚石炭世和晚二叠世的古地磁极。奥陶系－泥 盆系的岩石则由于磁性太弱或方向不稳定，未能获得可靠的特征剩磁方向。通过与准噶尔、 塔里木和西伯利亚地块同时代古地磁极的对比，发现：1）自晚石炭世以来，伊犁和准噶尔两 地块没有发生明显的相对运动；2）四个地块自晚石炭世以来在纬度上没有发生明显的相对运 动；3）从晚石炭世到晚二叠世，伊犁、准噶尔地块一起相对于塔里木和西伯利亚分别逆时针 旋转了（46.2° ±15.1° ）和（31.6 ° ±15.1° ） 。这些旋转表现为伊犁、准噶尔地块沿天山右旋 剪切带和阿勒泰左旋剪切带发生向东挤入式走滑剪切作用，在天山和阿勒泰山分别造成了约 1000km 和 600km 的侧向位移。 基于以上基本地质证据，剔除二叠纪走滑剪切作用和新生代陆内变形对天山古生代造山 带的改造，本文提出了一个西天山古生代构造演化的动力学模型。该模型强调西天山造山带 存在三条不同时代的缝合带，即南天山蛇绿混杂岩带、中天山北缘高压变质岩-蛇绿混杂岩带 和北天山蛇绿混杂岩带，分别代表位于塔里木、中天山、伊犁和准噶尔地块之间的三个洋盆， 先后向南的俯冲和碰撞过程，并形成了中天山早古生代岛弧和伊犁-北天山晚古生代岛弧。至 早二叠世，天山古生代造山带最终形成，随后西天山构造体制从碰撞造山转换为陆内走滑。关键词： 西天山造山带、伊犁地块、古生代、变形运动学、锆石 U-Pb 年代 学、Ar-Ar 年代学、地球化学、古地磁学、构造演化Paleozoic geodynamic evolution of Yili Block in West Chinese Tiansha nWang BoABSTRACTThe Yili Block is a triangular area bordered by the northern and southern branches of the Western Chinese Tianshan Belt, it is considered as a micro-continental block with Proterozoic basement extending westward into Kazakhstan. The Yili Block is important for understanding the Paleozoic geodynamic evolution of the Tianshan Belt, which resulted from polyphase subduction-collision orogenies. The western Tianshan Belt is classically divided into three subunits: North Tianshan, Central Tianshan and South Tianshan. On the basis of structural, geochemical and paleomagnetic studies, some of these subunits and their boundaries were redefined, and a new dynamic evolutionary model for the western Chinese Tianshan is proposed. The Yili Block, previously considered as a part of the Central Tianshan, is underlain by a Precambrian basement that develops along its northern and southern boundaries. Early Paleozoic strata, exposed mainly on the northern margin of Yili Block, consist of sedimentary rocks t hat were
formed in platform to shallow water environment of passive margin. Carboniferous volcanic rocks are widespread along the margins of Yili Basin. Petrological and geochemical features of Carboniferous volcanic rocks and granitoids show that: (1) volcanic rocks are mainly composed of andesite, rhyolite and minor basaltic rocks, granitoids consist of gabbro, diorite, granodiorite and granite, both volcanic and granitic rocks are belong to the calc-alkaline series, (2) magmatic rocks display prominent Nb-Ta negative anomalies consistent with subduction- related magmas, and (3) HFSE-based discriminations place volcanic rocks in the field of continental arcs, and granitoids in the fields of syn-collisional granites or arc-type granites. Rb-Sr and Sm-Nd isotopic studies indicate that these magmatic rocks derived from a depleted magma reservoir of mantle source, and suffered an important contamination of upper crust or terrigenous sediments. Taking into account the shallow water sedimentation associated with the magmatism, the Carboniferous magmatic rocks are suggested to form in an active continental margin setting. Systematic zircon U-Pb ICPMS dating on the volcanic and granitic rocks from the whole Yili area indicates that they were produced from 389 Ma to 301 Ma, i.e. Late Middle Devonian to Carboniferous time, but the peak magmatism took place during 360~301 Ma.
The northern boundary of the Yili Block is represented by the Late Carboniferous turbidite and ophiolitic mélange that are exposed in Bayingou-Motuogou areas, North Tianshan. Geometrical, stratigraphical and petrological studies suggest that the turbidite and ophiolitic mélange form a subduction complex. The ophiolitic mélange was a result of intra-oceanic tectonism, seafloor redeposition and subsequent deformation during the subduction of the North Tianshan oceanic basin, which existed at least during Late Devonian to Early Carboniferous on the basis of the microfossils found in chert of ophiolite. Blocks of Late Carboniferous turbitite are included in the mélange, which is in turn intruded by Early Permian mafic dykes, suggesting that the emplacement of the ophiolitic mélange occurred during Late Carboniferous to Early Permian. Structural, kinematic, chronological and geochemical evidences from ophiolitic mélange and turbidite argue that a southward subduction of the North Tianshan oceanic basin is responsible for the formation of the Late Paleozoic Yili magmatic arc. Since this subduction complex was redeformed and thrust northward upon the Junggar Cenozoic basin, the real North Tianshan Suture is probably hidden by the Cenozoic thrust. New geochemical studies from Houxia area indicate that the dolerite, andesite and dacitic rhyolite show similar features with those of Yili arc, and therefore correspond to the North Tianshan arc. Temporal consistency and spatial correlation between the North Tianshan subduction complex and the North Tianshan Arc suggest that the North Tianshan Suture extends probably eastwards until to the north of Houxia-Bogdashan areas. More detailed studies are needed to test this inference.
The southern boundary of the Yili Block is a complicated deformation zone including
high-pressure (HP) metamorphic complex, ophiolitic mélange, Proterozoic basement and Early Paleozoic intrusive rocks. Detail kinematic analyses along the Kekesu River revealed a top-to-the-North ductile shearing that is developed both in ocean-derived HP rocks and in Proterozoic to Early Paleozoic rocks that are characterized by flat foliation and N-S dipping lineation. Evidences for an extensional event, formed in retrograde greenschist facies conditions, are recognized in the HP metapelites. Ar-Ar laser probe dating of white mica in retrogressed blueschist facies metapelites and in greenschist facies quartzite provides 330-315 Ma ages that are interpreted as the date of the exhumation of the HP rocks. Taking into account the previous results, HP/UHP metamorphism should have taken place earlier than 345 Ma. Near to the HP metamorphic belt, Ophiolitic mélange of Changawuzi-Qiongkushitai areas extends eastward joining with Gangou - Mishigou ophiolitic mélanges, therein the mafic rocks are of Ordovician to Silurian. The kinematics of Gangou ophiolitic mélange is consistent with that of Kekesu HP metamorphic rocks. To the south of this HP metamorphic-ophiolitic mélange zone, Ordovician-Silurian calc-alkaline volcano-sedimentary rocks were recognized being unconformably covered by Carboniferous sandstone and carbonate. Proterozoic amphibolite facies metamorphic rocks are distinguished as the basement of the volcano-sedimentary series. This area is defined as the Central Tianshan block. Therefore, the metamorphic and mélange zone is interpreted as a southward subduction of Tianshan Ocean beneath the Central Tianshan block generating the Ordovician-Silurian volcanic arc.
In Aheqi, Wushi and Heiyingshan areas, along the southern slope of the Central Tianshan, a Late Devonian-Early Carboniferous ophiolitic mélange includes ca. 392 Ma gabbro blocks with a geochemical affinity of back-arc basalt, and schistose matrix of siliceous rocks bearing Late Devonian-Early Carboniferous radiolarian. Moreover, the evolution from platform carbonate sedimentation to banded cherts deposition argues for a progressive deepening of the southern margin of the Central Tianshan Block that is responsible for the opening of a back-arc basin between the Central Tianshan and Tarim during the Early to Middle Devonian. Field observation and kinematics suggest that the mélange has been thrust to the North above the deformed Silurian-Devonian volcaniclastic rocks and marble series. This ductile shearing occurred before the deposition of the Lower Carboniferous sandstone and limestone that unconformably cover the mélange and its tectonic substratum. These observations are quite consistent with those from Kulehu, Wuwamen and Kumux-Yushugou areas. Therefore, this ophiolitic mélange zone that stretches from Aheqi to Kumux is defined as the South Tianshan Mélange Belt. This mélange has usually been considered as south-directed tectonic klippes, but our study indicates that they are actually thrust from South to North, and rooted in a southernmost suture of the Chinese Tianshan Belt.
The two boundaries of the Yili Block have been reworked by the Permian strike-slip faulting.
The North Tianshan Fault redeformed the southern part of North Tianshan Carboniferous turbidite (the northern boundary of the Yili Block). First-hand kinematic results suggest that the North Tianshan Fault is a dextral ductile strike-slip fault, new Ar-Ar whole rock dating constraint this deformation at 285-245 Ma that is consistent with the age of Main Tianshan Shear Zone (280~250Ma). The Nalati-Qingbulak Fault extending eastwards to joint with the southern Central Tianshan Fault cuts the southern boundary of the Yili Block, kinematic observations from Kekesu, Laerdun Pass and Sangshuyuanzi coherently indicate a dextral shearing, thermal geochronology on deformed white mica from mylonite yields ages at 280-252 Ma. Permian K-granites and felsic volcanic rocks are distributed along the shear zones, some intrusive rocks show synkinematic fabrics, yielding zircon U-Pb ICPMS ages of 294-252 Ma. This magmatic complex shows geochemical features of high-K calc-alkaline, alkaline or transitional series, indicating that they are likely originated from a metasomatized mantle lithosphere and an uplifting asthenosphere. According to the previous studies, the uplifting of the asthenosphere could be correlated with lithosphere thinning resulted from an E-W extension. Regarding the major tectonic context of N-S convergence in the western Chinese Tianshan, this thesis suggests that the only possibility for E-W extension could be related to the post-collisional large scale strike-slip faulting. Late Permian redbeds and conglomerate are widespread in whole Tianshan Belt and unconformably cover the older rocks. Therefore, Permian tectonics appears to be geodynamically distinct from the convergent orogeny of the Tianshan Belt, and plays an important role on the final formation of its present architecture.
A paleomagnetic study on Ordovician to Permian rocks from the Yili Block and its adjacent areas was performed. More than 500 samples of sandstone, limestone and volcanic rocks were collected from 61 sites. Laboratory measurements on rock magnetism and magnetic remanence indicate that the magnetite and hematite are principal remanent carriers for characteristic remanent magnetization. After careful analysis of reliable characteristic remanences from Zhaosu, Xinyuan and Gongliu areas and detailed discussion on remanence ages, two primary poles of Late Carboniferous and Late Permian are calculated for the Yili Block. The Ordovician and Devonian rocks did not yield reliable character remanence due to either too weak magnetization or dispersal remanent directions. Comparison of these paleomagnetic poles of the Yili Block with coeval poles of Junggar, Tarim and Siberia indicates: (1) no significant relative motion between the Yili and Junggar blocks since Late Carboniferous, (2) no significant or weak latitudinal relative motion occurred since Late Carboniferous among these blocks, and (3) the 46.2°±15.1° and the 31.6°±15.1° counterclockwise rotations of the Yili-Junggar blocks with respect to Tarim and Siberia took place during Late Carboniferous to Permian. These rotations are accommodated by the Permian dextral strike-slip faults along the northern and southern sides of the Tianshan Belt and sinistral strike-slip
faulting along the Erqishi Fault of the Altay Belt, resulting in about 1000 km and 600 km lateral displacements in the Tianshan and Altay belts, respectively.
Finally, on the basis of the removal of Permian lateral displacement and Cenozoic reactivation during the Indo-Asian collision, a simplified evolutionary model involving the Yili Block and its adjacent areas is proposed. This model emphasizes that there are three suture zones of different ages in western Tianshan, namely South Tianshan ophiolitic mélange zone, Central Tianshan HP metamorphic- ophiolitic mélange zone and North Tianshan ophiolitic zone, they indicate successive south-directed subductions of three different oceanic crusts intercalated between Tarim, Central Tianshan, Yili and Junggar blocks, generating the Early Paleozoic Central Tianshan arc and Late Paleozoic Yili-North Tianshan arc. The Paleozoic Tianshan Orogen was finally produced in Early Permian, and the tectonic setting changed from convergent orogeny to intra-continental strike-slip faulting.
Key words: Western Tianshan Belt, Yili Block, Paleozoic, kinematics, Zircon U-Pb dating, Ar-Ar geochronology, geochemistry, paleomagnetism, tectonic evolution