KMS XINJIANG INSTITUTE OF ECOLOGY AND GEOGRAPHY，CAS
| 乌孙山石炭纪火山岩的时空分布特征 、岩石成因及地质意义 | |
| 苏文博 | |
| Subtype | 硕士 |
| Thesis Advisor | 蔡克大 |
| 2018-06-01 | |
| Degree Grantor | 中国科学院大学 |
| Place of Conferral | 新疆乌鲁木齐 |
| Degree Discipline | 工学硕士 |
| Keyword | 增生型造山带 弧后伸展 西天山 伊犁中天山板块 中亚造山带 Accretionary orogenesis, Back-arc extension, Western Chinese Tianshan Yili-Central Tianshan Block, CAOB |
| Abstract | 中亚造山带是全球典型的增生型造山带，夹持于北部的西伯利亚克拉通、西部的东欧克拉通和南部的塔里木-华北克拉通之间，主要由岛弧、海山、蛇绿岩、增生杂岩和微大陆等多种不同的地质体相互拼贴而成。天山造山带位于中亚造山带的南部，是由古生代洋盆经过多阶段的俯冲和闭合形成的，洋盆的闭合包括位于哈萨克斯坦-伊犁板块和塔里木板块之间的南天山洋以及位于哈萨克斯坦-伊犁板块和准噶尔洋内弧之间的北天山洋。伊犁-中天山板块，作为天山造山带的一个重要组成部分，广泛分布着大量的晚古生代火山岩，这些火山岩包含了关于天山造山带构造演化的重要信息。 这些分布在伊犁-中天山板块的南北缘的晚古生代火山岩可划分为四条岩浆岩带，分别是伊犁地块北缘的科古琴山-吐拉苏带和阿吾拉勒带，伊犁地块南缘的乌孙山带和那拉提带。这些火山岩岩石成因复杂，尤其在火山岩的形成环境上仍存在着裂谷、岛弧和弧后拉张的争议。本次研究选择乌孙山岩浆岩带作为研究对象，在详细野外地质工作的基础上，结合火山岩岩相学、同位素年代学(锆石 U-Pb 定年)、主微量元素地球化学和 Sr-Nd、 Lu-Hf 同位素地球化学的研究成果，查明该岩浆岩带火山岩的时空分布特征、揭示火山岩的岩石成因， 阐明该岩浆岩带形成的大地构造背景。本论文主要取得了以下几点认识：(1)通过对伊犁地块南缘乌孙山岩浆岩带石炭纪火山岩进行 SIMS 和LA-ICPMS 锆石 U-Pb 年代学研究表明： 该地区火山岩浆活动剧烈，喷发时代主要在 355-350Ma、 338Ma、 325-322Ma 和 313Ma，指示四期岩浆事件。 可将四期岩浆事件划分为早石炭世早期（355-350Ma）、早石炭世晚期和晚石炭世（338Ma、325-322Ma、313Ma）。早石炭世早期的岩浆事件产出从基性岩到酸性岩如玄武岩、粗面安山岩、安山岩、英安岩和流纹岩连续演化的岩石组合，岩石呈钙碱性系列。早石炭世晚期的火山岩具有双峰式的组合特征。这些形成不同时代的双峰式火山岩具有两种不同的岩石组合系列：一组岩石组合为碱性系列，岩性主要包括辉长岩、玄武岩、玄武质粗面安山岩和流纹岩；另一组火山岩主要包括玄武岩和英安斑岩，岩性为钙碱性系列。 该组火山岩地层可见一条侵入其中的花岗闪长岩脉，时代为 313Ma。(2)早石炭世早晚期的火山岩都具有正的 εNd(t)值。其中早石炭世早期(355-350Ma)的火山岩具有低的 εNd(t)(+0.3-+1.6)值，而早石炭世晚期的火山岩具有较高的 εNd(t)值(+2.3-+5.0)。同位素的结果表明，乌孙山早石炭世的火山岩岩浆源区可能来源于亏损地幔，并且随着火山岩形成时代逐渐变年轻，火山岩的岩浆源区呈现一个逐渐亏损的趋势。其产出的从基性到酸性连续演化的岩石组合以及双峰式火山岩组合具有相同的同位素组分，表明火山岩形成主要受控于结晶分异作用。(3)乌孙山地区石炭纪火山岩均具有富集大离子亲石元素(LILEs)和轻稀土(LREEs)，亏损高场强元素(HFSEs，包括 Nb,Ta,Ti)的特征，说明火山岩形成于与俯冲相关的环境。相比于早石炭世早期(355-350Ma)的火山岩，晚期的岩浆活动具有更强的碱性特征以及不同的 Th/Yb 和 Th/Nb 比值，表明晚期的火山岩岩浆具有更少的流体/熔体的加入。该地区的基性火山岩具有和弧后盆地玄武岩(BABB)十分相似的微量元素特征，结合逐渐亏损的地幔源区，指示该地区火山岩很可能形成于弧后伸展环境。(4)乌孙山岩浆岩带石炭纪火山岩是形成于南天山大洋板块向北俯冲引起的弧后伸展背景下。 那拉提岩浆岩带和乌孙山岩浆岩带构成了古洋-陆汇聚板块边缘的岩浆弧-弧后增生体系。 |
| Other Abstract | The Central Asian Orogenic Belt (CAOB) is a typical accretionary orogenic belt,which is bracketed by the Siberian Craton to the north, the European Craton to thewest, and the Tarim-North China Craton to the south. Its formation was primarilyrelated to multi-stage accretion and collision of numerous tectonic units, includingisland arcs, ophiolites, seamounts, accretionary prisms and micro-continents. TheTianshan orogenic belt located in the southern domain of the Central Asian OrogenicBelt (CAOB), was generated by Paleozoic multi-stage subduction and closure ofseveral exhausted oceanic plates, including the South Tianshan Ocean and the NorthTianshan Ocean. The Yili-Central Tianshan Block, as a major continental fragment inthe Central Asian Orogenic Belt, holds a vast volume of Carboniferous volcanic rocks,constituting several subparallel magmatic belts, including Keguqinshan-Tulasu beltand Awulale belt in the north, and Wusun Mountain belt and Haerk-Nalati belt in thesouth. However, the petrogenesis and tectonic implications of these volcanic rocksremain enigmatic. This study reported detailed geological field investigation,conducted isotopic age data compilation and mapping their temporal-spatial character,combined major and trace element, Sr-Nd and Lu-Hf isotope data to reveal thepetrogenesis of Wusun Mountain magmatic belt, aiming to understand their tectonicimplications. The major conclusions are summarized as follow:(1) Zircon U-Pb dating results define four episodes of volcanic cycles at ca.355-350 Ma、 338 Ma、 325-322 Ma and 313 Ma. These different volcanic cycles canbe divided into two groups based on their formation time. One group is that thosevolcanics formed in the early period of Early Carboniferous (355-350 Ma), andcomprise basalt, trachy-andesite, andesite, dacite and rhyolite, all these rocks arecalc-alkaline features. The other one is formed in the late period of EarlyCarboniferous (338 Ma、 3225-322Ma and 313Ma), and include a bimodal volcanicsrocks. These volcanics rocks also compose of two groups of bimodal rock associations: one group is alkaline rocks which are gabbroic, basalt, basaltictrachy-andesite and rhyolite; another group is calc-alkaline rocks which are basalt anddacite porphyry, and there also have a granitic diorite intruded this volcanic stratum at313 Ma.(2)All these samples in Wusun Mountain have positive εNd(t) values. The earlyperiod of Early Carboniferous (355-350 Ma) volcanics have slightly positive εNd(t)values (+0.3 - +1.6), while the later volcanics have higher εNd(t) values (+2.3 - +5.0).The isotope data suggest that the sources of volcanics maybe derived from depletionmantle, and the sources variations with time elapse of the Wusun Mountain magmaticbelt are inferred to be the result of strengthening depletion of the magma sources. Theformation of continuous rock associations and bimodal rock associations in WusunMountain all controlled by fractional crystallization.(3) Trace elements of all these Carboniferous volcanic rocks show enrichmentsof LILEs and LREEs, but depletions of HFSEs (including Nb, Ta, and Ti), indicatingthat these volcanics may formed in a subduction-related environment. Compared tothe early periods volcanics (355-350 Ma), the later periods volcanics have moreobvious alkaline features and different Th/Yb and Th/Nb ratios, which means the latermagma have less addition of subduction-related fluid/melt. The trace elements ofbasic rocks in Wusun Mountain have much similar characteristics with back-arc basinbasalt, and these volcanics also have gradually depleted magma sources, therefore,these volcanics maybe formed in a back-arc extension environment.(4) Wusun Mountain volcanics were likely emplaced in a dynamic environmentof a back-arc propagation stage due to the northward subduction of the SouthTianshan oceanic plate. The Haerk-Nalati magmatic belt and the Wusun Mountainbelt constitute an arc-back-arc system in southern Yili-Central Tianshan Block. |
| Subject Area | 地球探测与信息技术 |
| Language | 中文 |
| Document Type | 学位论文 |
| Identifier | http://ir.xjlas.org/handle/365004/14985 |
| Collection | 研究系统_荒漠环境研究室 |
| Affiliation | 中国科学院新疆生态与地理研究所 |
| First Author Affilication | 中国科学院新疆生态与地理研究所 |
| Recommended Citation GB/T 7714 | 苏文博. 乌孙山石炭纪火山岩的时空分布特征 、岩石成因及地质意义[D]. 新疆乌鲁木齐. 中国科学院大学,2018. |
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