【作者】 谭绿贵；

【导师】 周涛发；

【作者基本信息】 合肥工业大学 ， 矿物学岩石学矿床学， 2007， 博士

【摘要】 后碰撞作用可定义为：主海洋关闭以后，连续的板块会聚导致产生陆内的逆冲、扭动构造和地块的横向挤压或伸展，或沿巨大剪切带附近仍然有大量水平方向块体运动、岩浆活动和侧向增生，以及陆壳的垂向增生的陆内构造环境；时间上发生在主碰撞造山活动之后，后造山作用之前（即板内环境）这段时期内的板块地质作用。后碰撞作用是板块构造学说中整个造山旋回的一个重要阶段，而后碰撞岩浆活动（包括岩浆侵入活动和火山喷出活动）却是该过程中的一个重要地质构造事件。后碰撞岩浆活动的研究对于阐述板块构造活动过程完整性以及建立岩浆岩与板块构造的联系有着非常重要的意义。西准噶尔萨吾尔地区地处新疆阿勒泰地区吉木乃县及塔城地区和丰县，位于哈萨克斯坦—准噶尔板块北缘。本文基于野外地质研究开展了萨吾尔地区岩浆岩的常量元素、微量元素、稀土元素、同位素地球化学测试分析以及同位素精确定年工作，探讨了萨吾尔地区二叠纪火山-侵入岩浆活动规律，包括岩浆岩的地质特征及时空分布规律、岩石学、岩石化学、地球化学特征以及形成的地球动力学背景等。探讨了晚古生代侵入岩及二叠系火山岩形成的构造环境及其对中亚造山带演化的指示意义，以期对中亚造山带古生代地壳双向增生过程和大陆动力学背景提供有力的支持。区内广泛发育晚古生代后碰撞岩浆岩，侵入岩年龄在328.2—290.7Ma之间，时代上属于晚石炭世至早二叠世，区内侵入岩由早到晚（森塔斯岩体、沃肯萨拉岩体→塔斯特岩体→喀尔交岩体→阔依塔斯岩体、恰其海岩体）具有明显的地球化学演化特征。哈尔加乌组、卡拉岗组火山岩年龄在296.7—280Ma之间，为早二叠世火山活动产物。哈尔加乌组火山岩具有弱双峰式特征，卡拉岗组火山岩具有典型的双峰式特征，均形成于拉张的构造背景。据此认为晚石炭世至早二叠世，萨吾尔地区处于后碰撞构造背景，并逐渐由挤压—拉张过渡阶段演化到拉张阶段。区内侵入岩由I型花岗岩和A型花岗岩组成。其中，恰其海岩体、阔依塔斯岩体的岩石学和地球化学特征具有A型花岗岩的特征，属于A₂型花岗岩，侵位于板块碰撞后或造山后期（后碰撞阶段）的张性构造环境中。岩体具轻稀土富集的右倾稀土元素配分模型，δEu较低，Nd、Sr、Pb同位素显示出其幔源特征，O同位素组成δ¹⁸O值由于与大气水的同位素交换而较低。锆石SHRIMP U-Pb年龄分析表明，恰其海岩体结晶年龄为290.7±9.3Ma（1σ），阔依塔斯岩体结晶年龄为297.9±4.6Ma（1σ），时代上均属于早二叠世初。A₂型花岗岩恰其海岩体和阔依塔斯岩体的产出，表明西准噶尔萨吾尔地区在早二叠世初处于后碰撞阶段的伸展期。西准噶尔萨吾尔地区的A型花岗岩可以归入乌伦古富碱火成岩带。研究区早二叠世后碰撞A型花岗岩的确定为区域早二叠世地壳的垂向增生提供了新的证据。I型花岗岩有森塔斯、沃肯萨拉和塔斯特等岩体组成。其中，森塔斯岩体中二长花岗岩锆石SHRIMP U-Pb年龄为328.2±5.7Ma（1σ），沃肯萨拉岩体中二长花岗岩锆石SHRIMPU-Pb年龄为323.8±6.2 Ma（1σ），塔斯特岩体全岩⁴⁰Ar／³⁹Ar年龄为313.6±3.2Ma（1σ），均形成于晚石炭世。岩石偏碱性，具轻稀土富集的右倾稀土元素配分模型，森塔斯、沃肯萨拉岩体δEu较小，而塔斯特岩体δEu中等，Nd、Sr、Pb同位素显示出其幔源特征，具正常O同位素组成。森塔斯岩体、沃肯萨拉岩体和塔斯特岩体均属于后碰撞花岗岩，其形成表明晚石炭世萨吾尔地区乃至西准噶尔地区处于后碰撞构造环境，说明它们是后碰撞阶段伸展期或挤压—伸展转变期的产物。喀尔交岩体岩性以钠长花岗斑岩、钾长花岗斑岩为主，属过渡类型花岗岩。岩体锆石SHRIMP U-Pb年龄为302.6±7.6 Ma（1σ），时代上属于晚石炭世末。岩石偏碱性，具轻稀土富集的右倾稀土元素配分模型，δEu较小，Nd、Sr、Pb同位素显示出其幔源特征，O同位素组成由于与大气水的同位素交换而较低，成岩构造环境判别显示其形成于造山晚期（后碰撞阶段）挤压构造环境中。萨吾尔地区两类花岗岩（A型、I型）的稀土元素特征研究表明，两类花岗岩的稀土元素地球化学特征明显不同，这与其所处的不同后碰撞构造演化阶段密切相关。森塔斯岩体和沃肯萨拉岩体为形成于后碰撞阶段晚期挤压体制下的I型花岗岩，稀土元素特征显示其岩浆演化过程中分离结晶作用不发育，具幔源特征。阔依塔斯岩体和恰其海岩体为形成于后碰撞结束阶段拉张体制下的A型花岗岩，稀土元素特征显示其岩浆演化过程中分离结晶作用发育，其稀土元素显示一定的壳源特征，应为幔源岩浆受地壳物质混染所致。I型花岗岩和A型花岗岩的Nd、Sr、Pb同位素特征相似，均显示出幔源特征，它们是同源岩浆不同演化阶段的产物。两类花岗岩在O同位素以及稀土元素特征上存在明显差异。对比研究表明，可以将西准噶尔萨吾尔地区的A型花岗岩归入东准噶尔乌伦古富碱火成岩带。区内自泥盆纪至二叠纪均有火山活动，其中二叠纪火山作用尤其强烈。二叠纪火山岩地层包括哈尔加乌组和卡拉岗组，哈尔加乌组为一套陆相中基性—中性火山岩及火山碎屑岩，卡拉岗组为一套陆相中基性—中酸性火山岩及火山碎屑岩。哈尔加乌—卡拉岗旋回火山岩主要岩性包括橄榄玄武岩、玄武岩、粗玄岩、安山岩、粗安岩、流纹岩、火山碎屑岩等。根据火山岩地层综合剖面以及火山岩的岩石学、岩相学特征，萨吾尔地区二叠纪火山活动由早至晚可分为5个阶段：中性喷发阶段、间歇性基性喷发阶段、酸性爆发及喷溢阶段、小规模中性间歇性爆发及喷溢阶段、基性喷发阶段；火山岩为陆相火山岩，具有双峰式特征。对萨吾尔地区哈尔加乌组和卡拉岗组火山岩岩石Sm、Nd、Rb、Sr同位素测试结果显示，其成岩物质来源具有幔源特征，形成于伸展的构造背景下。通过研究该区火山岩的稀土元素特征，并利用稀土元素与常量元素相关关系以及稀土元素协变关系判别图解，结合其区域地质背景和岩石学、岩石化学特征，判断该地区二叠纪基性、中性火山岩成岩过程以平衡部分熔融作用为主，分离结晶作用不明显，而中酸性火山岩成岩过程则受到部分熔融作用和分离结晶作用的共同影响。更多还原

【Abstract】 Post-collision can be defined as: Continuous plate convergences will result in intracontinental thrusting, wrench structure, the block transverse compression or extention, or the inner-plate tectonic environment of significant block lateral movement, magmatism and the horizontal accretion, and vertical accretion of continental crust along horizontal direction following gigantic shear zone after major oceans shut down. Post-collision is a plate interaction which has taken place in a period between after the major orogenic movement and before the post orogeny （the tectonic environment of inner-plate）. Post-collision is an important stage of the whole orogenic cycle in plate tectonics, while post-collisional magmatic activities （including intrusive and extrusive magmatism） are important tectonic events. The study on post-collisional magmatic activities has very important meanings for both clarifying the integrity of plate tectonic activities and establishing relationships between magmatic rocks and plate tectonics.Sawu’er region is located in West Junggar, Jimunai County of Altay District and Hefeng County of Tacheng District, Xinjiang of China. It is along the north margin of Kazakstan-Junggar plate. Based on the field study, this work has carried out macroelements, microelements, rare earth elements, isotope geochemical analysis and isotope precise dating of the magmatic rocks in Sawu’er region, as well as studies on the rules of Permian volcanic-intrusive rocks in Sawu’er Region, including the geological characteristics and spatial and temporal distributions of magmatic rocks, petrology, petrochemistry, geochemical characteristics and geodynamic backgrounds etc. The forming tectonic environment of both the late Paleozoic intrusive rocks and the Permian volcanic rocks and their implications to the evolution of the Central Asian Orogenic Belt are discussed so as to furnish forceful supports for the reseach of Palaeozoic two-dimensional crustal growth in the Central Asian Orogenic Belt and the continental dynamic background.The post-collisional magmatic rocks of late Paleozoic is widespread in Sawu’er. The intrusions formed from 328.2 Ma to 290.7 Ma （from late Carboniferous to early Permian）. The geochemical evolvement characteristics of the intrusions from early to late （Sentasi intrusion, Wokensala intrusion→Tasite intrusion→Ka’erjia intrusion→Kuoyitasi intrusion, Qiaqihai intrusion） are obviously. The volcanic rocks in Haerjiawu Group and Kalagang Group formed from 296.7Ma to 280Ma （early Permian）. The volcanic rocks in Ha’erjiawu Group have weak bimodal characteristics and those in Kalagang Group have typical bimodal characteristics, indicating that they formed in an extensional setting. Based on the time frame, geochemical evolvement characteristics and tectonic setting of the late Paleozoic magmatic rocks, we think that the Sawu’er region was in a post-collisional setting from late Carboniferous to early Permian, that evolved from an compression-extension translational stage to an extensional stage gradually.The intrusions in the region consist of I granite and A ones, in which Qiaqihai and Kuoyitasi intrusions are important in the region with the characteristics of A-type granite, they belong to A2-type granite that were formed in an extensional tectonic setting of post-collision. The REE chondrite-normalized patterns of the intrusions show LREE enrichment and theδEu values are lower. The Nd, Sr, Pb isotope compositions of the intrusions indicate a mantle source, while the lowδ¹⁸O values resulted from the isotope exchange with meteoric water. According to SHRIMP U-Pb age dating results, the crystallization age of Qiaqihai intrusion is 290.7±9.3 Ma（1σ）,and that of Kuoyitasi intrusion is 297.9±4.6 Ma（1σ）,corresponding to the beginning of early Permian.The A₂-type granites indicate that the region was in the extensional period of the post-collisional stage at the beginning of early Permian in the Sawu’er region. The A-type granites in the Sawu’er region in west Junggar discovered from this work is analogous to the A-type granites found in east Junggar of the Ulungur alkali granites belt. The confirmatiom of post-collisional A-type granites of early Permian in the Sawu’er region provides new evidence for the regional vertical continental crust growth in early Permian. The former proposed Ulungur alkali granites belt may extend from the east Ulungur through the west Ulungur and to the Zhaisang in Kazakstan westwards.The I-type granites consist of Sentasi, Wokensala and Tasite intrusions. According to the SHRIMP U-Pb age analysis results, the crystallization age of Sentasi intrusion is 328.2±5.7 Ma（1σ） and that of Wokensala intrusion is 323.8±6.2 Ma（1σ）. According to ⁴⁰Ar/³⁹Ar age analysis result, the crystallization age of Tasite intrusion in the Sawuer region is 313.6±3.2 Ma（1σ）, which is corresponding to the productions of late Carboniferous. The intrusions are the partial alkali rock, whose REE distribution patterns are of the LREE rich type andδEu values in Sentasi, Wokensala intrusions are lower, whileδEu values are middle. The Nd, Sr, Pb isotope compositions of three intrusions indicate a mantle source, while theδ¹⁸O values are normal. These intrusions belong to post-collisional granite, indicating that the Sawu’er region indeed as well as the west Junggar was in the post-collisional setting in late Carboniferous. They might form in the extension period or from compressional to extensional period during the post-collisional stage.The Kaejiao intrusion in the Sawu’er region is mainly albite granite porphyry, potassium feldspar granite porphyry, it belongs to the transitional type of granite. The intrusion formed at the telophase of late carboniferous as its SHRIMP U-Pb zircon age is 302.6±7.6Ma（1σ） .The intrusion is the partial alkali, whose REE distribution patterns are of the LREE enrichment type,δEu value is low and Nd、Sr、Pb isotope reflects a mantle source characteristic. The O isotope of intrusion is low for the isotope exchange with meteoric water. Diagenetic distinguishing shows it formed in compressing structuring setting of the late orogenic period （post-collisional phase）.The characteristics of A-type and I-type granites in the Sawu’er region are obviously different, because the A-type and I-type granites formed at different stages of the post-collisional period. The Sentasi intrusion and Wokensala intrusion are the I type granites that formed at the late of the post-collisional period, and there was compressional stress. The characteristics of rare earth elements show that the fractional crystallization of the I-type granites is indistinct, and the sources of the I-type granites come from the mantle. The Kuoyitasi intrusion and Qiaqihai intrusion are the A-type granites, they were formed at the end of the post-collisional period in tensional setting. The characteristics of rare earth elements show that the fractional crystallization of the A-type granites is distinct. The sources of the A-type granites came from the mantle but contaminated by the crust.The Nd、Sr、Pb isotope characteristics of the I-type granites are similar to those of A-type granites. The I-type and A-type granites came from the mantle magma. They were the results of different evolusional phases of the same magma source. The O isotope and the REE characteristics of the I-type and the A-type granites were distinctly different. The A-type granites in the west of Zhungaer Sawu’er region should belong to the Ulungur alkali granites belt in East Zhungaer.The volcanic activities occurred in Sawu’er region during the middle Devonian to early Permian. Volcanic rocks are in the Haerjiawu Group and Kalagang Group of early Permian. The Haerjiawu Group consists of a series of basic to neutral continental volcanic rocks and pyroclastic rocks, and the Kalagang Group consists of a series of basic to acidic volcanic rocks and pyroclastic rocks. The volcanic rocks include olivine basalt, basalt, dolerite, andesite, trachyandesite, rhyolite, pyroclastic rock and so on. According to the characteristics of section, lithology and lithfacies, the Permian volcanic activity in Sawu’er Region can be grouped to five phases from early to late, neutral volcanic activity phase, intermadiate basic volcanic activity phase, acidic volcanic activity phase, small-scale intermadiate neutral volcanic activity phase and basic volcanic activity phase. The Permian volcanic rocks belong to continental volcanic rocks and have the characteristics of typical bimodal volcanic rock characteristics. This study indicates that they formed in an extensional tectonic setting.Based on the analysis of the REE’s geochemical characteristics of the volcanic rocks in the Sawu’er region, the correlativity of REE and major elements and diagrams of covariant relation of REE, and the research results of the regional geological setting, petrology and petrochemistry characteristics, it is inferred that the mechanism for formation of Premian basic and intermediate volcanic rocks is mainly the equilibrium partial melting, and the magmatic fractional crystallization is not significant, while the rock-foming processes of intermediate-acidic volcanic rocks were influenced by both the partial melting and the fractional crystallization. The REE geochemical research has provided the important evidence for the mechanism of magmatism of the Premian post-collision stage and the geodynamical evolution process.更多还原