| 东准噶尔北缘早石炭世构造体制转变:来自碱性花岗岩年代学和地球化学制约 |
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| 引用本文： | 梁培,陈华勇,韩金生,吴超,张维峰,赵联党,王云峰.东准噶尔北缘早石炭世构造体制转变:来自碱性花岗岩年代学和地球化学制约[J].大地构造与成矿学,2017,41(1):202-221. |
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| 作者姓名： | 梁培 陈华勇 韩金生 吴超 张维峰 赵联党 王云峰 |
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| 作者单位： | 1. 中国科学院 广州地球化学研究所,中国科学院矿物学与成矿学重点实验室,广东广州510640;中国科学院大学,北京100049;2. 中国科学院 广州地球化学研究所,中国科学院矿物学与成矿学重点实验室,广东广州510640 |
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| 基金项目： | 国家重点基础研究计划“973”项目“新疆北部古弧盆体系成矿机理” |
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| 摘 要： | 新疆东准噶尔北缘位于西伯利亚板块和哈萨克斯坦-准噶尔板块的结合部位,是中亚造山带的重要组成部分,也是新疆北部最重要的成矿带之一。老山口碱性花岗岩和乔夏哈拉碱性花岗岩即位于该区域,LA-ICP-MS锆石U-Pb年龄显示其结晶年龄分别为330.5±3.5 Ma和331.1±3.1 Ma。结合区域内存在的多处近同时期的碱性花岗岩(布尔根碱性花岗岩、哈腊苏碱性花岗斑岩、乌图布拉克碱性花岗岩),指示东准噶尔北缘存在一期重要的早石炭世碱性花岗岩岩浆活动,并大致可分为东、中、西三段。这些早石炭世碱性花岗岩具有高硅(SiO_2=67.14%~83.02%)、富碱(Na_2O+K_2O=5.37%~10.73%)、低钛(TiO_2=0.04%~0.23%)、贫钙(CaO=0.04%~1.19%)的特征,与典型A型花岗岩特征相类似,成因类型上属A1型花岗岩,个别具有A2-A1型花岗岩过渡性质。微量元素组成具有富集大离子亲石元素K、Rb及高场强元素Nb、Zr、Hf、Th,亏损Ba、Sr、P、Eu、Ti的特征。轻稀土元素明显富集(LREE/HREE=3.42~8.11),具强烈的负Eu异常(δEu=0.03~0.74),稀土元素配分模式呈右倾海鸥型。岩石具有较高的ε_(Hf)(t)(7.6~12.4)和ε_(Nd)(t)值(5.4~6.9)。上述特征表明,这些碱性岩的母岩浆具有复杂的成因,推测为幔源岩浆底侵到下地壳,促使下地壳先存的富Nb玄武岩部分熔融,并发生岩浆混合,经过一定程度的分离结晶形成。综合本文数据及地质事实,我们认为东准噶尔北缘在358 Ma部分地区开始进入板内后造山伸展环境,即板内早期环境,但早石炭世(360~327 Ma)整体处于由后碰撞向板内后造山环境转化的过渡阶段。东准噶尔北缘东、中、西段进入板内环境的时间不尽相同,可能与其多俯冲岛弧系统拼贴增生时代的不均一性有关。
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| 关 键 词： | 东准噶尔北缘 碱性花岗岩 LA-ICP-MS锆石U-Pb年龄 岩石地球化学 板内环境 |
The Early Carboniferous Tectonic Transition in the Northern Margin of East Junggar: Constrains from Geochronology and Geochemistry of Alkali Granites |
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| LIANG Pei,CHEN Huayong,HAN Jinsheng,WU Chao,ZHANG Weifeng,ZHAO Liandang,WANG Yunfeng.The Early Carboniferous Tectonic Transition in the Northern Margin of East Junggar: Constrains from Geochronology and Geochemistry of Alkali Granites[J].Geotectonica et Metallogenia,2017,41(1):202-221. |
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| Authors: | LIANG Pei CHEN Huayong HAN Jinsheng WU Chao ZHANG Weifeng ZHAO Liandang WANG Yunfeng |
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| Abstract: | The northern margin of East Junggar,known as the important tectonic metallogenic belt of the Central Asian Orogenic Belt (CAOB),is situated between the Siberian and the Kazakhstan-Junggar plates.LA-ICP-MS U-Pb dating of zircons constrains the timing of crystallization of the Laoshankou,Qiaoxiahala alkali granites and Halasu alkali granite porphyries in this area is 330.5±3.5 Ma,327.0±2.1 Ma and 331.1±3.1 Ma,respectively.Combined with synchronous alkali granites previously identified in this area,they indicated an Early Carboniferous alkali magmatism in the northern margin of East Junggar,which can be divided into three parts in space.The Early Carboniferous alkali granites are characterized by high SiO2 (67.14％-83.02％),high alkaline (Na2O+K2O=5.37％-10.73％),low TiO2 (0.04％-0.23％) and low CaO (0.04％-1.19％),which belong to the Al-type granites with the transitional character of the A2-A1 type granite.The alkali granites are enriched in light rare earth elements (LREE),Rb,K,Zr,Hf,Th and depleted in Ba,Sr,P,Eu,Ti.Moreover,the high εHf(t) (7.6-12.4),εNd(t) (5.4--6.9),the enrichment of Nb and the depletion of Ta,indicate the complicated petrogenesis of the alkali granites.The underplating of mantle-derived magma,the partial melting of Nb-rich basaltic lower crust,magma mixing between basaltic and crustal melts and a certain degree of fractional crystallization produced the alkali granites.Besides,the geochemical data indicate that the alkali granites mostly formed in the early stage of the intraplate system (i.e.,post-orogenic extension environment).Combined with the geological facts and our data,we consider that the northern margin of East Junggar was in the transition stage between post-collision and intraplate during 358 Ma to 327 Ma.Moreover,the variation of the crystallization ages for the alkali granites indicate a heterogeneous transition for the northern margin of East Junggar,representing the different history of accretion-collision of the Paleozoic arcs. |
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| Keywords: | northern margin of East Junggar alkali granite LA-ICP-MS zircon U-Pb geochemistry early intraplate system |
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