东准噶尔石炭系巴塔玛依内山组火山岩全岩Sm-Nd等时线年龄及其构造意义  

Whole-rock Sm-Nd isochron age of Carboniferous volcanic rocks in eastern Junggar and its tectonic significance

作　　者：张峰[1,2] 徐涛[2] 范俊杰[2] 潘爱军[2] 王斌[2] 朝银银[2] 

机构地区：[1]中国地质大学,北京100083 [2]中国人民武装警察部队黄金地质研究所,河北廊坊065000

出　　处：《地球化学》2014年第3期301-316,共16页Geochimica

基　　金：国土资源部地质矿产调查专项评价项目(1212010913028;1212011085018)

摘　　要：东准噶尔地区石炭系巴塔玛依内山组火山岩分布广泛,规模巨大,目前对其形成时代及构造背景的认识还存在着较大的争议。以火山岩中的玄武岩、玄武安山岩为研究对象,进行了岩石学、岩石地球化学和Sm-Nd同位素地球化学方面的研究。结果表明,该套火山岩属高钾钙碱性火山岩系,微量元素和稀土元素特征相似,（143Nd/144Nd）i变化幅度小,εNd（t）和T2DM近乎相同,具同源岩浆演化特征和良好的封闭条件。利用Sm-Nd等时线定年方法获得的玄武岩全岩等时线年龄为（319.7±5.9） Ma,（143Nd/144Nd）i =0.512414±0.000006, MSWD=0.34,与区域地质构造背景和已有化石证据基本吻合,代表了火山岩的形成时代。准噶尔地区晚古生代区域构造背景复杂。位于西伯利亚板块和哈萨克斯坦-准噶尔板块之间的古亚洲洋存在双向俯冲消减过程。南向俯冲带位于扎河坝-克拉玛依一线,俯冲作用至少延续至（319.7±5.9） Ma。持续的南向俯冲造就了东准噶尔地区扎河坝下泥盆统托让格库都克组火山岩代表的岛弧和卡拉麦里蛇绿岩代表的卡拉麦里不成熟弧后盆地的形成。东准噶尔地区石炭系巴塔玛依内山组火山岩就是该过程中不成熟弧后盆地的产物,成岩过程可能是：古亚洲洋持续南向俯冲,导致卡拉麦里地区幔源物质大量上隆并引起弧后扩张,并在消减沉积物和（或）俯冲洋壳脱水产生的流体作用下发生部分熔融,形成的玄武质岩浆不断底侵至壳幔边界,引起少量主体由古生代残余洋壳和岛弧体系组成的年轻下地壳物质部分熔融生成岩浆,并发生相互较完全的混合,而后随着混合岩浆的不断聚集和构造伸展作用的进一步持续,岩浆沿构造薄弱带快速上升至地表,喷发成岩。319.7-311 Ma 左右的中亚造山带持续南向增生导致了卡拉麦里弧盆北侧古亚洲洋的消亡,并最终迫使卡拉麦里弧盆北向俯冲消减The volcanic rocks from Carboniferous Batamayineishan formation in eastern Junggar basin, widely distributed with huge scale, have long been debated on the formation age and tectonic setting. Petrological, petrogeochemical and Sm-Nd isotopic geochemical characteristics indicate that the basalts and basaltic andesites of the formation are of high-K calc-alkaline volcanic series, with similar characteristics of trace elements and REE and similar values of （143Nd/144Nd）i, εNd（t） and T2DM, suggesting that they have homologous magmatic evolution features and good enclosed conditions. The basalt whole rock isochron age by Sm-Nd isochron dating method is （319.7＆#177;5.9） Ma, with （143Nd/144Nd）i= 0.512414＆#177;0.000006, MSWD = 0.34, which is consistent with the regional tectonic background and the existing fossil evidence. It is represents the volcanic rock formation age. Paleoasian Ocean between the Siberian and Kazakhstan-Junggar plates existed bidirectional subduction process. Southward subduction zone located along Zhaheba-Karamay, the subduction continued until at least （319.7＆#177;5.9） Ma. The continued southward subduction created an island arc that represented by Tuoranggekuduoke formation volcanic rocks and the Kalamaili immature back-arc basin that represented by Karameh ophiolite on Lower Devonian of Zhaheba in the East Junggar. The East Junggar Carboniferous Batamayineishan formation volcanic rocks are the products of immature back-arc basin, and the diagenetic mechanism may be that the subduction of the PaleoAsian Ocean trigger the evolvement of a large amount of mantle material in Kalamaili, and dehydration partial melting of subducted sediments and/or oceanic crust, the generated basaltic magmas constantly underplated to the crust-mantle boundary and heated the lower crust and triggered the formation of small amount of magmas by partial melting of young lower crust which was mainly composed of Paleozoic remnant oceanic crust and arc complex. The two types of magma mixed. Thereaft

关 键 词：火山岩 SM-ND同位素 弧后盆地 石炭纪 巴塔玛依内山组 东准噶尔 

分 类 号：P597[天文地球—地球化学]