地学前缘 ›› 2010, Vol. 17 ›› Issue (1): 49-60.

• 论文 • 上一篇    下一篇

东准噶尔东北缘后碰撞火山岩成因与构造环境

  

  1. 西部矿产资源与地质工程教育部重点实验室, 陕西 西安 710054
    2长安大学 地球科学与资源学院, 陕西 西安 710054
    3甘肃省地矿局 第三地质矿产勘查院, 甘肃 兰州 730050
    4中国冶金地质总局 西北局, 陕西 西安 710061
    5新疆维吾尔族自治区有色地质矿产勘察院, 新疆 乌鲁木齐 830000
  • 出版日期:2010-01-28 发布日期:2010-01-28
  • 作者简介:杨高学(1980—),男,博士研究生,从事于区域地质调查与花岗岩类研究。Email: mllygx@126.com
  • 基金资助:

    国家自然科学基金项目(40534020);新疆国土资源厅大调查项目(QD200508)

Genesis and tectonic settings of postcollision volcanic rocks in north eastern margin of East Junggar, Xinjiang.

YANG  Gao-Hua, LI  Yong-Jun, LI  Zhou-Cang, LIU  Xiao-Yu, YANG  Bao-Kai, TUN  Hong-En   

  1. 1Key Laboratory of Western Chinas Mineral Resources and Geological Engineering,Ministry of Education, Xian 710054, China
    2Earth Science ＆ Resources College of Changan University,  Xian 710054, China
    3No3 Geological Party, Gansu Bureau of Geology and Mineral Exploration and Development, Lanzhou 730050, China
    4Northwest Bureau of China Metallurgical Geology Bureau, Xian 710061, China
    5Xinjiang Institute of Geological Exploration for Nonferrous Resources, rümqi 830000, China
  • Online:2010-01-28 Published:2010-01-28

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摘要：

研究了东准噶尔东北缘5个地区(三塘湖盆地、陆东—五彩湾地区、扎河坝西北、陆梁隆起和贝勒库都克一带)不同时代的8个后碰撞火山岩。岩石岩性以玄武岩和玄武安山岩为主,有少量流纹岩,绝大多数属于钙碱性高钾钙碱性系列。样品TiO2质量分数较高(02％～33％),MgO的质量分数分布范围较广(111％～1074％),Mg＃指数为12～75,样品全碱含量较高w((Na2O+K2O)=34％～1016％),相对富集大离子亲石元素(LILE)和轻稀土元素(LREE),强烈亏损高场强元素(HFSE)Nb、Ta,弱亏损Zr、Hf和Ti,具有弱的Eu和Ce异常(δEu=060～121,δCe=089～115)。样品(87Sr/86Sr)i值为0702 78～0705 42,(143Nd/144Nd)i值为0512 517～0512 648,具有高正εNd(t)值(+4～+75),La/Nb值(10～53)均高于原始地幔(098～1),Nb/U值(2～37,大部分<30),明显低于MORB和OIB,介于原始地幔和陆壳之间,显示亏损地幔源区特征,同时在某些方面又显示源区富集的特征,可能是由于地壳物质参与岩浆形成的。火山岩在形成时代上属于整个准噶尔后碰撞深成岩浆活动的范围,既显示板内岩浆演化特征,又具有弧火山岩地球化学痕迹,形成于后碰撞伸展垮塌的构造背景,与岩石圈地幔底侵有关,是和东准噶尔东北缘后碰撞花岗岩相匹配的,均形成于后碰撞期。最新获得的锆石SHRIMP UPb定年数据和RbSr等时线年龄对认识准噶尔洋闭合的时限和建立东准噶尔的构造岩浆演化框架提供可靠依据。

关键词: 后碰撞期, 火山岩, 地球化学, 岩石成因, 东准噶尔, 新疆

Abstract:

 The statistical study of eight postcollision volcanic rocks of different times in five areas (Santanghu Basin, LudongWucaiwan region, Northwest Zhaheba, Luliang uplift and Beilekuduke) in north eastern margin of East Junggar, Xinjiang shows that the volcanic rocks are mainly composed of basalts and basaltic andesites with a small amount of rhyolite, which belong to calcalkaline and high K calcalkaline series. The volcanic rocks have a wide range of MgO(111％1074％)and Mg＃(1275) values, relatively high alkali ((Na2O+K2O)=34％1016％) and high content of TiO2 (TiO2=02％33％). The rocks are enriched in LILE (like Rb and Ba) and LREE, intensely depleted in HFSE (like Nb and Ta), and weakly depleted in Zr, Hf and Ti, without significant Eu and Ce anomalies (δEu=060121, δCe=089115). The (87Sr/86Sr)ivalues of volcanic rocks are 070278070542, and the (143Nd/144Nd)i values are 05125170512648, with a high positive εNd(t)(+4+75); the La/Nb ratios (1053) is higher than that of primitive mantle(0981), and the Nb/U ratios (237, the vast majority of rocks <30) are lower than those of MORB and OIB. Between the primitive mantle and crust, the rocks show the depletion of the mantle source characteristics, but in some aspects the rocks also show the enrichment of source characteristics, which may be due to the involvement of the magma in the formation of crustal material. The formation times of volcanic rocks belong to the era of postcollisional deep magmatic activity in Junggar; the rocks not only show the characteristics of intraplate magmatic evolution, but also have traces of arc volcanic rocks geochemistry; maybe they are from extensional settings of postcollisional period, and relate to lithospheric mantle underplating; they match the postcollision granite in northeastern margin of East Junggar, and they all formed in the postcollision period. The latest available zircon SHRIMP UPb and wholerock RbSr isochron dating ages provide strong evidence for rebuilding tectonic framework, recovering magma evolution and  recognizing the closure time of Junggar ocean in East Junggar.

Key words: postcollisional period, volcanic rocks, geochemistry, petrogenesis, East Junggar, Xinjiang

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