| 西准噶尔玛依拉山组志留纪玄武岩的地球化学特征及构造意义 |
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| 引用本文： | 杨高学,李永军,刘振伟,杨宝凯,张洪伟,佟丽莉.西准噶尔玛依拉山组志留纪玄武岩的地球化学特征及构造意义[J].大地构造与成矿学,2012,36(1):127-136. |
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| 作者姓名： | 杨高学 李永军 刘振伟 杨宝凯 张洪伟 佟丽莉 |
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| 作者单位： | 1. 长安大学地球科学与资源学院,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. 新疆维吾尔族自治区地质矿产勘查开发局第七地质大队,新疆乌苏,833000 |
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| 基金项目： | 中央高校基本科研业务费专项资金，国土资源大调查项目 |
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| 摘 要： | 西准噶尔地区中-上志留统玛依拉山组主要分布于玛依拉山一带,以玛依勒蛇绿岩的围岩产出,两者为断层接触,主要组成为灰绿-暗灰绿色凝灰质粉-细砂岩,砂岩和砂砾岩组合,夹硅质岩和玄武岩。对玄武岩进行详细的岩石地球化学研究表明,SiO2含量中等(47.1%～53.92%),高Fe2O3T(12.54%～17.82%)、Al2O3(13.3%～15.7%)、Na2O(3.84%～8.02%),低TiO2(0.45%～1.48%)、MgO(3.28%～5.77%,Mg#=27.01～41.96)、K2O(0.36%～0.7%),全碱K2O+Na2O含量为4.4%～8.39%,属于亚碱性拉斑玄武岩系列。稀土元素总量较低(∑REE=27.16×10-6～54.41×10-6),轻、重稀土分馏较为明显((La/Yb)N=1.53～2.74),无明显Eu异常(Eu/Eu*=0.96～1.16),稀土配分模式类似于E-MORB。相对富集LILE(如Rb、Ba、Th和K),亏损HFSE(如Zr、Ti),明显的Nb和Ta负异常,具有岛弧玄武岩的地球化学特征。综合研究认为玛依拉山组玄武岩形成于俯冲带上的弧后盆地环境,与玛依拉山蛇绿岩的形成环境不同,其岩浆来源于尖晶石二辉橄榄岩2%～10%的部分熔融,并有少量俯冲流体的参与。结合前人研究资料,认为西准噶尔在志留纪-石炭纪处在洋内弧演化阶段。
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| 关 键 词： | 玄武岩 弧后盆地 玛依拉山组 地球化学 西准噶尔 |
Geochemistry of the Basalts from the Silurian Maylashan Formation in the West Junggar and its Tectonic Implications |
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| YANG Gaoxue
,
LI Yongjun
,
LIU Zhenwei
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YANG Baokai
,
ZHANG Hongwei
,
TONG Lili.Geochemistry of the Basalts from the Silurian Maylashan Formation in the West Junggar and its Tectonic Implications[J].Geotectonica et Metallogenia,2012,36(1):127-136. |
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| Authors: | YANG Gaoxue LI Yongjun LIU Zhenwei YANG Baokai ZHANG Hongwei TONG Lili |
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| Institution: | 1 (1.Earth Science & Resources College of Chang′an University; Key Laboratory of Western China′s Mineral Resources and Geological Engineering, Ministry of Education, Xi′an 710054, Shaanxi, China; 2.No.7 Geological Survey Team, Xinjiang Bureau of Geology and Mineral Resource Exploration, Wusu 833000, Xinjiang, China) |
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| Abstract: | The Maylashan area is situated in the southern part of the West Junggar, NW China. The Middle-Upper Silurian Maylasha Formation consists of grayish green tuffaceous siltstone and fine-grained sandstone, sandstone and conglomerate, with intercalated beds of chert and basalt, and fault contacts with the Maylashan ophiolitic mélange. The basalts are of sub-alkaline tholeiitic showing geochemical characteristics similar to those of island arc basalt (IAB), with low TiO2 (0.45%~1.48%), MgO (3.28%~5.77%, Mg#=27.01~41.96), K2O (0.36%~0.7%) and total alkaline (K2O+Na2O=4.4%~8.39%), medium SiO2 (47.1%~53.92%), high Fe2OT3(12.54%~17.82%), Al2O3 (13.3%~15.7%) and Na2O (3.84%~8.02%). The basalts are lower in REE (∑REE=27.16×10-6~54.41×10-6), and exhibit slightly flat REE patterns, with (La/Yb)N=1.53~2.74, weak or no Eu anomaly (Eu/Eu*=0.96~1.16), which are similar to those of E-MORB. Moreover, the basalts are enriched in LILEs ( e.g. Rb, Ba, Th and K) and depleted in HFSEs (e.g. Ti and Zr) with pronounced negative Nb-Ta anomalies. It can be deduced that the volcanic rocks were derived from partial melting of spinel iherzolite mantle source (2%~10% partial melting) with the participation of small amount of subducted fluid, under back-arc basin setting different from that of the Maylashan ophiolitic mélange. Thus, an intra-oceanic subduction model was proposed for the Silurian-Carboniferous evolution of the West Junggar. |
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| Keywords: | basalt back-arc basin Maylashan Formation geochemistry West Junggar |
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