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| 扎河坝蛇绿混杂岩内富铌玄武(安山)岩的地球化学特征及其地质意义 | |
| 引用本文： | 牛贺才,单强,于学元,张兵,罗勇,杨武斌.扎河坝蛇绿混杂岩内富铌玄武(安山)岩的地球化学特征及其地质意义[J].岩石学报,2009,25(4):916-924. |
| 作者姓名： | 牛贺才 单强 于学元 张兵 罗勇 杨武斌 |
| 作者单位： | 1. 中国科学院广州地球化学研究所,广州,510640 2. 新疆维吾尔自治区地质矿产勘查开发局第七地质大队,乌苏,833000 3. 中国科学院广州地球化学研究所,广州,510640;中国科学院研究生院地球科学学院,北京,100049 |
| 基金项目： | 国家自然科学基金(40673036)、中国科学院知识创新工程重要方向项目(KZCX2-YW-107) 和“十一五”国家科技支撑计划(2006BAB07B02-03) |
| 摘 要： | 在新疆北部东准噶尔的扎河坝蛇绿混杂岩中发现的富铌玄武（安山）岩，其SiO2含量介于46.71%~57.65%，TiO2含量为1.00%~1.76%，与太古代绿岩带内富铌玄武（安山）岩相似，Na2O含量为3.86%~6.64%，P2O5为0.34%~0.82%，明显高于太古代绿岩带富铌玄武（安山）岩。扎河坝富铌玄武岩铌含量介于7.22×10-6~21.91×10-6之间，大于7×10-6，与典型的富铌玄武岩相同。该岩石轻重稀土元素分馏较明显，其分布模式为无明显铕至弱负铕异常的右倾曲线。尽管铌的绝对含量较高，但由于钍和轻稀土元素更加富集，在微量元素蛛网图中扎河坝富铌玄武（安山）岩仍表现为铌的明显亏损，同时高场强元素Zr、Hf及Ti也表现出一定程度的亏损。微量元素地球化学特征显示，扎河坝蛇绿混杂岩内富铌玄武（安山）岩形成于古亚洲洋的洋内弧，它是被埃达克质岩浆交代的地幔楔橄榄岩部分熔融的产物，同时大洋沉积物及俯冲板块释放的流体对成岩作用也有一定的贡献。富铌玄武（安山）岩作为弧前增生楔定位在扎河坝蛇绿混杂岩体内，与早前报道的超高压变质岩共存表明，该蛇绿混杂岩体至少记录了两次性质不同的古亚洲洋洋壳俯冲，这更进一步证实新疆北部晚古生代新增陆壳是古亚洲洋多次俯冲作用的产物。 |
| 关 键 词： | 富铌玄武(安山)岩 扎河坝蛇绿混杂岩体 洋壳俯冲 大洋沉积物 |
| 收稿时间： | 2008/11/25 0:00:00 |
| 修稿时间： | 2009/3/15 0:00:00 |
Geochemistry of the Nb-enriched basalt and its significances in Zaheba ophiolite melange |
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| NIU HeCai,SHAN Qiang,YU XueYuan,ZHANG Bing,LUO Yong and YANG WuBin.Geochemistry of the Nb-enriched basalt and its significances in Zaheba ophiolite melange[J].Acta Petrologica Sinica,2009,25(4):916-924. | |
| Authors: | NIU HeCai SHAN Qiang YU XueYuan ZHANG Bing LUO Yong and YANG WuBin |
| Institution: | Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China;No.7 Geological Survey Team, Xinjiang Bureau of Geology and Mineral Resource Exploration, Wusu 833000, China;Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; College of Earth Science, Graduate University of Chinese Academy of Sciences, Beijing 100049, China;Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China; College of Earth Science, Graduate University of Chinese Academy of Sciences, Beijing 100049, China |
| Abstract: | Nb-enriched basaltic rocks are identified within the Zaheba ophiolite melange in the eastern Junggar, northern Xinjiang. They show high Nb contents of 7.22×10-6 to 21.91×10-6, SiO2 contents of 46.71% to 57.65% and TiO2 contents of 1.00% to 1.76%, similar to Nb-enriched basalts from Archaean greenstone belt. The REE patterns are of LREE enrichment with weak Eu anomalies, suggesting obvious fractionation. Moreover, they are characterized by obviously negative Nb anomalies and negative Ti anomalies, suggesting that the Nb-enriched basalts were probably derived from partial melting of mantle peridotite that interacted with slab melt under high geothermal gradient in the intra-ocean arc setting of the Paleo-Asian Ocean. Moreover, Nb-enriched basalts occurred in the Zaheba ophilite as a fore-arc accretionary prism.The association of the Nb-enriched basalts with ultra-high pressure metamorphic rocks found previously by the authors implies that more than two times of the Paleo-Asian oceanic crust subduction with different characteristics were recorded in the ophiolite. Therefore, multiple partial melting of the subducting oceanic crust and ocean sediments, and the succedent interactions between the slab melt and peridotite in the mantle wedge was probably responsible for the crust growth and the formation of central Asian orogenic belts. |
| Keywords: | Nb-enriched basalt Zaheba ophiolite melange Oceanic crust subduction Oceanic sediment |
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