Provenance of the Greater Himalayan sequence: Evidence from mafic granulites and amphibolites in NW Bhutan
Provenance of the Greater Himalayan sequence: Evidence from mafic granulites and amphibolites in NW Bhutan
复制标题
DOI：
10.1016/j.tecto.2009.10.014
复制
发表时间：
2010-01
期刊：
影响因子：
2.9
通讯作者：
J. Chakungal;J. Dostal;D. Grujic;S. Duchêne;K. S. Ghalley
中科院分区：
文献类型：
--
作者：
J. Chakungal;J. Dostal;D. Grujic;S. Duchêne;K. S. Ghalley
对不丹喜马拉雅西北部马桑康地区的镁铁质麻粒岩和角闪岩进行了地球化学和同位素特征研究，以确定其原岩历史。块体岩石主量元素和微量元素地球化学特征表明，该岩石为拉斑玄武岩和碱性玄武岩，含少量超镁铁质。锆石U-PbSIMS数据显示镁铁质岩浆活动的年龄为1742±39 Ma。经年龄校正的岩石的εND(1742年)值变化很大，范围从高正(+8.4)到负(−3.3)。正值意味着原始岩浆来源，类似于与裂谷有关的拉斑玄武岩。我们认为，马桑康套岩是在晚古元古代一次重大的热事件中形成的，该热事件导致北印度边缘之下的次大陆岩石圈地幔的活化和富集化。这些与裂谷有关的变质基性岩的地球化学特征可能是在洋底俯冲或俯冲的早期阶段产生的，从那里可能获得了动员和富集岩石圈下地幔所需的流体。尽管它们的出现很罕见，但大喜马拉雅序列(GHS)中的古元古代火成岩，除了整个大喜马拉雅序列(LHS)中已发现的物源外，可能还贡献了碎屑锆石群，形成了小喜马拉雅序列(LHS)年龄谱中的1.7-1.9Ga峰。此外，LHS和GHS的同时代古元古代岩浆作用表明，这两个岩石构造单元在那个时期可能属于同一大陆板块。
Mafic granulites and amphibolites in the Masang Kang area of NW Bhutan Himalaya have been investigated for their geochemical and isotopic characteristics in order to determine their protolith history. Bulk-rock major and trace element geochemistry indicate that the rocks were originally tholeiitic and alkali basalts with minor ultramafics. U–Pb zircon SIMS data suggest an age of 1742±39Ma for mafic magmatism. The age-corrected εNd(1742)values of the rocks are highly variable, ranging from high positive (+8.4) to negative (−3.3). The positive value suggests a primitive magma source, similar to that of rift-related tholeiites. We suggest that the rocks of the Masang Kang suite were produced during a major late Paleoproterozoic thermal event that caused the mobilization and enrichment of the sub-continental lithospheric mantle beneath the north Indian margin. The geochemical signature of these rift-related metabasic rocks may have been produced during an earlier episode of oceanic underplating or subduction from which the fluid required to mobilize and enrich the overlying sub-lithospheric mantle may have been derived. Though their occurrence is rare, Paleoproterozoic igneous rocks within the Greater Himalayan Sequence (GHS), in addition to sources identified throughout the LHS, may have contributed to the detrital zircon population that form the 1.7–1.9Ga peak in the age spectra of the Lesser Himalayan Sequence (LHS). In addition, the coeval Paleoproterozoic magmatism in both LHS and GHS suggests that the two lithotectonic units may have belonged to the same continental plate at that time period.