阿尔金南缘构造带西段早古生代绿片岩的地球化学特征及构造环境  

Geochemical characteristics and tectonic setting of the Early Paleozoic greenschist in the western segment of the southern Altyn Tagh marginal tectonic belt

作　　者：覃小锋[1] 夏斌[1] 李江[2] 陆济璞[2] 许华[2] 周府生[2] 胡贵昂[2] 李乾[2] 

机构地区：[1]中国科学院广州地球化学研究所,广东广州510640 [2]广西区域地质调查研究院,广西桂林541003

出　　处：《中国地质》2007年第5期799-807,共9页Geology in China

基　　金：中国地质调查局地质大调查项目(19991300008091)资助。

摘　　要：阿尔金南缘构造带西段混杂岩伴生有大量较为新鲜的绿片岩构造岩块。对绿片岩的岩石学和地球化学的详细研究表明,其原岩属于基性火山岩类(拉斑玄武岩类),并存在洋岛(板内)型(OIB)、洋中脊型(E-MORB)和火山弧型(IAT)三类玄武岩。E-MORB型具有大体类似的地球化学性质,它们的TiO2含量均较低,为0.93%～1.75%,平均1.34%;P2O5含量为0.09%～0.15%,平均0.13%;高场强元素Zr为79×10-6～146×10-6,Hf为2.6×10-6～3.5×10-6,Nb为6.6×10-6～15.3×10-6,轻稀土呈亏损-略富集型,具洋中脊玄武岩特征。IAT型TiO2含量比E-MORB型更低,为0.4%,P2O5为0.08%;高场强元素Zr为56×10-6,Hf为1.6×10-6,Nb为5.9×10-6,轻稀土呈略富集型,具岛弧型玄武岩特征。而OIB型均富集TiO2,含量为1.96%～3.08%,平均2.49%;P2O5为0.23%～0.34%,平均值0.26%;高场强元素Zr为204×10-6～237×10-6,Hf为4.2×10-6～7.2×10-6,Nb为14.6×10-6～22.1×10-6,轻稀土呈富集型,具洋岛(板内)玄武岩特征。OIB、E-MORB和IAT组合的出现说明在早古生代阿尔金南缘可能存在过洋盆。There outcrop many fresh greenschist tectonic blocks in the western segment of the southern Altyn Tagh marginal tectonic belt. Intensive petrological and geochemical studies show that： the protoliths of the greenschist are basic volcanic rocks （tholeiites）, and in addition three types of basalt are also recognized, namely, oceanic island （within plate） basalt （OIB）, mid-oceanic ridge basalt （E- MORB） and island arc basalt （IAT）. The E-MORB have similar geochemical characteristics, with low Ti （TiO2=0.93%-1.75%, average 1.34%） and P （P2O5=0.09%-0.15%, average 0.13%） and the high field strength elements Zr=（79-146）×10^-6, Hf=（2.6-3.5）×10^-6 and Nb=（6.6-15.3）×10^-6, being LREE-depleted or slightly enriched. IAT have lower Ti （TiO2=0.4%） and P （P2O5=0.08%） than those of MORB and the high field strength elements Zr=56×10^-6, Hf=1.6×10^-6 and Nb=5.9×10^-6, being LREE-slightly enriched. OIB have high Ti （TiO2 = 1.96%-3.08%, average 2.49%） and P （P2O5=0.23%-0.34%, average 0.26%）, with the high field strength elements Zr=（204-237）×10^-6, Hf=（4.2-7.2）×10^-6 and Nb=（14.6-22.1）×10^-6, being LREE-enriched. The presence of the OIB, E- MORB and IAT assemblage suggests the existence of an ocean basin in the southern Altyn Tagh marginal tectonic belt during the Early Paleozoic.

关 键 词：绿片岩 地球化学 构造环境 阿尔金南缘构造带西段 

分 类 号：P588.344[天文地球—岩石学]