Discovery of the Late Paleozoic Ocean Island Basalts (OIB) in Hainan Island and Their Geodynamic Implications
详细信息
- 责任者：Wang Zhilin (Key Laboratory of Mineralogy and Metallogeny ; Guangzhou Institute of Geochemistry ; Chinese Academy of Sciences ; Guangzhou 510640 ; China) ; Xu Deru
- 刊名：Acta Petrologica Sinica
- 出版年：2013
- 卷期：29(3)
- 关键词：洋岛玄武岩 ; ocean-island basalts ; 地球动力学 ; geodynamics ; 海南 ; Hainan Province
- 页码：p.875-886
- 图表：illus., 3 tables, 33 refs.
- 分类号：0801
- issnNo：ISSN1000-0569
- isbnNo：CN11-1922/P
摘要
A suite of metamorphic mafic-ultramafic lavas outcrop in Junying-Bangxi area,Hainan Island,South China.Based on the geological,petrological,mineralogical and geochemical results,the Junying-Bangxi metamorphic mafic-ultramafic lavas can be classified into two major magma types,namely,the high-Mg and the low-Mg types,in which the former is high in Mg(Mg#=76.9～81.3),whereas the latter is high in TiO2(2.34%～3.27%) but low in Mg(Mg#=40.7～48.4).The chondrite-normalized REE patterns of this suite of rocks appear LREE-riched type((La/Yb)N=2.40～7.58) with no apparently Eu anomaly.Primitive mantle-normalized trace element patterns show no Nb depletion and slightly Ta positive anomaly.The 87Sr/86Sr(270Ma) and εNd(270Ma) values range from 0.70645 to 0.70956 and from +4.7 to +6.5,respectively.These geochemical characteristics are similar to that of ocean island basalt(OIB).Some trace element ratios characterizing the source regions,such as Ta/Hf,Th/Nb,Nb/Zr,La/Ta,La/Sm,(La/Nb)PM,and(Th/Ta)PM,reveal that the Junying-Bangxi lavas have affinity to OIB from intraplate magmatism associated with mantle plume activity.Electron microprobe analyses on olivine phenocrysts in the Junying-Bangxi ultramafic lavas further indicate that the high-Mg nature is caused by olivine accumulation.Combined with the low Fo(68～77) of olivine phenocrysts,we propose that the primary magma likely is low-Mg basaltic magma which have derived from the low degree partial melting of garnet lherzolite mantle.The lower contents in Cr and Ni for low-Mg type,relative to that for the high-Mg type,indicate fractional crystallization of olivine and clinopyroxene occurs subsequently.The Late Paleozoic OIB-type lavas in Junying-Bangxi area probably were produced in an extensional back-arc basin,owing to the subduction of Paleo-Tethys Ocean and the probably synchronous initiation of the mantle plume under South China continential margin.This suite of metamorphic mafic-ultramafic lavas,as new evidence,is significant for discussing the evolution of South China Eastern Paleo-Tethyan Ocean.
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