赣中地区早中生代OIB碱性玄武岩的厘定及构造意义  

Early Mesozoic OIB type alkaline basalt in central Jiangxi Province and its tectonic implications

作　　者：王岳军[1] 廖超林[1] 范蔚茗[1] 彭头平[1] 

机构地区：[1]中国科学院广州地球化学研究所,广东广州510640

出　　处：《地球化学》2004年第2期109-117,共9页Geochimica

基　　金：国家自然科学基金(40334039);中国科学院知识创新工程重要方向项目(KZCX2-102;GIGCX-03-01;KZCX2-SW-117)

摘　　要：通过40Ar/39Ar年代学、元素、同位素地球化学研究,在赣中地区安塘组上部厘定了早中生代OIB型碱性岩浆作用。研究表明,位于赣中安塘组上部的玄武岩为碱性橄榄玄武岩,形成于168Ma,具有狭窄的元素、同位素变化范围,地壳混染作用不明显,经历了橄榄石和单斜辉石的结晶分异。其LILE和HFSE富集,Nb/La=1.4～1.5,Ce/Pb=21～25,Nb/U=42～45,εNd(t)=+5.22～+6.58,(87Sr/86Sr)i=0.70313～0.70336,具有Hawaii-OIB型元素、同位素地球化学特征,是含石榴子石橄榄岩低度部分熔融的产物,其起源与软流圈地幔上涌和岩石圈伸展减薄有关。这为华夏陆块早中生代岩石圈伸展减薄提供了更为直接的证据。A set of 40Ar/39Ar geochronological, elemental and isotopic geochemical analyses of early Mesozoic OIB type alkaline basalts from Antang area in the central Jiangxi Province is reported. These basalts are found at the upper part of Antang Group (J1), and a representative sample gives a 40Ar/39Ar plateau age of 168 Ma. They are the alkaline olivine basalts and exhibit the narrow elemental and isotopic composition variation with LILE and HFSE enrichment, similar to that of OIB. These basalts also exhibit fractionated REE pattern with no Eu anomalies and Nb/La=1.4～1.5, Ce/Pb=21～25, Nb/U=42～45. Age corrected initial 87Sr/86Sr ratio spans a narrow range of 0.703 13～0.703 36 and εNd(t) of +5.22～+6.58. These features are similar to those of Hawaii OIB with insignificant crustal contamination and proportional fractionation of olivine and clinopyroxene. These alkaline basalts likely represent the lower degree partial melting products of a garnet bearing peridotite in response to the asthenosphere upwelling and the lithospheric extension. The occurrence of the OIB type alkaline olivine basalts (168 Ma) provides direct evidence for the intra lithospheric thinning extension in the Cathaysia block during early Mesozoic.

关 键 词：碱性玄武岩 早中生代 软流圈上涌 岩石圈伸展减薄 江西 

分 类 号：P588.145[天文地球—岩石学] P597[天文地球—地质学]