乔治王岛菲尔德斯半岛火山岩地球化学及生成与演化

本文详细讨论了南极菲尔德斯半岛岛弧火山岩的岩石化学、微量元素,稀土元素及同位素地球化学特征。区内务类火山岩普遍具高铝的特点,且有着相似的稀土元素分布模式。岩石富集Sr、Rb、Ba、K、Th等高度不相容元素,而极度亏损Ni、Cr、等过渡元素。Nd、Sr、Pb、O同位素特征显示岩石的幔源性质。主元素、微量元素混合模拟计算表明:本区高铝玄武岩可由上地幔中等程度(20—25％)部分熔融形成的橄榄拉斑质原始岩浆经一定程度的橄榄石(12％)和单斜辉石(28％)的分离结晶而成。以斜长石和辉石为主的分离结晶作用控制了本区岩石的演化。

GEOCHEMISTRY, ORIGIN AND EVOLUTION OF THE VOLCANIC ROCKS IN FILDES PENINSULA, KING GEORGE ISLAND

Geochemical characteristics, including petrochemistry, trace element, REE, and isotope, of island arc volcanic rocks in Fildes Peninsula are discussed thoroughly in this paper. It is showed that the volcanic rocks in the studied area which, consist-of high-Al basaltic--dacitic rocks are generally high in Al and the basaltic rocks are also depleted in K and Ti; the different type of rocks have the similar REE distribution patterns which are slightly enriched in LREE and, their total REE contents increase with increasing SiO2 contents, which indicate that the different type of rocks are cognate. The rocks have higher contents of highly incompatible elements , such as Sr, Rb, Ba, K, and Th ,than MORB and the abundences of these elements are similar to those of calc-alkaline series rocks; high depletion in Ni, Cr in the studied ro'cks suggests that they can not be derived from direct crystallization of primary basaltic magma and may be subjected to fractional crystallization of mafic phases; Nd, Sr, Pb, 0 isotopic features show their mantle-derived. Model calculation of major oxides and trace elements(REE) show that the high--Al basalt in the Peninsula can be formed by fractional crystallization Of olivine 12 % and clinopyroxene (28%) from primary olivine tholeiitic magma which is derived from partial melting (20 - 25%) of upper mantle spinel lherzolite and that fractional crystallization of plagioclase and pyroxene controls the evolving from high-Al basalt to andesite and to dacite.