蛇绿岩中辉长苏长岩的成因

Genesis of Gabbronorites in Ophiolites

在蛇绿岩的洋壳岩石和地幔岩石单元中通常可见少量的辉长苏长岩脉,其主要特征是含高钙长石以及斜方辉石作为主要的矿物相早先于斜长石结晶。已有的研究表明辉长苏长岩的母岩浆为相对于MORB更富水和高硅的钙碱性岩浆。尽管这种含水钙碱性岩浆的形成可能与俯冲过程有关,但是在现今大洋也发现有辉长苏长岩的存在,表明在洋中脊环境也存在有含水钙碱性岩浆的发育。通过对侵入到西藏普兰蛇绿岩地幔橄榄岩中的辉长苏长岩的研究,笔者提出它们可能是遭受海水蛇纹石化的大洋岩石圈地幔重熔而成,其形成过程可能与在洋中脊发育的拆离断层有关。

Gabbrronoritic dykes have been observed in both plutonic and mantle sections of global ophiolites. They are characterized by the occurrence of anorthitic plagioclase and the earlier crystallization of orthopyroxene relative to plagioclase. Previous studies had suggested that they were derived from ‘calc-alkaline＇ basaltic melts,i. e.,with higher water and Si O2 contents than MORB. Although formation of such calc-alkaline basalts had been related to subduction settings,the discovery of gabbronorites in modern oceans supports the existence of calc-alkaline basalts in the mid-ocean ridge setting. Mineralogical and petrological compositions of gabbronorites intruding into the mantle peridotites of the Purang ophiolite（ Tibet） had been studied. We proposed that they were formed via re-melting of oceanic mantle that were serpentinized by seawater. Genesis of gabbronorite in the mid-ocean ridge is probably related to the development of detachment fault.