蛇绿岩岩石组合及洋脊下岩浆作用

Rock Assemblages of Ophiolites and Magmatism beneath Oceanic Ridges

蛇绿岩的岩石组合从下至上分为 4个单元 ,即 :变质橄榄岩单元、深成杂岩单元、席状岩墙群杂岩单元和喷出岩单元。各单元的岩石组合是多种多样的 :变质橄榄岩单元主要由方辉橄榄岩、二辉橄榄岩和少量纯橄岩及斜长二辉橄榄岩组成 ;深成杂岩单元包括辉长岩 -镁铁质堆晶岩和超镁铁质堆晶岩 ,在深成杂岩和席状岩墙群杂岩单元内有复杂的岩浆侵入事件 ;喷出岩单元不仅仅由玄武岩组成 ,还包括安山岩、玻安岩、钠长岩以及角砾岩、凝灰岩等。蛇绿岩和深海钻探研究表明 ,许多蛇绿岩不具层状结构。蛇绿岩剖面可分为两类 :一类为具层状结构模型的蛇绿岩 ,另一类不具层状结构。不同的蛇绿岩剖面反映了洋脊之下不同的动力学过程 ,主要受板块扩张速度和岩浆供给的制约。

A complete ophiolite section can be divided from bottom to top into four units, namely metaperidotite unit, plutonic complex unit, sheeted dike complex unit and extrusive rock unit, each unit having varied rock assemblages. The metaperidotite unit is mainly composed of harzburgite and lherzolite together with minor dunite and plagio_lherzolite. The plutonic complex unit consists of gabbro, mafic cumulate and ultramafic cumulate. There exist complicated magmatic intrusive events in the plutonic complex and sheeted dike complex units. The extrusive rock unit includes basalt, andesite, boninite and albitite as well as breccia and tuff. Researches of ophiolites and Deep Sea Drilling Project and Ocean Drilling Project, however, indicate that many sorts of ophiolites have no layered structure. Ophiolite sections can thus be classified into two types: one is the section with layered structure, and the other is the section without layered structre. These different ophiolite sections actually reflect different dynamic processes beneath oceanic ridges, which are mainly controlled by the plate spreading velocity and the amount of magmatic supply.