蛇绿岩岩石组合及洋脊下岩浆作用

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在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、钠长岩以及乐砾岩、凝灰岩等

Rock Assemblages of Ophiolites and Magmatism beneath Oceanic Ridges

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.