深海橄榄岩研究进展

ADVANCE IN STUDY OF ABYSSAL PERIDOTITES

很久以来，深海橄榄岩一直被认为是洋中脊下地幔熔融残留体，但最近深海橄榄岩实际矿物组分研究和全岩化学成分重建的结果表明，深海橄榄岩是洋脊下地幔熔融残留体和过量橄榄石的混合物。深海橄榄岩的成因是洋脊下上隆地幔降压熔融作用和熔体上升通过地幔最上部的热边界层时发生冷却、结晶出橄榄石的联合作用的结果。地幔熔融程度越高，深海橄榄岩越亏损，则含有越多的过量橄榄石。为此，只要把深海橄榄岩中过量的橄榄石剔除后，其实际矿物组分就能有效地反映洋脊下地幔熔融作用和熔融萃取过程。

Abyssal peridotites have been long interpreted to be residues of mantle melting beneath mid ocean ridges,but the recent studies of their modal proportions and reconstructed whole rock compositions show that they are mixtures of mantle melting residues and excess olivine beneath an ocean ridge.The origin of abyssal peridotites results from a combination of decompression melting of upwelling mantle and olivine crystallization as a result of cooling of acending melts passing through the cold thermal boundary layer atop the mantle.The greater the extent of mantle melting,the more depleted the peridotites,and the higher the excess olivine contents.Hence peridotite modes can be used to reflect efficiently mantle melting and melt extraction processes beneath ocean ridges only if the excess olivine is removed appropriately.