大陆地壳熔融和酸性岩浆起源的热源问题

Heat source for continental crust melting and silicic magma generation

地壳的熔融受控于地壳的岩石成分、减压作用、外来水的加入和地壳内部的地温条件等众多因素,其中确定熔融所需热量的来源至关重要。本文简要回顾了板内环境下地壳熔融和酸性岩浆起源的相关研究,总结了引发地壳熔融热源的热源问题。目前一般认为地壳熔融是由底侵的高温幔源岩浆引发的,这种观点得到多学科资料的支持。不过底侵观点未能很好地解释大规模基性和酸性岩浆作用之间存在的显著不相关性和S型花岗岩的成因,相关数值模拟结果也高估了岩浆侵入所能引发的地壳熔融规模。本文提出岩石圈的不均一拉张和地表拉张裂谷内沉积物的快速加积可使地壳内部形成较高的地温梯度,进而造成以变沉积岩为主要成分的上地壳的大规模熔融和相关S型酸性岩浆作用的发生。

Crustal melting is dominated by the factors of rock type,water content and decompression melting.It requires a high geothermal gradient within the crust and its heat source is therefore the key to understanding the crustal anatexis and generation of silicic magma.This paper reviews studies on crustal melting and tries to summarize the proposed heat source that induces crustal anatexis.In most cases,heat has been believed to originate from the hot,mantle-derived mafic magma underplated into the crust or at the Mohorovic Discontinuity level.However,the underplating model,to some extent supported by certain evidence,has difficulty explaining the irrelevant occurrence between massive silicic and mafic magmatism and the fact that the genesis of S-type granite magma is closely related to melting of the upper crust.Moreover,extant results of underplating simulation overestimate the potential effect of basaltic magma intrusion on the crustal melting.A hypothesis is proposed as an alternative explanation of the large-scale crustal melting:the combined effects of the depth-dependent lithospheric extension and crustal thickness compensation of the rapidly-deposited sediments leads to an abnormally high geothermal gradient inside the crust,resulting in extensive melting of the upper crust consisting of meta-sedimentary rock and the generation of S-type silicic magma.