高级变质岩中深熔作用的相平衡研究

深熔作用在高级变质岩中非常普遍并受到广泛关注。自20世纪90年代以来,随着变质相平衡研究的突破性发展,利用THERMOCALC程序和视剖面图方法可以定量研究固相线以上的熔体形成、熔体分馏和退变质反应。变质沉积岩中的熔融作用主要有三种机制饱和水固相线上的熔融、白云母脱水熔融和黑云母脱水熔融。在模拟泥质岩石的KFMASH体系和NCKFMASH体系中的相平衡计算表明,NCKFMASH体系中铁镁矿物的相平衡关系受KFMASH亚体系中矿物相平衡关系的控制,但KFMASH亚体系中固相线位置要比实际的高50~60℃。因此,模拟泥质岩石的固相线以上的相平衡关系最好在NCKFMASH或组分更多的体系中进行。相平衡研究表明麻粒岩相岩石的保存与熔体丢失有关;混合岩的形成过程包括部分熔融作用、不同程度熔体分凝与汲取和不同程度的逆反应和退变反应。

Phase equilibria of anatexis in high-grade metapelites

Anatexis is pervasive in high grade metamorphic rocks and has received much attention from geoscientists. With the progress in the study of phase equilibria since the beginning of the 1990's, melt formation and fractionation and relevant retrograde reactions can be quantitatively studied using the software THERMOCALC and the pseudosection method. There are three main melting regimes in metasedimentary rocks: (1)melting at water-saturated solidus; (2)muscovite dehydration melting; and (3)biotite dehydration melting reactions. Calculation on phase equilibria in the KFMASH and NCKFMASH systems indicates that the phase relations of ferromagnesian minerals are controlled by the KFMASH. But the H_2O-saturated solidus in the KFMASH is 50-60℃ higher than the real minimum solidus in metapelites. Thus, the phase relations above the solidus of metapelite can be simulated better with the NCKFMASH. Or with other more multiple component systems. Recent research indicates that the preservation of granulite facies must have accompanied by melt loss. The formation of migmatite includes partial melting, partial segregation and extraction of melt and partial back and retrograde reactions.