冀东黑云母片麻岩在1GPa压力下脱水熔融实验

报道冀东黑云母片麻岩在1GPa压力下脱水熔融实验的相关系。其固相线温度为812℃,黑云母消失的温度为837℃,角闪石消失的温度为887℃,在862℃时开始形成斜方辉石和单斜辉石。实验表明,在温度812-950℃范围内形成水不饱和的花岗质岩浆,数量为20%-30%,而留下的难熔残余是斜方辉石+单斜辉石+石榴石+斜长石+石英±角闪石,后者与麻粒岩相岩石的矿物组合相符合,暗示下地壳岩石经生成花岗质熔浆的熔融事件后,留下的将是麻粒岩相岩石。

DEHYDRATION-MELTING EXPERIMENT OF THE BIOTITE-GNEISS,EASTERN HEBEI,AT 1 GPa PRESSURE

This paper presents phase relationships of dehydration-melting experiment of the biotite——gneiss, Eastern Hebei Province, China. The temperatures of the solidus, biotite-out, pyroxen-in and amphibole-out, are 812℃, 837℃, 862℃ and 887℃, respectively. The experimental results in tills paper show that the resulting granitic magma at temperature of 812-950℃ is water-undersaturated. The fact of the waterundersaturated granitic magma dominated in the nature suggests that the formation of the granitic magma from lower crust is controlled mainly by the mechanism ofdehydration-melting. The dehydration-melting of the biotite gneiss of Eastern Hebeiat IGPa pressure shows that after the generation of 20%-30% of granitic magma, the refractory residue is Opx+Cpx+Gax+Ga+Qz+Am. The latter is consistent with the assemblage of themineral assemblage of the granulite metamorphic factes, which suggests that the refractory residue after removing the granitic melts by the melting event of the lower continental crust will be the granulite-factes rock. It also showsthat the granulite is lesulted at least partly from the dehydration-melting which is satisfied with the water——undersaturated condition for the formation of the granulite. The upper amphibolite factes with the development of migmatization at the depth of 10-20km is formed at a temperature of about 650-700℃ where both the biedte and amphibole are stable and muscovite is absent. However, the lower amphibolite factes without migmatization is characterized by the developing of muscovite. It seems that the migmatization widespread by occurred in the upper amphibolite factes regions is dliven mainly from the muscovite-dehydration-melting.