950℃、1.0～3.5GPa下斜长角闪岩脱水熔融——压力和时间对结构的影响

利用YJ-3000t和JL-3600t多顶砧压力机,以哀牢山造山带南部红河县大白能—乐育剖面上的天然块状斜长角闪岩为初始样品,在950℃、1.0～3.5GPa、恒温20～300h条件下进行了两个系列的斜长角闪岩块状样品脱水部分熔融实验:(1)保持温度T=950℃,加热时间t=100h不变,改变压力(1.0～3.5GPa)的实验;(2)保持温度T=950℃,压力p=3.0GPa不变,改变加热时间(20～300h)的实验。结果表明,1.0～3.5GPa、950℃、恒温100h的条件下,随压力升高,斜长角闪岩中依次生成了单斜辉石+石榴石+熔体的矿物组合(1.0～1.5GPa)和单斜辉石+石榴石+熔体+硬玉+SiO2矿物+蓝晶石(2.0～3.5GPa)的矿物组合。3.0GPa、950℃条件下,随加热时间增加,实验产物中依次生成了单斜辉石+石榴石+熔体+硬玉+SiO2矿物+蓝晶石的矿物组合(20～100h)和单斜辉石+石榴石+熔体的矿物组合(150～300h)。斜长角闪岩的原岩结构决定了实验产物中新生矿物和熔体的分布。依据实验产物的矿物组合和新生矿物的分布特征,讨论了950℃、1.0～3.5GPa、恒温(20～300h)条件下,斜长角闪岩部分熔融过程的结构变化、变质反应以及石榴石冠状体的成因。

Textural development of dehydration-melting in amphibolite at 1.0-3.5 GPa and 950 ℃—Effect of pressure and time

Two sets of dehydration-melting with a natural solid amphibolite(56vol.% hornblende, 43vol.% plagioclase), collected from the Dabaineng-Leyu profile in the southern Ailaoshan orogenic belt, Honghe County, Yunnan Province, have been carried out in multi-anvil apparatus(YJ-3000t and JL-3600t) at 1.0-3.5 GPa and 950 ℃ for 20-300 h. One is keeping the temperature at 950 ℃ and the annealing time of 100 h, varying the pressure (1.0-3.5 GPa). The other is keeping the pressure at 3.0 GPa and temperature at 950 ℃, varying the annealing time (20-300 h). The products are inspected with microscope and electron probe. The results indicate that at 950 ℃, annealing time of 100 h, as the pressure in the range of 1.0-1.5 GPa, the mineral assemblage in the products is clinopyroxene+garnet+melt. As the pressure larger than 1.5 GPa, the mineral assemblage in the products is clinopyroxene+garnet+melt+Jadeite+SiO2±kyanite. However, at 3.0 GPa and 950 ℃, as the annealing time in the range of 20-100 h, the mineral assemblage of clinopyroxene+garnet+melt+Jadeite+SiO2±kyanite appears successively with time in the products. As the annealing time longer than 100 h, the mineral assemblage of clinopyroxene+garnet+melt appears in the products. The distribution of the newly-formed minerals and melt is restricted by the texture of the started amphibolite. Based on the mineral distribution and assemblage in the run products at 1.0-3.5 GPa and 950 ℃ for 20-300 h, the textural development of amphibolite during the partial melting process, the metamorphic reaction, and the garnet corona generation are discussed.