摘要
变质基性岩在高温-超高温下部分熔融可以形成TTG(英云闪长质-奥长花岗质-花岗闪长质)质熔体,有关熔融反应机理、熔体地球化学特征以及太古宙TTG质岩石成因问题备受国内外学者关注。本文基于对相关实验岩石学研究的总结,结合基性岩高温-超高温相平衡的模拟计算,分析了变质基性岩(斜长角闪岩)深熔变质反应过程、P-T条件及其与TTG质岩石成因的联系。变质基性岩高温-超高温深熔作用主要受角闪石脱水熔融反应控制。在1.0GPa以下的无石榴石域,角闪石分解反应主要为:角闪石=单斜辉石+斜方辉石+斜长石+熔体(R1),该反应为多变滑动反应,以斜方辉石出现(800℃)和角闪石消失(1000~1100℃)为标志,其滑动温度范围超过200~300℃。实验岩石学确定的斜长角闪岩开始熔融或缺流体固相线大致相当于斜方辉石出现温度。实际上角闪石脱水熔融反应是从饱和水固相线开始的,反应为:角闪石+石英=单斜辉石+斜长石+熔体(R1a),开始有黑云母参与熔融反应,但该反应对熔体贡献有限。在1.0GPa以上的石榴石域,不同实验所确定的石榴角闪岩缺流体固相线温度主要介于800~900℃之间,固相线表现为正斜率、负斜率、或者为与压力无关的直线等不同结果。相平衡模拟计算表明在石榴石稳定域角闪石脱水熔融反应为较陡的负斜率,分为两部分:当有斜长石存在时,反应为角闪石+斜长石+石英=石榴石+单斜辉石+熔体(R2),低温部分有白云母、绿帘石参与反应。该反应从饱和水固相线(约630℃)开始,到角闪石消失(超过1000℃),滑动温度范围可超过400℃,跨越石榴角闪岩亚相与角闪高压麻粒岩亚相范围;在斜长石消失后角闪石脱水熔融反应为角闪石+石英=石榴石+单斜辉石+熔体(R2a),低温部分有绿帘石、白云母参与熔融反应,该反应从饱和水固相线(约650℃)开始,到角闪石消失(超过900℃),滑动温度范�
Partial melting of metabasites under high-temperature （HT） and ultrahigh-temperature （UHT） conditions can form Tonalite-Trondhjemite-Granodiorite （TI＇G） melts. The related melting mechanism, melt geochemistry and petrogenesis of the Archean TTGs have been widely concerned. Based on the reviews of relevant experimental studies along with metamorphic phase equilibria calculation of metabasites at HT-UHT conditions, the present paper presents an overview of the melting process of metabasites （amphibolites） , P-T conditions and relations with the petrogenesis of TTGs. The HT-UHT metamorphic processes of metabasites are dominately controlled by amphibole dehydration melting reactions. The breakdown of amphibole in garnet-free domain under 1.0GPa is dominated by a multivariant continuous reaction of hb = cpx ＋ opx ＋ pl ＋ L （melt） （ R1 ） , occurring over a temperature range of 200-300℃ marked by the appearance of orthopyroxene at 800~C and the disappearance of amphibole at I000 - 1100℃. According to experimental data, the initial melting temperature or the fluid-absent solidus of amphibolites corresponds to the temperature when orthopyroxene appears. In fact, the dehydration melting of amphibole should have started at temperatures just over the fluid-saturated solidus, and is dominated by reaction of hb ＋ q = cpx ＋ pl ＋ L （Rla） with involvement of biotite in the initial melting stage, producing limited amount of melt. While in the garnet-bearing domains above 1.0GPa, many experiments suggest that the fluid-absent solidi of garnet amphibolite lie between 800 - 900℃ with positive or negative slopes. Metamorphic phase equilibria modeling suggest that amphibole dehydration melting reactions in the garnet-bearing domains have steeply negative slopes and behave differently with or without the presence of plagioclase. In the plagioclase-bearing domains, amphibole dehydration melting reaction is hb ＋ pl ＋ q = g ＋ cpx ＋ L （R2） with the involvement of muscovite and epid
出处
《岩石学报》
SCIE
EI
CAS
CSCD
北大核心
2017年第5期1381-1404,共24页
Acta Petrologica Sinica
基金
国家自然科学基金项目(41430207)资助
