麻粒岩相变质作用与花岗岩成因-Ⅰ:变质泥质岩/杂砂岩高温-超高温变质相平衡  

Granulite facies metamorphism and petrogenesis of granite(Ⅰ) : Metamorphic phase equilibria for HT-UHT metapelites/greywackes

作　　者：魏春景[1] 朱文萍[1] 

机构地区：[1]造山带与地壳演化教育部重点实验室北京大学地球与空间科学学院,北京100871

出　　处：《岩石学报》2016年第6期1611-1624,共14页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(41430207)资助

摘　　要：麻粒岩相岩石作为洞察下地壳的窗口一直备受重视。二十世纪九十年代以来麻粒岩研究的一个重要进展是利用变质相平衡的定量研究方法模拟岩石中所发生的深熔变质反应、熔体成分变化、及熔体丢失对变质矿物组合的影响等。本文利用KASH、NKASH和KFMASH等简单体系的相平衡关系,做出P-T投影图、组分共生图解和基于固定全岩成分的P-T视剖面图解,并结合有关实验岩石学结果,讨论了高温和超高温条件下变质泥质岩和杂砂岩中的变质熔融反应、矿物组合、全岩成分与P-T条件之间的相互关系。多数变质泥质岩和杂砂岩中饱和流体固相线熔融反应可利用NKASH体系中有水流体参与的熔融反应模拟,在没有外来流体注入时,这些反应可形成＆lt;3mol%熔体。在不同体系中白云母脱水熔融反应型式及其P-T条件不同,如在NKASH和KFMASH体系中模拟计算的白云母脱水熔融反应与相应的实验结果相似,分别控制了白云母分解熔融的温度下限和上限;白云母的分解温度会随着其中Fe、Mg和Ti含量的增加而升高,也随着共生斜长石中钙长石组分增加而升高,泥质岩中白云母脱水熔融可以形成-10mol%熔体。在KFMASH体系中黑云母脱水熔融反应表现为4条单变反应,其理论计算的温度比实验模拟的结果低一些。在NCKFMASH体系或实际岩石中黑云母脱水熔融反应为滑动反应,如NCKFMASH体系中黑云母从其开始熔融到最后消失在泥质岩中可跨越-100℃,在杂砂岩中可跨越30-50℃。黑云母的稳定温度随着镁值升高而升高,其稳定上限受钛影响更大,黑云母脱水熔融可以形成超过30mol%-40mol%熔体。KFMASH体系中的相平衡模拟表明以出现斜方辉石＋夕线石和假蓝宝石为特征的超高温组合易于出现于富镁泥质岩中,而对正常成分泥质岩在达到1000℃的超高温条件下,主要出现石榴石＋夕线石（即夕线榴）,该组合在更高Granulites have attracted much attention as a window of probing the lower crust tectonic evolution. Since 1990 s one of the most important advances in the study of granulite is quantitatively modeling the melting reactions,melt compositions,melt loss and its influence on mineral assemblages in high-grade rocks. Based on a series of P-T projections,compatibility diagrams and qualitative P-T pseudosections for fixed bulk-rock compositions in the simple systems involving KASH,NKASH and KFMASH,and available experimental results,discussions were presented in this paper in terms of the relations among melting reactions,mineral assemblages,bulk-rock compositions and P-T conditions for the meta-pelitic and greywacke rocks under HT-UHT conditions. The fluid-saturated solidus reactions for most meta-pelites / greywackes can be modeled by the fluid involving reactions in the NKASH system,which can produce melt of 3mol% without fluid infiltration. The P-T conditions of muscovite dehydration melting reactions vary in different systems. For example,muscovite melting reactions calculated in the systems NKASH and KFMASH,which are in good accordance with the relevant experimental results,constrain respectively the lower and upper temperature limits of muscovite breakdown. The muscovite breakdown temperature may increase as increasing its Fe,Mg and Ti contents,or the anorthite content in coexisting plagioclase. Muscovite melting can produce melt of - 10mol% in metapelites. In the system KFMASH biotite dehydration melting involves four univariant reactions,with calculated temperature conditions somewhat lower than the experimental results. These biotite melting reactions are continuous in the system NCKFMASH,covering a temperature range of - 100℃ in metapelites and 30 - 50℃ in metagreywackes. The biotite breaking temperature may increase as increasing its Mg#; and the upper temperature limit is greatly influenced by the involvement of Ti. Biotite melting can produce melt of 30mol% - 40mol% in metapelites. Phase modelling in th

关 键 词：麻粒岩 高温-超高温变质作用 变质相平衡 泥质岩与杂砂岩 

分 类 号：P588.34[天文地球—岩石学]