沂水杂岩中变泥砂质岩石的岩石化学特征及年代  

Geochemistry and age of a metapelite rock in the Yishui complex Shandong Province.

作　　者：赵子然[1] 宋会侠[1] 沈其韩[1] 宋彪[1,2] 

机构地区：[1]中国地质科学院地质研究所,北京100037 [2]北京离子探针中心,北京100037

出　　处：《岩石学报》2009年第8期1863-1871,共9页Acta Petrologica Sinica

基　　金：国家自然科学基金项目(40572110);基本科研业务经费资助项目(J0805;J0907)资助成果

摘　　要：含夕线石十字石榴二云斜长片麻岩是沂水杂岩中首次发现的一种少见的变泥砂质岩石,包裹于沂水牛心官庄岩浆杂岩体中,为残留的变质表壳岩透镜体,它经历了两期变质作用的改造。早期高角闪岩相变质与区域麻粒岩相变质有关,峰期矿物共生组合主要为:石榴子石(中心域)+黑云母±白云母+斜长石+石英,M_1峰期变质温压条件为:T=660±10℃,P=5.7±0.3kb;晚期角闪岩相变质矿物共生组合为:十字石+石榴子石(边部域)+黑云母±白云母+斜长石±夕线石+石英,以形成大量自形-半自形十字石和具有明显的成分环带的石榴子石为特征,晚期石榴子石的形成由核部→边部经历了一降温降压过程,石榴子石核部:T=650±10℃,P=7.7±0.5Kb,石榴子石边部:T=578±10℃,P=4.7±0.1kb;晚期变质作用早期(石榴子石成核)阶段与埋深导致的部分熔融有关,晚期石榴子石生长阶段与岩浆热事件有关。锆石SHRIMP U-Pb定年结果表明:碎屑锆石不一致线上交点年龄为2695±32Ma,代表变泥砂质岩石源区岩浆岩的结晶年龄,变泥砂质岩石的早期变质变质作用年龄小于此值;晚期变质作用年龄为2537±5Ma。A kind of metapelite of sillimanite-bearing staurolite-gamet-two-mica plagiogneiss is recognized at first time, which is as a relic of metamorphic supracrustal rock in the Niuxinguanzhuang magmatic complex. Two metamorphic phases are recognized by assemblage minerals in the rock. The first metamorphic phase (M(1)) is of high amphibolite facies, the peak-assemblage minerals include garnet (M(1)) + biotite muscovite + plagioclase + quartz +/- staurolite, which is related to the regional granulite facies metamorphism. The peak metamorphic conditions estimated by core-component of garnet are about T = 660 +/- 10 degrees C and P = 5.7 +/- 0.5kb respectively. The second metamorphic phases (M(2)) is of amphibolite facies which the assemblage minerals include staurolite + garnet (M(2)) + biotite +/- muscovite + plagioclase + sillimanite + quartz. The feature of assemblage minerals show that formed hair-sillimanite and garnet with clear component zones and a lots of subhedral-euhedral staurolite porphyroblasts. The metamorphic conditions that estimated by the components of garnet (M(2)) core and rim, are about T = 650 +/- 10 degrees C and P = 7.7 +/- 0.3kb, and T = 578 10 degrees C and P = 4.7 +/- 0.1 kb. It shows that garnet (M(2)) growing was at the conditions of decreasing temperature and pressure from core to rim, and garnet-core formed was related to partial melting of the upper crust resulted from burial and garnet growing was related to local contact metamorphism dued to the intrusion of magmatic complex. It is explained that the upper intercept age, 2695 +/- 32Ma by SHRIMP dating, of the detrital zircons in the metapelite is the crystallization time of magmatic rock as the source of metapelite, and the earlier metamorphism of the metapelite is obviously later than this time. The later stage of the second metamorphism, growth of the garnet (M(2)), took place at 2537 +/- 5Ma.

关 键 词：沂水 杂岩 变泥砂质岩石 岩石化学特征 complex supracrustal rock age 石榴子石 变质作用 角闪岩相变质 temperature and pressure related crystallization time 十字石 共生组合 峰期变质温压条件 GRANULITE FACIES the upper crust partial melting SHRIMP dating 

分 类 号：P58[天文地球—岩石学]