阴山陆块武川石榴基性麻粒岩P-T条件及其变质时代:来自相平衡模拟与锆石U-Pb定年的约束
发布时间：2018-10-21 10:42
【摘要】：武川高级片麻岩地体中石榴基性麻粒岩的变质用与同位素年代学研究对于揭示阴山陆块新太古代构造演化过程具有十分重要的研究意义。它们主要以不规则透镜体或变形岩墙/岩脉群的形式赋存于新太古代晚期英云闪长质片麻岩或变质表壳岩系之中,并切割近南-北向的区域性片麻理。岩相学观察、矿物相转变分析与矿物化学研究表明,武川石榴基性麻粒岩保留了十分典型的高压麻粒岩相矿物:石榴石+单斜辉石+斜长石+角闪石+石英+铁-钛氧化物。其中,粗粒石榴石边部常发育微弱的扩散环带,表现为从幔部至边部,镁铝榴石组分不断减少,相应地铁铝榴石组分不断增加,而钙铝榴石与锰铝榴石组分基本不变,指示晚期冷却降温作用对石榴石成分产生一定影响。斜长石具有细粒包体型与粗粒基质型两种不同的类型,它们具有十分相似化学成分,均为An=35~45的中长石。在NCFMASHTO(Na_2O-CaO-FeO-MgO-Al_2O_3-SiO_2-H_2O-TiO_2-Fe_2O_3)体系下,利用THERM OCA LC 3.33软件,对两件石榴基性麻粒岩样品进行了相平衡模拟,模拟的峰期矿物组合为:石榴石+单斜辉石+斜长石+角闪石+石英+铁-钛氧化物,与岩相学观察十分一致。采用石榴石中最小x(g)Fe~(2 +)/(Fe~(2 +)+Mg))与斜长石是中最小ca(pl)(Ca/(Ca+Na))等值线,将本区石榴基性麻粒岩峰期高压麻粒岩相的温压条件限定在P=1.31~1.40GPa,T=770~840℃的范围内。LA-ICP-MS锆石U-Pb定年结果表明,两件石榴基性麻粒岩麻粒岩中发育的变质锆石分别记录了2517±6Ma(BT58-1,MSWD=0.66,n=21)与2512±16Ma(LH66-1,MSWD=0.26,n=42)的加权平均年龄,与阴山陆块其它新太古代岩石记录的约2500Ma变质年龄一致,被解释为本区石榴基性麻粒岩遭受高压麻粒岩相变质时代。结合本区其它新的研究资料,本文认为武川石榴基性麻粒岩形成可能与区内新太古代晚期造山作用有关。
[Abstract]:Metamorphism and isotopic chronology of garnet granulites in the upper gneiss terrane of Wuchuan are of great significance for revealing the evolution of Neoarchean tectonics in the Yinshan block. They mainly occur in the form of irregular lens or metamorphic diornesian gneiss or metamorphic epidermal rock series in the late NeoArchean, and cut the regional schistemology in the near south to north direction in the form of irregular lens or metamorphic diornetic gneiss / vein group in the late NeoArchean. The petrographic observation, mineral phase transformation analysis and mineral chemistry study show that the garnet granulite retains a typical high-pressure granulite mineral: garnet monoclinopyroxene plagioclase hornblende quartz ferro-titanium oxide. Among them, the marginal coarse-grained garnet often develops a weak diffusion ring, which shows that from the mantle to the edge, the composition of the magnesia-aluminite decreases continuously, the corresponding component of the metro-garnet increases continuously, but the components of the calcium and manganese garnet are basically unchanged. It is indicated that the late cooling and cooling effect has certain influence on the composition of garnet. Plagioclase has two different types of fine-grained inclusions and coarse-grained matrix types. They have very similar chemical compositions and are both meso-feldspar of An=35~45. In NCFMASHTO (Na_2O-CaO-FeO-MgO-Al_2O_3-SiO_2-H_2O-TiO_2-Fe_2O_3) system, two garnet based granulite samples were simulated by using THERM OCA LC 3.33 software. The simulated peak mineral assemblage is: garnet monoclinopyroxene plagioclase hornblende quartz ferro-titanium oxide. It is very consistent with petrographic observation. The minimum x (g) Fe~ (2) / (Fe~ (2) Mg) and plagioclase are the minimum ca (pl) (Ca/ (Ca Na) isolines in garnet. The temperature and pressure conditions of the high pressure granulite facies during the peak period of pomegranitic granulites in this area are limited to the temperature range of Pu 1.31 ~ 1.40 GPA Tf770,840 鈩，
本文编号：2284847
[Abstract]:Metamorphism and isotopic chronology of garnet granulites in the upper gneiss terrane of Wuchuan are of great significance for revealing the evolution of Neoarchean tectonics in the Yinshan block. They mainly occur in the form of irregular lens or metamorphic diornesian gneiss or metamorphic epidermal rock series in the late NeoArchean, and cut the regional schistemology in the near south to north direction in the form of irregular lens or metamorphic diornetic gneiss / vein group in the late NeoArchean. The petrographic observation, mineral phase transformation analysis and mineral chemistry study show that the garnet granulite retains a typical high-pressure granulite mineral: garnet monoclinopyroxene plagioclase hornblende quartz ferro-titanium oxide. Among them, the marginal coarse-grained garnet often develops a weak diffusion ring, which shows that from the mantle to the edge, the composition of the magnesia-aluminite decreases continuously, the corresponding component of the metro-garnet increases continuously, but the components of the calcium and manganese garnet are basically unchanged. It is indicated that the late cooling and cooling effect has certain influence on the composition of garnet. Plagioclase has two different types of fine-grained inclusions and coarse-grained matrix types. They have very similar chemical compositions and are both meso-feldspar of An=35~45. In NCFMASHTO (Na_2O-CaO-FeO-MgO-Al_2O_3-SiO_2-H_2O-TiO_2-Fe_2O_3) system, two garnet based granulite samples were simulated by using THERM OCA LC 3.33 software. The simulated peak mineral assemblage is: garnet monoclinopyroxene plagioclase hornblende quartz ferro-titanium oxide. It is very consistent with petrographic observation. The minimum x (g) Fe~ (2) / (Fe~ (2) Mg) and plagioclase are the minimum ca (pl) (Ca/ (Ca Na) isolines in garnet. The temperature and pressure conditions of the high pressure granulite facies during the peak period of pomegranitic granulites in this area are limited to the temperature range of Pu 1.31 ~ 1.40 GPA Tf770,840 鈩，
本文编号：2284847
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