陰山陸塊武川石榴基性麻粒巖P-T條件及其變質(zhì)時代:來自相平衡模擬與鋯石U-Pb定年的約束
發(fā)布時間：2018-10-21 10:42
【摘要】：武川高級片麻巖地體中石榴基性麻粒巖的變質(zhì)用與同位素年代學(xué)研究對于揭示陰山陸塊新太古代構(gòu)造演化過程具有十分重要的研究意義。它們主要以不規(guī)則透鏡體或變形巖墻/巖脈群的形式賦存于新太古代晚期英云閃長質(zhì)片麻巖或變質(zhì)表殼巖系之中,并切割近南-北向的區(qū)域性片麻理。巖相學(xué)觀察、礦物相轉(zhuǎn)變分析與礦物化學(xué)研究表明,武川石榴基性麻粒巖保留了十分典型的高壓麻粒巖相礦物:石榴石+單斜輝石+斜長石+角閃石+石英+鐵-鈦氧化物。其中,粗粒石榴石邊部常發(fā)育微弱的擴(kuò)散環(huán)帶,表現(xiàn)為從幔部至邊部,鎂鋁榴石組分不斷減少,相應(yīng)地鐵鋁榴石組分不斷增加,而鈣鋁榴石與錳鋁榴石組分基本不變,指示晚期冷卻降溫作用對石榴石成分產(chǎn)生一定影響。斜長石具有細(xì)粒包體型與粗粒基質(zhì)型兩種不同的類型,它們具有十分相似化學(xué)成分,均為An=35~45的中長石。在NCFMASHTO(Na_2O-CaO-FeO-MgO-Al_2O_3-SiO_2-H_2O-TiO_2-Fe_2O_3)體系下,利用THERM OCA LC 3.33軟件,對兩件石榴基性麻粒巖樣品進(jìn)行了相平衡模擬,模擬的峰期礦物組合為:石榴石+單斜輝石+斜長石+角閃石+石英+鐵-鈦氧化物,與巖相學(xué)觀察十分一致。采用石榴石中最小x(g)Fe~(2 +)/(Fe~(2 +)+Mg))與斜長石是中最小ca(pl)(Ca/(Ca+Na))等值線,將本區(qū)石榴基性麻粒巖峰期高壓麻粒巖相的溫壓條件限定在P=1.31~1.40GPa,T=770~840℃的范圍內(nèi)。LA-ICP-MS鋯石U-Pb定年結(jié)果表明,兩件石榴基性麻粒巖麻粒巖中發(fā)育的變質(zhì)鋯石分別記錄了2517±6Ma(BT58-1,MSWD=0.66,n=21)與2512±16Ma(LH66-1,MSWD=0.26,n=42)的加權(quán)平均年齡,與陰山陸塊其它新太古代巖石記錄的約2500Ma變質(zhì)年齡一致,被解釋為本區(qū)石榴基性麻粒巖遭受高壓麻粒巖相變質(zhì)時代。結(jié)合本區(qū)其它新的研究資料,本文認(rèn)為武川石榴基性麻粒巖形成可能與區(qū)內(nèi)新太古代晚期造山作用有關(guān)。
[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，
本文編號：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，
本文編號：2284847
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