阿尔泰造山带花岗片麻岩穹窿的形成与演化

The Formation and Evolution of Migmatitic Granite-Gneiss Domes in Altaides,China

在中国阿尔泰造山带中,沿各区域热动力异常中心发育了巨大的混合花岗片麻岩穹窿。由变质围岩到混合花岗片麻岩,在地质产状、变形作用、变质作用、岩石学和地球化学等方面都表现出连续性和继承性的变化特点。可以划分为两个岩石系列:变质酸性火山岩—浅粒岩—浅色混合花岗片麻岩系列和千枚岩—云母片岩—黑云混合花岗片麻岩系列。以区域热动力异常为中心,形成了递增变质热穹窿—递进变质构造穹窿—混合花岗片麻岩穹窿这种具有密切成生联系、时空演化过程统一的三位一体的热—构造—片麻岩(Thermal—Structural—Gneiss)穹窿(简称TSG穹窿)。它们是在造山挤压缩短、沿区域热动力异常中心深部热流上涌和发生差异性塑性底辟隆起、剥蚀的过程中形成的。

The migmatitic granite--gneiss dome has the following characteristics: 1. It looks elliptic in plane and funnel--shaped in profile, being 50--100 kmlong and 20--40 km wide. 2. With the gradual intensification of metamorphism, migmatization andgranitization from the low--grade area to the center of the migmatitic granite-gneiss dome, there appear in turn sericite--chlorite zone, biotite zone, garnetzone, staurolite zone, kyanite (andalusite) zone, sillimanite--cordierite zone,migmatite zone and migmatitic granite--gneiss dome, indicating an increase intemperature from 400℃ to 700℃ and drop in pressure from 0.85 GPa to 0.35GPa. 3. From the low--grade area to the center of the dome, a progressive sequ-ence of metamorphic structures can be observed, which finds expression in aseries of prograde folds and schistodities. The nearer the rocks are to the centerof the dome, the higher grade of tectonism and more deformation they haveundergone. 4. The migmatitic granite--gneiss dome consists mainly of biotite migma-titic granite--gneiss and leuco--migmatitic granite--gneiss intercalated with migna-tized mica schist. In such aspects as attitudes, rock types, modal abundances, fabrics, petrocbemistry and rare earth elements, tbere exist continuous andgradual variations from Phyllite., mica schist, migmatized inica schist to biotitemigmatitic granite--gneiss and from metamorphic rhyolite, leptite, migmatizedleptite to leuco--migmatitic granite-gneiss, suggesting that the two sorts of mig-matitic granite--gneiss are genetically related to meta--pelite and metamorphicacid volcanic rocks respectively and should attribute their formation to meta-morphism, migmatization and granitization. The thermal dome of progressive metamorphism, the structural dome ofprogressive deformation and the migmatitic granite--gneiss dome constitute athermal--structural--gneiss (TSG) trinity dome. The unified temporal--spatial evo-lutionary process of progressive metamorphism, deformation, migmatization andgranitization implies that the formation of the TSG dome is attributed to heatflow, upward gushing of fluids rich in K, Na and Si, and differential diapricuprise around the center of the regional thermodynamic anomaly.