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南秦岭造山带分布于商丹和勉略两条缝合线之间,其东段变质地层以志留系和泥盆系为主,包括少量的震旦系和上古生界。主要岩性包括变质泥质岩、石英岩、大理岩和少量的变质基性岩及片麻岩等。根据野外分布和显微组构特征发现这些岩石至少遭受了两期变质作用:早期为递增变质作用,它以佛坪地区的高角闪岩相—麻粒岩相为中心,向外依次变为低角闪岩相(十字石—蓝晶石带)、绿帘角闪岩相(石榴石带)和绿片岩相(绿泥石和黑云母带),变质时代约为220～260 Ma。麻粒岩相以出现二辉石为特征,包括基性和中酸世麻粒岩等,野外只见于佛坪县城附近。高角闪岩相在泥质岩石中的矿物组合为夕线石-石榴石-黑云母-斜长石-钾长石-石英,其变质条件为t=688～693℃,P=0.5～0.6 GPa;低角闪岩相在泥质岩石中的矿物组合为蓝晶石(十字石)-石榴石-黑云母-白云母-斜长石-石英,其变质条件为t=570～598℃,P-0.7～1.0 CPa;绿帘角闪岩相在泥质岩石中的矿物组合为石榴石-黑云母-白云母-斜长石-绿泥石-石英,变质条件为t=518～545℃,P=0.5～0.8GPa;绿片岩相的矿物组合为白云母-绿泥石-石英-斜长石-(黑云母),其变质压力为0.6～0.65 GPa,温度可能为400～450℃。采用Spear提出的吉布斯方法,以石榴石变斑晶的环带变化得到高角闪岩相、低角闪岩相?
The South Qinling orogenic belt is distributed between Shangdan and Mianlue sutures. The metamorphic strata in the eastern part are mainly Silurian and Devonian, including a small amount of Sinian and Upper Paleozoic. The main lithology includes metamorphic mudstone, quartzite, marble and a small amount of metamorphic basic rocks and gneiss. According to the field distribution and microstructure characteristics, these rocks have been found to have metamorphosed at least two stages: the early metamorphic rocks are characterized by increasing metamorphism in the early stage. They are characterized by the high-amphibolite facies-granulite facies in Foping area, Amphibolite-kyanite belt, epidote amphibolite facies (garnet belt) and greenschist facies (chlorite and biotite belt), the age of metamorphism is about 220-260 Ma. The granulite facies is characterized by the presence of diopside, including basal and intermediate acid granulites, which are found only in the vicinity of Foping County. The metamorphic conditions of high amphibolite facies in shaly rocks are sillimanite, garnet, biotite, plagioclase, potash feldspar and quartz. The metamorphic conditions are t = 688-693 ℃, P = 0.5-0.6 GPa . The mineral assemblages of low amphibolite facies in shaly rocks are kyanite (garnet) -garnet-biotite-muscovite-plagioclase-quartz with metamorphic conditions of t = 570-589 ℃ and P -0.7 ~ 1.0 CPa. The mineral assemblage of the amphibolite facies in shaly rocks is garnet-biotite-muscovite-plagioclase-chlorite-quartz. The metamorphic conditions are t = 518-545 ℃, P = 0.5-0.8GPa. The mineral assemblage of the greenschist facies is muscovite-chlorite-quartz-plagioclase- (biotite) with a metamorphic pressure of 0.6-0.65 GPa and a temperature of 400-450 ° C. Using the Gibbs method proposed by Spear, high-amphibolite facies and low amphibolite facies are obtained by changing the zonal band of the garnet apamorphism