苏北东海—胶南日照两种不同成因榴辉岩的P—T轨迹及构造意义

P-T PATHS OF ECLOGUES OF TWO DIFFERENT GENESES FROM DONGHAI, NORTH JIANGSU AND RIZHAO, SOUTH SHANDONG, AND THEIR TECTONIC SIGNIFICANCE

本文就苏北东海青龙山和胶南日照梭罗树两种不同成因榴辉岩的地质产状、岩石学、矿物学特征以及热力学等方面进行了研究。根据其矿物共生组合及相互关系将产于黑云斜长片麻岩中的苏北东海青龙山榴辉岩划分出三期变质阶段:Ec(Ⅰ):榴辉岩相前变质阶段期。早期以包裹体形式残存于王期榴辉岩相中的石榴石、绿辉石中,它们是榴辉岩相变质作用之前变质阶段的产物。Ec(Ⅱ):榴辉岩相主变质期。该期主要为石榴石和绿辉石为主的典型组合,是主期变质作用所形成。Ec(Ⅲ):榴辉岩相退变质期。榴辉岩相又经历了退变质作用如石榴石被绿泥石交代,绿辉石分解为角闪石、斜长石、石英等。产于超基性岩中的梭罗树榴辉岩根据其矿物的相互关系也可划分为三期变质矿物组合:Ec(Ⅰ):顶峰变质榴辉岩期。矿物以包裹体形式存在于一般榴辉岩期的石榴石、单斜辉石中。主要为石榴石残存于单斜辉石中,且以包裹体形式出现。Ec(Ⅱ):即一般榴辉岩期。主要矿物组合为石榴石、透辉石、金红石等。Ec(Ⅲ):榴辉岩所经历的退变质作用后而形成的后成合晶阶段。主要矿物组合为细粒石榴石集合体、斜长石、绿泥石、绿帘石等。并通过矿物共生组合和矿物温压计求得了两种不同成因榴辉岩的P-T轨迹。该轨迹表明榴辉岩的抬升历史都经历了早期的碰撞和晚期随胶南隆起的抬升阶段。从而证明了胶南隆起和大别造山带属同期碰撞造山作用所致。

The geological occurrence, petrological, mineralogical and thermodynamic characteristics of eclogites of two different geneses from Qinglongshan, Donghai, North Jiangsu and Suoluoshu, Rizhao, South Shandong are studied in detail. Based on the mineral assemblages and their relationship, the Qinglongshan eclogite occurring in biotite plagioclase gneiss shows three metamorphic stages; Ec (Ⅰ)—premetamorphic stage of eclgite facies: it is proved by the early formed residual inclusions in garnet and omphacite formed in the main metamorphic stage; Ec (Ⅱ)—main metamorphic stage of eclgite facies: it is proved by the typical assemblage of garnet and omphacite; Ec (Ⅲ)—retrograde metamorphic stage of eclogite facies: the retrograde metamorphism is proved by some evidence (eg. garet was replaced by chlorite; omphacite was decomposed into amphibole, plagioclase and quartz, etc.). On the basis of relations among minerals, the Suoluoshu eclogite occurring in ultrabasic rocks also shows three metamorphic stages: Ec (Ⅰ)—top metamorphic stage of eclogite facies: it is proved by mineral inclusions existing in garnet and clinopyroxene which were formed in normal metamorphic stage with garnet inclusions mainly in clinopyroxene; Ec (Ⅱ)—normal metamorphic stage of eclogite facies: it is proved by mineral assemblages of garnet,diopside and rutile,etc.;Ec(Ⅲ)—symplektitc stage: it is the result of retrograde metamorphism. The main mineral assemblage is fine-grained garnet aggregate, plagioclase, chlorite, epidote, etc.. P-T paths of two different eclogites are obtained through analysis of mineral assemblages according to geothermometer and geobarometer. The paths indicate that the history of eclogites in the studied area underwent collision in early stage and elevation in later stage along with South Shandong uplift. Therefore, it is proved that the South Shandong uplift and the Dabie orogenic belt result from contemporaneous collision orogeny.