Study On The Tectonic Deformation Characteristics And Geo-dynamics Of Changle-nan'ao Metamorphic Zone

Changle-Nan'ao metamorphic zone was proved to be a huge Mesozoic ductile shear zone. However, the geological world is divided on its metamorphic and deformation stages, kinematics characteristics and geotectonic property.By stratigraphic division and correlation, the metamorphic stratum in east sub-zone of this metamorphic zone can be divided into the pre-Devonia Qinyingshan group. The latter, which includes many intermediate and acid volcanic rocks, is different from the the upper Triassic-lower Jurassic stratum in west sub-zone, but is similar to the lower Jurassic Fankeng group in southwestern Fujian. Thus, it belongs still among the volcanic system in the Zhejiang-Fujian coastal.According to the geological contact relations, the petrographica, petrochemical, geochemical characteristics, Metamorphic and deformed granitic rocks in this metamorphic zone was divided to early Jurassic (earlier than 149.3 Ma), late Jurassic (145.4 Ma), and early Cretaceous Intrusive rocks (139.4-137 Ma). The early Jurassic intrusive rocks, which magma belongs to the crust-mantle mixed type (I-type), were formed during changing of tectonic system (PAG-type); The late Jurassic intrusive rocks, which magma belongs to the crust type (S-type), were syn-collisional pluton (ACG-type); The early Cretaceous intrusive rocks, which magma also belongs to the crust-mantle mixed type (I-type), were formed during changing of tectonic system (KCG-type).In Mesozoic, three stages of tectonic deformation and dynamic metamorphism were developed in this Metamorphic zone: the first is characterized by deep structural level plastic deformation and low amphibole facies metamorphism, which took place at the end of middle Jurassic-early stage of late Jurassic (about 165 Ma); the second is characterized by middle-deep structural level ductile shear deformation and high greenschist facies metamorphism , which occurred in late Jurassic (152-141 Ma); The third was characterized by mid-shallow brittle-ductile shear strain and low greenschist facies metamorphism , which happened on the middle period of early Cretaceous (about 125 Ma). Kinematic characteristics of these shear deformation were respectively dextral-thrusting from NWW to SEE (displacement about 52 km), sinistral-thrusting from NNW to SSE (displacement about 84 km), and normal-dextral strike slip (displacement about 2 km).After comprehensive analysis of the geological, geotectonic and geophysical signatures, the author believes that, during changing of the tectonic system from Tethyan tectonic domain to Marginal west-pacific tectonic domain, Changle-Nan'ao metamorphic zone is one of shear zones which derived from the subduction zones along Median-Tectonic-Line in Japan and the Central-Range in eastern Taiwan, where izanag plate divided into the Eurasian plate.