Superimposed relation of deformation in ultrahigh-pressure stage and exhumed deformation in main borehole from CCSD, Donghai County, Jiangsu Province
江苏东海CCSD主孔超高压变形与折返变形的叠加关系

Rock in main borehole of Chinese Continental Scientific Drilling (CCSD) located in southern part of SuLu ultrahigh-pressure metamorphic terrane experienced deformation in ultrahigh-pressure stage and multiperiodic exhumed deformations. Exhumed deformation of the first stage is extensional exhumed deformation, eclogite happened retrogressive metamorphism in amphibolite faces condition, did not have new foliation and lineation, kept S-L fabrics in ultrahigh-pressure stage, and have strongly retrogressive metamorphic eclogite melting partly. Exhumed deformation of the second stage is compression exhumed deformation of SEE-NWW direction, different rock style that formed in ultrahigh-pressure stage had different superimposed deformation in this stage, foliation dipping to south of eclogites in the first stage turned to dipping mainly to SEE, but attitude of stretching lineation is identical basically with SN strike in the first stage, reflect foliation in the first stage refolded along NNE arial line, dissected partly by ductile shear zone dipping to SEE; S-L fabric of gneiss formed in ultrahigh-pressure stage has been replaced mainly by new S-L fabric dipping to SEE, reflect foliation in the first stage not only refolded, but deformed ductilely, have SEE-NWW thrust shear sense, mineral oriented again. Exhumed deformation of the third stage is ductile shear zone with NWW-SEE normal-slip shear sense, and have a lot of fold structure of "Z" style. Exhumed deformation of the fourth stage is extensional brittle faulting with NWW-SEE normal-slip shear sense. This article discusses mechanical mechanism of exhumed deformation of SuLu ultrahigh-pressure metamorphic terrane and forming mechanism of foliation changing in main borehole of CCSD.