• 文章目录 •
郭震宇1， 董火根2， 郭令智2
GUO Zhen-yu1, DONG Huo-gen2, GUO Ling-zhi2
Abstract: There are abundant mineral textures and deformational structures in different scales within ultrahigh-pressure （UHP） and high-pressure （HP） metamorphic rocks in Dabie Mountains，which were developed during metamorphism. Based on textural-structural analysis and PTt research， we present the PTt-D paths of UHP and HP metamorphic rocks. They show firstly，the mineral textures change from static texture of garnet to quartz pseudomorphs after coesite and radiating fractures； secondly，the linear and planar fabrics change from L>S fabric of eclogites to L-S or S>L fabric of retrograded eclogites；lastly and most importantly，the main meso-scale deformational structures developed from original mineral foliation Se to D1 deformation，and then superimposed D2 deformation. The D1 is pre-amphibolite facies deformation. It formed recumbent fold F1e and boudinage in eclogites. The D2 is amphibolite facies deformation. It formed amphibolite facies foliation Sam， A-type lineation Lam， sheath fold Sh and lineation-parallel isoclinal fold F2am. Structural geometry of F1e and F2am accords with type-Ⅲ interference pattern of superimposed folds of Ramsay. The microstructures of XZ plane on Sam and small-scale structures at UHP metamorphic rocks outcrops show a top-to-NW-NNW shearing sense during amphibolite facies retrogradation accompanied with D2 deformation. The PTt-D paths of UHP and HP metamorphic rocks also reveal the exhumation history of these rocks and the evolution of collisional tectonics of Dabie Mountains. This paper gives some discussions in the following：（1） The passive continental margin of Yangtze craton subducted under Sino-Korean craton with a maximum strength at 232～221Ma. The materials of transitional crust of Yangtze passive continental margin experienced UHP metamorphism at 100 km of asthenospheric depth，and the other shallower structural layers experienced HP metamorphism. In this stage，the static texture of garnet shows that the UHP rocks stayed in their peak metamorphic region for a period of time.（2） By the mechanisms of buoyancy and high flexural rigidity of subducted passive continental margin，the UHP and HP rocks broke up to slabs and returned to the level of the boundary of crust and mantle during 220～207Ma， accompanied with D1 deformation.（3） By the mechanisms of retro-thrust， the UHP and HP rocks returned to upper-middle crust level during 206～178Ma，accompanied with D2 deformation.（4） Since then，the whole orogen was controlled by denudation，accompanied with granite intrusion and movement of Tan-Lu fault in Cretaceous age. The UHP and HP rocks exposed to near surface during 120～110Ma， and orogeny in Dabie Mountains completed.
郭震宇， 董火根， 郭令智
GUO Zhen-yu1, DONG Huo-gen2, GUO Ling-zhi2. A PTt- D Paths Study: Textural and Structural Evolution of Ultrahigh-Pressure and High-Pressure Metamorphic Rocks from Dabie Mountains，China[J]. J4.