The Imjingang Belt preserved the deformation and metamorphism of rocks related to the Permo-Triassic continental collision between the North and South China Cratons.To understand the microstructural evolution of amphi...The Imjingang Belt preserved the deformation and metamorphism of rocks related to the Permo-Triassic continental collision between the North and South China Cratons.To understand the microstructural evolution of amphibolites,microstructures of hornblendes in Yeoncheon amphibolites and psammitic schists were analyzed using electron back-scattered diffraction mapping and transmission electron microscopy.Two different types of lattice preferred orientations(LPOs)of amphibole were observed:type-II and type-IV.The subgrain boundaries of hornblende,misorientation axes distribution of hornblende,and existence of relict clinopyroxenes inside the amphibole indicate that the type-IV LPO of amphibole resulted from deformation by dislocation creep and topotactic growth of hornblende.The low-angle boundaries of hornblende associated with cracks and fractures in some samples indicate that type-II LPO of amphibole resulted from cataclastic flow associated with rigid body rotation during retrogression.The seismic velocity and anisotropy of the Yeoncheon amphibolites showed that the seismic anisotropy of the amphibolites followed that of the hornblende.Seismic anisotropy of the amphibolites with type-IV LPO of amphibole was significantly weaker than that of the amphibolites with type-II LPO,suggesting that the fabric transition from type-IV to type-II LPO of amphibole may significantly strengthen the seismic anisotropy of the amphibolite.展开更多
The basement of the central Qilian fold belt exposed along the Minhe-Ledu highway consists of psammitic schists, metabasitic rocks, and crystalline limestone. Migmatitic rocks occur sporadically among psammitic schist...The basement of the central Qilian fold belt exposed along the Minhe-Ledu highway consists of psammitic schists, metabasitic rocks, and crystalline limestone. Migmatitic rocks occur sporadically among psammitic schist and metabasitic rocks. The mineral assemblage of psammitic schist is muscovite + biotite + feldspar + quartz ± tourmaline ± titanite ± sillimanite and that of metabasitic rocks is amphibole + plagioclase + biotite ± apatite ± magnetite ± pyroxene ± garnet ± quartz. The migmatitic rock consists of leucosome and restite of various volume proportions; the former consists of muscovite + alkaline feldspar + quartz ± garnet ± plagioclase while the latter is either fragments of psammitic schist or those of metabasitic rock. The crystalline limestone consists of calcite that has been partly replaced by olivine. The olivine was subsequently altered to serpentine. Weak deformations as indicated by cleavages and fractures were imposed prominently on the psammitic schists, occasionally on metabasitic rocks, but not on migmatitic rocks. The basement experienced metamorphism up to temperature 606-778± and pressure 4.8-6.1 kbar (0.48-0.61 GPa), equivalent to amphibolite-granulite facies. The peak of the metamorphism is marked by a migmatization which occurred at several localities along the studied route 587-535 Ma ago. The basement also recorded a retrograde metamorphism of greenschist facies, during which biotite, garnet, amphibole, and pyroxene were partly altered to chlorite.展开更多
基金supported by the Basic Science Research Program through the National Research Foundation(NRF)of Korea funded by the Ministry of Education(NRF:2021R1A6A3A01086519)to S.J.grants from the NRF of Korea(NRF:2020R1A2C2003765 and NRF:2022R1A5A1085103)to H.J.
文摘The Imjingang Belt preserved the deformation and metamorphism of rocks related to the Permo-Triassic continental collision between the North and South China Cratons.To understand the microstructural evolution of amphibolites,microstructures of hornblendes in Yeoncheon amphibolites and psammitic schists were analyzed using electron back-scattered diffraction mapping and transmission electron microscopy.Two different types of lattice preferred orientations(LPOs)of amphibole were observed:type-II and type-IV.The subgrain boundaries of hornblende,misorientation axes distribution of hornblende,and existence of relict clinopyroxenes inside the amphibole indicate that the type-IV LPO of amphibole resulted from deformation by dislocation creep and topotactic growth of hornblende.The low-angle boundaries of hornblende associated with cracks and fractures in some samples indicate that type-II LPO of amphibole resulted from cataclastic flow associated with rigid body rotation during retrogression.The seismic velocity and anisotropy of the Yeoncheon amphibolites showed that the seismic anisotropy of the amphibolites followed that of the hornblende.Seismic anisotropy of the amphibolites with type-IV LPO of amphibole was significantly weaker than that of the amphibolites with type-II LPO,suggesting that the fabric transition from type-IV to type-II LPO of amphibole may significantly strengthen the seismic anisotropy of the amphibolite.
文摘The basement of the central Qilian fold belt exposed along the Minhe-Ledu highway consists of psammitic schists, metabasitic rocks, and crystalline limestone. Migmatitic rocks occur sporadically among psammitic schist and metabasitic rocks. The mineral assemblage of psammitic schist is muscovite + biotite + feldspar + quartz ± tourmaline ± titanite ± sillimanite and that of metabasitic rocks is amphibole + plagioclase + biotite ± apatite ± magnetite ± pyroxene ± garnet ± quartz. The migmatitic rock consists of leucosome and restite of various volume proportions; the former consists of muscovite + alkaline feldspar + quartz ± garnet ± plagioclase while the latter is either fragments of psammitic schist or those of metabasitic rock. The crystalline limestone consists of calcite that has been partly replaced by olivine. The olivine was subsequently altered to serpentine. Weak deformations as indicated by cleavages and fractures were imposed prominently on the psammitic schists, occasionally on metabasitic rocks, but not on migmatitic rocks. The basement experienced metamorphism up to temperature 606-778± and pressure 4.8-6.1 kbar (0.48-0.61 GPa), equivalent to amphibolite-granulite facies. The peak of the metamorphism is marked by a migmatization which occurred at several localities along the studied route 587-535 Ma ago. The basement also recorded a retrograde metamorphism of greenschist facies, during which biotite, garnet, amphibole, and pyroxene were partly altered to chlorite.
