Phase equilibria and metamorphic evolution of garnet-mica-plagioclase gneisses from the Qiliping terrane in the western Dabie Orogen, central China

作者：Zhang Jing Sen^*; Zhang Jing; Zhou Jun Jie; Zhang Hong Fen

来源：Island Arc, 2012, 21(4): 235-254.

DOI：10.1111/j.1440-1738.2012.00818.x

• garnet mica plagioclase gneiss
• metamorphic evolution
• P-T pseudosection
• Qiliping terrane
• western Dabie Orogen

The extensive gneisses in the high-pressure and ultrahigh-pressure metamorphic terrane in the Dabie-Sulu orogen usually show no evidence of eclogite-facies metamorphism. The garnet-mica-plagioclase gneisses from the Qiliping region in the western Dabie Orogen, comprise garnet, phengite, biotite, plagioclase, quartz, rutile, ilmenite, chlorite, epidote, and hornblende. The garnet porphyroblasts, with inclusions of quartz, epidote, and rutile, exhibit slight compositional zonations, from core to mantle with an increase in pyrope and a decrease in spessartine, and from mantle to rim with a decrease in pyrope and grossular and an increase in spessartine. The high-Si phengite indicates that the gneisses may be subjected to a high-pressure metamorphism. By the PT pseudosections calculated in a system NCKMnFMASHTO (Na2O-CaO-K2O-MnO-FeO-MgO-Al2O3-SiO2-H2O-TiO2-O) for two representative samples, the metamorphic PT path, reconstructed by the compositionally zoned garnet, shows that the prograde metamorphism is characterized by a temperature increase with a slight pressure increase from the conditions of 17.6 +/- 1.5?kbar at 496 +/- 15 degrees C to the peak-pressure ones of 21.8 +/- 1.522.7 +/- 1.5?kbar at 555 +/- 15561 +/- 15 degrees C; the early retrograde stage is dominated by decompression with a temperature increase to the maximum of 608 +/- 15611 +/- 18 degrees C at 10.3 +/- 1.511.0 +/- 1.5?kbar; and the late retrograde one is predominated by pressure and temperature decreases. The mineral assemblages in the prograde metamorphism are predicted to contain garnet, glaucophane, jadeite, lawsonite, phengite, quartz, rutile, and/or chlorite, which is different from those observed at present. Such high-pressure metamorphism can partly be reconstructed by the PT pseudosection in combination with the high-Si phengite and garnet compositions in the core and mantle. This provides an important constraint on the subduction and exhumation of the terrane during the continentcontinent collision between the Yangtze and Sino-Korean cratons.

• 出版日期2012-12
• 单位河北工程大学