粤西高州泥质麻粒岩变质P-T-t演化及其对华南早古生代构造背景的指示
摘要
<p indent="0mm">The formation and evolution of the early Paleozoic tectono-thermal event in South China remains a hotly debated topic within the academic community. Studies of metamorphism can provide pivotal insight into this issue. In this contribution, detailed studies of petrography, mineral chemistry, phase equilibria modelling and zircon U-Pb geochronology have been carried out on pelitic granulite from Gaozhou, southwestern part of the Cathaysia Block, South China. This paper will compare the early Paleozoic metamorphic data in the Cathaysia block to the new data provided here in order to discuss tectonic setting in South China. The pelitic granulite contains three generations of mineral assemblage, namely the inclusion, matrix and retrograde mineral assemblages. The inclusion mineral assemblage consists of garnet core and the wrapped K-feldspar, biotite, sillimanite, quartz, rutile and ilmenite within garnet. <italic>P</italic>-<italic>T</italic> conditions of the inclusion mineral assemblage are <sc>~0.95 GPa</sc> and 800°C (<italic>P</italic><sub>max</sub> stage), obtained by phase equilibria modelling using software THERMOCALC. The matrix mineral assemblage consists of garnet porphyroblast and the matrix-type cordierite, K-feldspar, biotite, quartz, sillimanite and ilmenite. Combined with the domain of matrix mineral assemblage in the pseudosection, the Ti content of matrix-type biotite and the Ab value of matrix-type K-feldspar, <italic>P</italic>-<italic>T</italic> conditions of the matrix mineral assemblage are defined to be <sc>0.57−0.69 GPa</sc> and 815−865°C (<italic>T</italic><sub>max</sub> stage). The retrograde mineral assemblage is composed by late cordierite, K-feldspar, biotite, plagioclase, sillimanite, quartz and ilmenite. Mineral compositions and stabilities indicate that the retrograde metamorphism is characterized by cooling and decompression. Zircon U-Pb dating of the pelitic granulite yields a metamorphic age of <sc>441±1.4 Ma.</sc> Ti-