Abstract

The evolutionary history of the NW Yangtze Block is important to interpret its location and relationship with the Rodinia supercontinent. Although Neoproterozoic arc-related tectono-thermal event is recognized in the Micangshan area, NW Yangtze Block, its timing and pressure-temperature (P-T) conditions are poorly constrained so far. This study focuses on the garnet-biotite gneiss that represents the main lithology of the Huodiya Group in the NW margin of the Yangtze Block to address this issue. This gneiss is predominantly composed of garnet, biotite, feldspar and quartz. The peak mineral assemblage consists of garnet + biotite + quartz + plagioclase + K-feldspar in the matrix. The retrograde stage is characterized by embayed rim of garnet and its associated biotite in the matrix. P-T conditions in the peak and retrograde stages are constrained to 7-8kbar/c.710oC and 5-6kbar/650-675oC, respectively, and suggested that 4-5vol.% melt was produced during an upper amphibolite-granulite facies metamorphic event. The first report of monazite U-Pb dating in the Huodiya Group, Micangshan area yielded a weighted mean 206Pb/238U age of 802 ± 5Ma. Studied samples contained detrital, igneous zircons with 206Pb/238U dates>800Ma, whereas metamorphic zircons yielded weighted mean 206Pb/238U age of 797 ± 9Ma. We propose that the Yangtze Block was probably located on the periphery of the Rodinia with consideration of compressional tectonic environment and previous studies.

Supplementary material:https://doi.org/10.6084/m9.figshare.c.4698356

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