Metamorphism and chronology of Paleoproterozoic mafic granulite from the Kuluketage area, northern Tarim and its tectonic applications

Abstract

<p>Mafic granulites provide key insights for understanding the composition and evolution of the lower crust but are rarely reported in northern Tarim. In the present study, a systematic petrographic, phase equilibrium modeling and zircon U-Pb geochronological study of a Paleoproterozoic mafic granulite (garnet two-pyroxene granulite) from the Kuluketage area, northern Tarim were conducted. Phase equilibrium modeling demonstrates a decompression-heating clockwise P-T path involving the prograde metamorphic stage (M1) at -950 degrees C / 12 kbar, the peak metamorphic stage (M2) at -1020 degrees C / 10 kbar, and the retrograde stage (M3) at -880 degrees C / 7 kbar. The decompression heating P-T path generally occurs in the post-collisional lithospheric extension setting which may contribute the UHT metamorphism of the M2 stage. Zircon U-Pb geochronological study reveals four age peaks at -2.45, -2.3, -1.91, and -1.85-1.78 Ga. We interpret the -2.45 Ga magmatic event as an older captured zircon age corresponding to a widely reported magmatic event of -2.4-2.5 Ga in Kuluketage. The slightly younger -2.3 Ga magmatic event may correspond to the crystallization age of the mafic granulite's protolith, however, rarely reported in northern Tarim. The metamorphic age of -1.91 Ga represents a collisional-related high-pressure metamorphic age corresponding to the M1 stage and the age peaks of -1.85-1.78 Ga may represent post-peak cooling events corresponding to the M2-M3 stage.<br></p>