The Petrogenetic Link Between The Late Paleozoic High-temperature Granulite Metamorphism In The Altay Orogen And The Tarim Mantle Plume

The Altay orogeny is an important part of the Central Asian Orogenic Belt(CAOB) and outcrops high-temperature metapelitic and mafic granulites on its southern margin. Constructing their P-T paths is of great significance to understand the late Paleozoic tectonic evolution history of the southern Chinese Altay. Detailed petrographic observations on the metapelitic and mafic granulites at Wuqiagou area show that the pre-peak metamorphic assemblages(M0) of metapelitic granulite is biotite + cordierite ± spinel + plagioclase + quartz + ilmenite, and peak metamorphic assemblage(M1) comprises garnet + cordierite + biotite + plagioclase + quartz + magnetite + ilmenite ± orthopyroxene± spinel ± k-feldspar, whereas the assemblage biotite + plagioclase + quartz ± cordierite represents a post-peak assemblage(M2). The pre-peak metamorphic assemblages(M0) of mafic granulite consists of biotite and plagioclase, and peak metamorphic assemblage(M1) comprises orthopyroxene + clinopyroxene + biotite + plagioclase + k-feldspar + amphibole + magnetite + ilmenite + quartz, whereas the ssemblage of amphibole + plagioclase formed during the retrograde period(M3). Peak and post-peak metamorphic P-T conditions are estimated using conventional thermobarometers and average P-T approach, and P-T pseudosections for two metapelitic granulites are caculated via the Thermocalc program, with peak metamorphic P-T conditons of 770-865 ℃/3.0-5.1 kbar and two post-peak near-isobaric cooling(IBC) P-T paths. Such IBC P-T paths suggest that high-temperature metamorphism likely occurred in an overall extensional tectonic setting. Combined with the the available age results(270-280 Ma), the Altay Permian high-temperature metamorphism is coeval with the Tarim mantle plume activity(~ 275 Ma). This indicates that the Altay Permian high temperature metamorphism is likely associated closely with the Permian Tarim mantle plume activity. We can conclude that the high-heat flow necessary for the Permian high-ultrahigh temperature metamorphism from the Wuqiagou area was most probably generated by underplating and heating of mantle-derived mafic magma as a result of the Tarim mantle plume.