Late Permian medium-pressure metamorphism in the eastern Songnen Massif, eastern Central Asian Orogenic Belt (NE China): implications for the final closure of the Paleo-Asian Ocean

摘要: Abstract The nature of late Paleozoic metamorphism in the eastern Central Asian Orogenic Belt (CAOB) is controversial. This paper reports mineral chemistry, petrological, and zircon titanite U–Pb age data for representative rocks Dongfengshan Group from margin Songnen Massif. We use these to determine rock associations, P–T conditions, timing metamorphism. conditions were estimated 54 pairs rocks, including garnet–biotite schist, garnet–two-mica garnet–biotite–plagioclase gneiss, garnet amphibolite, indicate experienced at P = 5.5–7.1 kbar T = 592–630 °C (i.e., a geothermal gradient ranging 25 30 °C/km) under medium-pressure lower amphibolite-facies conditions. biotite–plagioclase gneiss amphibolite yielded ages 251 260 Ma, respectively, which are interpreted represent regional metamorphic (260–251 Ma). consistency dates rims zircons biotite plagiogneiss (252 Ma) confirm that occurred Permian rather than Neoproterozoic, as assumed previously. Based on metamorphic, magmatic, stratigraphic, paleontological constraints, well tectonic history, we propose during collision amalgamation Siberian North China cratons following final closure Paleo-Asian Ocean.