HP-UHP metamorphic belt in the East Kunlun Orogen: final closure of the Proto-Tethys Ocean and formation of the Pan-North-China Continent

Abstract

The East Kunlun Orogen, the northwestern part of the Central China Orogenic Belt, is a long-lived accretionary orogenic belt that records the evolution and eventual destruction of branches of the Tethys Ocean, from the Cambrian to the Triassic. Here we report an Early Paleozoic eclogite belt that extends for ∼ 500 km within the East Kunlun Orogen. This belt consists of eclogite blocks, meta-sedimentary rocks and minor serpentinite blocks, accompanied by ophiolites (530-460 Ma) and concurrent arc volcanic sequences and granitic plutons. Geochemical data show that the eclogites have N-MORB- to OIB-like compositions. U-Pb dating of metamorphic zircons from eclogites and their surrounding rocks gave peak and retrograde metamorphic ages of 430-410 Ma. Coesite pseudomorphs in garnet, quartz exsolution rods in omphacite, as well as P-T calculations, suggests that some eclogites experienced UHP metamorphic conditions at 29-30 kbar and 610-675 °C; these could represent oceanic crust subducted to and exhumed from coesite-forming depths (100–120 km). The UHP metamorphic eclogite belt in the East Kunlun Orogen may represent the final closure of the Proto-Tethys Ocean (opening at ∼580 Ma, subduction initiating at ∼520 Ma) at ∼ 430-410 Ma in the East Kunlun, with the formation of Pan-North-China Continent in the Early Paleozoic and expansion of Paleo-Tethys Ocean in the south.