The tectonic evolution of the North Qinling Terrane, Qinling Orogen, Central China

Abstract

The Qinling Orogenic Belt represents a collisional orogen, involving a complex architectural and geological history from the Proterozoic to late Palaeozoic. The timing of plate collision and orogenesis is under debate, due to the presence of highly deformed and metamorphosed exotic terranes within the orogeny. One such terrane is the North Qinling Terrane, which comprises a metasedimentary sequence of gneisses, schists, marbles and amphibolites known as the Qinling Group. Its origin and evolution are not well known, but it forms a well-defined tectonic unit separated from the North China Craton by Neoproterozoic and Palaeozoic suture zones and volcanic terranes. Here I present zircon and apatite U-Pb data, coupled with Perple_X metamorphic constraints. Four metamorphic samples were chosen to examine the tectonic affinity of this terrane, timing of major metamorphic events and the age of the potential basement. Two granitoid samples are dated to constrain the age of magmatic activity. Detrital zircon U-Pb data puts the formation of the Qinling group schist younger than the late Mesoproterozoic (1067 Ma), showing limited similarities in the zircon age spectra to the Cathasyia Terrane. Felsic gneiss samples are interpreted to be metagranitoids, with their protoliths intruding at ca. 850-900 Ma. Granitoids yielded two ages of magmatism, one in the Neoproterozoic (889.9 ± 6.9 Ma), suggesting similarities with the metagranitoid protoliths. The other intruded in the Palaeozoic (414 ± 18 Ma), with an apatite U-Pb age constrained to 421 ± 16 Ma, suggesting the suite did not reach the apatite closure temperature of 450 ºC in subsequent tectonic events. Timing of metamorphisim is constrained by the zircon record, with an age range between ca. 494-463 Ma through the use of low Th/U ratios of the youngest zircon in three of the four metamorphic samples. This study furthers understanding of Neoproterozoic and Palaeozoic tectonic evolution North Qinling Terrane.