Age and material composition of the Foping metamorphic crystalline complex in the Qinling Mountains ： SHRIMP zircon U-Pb and whole-rock Sm-Nd geochronology

Abstract：The Qinling is a complex continental collisional orogenic belt resulting from long-continued， multi-stage development. This paper reports the results of isotopic analyses of the SHRIMP zircon U-Pb ages and whole-rock Sm-Nd ages for the Foping metamorphic crystalline complex in the central part of the orogenic belt. The SHRIMP zircon U-Pb ages are very complex； except for small amount of Archean zircon， there are also significant amounts of Proterozoic to Phanerozoic zircon.The metamorphic peaks occurred at -1 200， 800， 400 and 200 Ma. Gneiss has a Nd model age tDM of 1 372-208 Ma. The main part of the Foping metamorphic crystalline rock series possibly formed in the Paleoproterozoic， with an age of -2 000 Ma. In the subsequent strong geological processes， a small amount of mantle material was introduced. The view of the formation of the rock series in the Neo-archean has not been verified by the authors. Archean crystalline basement rocks may occur or may have occurred in the central part of the Qinling orogenic belt.