An Archean block in the Central Qinling orogenic belt： zircon SHRIMP U-Pb ages of the Loufanggou amphibolite-leucogranulitite (leptite) in the Xianghe area，Sｈanｇnan, Shaanxi, and their implications

Abstract：The Qinling orogenic belt is the junction between the North China plate of the Sino-Korean craton and the Yangtze cratonic plate and its basement arouses attention of many geologists. This paper reports the zircon SHRIMP U-Pb age data for the Loufanggou metamorphic crystalline rock sheet amphibolite-leptite and biotite-bearing monzonitic quartz schist in the Xianghe area, Shangnan, Shaanxi, in the central part of the Qinling orogenic belt and discusses their geological significance. Amphibolite-leptite is meta-volcanic rocks resulting from continuous differentiation of the same magma. Zircon Pb loss is serious and the 207Pb/206Pb age is ≥2488±8 Ma. This age is consistent with the available Sm-Nd isochron age with the error limits. Biotite-bearing monzonitic quartz schist is parametamorphite with a zircon U-Pb age of 978±13 Ma. The discovery of an Archean sheet (block) in the central part of the Qinling orogenic belt suggests that the Archean crystalline basement may have existed in the lower part of the Qinling orogenic belt.