Lao’ansi terrane and its geological tectonic characteristics in Zhashui area,Shaanxi

Within the 1/50000 field maping in Zhashui area,we have distinguished a medial-plutonic metamorphic belt that is composed of biotite-plagioclase granulitite,amphibolite and a little marble from the ploted Tongyusi formation of Liuling group in Devonian system By investigating the petrology and initial formation of the rock,adoption tectonic-lithostratigraphy-event' way,esrablished a new tectonic-ithostratic unit named Lao'ansi terrane.By Sm-Nd mean date(2 83 Ma),it is fixed in middle Proterozoic.The new result is important to study the geological composition and the geological-tectonic charact eristic of the center mountain-Qinling or ogen and the Shang dan assemblage zone between the North China and Yangtse block.