Geochemistry of alkali-rich igneous rocks of northern Xinjiang and its implications for geodynamics

Five nearly E-W-trending alkali-rich igneous rock belts are distributed fro m north to south in northern Xinjiang, and they are composed mainly of rieb eckite, K-feldspar granite and high-K and medium-K calc-alkaline volcanic r ocks and shoshonite. They were mainly emplaced or erupted between the Carbo niferous and Permian. The compositions of Sr, Nd, Pb, and O isotopes imply that their principal resource materials are derived from the upper mantle o r juvenile crust: indicating obvious continental growth in the Phanerozoic. The trace element association implies that their tectonic settings are wit hin plate and volcanic are for alkali-rich granites, and post-collisional a re, late oceanic are and continental are for alkali-rich volcanic rocks. An archipelago model was suggested for the tectonic evolution in northern Xin jiang. It can be named the central-Asia-type orogeny, which is different fr om the so called circum-Pacific ocean-continent-type tectonics or the Alpin e-Himalayan continent-continent-collisional orogeny.