Mesozoic and Cenozoic crust-mantle interaction in the Central Asian Orogenic Belt: A comparative study of mantle-derived magmatic rocks in northern Xinjiang.

Meso-Cenozoic mantle-derived magmatic rocks mainly occur near oft belts and major stoke slip faults in northern Xinjiang They are characterized by high TiO2, alkali contents and enrichment in incompatible elements and light rare earth elements (LREE), and their La/Nb and Nb/U ratios show that the Meso-Cenozoic basaltic magma underwent typical crust-mantle interaction as ascending to the surface, while low positive to negative epsilon(Nd)(t) and high (Sr-87/Sr-86), values indicate a source in the enriched mantle similar to that for OIB. Penman mafic-ultramafic rocks in northern Xinjiang were originated from partial melting of depleted mantle contaminated by arc and continental crust as well as subducted oceanic crust. In the central Asian Orogenic Belt, the Late Paleozoic orogenies caused by nearly concurrent closure, of branches of the Paleo-Asian Ocean between terranes resulted in the thickened lithosphere, and then delamination of lithosphere and upwelling of asthenosphere generated Penman mafic-ultramafic magma. Therefore, the mantle in Central Asian Orogenic Belt was strongly modified by metasomatic melts from the delaminated lithosphere or ancient subducted oceanic crust and overlying sediments during the Paleozoic, making the mantle enriched in alkali, light rare earth elements (LREE) and incompatible elements As a result, the Meso-Cenozoic mantle-derived magmatic rocks intruded or erupted along rift belts and major strike slip faults exhibit the geochemical signatures of the enriched mantle.