Adakite-type sodium-rich rocks in Awulale Mountain of west Tianshan: Significance for the vertical growth of continental crust

The sodium-rich dacites and albite porphyries of Permian in the Awulale Mou ntain of west Tianshan have unique chemical and trace element signatures id entical to adakite. These intermediate-acidic igneous rocks are characteriz ed by high Na2O, Al2O3 and Sr contents and high Sr/Y and La/Y ratios (>40 a nd >20, respectively), and low Y and Yb contents, and strong depletion in H REE, and positive Eu anomaly. The (Nd-143/Nd-144)(i) is i, the range from 0 .51236 to 0.51248 and the epsilon (Nd)(t) is positive value (+0.79- +3.11); the (Sr-87/Sr-86)(i) is in the range from 0.7052 to 0.7054, These Nd and S r isotopic composition features indicate that the source rocks of these ada kite-type rocks are from a weakly depleted mantle, or a depleted mantle, bu t was contaminated by the crustal materials. These adakite-type reeks were mast likely derived from the partial melting of new underplated basaltic ro cks under the conditions of amphibolite to eclogite transition in the postc ollisional environment of North Xinjiang during the Permian Period. They ar e not only the Phanerozoic juvenile crust materials, but also are probably an important symbol of the underplating of mantle-derived basaltic magmas a nd the vertical growth of continental crust in the west Tianshan area durin g the postcollision of Late Paleozoic.