Association of Late Paleozoic Adakitic Rocks and Shoshonitic Volcanic Rocks in the Western Tianshan, China

Abstract

Abstract The late Paleozoic adakitic rocks are closely associated with the shoshonitic volcanic rocks in the western Tianshan Mountains, China, both spatially and temporally. The magmatic rocks were formed during the period from the middle to the late Permian with isotopic ages of 248–268 Ma. The 87Sr/86Sr initial ratios of the rocks are low in a narrow variation range (˜0.7050). The 143Nd/144Nd initial ratios are high (˜0.51240) with positive εNd(t) values (+1.28–***+4.92). In the εNd(t)–(87Sr/86Sr)i diagram they fall in the first quadrant. The association of the shoshonitic and adakitic rocks can be interpreted by a two‐stage model: the shoshonitic volcanic rocks were formed through long‐term fractional crystallization of underplated basaltic magma, while the following partial melting of the residual phases formed the adakitic rocks.