Late Paleozoic Southward Migration of the Dananhu Arc in the Eastern Tianshan (NW China).

The process of continental growth and closure of the Paleo‐Asian Ocean are controversial. To address this problem, we report new geochemical and geochronological data of granitic rocks along a N‐S corridor of the Dananhu arc. These rocks yield 401–270 Ma U‐Pb zircon ages. The arc‐related granites are enriched in the light rare earth elements (LREE), Rb, Ba, Th, Sr and Pb, but depleted in Nb and Ta, and have high zircons values of εHf(t) (+7.7−+19.6) and εNd(t) (+5.4−+7.2); they were possibly generated by partial melting of juvenile intermediate or mafic arc crust. A 356 Ma high‐K calc‐alkaline granite has high Ga/Al (3.28–3.37), low Mg# (14–16), and high zircon εHf(t) (+8.9−+12.0); it can be classified as A2‐type‐granite, suggesting it was a product of substantial fractional crystallization of a mantle‐derived arc‐related magma in an intra‐arc extensional setting. The youngest granite (254 Ma) is an adakite‐like granite which is characterized by high Sr/Y (26–38), depletion in heavy rare earth elements (HREE), and high εNd(t) (+7.0) and εHf(t) (+10.4 to +15.4) values, most likely it was derived from a subducted oceanic slab. Therefore, all the granitic rocks formed in subduction‐related settings. The granitic rocks are generally young southwards from the Kezier area (ca. 401–335 Ma) to the Tuwu area (334–315 Ma), and to the Kanguer area (ca. 280–254 Ma), indicating that the arc grew southwards, and the Paleo‐Asian Ocean closed possibly after 254 Ma. Therefore, our data provide a robust constraint on the prolonged growth of the Altaids. Plain Language Summary: The continental growth mechanism and closure time of the Paleo‐Asian Ocean in the Altaids are global research hotspots. The arcs (especially the intra‐oceanic type) in the Paleo‐Asian Ocean are the essential accretionary component in the Altaids, however, detailed knowledge of the growth processes of the arcs that generated the different types of magmatism is still insufficient. The voluminous, continuous, and well‐exposed granitic rocks in the Dananhu arc provide an ideal opportunity to study the complicated processes of subduction and evolution of the southern Altaids. We report geochemistry and geochronology of granitic rocks along a N‐S corridor of the Dananhu intra‐oceanic arc in the Eastern Tianshan (NW China), southern Altaids. These I‐type, A2‐type and adakite‐like subduction related granitic rocks were emplaced from Devonian (ca. 401 Ma) to Latest Permian (ca. 254 Ma) with a general younging southward, indicating a complex episodic switch of subduction processes from the Devonian to Late Permian. Our results suggest that the arc grew southwards by retreat and rollback of the Kanguer oceanic plates where overall compressional and extensional events alternated, and the closure time of the Paleo‐Asian Ocean was possibly after 254 Ma. Key Points: The subduction related granites are a general southward younging southward from Devonian (ca. 401 Ma) to Latest Permian (ca. 254 Ma)The arc grew southwards by retreat and rollback of the Kanguer oceanic plates where overall compressional and extensional events alternatedThe continental growth accompanied with volumes of granitic rocks and Paleo‐Asian Ocean possibly closed after 254 Ma in the southern Altaids [ABSTRACT FROM AUTHOR]