Paleozoic tectonic setting and evolution of the Central Tianshan Block: Insights from Devonian arc-related granitoids

Abstract

• Distinct Devonian arc-related granitoids record three phases of magmatism . • Devonian granitoids were derived from remelting of Mesoproterozoic rocks with addition of mantle and juvenile crustal components. • The Central Tianshan Block was a continental arc during the Paleozoic bipolar subduction of the Kangguer oceanic slabs. The Central Tianshan Block of the Central Asian Orogenic Belt (CAOB) contains Precambrian metamorphic basement and voluminous Paleozoic granitoids, but its Paleozoic tectonic setting remains debated. This study presents new geochronological and geochemical data for the granitoids in the Shuangqing district in combination with published data from the Central Tianshan Block to constrain the tectonic setting and evolution of the Central Tianshan Block. Zircon U–Pb dating of the different granitoid plutons identified three phases of magmatism, a foliated granite (408.9 ± 2.6 Ma), a K-feldspar granite (397.7 ± 2.5 Ma), and a granodiorite (porphyry) (ca. 390–388 Ma). These Devonian granitoids show medium- to high-K calc-alkaline affinities, large ion lithophile elements (LILE; e.g., Rb and Ba) enrichment, and high field strength elements (HFSE; e.g., Nb, Ta, and Ti) and Eu depletion, consistent with subduction-related I-type granitoids. They have negative ε Nd (t) values (−5.2 to −3.4), old zircon T DM C ages (1623–1036 Ma), and variable zircon ε Hf (t) values (−3.54 to +5.70), indicating they were mainly sourced from remelting of Mesoproterozoic rocks with variable incorporation of mantle and juvenile crustal components in their magma sources. Combining with published data and this study, we suggest the Central Tianshan Block was a continental arc in the Ordovician to Carboniferous during the bipolar subduction of the Kangguer oceanic slabs. During the Devonian, the subduction of the Kangguer oceanic slabs formed the Central Tianshan continental arc to the south, accompanied by emplacement of multiphase arc-related granitoids in the Shuangqing district.