Episodic Paleozoic Adakitic Magmatism in the Eastern Tianshan, Southern Altaids: Implications for Petrogenesis and Geodynamics

Abstract

The adakites rocks are typically considered as direct diagnostic evidence for subduction and continental growth, as well as the important evidence to determine the location of the major oceanic basin and evolution history of lost oceanic basins, which are longstanding conundrums for understanding the tectonics of the Paleo‐Asian Ocean (PAO). As the processor of the Altaids, the PAO was a long‐lived ocean, and its multiple subductions led to substantial continental growth in the Central Asian continent. Here we report our newly discovered Paleozoic adakitic rocks (granite and dacite) developed in Jijitaizi in the Eastern Tianshan of the southern Altaids to address the above issues. The Jijitaizi granite and dacite contain high concentrations of Sr (203–343 ppm) and low concentrations of Y (3.00–6.36 ppm) and Yb (0.23–0.62 ppm), indicative of the adakitic affinity. Zircon U‐Pb dating results show that the adakitic rocks were formed in three episodes at 372.26 ± 1.51 Ma, 356.02 ± 1.11 Ma and 334.51 ± 0.68 Ma from the Late Devonian to Carboniferous. The rocks are depleted in Nb, P and Ti, and possess variable Mg# values (28.51–57.22), high Na2O/K2O ratios (1.39–4.94), as well as relatively depleted Hf isotopic compositions, all of which point to a subduction origin from slab melting. Our new finding with the date from the Jijitaizi complex (ca. 321 Ma) suggests continuing subduction of the Paleo‐Asian oceanic slab beneath the Central Tianshan from the Late Devonian to Carboniferous. Our work provides a solid line of key evidence demonstrating that continuous oceanic subduction of the major PAO evolved into its mature stage following subducting beneath the Central Tianshan from ca. 372 to 321 Ma.

Lithium‐bearing Pegmatite Exploration in Western Altun, Xinjiang, using Remote‐Sensing Technology

“…The junction of the Tarim Plate and South China-Yangtze Plate has experienced multiple orogenies and simultaneously induced frequent, intense and multiperiod tectonic-magmatic activities during the Jinning and Caledonian periods. There are magmatic activities on different scales, resulting in a wider distribution of regional intrusive rocks and extrusive rocks (Kang et al, 2016). The research area is located in the western section of the Altun Mountain to the south of Ruoqiang County, Xinjiang.…”

Geochronology and Geochemistry of the Xingxingxia Triassic A‐type Granites in Central Tianshan, NW China: Petrogenesis and Tectonic Implications

“…It is one of the principal areas of juvenile crustal growth in the Phanerozoic and comprises small continental blocks separated by magmatic arcs and tectonic zones (Jahn et al, 2000). This area has undergone multi-stage tectonic evolutionary processes including Proterozoic to Paleozoic accretions and collisions, Mesozoic intracontinental modifications, Cenozoic compressional deformations and rapid uplift (Xiao et al, 2009;Wang et al, 2022). In the southwestern part of the CAOB, the Tianshan orogenic belt is a crucial link between the Junggar Terrane and the Tarim Craton, playing a vital role in the tectonic evolution of the CAOB (Fig.…”