Timing of the final closure of the Irtysh–Zaysan Ocean: New insights from the earliest stitching pluton in the northern West Junggar, NW China

Abstract

A tight constraint on the closure time of the Irtysh–Zaysan Ocean, a major southwestern branch of the Paleo‐Asian Ocean, is crucial for understanding the final amalgamation of the Central Asian Orogenic Belt; however, no agreement has been reached. This study presents new zircon U–Pb ages and whole‐rock geochemical data for the Keluke composite pluton in the Zharma–Saur arc of the northern West Junggar (NW China). The Keluke composite pluton mainly includes the hornblende gabbro, gabbroic diorite, and K‐feldspar granite. The laser ablation inductively coupled plasma mass spectrometry zircon U–Pb dating indicates that the hornblende gabbro and K‐feldspar granite formed at 334 ± 1 Ma and 319 ± 4 Ma, respectively. The gabbroic and dioritic rocks are calc‐alkaline and arc‐related plutonism characterized by strong depletions in Nb–Ta–Ti, thus being the product of the subduction of the Irtysh–Zaysan Ocean. By contrast, the K‐feldspar granite is geochemically similar to the post‐collisional highly fractionated I‐type granite. In particular, when compared with regional magmatic events, the Keluke K‐feldspar granite represents the first stitching plutonism in response to the termination of the Irtysh–Zaisan Ocean, which strongly indicates that the Irtysh–Zaisan Ocean was closed prior to the earliest late Carboniferous.