Paleozoic amalgamation of the Chinese Altai and East Junggar: Insight from the anatomy of Erqis tectonic belt

As one of the most immense orogenic belts, the Altaids (or southern Central Asian Orogenic Belt) primarily comprises Kazakhstan, Mongolia, and Tarim-North China cartons collage systems. The Chinese Altai-East Junggar orogenic collage in the northern Xinjiang, NW China, links the Mongolia collage system to the east with Kazakhstan collage system to the east, occupying a critical tectonic position and retaining the fundamental architecture of the southern Altaids. The Erqis tectonic belt, situated at the junction of the Chinese Altai and East Junggar, originated through the subduction of the Ob-Zaisan Ocean, playing a pivotal role in unraveling the tectonic evolution of the southern Altaids.

Tectonic and provenance analyses of the Erqis tectonic belt discern three distinct arcs: the Chinese Altai, a Japan-type island arc, in the north, exhibits a protracted history from the late Cambrian to early Permian with a slender accretionary complex (AC) termed the Supute AC; The Kuerti intra-oceanic arc in the middle eemerged in the late Silurian to Devonian with a minor coeval AC as the Tesibahan AC; The Dulate arc in the south predominantly evolved from the middle Devonian to Permian, giving rise to the Fuyun AC that independently developed on its northern margin at least until ~273 Ma.

Our findings indicate the existence of multiple arcs within the Ob-Zaisan Ocean, forming an archipelago paleogeography in the Paleo-Asian Ocean (PAO). Provenance studies lead us to propose that cryptic sutures demarcating the Chinese Altai, Kuerti, and Dulate lie approximately along the Kuerti and Tesibahan faults, respectively. In addition, the tectonic facies matching between accretionary complex and the corresponding parental island arcs demonstrate that he oceanic branches between these arcs subducted northward beneath the Chinese Altai and Kuerti arcs and southward beneath the Dulate arc. Additionally, our work demonstrates the closure of the Ob-Zaisan Ocean most probably postdates ~273 Ma. Combining our data with previous research, we present a novel tectonic evolution model, elucidating several arc amalgamations with multiple subduction polarities between Chinese Altai and East Junggar throughout the late Cambrian to Permian.