Paleo‐Suture Zone Disrupted by Thrusting: Example From East Junggar (NW China), Southern Altaids

Abstract Understanding the tectonic evolution of ancient orogens relies on reconstructing the primary architecture of suture zones that may be modified by post‐subduction events. Modifications in East Junggar, southern Altaids, have led to controversial interpretations about the Paleozoic tectonic evolution. To clarify these relationships, we report the Mesozoic thrust horizon in East Junggar that has displaced the Baishanbao Klippe, which contains siltstone, sandstone, conglomerate and biogeographical Tuva‐Mongolia Tuvaella fauna. This klippe is distinct from units in the footwall that contain Ordovician‐Early Devonian accretionary complexes with dismembered basalts, cherts and deep marine tuffaceous siltstones, Carboniferous volcanic rocks and granites, Middle‐Late Jurassic sediments, and Kazakhstan biogeographic Ordovician‐Late Devonian coral‐brachiopod‐ammonoid fauna. The thrust horizon and the aforementioned units are unconformably capped by Late Jurassic‐Early Cretaceous alluvial fan deposits; it constrains the thrust to a Mesozoic age. These two biogeographic domains were separated by the Paleo‐Asian Ocean until the Late Paleozoic, as evidenced by the 478 Ma Kujibai MOR‐type ophiolite that involved into subduction zone in the Carboniferous. This Mesozoic thrust transported the Baishanbao Klippe for over 100 km southwards from its root in the Altay‐Fuyun area and crossed a cryptic suture zone of the Paleo‐Asian Ocean as an allochthonous unit in East Junggar. It extensively disrupted the primary Paleozoic orogenic architecture of East Junggar that leads to misinterpretation of the regional tectonic evolution. A lesson from disruption of this Mesozoic thrusting is that care must be taken in studies of the architecture of paleo‐suture zones.