Late Paleozoic tectonic evolution of the Paleo-Asian Ocean in the
northern Alxa Block (NW China)
Abstract
The northern Alxa Block occupies a key position in the southern margin
of Central Asian Orogenic Belt (CAOB) and records late Paleozoic
subduction and closure processes of the Paleo–Asian Ocean (PAO).
However, there are still controversies regarding the timing and location
of the final closure of the PAO. This study presents structural
deformation data, geochronological and geochemical data for Permian
volcanic rocks, as well as detrital zircon provenance analysis of
Permian sedimentary rocks along the Nuoergong - Langshan Zone (NLZ) in
the northern Alxa Block. During the Carboniferous to middle Permian, the
Paleo-Asian Ocean (PAO) lithospheric slab subducts beneath the northern
Alxa Block, rendering a continental volcanic arc in the NLZ and also
giving rise to extensive folding, thrusting and crustal thickening.
Subsequently, a retroarc foreland basin was developed behind the
continental volcanic arc, where pyroclastic material with Carboniferous
to Permian ages from the volcanic arc and sediments eroded from the Alxa
Precambrian basements were deposited (Dahongshan Formation) during
middle Permian (Ca. 261 Ma). A large-scale dextral ductile shear
deformation in the NLZ resulting from the lateral extrusion of the
thickened crust after the continental collision was constrained between
272 Ma and 249 Ma, suggesting a middle Permian tectonic transition from
compression to transpression. Combining with published data, we suggest
that the final consumption of the PAO occurred in the middle to late
Permian, probably along the Qagan Qulu suture zone in the northern Alxa
Block.