Lithostratigraphic and geochronological constraints on the evolution of the Central Asian Orogenic Belt in SW Mongolia: Early Paleozoic rifting followed by late Paleozoic accretion

Abstract

New SHRIMP U-Pb and evaporation Pb-Pb zircon ages, together with a revision of the lithostratigraphy of "suspect" terranes in SW Mongolia, suggest that the collage of continental and oceanic units in this region resulted from recurrent magmatic reworking and deformation of Silurian-early Devonian proximal and distal passive margin sequences of the Paleo-Asian Ocean. The zircon ages from early Ordovician volcaniclastic rocks and syntectonic felsic dikes reveal an heterogeneous stretching of the Precambrian Dzabkhan microcontinent (Lake Zone basement) during the Ordovician, followed by the development of a carbonate platform on a proximal margin (Gobi-Altai Zone), serpentinite breccias and Silurian chert sequences on a distal margin and possibly also the formation of oceanic crust. The assumed early Neoproterozoic South Gobi continental zone may either represent an allochthonous block detached from Dzabkhan or, less likely, the conjugate margin of a Paleo-Asian continental rift. Early Devonian volcanism subsequently affected both types of margins with back-arc spreading centers and arcs located in the core of the future Trans-Altai Zone. During the late Devonian to early Carboniferous a Japan-type magmatic arc developed on the previously stretched continental crust of the Gobi-Altai Zone. This event was associated with shortening of the entire domain, exhumation of the deep arc core and formation of intramontane basins with Devonian and Carboniferous detrital zircons of the adjacent Lake Zone continent. Clastic, flysch-type sedimentation occurred on the former distal margin and in oceanic areas. During this early Carboniferous contraction event the continental and oceanic units were imbricated and accreted to the continent in the north. Subsequently, late Carboniferous volcanic arc sequences and a Japan-type magmatic arc developed on the Trans-Altai oceanic crust and the southern South Gobi Zone, respectively. Finally, a Permian thermal event was localized in the Gobi-Altai-Lake Zone contact domain and was responsible for formation of Permian grabens, bimodal volcanism and substantial melting of the accreted crust.

Geochemistry and Nd isotopic composition of the Early Paleozoic flysch sequence in the Chinese Altai, Central Asia: Evidence for a northward-derived mafic source and insight into Nd model ages in accretionary orogen

“…Sengör and Natal'in, 1996;Jahn et al, 2000;Windley et al, 2002;Khain et al, 2003;Xiao et al, 2003;Dobretsov et al, 2004;Hong et al, 2004;Kuzmichev et al, 2005;Helo et al, 2006;Windley et al, 2007;Jian et al, 2008;Sun et al, 2008;Xiao et al, 2008;Wang et al, 2009;Glorie et al, 2011). The lateral growth of the CAOB was dominated by accretion of island arcs, ophiolites, oceanic islands, seamounts, accretionary wedges and Precambrian microcontinents in a manner comparable with that of circum-Pacific Mesozoic-Cenozoic accretionary orogens (Windley et al, 2007;Xiao et al, 2009;Kröner et al, 2010a). Mainly based on Nd model ages (T DM ) of granitic rocks, some Precambrian microcontinents (e.g., Chinese Altai) were distinguished from various terranes in such accretionary orogen (Kozakov et al, 1997;Hu et al, 2000;Wu et al, 2000;Kovalenko et al, 2001;Hu and Wei, 2003;Kozakov et al, 2003;Li et al, 2006;Wang et al, 2009).…”

Geology of the Gobi Altai and Tseel terranes in the central part of the Sagsai River Watershed, SE Mongolian Altai

“…This area is located south of the Main Mongolian Lineament (Figure 1), which represents the main tectonic boundary separating the Neoproterozoic domain in the north, affected by early Palaeozoic orogenic event, from the early Palaeozoic domain to the south (e.g. Badarch, Cunningham, & Windley, 2002;Kröner et al, 2010;Ruzhentsev & Pospelov, 1992) affected by late Devonian to late Palaeozoic deformation and metamorphism (Edel, Schulmann, Hanžl, & Lexa, 2014;Lehmann et al, 2010;Xiao et al, 2009).…”

“…This pervasive fabric is refolded by open to closed, upright folds with steep NW-SE trending axial planar cleavage (S 2 ). Kröner et al (2010), Guy et al (2014) and Hanžl et al (2016). MML, Main Mongolian Lineament.…”

Evolution of the Early Permian volcanic-plutonic complex in the western part of the Permian Gobi-Altay Rift (Khar Argalant Mts., SW Mongolia)

“…) and high-grade metamorphic rocks of the Tsakhir Uul Crystalline Complex (Hanžl and Aichler eds. 2007;Hrdličková et al 2008;Kröner et al 2010;Lehmann et al 2010;Štípská et al 2010). The volcanic and sedimentary rocks in the Khar Argalant Mts.…”