Sedimentary response to arc-continent collision, Permian, southern Mongolia

Abstract

The Eurasian Tien Shan-Yin Shan suture is a ̃3000-km-long boundary between Paleozoic arc and accretionary complexes (the Altaids) and Precambrian microcontinental blocks (Tarim and North China block). Stratigraphic data are presented from localities in southern Mongolia spanning >800 km along the northern margin of the suture. Facies descriptions, climatic indicators, sandstone provenance, and paleocurrent data help reconstruct Permian basin evolution during and following arc- continent collision, and results are integrated with previously published data to create a preliminary regional synthesis. Upper Permian strata of southern Mongolia comprise fl uvial successions in the southwest and marine turbidite deposits in the southeast. Floral assemblages show mixing of Siberian craton and North China block communities, indicating their close proximity to Mongolia by Permian time. There was a rapid transition from humid environments in the Late Permian to more arid conditions in the Early Triassic, corresponding to the global Permian-Triassic boundary event, but which may also refl ect more local driving mechanisms such as rain shadow effects. Permian sandstones from Mongolia have undissected to dissected arc provenance, with little contribution from continental or recycled orogen sources. The timing of the nonmarine-marine facies transition and cessation of arc magmatism broadly supports earlier collision along the western part of the suture zone than along the eastern part (e.g., Late Carboniferous-Late Permian). However, when regional geologic constraints are integrated, a more complex model involving differential rotation of Tarim and the North China block is preferred. Late Paleozoic rocks of southern Mongolia have been subsequently dismembered along Mesozoic-Cenozoic strike-slip faults, and thus also represent the long-term record of intracontinental deformation within accreted, heterogeneous crust. © 2008 The Geological Society of America.