Abstract: Carboniferous-Early Permian Post-Collisional Extension of Tian Shan and Northern Tarim, Northwestern China

Da Zhou, E. Chang, A.R. Carroll

Evidence for the collisional tectonic amalgamation of the Tarim block and Yili-Central Tian Shan terrane of northwest China during the Late Devonian includes: (1) absence of Upper Devonian strata over the south and central Tian Shan and the northern margin of the Tarim block; (2) conglomeratic nonmarine Lower Carboniferous sequences unconformably overlying tilted pre-Upper Devonian strata; and (3) components of the intervening collapsed ocean basin in the South Tian Shan, such as middle Paleozoic (440 Ma) ophiolite,

a subduction-related blueschist belt (415-419 Ma) and a paired high temperature metamorphic/intrusive belt (383 Ma).

After a brief period of contractile uplift and erosion in Late Devonian, the amalgamated Tarim and Yili-Central Tian Shan block was extended beginning in the Early Carboniferous. Stratigraphic sequences above the Late Devonian unconformity fine and deepen upward from thin, localized Lower Carboniferous nonmarine conglomerates to widespread shelfal carbonates, consistent with Early Carboniferous continental rifting and subsequent subsidence and broadening of sedimentary basins. The northern margin of the amalgamated Yili-Central Tian Shan and Tarim block remained a convergent margin, and itself extended by intra-arc rifting in the Yili and Turpan-Hami regions, as recorded by Carboniferous andesitic volcanic strata interbedded with shallow marine carbonate deposits. Cessation of extensi n in Late Permian is marked by nonmarine conglomeratic molasse in northern Tarim basin, reflecting renewed compression and uplift of the Tian Shan to the north.

AAPG Search and Discovery Article #90986©1994 AAPG Annual Convention, Denver, Colorado, June 12-15, 1994