MESOZOIC INTRACONTINENTAL OROGENY IN THE TECTONIC HISTORY OF THE KOLYVAN’-TOMSK FOLDED ZONE (southern Siberia): A SYNTHESIS OF GEOLOGICAL DATA AND RESULTS OF APATITE FISSION TRACK ANALYSIS
F.I. Zhimulev1, E.V. Vetrov1, I.S. Novikov1, G. Van Ranst2, S. Nachtergaele2, S.A. Dokashenko1, J. De Grave2
a:2:{s:4:"TEXT";s:203:"1V.S. Sobolev Institute of Geology and Mineralogy, Siberian Вrаnch of the Russian Academy of Sciences, Novosibirsk, Russia
2Department of Geology, Ghent University, Gent, Belgium";s:4:"TYPE";s:4:"html";}
Keywords: Intracontinental orogeny, Mesozoic, apatite fission track thermochronology, planation surface, molasse, granites, Central Asian Orogenic Belt, West Siberia
Abstract
The Kolyvan’-Tomsk folded zone (KTFZ) is a late Permian collisional orogen in the northwestern section of the Central Asian Orogenic Belt. The Mesozoic history of the KTFZ area includes Late Triassic-Early Jurassic and Late Jurassic-Early Cretaceous orogenic events. The earlier event produced narrow deep half-ramp basins filled with Early-Middle Jurassic molasse south of the KTFZ, and the later activity rejuvenated the Tomsk thrust fault, whereby the KTFZ Paleozoic rocks were thrust over the Early-Middle Jurassic basin sediments. The Mesozoic orogenic events induced erosion and the ensuing exposure of granitoids (Barlak complex) that were emplaced in a within-plate context after the Permian collisional orogeny. Both events were most likely associated with ocean closure, i.e., the Paleothetys Ocean in the Late Triassic-Early Jurassic and the Mongol-Okhotsk Ocean in the Late Jurassic-Early Cretaceous. The apatite fission track (AFT) ages of granitoids from the Ob’ complex in the KTFZ range between ~120 and 100 Ma (the Aptian and the Albian). The rocks with Early Cretaceous AFT ages were exhumed as a result of denudation and peneplanation of the Early Cretaceous orogen, which produced a vast Late Cretaceous-Paleogene planation surface. The tectonic pattern of the two orogenic events, although being different in details, generally inherited the late Paleozoic primary collisional structure of the Kolyvan’-Tomsk zone.
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