|Title:||Tectonic development of the southern Chinese Altai Range as determined by structural geology, thermobarometry, 40Ar/39Ar thermochronology, and Th/Pb ion‐microprobe monazite geochronology|
|Authors:||S.M. Briggs, A. Yin, C.E. Manning, Z.L. Chen, and X.F. Wang|
|Publication:||Geol. Soc. Am. Bull., v. 121, p. 1381‐1393.|
The 2500‐km Altai Range is located in the central part of the Central Asia Orogenic System, a tectonic collage comprising oceanic and continental fragments that were assembled during the Paleozoic continental growth of Eurasia. We conducted field mapping, 40Ar/39Ar thermochronology, metamorphic petrology, and Th/Pb ion‐microprobe monazite dating in the southern Chinese Altai Range. This study demonstrates the presence of a south‐vergent, Permo‐Triassic thrust belt active across the region. Metamorphic conditions of 610 ± 35 °C and 5.7 ± 1.8 kbar were reached by schists with Permo−Triassic monazite ages. Mica 40Ar/39Ar ages range from Late Permian to Jurassic, and cooling in these rocks is correlated with thrust faulting. This shortening was synchronous with localized left‐lateral, strike‐slip shear deformation. Our work suggests that the high‐grade schists of the Altai orogen were buried to depths of more than 18‐20 km and were exhumed in the Permian to Jurassic. The Permo‐Triassic Altai thrust belt was reactivated locally by Late Jurassic contraction after ca. 160 Ma, which may result from the final closure of the Mongol‐Okhotsk Ocean or the collision of the Lhasa block onto the southern Asian margin.