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Abstract: Zircon and apatite fission-track (FT) analyses were used to reveal the exhumation of Phanerozoic granitoid intrusions in the Dahinggan Mountains, northeastern China. Zircon FT ages ranging from 84±5 to 97±8Ma, and apatite FT ages from 47±3 to 67±4Ma with mean track lengths between 12.3±2.3 and 13.3±2.2μm, respectively, were obtained for the Phanerozoic granitoids sampled along a south–south-west to north–north-east transect across the Dahinggan Mountains. Three cooling stages from the Late Mesozoic to the Cenozoic have been identified in the studied region based on FT results and modeling. Stage one was a rapid cooling period from the closure temperature of zircon FT to the high temperature part of the apatite FT partial annealing zone (∼210–110°C) during ∼90–57Ma. Stage two was a relatively slow cooling period (∼110–60°C) occurred between ∼57Ma and 20Ma, suggesting that the granitoids had been exhumed to depths of ∼1–2km. The final stage was a cooling period (60–20°C) occurred since the Miocene, which bring studied samples to the Earth’s surface at an accelerated exhumation rate. The estimated maximum exhumation is ∼5km assuming a steady-state geothermal gradient of 35°C/km. Our results indicate that this exhumation is possibly led by the Pacific plate subduction combined with intracontinental orogeny associated with asthenospheric upwelling. [Copyright &y& Elsevier]

Abstract: The Dulong-Song Chay tectonic dome lies on the border of China (SE Yunnan Province) and northern Vietnam, and consists of two tectonic and lithologic units: a core complex and a cover sequence, separated by an extensional detachment fault. These two units are overlain unconformably by Late Triassic strata. The core complex is composed of gneiss, schist and amphibolite. SHRIMP zircon U–Pb dating results for the orthogneiss yield an age of 799±10Ma, which is considered to be the crystallization age of its igneous protolith formed in an arc-related environment. A granitic intrusion within the core complex occurred with an age of 436–402Ma, which probably formed during partial closure of Paleotethys. Within the core complex, metamorphic grades change sharply from upper greenschist-low amphibolite facies in the core to low greenschist facies in the cover sequence. There are two arrays of foliation within the core complex, detachment fault and the cover sequence: S1 and S2. The pervasive S1 is the axial plane of intrafolial S0 folds. D1 deformation related to this foliation is characterized by extensional structures. The strata were structurally thinned or selectively removed along the detachment faults, indicating exhumation of the Dulong-Song Chay tectonic dome. The major extension occurred at 237Ma, determined by SHRIMP zircon U–Pb and 39Ar/40Ar isotopic dating techniques. Regionally, simultaneous tectonic extension was associated with pre-Indosinian collision between the South China and Indochina Blocks. The S2 foliation appears as the axial plane of NW-striking S1 buckling folds formed during a compressional regime of D2. D2 is associated with collision between the South China and Indochina Blocks along the Jinshajiang-Ailao Shan suture zone, and represents the Indosinian deformation. The Dulong granites intruded the Dulong-Song Chay dome at 144±2, 140±2 and 116±10Ma based on 39Ar/40Ar measurement on muscovite and biotite. The dome was later overprinted by a conjugate strike-slip fault and related thrust fault, which formed a vortex structure, contemporaneously with late Cenozoic sinistral movement on the Ailao Shan-Red River fault. [Copyright &y& Elsevier]