Structural characteristics and active time of the Kangmar detachment,southern TibetEI北大核心CSCD

The Kangmar gneiss dome, typical of the north Himalayan gneiss domes, is composed of three tectono- lithologic units separated by an upper and a lower detachment fault (Kangmar detachment fault). The low-grade metamorphic Tethyan Himalayan sedimentary sequence formed the upper unit above the brittle upper detachment fault. The mylonitic granites and two-mica granites made up the lower unit beneath the ductile lower detachment fault. The mylonitc middle-grade garnet two-mica schist and biotite-plagioclase gneiss constituted the middle unit inbetween the two detachment faults and were involved in the ductile deformation of the Kangmar detachment fault. The meso- and micro-scale structural analyses on the tectonites from the detachment fault zone indicated that the Kangmar detachment fault experienced a top-down-to-north shear. Integrating macro-/micro-analyses of petrology and mineralogy, this study adopts 40Ar/39Ar dating method to constrain the active time of the Kangmar detachment fault. Analyses of the syn-deformation muscovite from the mylonitic garnet two-mica schist yield a 40Ar/39Ar plateau age of 13.23±0.15 Ma, representing the active time of the Kangmar detachment fault. The chronological result hints that the Kangmar detachment was synchronous with the south Tibet detachment systems to the south and was probably part of the south Tibet detachment systems exposed in the Tethyan Himalayan sedimentary sequence. However, this hypothesis needs from the supports of more geological and geophysical evidence. ©, 2015, Science Press. All right reserved.