The strong activities of the Namula fault zone in the eastern Himalayan syntaxis since Pliocene, constraints from thermochronological data

Abstract

To reveal the strong activities of the Namula fault zone in the eastern Himalayan syntaxis since Pliocene, this paper reports biotite 40Ar/39Ar and apatite fission track ages of 3 rock samples from the Namula fault zone, and quantitatively interpret these ages and the published ages from the adjacent areas, using a modeling code "Pecube". Biotite 40Ar/39Ar ages range from 4.44±0.71 Ma to 3.45±0.24 Ma, and apatite fission track ages range from 3.7±0.4 Ma to 1.8±0.2 Ma. The ages and simulation results show that, prior to ~3 Ma the highest exhumation rate had been located in the south of the Namula fault zone and was about 2.5 km/Ma, and the Namula fault zone had a motion feature of normal fault; Since ~3 Ma the highest exhumation rate have been located in the north of the Namula fault zone and was about 1.3 km/Ma, and the Namula fault zone had a motion feature of thrust fault. The evolution of the Namula fault zone's motion, probably have resulted from the south to north migration of the fast crust exhumation area in the eastern Himalayan syntaxis since ~8 Ma.

Keywords

• the namula fault zone
• the eastern himalayan syntaxis
• biotite 40ar/39ar
• apatite fission track