Preliminary paleomagnetic study of Cretaceous dykes in SE-Tibet

Abstract

The SE Tibetan area is a key region to better understand Tibetan Plateau formation. Lateral motion is evident by the alignment of major rivers in Southeast Asia and GPS velocities indicating motion around and away from the Eastern syntaxis. We try to find vertical axes rotations utilizing paleomagnetic studies combined with geological-petrological investigations to clarify the process of uplift of the Himalaya-Tibetan Plateau in the south eastern Tibet.A total of 17 sites with about 10 cores per site were drilled in Lower Cretaceous diorite dykes. These dykes intruded widespread into the Triassic flysch of the Tethyan Himalaya. A total of 11 dykes were drilled in Nagarze area and 6 sites more to the east (south of Tsetang-Gyaca) (Figure 1).Rock magnetic analysis demonstrates the presence of pyrrhotite as the principle carrier of the remanence. IRM saturates from 300 mT to 500 mT and thermal demagnetization of SIRM is mainly achieved around the Curie temperature of pyrrhotite (325°C). Most of the samples show also a decay of the SIRM around 580°C indicating the additional presence of magnetite.The values of the intensity of the natural remanent magnetization varies strongly from 0.5 to 446 mA\m. In about 50% of the samples it is possible to isolate a significant pyrrhotite component, usually unblocking between 250°C and 350°C. Equal area projection mostly shows a scattered distribution of the pyrrhotite components. In three sites the characteristic pyrrhotite remanence components are well grouping and in four sites a small circle distribution can be observed. We relate the origin of the pyrrhotite remanence to last metamorphic cooling in the area (K/Ar ages indicate ~24 Ma). Sulphor for pyrrhotite formation has been likely delivered from the adjacent schists during peak metamorphism. The remanence is therefore probably secondary,

Kinematics of the Dadeldhura klippe shear zones (W Nepal): implications for the foreland evolution of the Himalayan metamorphic core

“…(b) Simplified geological map of central and eastern Himalayas with location of the studied Dadeldhura klippe and dip‐slip displacements on the STDS . The map has been constructed after Gansser, ; Pan et al ., ; Robinson et al ., ; Yin, ; Antolín et al ., ; Kellett and Grujic, ; Yakymchuk and Godin, ;. Red line shows location of the cross‐section; KFS, Karakorum Fault system; TKG, Thakkhola Graben; ADM, Ama Drime Massif; YGG, Yadong Gulu Graben; CG, Cona Graben and KT, Kahtang Thrust.…”

Leucogranite intruding the South Tibetan Detachment in western Nepal: implications for exhumation models in the Himalayas

“…The STD separates the GHS from the overlying THS (Burchfiel et al ., ). The THS is a folded sequence of marine sediments of Cambrian to Eocene age that was deposited on the northern Indian continental margin (Antolín et al ., ). The bottom of the THS is made of low‐grade metamorphic rocks derived from Cambro–Ordovician impure limestones, calcschists and quartzites (Crouzet et al ., ; Myrow et al ., ; Dunkl et al ., ).…”