Kinematics of the crust around the Ama Drime massif (southern Tibet) - constraints from paleomagnetic results.
Résumé
Secondary magnetic remanences are used to study late-orogenic rotation and tilting on a E-W transect in southern Tibet at _28.5_N. Sampling was performed on both sides of the Ama Drime Massif (ADM). Remanent magnetization resides in pyrrhotite formed during metamorphism and is related to the last cooling event through 325 _C (Curie temperature of pyrrhotite). The existence of antipodal pTRMs demonstrates that the ChRM is of thermoremanent origin and was acquired during cooling of the Tethyan metasediments. Penetrative deformation was still going on in Ronghbuk area until ca 250 _C, whereas it was already completed in Dinggye area. Significant departures from the expected field direction during the age of remanence acquisition cannot be interpreted by consistent vertical axis rotation of blocks. Antagonist deviations on both sides of the ADM are explained as tiltings around an horizontal axis striking _N20_. These tiltings are estimated to be younger than 13-12 Ma and they are related to the ADM exhumation initiated since 33 Ma.