Phanerozoic Paleomagnetism Characteristics of the Qomolangma Area in Tibet

This paper conducts systematic test research on the 2920 paleomagnetic directional samples taken from Ordovician-Paleogene sedimentary formation in the north slope of Qomolangma in south of Tibet and obtains the primary remanent magnetization component and counts the new data of paleomagnetism the times. Based on the characteristic remanent magnetization component, it calculates the geomagnetic pole position and latitude value of Himalaya block in Ordovician- Paleogene. According to the new data of paleomagnetism, it draws the palaeomagnetic polar wander curve and palaeolatitude change curve of the north slope of Qomolangma in Ordovician-Paleogene. It also makes a preliminary discussion to the structure evolution history and relative movement of Himalaya bloc. The research results show that many clockwise rotation movements had occurred to the Himalaya block in northern slope of Qomolangmain the process of northward drifting in the phanerozoic eon. In Ordovician-late Cretaceous, there the movement of about 20.0~ clockwise rotation occurred in the process of northward drifting. However, 0.4° counterclockwise rotation occurred from the end of late Devonian epoch to the beginning of early carboniferous epoch; 6.0° and 8.0° counterclockwise rotation occurred in carboniferous period and early Triassic epoch respectively, which might be related with the tension crack of continental rift valley from late Devonian period to the beginning of early carboniferous epoch, carboniferous period and early Triassic epoch. From the Eocene epoch to Pliocene epoch, the Himalaya block generated about 28.0° clockwise while drifting northward with a relatively rapid speed. This was the result that since the Eocene epoch, due to the continuous expansion of mid-ocean ridge of the India Ocean, the neo-Tethys with the Yarlung Zangbo River as the main ocean basin closed to form orogenic movement and the strong continent-continent collision orogenic movement of the east and west Himalayas generated clockwise movement in the mid- Himalaya area. According to the calculation of palaeolatitude data, the Himalaya continent- continent collusion orogenic movement since the Eocene epoch caused the crustal structure in Indian Plate- Himalaya folded structural belt- Lhasa block to shorten by at least 1000 km. The systematic research on the paleomagnetism of Qomolangma area in the phanerozoic eon provides a scientific basis to further research the evolution of Gondwanaland, formation and extinction history of paleo- Tethys Ocean and uplift mechanism of the Qinghai-Tibet Plateau.

Geomagnetic polarity transitions recorded in the Miocene lavas of the Wuyu basin,Tibet

Geomagnetic polarity transitions were the most important phenomena in the study of the geomagnetic field evolution and the earth's deep interior dynamics.The Miocene postcollisional ultrapotassic-potassic rocks are widely distributed in the Lhasa Block of southern Tibet.Paleomagnetic studies on the Wuyu Formation indicated that these volcanic rocks recorded the C5Bn.2n-C5Bn.1r and C5ACr-C5ACn geomagnetic polarity transitions.The virtual geomagnetic poles(VGPs) of these two polarity transitions were located in the Atlantic and the central Pacific,respectively.Due to data scarcity,it remains unclear whether VGP paths of Miocene geomagnetic polarity transitions were longitudinal preference and/or 90° away from the sampling sites.