~(40)Ar/~(39)Ar age evidence for Altyn fault tectonic activities in western China

As the northern boundary of the Tibetan Plateau theAltyn fault is a huge NEE strike-slip fault belt in the inner Asian continent. Its formation and evolution are closelyrelated to the uplift of the whole plateau and the mass es-cape to the east. In recent years the Altyn fault has be-come a hot point of geological study in the Tibetan Pla-teau. The formation age of the Altyn fault was argued for a long time. Some researchers emphasized that the Altyn fault had commenced since early Paleo…

40Ar/39Ar age evidence for Altyn fault tectonic activities in western China

Four 40Ar/39Ar age groups of mica, hornblende and K-feldspar were obtained from Proterozoic and early Paleozoic metamorphic rocks in the Aksay-Dangjin Pass area, western China. The samples away from the middle shear zone of the Altyn fault belt yield two plateau age groups in the range of 461-445.2 Ma and 414.9-342.8 Ma, respectively. They represent the tectono-thermal events that had been recorded in the rocks that were displaced by the Altyn strike-slip fault in late Ordovician-early Silurian and Devonian, respectively. These two age groups should be related to the closures of Northern and Southern Qilian Oceans. The deformed granitic gneiss from the northern belt gives a plateau age group of 178.4-137.5 Ma, which is interpreted as the active age of the Altyn fault in the middle-late Jurassic- early Cretaceous and should be related to the accretion of Lhasa block to the north. The sample from the middle shear zone of the Altyn fault belt yields two plateau ages of 36.4 and 26.3 Ma, respectively, suggesting the strike-slip movement with strong metamorphism at greenschist facies along the Altyn fault in the late Eocene. This event occurred in the most areas of the northern Tibet Plateau and should be in response in the north to the collision between Indian and Eurasian continents. The present study demonstrates that the Altyn fault is characterized by multiple pulse-style activities under the tectonic setting of convergence between the Indian and Eurasian continents.