ABSTRACT

Episodic Neoproterozoic magmatic suites in the Altyn Tagh, NW China, are thought to be related break-up of the Rodinia supercontinent. These suites resulted from long-term extension of the lithosphere during orogenic collapse and subsequent rifting. New geochemical and U-Pb-Hf zircon data indicate that the 825 Ma Hongliugou granite displays the characteristics of A-type granites derived from a juvenile source. Gneissic granites (780–760 Ma) are characterized by high Rb (>200 × 10⁻⁶), low Zr/Hf (23.28–29.28) and low Nb/Ta (4.20–12.99) typical of highly fractionated granites. A diabase exhibits trace element patterns between OIB and E-MORB which we infer as derivation from an enriched asthenosphere mantle. Combined with previous reported ca. 850 Ma and 620 Ma extension-related magmatism in this region, we interpreted the Altyn Tagh sequences as part of a lengthy supercontinental break-up process. Neoproterozoic magmatism in the Altyn Tagh is broadly correlative with magmatism in East Kunlun and North Qaidam orogenic belts around the Qaidam basin. Collectively, the Qaidam block, exposed mainly in the Altyn Tagh, East Kunlun and North Qaidam, represents a succession of accretionary orogenic, postorogenic, and within plate magmatism between 1200 and 620 Ma. The similarity in age of magmatism and metamorphism in the Altyn Tagh-North Qaidam-East Kunlun regions indicate that these Precambrian sequences collectively represent the basement of Qaidam block.