Pan-African and Early Paleozoic orogenic events in the Himalaya terrane: Inference from SHRIMP U-Pb zircon ages
喜马拉雅地体的泛非-早古生代造山事件年龄记录

The Himalayan terrane is an accretional terrane formed during the collision between the India Plate and the Eurasian Plate since 55 10 Ma. SHRIMP U-Pb dating has been performed on zircons from the amphibolite facies aluminum-rich metasediments and granitic gneisses from the Greater Himalaya and the Tethyan-Himalayan units of the Himalayan terrane. The dating results indicate an widespread 529 - 457Ma deformation and metamorphism event, and greater than 835 Ma metamorphic basement formation age, except for the latest tectonic event at 12 -20 Ma. Field observations on the Himalayan slice which has been exhumed since 20 Ma have documented earlier than Cenozoic tectonic events represented by the early intense folding, oblique southward thrusting and concurrent amphibolite facies metamorphism and the Ordovician basal conglomerate. Recent studies also yielded a number of Pan-African and Early Paleozoic ages for the metasedimentary and metamorphic basement rocks by Ion Probe U-Pb zircon dating. These lines of evidence together with our new dating results lead us to propose that the Early middle Proterozoic metamorphic basement of the India block once located in the southern hemisphere has undergone the Pan-African - Early Paleozoic orogenic events. The geochronological data suggest that: (1) the Proto-Himalaya formed as a result of the Pan-African and the Early Paleozoic orogenic events; (2 ) reactivation of the Early-middle Proterozoic metamorphic basement of the India block has played a key role in the formation of the Proto-Himalayan Mountains; ( 3) the building of the present-day Himalaya Mountains may have been initiated as early as the Pan-African and the Early Paleozoic.