Paleozoic Multi-Stage Magmatic Events Related to Proto-Tethys and Paleo-Tethys Evolution:Insights from Intrusive Rocks in the Eastern Altyn Orogen,NW China

Abundant mafic-felsic intrusions distributed in the Altyn Orogen record orogenic histories related to Proto-Tethys and Paleo-Tethys evolution. Zircon U-Pb dating of the intrusive rocks in the eastern Altyn Orogen identifies at least three major tectono-magmatic episodes, yielding ages of ～426,～376 – 373 and ～269 – 254 Ma. The first two emplacement episodes correspond to the post-collisional magmatism in the Altyn Orogen. The ～426 Ma granitoids possess adakitic characteristics coupled with enriched isotopes, suggesting that they originated from partial melting of thickened lower continental crust induced by upwelling asthenospheric mantle after slab break-off of the South Altyn Ocean Plate.Next, the ～376–373 Ma mafic-intermediate rocks and coeval granitoids represent a large thermal event that involved mantle melting with induced new juvenile lower continental crust melting in a postcollisional extensional setting. Finally, the ～254 Ma diabase dykes intruded into the ～269 Ma granitoids, which were related to the widespread Late Paleozoic magmatism resulting from Paleo-Tethys Ocean subduction. Post-collisional magmatism in the Altyn Orogen significantly enhances understanding of the tectono-magmatic evolution in the northern Tibetan Plateau. The penetrative influence of Paleo-Tethys Ocean subduction was more extensive than previously thought.