Geochemical Characteristics And Geological Significance Of Late Paleozoic Intrusive Rocks In Ubud,Beidashan,Alxa

Paleozoic intrusive rocks are widely exposed in Beidashan,western Alxa League,Inner Mongolia.The spatial and temporal distribution and source compositions of these intrusive rocks are of great significances for understanding the tectonic division and evolution of Western Alxa.In this paper,detailed petrology,geochronology and zircon Hf isotopes of Yaoquan and Shazaoquan granitic bodies in Ubu Ribot area,northern Beidashan Mountains are studied in order to explore the tectonic division and evolution of the area.Zircon LA-ICP-MS U-Pb dating results show that the ages of Yaoquan biotite granite and Shazaoquan biotite granite are 261.8±1.3 Ma and 303.8 ±1.6 Ma.The two intrusions were both formed in the Late Paleozoic and belong to the products of Variscan magmatism.Both Yaoquan biotite plagioclase granite and Shazaoquan biotite granite belong to weak peraluminous.The REE patterns of Yaoquan biotite granite and Shazaoquan biotite granite are similar,and both of them show relative enriched light REE and depleted heavy REE with weak-medium Eu negative anomalies.Both Yaoquan biotite granite and Shazaoquan biotite granite have positive zircon ?Hf(t)values.The ?Hf(t)of the Yaoquan biotite granite and the Shazaoquan biotite granite are in the ranges of +1.93~+7.40 and +0.35~+10.00,respectively,showing that the sources of the two plutons were from depleted mantle or juvenile crust.The source characteristics are similar to the intermediate-acid plutons from Zongnaishan-Shalazashan area in the mid-eastern part of the Alxa and Central Asian orogenic belt,but distinctly different from the intermediate-acid plutons in the southern part of the Beidashan and the Yabulai-Nurgong-Honggueryulin area in the mid-eastern part of the Alxa.Therefore,the northern Beidashan may not belong to the Alxa block,but have the same tectonic affinity as the Zongnaishan-Shalazashan area in mid-eastern Alxa.Both of the northern Beidashan and the Zongnaishan-Shalazashan area could be part of Central Asian orogenic belt.