Detrital Zircon U-pb Age?hf Isotopes And Geological Significance Of The Early Paleozoic Schists In The Baoshan Block And Its Adjacent Area,west Yunnan

It is indicated that the Baoshan block is originated from the eastern Gondwana;however,the tectonic affinity with Indian Gondwana or a Austrilian Gondwana is still under debate.Thus,in this paper,Petrology,geochemistry,LA-ICP-MS zircon U-Pb dating and Hf isotopic studies were carried out on detrital zircons from Early Paleozoic strata in the Baoshan block.The conclusions are as follows:1.The age distributions from the Changning formation in the Baoshan block yield dominant Neoarchean-Paleoproterozoic(2.8-2.0 Ga),Mesoproterozoic(1.6-1.0 Ga),Grenvillian(~0.95 Ga),and Pan-African(0.65-0.5 Ga)age groups.2.Zircons of Mesoproterozoic(1.6-1.0 Ga),Grenvillian,and Pan-African age groups exhibit wide range of ?Hf values from strong negative to positive,which means they are derived from different source area.The oldest Hf model ages indicate that the source magma included reworked Meso-Eoarchean crustal materials.3.The remarkable resemblance of zircon U-Pb ages and Hf isotopes from the Baoshan block with those from Indochina,western Qiangtang and Tethyan Himalayan suggests that the Baoshan block should be originated from the Indian margin of Gondwana during the Early Paleozoic.4.The U-Pb ages comparison shows that the Baoshan block contains abundant ~2500 Ma zircons,indicating that Neoarchean-Paleoproterozoic substance was involved in the deposition,while the west margin of the Indochina block contains plenty of ~1200 Ma zircons,which reconds that the Mesoproterozoic substance was involved in the deposition.5.The main crust of the Baoshan block was formed before 1.6 Ga.Crustal activities of the baoshan block after Mesoproterozoic are mainly composed of the recycling of ancient crust.A portion of juvenile crust was formed during Early Paleozoic,nevertheless Grenvillian and Pan-African crustal growth for the source areas was unapparent.