Petrogenesis Of The Neogene Basalt In The Baoshan Block,Western Yunnan Province: Implications For The Geodynamics Of The Volcanism,Structure And Mineralize In The Sanjiang Tethyan Domain

Since the Neogene(<20Ma)of the Sanjiang Tethys,volcanic-hot spring activities and related gold mineralization have been active,which profoundly affects the regional geology and ecological environment,but its tectonic dynamics drive has been controversial.Recent geological surveys revealed a set of Neogene basalts in the Baoshan block,providing a new breakthrough point for restricting this problem.Taking this set of basalts as the research object,this paper reports for the first time the Ar-Ar age,major trace elements and Sr-Nd composition of the whole rock.Based on this,it discusses the genesis and source attributes of magmatic rocks,and compares the geochemical data and geophysics of volcanic rocks in Southeast Asia.Deep exploration images to explore the genesis and deep driving of regional volcanic rocks.The ages of the two basalts in the Baoshan block are 6.28±0.58Ma and 8.70±1.12Ma.The elemental composition shows calc-alkaline,light rare earth enrichment(LREE/HREE=6.73-8.02and 10.13-12.32)and Nb-Ta depletion(Th/Nb=0.45-0.49 and 0.61-1.10)characteristics,⁸⁷Sr/⁸⁶Sr=0.706989-0.707568 and 0.706962-0.707203,?_Nd=-6.8 to-3.3 and-3.3 to-3.0are significantly more enriched than the depleted mantle,series elements-isotope covariance The graphs and isotope simulation results show that magma is not obviously contaminated with crustal materials.The magmatic rock series are enriched with products of partial melting of the lithospheric mantle.The enrichment originates from the subduction and transformation of the Meso-Neoproterozoic ocean slab.Regional comparison results show that the volcanic rocks in northern Myanmar and Tengchong are mainly the result of partial melting of the early-enriched lithospheric mantle.The volcanic rocks near deep faults in the Ailaoshan area and northern Myanmar are similar to the mantle plume OIB volcanic rocks in Hainan.This study proposes that the Neogene subduction and retreat of the Indian Ocean slab led to the decompression of the upper mantle of the Southeast Asian continent,and the Hainan mantle plume with high thermal anomaly was extracted under the Sanjiang Tethys lithospheric mantle to form the low-speed seismic wave anomaly in the upper mantle of the Tengchong block Area:Tengchong,Baoshan,and northern Burma and other areas of the rich lithospheric mantle are heated to bake and partially melted to form volcanic rocks with enriched characteristics,part of the mantle plume material emplaces along the Ailaoshan-Honghe and Sagaing faults to form OIB volcanic rocks.This model constructs the link between the subduction of the Indian Ocean plate and the activity of the Hainan mantle plume.More research and verification work needs to be carried out.