U-Pb dating,geochemical characteristics,and geological significance of cumulate gabbro in the Luobusha ophiolite mélange
The Luobusha ophiolite is a typical site of the eastern part of the Yarlung Zangbo ophiolite belt,but so far there has been no consensus concerning its formation time and tectonic setting.We conducted LA-ICP-MS zircon U-Pb dating and geochemistry studies on the cumulate gabbro within the ophiolite mélange,aiming to explore the formation age and tectonic setting of the Luobusha ophiolite.The mean zircon 206Pb/238U ages for the cumulate gabbro is(144±3)Ma(MSWD=0.19,n=25),suggesting that the Luobusha ophiolite was formed during the Early Cretaceous.The cumulate gabbro exhibits depletion in high field strength elements such as Nb and Hf,as well as light rare earth elements(LREE).Additionally,its rare earth element distribution curve shows characteristics consistent with N-MORB(Normal Mid-Ocean Ridge Basalt),indicating its formation in a depleted mantle source region.The negative Nb anomaly indicates that the magma related to the studied cumulate gabbro was influenced by plate subduction.This suggests that the Luobusha ophiolite is an SSZ-type ophiolite.Combined with regional data,the tectonic setting for the formation of the Luobusha ophiolite is likely a back-arc basin.
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