Magmatic Events And Geological Significance Of Mesozoic In The Central Tethyan Himalaya

The Mesozoic Gondwana continental rifting is a necessary condition for the opening and formation of the Atlantic Ocean and the Indian Ocean.Therefore,it is of great importance to discovery the geological evidence of rifting process and to reconstruct its evolution process.There are a large number of Mesozoic rock dikes in the Tethyan Himalaya,most likely the record of the above rifting events.A large amount of studies has been conducted on these mafic magmatic rocks,but the main investigated areas are concentrated in the eastern part of the Tethyan Himalayas such as the Comei-Longzi-Yanghu,while the certal Tethyan Himalaya has less been concerned.Previous studies have revealed that the age of the mafic rock is mainly concentrated in the Cretaceous,but the lack of Jurassic age.In order to address the above problems,this thesis reported the petrological data,whole-rock major and trace element geochemical data,and zircon U-Pb ages and Lu-Hf isotopic compositions of mafic rocks in the central TH,adjacent to the southern Yarlung Zangbo Suture Zone.The mafic rocks are mainly gabbros and diabases,which are intrusive into the Triassic strata.They exhibit a distinct LREE-enriched pattern that is similar to OIB.In the PM-normalized trace element diagram,they show significant depleted HFSE,indicating they were contaminated by the continental crust.The compositions of clinopyxenes also indicate that they were formed within-plate setting.Two stages of zircon U-Pb ages are recognized: the first stage is 165±2 Ma,while the second is 140 ± 2 Ma.The above observations,in a combination with the regional geological setting,this thesis proposed that the Early Cretaceous zircon U-Pb age may represent the activity timing of the mafic dykes,while the Middle Jurassic zircons should be sourced from the country rock.The Middle Jurassic felsic magmatism may record the rifting of the East and West Gondwana,while Early Cretaceous mafic magmatism may record the rifting of India and Australia.