The Mesozoic Volcanic Magmatism And The Geodynamics Evolution In South Lhasa Block

Many Mesozoic volcanic rocks and magmatic intrusions are widely distributed in the Lhasa block.This is a good place to study the Neo-Tethys Ocean's northward subduction during the Mesozoic and the magma evolution history of the Lhasa block.In this paper,a systematic field survey of Shigatse and Sangri regions was conducted to systematically study petrology,chronology,and petrogeochemistry of the Danshiting Formation volcanic rocks in the Bima Formation and the Sangri region of Shigatse.The analysis of isotope geochemistry and other aspects aims to determine the temporal and spatial sequence of the magmatic activities in the Mesozoic Era of the southern margin of the Lhasa block,and to analyze the magmatic origin,rock genetics,and tectonic settings.The south margin of the Lhasa block and Neo-Tethys The magmatic evolution and tectonic setting during the Mesozoic provided evidence.The following research results have been obtained:1?In this paper,the zircon SHRIMP U-Pb age of the volcanic rocks of the Bima Formation in the Xigaze region is 177.9±2.5 Ma,combined with the zircon ages of the volcanic rocks of the Bima Formation in the Sangri area obtained by previous generations.It can be assumed that the Bima Formation volcanic rocks formed at 177.9±2.5 Ma.-195.2 ± 3.0 Ma,belonging to the Jurassic strata.The rocks in the Bima Formation are mainly composed of basic-neutral-acidic,and lithology is metamite,andesite,and basalt,which belong to the tholeiitic series.The Bima volcanic rocks show enrichment of large ion lithophile elements(LILE)Th,U,Sr,etc.,and loss of high field strength elements(HFSE)Nb,Ta,Ti,etc.,which are characteristic of typical island arc volcanic rocks.The group of volcanic rocks should be the product of the process of the northward descent of the Lhasa block towards the southern Tethys Ocean during the Jurassic period.2?In this paper,the first detailed analysis of the volcanic rocks of the Danshiting Formation in the Sangri area shows that its zircon LA-ICP-MS U-Pb age is 97.1±0.8 Ma-90.1±0.7 Ma,which is a Cretaceous stratigraphy.Its lithology is characterized by basalt,andesite,enrichment of large ionic lithophilic elements(LILE)Ba,U,Sr,La,loss of high field strength elements(HFSE)Th,Nb,Ta,Ti elemental characteristics,may form in the Andean Type construction background.3?In this study,a systematic study of the volcanic rocks of the Mazu volcanic rocks and the Danshiting Formation volcanic rocks was carried out,which complements the tectonic setting and magmatic evolution model maps of the Lhasa block and the Neo-Tethys ocean's northward subduction during the Mesozoic era.Summarizing our research and previous achievements,we can divide the history of the Neo-Tethys northward subduction into four phases: During the Jurassic period(195-150 Ma),magmatic activity was controlled by the Neo-Tethys Ocean North Steep subduction,the formation of the Yeba Formation and the Bima Formation volcanic rocks;the Neo-Tethys during the Late Jurassic to Early Cretaceous(150-110Ma)was dominated by low-angle flat-plate subduction,with magmatic activity weak and migrating to the north During the Late Cretaceous(110-80 Ma),the Neo-Tethys was dominated by Andean-type subduction,mainly forming the Dan-Shi-Ting volcanic rocks;the Neo-Tethys Ocean experienced a land-and-land subduction during the Paleogene(70-40 Ma).The process of land-continent collisions changed during the period when the volcanic rocks responded to the Linzong volcanic rocks.