Study On The Characteristics,Genesis And Evolution Of Rhyolitic Volcanoe Geological Relics In Yandangshan Global Geopark

Yandang Mountain,located in the southeast coast of Zhejiang Province,is a typical Cretaceous reactivated caldera.It is mainly composed of various types of rhyolitic volcanic rock geological relics.It is rated as Global Geopark for its"natural three-dimensional model of caldera".In the park,there is a complete set of continental eruptive rhyolites with different structures and Genesis formed by Mesozoic Cretaceous volcanoes through eruptive,exhalative,intrusive and magmatic processes.As a result,a variety of geological relics of volcanic landforms are formed.Meanwhile,the geological relics of volcanic associated landforms are also widely distributed and unique,It is the first Global Geopark with the theme of Cretaceous rhyolitic volcanic remains.On the basis of fully absorbing and summarizing the previous research results,through the field geological heritage survey,hand specimen identification,indoor microscopic observation,LA-ICPMS zircon U-Pb dating,Quaternary Geology and geomorphology and other survey methods and means,This paper discusses and studies the geological characteristics,petrographic characteristics,diagenetic age and geological relic characteristics of Yandangshan area,and puts forward some new views and understandings on the formation and evolution mechanism of volcanic geological relic in Yandangshan area.(1)Zircon U-Pb dating(LA-ICPMS)was used to determine the four stratigraphic unit of the Yandangshan caldera.The results show that the weighted average age of ²⁰⁶Pb/²³⁸U of the four lithostratigraphy ranges from 95.08 to 96.9 Ma,belonging to the late Early Cretaceous.(2)This paper divides the types of volcanic geological relics in Yandangshan Global Geopark,it can be divided into 4 categories,22 subclasses,and introduces the representative scenic spots,analyzes the genesis of volcanic geological relics with scientific significance.(3)This paper discusses the formation control and appearance shaping of Yandangshan volcano landform by rock lithology,structural background and external dynamic geological conditions.Among them,the volcanic lithology is the material basis for the formation of Yandangshan rhyolitic volcanic rock geological relics.The internal dynamic geological conditions play a leading role in controlling the formation of Yandangshan rhyolitic volcanic rock geological relics,while the external dynamic geological conditions are the catalyst for the formation of Yandangshan rhyolitic volcanic rock geological relics.(4)The formation process of Yandangshan landform can be summarized as follows:in the late Cretaceous(96?66 Ma),Yandangshan rhyolitic volcanic rocks cooled to form primary planation surface?in the early Cenozoic(66?33.5 Ma),Affected by India Eurasia plate collision,Yandangshan was uplifted and eroded to form a main ridge line of 850?1000 m?the beginning of late Eocene(16?11.5 Ma),India Eurasia continent hard collision and continued to wedge northward,The Yandang Mountain was uplifted and denuded again,forming a secondary planation surface between 450-500m?the beginning of Miocene(5-0Ma),Affected by the collision and collage between Taiwan Island and Luzon island arc,the Yandang Mountain area was uplifted and denuded again,forming a third-order planation surface between 100-200m.Under the long-term influence of erosion and collapse,the planation surface was divided,the geomorphic evolution process was strong,and gradually forming the volcanic landscape such as crossheading,screen-like peaks,stone cluster,valley and so on.According to the geomorphic morphology and weathering degree of Yandang Mountain,the overall geomorphic development period of Yandang Mountain is defined as the youth period.(5)The evolution of Yandangshan volcanic geological relics can be summarized into four sequences.These four sequences show that the formation of Yandangshan volcanic geological relics has a certain order and polycyclicity,The first sequence is the most typical in Yandangshan area.