Geological, Geochemical Characteristics And Tectonic Significance Of The Ophiolitic Melange In Wunuer, Inner Mongolia

Wunuer ophiolitic mélange is located in the east of Central Asian Orogenic Belt and southwest of Wunuer-Xinlin ophiolitic mélange Belt.The tectonic evolution of the region is complex,which is expressed that the Blocks collage process is controversial.The aim of this dissertation is to ascertain the rock assembly,genetic type,tectonic setting and forming age of Wunuer ophiolitic mélange by the means of its characteristics of petrology,geochemistry and zircon U-Pb chronology,providing scientific basis for the tectonic evolution of research area.The results are as follows:1?Through field surveys and rock-chip identification,it is found that the Wunuer ophiolitic mélange,whose assembly are composed of gabbro,diabase,basalt,and radiolarian siliceous rock,is spreading from north to east along the Sixty-four meters bridge,north of Wunuer Town,Wuchuan,Zhadunhe Forest Farm.The basic rocks are distributed in remnant blocks and is in fault contact with wall rock.2?It measured the gabbro and basalt formation ages of 450.2 ± 1.4Ma and 363.6 ± 1.8Ma through the LA-ICP-MS zircon U-Pb dating technology,respectively,representing the Late Ordovician and Late Devonian oceanic crust.3?Through the study of the major and trace element geochemical characteristics,it is found that the basic rock composition has the characteristics of island arc and MORB.The radiolarian silicalite belongs to the biological cause and formed in the continental margin environment.It's my opinion that Wunuer ophiolitic mélange belongs to the SSZ ophiolite and formed in the arc-basin system in the subduction zone environment.4?Combined with the characteristics of regional magmatic activity and ophiolitic mélange,the Neoproterozoic-Paleozoic evolutionary model of Erguna Block and Xing'an Block is proposed:(1)750~540Ma: The Rodinia supercontinent cracked at 750 Ma approximately,resulting in the continuous extension.About at 700 Ma,Xinlin Ocean began the process of subduction and closing,forming Alihe ophiolitic mélange(698~630Ma).(2)540~480Ma:The subduction of Xinlin Ocean ceased,resulting in the emplacement of Xinlin Ophiolite(540~510Ma).And the closing of Xinlin Ocean resulted in a series of collisional magma activities.(3)480~380Ma: The subduction and closing process of Wunuer ocean begins at late Ordovician,which results in the formation of the gabbro(450Ma)of Wunuer ophiolitic mélange.And the Daminshan Group are deposited in the Wunuer region.(4)380~330Ma: With the continuous subduction of Wunuer Ocean,at late Devonian to early Carboniferous,island arc volcanic rock formed(373Ma).Back-arc expansion happened on the northern part of Wunuer later,forming the basalt(363Ma)of Wunuer ophiolitic mélange.(5)330~290Ma: Taking the Late Carboniferous collisional granite as a sign,the Wunuer Ocean closed.The northern back-arc basin contracted and the Wunuer ophiolitic mélange accumulated in the Wunuer area.