Characteristics And Geology Significance Of Late Paleozoic-Mesozoic Magmatic Rocks In The Central Great Xing’an Range

This paper takes magmatic rock of The Late Paleozoic-Mesozoic as the research object in the Great Xing’an Range,utilize the characteristics of Late Paleozoic-Mesozoic magmatic rocks in this area by using petrology、geochemistry、chronology,discuss petrogenesis、magma source and structural setting,for more information about Magma issue and geodynamic background of Late Paleozoic-Mesozoic Magmatic Rock combined with regional geological conditions in the Great Xing’an Range area,explore the cause of the uplift of the Great Xing’an Range。According to data analysis results and historical data,the magmatic activities in the middle of the Great Xing’an Range are mainly concentrated in three periods: Carboniferous,Triassic and Cretaceous.The Carboniferous is mainly characterized by the emplacement of intrusive rocks in the Early Carboniferous and the eruption of intermediate acid volcanic rocks in the Late Carboniferous.Early Carboniferous intrusive rocks are mainly medium-coarse monzonitic granites(352.1±1.7 Ma)and medium-fine-grained monzonitic granite(339.1±4.2 Ma).The two intrusive rocks have the same lithology,with the similar geochemical composition,Both of them are mainly I-type granites.The primordial rocks of magma are all generated by the melting of crustal materials.It’s created by the upwelling asthenosphere melting the lower crust.The volcanic rocks of the Late Carboniferous Gegenaobo Formation are mainly composed of neutral coarse andesite(304.4±2.3 Ma)and acid rhyolite tuff(307.6±2.0 Ma),they are close in age.The Late Carboniferous region experienced a complete deposition-eruption cycle due to the field stratigraphic contact.Volcanic rocks are relatively enriched in large ion lithophile elements such as Ba、K and Rb etc.,obviously deficient in high field strength elements such as Nb etc.,especially acid rocks are strongly depleted of Sr、P、Ti.The volcanic rocks of this period all came from the Earth’s Crust,and was participated by the molten mantle.The Late Triassic mainly shows trachyandesite(235.8±1.0 Ma)which is formed by volcanism and intrusive porphyritic biotite granodiorite(215.5±2.6 Ma)and biotite adamellite(226.6±4.7 Ma).The magma of trachyandesite is derived from lithospheric mantle and has Crustal material composition.The intrusive rocks are all A-type granite,judging according to trace element and ratio,they are generated from the differentiation of the crust which is generated from melting of the upwelling asthenosphere,and granodiorites are more likely to have been generated from melting of basic rocks.The Cretaceous is mainly characterized by the intrusion of middle-fine-grained syenogranite(134.1±1.2 Ma)、fine-grained alkali feldspar granite(135.6±0.9 Ma)、fine-grained porphyritic syenogranite(135.1±0.9 Ma),and the volcanism of the Baiyingaolao Formation dominated by rhyolitic tuff(134.1±1.2 Ma).The intrusive rocks should have the same magma source area due to the close time,they all show obvious enrichment of K、Th、U、Nd、Hf etc.,and deficiency of high field strength elements such as Nb,Sr、Ti and P etc.,they are all basically A-type granite according to Petrological characteristics and Geochemical characteristics.The protoliths of intrusive rocks in this period are all generated by crust melting judging from its elements and ratios.They are formed in the combined action of the upward movement of magma which is generated from the crust by upwelling asthenosphere melting and the participation of mantle materials.The source rocks of the acidic volcanic rocks of the Baiyingaolao Formation generated from volcanism are also mainly from the crust.Based on the above data and comprehensive research,it is believed that the middle section of the Great Xing’an Range was in the subduction stage of the Paleo-Asian oceanic plate during the Carboniferous,formed the early Carboniferous intrusive rocks and Late Carboniferous volcanic rocks with island arc properties,it’s a tectonic environment of collision and compression.The Late Triassic,the transition from plate subduction to post collision extension began.The Paleo-Asian Ocean closed,the oceanic crust disappeared,and the North China Plate and Xing’an block collided and closed along the Xilamulun River-Changchun-Yanji line,forming a unified whole,starting to enter the post-collision extensional phase,the upwelling of the asthenosphere leads to the thinning of the lithosphere and the intensification of underplating.The early Cretaceous,the entire Great Xing’an Range area was in a kind of intracontinental extensional orogenic stage.Asthenospheric upwelling led to intensified underplating,thinning of the lithosphere,and a large amount of mantle material participated in the original magma,forming a large amount of A-type granite in the area,which culminated in the vertical growth of the Great Xing’an Range.This paper has 76 pictures,26 tables,319 references...