Crustal Growth And Mineralization Of The Granitoids In The Eastern Songliao Massif,NE China

Major issues related to granitoids have been extremely hot in geological research in the World.The eastern Songliao Massif located in the eastern part of the Central Asian Orogenic Belt?CAOB?is a important orogenic belt where granitoids and mineralization occur widespreadly.However,several issues about the diagenesis of granitoids,crustal accretion,derivation,tectonic evolution,existence or not of the Precambrian basements,mineralization related to granitoids in the eastern massif have been unclear.This paper will try to solve the above key issues through the researches of U-Pb-Hf isotope,major,trace and REE elements of granitoids and ore deposits in the region,combined with the previous data about chronology,sedimentology and petrology.?1?At least Eight stages of granitoids occurred in the eastern Songliao Massif,namely,?1850,?1000-800,?500-471,?380-300,?259?220-190,?180-160 and?120-100 Ma,but the Mesozoic granitoids are dominant,with a Cenozoic stage of granitoids concealed.The granitoids in the eastern Songliao Massif are mainly characterized by I–and highly fractionated I–type,with a small amount of A–type,and most of them show calc-alkaline-high K calc-alkaline-shoshonitic,metaluminous-peraluminous-strongly peraluminous series,with the evolution to enrichment–potassium and enrichment–aluminum.Here,we propose that the peraluminous and strongly peraluminous granitoids are fractionated I–type related to the fractionation of pyroxene and amphibole with low ASI values.In addition,my study also shows a terrestrial reservoir with higher Nb/Ta values than 19.9 or 17.5occurs in the Upper crust of the eastern Songliao Massif.?2?The crustal growth of the eastern Songliao Massif predominantly occurred in the Meso-Neoproterozoic but the mid-west mainly occurred in the Neoproterozoic-Early Paleozoic with a more juvenile trend.The crustal thickness of the massif was more than?50 km in the Middle Jurassic,then thinning to?35 km due to extensively lithosphere extension after the Early Cretaceous.Large-scale Precambrian basements existed within the massif in the Pre-Late Jurassic,but most of which were eroded and reworked after the Early Cretaceous.?3?The Songliao and other massifs?Erguna,Xing'an and Jiamusi?in NE China were most likely torn off from the Tarim craton in the Late Neoproterozoic,however,different from other massifs in NE China,it didn't accrete to the southern Siberia at?500 Ma,so tectonism didn't occur between the Songliao and other micro-massifs in NE China?today?before?500Ma.?4?The eastern Songliao Massif occurred in an active continental margin setting during the Early Paleozoic?520?430 Ma?,and it finished the first collision with the Jiamusi Massif in the Middle Silurian?430?420 Ma?.The reunion of the two massifs occurred in the Middle Jurassic?180?165 Ma?.In the western Songliao Massif,the collision of the Xing'an and Songliao Massifs occurred in the Late Carboniferous?330?310 Ma?.However,in its southern margin,the Songliao Massif collided with the North China craton in the Late Permian??250 Ma?.The Songliao Basin within the massif was formed in the middle-late Early Cretaceous,and its genesis might be attributed to the retreat of the Paleo-Pacific plate beneath the Eurasian continent.Here,we suggest that the diagenesis and mineralization in the eastern Songliao Massif are mainly constrained by the Songliao-Jiamusi and paleo-pacific tectonic systems.?5?At least four stages of mineralization occurs in the eastern Songliao Massif,namely,the Early Triassic skarn-porphyry Cu-Mo poly-metal deposits,the Late Triassic-Early Jurassic skarn Fe-Pb-Zn poly-metal deposits,the Middle Jurassic porphyry Mo deposits and the Early Cretaceous epithermal Au deposits,with absence of W-Sn deposits,distinguishing from the deposits in the western Songliao Massif?southern Great Xing'an Range?.Evidences from S,Pb and Hf isotopes show the mineralized source of the Early Triassic Baoshan skarn Cu-poly-metal deposits is mainly derived from a juvenile lower crust with the assimilation of old crustal materials.My data of dating and whole rock geochemistry show the Cuihongshan skarn Fe-polymetal deposits occurred in the Late Triassic??205 Ma?,and the mineralization was attributed to the fine-grained alkaline-feldspar granite which are in apophyses and dikes.The mineralization of the Middle Jurassic Luming porphyry Mo deposit has a close relationship with granite porphyry rather than monzogranite.My dating data shows the Tuanjiegou epithermal Au deposit occurred in the Early Cretaceous??101 Ma?.The primary magma of granodiorite porphyry is derived from the partial remelting of a juvenile and deep lower crust?>0.4 GPa?with the crystallization differentiation of quartz in the early stage through the study of petrography,phase diagram and Hf isotope,and the quartz in the early stage react with melt during the process of magma ascending,leading to the corrosion of quartz.We also find that the mineralized granitoids are predominantly oxidized,in favor of mineralization of Fe,Cu,Pb,Zn,Mo and Au,hindering the cumulate of meta-sulfide phases into the lower crust and mantle during the process of magmatic differentiation.My study also show the ore-forming materials in the deposits from the eastern Songliao Massif are mainly derived from juvenile lower crust,with some assimilation from old crust materials,through the line of evidences from Sr,S and Hf isotopes.At last,a tectonic model for ore forming processes of the deposits in the eastern Songliao Massif was build.?6?On the basis of the study of ore-bearing and ore-barren granitoids and modifications and preservation of the rocks and deposits in the eastern Songliao Massif,I propose that the Precambrian mineralization is not potential,in the contrast,the Paleozoic and Cenozoic mineralization related to granitoids with prospect,but the Cenozoic granites and deposits are still overplay in the deep.Based on the study of petrography,phase diagram,here I suggest that the granitoids with special textures?e.g.,aplitic texture,anhedral to subhedral granular structure,spherical structure metasomatic texture,corrosion texture,filling texture and other irregular textures?,key minerals?e.g,fluorite,tourmaline and Topaz?should be more focused during the process of geological exploration,because the magmas of ore-barren granitoids usually evolve in a simple eutectic system of quartz and feldspars,and the minerals in this environment usually display regular crystal shapes,going against mineralization.In contrast,the magmatic system enriched in volatiles and mineralizing agent?e.g.,F,B,Li,Cl,CO₂?,will decrease solidus temperature and change its crystallizing path,in favor of efficiently extracting the metallogenic elements from parental magmas.