The Petrogenesis And Evolution Of Neoarchean Diaoyutai Granitoid In Western Liaoning Province

The Neoarchean Diaoyutai granitoid in western Liaoning Province is an important part of Suizhong granitoid,which is a rock association with bimodal components.It consists of granitic series and dioritic series.The zircon U-Pb chronology shows that the two sets of rock series of Diaoyutai granitoid generated in the late of Neoarchean.The granitic series mainly includes porphyraceous granodiorite,gneissic biotite adamellite,massive medium-grain adamellite and vein-shape granite,etc.The dioritic series is mainly composed of enclave-shape fine grained biotite diorite,fine grained amphibolite biotite diorite,vein-shape diorite plagioclase lamprophyre and underplating quartz diorite,etc.The rocks of Diaoyutai granitic series are the products of partial melting with high degree,and different evolutionary stages correspond to different rock types.The close accumulative texture and non-close accumulative texture of plagioclase crystals in porphyraceous granodiorite are developed,and melt exists only between the solid crystals in the form of melt capsule or string of beads.The gneissic biotite adamellite is mainly composed of plagioclase solid skeleton,non-close accumulative texture,the melt exists next to the boundaries of solid crystals,and has formed a melt channel.The plagioclase crystals in massive medium-grain adamellite are irregular presenting in the melt,and the massive medium-grain adamellite is fractionated magma.The differentiated vein-shape granites are present in all types of granite mentione above.The fabrics of vein-shape granite are similar to that of massive medium-grain adamellite.Combined with the relationship of occurrence,it may represent the channels of migration-emplacement of the residual magma.The above study of the rock fabrics shows that the porphyraceous granodiorite,gneissic biotite adamellite and massive medium-grain adamellite are the products of different evolutionary stages of the same magma sequence.Their contents of melt and the degrees of melting are gradually increased,and their characteristics change from the in situ mixed granite to semi-in situ mixed granite and to the magmatic granite emplace in other place.Geochemical studies have also validated this evolutionary trend.The geochemical studies have also validated this evolutionary trend.The content of SiO₂ and K₂ O increased,the ?Eu value gradually changed from positive to negative,and the Sr and Ba changed from weak enrichment to strong loss,the degree of P loss gradually increased,all these indicate that the degree of differentiation and maturity of the anatectic magma is increasing and the enrichment of the melt is gradually increasing.The Diaoyutai dioritic rock series recorded the episode magma underplating and the interaction between crust-mantle in the late of Neoarchean in Xingcheng area.The content of SiO₂ in all kinds of rocks of dioritic series is low.And they are rich in Fe,Mg,Cr,Ni and other elements,with the characteristics of the basic mafic magma.The dioritic series belongs to different magma series from granite series and its the invasive deep-based basic magnesia magma when the granitic crust melted The finegrained?hornblendic?biotite-diorite with quenched boundary,reverse veins is in the form of inclusions,and developed magma mixing and magma miging with highly molten granitic crust.The diorite plagioclase lamprophyre invade into massive medium-grain adamellite in the form of vines or dykes,and the presence of tectonic necking indicates that they are contemporaneous products.Finally,a large amount of quartz diorite intrude into the crust.The frequent vertical addition of deep source magma may be one of the main dynamics reasons for the deep melting-reconstruction – growth of the crust of North China Craton.The Diaoyutai granitoid records the late Neoarchean process of crust anataxis and the interaction between crust and mantle,which is a long-term meltingdifferentiation-crystallization process related to the vertical addition of mantle-derived basic mafic magma.