The Petrogenesis Of Diaoyutai Neoarchean Granitic Rocks In The Xingcheng City, Liaoning Province

The Diaoyutai is one of a few outcrops of Archaean granitoid，is situated in the costalof northeastern Xingcheng City, Liaoning Province, and tectonically located innortheastern part of North China Craton. The lithology is relative simple and we haveobtained a batch of isotope chronology data, which make it possible to be the key“windows” to investigate the composition and evolution of continental crust duringNeoarchean.Based on field observations and petrographic features, the Diaoyutai Neoarcheangranitoids can be divided into two units, i.e., porphyritic biotite monzonite granite andquartz diorite dykes. The former contains dark fine-grained dioritic enclaves with varioussizes, different shapes and plastic deformation, showing a typical characteristic of magmamixing/mingling. They have sharp or progressive contacts with their host granitoid,Sometimes, dozens of centimeters transitional zones, with k-feldspar pheneocrysts andfragments of host rock, can be observated between them. In addition, many types of thedisequilibrium mineral symbiosis are developed in the enclaves and porphyritic biotitemonzogranite, showing characteristic of mafic and acidic magmas mixing/mingling. Thequartz dioritic dykes have clear boundary with the porphyritic biotite monzogranite, whichhave characteristics of intrusive.Zircon U-Pb dating gives that the emplacement ages of porphyritic biotite monzonitegranite and quartz dioritic dikes are same within errors (2.44~2.55Ga), further indicating that they are the products of the same magmatic thermal event.The porphyritic biotite monzonite granite has high content of SiO2and low contentsof TFe2O3, MgO, CaO, TiO2and P2O5, they have trace elements similar to those of crustmaterials and are characterized by depletions in compatible element (Ni, Co and Cr), withcrust-like Nb/Ta ratios. Whereas, the dioritic enclaves and quartz diorite dikes have similargeochemical characteristics and they have high TFe2O3, MgO, CaO, TiO2and P2O5contents, enriched in the compatible element (Ni, Co and Cr) and havesimilar Nb/Ta ratiosto the primitive mantle, indicating that they were possibly derived from a mantle source.In the TFeO versus MgO, R1versus R2and Harker diagrams, all of the host granite andenclaves are plotted on a evolution line, indicating magma mixing. The host granites andenclaves have similar chondrite-normalized rare earth patterns and PM-normalized traceelement diagrams, indicating homogenization in the magma mixing/mingling. Otherwise,quartz dioritic dykes, with characteristics of highly differentiation, are products of crystalfractionation of late mantle-derived magma after contaminated by crust materials.Combined with the regional geology, we suggest that the generation of DiaoyutaiNeoarchean granitic rocks is related to underplating of mantle-derived magmas. Theporphyritic biotite monzonite granite and dioritic enclaves are the products of mixingbetween crustal-derived felsic and mantle-derived mafic magmas, while the quartz dioritedykes are the syn-plutonic mafic dykes and also record this process during magmaevolution. All these imply the important event of vertical growth and reworking of thecontinental crust in the North China craton during Neoarchean.