Magma Source And Genesis Mechanism Of Granites In The Niutougou District,Songxian County,Henan Province

There are many granite dikes including granite porphyry dikes and porphyritic monzogranite dikes in the Niutougou gold ore field,Songxian County,Henan Province.In order to ascertain the age,genesis mechanism and tectonic setting,two types of granites were sampled from the Songligou,Shatuwa,Xiazhuang granite porphyries and the Shatuwa,Muergou porphyritic monzogranites.By doing petrography,geochemistry,zircon U-Pb chronology and Hf isotopic composition,this paper gets some conclusions as follows.(1)The Songligou and Xiazhuang granite porphyries are calc-alkaline,high-Kgranites.The Shatuwa granite porphyry and porphyritic monzogranites are alkaline and shoshonite series granites.All granite dikes in this area enrich large ion lithophile elements(LILE)Rb and K,and deplete high field strength elements(HFSE)Nb,Ta,Ti,P,and mainly show negative Eu abnormity.Granite porphyries and porphyritic monzogranites are depleting middle rare earth elements(MREE)and depleting heavy rare earth elements(HREE)respectively.(2)The results of LA-MC-ICPMS zircon U-Pb analysis yield ages of 168.8±4.1Ma,162.6±5.7Ma and 166.8±1.6Ma,163.1±2.3Ma for the Songligou,Shatuwa granite porphyries,and the Shatuwa,Muergou porphyritic monzogranites.Combining the age of the Xiazhuang granite porphyry,the time of granitic magma activities in Niutougou ore field is 160~169Ma.(3)The ?Hf(t)values of the Songligou,Shatuwa,Xiazhuang granite porphyries and the Shatuwa,Muergou porphyritic monzogranites are-24.43~-19.79,-24.10~-20.92,-24.18~-20.17,-22.96~-15.84,-21.35~-16.04,and the TDM2 values of them are 2434 ~ 2718 Ma,2511 ~ 2706 Ma,2473 ~ 2720 Ma,2190 ~ 3140 Ma,2198 ~2566Ma respectively.They are genesis from partial melting of the Taihua group,and they are I type granites.(4)The Shatuwa and Muergou porphyritic monzogranites are mainly partial melting from amphibolite and plagioclase amphibolite under the condition of 800~850? and 1.4~1.7GPa,and these restite consist of garnet,rutile,ilmenite,and less clinopyroxene,hornblende,plagioclase.The Songligou and Xiazhuang granite porphyries are partial melting from biotite plagioclase gneiss,high Si TTG gneiss and kfs.granite gneiss.The Shatuwa granite porphyry is mainly partial melting from amphibolite and plagioclase amphibolite.All of granite porphyries are genesis under the condition of 707~728?,687~743?,718~737?respectively and lower pressure than porphyritic monzogranites.These restite consist of plagioclase,hornblende and apatite.(5)These granites in the Niutougou ore field may result from westward subduction of paleo-pacific plat,lithosphere extension and mantle upwelling.