Geochemical Characteristic And Geological Significance Of The Mazhuang Neoarchean Pluton In Songshan Area

Songshan area is the typical area where research precambtain geology which record the evolution history of the south of North China Craton.The Mazhuang pluton is a Metamorphic deformation granitic pluton which disintegrated from Dengfeng complex rock.Through studying the petrologic features,petro-graphic features,geochemistry and geochronology of Mazhuang pluton.We analysis the geochemical characteristics,origin and tectonic environment of Mazhuang pluton and obtain the following resuits:?1?Mazhuang pluton presents east-west strip distribution,the exposed area of about 1.5km2.The main lithology of the pluton is trondhjemite with the features of grayish-white colour,medium-grained structure,Fine grained granite structure,gneissic structure,main mineral plagioclase?60%⁷0%?,quartz?30%⁴0%?,minor mineral biotite?10%¹5%?.There is a large amount of residual body like hornblende schist from Guojiayao Formation in the pluton.?2?The rocks have features of high NaO₂ with that the date of Na₂O/K₂O range from 2.0³.2,high SiO₂ amount?69.24%⁷4.32%?,Al₂O₃ 14.35%¹7.68% which presents a feature of high aluminum and poor of magnesium iron oxide.The pluton shows calcium alkaline characteristics with ??1.14².13?.the content of TiO₂,Al₂O₃,FeOt,CaO,MgO and P₂O₅ decrease with the content of SiO₂ increase which shows that they are from the same origin,and mainly dominated by crystallization differentiation.?3?The pluton reveals enrichment of LREE and deficit of HREE with low ?REE,HREE strongly loss,LREE/HREE=6.9⁷.7,?La/Yb?N=21.07⁵6.67,?La/Sm?N= 4.21⁷.74,?Gd/Yb?N=2.01⁴.97.positive Eu anomaly possibly related with the differentiation of plagioclase.The pluton has features of Enrichment of LILE like Rb?Sr?Ba?K,but deficit of HFSE like Nb?Ta,low in Cr?Ni?Yb and Y amount,high Sr/Y date?339¹233?,average of 662.7,consistent K?La?Sm positive anomaly,U,Nb,Ti negative anomaly,high field strength element Zr-Hf and Ce weakly negative anomaly or no anmalies which shows that the pluton has the similar geochemical characteristics with the high Si Cenozoic adakite,possibly from partial melt of basaltic that contain garnet of amphibolic or eclogitic residual.?4?We obtain that the weighted average age: 2581 Ma ± 23Ma?MSWD=1.3?is agreement with the upper intersection age: 2636 Ma ± 25Ma?MSWD=8.4?by U-Pb zircon chronology study.So The crystallization age of The Mazhuang pluton is 2580Ma²636Ma,and its intrusion age is Neoarchean Era.The 2370 Ma possibly is later stage metamorphic recrystallization age of the pluton.?5?The mineral assemblages and geochemical characteristics of the pluton shows that Mazhuang pluton possibly formed by the moisture content basaltic oceanic crust patial melting in the subduction environment and contaminated by the mantle wedge during oceanic crust emplacement.