Magma Mixing And Its Origin Of Xuejiashiliang Complex In Changping,beijing

Xuejiashiliang complex is located in the south of Yanshan Belt where is the centre of North China Craton which is consisted of five little plutons,respectively,they are Shangzhuang intrusion,Xuejiashiliang intrusion,Heishanzhai intrusion,Humen intrusion and Heixiongshan intrusion.There are many enclaves and veins in Xuejiashiliang intrusion and Heishanzhai intrusion.Shangzhuang intrusion is made up of four kinds of rocks which are troctolite,gabbronorite,gabbro,gabbro-diorite from the bottom to up.Titanomagnetite ore deposit is benificiated between troctolite and gabbronorite and interbeds with troctolite.Xuejiashiliang intrusion is made up of hornblende diorite,and there are some pyroxene diorite next to the boundary with Shangzhuang intrusion and Heishanzhai intrusion.Heishanzhai intrusion consist of hornblende monzonite,and there is biotite monzonite next to the boundary with Humen intrusion.Humen intrusion is composed of synite,the crystal size taper gradually from North to South that reveals the disequilibrium of condensation rate.Heixiongshan intrusion is made up of synogranite and monzogranite.Except that between Xuejiashiliang intrusion and Heishanzhai intrusion is transitional boundary,other boundaries are all intrusion-type boundaries.According to the types of enclaves after Ma et al(1994),the enclaves are classified into mingled enclave and mixed enclave two kinds.Through the compute of viscosity and density of enclaves and veins,and combined with the analysis of petrography and Harker diagram,author thinks that magma mingling occurred in Xuejiashilaing intrusion boundary next to Shangzhuang intrusion,the interior of Heishanzhai intrusion is the same phenomenon.The transitional boundary between Xuejiashiliang intrusion and Heishanzhai intrusion is the result of magma mixing,where consist of mixed enclaves,and the rate of magma mixing of Xuejiashiliang intrusion is higer than it,the hightest can up to 76%.The similar parallel of Masuda-Coryell diagram and spider diagram among Xuejiashiliang intrusion,Heishanzhai intrusion and Humen intrusion reveals that they are the same origin.The beneficiation elements of Ba,Sr,Nb and Ta and the depletionelements Pb suggest that the three intrusions are derived from the lower crust and are mixed with mantle-derived matter.The Masuda-Coryell diagram and spider diagram of mingled enclaves in Xuejiashiliang intrusion and Heishanzhai intrusion are similar with Shangzhuang intrusion,and combine with the evidence of many antecryst of plagioclase in Shangzhuang troctolite suggest that the mixed enlcaves are the generation of partial melting because Fe-bearing fluid inject into Shangzhuang intrusion.The initial tempreture of patial melting is higher than 1130?.The age of the mingled enclave is 127.5Ma which is get by the dating of SHRIMP zircon U-Pb which is later than Xuejiashilaing intrusion approximately 3Ma that revealed the speed of the North China Craton's uplift is fast which is the direct response of the delamination.