Geological Geochemical Characteristics of Fang Shan Intrusion and Origin Research
Huang Fusheng (Geological Department of Peking University) Jiang Changyi (Xi'An College of Geology)
Fang Shan intrusion is a domed composite one lain inside north cbanese plate.The magma had been made during Mesozoic era, afterwards slowly diapiriclly uprised and pricked kernel position,finaly emplaced at mesogene-tic environment.All its mineral association,petrochemistry,trace elements and O, H, Sr isotope composition show characteristics of 'I-type' granites. And the partition of four coordinate Al, Fe,Mg and O,H isotopes between coexist minerals accomplished fundamentally equilibrium state.The FH2O of biotites in earlier magma episode are lower than 2kb, however, those in later, surpass 2kb, simultaneously to consider textures of the rocks, it can be indicated that volatile component contents of the magma surpassed saturation during later stage of magma evolution and fractionated out some fluid phase. Moreover, it may be also indicated that source area of Fang Shan intrusion consist mainly of intermediated and basic metaigneous rocks of Archean group which were derived from the earth's mantle.The rock associations of tectonic-magmatic belt in Tai Hang mountain, from south to north, evolve from intermediate-basic to intermediate-acid one,reflect their source depth, deeper at south but shallower at north; reflect also sucha tectonic setting, that is, levels of rise for the upper mantle are higher at south but lower at north .