Gibbs, Pt Path Of Metamorphism The North Qinling Dan Fung Kwan Ring Hornblende

One of the purpose of metamorphatism is estimating P-T paths. Gibbs' method is a method which calculates the P-T paths of metabasic system through the compenent of metabasic rocks .In the process of calculation ,there are two basic constraints for intensive variables:1) thennodynamic equilibria; 2)stoichiometry. In the process of calculation ,the thennodynamic relationships are written with dP,dT,dX. T, P are derived through dP,dT.At first , I make a framework for estimating quantitative P-T paths from compositions of a zoned amphibole of 226 from Danfeng Group in metabasite that consists of amphibole, chlorite, epidote, plagioclase , quartz and water in the system Na₂O-CaO-MgO-FeO-Fe₂O₃-Al₂O₃-SiO₂-H₂O. In the precess of calculation ,we express amphibole by the combination of tremolite(Tr) , edenite(Ed) , tschennakite(Ts) , glaucophane(Gln) , magesioriebeckite(Mrb) and Fe-tremolite and differentiate five independent thennodynamic constraints and three stoichiometric constraints through the differentiation of tempreture, pressure,mol fraction. We assume that the amphibole of rim is in the equilibrium condition with the chlorite,epidote, plagioclase, quart and water of the rim and calculate its P-T path.The inner core of the amphibole was formed during earlier phase metamorphism and its rim during the main phase of metamorphism. Earlier phase metamorphism belongs to the actionlite plagioclase facies of the low pressure facies series and main phase metamorphism occurred in the amphibole facies of the middle pressure facies sequence.The values of T-P I calculate are consistient with the values from reality.In the last, there is Danfeng Group tectonic process in the paper. The evolution process can be divided three stages. They are : 1) outspread stage; 2) In the end of Caledonian metamorphism basin closed , the underthrust stage; 3)Afterward Danfeng Group passed through multiple phases of metamorphic_deformational function becomes that now we see Danfeng Group.