新疆东天山花岗岩类岩石形成的物理化学条件

PHYSICO—CHEMICAL CONDITIONS OF FORMATION OF GRANITOIDS FROM EASTERN TIANSHAN MOUNTAINS,XINJIANG CHINA

通过对新疆东天山花岗岩类岩石中的角闪石、斜长石、碱性长石、磷灰石、黑云母成分的系统研究,确定花岗岩类岩石在11—17km深处结晶;无矿化、蚀变的二长花岗岩结晶温度约550℃,花岗闪长岩、石英二长岩的结晶温度为552—650℃,钠长石化的含矿二长花岗岩其二长石平衡温度均低于510℃,蚀变愈强烈,平衡温度愈低。二长花岗岩的起源温度为780—840℃,石英二长岩的起源温度为860—880℃,碱长花岗岩的起源温度最低。推算得到二长花岗岩的极限起源深度为28—32km,石英二长岩的极限起源深度为33—34km。HF,HCI逸度计算表明,它们趋向于岩浆晚阶段富集,但无论是早结晶的磷灰石,还是晚结晶的黑云母,总是钠长石化的含矿花岗岩低于正常无蚀变、无交代现象花岗岩的逸度值,正常花岗岩类岩石由黑云母指示的f_(HC(?)),f_(HF)分别为36.60—51.10kPa,1.20—1.60 kPa。花岗岩类岩石形成的fo_2为1.05×10^(-11)—3.11×10^(-11)Pa,而钠长石化的含矿二长花岗岩具最低的氧逸度,为1.48×10^(-17)—2.45×10^(-15)Pa。

Through systematic study of compositions of hornblendes, plagioclases, alkali feldspars, apatites and biotites from granitoids in Eastern Tianshan Mountains,Xinjiang China,it is determined that the granitoids crystallized at the depth of 11—17 km; crystallizing temperature of barren and unaltered monzonitic granites was about 550℃ the temperature of granodiorites and quartz monzonites was about 552℃—650℃ the equilibrium temperature of two-feldspar from greisenization and albitization monzonitic granites was lower than 510℃ the stronger the alteration was,the lower the equilibrium temperature was;originated temperature of monzonitic granites was 780℃—840℃ the temperature of quartz monzonites was 860℃—80℃and alkalifeldspar granites had the lowest originated temperature. Reckoned maximum originated depth is 28—32 km for monzonitic granites,33—34 km for quartz monzontes. The results of fugacity calculations show that HF and HCl tended to be rich at the late stage of magmatism. Regardless of early crystallized apatite or late crystallized biotite, the fugacities of albitization ore-bearing granites are always lower than that of unaltered and unmetasomated granites. The HCl, HF and O_2 fugacities indicated by biotites from unaltered granitoids are 36.6—51.1 kPa,l.2—1.6 kPa and 1.05×10^(-11)—3.11×10^(-1) Pa respectively. Oxygen fugacity of albitization ore-bearing monzonitic granites is 1.48×10^(-11)—2.45×10^(-15) Pa and the lowest among that of the granitoids.