中文摘要：

对藏北可可西里中新世钾质火山岩的主要斑晶矿物化学成份进行了电子探针分析，结果表明，火山岩中的辉石为普通辉石、紫苏辉石和古铜辉石，角闪石为钙质角闪石，云母为钛铁黑云母和富铁黑云母，长石为中长石、更长石、钠透长石和透长石，不透明矿物主要为钛铁矿和磁铁矿，可见钛铁矿-磁铁矿固溶体。根据火山岩中单斜辉石-熔体温压计估算的辉石斑晶的形成温度和压力分别为1065～1100℃和5．3～9．1kbar。二辉石地质温度计结果表明，辉石的共结温度为976—1020℃。而钛铁矿-磁铁矿固溶体平衡计算结果表明，钛-磁铁矿的平衡温度为841～974℃，logfO2为-13．71--10．87。研究结果显示，可可西里火山岩岩浆房的埋深深度小于30km，中-酸性系列火山岩是岩浆房在相对低压条件下的中上部地壳部位，经分离结晶后形成。

英文摘要：

Electron microprobe analysis of the phenocrysts in Miocene potassic volcanic rocks in the Hoh Xil area of northern Tibetan Plateau shows：pyroxenes in the rocks are augite,hypersthene and bronzite; amphiboles are calcic amphibole; micas are biotite; feldspars are andesine, oligoclase,Na-sanidine and sanidine; main opaque minerals are ilmenite and magnetite,which commonly develop solid solution. Based on the calculation of clinopyroxene-liquid thermobarmeters, the range of equilibrium temperatures and pressures of clinopyroxene phenocryst are 1 065 - 1 100 ℃ and 5.3 - 9. 1 kbar respectively. And two-pyroxene geothermometer tells that equilibrium temperatures of pyroxenes are between 976℃ and 1 020 ℃ , while the range of equilibrium temperatures and oxygen fugacity（ logfO2 ）are 841 -974 ℃ and - 13.71 - - 10.87, calculated by ilmenite-magnetite geothermometry and geobarometry. The above results show that the depth of magma chamber in Hoh Xil area is less than 30 kin; these intermediate-acidic volcanic rocks evolved from the upper-middle crust after the fractional crystallization process in the condition of relatively low-pressure.