Mineral assemblages and associated textures in the low and middle part of the Panzhihua intrusion indicate that plagioclase, olivine and Fe-Ti oxides were crystallized at a similar temperature range. Thus, it is possible to estimate variation of temperature, oxygen fugacity (f(O2)) and magma composition during the formation of the magnetite gabbro and gabbro in different cycles of the Panzhihua layered intrusion by means of compositions of plagioclase and olivine. Electron microprobe data indicate that plagioclase has small compositional variation (An(58.0-52.5)) from the low zone to the middle zone. Whereas, forsterite percentages of olivine (Fo) decrease significantly upwards from magnetite gabbro to gabbro within a single cycle unit. These features indicate that the Panzhillua intrusion was developed by replenishment of many pulses of Fe-Ti enriched magmas. Small and regular composition variations of plagioclase suggest that variations of f(O2) and Fe(3+)/Fe(2+) of the magma have little effect on crystallization of plagioclase. Therefore, compositions of plagioclase can be used to estimate temperature of crystallization of Fe-Ti oxides. In contrast, large variations of Fo of olivine within a cycle unit suggest that the compositions of olivine depend on values of Fe(3+)/Fe(2+) and Fe(2+)/Mg of the magma, from which the olivine crystallized. Thus, Fo of olivine was used to rebuild variation of f(O2) during the formation of the magnetite gabbro and gabbro. Crystallizations of plagioclase of the lower and middle zones of the Panzhihua intrusion occurred between 1079 degrees C and 1121 degrees C, we estimate that Fe-Ti oxide probably crystallized at the same temperature range as well. On the other hand, decrease of Fo of olivine from magnetite gabbro to gabbro within a cycle unit indicate that f(O2) decreased during fractional crystallization of a new replenished magma. This conclusion is consistent with previous experimental studies about the f(O2) variations during fractional crystallization process at a system closed to oxygen.

Publication name	ACTA PETROLOGICA SINICA　Volume: 27 　Issue: 12 　Pages: 3675-3688 　Published: DEC 2011
Author(s)	Zhang XiaoQi; Zhang JiaFei; Song XieYan; Deng YuFeng; Guan JianXiang; Zheng WenQin
Corresponding author	ZHANG Xiaoqi  wish-you@live.cn, songxieyan@vip.gyig.ac.cn  Chinese Acad Sci, Inst Geochem, State Key Lab Ore Deposit Geochem, Guiyang 550002, Peoples R China

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