斜长石和橄榄石成分对四川攀枝花钒钛磁铁矿床成因的指示意义

	斜长石和橄榄石成分对四川攀枝花钒钛磁铁矿床成因的指示意义
其他题名	Implications of compositions of plagioclase and olivine on the formation of the Panzhihua V-Ti magnetite deposit, Sichuan Province
	张晓琪; 张加飞; 宋谢炎; 邓宇峰; 官建祥; 郑文勤
通讯作者	宋谢炎
	2011
发表期刊	岩石学报
卷号	27 期号:12 页码:3675-3688
摘要	攀枝花岩体下部和中部岩相带各旋回中磁铁辉长岩和辉长岩的岩相结构特征表明,钛铁氧化物和斜长石、橄榄石的结晶发生在相近的温度区间内,这为我们利用斜长石和橄榄石的成分探讨磁铁矿形成时温度、氧逸度和岩浆成分的变化提供了可能。电子探针分析结果表明,下部和中部岩相带中斜长石An牌号自下向上有规律地逐渐降低,而在每一个旋回内部,橄榄石的Fo值总是由磁铁辉长岩向辉长岩表现出强烈降低的趋势。这些特征说明攀枝花岩体经历了多次富铁钛的岩浆的补充。斜长石An牌号小幅度的规律性降低说明岩浆氧逸度和Fe3+/Fe2+比值变化对斜长石成分影响很小,因此,我们可以根据斜长石成分估计钛铁氧化物结晶过程中温度变化。然而,同一旋回中橄榄石Fo值变化较大说明橄榄石成分在很大程度上取决于岩浆中的Fe3+/Fe2+和Fe2+/Mg含量,因此,可以根据橄榄石成分分析磁铁辉长岩与辉长岩形成过程中氧逸度和Fe3+/Fe2+比值的相对变化。计算得到下部和中部岩相带中斜长石的结晶温度介于1079～1121℃之间,认为钛铁氧化物的结晶也大致发生在此温度区间;根据同一旋回中磁铁辉长岩与邻近辉长岩中橄榄石Fo值的差异,发现每次新补充的岩浆分离结晶过程中氧逸度总是逐渐降低,这与前人对封闭体系岩浆结晶分异过程中氧逸度变化规律的认识一致.
其他摘要	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.
关键词	斜长石橄榄石氧逸度层状岩体攀枝花钒钛磁铁矿床峨眉大火成岩省
学科领域	矿床地球化学
语种	中文
文献类型	期刊论文
条目标识符	http://ir.gyig.ac.cn/handle/352002/4886
专题	矿床地球化学国家重点实验室_矿床地球化学国家重点实验室_期刊论文
通讯作者	宋谢炎
推荐引用方式 GB/T 7714	张晓琪,张加飞,宋谢炎,等. 斜长石和橄榄石成分对四川攀枝花钒钛磁铁矿床成因的指示意义[J]. 岩石学报,2011,27(12):3675-3688.
APA	张晓琪,张加飞,宋谢炎,邓宇峰,官建祥,&郑文勤.(2011).斜长石和橄榄石成分对四川攀枝花钒钛磁铁矿床成因的指示意义.岩石学报,27(12),3675-3688.
MLA	张晓琪,et al."斜长石和橄榄石成分对四川攀枝花钒钛磁铁矿床成因的指示意义".岩石学报 27.12(2011):3675-3688.

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