Peralkaline acid liquids: A petrological study
Peralkaline acid liquids: A petrological study
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全碱性酸性液体：岩石学研究
DOI：
10.1007/bf00377480
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发表时间：
1969
影响因子：
3.5
通讯作者：
J. S. E. Carmichael
中科院分区：
文献类型：
--
作者：
J. Nicholls;J. S. E. Carmichael
电子探针分析过碱性火山岩，comendites和pantellerites中的菱镁矿和相关的铁镁矿物，与岩石和残余玻璃的主要和微量元素的新数据一起提出。在pantellerites的长石斑晶跨度较窄的范围（Or 33-Or 39）比那些的comendites（Or 30-Or 46）;两套显示只有有限的增加或向外，和分区是最大的石英轴承组合。残余玻璃中的长石微晶总是比其伴生斑晶含钾量高（2-4%）。在碱碲矿中，钾长石的含钾量随着残余液体的含钠量的增加而增加;因此，大多数钾长石存在于含钠量最高的（和过碱性的）碱碲矿中。在铁镁斑晶中，霓辉岩是最普遍存在的，通常与铁硼镁石或铁硼镁石共生;在结晶的后期（基质），它与尖晶石、钠铁闪石和土华石共生。除了Ti/Fe+Ti比值略有变化外，镍黑云母的成分几乎不变。来自不同组合的辉石具有带，这些带加在一起几乎跨越acmitehedenberten的范围。铁黄长石和钠铁闪石都含有F，但不含Cl，并且具有轻微的钾质。土华里石有两个变种;一个是蓝色和钾质，另一个是紫色和钠质;两个变种都拒绝卤素。使用（估计）的自由能数据，在fo 2，T空间的字段被假定为其中不存在的铁钛氧化物，他们的地方是由辉石和霓霞岩。无氧化物场将被冷却液截断，在冷却液中过碱度增加，fo 2接近但高于FMQ缓冲区。高Nb、Ta、Zr、Mo、Zn、Cd、R.E等;低Sr、Ba、Mg）被认为是过碱性（盐成）条件的证据。几条证据表明，在液相线温度下，过碱性流纹岩基本上是无水的。
Electron-microprobe analyses of the feldspars and associated ferromagnesian minerals in the peralkaline volcanics, comendites and pantellerites, are presented together with new data on the major and trace-elements of the rocks and residual glasses. The feldspar phenocrysts in the pantellerites span a narrower range (Or33–Or39) than those of the comendites (Or30–Or46); both sets show only limited increase in Or outwards, and the zoning is greatest in quartz-bearing assemblages. The feldspar microlites in the residual glasses are invariably more potassic (2–4% Or) than their associated phenocrysts. In pantellerites the feldspars become more potassic as the residual liquids become more sodic; thus the most potassic feldspar is found in the most sodic (and peralkaline) pantellerite.Of the ferromagnesian phenocrysts, aenigmatite is the most ubiquitous and is commonly associated with hedenbergite±fayalite, or ferrorichterite; in the later stages of crystallization (groundmass), it is associated with acmite, arfvedsonite and tuhualite. Aside from slight variation in Ti/Fe+Ti ratio, aenigmatite is virtually constant in composition. The pyroxenes from the different assemblages have zones which together almost span the range acmitehedenbergite. Both ferrorichterite and arfvedsonite incorporate F but not Cl, and are slightly potassic. Tuhualite exists as two varieties; one blue and potassic, the other violet and sodic; both varieties reject halogens. Using (estimated) free-energy data, a field in fo2, T space is postulated in which Fe-Ti oxides are absent; their place is taken by pyroxene and aenigmatite. The no-oxide field will be intercepted by a cooling liquid in which peralkalinity is increasing and in which fo2 is near but above the FMQ buffer.The characteristic pattern of trace-elements in peralkaline volcanics (e.g., high Nb, Ta, Zr, Mo, Zn, Cd, R.E, etc; low Sr, Ba, Mg) are considered to be as much evidence for the peralkaline (salic) condition as of the genetic process. Several lines of evidence suggest that at liquidus temperatures, peralkaline rhyolites are essentially anhydrous.