NaSi⇌CaAl exchange equilibrium between plagioclase and amphibole
NaSi⇌CaAl exchange equilibrium between plagioclase and amphibole
复制标题
NaSi⇌CaAl 斜长石与角闪石之间的交换平衡
DOI：
10.1007/bf00375566
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发表时间：
1980
影响因子：
3.5
通讯作者：
F. Spear
中科院分区：
文献类型：
--
作者：
F. Spear
利用天然斜长角闪岩的数据，对斜长石与角闪石之间的交换平衡进行了经验标定：2钠长石+钙黄长石=2钙长石+蓝闪石。交换反应的分配系数KD为（Xan/Xab）plag·（Na，M_4/Ca，M_4）amph。在单次暴露收集的样品中，斜长石和角闪石之间的分配是系统的，但固溶体非常不理想：在一个单一的道路切割样品中，InKD值从-3.0 atXan=0.30到-1.0 atXan=0.90。随着变质程度的增加，KD和三元交换图的拓扑结构都发生了变化。在Xan =0.25时，InKD的温度依赖性适中，Δ <$H为35 ~ 47 kcal;压力依赖性较小，Δ <$V为−0.24 cal/bar。这种交换平衡作为地质温度计的准确性受到微探针分析计算角闪石公式的不确定性的限制，特别是关于角闪石中的Na，M4，约±50 ° C。
The exchange equilibrium between plagioclase and amphibole, 2 albite+tschermakite=2 anorthite+glaucophane, has been calibrated empirically using data from natural amphibolites. The partition coefficient,KD, for the exchange reaction is (Xan/Xab)plag·(Na, M4/Ca, M4)amph.. Partitioning is systematic between plagioclase and amphibole in suites collected from single exposures, but the solid solutions are highly non-ideal: values of InKDrange from −3.0 atXan=0.30 to −1.0 atXan=0.90 in samples from a single roadcut. Changes in bothKDand the topology of the ternary reciprocal exchange diagram occur with increasing metamorphic grade. Temperature dependence of InKDis moderate with Δ¯H≃35 to 47 kcal atXan=0.25; pressure dependence is small with Δ¯V≃ −0.24 cal/bar. Usefulness of this exchange equilibrium as a geothermometer is restricted by uncertainties in the calculation of the amphibole formula from a microprobe analysis, especially with regard to Na,M4 in amphibole, to approximately ±50 ° C.