Experiments on liquid immiscibility along tholeiitic liquid lines of descent
Experiments on liquid immiscibility along tholeiitic liquid lines of descent
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DOI：
10.1007/s00410-012-0723-y
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发表时间：
2012-07-01
影响因子：
3.5
通讯作者：
Grove, Timothy L.
中科院分区：
文献类型：
--
作者：
Charlier, Bernard;Grove, Timothy L.
对沿着拉斑玄武岩液体下降线的组成进行了结晶实验，以确定硅酸盐液体不渗透性发展的组成空间。起始材料具有46-56重量%的SiO2、11.7-17.7重量%的FeOtot和0.29 - 0.36的Mg值。这些熔体落在玄武岩的趋势相关的穆尔，冰岛，蛇河平原熔岩和Sept Iles分层侵入，其中大规模的液体不可渗透性已被确认。在无水条件下的一个大气压下，在所有这些成分不同的熔岩中，在1，000 -1，020 A摄氏度以下，不溶性发展。极端的铁富集是不必要的;在铁贫化和硅富集期间也会产生不溶性。熔体成分的变化控制着硅酸盐液体不渗透性沿着拉斑玄武岩走向的发展。Na_2 O + K_2 O + P_2 O_5 + TiO_2的升高促进了两种不互溶液体的形成。增加熔体CaO和Al 2 O3稳定了单液场。新的数据和公布的相平衡表明，无水，低压分步结晶是分化过程中的非混合最有利的条件。压力抑制不溶性，因为它扩大了高钙单斜辉石的稳定领域，这减少了斜长石的比例结晶组合，从而提高早期铁贫化。原始玄武岩和富铁钛磷铁基玄武岩之间的岩浆混合作用可提高磷和碱含量，从而促进不混合作用。水可能会降低温度和大小的两个液体领域，潜在的双节点（固溶线）低于液相线，导致系统演变为一个单一的熔体相。
Crystallization experiments have been conducted on compositions along tholeiitic liquid lines of descent to define the compositional space for the development of silicate liquid immiscibility. Starting materials have 46-56 wt% SiO2, 11.7-17.7 wt% FeOtot, and Mg-number between 0.29 and 0.36. These melts fall on the basaltic trends relevant for Mull, Iceland, Snake River Plain lavas and for the Sept Iles layered intrusion, where large-scale liquid immiscibility has been recognized. At one atmosphere under anhydrous conditions, immiscibility develops below 1,000-1,020A degrees C in all of these compositionally diverse lavas. Extreme iron enrichment is not necessary; immiscibility also develops during iron depletion and silica enrichment. Variations in melt composition control the development of silicate liquid immiscibility along the tholeiitic trend. Elevation of Na2O + K2O + P2O5 + TiO2 promotes the development of two immiscible liquids. Increasing melt CaO and Al2O3 stabilizes a single-liquid field. New data and published phase equilibria show that anhydrous, low-pressure fractional crystallization is the most favorable condition for unmixing during differentiation. Pressure inhibits immiscibility because it expands the stability field of high-Ca clinopyroxene, which reduces the proportion of plagioclase in the crystallizing assemblage, thus enhancing early iron depletion. Magma mixing between primitive basalt and Fe-Ti-P-rich ferrobasalts can serve to elevate phosphorous and alkali contents and thereby promote unmixing. Water might decrease the temperature and size of the two-liquid field, potentially shifting the binodal (solvus) below the liquidus, leading the system to evolve as a single-melt phase.