Experimental investigation of the effect of Ca, Fe and Ti on cotectic compositions of the rhyolitic system
Experimental investigation of the effect of Ca, Fe and Ti on cotectic compositions of the rhyolitic system
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DOI：
10.1127/ejm/2015/0027-2423
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发表时间：
2015-03
影响因子：
2.1
通讯作者：
S. Wilke;Carolin Klahn;T. Bolte;R. Almeev;F. Holtz
中科院分区：
文献类型：
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作者：
S. Wilke;Carolin Klahn;T. Bolte;R. Almeev;F. Holtz
在 200 MPa 和水活度为 0.5 的条件下，研究了标准钙长石含量对 Qz-Ab-Or-An 体系中共晶曲线位置的影响。为了模拟尽可能接近天然高硅流纹岩的成分，所有研究的成分还含有约 1 wt% FeO 和 0.2 wt% TiO 2。共晶曲线的位置是根据在 790 至 850°C 之间进行的结晶实验推导出来的，并使用含有约 3 wt% H 2 O 的十四种起始玻璃组合物。不同起始材料的液相线用于约束石英的主要场，斜长石和sanidine。与固相共存的残余熔体的组成用于定义共晶曲线的位置。与单方花岗岩体系相比，共晶点偏离了 Ab 顶点，当投影到单方花岗岩体系上时，其组成估计为 Qz 42 Ab 21 或 37。以蛇河平原高硅流纹岩为例，讨论了岩浆储存条件深度估算的意义。
The effect of the normative anorthite content on the position of cotectic curves in the Qz–Ab–Or–An system has been investigated at 200 MPa and a water activity of 0.5. To simulate compositions as close as possible to those of natural high-silica rhyolites, all investigated compositions also contained ~ 1 wt% FeO and 0.2 wt% TiO 2. The position of the cotectic curves was deduced from crystallization experiments carried out between 790 and 850°C and using fourteen starting glass compositions containing ~ 3 wt% H 2 O. The liquidus phase of the different starting materials was used to constrain the primary fields of quartz, plagioclase and sanidine. The compositions of residual melts coexisting with solid phases were used to define the position of cotectic curves. Compared to the haplogranite system, the eutectic point is shifted away from the Ab apex, and its composition is estimated to be Qz 42 Ab 21 Or 37 when projected onto the haplogranite system. The implications for the estimation of the depth of magma storage conditions are discussed on the basis of an example from the Snake River Plain high-silica rhyolites.