Collaborative Research: Investigation of Volatile Gradientsin Silicic Magma Chambers

两个来自化学分区岩浆室的物质例子是加利福尼亚州的毕晓普凝灰岩和新墨西哥州的下班德利耶凝灰岩。在主教凝灰岩中，喷发似乎颠覆了岩浆室的内容物，保存了岩浆室化学成分的地层记录。下班德利耶凝灰岩的喷发并没有保留化学分层，据推测，这种化学分层存在于洞穴中。两次喷发的差异表明，毕晓普凝灰岩室具有密度(挥发性)梯度，而下班德利尔岩浆室的挥发物更为均匀。该项目将通过分析斑晶中捕获的熔体包裹体来量化两个房间中的挥发性含量，斑晶代表不同的地层层位。用离子和电子探针技术测定熔体包裹体中H、F、Cl和S的含量，作为原始岩浆室深度的函数，从而确定挥发分梯度的大小。主要元素的电子探针分析将有助于确定熔体包裹体的不变性质，对选定的亲石微量元素的离子探针微量分析将有助于确定每个斑晶的原始地层位置。PI将完成除离子探针分析以外的所有工作，离子探针分析将由亚利桑那大学的理查德·赫维格博士在一个合作项目中完成。

Two examples of material from chemically zoned magma chambers are the Bishop Tuff in California and the Lower Bandelier Tuff in New Mexico. In the Bishop Tuff, the eruption appears to have overturned the contents of the magma chamber, preserving a stratigraphic record of the chemistry of the chamber. The eruption of the Lower Bandelier Tuff did not preserve the chemical layering which has been deduced to have been present in the chamber. The difference between the two eruptions suggests that the Bishop Tuff chamber had a density (volatile) gradient while the Lower Bandelier magma chamber was more homogenous with respect to volatiles. This project will quantify the volatile content in the two chambers by analyzing trapped melt inclusions in phenocrysts which represent different stratigraphic horizons. Ion and electron microprobe techniques will be used to determine the content of H, F, Cl and S in the melt inclusions as a fuction of depth in the original magma chamber, thereby determining the magnitude of the volatile gradient. Electron probe analyses for major elements will help determine the unaltered nature of melt inclusions and ion probe microanalyses of selected lithophile trace elements will help determine the original stratigraphic position of each phenocryst. The PI will do everything except the ion probe analyses, which will be done by Dr. Richard Hervig of the University of Arizona in a collaborative project.