Completion of a Petrologic Geochronologic and Istopic Study of the Southeast San Juan Volcanic Field, Colorado

这是为了完成岩石学和地质年代学 西南部与破火山口有关的火山活动的调查 胡安火山区。 普拉托-萨米特维尔火山口复杂， 其中包括大量的前和后破火山口安山岩英安岩 记录了圣胡安油田的早期发展。 相对镁铁质成分的宝山灰- 流动凝灰岩及其与破火山口后安山岩熔岩的关系， 表明这个岩浆系统代表了一个原始阶段 在巨大的岩浆体的生长过程中， 随后在中部和西部的圣胡安火山口下 集群 这是一个现场，岩石学，和同位素研究的 整个火山口有关的火山序列的东南圣 胡安场，包括共济会公园凝灰岩。 虽然基本 大部分序列的地球化学特征几乎 完整的，额外的同位素分析（铅，锶和钕）将 将对凝灰岩进行完整的和进一步的岩石学工作。

This is for completion of a petrologic and geochronologic investigation of caldera-related volcanism of the southeast San Juan volcanic field. The platoro-Summitville caldera comples, which includes voluminous pre- and postcaldera andesite to dacite volcanoes, records the early development of the San Juan field. The relatively mafic compositions of the Treasure Mountain ash- flow tuffs and their association with postcaldera andesite lavas, indicates that this magmatic system represents a primitive stage in the growth of the large silicic magma body which formed subsequently under the central and western San Juan caldera clusters. This is a field, petrologic, and isotopic study of the entire caldera-related volcanic sequence of the southeast San Juan field, including the Masonic Park Tuff. Although the basic geochemical characterization of much of the sequence is nearly complete, additional isotopic analyses (Pb, Sr and Nd) will be completed and further petrologic work will be done on the tuffs.