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

这是为了完成对圣胡安火山田东南部与火山口有关的火山活动的岩石学和年代学调查。Ploro-Summitville火山口组合记录了圣胡安油田的早期发展，其中包括大量的前火山口和后火山口安山岩到英安岩火山。宝山火山灰流凝灰岩的相对镁铁质成分及其与火山口后安山岩熔岩的共生表明，该岩浆系统代表了随后在圣胡安火山口中西部形成的大型硅质岩浆体生长的原始阶段。这是对圣胡安油田东南部整个与火山口有关的火山序列的野外、岩石学和同位素研究，包括共济会公园凝灰岩。尽管大部分层序的基本地球化学特征已接近完成，但将完成额外的同位素分析(铅、锶和钕)，并将对凝灰岩进行进一步的岩石学研究。

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.