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

这是为了完成圣胡安火山田东南部与破火山口有关的火山作用的岩石学和地质年代学调查。platoro-Summitville破火山口复合体，包括大量破火山口前后的安山岩和英安岩火山，记录了圣胡安油田的早期发展。宝山火山灰流凝灰岩的相对基性成分及其与火山口后安山岩熔岩的联系表明，该岩浆体系代表了随后在圣胡安火山口群中部和西部形成的大型硅质岩浆体生长的原始阶段。这是对圣胡安东南部整个破火山口相关火山序列的野外、岩石学和同位素研究，包括共济会公园凝灰岩。虽然大部分层序的基本地球化学特征已接近完成，但还需要完成额外的同位素分析（Pb、Sr和Nd），并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.