Petrogenesis of Mid-Tertiary Synextensional Volcanic Rocks in the Basin and Range Province, East-central Nevada and Adjacent Utah

该项目将进行详细的岩石学和同位素 研究与中第三纪、大- 在东部盆岭省的规模扩展。 的 目标是：1）完全表征这种中等至高K 钙钾岩套; 2）岩石成因模式 随着不断的扩展，套件中的变化;以及3）评估 的相对化学和同位素贡献 大陆地壳和下伏地幔。 在伸展开始时（-39 Ma），火山活动似乎是 粗糙的双峰（安山岩到英安岩，和高硅 流纹岩），其特点是小喷发从分散 通风口。 在-35 Ma，火山活动从英安岩转变为低硅质 流纹岩的成分大量喷发， 凝灰岩和熔岩。 该地区岩浆活动的现有模型 表明地幔的贡献从零到50%不等- 衍生岩浆 的成分和同位素多样性 套组表明了一个复杂的成岩历史， 岩浆源在早期阶段的岩浆活动，其次是 这些岩浆在中部（？）地壳 持续的延伸和热量输入。 拟议的工作是 多方面的，包括野外、岩石学和同位素研究 这将补充该领域正在进行的研究工作， 处理构造、变质作用和同位素 基底岩石的组成。

This project will undertake a detailed petrologic and isotopic study of volcanic rocks associated with mid-Tertiary, large- magnitude extension in the eastern Basin and Range Province. The goals are to: 1) completely characterize this moderate- to high-K calcalkalic suite; 2) petrogenetically model compositional changes in the suite with continued extension; and 3) evaluate the relative chemical and isotopic contributions of the continental crust and underlying mantle. At the onset of extension (-39 Ma), it appears that volcanism was crudely bimodal (silicic andesite to dacite, and high-silica rhyolite) and was characterized by small eruptions from scattered vents. At -35 Ma, volcanism shifted to dacite to low-silica rhyolite compositions erupted as voluminous, areallly extensive tuffs and lavas. Existing models for magmatism in the region suggest a contribution ranging from zero to as much as 50% of mantle- derived magmas. The compositional and isotopic diversity of the suite suggest a complex petrogenetic history involving several magma sources during early stages of magmatism, followed by large-scale mixing of these magmas in the middle (?) crust with continued extension and heat input. The proposed work is multifaceted, including field, petrologic and isotopic studies which will compliment ongoing research efforts in the area dealing with the structure, metamorphism, and isotopic composition of the basement rocks.