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

内华达州中东部和毗邻犹他州盆地省中第三纪同伸展火山岩的岩石成因

• 批准号: 8706875
• 负责人: Anita Grunder
• 金额: $ 7.47万
• 依托单位: Oregon State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1987
• 资助国家: 美国
• 起止时间: 1987-08-01 至 1990-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=8706875&HistoricalAwards=false
• 关键词: Petrogenesis; Mid; Tertiary; Synextensional; Volcanic

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.

该项目将对东部盆地省与第三纪中期大规模扩张有关的火山岩进行详细的岩石学和同位素研究。 目标是：1) 完全表征这一中等到高 K 的钙碱性套件； 2) 岩石成因模型在不断延伸的套件中的成分变化； 3) 评估大陆地壳和下伏地幔的相对化学和同位素贡献。 在伸展开始时（-39 Ma），火山活动似乎是粗略的双峰式（硅质安山岩到英安岩和高硅流纹岩），其特征是从分散的喷口小规模喷发。 在-35Ma时，火山活动从英安岩转变为低硅流纹岩成分，喷发为大量、广泛的凝灰岩和熔岩。 该地区现有的岩浆作用模型表明，地幔岩浆的贡献率从零到 50% 不等。 该套件的成分和同位素多样性表明复杂的岩石成因历史，涉及岩浆作用早期阶段的多个岩浆源，随后这些岩浆在中（？）地壳中大规模混合，并持续延伸和热量输入。 拟议的工作是多方面的，包括现场、岩石学和同位素研究，这将补充在处理基岩的结构、变质作用和同位素组成领域正在进行的研究工作。