| 项目编号: | 1650411
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| 项目名称: | The Proterozoic Missing Link? Deposition, Volcanism, and Deformation between 1.6 and 1.45 Ga in the McDowell Mountains, south-central Arizona. |
| 作者: | Matthijs Van Soest
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| 承担单位: | Arizona State University
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| 批准年: | 2017
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| 开始日期: | 2017-01-01
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| 结束日期: | 2018-12-31
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| 资助金额: | 52569
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| 资助来源: | US-NSF
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| 项目类别: | Standard Grant
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| 国家: | US
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| 语种: | 英语
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| 特色学科分类: | Geosciences - Earth Sciences
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| 英文关键词: | middle proterozoic
; mcdowell mountain
; section
; mcdowell mountain section
; age
; year
; uranium-lead
; deformation
; nature
; south-central arizona
; mcdowell sonoran preserve
; new mountain range building event
; early proterozoic uranium-lead age
; magmatic gap
; missing link
; mcdowell sonoran conservancy
; mcdowell sonoran
|
| 英文摘要: | The McDowell Mountains in south-central Arizona are composed of a newly identified approximately 10 kilometer-thick section of rocks of Middle Proterozoic age. This is a time period in North American geologic history for which very little concrete information exists. Detailed geologic, isotopic age determinations, and structural study of the McDowell Mountains section will greatly increase current knowledge and understanding of geologic events occurring in North America during this period. The results may also provide constraints to evaluate proposed plate tectonic reconstructions during the Middle Proterozoic. The research is unique in that it the field area lies within the McDowell Sonoran Preserve, one of the largest municipal preserves in the nation (greater than 122 square kilometers), located adjacent to the Greater Phoenix metropolitan area. The scientific results of this study will be communicated to the public via the McDowell Sonoran Preserve by the preparation of outreach materials (geologic trail guides) available for download on the web and public lectures by the project team. Research products and samples will be turned over to the McDowell Sonoran Conservancy, the volunteer branch of the Preserve, for archiving and their use in public outreach to visitors of the Preserve. The project will also contribute to the training of a graduate student and will contribute to the broadening of underrepresented groups in an important science, technology, engineering and math (STEM) discipline.
The McDowell Mountains rock section is comprised of metamorphosed sedimentary and volcanic rocks that are intruded by several granite bodies. The age of the section is bracketed by an early Proterozoic uranium-lead age (1630 million years) in the oldest volcanic tuff and a Middle Proterozoic uranium-lead age (1423 million years) for the youngest granite body intruding the section. In the last four years at least two, much smaller, sections in Arizona and New Mexico, were identified as Middle Proterozoic in age. The observations that these rocks are folded and/or are cut by large thrust faults, which were then deeply buried and metamorphosed, led to the identification of a new mountain range building event of regional extent: the Picuris orogeny. The thickness and nature of the McDowell Mountains section provides a unique opportunity to gain a better understanding of the timing, nature, and regional extent of this orogeny. Geologic and structural mapping and rock sampling was recently completed in the McDowell Mountains. A pilot zircon uranium-lead dating study on 3 samples yielded Middle Proterozoic ages for all three, but the most significant age is 1546 million years for the youngest volcanic rocks in the section, confirming the age of the section as Middle Proterozoic. These ages make it the only currently known North American Middle Proterozoic section that contains thick deposits of volcanic rocks. The research proposed here intends to build on the initial work to address the following objectives for the McDowell Mountains section: (1) further constrain its age range, (2) determine the timing and nature of metamorphic events, (3) characterize the age, chemistry, deformation, and mantle model ages of the igneous rocks, (4) constrain the age and nature of deformation, and (5) characterize the detrital zircon uranium-lead populations of the sedimentary rocks. A carefully selected set of samples will be used for this study: 23 for zircon and monazite uranium-lead dating, a subset of which will be analyzed for lutetium-hafnium isotopes, 15 for major and trace element geochemistry of the volcanic and granitic rocks, and 90 for petrographic and micro-structural fabric thin section study of the rocks in the section. The results of the five research objectives will provide a comprehensive geologic, geochronologic and structural characterization of the McDowell Mountains sequence. In addition, the section represents the only significant volcanic and intrusive rocks within the North American "magmatic gap" (between about 1.6 and 1.45 billion years ago) and may represent the "missing link" for plate reconstruction models that have, heretofore, always required the presence of an exotic source terrain e.g. Australia, northwestern Europe, or associated continental fragments to explain the occurrence of 1.5 to 1.6 billion year old zircons in North American sedimentary sequences for which no local source was known. |
| 资源类型: | 项目
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| 标识符: | http://119.78.100.158/handle/2HF3EXSE/90716
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| Appears in Collections: | 全球变化的国际研究计划
科学计划与规划
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| Recommended Citation: | |
Matthijs Van Soest. The Proterozoic Missing Link? Deposition, Volcanism, and Deformation between 1.6 and 1.45 Ga in the McDowell Mountains, south-central Arizona.. 2017-01-01.
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