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Collaborative Research: How Does Lower Continental Crust Form? A Petrochronological Investigation of the Ivrea Zone

合作研究：下陆壳是如何形成的？

基本信息

批准号：
1927631
负责人：
Andrew Smye
金额：
$ 23.36万
依托单位：
Pennsylvania State Univ University Park
依托单位国家：
美国
项目类别：
Standard Grant
财政年份：
2019
资助国家：
美国
起止时间：
2019-07-01 至 2023-06-30
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1927631&HistoricalAwards=false
关键词：
Collaborative Research How Does Lower

项目摘要

Continental crust occupies about 40 percent of the surface area of the Earth and is critical for the sustenance of habitability. Whereas the upper continental crust is known to be dominated by sedimentary rocks formed by the erosion of mountains, the composition and origin of lower continental crust is not well understood. The prevailing paradigm is that the lower crust is made of dense rock, rich in the elements iron (Fe) and magnesium (Mg), emplaced as rising melts from the mantle below. However, metamorphosed sediments are common in sections of lower crustal rock that are now exposed at the surface of the Earth. This research addresses the question: How are sediments incorporated into the lower crust? This question is addressed via a reconstruction of the pressure-temperature-time history of a characteristic section of the lower crustal, the Ivrea-Verbano Zone in Italy, to evaluate competing hypotheses for the formation of lower continental crust. The research project incorporates a new collaboration between Penn State, UC Santa Barbara, and the University of Lausanne, supports the training of two graduate students from under-represented groups, and engages undergraduates in academic research. Characterizing how lower continental crust forms is fundamental to understanding crustal evolution, development of body forces, flow of crust, and chemical differentiation of the Earth. Using a suite of complementary techniques, this project tests three hypotheses for the formation of the Ivrea-Verbano Zone: Burial, Crustal Underplating, and Relamination. Detrital zircon U-Pb dates are used to determine how sediment deposition ages vary with depth. Lu-Hf garnet dates are used to bracket the timing of prograde garnet growth and residence at peak temperatures. Metamorphic zircon and monazite U/Th-Pb dates + trace-element abundances obtained by laser-ablation split-stream petrochronology enable assessment of the timescale over which the Ivrea Zone was assembled. Petrologic constraints are derived from pseudosections, optimal thermobarometry, and trace- element thermometry. In conjunction, these techniques facilitate reconstruction of the downsection variation in prograde P-T-t paths and peak metamorphic conditions. The complete dataset is used for rigorous testing of the three hypotheses. This project is jointly funded by the Tectonics program and the Petrology & Geochemistry program in the division of Earth Sciences.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

大陆地壳约占地球表面积的40%，对维持宜居性至关重要。虽然已知上部大陆地壳主要由由山脉侵蚀形成的沉积岩组成，但下部大陆地壳的组成和起源却不太清楚。普遍的范式是，下地壳是由致密的岩石组成的，富含铁（Fe）和镁（Mg）元素，是随着地幔的上升融化而形成的。然而，变质沉积物在现在暴露在地球表面的下地壳岩石中很常见。这项研究解决了这样一个问题：沉积物是如何融入下地壳的？这个问题是通过重建下地壳特征部分的压力-温度-时间历史来解决的，意大利的Ivrea-Verbano带，以评估下大陆地壳形成的竞争性假设。该研究项目包括宾夕法尼亚州立大学、加州大学圣巴巴拉分校和洛桑大学之间的一项新合作，支持培训两名来自代表性不足群体的研究生，并让本科生参与学术研究。描述下大陆地壳是如何形成的，是理解地壳演化、体力发展、地壳流动和地球化学分异的基础。使用一套互补的技术，该项目测试了Ivrea-Verbano带形成的三种假设：埋藏、地壳下覆和再分层。碎屑锆石U-Pb测年用于确定沉积物沉积年龄如何随深度变化。Lu-Hf石榴石日期被用来确定石榴石生长和停留在峰值温度下的时间。变质锆石和独居石U/Th-Pb日期+微量元素丰度通过激光烧蚀裂流岩石年代学获得，可以评估伊夫雷亚带形成的时间尺度。岩石学约束来自于伪剖面、最佳热气压测定法和微量元素测温法。同时，这些技术有助于重建顺行P-T-t路径和峰值变质条件的下行变化。完整的数据集用于三个假设的严格测试。本项目由地球科学部构造学项目和岩石与地球化学项目共同资助。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。