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？

• 批准号: 1927635
• 负责人: Bradley Hacker
• 金额: $ 18.66万
• 依托单位: University of California-Santa Barbara
• 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 2022-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1927635&HistoricalAwards=false
• 关键词: Collaborative; Research; How; Does; Lower

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%，对于维持宜居性至关重要。尽管已知上大陆地壳主要是由山脉侵蚀形成的沉积岩，但下大陆地壳的组成和起源尚不清楚。普遍的观点是，下地壳由致密的岩石组成，富含铁 (Fe) 和镁 (Mg) 元素，随着熔体从下面的地幔上升而形成。然而，变质沉积物在现在暴露在地球表面的下地壳岩石部分中很常见。这项研究解决了这个问题：沉积物如何融入下地壳？这个问题是通过重建下地壳特征部分（意大利伊夫雷亚-韦尔巴诺带）的压力-温度-时间历史来解决的，以评估下大陆地壳形成的竞争假设。该研究项目包含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。 描述下大陆地壳的形成方式对于理解地壳演化、体积力的发展、地壳流动和地球化学分异至关重要。该项目使用一套互补技术，测试了伊夫雷亚-韦尔巴诺带形成的三种假设：埋藏、地壳底板作用和重层作用。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 石榴石日期用于确定石榴石在峰值温度下的顺行生长和停留时间。通过激光烧蚀分流岩石年代学获得的变质锆石和独居石 U/Th-Pb 年代 + 微量元素丰度能够评估伊夫雷亚带形成的时间尺度。岩石学约束源自伪剖面、最佳温压测量和痕量元素测温。结合起来，这些技术有助于重建顺行 P-T-t 路径和峰值变质条件中的断面变化。完整的数据集用于严格测试这三个假设。该项目由地球科学部的构造学项目和岩石学与地球化学项目共同资助。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。