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.

大陆壳约占地球表面积的40％，对于维持可居住性至关重要。众所周知，上大陆壳由山侵蚀形成的沉积岩所占据，而下大陆壳的组成和起源尚不清楚。盛行的范式是，下层地壳是由浓密的岩石制成的，富含铁（Fe）和镁（mg），并从下面的地幔中融化为上升的融化。然而，变形沉积物在现在暴露在地球表面的下层岩石的部分中很常见。这项研究解决了一个问题：如何将沉积物纳入下层地壳中？通过重建意大利下层地壳特征段的压力温度时历史的重建来解决这个问题，以评估竞争的假设，以形成下部大陆地壳的形成。该研究项目结合了宾夕法尼亚州立大学，加州大学圣塔芭芭拉分校和洛桑大学之间的一项新合作，支持对来自代表性不足的群体的两名研究生的培训，并在学术研究中吸引了本科生。 表征较低的大陆地壳形式是如何理解地壳进化，身体力的发展，地壳流动和地球化学分化的基础。该项目使用一套互补技术来检验三个假设，以形成伊维德里亚 - 维巴诺（Ivrea-Verbano）区域：埋葬，地壳底漆和伴随。碎屑锆石U-PB日期用于确定沉积物沉积年龄如何随深度变化。 LU-HF石榴石日期用于括起来在峰值温度下的训练石榴石生长和居住时间。变质锆石和独居石U/TH-PB日期 +通过激光燃烧裂隙流式石化学获得的痕量元素丰度，使得可以评估伊维德里亚区域的时间表。岩石学约束源自伪选择性，最佳热压法和痕量元素温度计。结合起，这些技术有助于重建前p-t-t路径和峰值变质条件的下分裂变化。完整的数据集用于对三个假设的严格测试。该项目由地球科学系的构造计划和岩石学和地球化学计划共同资助。该奖项反映了NSF的法定任务，并被认为是值得通过基金会的知识分子和更广泛影响的评估评估标准的评估来支持的。