Constraints on Plateau Architecture and Assembly From Deep Crustal Xenoliths, Northern Altiplano (Southern Peru)

北阿尔蒂普拉诺（秘鲁南部）深地壳捕虏体对高原建筑和组装的限制

• 批准号: 1524110
• 负责人: Mihai Ducea
• 金额: $ 10.42万
• 依托单位: University of Arizona
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-08-15 至 2017-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1524110&HistoricalAwards=false
• 关键词: Constraints; Plateau; Architecture; Assembly; Deep

This award will support a petrologic and geochemical study of the portions of the crust that were picked up and embedded in volcanic rocks (xenoliths) once used by the Incas to build the city of Cuzco, in Peru. The geologic history of this part of the Andes is still poorly understood, specifically the reason for the high altitude that characterizes the region called the Altiplano. The rocks to be analyzed sampled the deepest portions of the crust in the Altiplano that are not exposed anywhere else in the region. It is expected that the results will provide us with a new understanding of how the deepest portions of continents evolve in mountainous areas. This study will also foster scientific collaborations with Peruvian and Chilean experts on local and regional Andean geology. Results of this project will be incorporated into the teaching curriculum at the University of Arizona, and will serve as the basis for the training of a M.Sc. student and also that of an undergraduate student. Because the volcanic rocks were the main building materials used by the Incas in Cuzco, knowledge derived from this project may impact our understanding of archeology in this famous heritage site. It is proposed to conduct a petrographic, thermobarometric, geochemical, isotopic and geochronologic study of newly discovered lower crustal xenoliths in Quaternary volcanic rocks from the northernmost Altiplano Plateau, Peru. At least eight individual lava flows contain xenoliths. Together, they are the second known occurrence of crustal xenoliths from the Altiplano and can provide invaluable information about the plateau's origin and development. This award will support a study of the crustal xenoliths aimed at (a) resolving the timing of crustal thickening and metamorphism initiation under the northern Plateau, (b) understanding whether crustal shortening was primarily driven by material underplated from the west (arc-side) or east (fold and thrust belt side), and finally (c) quantifying the role of magmatism to crustal thickening/loading. These xenoliths fill an important gap in our convergent margin rock record. The research plan comprises a field-sampling component followed by a petrographic and petrologic study of xenoliths. Sm-Nd and Lu-Hf garnet geochronology and monazite U-Th-Pb geochronology will be used to determine the age of metamorphism in conjunction with a thermobarometric study of the garnet-bearing assemblages. Igneous and detrital zircon geochronology will be employed to determine the age of magmatic intrusions in the Altiplano crust, and to constrain the origin of metasedimentary rocks, respectively. Elemental and radiogenic isotopic geochemistry will further illuminate the origin and crustal age of the assemblages studied here. The main deliverable after this project is a manuscript that will be submitted to a scholarly journal. Samples collected from this study will be made available to other interested members of the community.

该研究金将用于支持对火山岩（捕虏体）中被拾起和嵌入的地壳部分进行岩石学和地球化学研究，这些火山岩曾被印加人用来建造秘鲁的库斯科市。 安第斯山脉这一部分的地质历史仍然知之甚少，特别是被称为高原地区的高海拔的原因。待分析的岩石取样于阿尔蒂普拉诺地壳最深处，该地区其他任何地方都没有暴露。预计这些结果将使我们对大陆最深处在山区的演变有一个新的认识。 这项研究还将促进与秘鲁和智利专家在安第斯当地和区域地质学方面的科学合作。该项目的成果将被纳入亚利桑那大学的教学课程，并将作为培养硕士生和本科生的基础。 由于火山岩是印加人在库斯科使用的主要建筑材料，因此从该项目中获得的知识可能会影响我们对这一著名遗址考古学的理解。本文拟对秘鲁高原最北端第四纪火山岩中新发现的下地壳捕虏体进行岩相学、温压学、地球化学、同位素和年代学研究。至少有八个独立的熔岩流含有捕虏体。它们是第二个已知的高原地壳捕虏体，可以提供有关高原起源和发展的宝贵信息。该奖项将支持对地壳捕虏体的研究，旨在（a）解决北方高原下地壳增厚和变质作用开始的时间，（B）了解地壳缩短主要是由西部（弧侧）还是东部（褶皱和冲断带侧）底侵的物质驱动的，最后（c）量化岩浆作用对地壳增厚/负荷的作用。这些捕虏体填补了会聚边缘岩石记录中的一个重要空白。研究计划包括实地取样部分，然后是捕虏体的岩相学和岩石学研究。Sm-Nd和Lu-Hf石榴石地质年代学和独居石U-Th-Pb地质年代学将用于确定变质作用的年龄，并结合含石榴石组合的温压研究。岩浆锆石和碎屑锆石年代学将分别用于确定高原地壳中岩浆侵入体的年龄，并限制变质沉积岩的起源。元素和放射性同位素地球化学将进一步阐明这里研究的组合的起源和地壳时代。这个项目之后的主要交付成果是一份将提交给学术期刊的手稿。从这项研究中收集的样本将提供给社区其他感兴趣的成员。