Establishing the Time and Length Scales of Initial Arc Construction: The Mantle-crust Connection

建立初始弧构造的时间和长度尺度：地幔-地壳连接

• 批准号: 1049884
• 负责人: George Bergantz
• 金额: $ 32.25万
• 依托单位: University of Washington
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2011
• 资助国家: 美国
• 起止时间: 2011-03-01 至 2015-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1049884&HistoricalAwards=false
• 关键词: Establishing; Time; Length; Scales; Initial

Establishing the time and length scales of initial arc construction: The mantle-crust connection(project jointly supported by EAR/Petrology & Geochemistry and OISE/Americas)This project aims to characterize exposed plutonic roots and compositional cycles in a 100 km long, continuous exposure of a continental arc section, the Sierra Valle Fértil - La Huerta (Argentina), with paleo-depths of 25 km to 8 km or less. A tilted section exposes identifiable end-member components of the continental arc: large bodies of granodiorite and tonalites in the upper crust, and a mafic- and ultramafic dominated lower crust that is interlayered with a lithologically homogenous sequence of metapelites and other supracrustal compositions. The "circulatory system" of the arc is continuous and decipherable: all units described above are physically linked via a complex of 'granitic' veins and dikes that connect source rocks to plutons. The preservation is exceptional because arc magmatism was largely arrested by a soft collision during the prograde peak, before long-lasting magmatism had obliterated the architecture of a voluminous mafic complex and a granodiorite batholith, formed over a span of 4-6 Ma. Hence much as volcanic systems are a 'snapshot' of a magmatic system, the Sierra Valle Fértil provides a 'snapshot' of a crustal-scale plutonic system, without significant overprint of high temperature structures and very long-lived repeated magmatic processing.Intellectual merit. The study will combine extensive field mapping with detailed geochronology, geochemistry and Sr, Nd and O isotopic fingerprinting to resolve composition-volume-time relationships on the scale of an arc section. This will allow us to make comparisons to volcanic systems, where source region processes can only be inferred and to combine 'hot zone' and mushy/MASH zone models for arc petrogenesis in a unified numerical model constrained by this natural example. This work will provide independent constraints on the compositional effects of mafic magmatic inputs to the crust, and the processes of homogenization and migration of mixed magmas into the upper crust. Major questions addressed are: (1) How does a large mafic complex assemble itself and on what time and space scales is internal differentiation important?; (2) How many mechanisms of assimilation can be documented and under what conditions are they most efficient and provide the most compositional leverage?; (3) Is mantle input simultaneously active along the strike of the arc, or does it vary in intensity alon strike and with time?; (4) Amphibole is widespread throughout the section - can its importance as a fractionating and hydrous phase be indentified in a geological example?; (5) Can a geological example of arc crust in high-flux mode be reconciled with both geophysical data from regions like the Altiplano-Puna or active island arcs and xenoliths studies from other batholithic belts?Broader impacts. This project will provide support for graduate students at both the University of Arizona and the University of Washington, as well as funding for undergraduate hands-on research measuring the radiogenic heat production in an intact arc section. We are working with the village of San Agustin del Valle Fértil to provide outreach materials. Closely involving Argentinean colleagues Prof. Juan Otamendi and Dr. Alina Tibaldi and their students in the project will foster international scientific collaboration and exchange.

建立初始弧形成的时间和长度尺度：地幔-地壳连接（EAR/岩石与地球化学和OISE/Americas联合支持的项目）该项目旨在描述一个长达100公里、连续暴露的大陆弧剖面，即Sierra Valle f<s:1> - La Huerta（阿根廷），古深度为25公里至8公里或以下。倾斜剖面暴露出大陆弧的可识别的端部成分：上部地壳中的大型花岗闪长岩和调性岩体，下部地壳中的基性和超基性占主导地位，与变质岩和其他表壳成分的岩性均匀序列相互交错。弧的“循环系统”是连续的，可识别的：上面描述的所有单元都是通过连接源岩和岩体的“花岗质”脉和脉的复杂结构在物理上连接起来的。这种保存是特殊的，因为弧岩浆作用在很大程度上被前进高峰期间的软碰撞所阻止，在此之前，长期的岩浆作用在4-6 Ma的跨度中形成了一个庞大的基性复杂岩体和花枝闪长岩基的结构。因此，就像火山系统是岩浆系统的“快照”一样，Sierra Valle fsamrtil提供了地壳规模的深部系统的“快照”，没有明显的高温结构叠加和非常长时间的重复岩浆作用。知识价值。该研究将结合广泛的野外测绘与详细的地质年代学、地球化学和Sr、Nd和O同位素指纹图谱，以解决弧段尺度上的成分-体积-时间关系。这将使我们能够与火山系统进行比较，在火山系统中，源区过程只能推断，并将“热区”和糊状/MASH带模型结合在一个统一的数值模型中，用于弧岩成因，受这个自然例子的约束。这一工作将为基性岩浆输入地壳的成分效应以及混合岩浆进入上地壳的均匀化和迁移过程提供独立的约束条件。研究的主要问题是：(1)大型城市综合体是如何自我组装的，内部分化在什么样的时间和空间尺度上是重要的？(2)有多少种同化机制可以被记录下来，在什么条件下它们是最有效的，并提供最有效的组合杠杆？(3)地幔输入是沿弧形走向同时活跃，还是随走向和时间变化强度不同？(4)角闪孔在剖面中分布广泛，其作为分馏和含水相的重要性能否通过地质实例来确定？(5)高通量模式下的弧壳地质实例能否与Altiplano-Puna或活动岛弧等地区的地球物理数据和其他岩石带的捕虏体研究相一致？更广泛的影响。该项目将为亚利桑那大学和华盛顿大学的研究生提供支持，并为本科生提供资金，用于在完整弧段中测量放射性生热的动手研究。我们正在与圣奥古斯丁·德尔瓦莱·法萨蒂尔村合作，提供外联材料。阿根廷同事Juan Otamendi教授和Alina Tibaldi博士及其学生密切参与该项目，将促进国际科学合作与交流。