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

确定初始弧形构造的时间和长度尺度：地幔-地壳连接(由EAR/Petroology&Amp；地球化学所和OISE/America共同支持的项目)该项目旨在描述长达100公里、连续暴露的大陆弧段(阿根廷)塞勒瓦莱-费里特拉-拉韦尔塔段中暴露的深成岩根和成分旋回，其古深度为25公里至8公里或更小。倾斜的剖面暴露出大陆弧的可识别的端元成分：上地壳中的大量花岗闪长岩和英云闪长岩，以及以镁铁质和超镁铁质为主的下地壳，其夹层有一系列岩性均一的变质岩和其他表壳成分。弧形的“循环系统”是连续的和可辨认的：上面描述的所有单元都通过连接源岩和深成岩的花岗岩脉和岩脉的复合体物理连接在一起。这种保存是特殊的，因为弧形岩浆活动在很大程度上被进行性高峰期间的软碰撞所阻止，之后长期的岩浆活动摧毁了巨大的镁铁质杂岩和花岗闪长岩基的结构，形成的时间跨度为4-6 Ma。因此，就像火山系统是岩浆系统的“快照”一样，塞拉山谷Fértil提供了地壳规模的深成岩系统的“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。这项研究将广泛的野外测绘与详细的地质年代学、地球化学和锶、钕和氧同位素指纹相结合，以解决弧形剖面尺度上的成分-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，只能推断源区过程，并将弧形岩石形成的“热区”和MASY/MASH带模型结合在一个受此自然例子约束的统一数值模型中。这项工作将对镁铁质岩浆输入地壳的成分效应以及混合岩浆均一化和迁移到上地壳的过程提供独立的约束。讨论的主要问题是：(1)大型镁铁质杂岩是如何自我组装的，内部分异在什么时间和空间尺度上是重要的？(2)有多少同化机制可以被记录下来，在什么条件下它们是最有效的，并提供最大的成分杠杆？(3)地幔输入是沿着弧形走向同时活跃的，还是在单独走向的强度和时间上变化？(4)角闪石在整个剖面中分布广泛--它作为分馏和含水相的重要性能否通过地质例子来识别？(5)高通量模式的弧壳的地质例子能否与阿尔蒂普诺-普纳等地区的地球物理数据或活动岛弧和其他石器时代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，并为测量完整弧形截面中的辐射热产生的本科生动手研究提供资金。我们正在与San Agustin del Valle FéRTIL村合作，提供外展材料。让阿根廷同事胡安·奥塔曼迪教授和Alina Tibaldi博士以及他们的学生密切参与该项目将促进国际科学合作和交流。

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.