Collaborative Research: Evaluating the Tempo, Size, and Chemical Connectivity of Magma Batches in a Tilted Plutonic Complex

知识价值。在岩浆弧研究领域，对于单个岩浆脉冲如何在物理和化学上与生长中的岩体中现存的岩浆/岩石相互作用，侵位深度如何影响垂直扩展的岩体中不同成分带的结晶历史和寿命，我们的理解存在根本性的空白；(c)大型、垂向扩展的岩体是否可能形成单一、混合良好的开放体系储层。研究人员将对倾斜的15公里厚的Wooley Creek - slinkard岩体系统进行研究，以验证两个中心假设：(1)岩体的形成是通过岩浆的多次增量，在侵位处几乎没有物理和化学交流（即孤立的批）；(2)系统上部在侵位部位(即？大柜?)。将利用实地研究、高精度U/Pb分析、岩石学、原位氧同位素分析和LA-ICPMS微量元素分析来验证这些假设。本研究的目的是：(1)描述侵入、结晶和凝固的时间尺度；（ii）评估岩浆补给重新调动现有晶体浆液的可能性；（iii）验证开放系统过程（例如岩浆混合和同化）发生在一个大体积、垂直扩展的岩浆系统中的假设；(4)验证了岩体岩浆组构的历时性，并反映了结晶过程中的区域构造应变场。焦点位置是实现这些目标的一个近乎理想的系统，因为(a)侵入体显示出垂直组成分带，从构造下部辉长岩/闪长岩向上穿过石英闪长岩、闪长岩、花岗闪长岩和花岗岩；(b)以前已确定各相之间的共岩浆成分联系；(c)乡村岩石的独特岩性、同位素组成和年龄使研究岩浆系统内物理和化学污染的空间变化成为可能；(d)岩浆组构横切成分带；(e) ？屋顶区域?代表下伏基构造过程中开采的岩浆；(f)岩体含有矿物（辉长岩、锆石、石英），其氧同位素和微量元素组成将追踪岩浆组成的上行和横向变化，因此具有开放系统行为。该项目将测试具有相同结晶年龄和具有从一个侵入相到另一个侵入相的开放系统化学联系的离散的大型、垂直扩展的岩浆系统可能共存的可能性。？大柜?模型)。相比之下，一种新兴的范式倾向于通过数百万年的小岩浆批次的逐渐就位，以及具有不同化学历史的不同脉冲来形成大型岩基。这两种结果都将对解释大岩基是如何在弧形环境中形成的具有长期的、面向过程的影响。更广泛的影响。该项目将支持本科生和研究生参与最先进的分析和实地项目。这项工作的结果也将被整合到教学活动中，由于研究区域位于一个旅游繁忙的荒野地区，地质摘要将由美国林务局向公众分发。

Intellectual Merit. In the realm of magmatic arc studies, fundamental gaps exist in our understanding of how individual pulses of magma may physically and chemically interact with extant magma/rock in a growing pluton, how emplacement depth affects the crystallization history and longevity of distinct compositional zones within a vertically-extensive pluton; and (c) whether large, vertically-extensive plutons may form as single, well-mixed open-system reservoirs. The tilted, 15-km thick Wooley Creek batholith-Slinkard pluton system will be examined to test two central hypotheses: (1) pluton construction was via multiple increments of magma with little to no physical and chemical communication at the site of emplacement (i.e., isolated batches); and (2) the upper portions of the system represent a large volume of well-mixed magma at the site of emplacement (i.e., ?big tank?). Field study, high-precision U/Pb analyses, petrography, in situ oxygen isotopic analysis, and LA-ICPMS trace element microanalysis will be utilized to test these hypotheses. The objectives of this research are to (i) delineate the timescale of intrusion, crystallization and solidification; (ii) evaluate the possibility that recharge of mafic magmas remobilized existing crystal mushes; (iii) test the hypothesis that open system processes (e.g., including magma mixing and assimilation) occurred in a large volume, vertically-extensive magmatic system; and (iv) test the hypothesis that magmatic fabrics in plutons form diachronously and reflect the regional tectonic strain field during crystallization. The focus site is a near-ideal system to attain these objectives because (a) the intrusion displays vertical compositional zonation from structurally lower gabbro/diorite upward through quartz diorite, tonalite, granodiorite and granite; (b) co-magmatic compositional links between various phases have been previously established; (c) distinctive lithology, isotopic composition, and ages for the country rocks make it possible to investigate spatial variations in physical & chemical contamination within the magmatic system; (d) magmatic fabrics cross-cut compositional zones; (e) fine-grained dikes in the ?roof zone? represent magmas tapped during construction of the underlying batholith; and (f) the pluton contains minerals (augite, zircon, quartz) whose oxygen isotope and trace element compositions will track upward and lateral variations in magma composition, hence, open-system behavior. This project will test the possible coexistence of discrete large, vertically-extensive magmatic systems having identical crystallization ages and have open-system chemical links from one intrusive phase to another Ie.g., the ?big tank? model). In contrast, an emerging paradigm favors large batholith formation by incremental emplacement of small magma batches, over millions of years, and with distinct pulses with distinct chemical histories. Either outcome will have long-ranging, process-oriented implications for interpreting how large batholiths are constructed in arc settings.Broader Impacts. This project will support undergraduate & graduate student involvement in state-of-the-art analytical and field projects. Results from this work will also be integrated into teaching activities, and because the study area lies in a heavily traveled wilderness area, geologic summaries will be produced for distribution by the U.S. Forest Service to the general public.