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

合作研究：评估倾斜深成杂岩中岩浆批次的速度、大小和化学连通性

• 批准号: 0838546
• 负责人: Kevin Chamberlain
• 金额: $ 13.89万
• 依托单位: University of Wyoming
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2009
• 资助国家: 美国
• 起止时间: 2009-03-15 至 2013-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0838546&HistoricalAwards=false
• 关键词: Collaborative; Research; Evaluating; Tempo; Size

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.

智力上的功绩。在岩浆弧研究领域，我们对岩浆脉冲如何与成长岩体中现存的岩浆/岩石进行物理和化学作用，侵位深度如何影响垂直扩展的岩体内不同成分带的结晶历史和寿命，以及(C)大型垂直扩展的岩体是否可能形成单一的、混合良好的开放系统油藏的理解存在根本差距。将研究倾斜的、15公里厚的Wooley Creek Batholek-Slink ard岩体系统，以检验两个中心假设：(1)岩体的构造是通过多次岩浆增量进行的，在侵位地点(即孤立的批次)几乎没有物理和化学联系；(2)系统的上部代表侵位地点(即大水箱？)大量混合良好的岩浆。将利用野外考察、高精度U/Pb分析、岩石学、原位氧同位素分析和LA-ICPMS痕量元素分析来验证这些假设。这项研究的目的是：(I)描述侵入、结晶和凝固的时间尺度；(Ii)评估镁铁质岩浆补给重新动员现有结晶泥的可能性；(Iii)检验开放系统过程(例如，包括岩浆混合和同化)发生在大体积、垂直扩展的岩浆系统中的假说；以及(Iv)检验深成岩浆中岩浆组构历时形成并反映结晶过程中区域构造应变场的假说。焦点地点是实现这些目标的近乎理想的系统，因为：(A)侵入体显示出垂直的成分分带，从构造较低的辉长/闪长岩向上穿过石英闪长岩、英云闪长岩、花岗闪长岩和花岗岩；(B)不同阶段之间的共岩浆成分联系已建立；(C)围岩独特的岩性、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)顶板带中的细粒岩脉？(F)岩体含有矿物(辉石、锆石、石英)，其氧同位素和微量元素组成将跟踪岩浆成分的向上和横向变化，因此，开放系统行为。该项目将测试离散的大型、垂直扩展的岩浆系统是否可能共存，这些岩浆系统具有相同的结晶年龄，并具有从一个侵入相到另一个侵入相的开放系统化学联系，例如？大储罐？模型)。相比之下，一种新兴的范式有利于大型岩基的形成，这种形成方式是通过递增侵位小岩浆批次，持续数百万年，并具有不同的脉冲和不同的化学史。这两种结果都将对解释弧形环境下建造多大熔池具有长期的、面向过程的影响。更广泛的影响。这个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，由于研究区域位于经常出行的荒野地区，将制作地质摘要，由美国林务局向公众分发。