Death of a Backarc Rift: A Petrologic Site Survey of Godzilla Mullion

弧后裂谷之死：哥斯拉竖框的岩石学现场调查

• 批准号: 1030950
• 负责人: Jonathan Snow
• 金额: $ 37.53万
• 依托单位: University of Houston
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-09-01 至 2016-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1030950&HistoricalAwards=false
• 关键词: Death; Backarc; Rift; Petrologic; Site

Compared to mid-ocean ridges, the life cycle of back-arc spreading is short, averaging ~15 Ma of extension between arc-ward ridge jumps. Once initiated, back-arc volcanism evolves from relatively arc-like to relatively MORB-like compositions (Taylor and Martinez, 2003; Langmuir et al., 2006). Both of these observations are ascribed to the over-increasing distance to the back-arc spreading center from secondary convective upwelling above a subduction zone (Taylor and Martinez, 2003; Martinez and Taylor, 2006). This hypothesis makes substantial predictions for the geochemistry of any mantle rocks that may be exposed during the end phase of the magmatic system. Melting should become drier, productivity lower and lithospheric melt stagnation more common as a back-arc rift approaches the end of its life cycle. We propose to test this hypothesis using mineral chemistry of spinel and clinopyroxene, and whole rock Os isotopes from a substantial suite of abyssal peridotites recovered from a time line from the Godzilla Mullion in the Parace Vela Rift, the former back arc spreading center behind the Mariana arc (19-20 Ma). A declining magmatic budget would confirm the notion that secondary slab upwelling is the driving force in back-arc spreading in general, and suggests a mechanism for triggering ridge jumps. Preliminary mineral chemical data suggests that a coherent and interpretable melting signal is present in the Godzilla Mullion mantle rocks. Os isotopes will be used to determine whether the depleted signatures found are representative of the recent geodynamic configuration or are inherited ancient signals (e.g., Liu et al., 2008). This work will also provide an important comparison between in-situ back-arc and fore-arc mantle rocks, and serve as a petrologic characterization of mantle rocks supporting IODP drilling proposal 640-Full.This proposal furthers the basic understanding of core-complex style ocean crustal formation in a back-arc. This is an important new and still relatively poorly understood type of crust accretion. For this reason, it belongs to a class of basic geologic problems related to the formation of the ocean floor that can best be investigated via direct ocean floor observations. This project will support the career development of an excellent young female scientist, who will help mentor undergraduate and graduate student participants. She will also extend her current skill set in learning LA-ICP-MS and Os isotope techniques, and participate in research and teaching as appropriate. Grad student support is for an undergrad who began as an REU student on the sampling cruise. This project is part of a collaboration of long standing between the PI, the Japanese Research Institute, JAMSTEC, and the Japanese Hydrographic Office. Separate funding has been acquired for minority undergraduates, including two female undergraduates interested in pursuing work in this area for later graduate school. The UH is the second most diverse among 250 ranked universities (US News and World Report, 2010), serving the surrounding working class Houston community. This project provides an essential point of contact between students from traditionally underserved groups (~60%) at UH and the cutting edge of scientific research. The results of this study also flow directly into the teaching of the PI, who had 105 beginning mineralogy students in Fall 2009, a majority of whom were minorities. The impact on traditionally underserved communities is thus disproportionately large.

与中山脊相比，后弧传播的生命周期很短，平均弧形山脊跳跃之间的延伸约为15 mA。一旦启动，后弧火山主义就会从相对弧形变为相对较大的形成（Taylor and Martinez，2003; Langmuir等，2006）。这两个观察结果都归因于从俯冲带上方的次要对流上升流到后弧扩散中心的过度距离（Taylor和Martinez，2003； Martinez and Taylor，2006）。该假设对岩浆系统末期可能暴露的任何地幔岩石的地球化学做出了实质性的预测。熔化应该变得更干燥，生产率较低和岩石圈熔体停滞更为普遍，因为背面裂谷接近其生命周期的末期。我们建议使用尖晶石和斜氧烯的矿物质化学来检验这一假设，以及从从哥斯拉·莫里恩（Godzilla Mullion）的哥斯利亚·穆里恩（Godzilla Mullion）中回收的大量深处的橄榄岩的全岩os同位素。岩浆预算下降将证实一个观点，即二级平板上升流是一般背部蔓延的驱动力，并提出了一种触发山脊跳跃的机制。初步的矿物化学数据表明，哥斯拉mullion地幔岩石中存在相干且可解释的熔解信号。 OS同位素将用于确定发现的耗尽的特征是代表最近的地球动力学构型还是遗传的古代信号（例如Liu等，2008）。这项工作还将在原位的后弧和前弧地幔岩石之间进行重要的比较，并充当支持IODP钻井建议的地幔岩石的岩石学表征640-Full。此提案进一步进一步了解了核心核心 - 杂乱无章的型号的基本理解。这是一种重要的新的且相对较少的地壳积聚类型。因此，它属于与海底形成有关的一类基本地质问题，这些问题可以通过直接的海底观测来调查。该项目将支持一位优秀的年轻女科学家的职业发展，他们将帮助指导本科生和研究生参与者。她还将扩展自己目前的学习LA-ICP-MS和OS同位素技术的技能，并适当参与研究和教学。研究生的支持是针对一名本科生，他最初是在抽样巡游中的REU学生。该项目是PI，日本研究所，Jamstec和日本水文办公室之间长期合作的一部分。已经为少数族裔大学生获得了单独的资金，其中包括有兴趣在该领域从事以后研究生院工作的女性本科生。 UH是250所大学中第二多样的（美国新闻和世界报告，2010年），为周围的工人阶级休斯顿社区提供服务。该项目提供了来自UH的传统服务不足群体（约60％）的学生和科学研究的最前沿的基本接触点。这项研究的结果也直接流入了PI的教学，他们在2009年秋季有105名开始的矿物学学生，其中大多数是少数群体。因此，对传统服务不足的社区的影响不成比例。