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.

与洋中脊相比，弧后扩张的生命周期较短，弧向洋脊跳跃之间的平均延伸约为 15 Ma。一旦开始，弧后火山活动就会从相对弧状的成分演变为相对 MORB 状的成分（Taylor 和 Martinez，2003 年；Langmuir 等人，2006 年）。这两个观察结果都归因于俯冲带上方二次对流上升流到弧后扩张中心的距离过度增加（Taylor 和 Martinez，2003；Martinez 和 Taylor，2006）。这一假说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预测。当弧后裂谷接近其生命周期的终点时，熔融会变得更加干燥，生产率会降低，并且岩石圈熔融停滞会更加常见。我们建议使用尖晶石和单斜辉石的矿物化学，以及从帕拉斯韦拉裂谷（马里亚纳河后面的前弧后扩张中心）的哥斯拉竖框的时间线上回收的大量深渊橄榄岩中的全岩骨同位素来检验这一假设。弧 (19-20 Ma)。岩浆预算的下降将证实次生板片上升流是弧后扩张总体驱动力的观点，并提出了触发山脊跳跃的机制。初步矿物化学数据表明，哥斯拉竖框地幔岩石中存在连贯且可解释的熔化信号。 Os 同位素将用于确定所发现的耗尽特征是否代表了最近的地球动力学配置，或者是继承的古代信号（例如，Liu 等人，2008）。这项工作还将提供原位弧后和弧前地幔岩石之间的重要比较，并作为支持 IODP 钻探建议 640-Full 的地幔岩石岩石学表征。该建议进一步加深了对岩心杂岩样式的基本理解弧后的洋壳形成。这是一种重要的新地壳增生类型，人们对它的了解仍然相对较少。因此，它属于与海底形成相关的一类基本地质问题，最好通过直接海底观测来研究。该项目将支持一名优秀年轻女科学家的职业发展，她将帮助指导本科生和研究生参与者。她还将扩展她目前学习 LA-ICP-MS 和 Os 同位素技术的技能，并酌情参与研究和教学。研究生支持是为在采样巡游中作为 REU 学生开始的本科生提供的。该项目是 PI、日本研究所、JAMSTEC 和日本海道测量局之间长期合作的一部分。已经为少数族裔本科生获得了单独的资金，其中包括两名有兴趣在以后的研究生院从事这一领域工作的女本科生。休斯敦大学是 250 所排名大学中第二多元化的大学（《美国新闻与世界报道》，2010 年），为周边的休斯顿工人阶级社区提供服务。该项目为来自夏威夷大学传统上服务不足群体（约 60%）的学生与科学研究前沿提供了一个重要的接触点。这项研究的结果也直接融入到 PI 的教学中，2009 年秋季，PI 有 105 名矿物学初学者，其中大多数是少数族裔。因此，对传统上服务不足的社区的影响异常之大。