Collaborative Research: Tracking the thermal and petrologic evolution of magmatically robust fast spread lower ocean crust

合作研究：追踪岩浆强劲、快速扩张的下洋地壳的热学和岩石学演化

• 批准号: 1459387
• 负责人: Jeffrey Gee
• 金额: $ 27.51万
• 依托单位: University of California-San Diego Scripps Inst of Oceanography
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2015
• 资助国家: 美国
• 起止时间: 2015-06-15 至 2021-05-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1459387&HistoricalAwards=false
• 关键词: Collaborative; Research; Tracking; thermal; petrologic

Ocean crust, which makes up about 65% of the volume of Earth's surface, is created at mid-ocean ridges, one of the most dynamic geological environments on the planet. Vast quantities of heat are dissipated along these features, facilitating the generation of large, potentially economic, mineral deposits and hydrothermal vents that host unique chemosynthetic ecosystems that live without the need for sunlight. At mid-ocean ridges, melts from the upwelling mantle rise toward the surface and either erupt as lavas on the seafloor or freeze on their way up, resulting in ocean crust that has a thick coarsely crystalline base made of gabbroic and peridotitic rock covered by a veneer of basaltic lava. With the exception of the surface lavas, the lower portions of crust can only be sampled and studied from deep rips and tears in the seafloor caused by structural features or tectonic processes. One of the places where the gabbroic layer is exposed is a place called the Pito Deep in the eastern Pacific Ocean. This research involves a major multidisciplinary oceanographic expedition to the Pito Deep to both sample and study the lower crustal gabbros of fast spread ocean crust and their relation to overlying basalts and underlying crustal components. On the expedition, samples will also be taken to determine the ancient thermal structure at the ridge axis. Broader impacts of the work include support of an institution and faculty in an EPSCoR state (Wyoming); good student training at the college, community college, and K-12 level; and the inclusion of a K-12 teacher on the cruise to produce educational materials for K-12 and communicate with students back on land. The science being done in this project has the potential to resolve long standing debates about how gabbroic lower crust is accreted at fast spread mid-ocean ridges and will shed light on unresolved questions regarding the depth of hydrothermal circulation in the seafloor, the width and temporal evolution of the axial magma chamber of mid-ocean ridges, and the processes of melt transport and crystallization between the mantle and the seafloor. Samples will be collected using a remotely operated vehicle, with sampling taking place along a ~20-km long flow line at Pito Deep. The nearly ridge-perpendicular exposures at Pito Deep span multiple geomagnetic polarity intervals, providing a unique opportunity to document the shape of the fossil 580°C isotherm in the lower crust and thus to differentiate between the different thermal predictions of lower crustal accretion models. These end-member models also make predictions of the variation of geochemical, petrologic and microstructural parameters with depth. Major and trace element geochemistry combined with petrofabrics from electron backscattered diffraction will be examined for a significant vertical portion (1km) of the upper gabbroic layer to further discriminate between these accretion models. While no single crustal exposure is likely to definitively resolve the processes by which the gabbroic lower crust is accreted, the exposures at Pito Deep offer the possibility of addressing outstanding questions regarding the depth of hydrothermal heat extraction, the width and temporal evolution of the axial magma chamber, and the processes of melt transport and crystallization.

海壳约占地球表面体积的65％，是在地球中部山脊中产生的，这是地球上最具动态的地质环境之一。沿这些特征散发出大量的热量，以支撑大型，潜在的经济，矿物质沉积物和水热通风孔的产生，这些通风孔容纳了独特的化学合成生态系统，这些生态系统无需阳光。在海洋中部的山脊中，从上层地幔上升到地面上的融化，要么在海底散发为熔岩，要么在途中冻结，从而导致海壳具有浓密的岩心质结晶基，由gabbroic和橄榄岩覆盖在底层岩石上，覆盖在底座上。除表面熔岩外，只能对地壳的下部进行采样，并从结构特征或构造过程引起的海底深处和泪水中进行研究。 gabbroic层暴露的地方之一是东太平洋深处的Pito。这项研究涉及一项主要的多学科海洋探险，以对pito进行样品深处，并研究快速扩散海角的下层地壳gabbros及其与上覆的玄武岩和潜在的地壳成分的关系。在探险中，还将采集样品以确定山脊轴的古老热结构。这项工作的更广泛的影响包括在EPSCOR国家（怀俄明州）的机构和教职员工的支持；在学院，社区学院和K-12级的良好学生培训；并在巡航中包括一名K-12老师，以生产K-12的教育材料，并与学生回到陆地上。 The science being done in this project has the potential to resolve long standing debates about how gabbroic lower crust is accepted at fast spread mid-ocean ridges and will shed light on unresolved questions regarding the depth of hydrothermal circulation in the Seafloor, the width and temporary evolution of the axial magma chamber of mid-ocean ridges, and the processes of melt transport and crystallization between the mantle and the seafloor.将使用远程操作的车辆收集样品，并在皮托深处的长流线沿着约20公里的长流程进行采样。在皮托深处的几乎脊 - 垂直的暴露跨度多个地磁间隔，提供了一个独特的机会，可以记录下层外壳中化石580°C等温线的形状，从而区分了下层壳积分模型的不同热预测。这些末端成员模型还可以预测具有深度的地球化学，岩石学和微结构参数的变化。将检查高gabbroic层的显着垂直部分（1km），将检查主要和痕量元件地球化学与电子反向衍射中的石油相结合，以进一步区分这些增生模型。尽管没有单一的地壳暴露可能会明确地解决gabbroic较低地壳被接受的过程，但Pito深处的暴露量提供了有关关于水热萃取，轴向岩浆腔室的宽度和临时进化以及熔体运输和结晶的过程的问题的可能性。