Geochemical and geophysical constraints on the causes of widespread active volcanism in the Galápagos Archipelago

加拉帕戈斯群岛广泛活动火山活动的地球化学和地球物理约束

• 批准号: NE/H01053X/1
• 负责人: Sally Gibson
• 金额: $ 6.82万
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2010
• 资助国家: 英国
• 起止时间: 2010 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FH01053X%2F1
• 关键词: Geochemical; geophysical; constraints; causes; widespread

The proposed research focuses on one of the most volcanically active regions on Earth, the Galápagos Archipelago in the Pacific Ocean. The last major eruption was in April 2009 at Fernandina which is close to the postulated centre of a high-temperature anomaly (known also as a hot spot or mantle plume). Results of geophysical and geochemical studies have shown that the volcanism results from the juxtaposition of a mantle plume with a major oceanic spreading centre. The combination of thin lithosphere (~7 km) at the Galápagos Spreading Centre and high temperature (~1400oC) of the plume results in a large amount of mantle melting as the plume upwells. The Galápagos Archipelago is an ideal place to study the complex mass-transfer and chemical-mixing processes that occur in this dynamic tectonic setting because the mantle plume and oceanic spreading centre are sufficiently close to interact but still able to remain as distinct physical entities. The distribution and composition of volcanism in the Galápagos archipelago is different to that associated with conventional hotspots (such as Hawaii): there is no linear chain of ocean islands and active volcanism is widespread away from the zone of plume upwelling. A recent high-resolution regional geophysical study (published in 2007) has shown an anomalous zone of low seismic velocity, extending away from the hot spot towards the spreading centre. The anomaly is greatest at a depth of ~ 70 km beneath Santiago; an island located in the centre of the archipelago and on the periphery of the plume. The cause of the anomaly is unknown; it may represent a change in temperature and/or a zone of intense mantle upwelling and melting. Santiago is the fourth largest island in the archipelago but there are very few published geochemical analyses. The most recent volcanic eruptions on the island were in 1795, 1897 and 1904. The limited geochemical data indicates that lavas erupted from volcanoes in the west of the island are of different composition to those in the east, a distance of <20 km. Some of this variation may be a consequence of sub-volcanic magma chamber processes but large ranges in ratios of elements which readily partition in to magmas during mantle melting suggest that the island is located either above lithosphere that varies dramatically in thickness, from west to east, or that the underlying convecting mantle has a varied composition. This proposal seeks funding to undertake high-precision geochemical analyses on lavas from Santiago where systematic sample collection has already been done by the PI. Numerical modelling of the chemistry of these lavas together with published data for other Galápagos volcanoes will be used to constrain the composition, temperature and pressure of melting of the underlying mantle. The results will be combined with temperatures calculated from seismic velocity data, using newly published equations, to shed light on the physical processes that are operating between the axis of plume upwelling and the spreading centre, causing widespread volcanism. The presence of a large body of melt extending from the zone of mantle-plume upwelling towards the spreading ridge would place important constraints on the nature of mass transport that occurs when these two dynamic systems are juxtaposed. The proposed research will build on the PI's previous research on mantle melting. It is novel because it will produce the first integrated geochemical and geophysical model to account for the causes of widespread active volcanism in the Galápagos Archipelago. This will aid our understanding of the causes of volcanic activity in much less accessible settings, such as the Mid-Atlantic Ridge, and increase constraints on identifying where plume-ridge interactions have occurred in the geological past. This will in turn will increase our knowledge of global-scale deep-mantle and Earth surface processes.

拟议的研究集中于地球上最有活跃的地区之一，即太平洋的加拉帕戈斯群岛。最后一次重大喷发是在2009年4月在费尔南迪纳（Fernandina），该爆发靠近高温异常的假定中心（也称为热点或地幔羽）。 Results of geophysical and geochemical studies have shown that the volcanism results from the juxtaposition of a mantle plume with a major oceanic spreading centre.羽流的稀薄岩石圈（〜7 km）在羽流中的高温（〜1400 oC）的组合会导致大量的地幔熔化，因为羽流上升。 Galápagos群岛是研究这种动态构造环境中发生的复杂质量转移和化学混合过程的理想场所，因为地幔羽和海洋扩散中心足够接近相互作用，但仍然能够保持独特的物理实体。 GalápagosArchivelago的火山主义的分布和组成与与常规热点（例如夏威夷）相关的火山不同：没有线性链的海洋岛和活性火山链远离羽羽上升区。最近的一项高分辨率区域地球物理研究（于2007年出版）显示了一个低地震速度的异常区域，从热点延伸到扩散中心。在圣地亚哥下方约70公里的深度非常出色。一个位于群岛中心和羽流周围的岛屿。异常的原因是未知的。它可能代表温度的变化和/或强烈的地幔上升和熔化区域。圣地亚哥是群岛第四大岛屿，但很少有地球化学分析。岛上最近发生的火山喷发是在1795年，1897年和1904年。有限的地球化学数据表明，岛西部火山爆发的熔岩与东方的熔岩组成不同，距离距离小于20公里。这种变化中的某些可能是亚山谷岩浆腔室过程的结果，但是在地幔熔化过程中很容易分配与岩浆的元素比例很大，这表明该岛位于岩石圈上方，其厚度在厚度大大变化，从西部到东，或者是对令人信服的对流的壁炉架具有变化的作品。该提案寻求资金对圣地亚哥的熔岩进行高精度的地球化学分析，在那里PI已经完成了系统的样本收集。这些熔岩化学的数值建模以及其他加拉帕戈斯火山的已发表数据将用于限制基础地幔熔化的组成，温度和压力。结果将与使用新公布的方程式从地震速度数据计算得出的温度结合，以阐明在羽流上流轴和扩散中心之间运行的物理过程，从而导致宽度散布火山。从向上向上延伸到扩散山脊的地幔区域延伸的大量熔体的存在将对这两个动态系统并列时发生的质量运输的性质构成重要限制。拟议的研究将基于PI先前关于地幔融化的研究。之所以新颖，是因为它将生成第一个综合的地球化学和地球物理模型，以解释加拉帕戈斯群岛宽度活跃火山的原因。这将有助于我们理解在诸如中大西洋山脊之类的较少接近的环境中火山活动的原因，并增加了识别地质过去的羽毛岩相互作用的限制。反过来，这将增加我们对全球尺度深层和地面表面过程的了解。

项目成果

Deep Carbon and the Life Cycle of Large Igneous Provinces

• DOI: 10.2138/gselements.15.5.319
• 发表时间: 2019-10-01
• 期刊: ELEMENTS
• 影响因子: 4.5
• 作者: Black, Benjamin A.;Gibson, Sally A.
• 通讯作者: Gibson, Sally A.

Delivery of deep-sourced, volatile-rich plume material to the global ridge system

• DOI: 10.1016/j.epsl.2018.07.028
• 发表时间: 2018-10-01
• 期刊: EARTH AND PLANETARY SCIENCE LETTERS
• 影响因子: 5.3
• 作者: Gibson, Sally A.;Richards, Mark A.
• 通讯作者: Richards, Mark A.

Novel insights from Fe-isotopes into the lithological heterogeneity of Ocean Island Basalts and plume-influenced MORBs

• DOI: 10.1016/j.epsl.2020.116114
• 发表时间: 2020-04-01
• 期刊: EARTH AND PLANETARY SCIENCE LETTERS
• 影响因子: 5.3
• 作者: Gleeson, Matthew L. M.;Gibson, Sally A.;Williams, Helen M.
• 通讯作者: Williams, Helen M.