Collaborative Research: Rejuvenescent Volcanism on Mauritius

这个项目将调查印度洋毛里求斯岛上的火山演化。这项研究的动机是这些问题：为什么海洋火山会随着时间的推移而进化？为什么在数百万年的不活动之后又会出现火山活动？是什么导致了成分随时间的变化？众所周知的夏威夷火山演化模式有多普遍？夏威夷火山的演化经历了一系列有记载的阶段。主要的火山大厦在盾构期迅速建成（例如基拉韦厄火山）。随后，火山活动减弱，只有偶尔的碱性熔岩喷发（例如华拉莱火山和莫纳克亚火山）。然后会有一个几十万到几百万年的活动间歇期。在这之后，有时会有一个后侵蚀期或回潮期，在这个阶段，小体积的极碱性熔岩会爆发。火奴鲁鲁火山，包括Diamondhead火山，就是这个阶段的一个很好的例子。毛里求斯位于印度洋，是夏威夷以外最引人注目的火山活动复活的例子之一。像夏威夷一样，毛里求斯被认为是由地幔柱（留尼汪地幔柱）形成的。早期的研究已经确定了毛里求斯火山活动的三个阶段：较老系列（780万至540万年），中期系列（350万年）。至190万年)和更年轻的系列（100万年至17万年）。较老的系列火山活动在毛里求斯构造了主要的火山盾，似乎明显类似于夏威夷盾的构造阶段。中间系列似乎类似于夏威夷的后侵蚀阶段。年轻系列可以简单地代表中间系列阶段的延伸；如果不是，那它在夏威夷火山演化中就没有明确的相似之处。因此，毛里求斯的火山活动提供了与夏威夷火山活动进行比较和对比的机会，并为海洋岛屿火山演化建立了一般模式。毛里求斯也是一个合适的研究对象，因为毛里求斯政府的水资源股拥有大量的岩心（钻井最初是为了寻找水资源）。这些岩心经常穿透覆盖大部分岛屿的后侵蚀熔岩的表面，并采集在盾构阶段喷发的新鲜原始熔岩的样本。较深的岩心也为地层控制取样提供了机会。样品将进行岩石学研究，并分析主要元素、微量元素以及Sr、Nd、Pb和Hf同位素比率。这将为毛里求斯产生一个全面的地球化学数据集。俄勒冈州立大学的Ar-Ar将测定25个关键样本的年代。在与康奈尔大学同事的合作中，这些观测结果将与计算机模拟的由橄榄岩基质中榴辉脉组成的岩性不均匀的地幔柱融化进行比较。正在开发的这种现象的有限元模型是试图模拟岩浆成分随时间的演变。该团队将通过将压力、温度和成分相关的微量元素划分纳入热力学代码来参与建模项目。这项研究将提高我们对火山作用和地幔性质的基本认识。它将研究岩石非均质性在火山组成演化中可能发挥的作用，并检验夏威夷火山演化模式的普遍性。这项研究将支持康奈尔大学和德克萨斯大学圣安东尼奥分校（少数民族服务机构）的一名博士研究生和几名本科生。此外，研究成果将被整合到pi定期教授的本科和研究生地球化学/岩石学课程中。

This project will investigate volcanic evolution on the island of Mauritius in the Indian Ocean. This study is motivated by these questions: Why do oceanic volcanoes evolve over time? Why does rejuvenescent volcanism occur after millions of years of inactivity? What accounts for the changes in composition with time? How universal is the well-known Hawaiian pattern of volcanic evolution? Hawaiian volcanoes evolve through a well-documented series of stages. The main volcanic edifice is constructed rapidly during the shield stage (Kilauea for example). Subsequently, activity wanes and there are only occasional eruptions of alkalic lavas (Hualalai and Mauna Kea for example). Then there is a hiatus of activity of anywhere from a few hundred thousand to a few million years. This is sometimes followed by a post-erosional or rejuvenescent phase in which small volumes of very alkali lava erupt explosively. The Honolulu volcanics, including Diamondhead, are a good example of this stage.Mauritius, located in the Indian Ocean, represents one of the most striking examples of rejuvenescent volcanism outside Hawaii. Like Hawaii, Mauritius is thought to result from a mantle plume (the Reunion mantle plume). Earlier studies have identified three phases of volcanism on Mauritius: the Older Series (7.8 to 5.4 million years), the Intermediate Series (3.5. to 1.9 million years), and the Younger Series (1.0 to 0.17 million years). Older Series volcanism constructed the main volcanic shield on Mauritius and seems clearly analogous to the Hawaiian shield-building stage. The Intermediate Series seems analogous to the Hawaiian post-erosional phase. The Younger Series may simply represent an extension of the Intermediate Series phase; if not, it has no clear analog in Hawaiian volcanic evolution. Thus, volcanism on Mauritius provide an opportunity to compare and contrast with Hawaiian volcanism and to develop a general model for oceanic island volcanic evolution. Mauritius is also an opportune target for study because the Water Resources Unit of the Government of Mauritius has a large collection of drill cores (drilling was originally undertaken in the search for water resources). These cores often penetrate the veneer of post-erosional lavas that cover most of the island and sample fresh, primitive lavas erupted during the shield-building stage. The deeper cores also provide an opportunity for stratigraphically controlled sampling.Samples will be studied petrographically and analyzed for major elements, trace elements, and Sr, Nd, Pb, and Hf isotope ratios. This will produce a comprehensive geochemical data set for Mauritius. Twenty-five key samples will be dated by Ar-Ar at Oregon State University. In collaboration with colleagues at Cornell, these observational results will compared with computer simulations of melting of a lithologically heterogeneous mantle plume consisting of eclogitic veins in a peridotitic matrix. The finite element model of this phenomenon that is being developed is an attempt to simulate the evolution of magma composition through time. The team will participate in the modeling project by incorporating pressure-, temperature-, and composition-dependent trace element partitioning into the thermodynamic code.This study will improve our fundamental understanding of volcanism and the nature of the Earth's mantle generally. It will examine the role of lithologic heterogeneity might play in the compositional evolution of volcanoes and test the universality of the Hawaiian pattern of volcanic evolution. This research will support a doctoral graduate student and several undergraduates from both Cornell University and University of Texas at San Antonio (a minority serving institution). In addition, research findings will be integrated to undergraduate and graduate geochemistry/petrology courses regularly taught by the PIs.