Collaborative Research: Rejuvenescent Volcanism on Mauritius

该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演变？为什么在几百万年的不活动之后会发生新生的火山活动？构成随时间变化的原因是什么？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据可查的阶段。主要的火山建筑是在地盾阶段快速建造的(例如基拉韦厄火山)。随后，活动减弱，只有偶尔爆发的碱性熔岩(例如，华拉莱和莫纳克亚)。然后有一个从几十万年到几百万年的活动中断。在这之后，有时会出现侵蚀后或恢复活力的阶段，在这个阶段，少量极碱性的熔岩会爆炸地喷发。火奴鲁鲁火山，包括Diamondhead，就是这一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复兴的例子之一。和夏威夷一样，毛里求斯被认为是地幔热柱(留尼汪岛地幔热柱)的产物。早些时候的研究已经确定了毛里求斯火山作用的三个阶段：较老的系列(780万至540万年)，中间系列(3.5年。至190万年)，以及较年轻系列(1.0至17万年)。古老的系列火山作用构成了毛里求斯的主火山屏障，显然类似于夏威夷的盾牌建造阶段。中级系列似乎类似于夏威夷的后侵蚀阶段。年轻系列可能只是代表了中间系列阶段的延伸；如果不是，它在夏威夷火山演化中没有明显的相似之处。因此，毛里求斯的火山活动提供了与夏威夷火山作用进行比较和对比的机会，并为大洋岛火山演化提供了一个一般模式。毛里求斯也是一个很好的研究对象，因为毛里求斯政府水资源股有大量钻芯(钻探最初是为了寻找水资源)。这些岩芯经常穿透覆盖该岛大部分地区的侵蚀后熔岩的表面，并在盾牌建造阶段喷发出新鲜、原始的熔岩样本。更深的岩心也提供了进行地层控制采样的机会。将对样品进行岩石学研究，并对样品进行常量元素、微量元素以及锶、钕、铅和氢同位素比值的分析。这将为毛里求斯产生一套全面的地球化学数据。俄勒冈州立大学的Ar-Ar将测定25个关键样本的年代。与康奈尔大学的同事合作，这些观测结果将与计算机模拟的岩石不均匀地幔热柱融化进行比较，地幔热柱由橄榄岩基质中的榴辉岩脉组成。正在开发的这种现象的有限元模型是一种试图模拟岩浆成分随时间演变的尝试。该团队将通过将依赖于压力、温度和成分的微量元素分配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活动和地幔性质的基本理解。它将研究岩性非均质性在火山成分演化中可能发挥的作用，并测试夏威夷火山演化模式的普遍性。这项研究将支持一名博士研究生和几名来自康奈尔大学和德克萨斯大学圣安东尼奥分校(一家少数族裔服务机构)的本科生。此外，研究成果将被整合到由私人投资促进机构定期教授的本科生和研究生地球化学/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.