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.
