The Role Of Mafic Heterogeneity In The Generation Of Lavas On Mauritius

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Mauritius Island (20 degree 20' S, 57 degree 30' E) is the penultimate volcanic island of the Reunion mantle plume. Mauritius has a unique history of episodic volcanism characterized by three temporally distinct eruptive phases: 1) the shield-building Older Series lavas (8.4-5.5 Ma), 2) the Intermediate Series (3.5-1.9 Ma), and 3) the Younger Series (1.0-0.00 Ma). The study of newly available drill cores has facilitated an advanced subsurface investigation into the evolution of the island. Radiometric dating of deep lava units has identified the earliest known samples (8.4 Ma) and demonstrated the existence of deep post-erosional lavas ( greater than 200 m). The Intermediate and Younger Series remain chemically indistinguishable, apart from curious differences in 206Pb/204Pb and 208Pb/204Pb. Contrary to other worldwide observances of post-erosional volcanism (e.g., Hawaii, Tahaa, Madeira), the Older Series lavas are enriched in incompatible trace elements relative to the post-erosional lavas. However, isotope systematics remain consistent with other islands, with shield building lavas having more enriched isotopic signatures. Calculated volumes for the combined posterosional lavas exceed 35 km3, closely resembling Hawaiian analogues (20-60 km3), and form decreasing linear trends with increasing shield volume. The chemically distinct shield and post-erosional lavas cannot be explained solely by variations in the extent of partial melting and require distinct sources for each class. Two scenarios for magma generation from a lithologically heterogeneous plume composed of enriched (eclogitic) and depleted (peridotitic) components are modeled using Adiabat_1ph: 1) mixing of melts from the enriched and depleted components, and 2) generation and melting of a hybrid pyroxenite component. P-T conditions for the system are modeled as a weighted composite of the two components, producing enhanced eclogite and depressed peridotite productivity. Iterative forward modeling of trace element data to the shield lavas allows for the calculation of post-erosional and source component compositions. The post-erosional lavas are plausibly reproduced in each model with a TP = 1525 degrees C and maximum post-erosional ascent pressure of 2.5 GPa. Light REE enriched source components are required by both models. A lithologically heterogeneous plume consisting of stretched heterogeneous filaments can plausibly account for the required generation of the Intermediate and Younger Series from a single packet of plume material.

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