Mantle Heterogeneity Through Mid-Ocean Ridge Basalts
The chemical heterogeneity of Earth's upper mantle is often examined through mid-ocean ridge basalts (MORB), which contest the prevalent assumption of a well-mixed convecting mantle. This dissertation delves into studying mantle heterogeneity from a local to regional scale. Initially, petrological models were utilized to scrutinize the source and melting conditions of potassium-enriched MORB (K-MORB) from the Central Lena Trough in the Arctic Ocean. The findings suggest a complex mantle source with phlogopite acting as the dominant H2O-K bearing mineral and indicate a binary mixing of 40% K-MORB and 60% N-MORB-like endmember, thereby providing insights into the area's tectonic evolution. Further into the study, advanced statistical methods like principal component analysis and partial least squares regression were used to decipher the isotopic compositions of Mid-Atlantic Ridge (MAR) basalts. These analyses reveal five distinct "zoo" signatures (akin to EMI, EMII, DM, HIMU, FOZO) in the mantle components and surprisingly, establish isotopic signatures as reliable predictors of geographic location along the ridge, suggesting a more potent connection between mantle geochemistry and location than previously believed. Finally, the study considers the implications of these findings on our current understanding of mantle convection. Discrepancies in the well-stirred mantle hypothesis are underscored, and recent geodynamic models proposing limited mixing and stirring between the actively upwelling mantle and sub-ridge mantle are examined with the k-means clustering and artificial Neural Network models. The examination of MAR basalts indicates that mantle parcels may have unique and prolonged geologic histories, implying a mantle convection system potentially composed of interconnected subsystems contributing to overall mantle heterogeneity. The research underscores a perspective of Earth's upper mantle that is significantly more heterogeneous and regionally influenced than traditionally understood, suggesting a strong linkage between mantle geochemistry, chemical geography, and geological history, thereby illuminating chemical geodynamics in Earth's mantle.