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This investigation focuses on gaining a better understanding of the complex
relationship between melt generation, source variability and mid-ocean ridge
morphology. The approach adopted here uses a variety of geochemical techniques to
evaluate the ability of 'global' models to predict regional scale geochemical variability
associated with axial depth and axial morphologic changes. Three separate regional scale
studies were conducted along ridges characterized by intermediate spreading rates (where
the system is very sensitive to variations in magma production).
The first study focuses on the development of the Australian-Antarctic
Discordance (AAD), an anomalously deep portion of the modern global ridge system
located in the eastern Indian Ocean, over the period from 28 to 14 Ma during which the
eastern Indian Ocean basin was in a relatively young stage of formation. Major and trace
element results from this study suggest a more magmatically robust ridge was present
during this period.
The second study investigates the link between U-series disequilibria and axial
ridge depth. In this study U and Th isotopic compositions and elemental concentrations
were analyzed along the Southeast Indian Ridge. The results of this study suggest that a
simple relationship, such as that predicted from global MORB variations, does not exist
on a regional scale in this part of the Indian Ocean. Plausible explanations of this data set
require the consideration of other intrinsic variables such as residual porosity and mantle
melting rates.
The third investigation focuses on the western Galapagos Spreading Center
(GSC), an intermediate spreading ridge whose axial morphology is affected by the
addition of heat and material from the nearby Galapagos hotspot. This study investigates
the origin and nature of the transfer of this material through analysis of rare earth element
concentrations in melt inclusions. The results from this study support a deep (≥ 60 km),
strong lateral flow of hotspot-derived mantle toward the GSC.
Collectively these studies support a strong link between axial morphology and
melt generation and verify that geochemical investigations along regional morphologic
gradients provide a meaningful 'window' into the underlying mantle, while
demonstrating that although 'global' models succeed in providing a valid platform from
which to evaluate regional-scale observations, they do not accurately describe the
complex process of melt generation on a regional scale. |
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