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Richard Jason Antonio

Institution: University of Bremen
Room: GEO build­ing, room 5160
Phone: +49 421 218-65136
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Other webpage(s): Richard's working group web page



Richard Jason Antonio

PhD project:

Magma Plumbing Dynamics of the Ultra-slow Spreading Southwest Indian Ridge from 9-25°

Mid ocean ridges are magmatic regions that serve as boundaries between tectonic plates. It is a series of linked mountain ranges which span more than 50,000 km in length but are mostly submerged beneath the oceans. At the center of these mountain ridges are magmatic valleys or rifts which produce new oceanic crust and spread laterally, hence they are considered, in terms of tectonics, as divergent plate boundaries. These ridges are classified according to how fast they move away from each other or spreading rate.

Previous classifications categorized ridges as slow, intermediate and fast spreading ridges and each has a distinct morphology or appearance. More recent expeditions along the Arctic and Southwest Indian Ridge revealed segments that possess even slower spreading rates and were classified as ultraslow spreading ridges. For other ridge types, the thickness of the oceanic crust does not vary significantly but at ultraslow rates (< 20 mm/year), the thickness falls sharply with decreasing spreading rate. Magma production in these ridges is limited and is attributed to the lowering of temperatures and reduced melting in the underlying mantle column due to conductive cooling. In effect, other factors such as the geometry of the ridge, mantle composition, and the thermal structure play a larger role in the morphology of ultraslow ridges compared to the faster ridges which consider these factors almost negligible. These factors produce the peculiar geomorphology of the ultraslow spreading ridges where there are discrete areas where magmatism is active and stretches of non-magmatic or amagmatic segments in between. It is believed that what little magma is produced underneath the ridge is funneled or channeled into the active magmatic centers leaving the amagmatic segments bare.

The project’s primary goal is to understand how magma is generated, transported, stored, and eventually erupted underneath these ultraslow-spreading ridges. Rocks dredged from the Southwest Indian Ridge and the Gakkel Ridge will be analyzed petrographically to gain initial insight on the magmatic processes through rock and mineral textures. Major and trace element compositions of the groundmass will be utilized to infer mantle source properties. Mineral element compositions of clinopyroxene will be used to determine magma storage depths and compositional changes in olivine will be used to approximate magma ascent rates. Variations in chemical compositions of mineral zonations and melt inclusions will be utilized to infer melt interaction and evolution as the magma is stored and transported. Ultimately, the research aims to gain more insight on mid-ocean ridge melt production and oceanic crust and mantle interaction, where geochemical signatures are not overwritten by high-volume generation and mixing of melt which is common in fast spreading ridges.

Thesis committee:

Prof. Dr. Wolfgang Bach University of Bremen
PD. Dr. Andreas Klügel University of Bremen
Prof. Dr. Marta Perez Gussinye University of Bremen


GLOMAR Research Theme B