Mapping the Mantle on the Marion Rise
Abstract
The global ridge system is dominated by ocean rises where they shoal to shallow depth depth near mantle hotspots. The classic case is the Icelandic Rise, which, like most such rises is generally believed supported by a hot deep mantle plume and thick crust. The Marion Rise on the SW Indian Ridge, is nearly the same size: though a kilometer deeper it is 1000-km longer. While closely associated with a hotspot track originating at the Madagascar Plateau and terminating near Marion Island, Zhou and Dick, 2013 suggested the Rise is supported by buoyant depleted mantle not a mantle plume associated with the Marion Hotspot. Instead the plateau represents the initial burst of melting of delaminated subducted crust and sediment in the upper mantle with Gondwana breakup, followed by melting of the vestigial remains of this material to produce the hotspot track. RV Thomas Thompson Cruise TN365 in February and March 2019 mapped and sampled the Marion Rise between the Discovery and Indomed FZ's, as part of a 2 cruise US, German, Chinese effort to test this hypothesis. The 2nd cruise in March 2020 on the RV Sonne will map and sample the remaining unmapped portion of the ridge on the Marion Rise between 37.5° and the Discovery FZ, and finish sampling left undone by the Thompson to the east. Using multibeam mapping, gravity, magnetics, and dredging, the cruise showed that the ridge between the two FZ's consisted of orthogonal magmatic ridge segments, one next to each fracture zone, linked to amagmatic spreading centers with an intervening newly formed young volcanic ridge segment. The mapping and sampling showed that almost 50% of the 26,000 km2 of seafloor surveyed is exposed mantle with no crust. Thus, unequivocally, the central portion of the Marion Rise is supported by buoyant depleted mantle. Exposures of mantle peridotite found by earlier dredging to the west of the Discovery FZ suggest that the Sonne will also find large regions of the seafloor with no or little crust, which will then confirm the Zhou and Dick hypothesis. These observations then, suggest the possibility that the mantle hotspots in the Indian and South Atlantic Oceans all have a similar origin.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.T13A..01D
- Keywords:
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- 1032 Mid-oceanic ridge processes;
- GEOCHEMISTRY;
- 1037 Magma genesis and partial melting;
- GEOCHEMISTRY;
- 8140 Ophiolites;
- TECTONOPHYSICS;
- 8416 Mid-oceanic ridge processes;
- VOLCANOLOGY