Flow and Melting in a Heterogeneous Mantle: A Case Study from the Galápagos Spreading Center
Abstract
The Galápagos Spreading Center (GSC, ~83-98°W, 1-3°N) in the Eastern Pacific Ocean interacts with the nearby Galápagos hotspot (~92°W, ~0.5°S). This is manifested in both physical (e.g., axis morphology, crustal thickness) and chemical variations along the ridge. Lavas recovered along the ridge closest to the hotspot have geochemical characteristics distinct from more distal lavas, as well as from lavas of non-hotspot-influenced segments of other mid-ocean ridges. Within a 500 km radius of the hotspot (e.g., between 92°W and 95.5°W), regular patterns are observed in crustal thickness, axial morphology, and some incompatible trace element ratios, whereas radiogenic isotope compositions show weak to no correlation with increasing distance from the hotspot. The largest variability in several geochemical indicators along this portion of the ridge is observed over an along-axis distance of ~10 km near a propagating ridge tip (95.5°W). West of this ridge offset, evidence for any geochemical influence by the hotspot is completely absent. Here, we evaluate three possible models that may explain observed geochemical and geophysical variations along the ridge. These models include: 1) a ridge fed by a narrow, geochemically distinct mantle plume conduit that becomes progressively diluted by ambient mantle farther from the plume (e.g., Schilling et al. G-cubed 2003), 2) a narrow, geochemically distinct plume that does not mix with the ambient mantle over the distance it feeds the ridge (e.g., Ito et al. JGR 1997), and 3) a broad region of active upwelling of a uniformly heterogeneous mantle (Ito and Mahoney EPSL 2005a,b). The high geochemical and geophysical data density along the western GSC provide an opportunity for a robust case study of the predictions of these three models.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFM.U14A..03I
- Keywords:
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- 8120 Dynamics of lithosphere and mantle: general (1213);
- 8137 Hotspots;
- large igneous provinces;
- and flood basalt volcanism;
- 8178 Tectonics and magmatism;
- 8410 Geochemical modeling (1009;
- 3610);
- 8416 Mid-oceanic ridge processes (1032;
- 3614)