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Abstract Rio Grande Rise (RGR) and Walvis Ridge (WR) are South Atlantic large igneous provinces (LIPs), formed on the South American and African plates, respectively, mainly by volcanism from a hot spot erupting at the Mid‐Atlantic Ridge (MAR) during the Late Cretaceous. Both display morphologic complexities that imply their tectonic evolution is incompletely understood. We studied bathymetry, gravity, and vertical gravity gradient maps derived from satellite altimetry to trace faults providing indications of seafloor spreading directions and changes. We also examined magnetic anomalies for time constraint and reflection seismic data for structural information. Abyssal hill fabric and magnetic anomaly data indicate that the area between RGR and WR was anomalous between anomalies C34 (83.6 Ma) and C30 (66.4 Ma) owing to reorganization of a right‐lateral transform on the MAR. This event began ∼92 Ma as the transform shifted south to form multiple, short‐offset right‐lateral transforms, with the reorganization extending through anomaly C34 and ending before anomaly C30. Anomalous spacing of magnetic anomalies and discordant fault fabric indicate that a microplate formed with a core of Cretaceous Quiet Zone seafloor. As the MAR jumped eastward, this microplate was captured by the South American plate and now resides mostly in a basin between the main RGR plateau and a related ridge to the east (East Rio Grande Rise). The microplate is ringed by igneous massifs, implying a link with volcanism. The results presented here indicate that these two LIPs had a complex Late Cretaceous history that belies simple hot spot models.
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Drivers of Biomass and Biodiversity of Non-Chemosynthetic Benthic Fauna of the Mid-Atlantic Ridge in the North Atlantic
We examine the main drivers that may elevate biomass and biodiversity of non-chemosynthetic benthic megafauna of the lower bathyal (800-3500m depth) of the Mid-Atlantic Ridge in the North Atlantic Ocean (MAR). Specifically: 1. Primary production in surface waters (10°-48°N) from remote sensing data 2002-2020 over the MAR was not significantly different from abyssal regions to the east and west. We reject the hypothesis that presence of a mid ocean ridge may enhance surface primary production. 2. The quantity of particulate organic matter reaching the sea floor was estimated as a proportion of surface export production scaled by bathymetry. Flux was 1.3 to 3.0 times greater on the MAR as a function of shorter vertical transport distance from the surface than on adjacent abyssal regions. 3. Depth variation effect on species richness. Demersal fishes living between 41° and 60°N showed a maximum of species richness at 2000 m depth and linear increase in regional (Gamma) diversity of 32 species per 1,000 m elevation of the MAR above the abyss. Elevated topography provides niches for species that cannot otherwise survive. 4. Substrate heterogeneity. The MAR >95% covered with soft sediment with frequent hard rocky patches spaced at a mean nearest neighbour distance of <500 m. Over 90% were <1 km apart. Animals are readily able to disperse between such patches increasing biodiversity through the additive effect of soft and hard substrate fauna on the MAR. 5. Presence of a biogeographic overlap zone. The MAR harbours bathyal species known from Western Atlantic and Eastern Atlantic continental slopes with meridional asymmetry resulting in bias toward predominance of Eastern species. The mix of species contributes to increased diversity to the east of the MAR. Multiple factors support increase in biomass and biodiversity on the MAR. Biological data are almost entirely absent from 12° to 33°N, the part of the MAR which may be mined for polymetallic sulphide ore deposits. This study enables some predictions of biomass and biodiversity but there is urgent need for intensive biological sampling across the MAR throughout the proposed mining areas south of the Azores.
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- Award ID(s):
- 1762493
- PAR ID:
- 10440652
- Date Published:
- Journal Name:
- Frontiers in Marine Science
- Volume:
- 9
- ISSN:
- 2296-7745
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.3389/fmars.2022.866654
