Slab-rollback induced upper mantle upwelling near lateral slab edges: A new mechanism for generating intra-plate magmatism in the central Mediterranean
Abstract
Most volcanism on Earth is associated with plate boundaries and can thus be explained in a plate tectonic framework. Intra-plate volcanism, however, cannot directly be explained with plate tectonic theory. Intraplate volcanism is frequently explained with the plume model, in which a relatively fixed buoyant plume rises from the lower mantle to the surface and, as the overlying plate moves with respect to the plume source, produces a linear hotspot track along which the age of volcanoes progressively changes. This model has been applied to linear volcanic chains such as the Hawaii-Emperor Ridge in the Pacific and the Walvis Ridge in the Atlantic Ocean. Other intra-plate volcanism that does not occur in linear chains and does not show a preferred age progression in a specific geographical direction is more difficult to explain with the plume model, and might require an alternative explanation. There are several examples of intraplate volcanism on Earth located close to lateral slab edges, suggesting that they might be genetically related to these slab edges. One example of such volcanism is located in Sicily in the Mediterranean, which took place at ~7.0-1.1 Ma on the Iblean plateau and at 0.5 Ma to Present to form Mount Etna. The volcanics are located in close proximity but are laterally offset with respect to the Eolian magmatic arc and the Calabrian subduction zone, where Ionian oceanic lithosphere is subducting west-northwestward below Calabria. The volcanics in Sicily can therefore not be interpreted as arc volcanism. Previous work, primarily based on the geochemistry and petrology of the volcanics, suggests that the volcanism resulted from a plume. The volcanics in Sicily and surrounding seas, however, do not align along a linear chain and show no lateral age progression. Here it is proposed that Mount Etna and the Iblean volcanics are related to decompression melting of upper mantle material that is flowing around the southern Ionian slab edge to accommodate east-directed rollback of the Ionian slab that started at ~8 Ma. Three-dimensional fluid dynamic models of progressive subduction demonstrate that rollback-induced mantle return flow occurs in a quasi-toroidal fashion with a component of downwelling directly below and above the slab, and a component of upwelling next to the subduction zone with maximum upwelling observed next to the sub-slab region and reduced upwelling next to the mantle wedge region. Significant upwelling is observed at 90-430 km depth and extends 55-660 km away from the projected distance of inferred arc magmatism at the slab edge. The models can thereby explain the large spatial separation of up to 400 km between volcanism in Sicily and the magmatic arc during the last ~7 Myr, the contemporaneous activity of arc magmatism in the Tyrrhenian Sea and volcanism in Sicily, and the intra-plate character of the volcanics in Sicily. Finally, it explains a broad slow S-wave anomaly at ~300 km depth below Sicily, and more local low Qp and high Vp/Vs anomalies at 50-150 km depth below northeastern Sicily.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2010
- Bibcode:
- 2010AGUFM.T13G..08S
- Keywords:
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- 8104 TECTONOPHYSICS / Continental margins: convergent;
- 8121 TECTONOPHYSICS / Dynamics: convection currents;
- and mantle plumes;
- 8170 TECTONOPHYSICS / Subduction zone processes;
- 8178 TECTONOPHYSICS / Tectonics and magmatism