Thermal Structure of the Ionian Slab

Abstract

We propose a thermal model of the subducting Ionian microplate. The slab sinks in an isothermal mantle, and for the boundary conditions we take into account the relation between the maximum depth of seismicity and the ''thermal parameter'' L th of the slab, which is a product of the age of the subducted lithosphere and the vertical component of the convergence rate. The surface heat-flux dataset of the Ionian Sea is reviewed, and a convective geotherm is calculated in its undeformed part for a surface heat flux of 42 mW m )2 , an adiabatic gradient of 0.6 mK m )1 , a mantle kinematic viscosity of 10 17 m 2 s )1 and an asthenosphere potential temperature of 1300°C. The calculated temperature-depth distribution compared to the mantle melting temperature indicates the decoupling limit between lithosphere and asthenosphere occurs at a depth of 105 km and a temperature of 1260°C. A 70-km thick mechanical boundary layer is found. By considering that the maximum depth of the seismic events within the slab is 600 km, a L th of 4725 km is inferred. For a subduction rate equal to the spreading rate, the corresponding assimilation and cooling times of the microplate are about 7 and 90 Myr, respectively. The thermal model assumes that the mantle flow above the slab is parallel and equal to the subducting plate velocity of 6 cm yr )1 , and ignores the heat conduction down the slab dip. The critical temperature, above which the subduced lithosphere cannot sustain the stress necessary to produce seismicity, is determined from the thermal conditions governing the rheology of the plate. The minimum potential temperature at the depth of the deepest earthquake in the slab is 730°C.

Magmatic diversity of western Mexico as a function of metamorphic transformations in the subducted oceanic plate

“…Nevertheless, the Ionian slab is very old, rich in sediments, and one of the coldest on Earth, and is only comparable to Rivera by its high dipping angle (Pasquale et al, 2005). In contrast, the Juan de Fuca plate subducting western North America is as young as Rivera (Wilson, 2002), and thus amongst the warmest in the world (Hacker et al, 2003), but rests at 70-100 km depth beneath Cascadia (McCrory et al, 2006), a continental arc that is entirely devoid of K 2 O-rich magmas (Hildreth, 2007).…”

Some first-order observations on magma transfer from mantle wedge to upper crust at volcanic arcs

“…Bird (2003) models this area as part of the Alps orogen. Thus, the convergence rate of 60 mm year 21 adopted here is instead taken from a regional study of the Ionian slab (Pasquale et al 2005 CVA, Central Vanuatu/New Hebrides: formed due to subduction of the Australia plate beneath the New Hebrides plate. Volcanoes with Holocene effusive eruptions: Aoba, Ambrym, Lopevi.…”

Did Adria rotate relative to Africa?

“…The Ionian Abyssal Plain is the only relatively undeformed portion that serves as the foreland of the central Mediterranean subduction systems (Hieke et al, 2006;Gallais et al, 2011;Speranza et al, 2012). Given the crustal thickness of 7-9 km (Chamot-Rooke and Rangin, 2005) and very low heat flow (Pasquale et al, 2005), this ocean floor is likely an old remnant of the Neotethys Ocean (e.g., Gallais et al, 2011;Speranza et al, 2012). The age of the Ionian Basin has been estimated to range from late Paleozoic to Cretaceous (Sengör et al, 1984;Dercourt et al, 1986;Robertson et al, 1991;Stampfli and Borel, 2002;Golonka, 2004;Frizon de Lamotte et al, 2011;Gallais et al, 2011;Schettino and Turco, 2011), with the most recent suggestion giving a Late Triassic age (Speranza et al, 2012).…”