Crustal structure of the northern Reykjanes Ridge and Reykjanes Peninsula, southwest Iceland

Abstract

Abstract. Results from the Reykjanes-Iceland Seismic Experiment (RISE)show that the thickness of zero-age crust decreases from 21 km in southwest Iceland to 11 km at 62ø40•N on the Reykjanes Ridge. This implies a decrease in mantle potential temperature of •-130 øC, with increasing distance from the center of the Iceland mantle plume, along this 250 km transect of the plate boundary. The crust thins off-axis at 63øN, from 12.7 km thick at 0 Ma to 9.8 km at 5 Ma, most likely due to a •40øC change in asthenospheric mantle temperature between these times. This provides evidence for the passage of a pulse of hotter asthenospheric mantle material beneath the present spreading center. A reflective body, the top of which lies at 9-11 km depth, is identified in the lower crust just west of the tip of the Reykjanes Peninsula. Synthetic seisrnogram modeling of the wide-angle reflections from this body suggests that it corresponds to a zone of high-velocity (>_7.5 krn s -x), high-magnesium rocks in the lower crust. The P to S wave velocity ratio beneath the peninsula is 1.78, implying that crustal temperatures are below the solidus. Gravity modeling shows the RISE models to be consistent with the observed gravity field. Mantle densities are lower beneath the ridge axis than beneath older crust, consistent with lithospheric cooling with age. Iceland and the Reykjanes RidgeIceland has been created where the slow spreading Mid-Atlantic Ridge passes directly over a mantle plume.McKenzie and Bickle [1988] showed that for decompression melting of the mantle at oceanic spreading centers the melt volume produced relies sensitively on the mantle temperature. Thus, assuming passive upwelling, the presence of the spreading center allows us to estimate the mantle temperature at a range of distances from the plume by measuring the igneous crustal thickness.•

Low δ18O in the Icelandic mantle and its origins: Evidence from Reykjanes Ridge and Icelandic lavas

“…We see little reason why contamination should be restricted to the lower crust, especially given the shallow crystallization pressures inferred for the Reykjanes Ridge by Michael and Cornell (1998). • There is no objective reason why this process should not occur on other ridges, or in the southern part of the Reykjanes Ridge, unless the increase in crustal thickness towards Iceland (by a factor of <1.6 on our traverse, Weir et al, 2001; and represented by sampling depth in Fig. 7) results in lavas erupted closer to Iceland being more prone to crustal contamination.…”

Thin crust as evidence for depleted mantle supporting the Marion Rise

“…Studies of the Reykjanes Ridge support this, with seismic crust thickening from ~6 km near the Gibbs FZ for 1600 km to ~18 km at the Reykjanes Peninsula e.g. : 3 . The Icelandic Rise, also has a long axial high consistent with such robust magmatism 4 (Table 1).…”

The Iceland Deep Drilling Project 4.5 km deep well, IDDP-2, in the seawater-recharged Reykjanes geothermal field in SW Iceland has successfully reached its supercritical target

“…Although the Reykjanes ridge is a slow spreading ridge, it is magmatically robust due to the influence of the Iceland hotspot. Enhanced magmatism results in much thicker crust (∼ 16 km) compared to normal mid-ocean ridges (Weir et al, 2001). While the ophiolite conceptual model (Fig.…”