Petrological Constraints on Magma Chamber Depths, Magma Plumbing Systems, and Crustal Thickness along the Reykjanes Ridge, North Atlantic
Abstract
Plate spreading is accompanied by intrusion of dikes and eruption of lava mainly along the axis of mid-ocean ridges. The dikes are fed by magma chamber(s) located beneath the ridge. It has been suggested that the depth of magma chambers is related to the rate of spreading. In order to examine this hypothesis we determined the depths of magma chambers beneath the slow spreading Reykjanes Ridge that extends form the Charlie Gibbs fracture zone at 53° N to the southern tip of Iceland at 64° N in the North Atlantic. The method involves comparing the compositions of natural liquids with those of liquids in equilibrium with the minerals olivine, plagioclase, and clinopyroxene. We used pressures calculated by this method to estimate the depths of partial crystallization of the liquids in sub-crustal chambers or reservoirs. Chemical analyses of mid-ocean ridge basalts (MORB) glasses collected along the Reykjanes Ridge were used as liquid compositions. The glasses form by rapid cooling of magma when quenched by contact with seawater, and provide unambiguous samples of natural basalt liquids. The results indicate that the depth of magma chambers decreases from 4 to 8+/-0.75 km near the Charlie Gibbs fracture zone to 1.17+/-0.53 km at 55.67° N. Further north, the average depth of chambers increases to 9.71+/-3.17 km as the ridge approaches Iceland. The shallow depths obtained for chambers beneath the southern part of the ridge are contrast with results obtained for slow-spreading ridges elsewhere. This may reflect increased magma flux associated with the Iceland plume, and this is consistent with the crust thickening farther north towards Iceland as interpreted from the northerly increase in the maximum depths calculated for chambers along the ridge. The northward thickening of crust indicated by the maximum calculated depths of magma chambers is consistent with seismic data for this region. The influence of the Iceland plume is apparent from the chemical analyses of the glasses. The abundances of Ti, Na, K, P, and Fe increase whereas the abundances of Si, Mg, Al, and Ca decrease as Iceland is approached.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFM.V33D2245S
- Keywords:
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- 3614 Mid-oceanic ridge processes (1032;
- 8416);
- 3630 Experimental mineralogy and petrology;
- 3651 Thermobarometry;
- 7220 Oceanic crust;
- 8400 VOLCANOLOGY