Variations in the Composition of MORB Chilled Glasses from the Mid-Atlantic Ridge, 12°–31° N: Reflection of Composition Evolution of Parent Melts and the Influence of the Hydrothermal Component

Abstract

The geochemical peculiarities of sample collection of MORB chilled glasses obtained in six areas of the axial zone of the Mid-Atlantic Ridge (MAR), 12°–31° N have been studied. The results of this study provided information on the composition of the parent melts for these glasses and made it possible to assess probable geochemical effects reflecting the interaction of magmatic melts with hydrothermal systems of the MAR axial zone or with altered oceanic crust (AOC). It is shown that basalts of the E-MORB family which includes most of samples are localized mainly in the “cold” segments of the MAR in the crustal section of which serpentinites predominate. On the other hand, samples with depleted signature (N-MORB) belong to segments of the MAR in which serpentinite outcrops are either absent or play a subordinate role. The E-MORB chilled glasses from “cold” segments of the MAR show signs of contamination of basaltic melts with components borrowed either from the host serpentinites or from aqueous-saline fluids circulating in hydrothermal systems located in serpentinites (“serpentinite hosted”). Judging by the data obtained on the nature of variations in the content of Cl, U, and Sr in the studied chilled glasses belonging to the N-MORB family, there are no signs of intracrustal contamination. It is assumed that relics of the ancient continental lithosphere preserved under axial zone of the MAR and involved in the process of partial melting of the shallow mantle took part in the formation of E-MORB parental melts in some segments of the MAR.