Spinels in Mid-Atlantic Ridge basalts: Chemistry and occurrence

Authors

Haraldur Sigurdsson, University of Rhode Island
J. G. Schilling, University of Rhode Island

Document Type

Article

Date of Original Version

1-1-1976

Abstract

Three groups of spinels have been identified in dredged basalts from the Mid-Atlantic Ridge in the Azores region (30-40°N): (1) magnesiochromites with 0.4-0.5 Cr (Cr + Al) are most common and characteristic of olivine tholeiites of the region; (2) titaniferous magnesiochromites are found in an olivine basalt with alkali affinities, of local occurrence and evolved in relatively high fugacity of oxygen; (3) chromian spinels with 0.23 Cr (Cr + Al) occur in unusual high-Al picrites of local occurrence and possible high-pressure origin. Spinels are restricted in occurrence to the least fractionated lavas, with FeO*/FeO* + MgO ratio less than 0.575 and with Cr content greater than 350 ppm. A close relationship between Al content of liquidus spinel and Al content of magma has been observed for basaltic types. High-Al spinels deviating from this relationship, such as those found in picritic lavas from the Mid-Atlantic Ridge, may have crystallized at high pressure. The use of spinels as geobarometers in magmas of a restricted compositional range seems a promising prospect. There is no evidence of systematic variation in spinel chemistry of occurrence along the Mid-Atlantic Ridge, such as could be related to different mantle sources of the basalts, plume versus non-plume or binary mantle mixing. © 1976.

Publication Title, e.g., Journal

Earth and Planetary Science Letters

Volume

29

Issue

1

Citation/Publisher Attribution

Sigurdsson, Haraldur, and J. G. Schilling. "Spinels in Mid-Atlantic Ridge basalts: Chemistry and occurrence." Earth and Planetary Science Letters 29, 1 (1976). doi: 10.1016/0012-821X(76)90021-2.