Whole-rock geochemistry of gabbros from the Southwest Indian Ridge; constraints on geochemical fractionations between the upper and lower oceanic crust and magma chamber processes at (very) slow-spreading ridges

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doi: 10.1016/S0009-2541(00)00424-1
Authors:Coogan, L. A.; MacLeod, C. J.; Dick, H. J. B.; Edwards, S. J.; Kvassnes, A.; Natland, J. H.; Robinson, P. T.; Thompson, G.; O'Hara, M. J.
Author Affiliations:Primary:
Cardiff University, Department of Earth Sciences, Cardiff, United Kingdom
Other:
Woods Hole Oceanographic Institute, Woods Hole, MA, United States
University of Greenwich, United Kingdom
Rosenstiel School of Marine and Atmospheric Sciences, United States
Dalhousie University, Canada
University of Hong Kong, China
Volume Title:Chemical Geology
Source:Chemical Geology, 178(1-4), p.1-22. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0009-2541
Publication Date:2001
Note:In English. 61 refs.; illus., incl. 2 tables, sketch map
Summary:Whole-rock major and trace element compositions are presented for a suite of gabbroic samples formed at the Southwest Indian Ridge with the aim of constraining magmatic processes at ultra slow-spreading centres. The gabbros, together with subordinate basalts, dolerites and peridotites were collected from a ∼700 km2 area around Atlantis Bank, adjacent to the Atlantis II Fracture Zone during cruise JR31 of the RRS James Clark Ross. The large area sampled, the abundance of gabbro, and the recovery of samples representative of all other levels in the oceanic lithosphere, allow an average lower crustal composition to be estimated. The estimated composition is not sufficiently primitive in terms of Mg/Fe or compatible trace element abundances (Ni, Cr) for the bulk crust to be in equilibrium with the mantle. This is probably due to compositional modifications within the mantle during melt extraction, although crystallisation within the crust in an unsampled area, either towards the segment centre or along a flow line, cannot be ruled out. Gabbro compositions show evidence for being mixtures of cumulate crystals and significant proportions of basalt, with the proportion of each end-member dependent on the distribution coefficient of the element in question. This suggests that the concept of "trapped melt" cannot be used to understand the origin of these compositions and consideration of the migration of interstitial liquid within a crystal mush is necessary. The fractionation of incompatible elements between the upper and lower crust correlates with the observed degree of variation in trace element concentrations in basalts from the same spreading segment. This suggests that interstitial liquids are, in part, extracted from the crystal mush and mixed back into subsequently erupted basalts leading to their compositional modification. Abstract Copyright (2001) Elsevier, B.V.
Sections:Geochemistry
Subsections:Igneous rocks
Subjects:Basalts; Chemical composition; Chemical fractionation; Crust; Dredged samples; Gabbros; Geochemistry; Igneous rocks; Lithosphere; Magma chambers; Magmas; Magmatic differentiation; Major elements; Mid-ocean ridge basalts; Mid-ocean ridges; Minor elements; Mixing; Ocean Drilling Program; Ocean floors; Oceanic crust; Oceanic lithosphere; Plate tectonics; Plutonic rocks; Sea-floor spreading; Spreading centers; Trace elements; Volcanic rocks; Whole rock; Atlantis II fracture zone; Indian Ocean; Leg 121; ODP Site 735; Southwest Indian Ridge; Atlantis Bank
Coordinates:S330000 S323000 E0573000 E0570000
Abstract Numbers:03M/1698
Record ID:2001055324
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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