Skip Navigation



Journal of Petrology Advance Access published online on July 20, 2005
Journal of Petrology, doi:10.1093/petrology/egi060
This Article
Right arrow FREE Full Text (PDF) Freely available
Right arrow All Versions of this Article:
46/12/2427    most recent
egi060v2
egi060v1
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Alert me to new issues of the journal
Right arrow Add to My Personal Archive
Right arrow Download to citation manager
Right arrowRequest Permissions
Google Scholar
Right arrow Articles by JANNEY, P. E.
Right arrow Articles by CARLSON, R. W.
Right arrow Search for Related Content
GeoRef
Right arrow GeoRef Citation
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us  
What's this?

© The Author 2005. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oupjournals.org
Received July 6, 2004
Accepted June 10, 2005

Article

Hafnium Isotope and Trace Element Constraints on the Nature of Mantle Heterogeneity beneath the Central Southwest Indian Ridge (13°E to 47°E)

P. E. JANNEY 1*, A. P. LE ROEX 2, and R. W. CARLSON 1

1 DEPARTMENT OF TERRESTRIAL MAGNETISM, CARNEGIE INSTITUTION OF WASHINGTON, 5241 BROAD BRANCH ROAD, NW, WASHINGTON, DC 20015, USA
2 DEPARTMENT OF GEOLOGICAL SCIENCES, UNIVERSITY OF CAPE TOWN, PRIVATE BAG, RONDEBOSCH 7701, SOUTH AFRICA

* To whom correspondence should be addressed.
P. E. JANNEY, E-mail: pjanney{at}fieldmuseum.org


  Abstract

Hafnium isotope and incompatible trace element data are presented for a suite of mid-ocean ridge basalts (MORB) from 13 to 47°E on the Southwest Indian Ridge (SWIR), one of the slowest spreading and most isotopically heterogeneous mid-ocean ridges. Variations in Nd-Hf isotope compositions and Lu/Hf ratios clearly distinguish an Atlantic-Pacific-type MORB source, present west of 26°E, characterized by relatively low {varepsilon}Hf values for a given {varepsilon}Nd relative to the regression line through all Nd-Hf isotope data for oceanic basalts (termed the ‘Nd-Hf mantle array line’; the deviation from this line is termed {Delta}{varepsilon}Hf) and low Lu/Hf ratios, from an Indian Ocean-type MORB signature, present east of 32°E, characterized by relatively high {Delta}{varepsilon}Hf values and Lu/Hf ratios. Additionally, two localized, isotopically anomalous areas, at 13-15°E and 39-41°E, are characterized by distinctly low negative and high positive {Delta}{varepsilon}Hf values, respectively. The low {Delta}{varepsilon}Hf MORB from 13 to 15°E appear to reflect contamination by HIMU-type mantle from the nearby Bouvet mantle plume, whereas the trace element and isotopic compositions of MORB from 39 to 41°E are most consistent with contamination by metasomatized Archean continental lithospheric mantle. Relatively small source-melt fractionation of Lu/Hf relative to Sm/Nd, compared with MORB from faster-spreading ridges, argues against a significant role for garnet pyroxenite in the generation of most central SWIR MORB. Correlations between {Delta}{varepsilon}Hf and Sr and Pb isotopic and trace element ratios clearly delineate a high-{Delta}{varepsilon}Hf ‘Indian Ocean mantle component’ that can explain the isotope composition of most Indian Ocean MORB as mixtures between this component and a heterogeneous Atlantic-Pacific-type MORB source. The Hf, Nd and Sr isotope compositions of Indian Ocean MORB appear to be most consistent with the hypothesis that this component represents fragments of subduction-modified lithospheric mantle beneath Proterozoic orogenic belts that foundered into the nascent Indian Ocean upper mantle during the Mesozoic breakup of Gondwana.

Keywords: mid-ocean ridge basalt; isotopes; incompatible elements; Indian Ocean.
Add to CiteULike CiteULike   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us    What's this?


This article has been cited by other articles:


Home page
 J PetrologyHome page
J. J. Mahoney, A. D. Saunders, M. Storey, and A. Randriamanantenasoa
Geochemistry of the Volcan de l' Androy Basalt-Rhyolite Complex, Madagascar Cretaceous Igneous Province
J. Petrology, June 1, 2008; 49(6): 1069 - 1096.
[Abstract] [Full Text] [PDF]

Home page
 Geological Society of America Special PapersHome page
J. G. Fitton
The OIB paradox
Geological Society of America Special Papers, January 1, 2007; 430(0): 387 - 412.
[Abstract] [Full Text] [PDF]


Disclaimer: Please note that abstracts for content published before 1996 were created through digital scanning and may therefore not exactly replicate the text of the original print issues. All efforts have been made to ensure accuracy, but the Publisher will not be held responsible for any remaining inaccuracies. If you require any further clarification, please contact our Customer Services Department.