Skip Navigation



Journal of Petrology Advance Access published online on March 7, 2006
Journal of Petrology, doi:10.1093/petrology/egl004
This Article
Right arrow FREE Full Text (PDF) Freely available
Right arrow All Versions of this Article:
47/6/1095    most recent
egl004v1
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 ANDREOLI, M. A. G.
Right arrow Articles by COETZEE, H.
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 2006. Published by Oxford University Press. All rights reserved. For Permissions, please e-mail: journals.permissions@oxfordjournals.org
Received July 1, 2004
Accepted January 13, 2006

Article

Correlations between U, Th Content and Metamorphic Grade in the Western Namaqualand Belt, South Africa, with Implications for Radioactive Heating of the Crust

MARCO A. G. ANDREOLI 1 *, RODGER J. HART 2, LEWIS D. ASHWAL 1, and HENK COETZEE 3

1 SCHOOL OF GEOSCIENCES, UNIVERSITY OF THE WITWATERSRAND, PRIVATE BAG 3, WITS 2050, JOHANNESBURG, SOUTH AFRICA
2 ITHEMBA LABS (GAUTENG), P. BAG 3, WITS 2050, JOHANNESBURG, SOUTH AFRICA
3 COUNCIL FOR GEOSCIENCES, P.O. BOX 112, PRETORIA 0001, SOUTH AFRICA

* To whom correspondence should be addressed.
MARCO A. G. ANDREOLI, E-mail: marco{at}necsa.co.za


  Abstract

The digital image of airborne radiometric data across South Africa reveals that the largest anomaly, ≥100 nGy/h, is caused by the granulite-facies rocks of the Namaquan metamorphic complex, whereas most of the country is <60 nGy/h. This observation is consistent with geochemical data that show that the ~1900 ± 100 Ma greenschist-facies Richtersveld Terrane near Namibia (max. U = 3·4 ppm; Th = 20·1 ppm) and the adjacent, 1100 ± 100 Ma, amphibolite-facies Aggeneys/Steinkopf Terranes (max. U {approx} 10 ppm; Th {approx} 52 ppm) are the least enriched in U, Th and K. In contrast, the lower-T granulite-facies Okiep Terrane near Springbok hosts more enriched granites (max. U {approx} 17 ppm; Th {approx} 66 ppm) and noritic intrusions (max. U = 14 ppm; Th = 83 ppm). The most enriched rocks are found in the 1030 Ma higher-T granulite-facies core of the Namaquan belt and include quartzo-feldspathic gneisses (max. U = 46 ppm; Th = 90 ppm) and charnockites (max. U = 52 ppm; Th = 400 ppm). Our findings contradict the notion that granulite-facies terrains are characteristically depleted in U and Th. In this study we modeled the heat production in the core of the Namaquan complex, where the granulites have had a very unusual metamorphic history, and show that ultra-high-T (~1000°C, P ~ 10 kbar) metamorphic conditions could have been achieved by radiogenic heating without invoking external heat sources. However, monazite-rich veins of charnockite and patches of granulites mark the passage of CO2-dominated melts and fluids derived from fractionated noritic intrusions.

Keywords: charnockite; granulite; Namaqualand; thorium; uranium; radioactive heating; metamorphism.
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
 Geological Society, London, Special PublicationsHome page
M. Brown
Metamorphic patterns in orogenic systems and the geological record
Geological Society, London, Special Publications, January 1, 2009; 318(1): 37 - 74.
[Abstract] [Full Text] [PDF]

Home page
 Geological Society, London, Special PublicationsHome page
A. Pettersson, D. H. Cornell, M. Yuhara, and Y. Hirahara
Sm-Nd data for granitoids across the Namaqua sector of the Namaqua-Natal Province, South Africa
Geological Society, London, Special Publications, January 1, 2009; 323(1): 219 - 230.
[Abstract] [Full Text] [PDF]

Home page
 South African Journal of GeologyHome page
A. Kounov, G. Viola, M.J. de Wit, and M. Andreoli
A Mid Cretaceous paleo-Karoo River valley across the Knersvlakte plain (northwestern coast of South Africa): Evidence from apatite fission-track analysis
South African Journal of Geology, December 1, 2008; 111(4): 409 - 420.
[Abstract] [Full Text] [PDF]

Home page
 Journal of the Geological SocietyHome page
M. Brown
Crustal melting and melt extraction, ascent and emplacement in orogens: mechanisms and consequences
Journal of the Geological Society, July 1, 2007; 164(4): 709 - 730.
[Abstract] [Full Text] [PDF]

Home page
 South African Journal of GeologyHome page
R. Bailie, R. Armstrong, and D. Reid
The Bushmanland Group supracrustal succession, Aggeneys, Bushmanland, South Africa: Provenance, age of deposition and metamorphism
South African Journal of Geology, March 1, 2007; 110(1): 59 - 86.
[Abstract] [Full Text] [PDF]

Home page
 South African Journal of GeologyHome page
R. Bailie, R. Armstrong, and D. Reid
Composition and single zircon U-Pb emplacement and metamorphic ages of the Aggeneys Granite Suite, Bushmanland, South Africa
South African Journal of Geology, March 1, 2007; 110(1): 87 - 110.
[Abstract] [Full Text] [PDF]

Home page
 Geological Society of America Special PapersHome page
J. H. Natland
{Delta}Nb and the role of magma mixing at the East Pacific Rise and Iceland
Geological Society of America Special Papers, January 1, 2007; 430(0): 413 - 449.
[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.