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Cosmogenic ^(3)He in hematite and goethite from Brazilian “canga” duricrust demonstrates the extreme stability of these surfaces

Shuster, David L. and Farley, Kenneth A. and Vasconcelos, Paulo M. and Balco, Greg and Monteiro, Hevelyn S. and Waltenberg, Kathryn and Stone, John O. (2012) Cosmogenic ^(3)He in hematite and goethite from Brazilian “canga” duricrust demonstrates the extreme stability of these surfaces. Earth and Planetary Science Letters, Elsevier (329-330). pp. 41-50. ISSN 0012-821X. https://resolver.caltech.edu/CaltechAUTHORS:20120606-110644084

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Abstract

Helium isotopes were measured in hematite and goethite samples from several lateritiric duricrusts (canga) developed on banded iron formations. These samples uniformly have high ^(3)He concentrations which must arise from long periods of cosmic ray exposure. From coexisting phases from the Quadrilátero Ferrífero in east central Brazil, we determined the ratio of cosmogenic ^(3)He in hematite to that of ^(21)Ne in quartz to be 3.96 ± 0.19. Combined with best current estimates of the ^(21)Ne production rate in quartz, this ratio implies a sea-level high latitude (SLHL) ^(3)He production rate in hematite of 68.1 ± 8.1 atoms/g/yr; from the chemical composition we estimate the ^(3)He production rate in goethite to be ~5% higher. We use these production rate estimates to interpret ^(3)He concentrations measured in goethite and hematite from a ~10 m depth profile collected from a surface canga in Carajás, in the Amazon basin of Brazil. We find that the Carajás canga has experienced a very low rate of surface erosion (~0.16–0.54 m/Myr) over at least the last few millions of years. This iron-rich canga surface is remarkably resistant to erosion despite its location in a wet tropical environment. Details of the depth profile suggest that despite its stability, the canga has also been internally dynamic (translocation of material; solution and reprecipitation) over million-year timescales.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1016/j.epsl.2012.02.017DOIUNSPECIFIED
http://www.sciencedirect.com/science/article/pii/S0012821X1200101XPublisherUNSPECIFIED
ORCID:
AuthorORCID
Farley, Kenneth A.0000-0002-7846-7546
Monteiro, Hevelyn S.0000-0002-3797-1869
Additional Information:© 2012 Elsevier B.V. Received 1 November 2011. Revised 9 February 2012. Accepted 17 February 2012. Available online 21 March 2012. Editor: B. Marty. We thank Vale S.A. for providing us access to the sampling sites at Carajás, Carlos Spier (then at MBR) for providing access and field support for sampling that the Pico Mine, and M. Honda and P.-H. Blard for constructive reviews of the manuscript. Funding was provided by the following sources: UQ-AGES for funding the field sampling exercises at Carajás and Pico, grants NSF- EAR-0738474 (to DLS) and NSF- EAR-0921295 (to KAF), and the Ann and Gordon Getty Foundation.
Funders:
Funding AgencyGrant Number
UQ-AGESUNSPECIFIED
NSFEAR-0738474
NSFEAR- 0921295
Ann and Gordon Getty FoundationUNSPECIFIED
Subject Keywords:cosmogenic nuclide geochronology; 3He; 21Ne; laterite; chemical weathering; production rate calibration
Issue or Number:329-330
Record Number:CaltechAUTHORS:20120606-110644084
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20120606-110644084
Official Citation:David L. Shuster, Kenneth A. Farley, Paulo M. Vasconcelos, Greg Balco, Hevelyn S. Monteiro, Kathryn Waltenberg, John O. Stone, Cosmogenic 3He in hematite and goethite from Brazilian “canga” duricrust demonstrates the extreme stability of these surfaces, Earth and Planetary Science Letters, Volumes 329–330, 1 May 2012, Pages 41-50, ISSN 0012-821X, 10.1016/j.epsl.2012.02.017. (http://www.sciencedirect.com/science/article/pii/S0012821X1200101X)
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:31825
Collection:CaltechAUTHORS
Deposited By: Jason Perez
Deposited On:06 Jun 2012 19:31
Last Modified:09 Mar 2020 13:19

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