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A combined (U-Th)/He and cosmogenic ^3He record of landscape armoring by biogeochemical iron cycling

Monteiro, H. S. and Vasconcelos, P. M. P. and Farley, K. A. (2018) A combined (U-Th)/He and cosmogenic ^3He record of landscape armoring by biogeochemical iron cycling. Journal of Geophysical Research. Earth Surface, 123 (2). pp. 298-323. ISSN 2169-9003. https://resolver.caltech.edu/CaltechAUTHORS:20180130-105653677

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Abstract

(U‐Th)/He geochronology and cosmogenic ^3He in iron oxides reveal mineral precipitation ages as old as 55 Ma and exposure ages greater than 5 Ma for canga‐cemented plateaus in the Quadrilátero Ferrífero, Brazil, showing that lateritic profiles overlying banded iron‐formation (BIF) landscapes in tropical regions have a long history of surface exposure. The long‐term erosion history obtained from cosmogenic ^3He on BIF plateaus confirms that relic surfaces persist in the landscape for millions of years. Combined ^3He and (U‐Th)/He dating shows that cangas are preferentially goethite cemented by biogeochemical reactions in the subsurface. Importantly, pebbles of hematite‐magnetite in colluvia or shallow creeks draining the canga‐cemented plateaus record a much longer exposure history than in situ canga blocks, showing that even older duricrusts, now eroded, once blanketed these plateaus. Physically stable but biogeochemically dynamic, cangas armor the landscape by pervasive and recurrent iron cycling and cementation, slowing down the delivery of weathered BIF or friable hematite–magnetite ore to erosion.


Item Type:Article
Related URLs:
URLURL TypeDescription
https://doi.org/10.1002/2017JF004282DOIArticle
http://onlinelibrary.wiley.com/doi/10.1002/2017JF004282/abstractPublisherArticle
ORCID:
AuthorORCID
Monteiro, H. S.0000-0002-3797-1869
Farley, K. A.0000-0002-7846-7546
Alternate Title:A combined (U-Th)/He and cosmogenic 3He record of landscape armoring by biogeochemical iron cycling
Additional Information:© 2018 American Geophysical Union. Received 8 MAR 2017; Accepted 5 DEC 2017; Accepted article online 29 JAN 2018; Published online 20 FEB 2018. We thank Shirley Barros, Carolina Silva, MBR and Vale for logistic support; UQ‐CMM staff for help during microanalysis; and, particularly, Lindsey Hedges for help and guidance during (U‐Th)/He analyses. We also thank D. Granger, A. Ault, M. Schulz, and two Editors from JGR for their constructive comments and suggestions. This project was supported by the Australian Research Council (ARC Discovery grant DP160104988) to Paulo Vasconcelos and Kenneth Farley and the Brazilian Research Council (CNPq), which sponsored Hevelyn Monteiro's PhD studies. Geochronological data set is available at http://dx.doi.org/10.1594/IEDA/100730.
Funders:
Funding AgencyGrant Number
Australian Research CouncilDP160104988
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)UNSPECIFIED
Subject Keywords:(U-Th)/He dating; canga; Cosmogenic 3He; BIF landscapes
Issue or Number:2
Record Number:CaltechAUTHORS:20180130-105653677
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20180130-105653677
Official Citation:Monteiro, H. S., Vasconcelos, P. M. P., & Farley, K. A. (2018). A combined (U-Th)/He and cosmogenic 3He record of landscape armoring by biogeochemical iron cycling. Journal of Geophysical Research: Earth Surface, 123, 298–323. https://doi.org/10.1002/2017JF004282
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:84577
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:31 Jan 2018 00:13
Last Modified:03 Oct 2019 19:20

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