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Age and evolution of diachronous erosion surfaces in the Amazon: combining (U-Th)/He and cosmogenic ^3He records

Monteiro, H. S. and Vasconcelos, P. M. P. and Farley, K. A. and Lopes, C. A. M. (2018) Age and evolution of diachronous erosion surfaces in the Amazon: combining (U-Th)/He and cosmogenic ^3He records. Geochimica et Cosmochimica Acta, 229 . pp. 162-183. ISSN 0016-7037. doi:10.1016/j.gca.2018.02.045.

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(U-Th)/He geochronology of two weathered plateaus in the Carajás Mountains, Pará, Brazil, reveals a history of weathering spanning from ca. 80 Ma to the present for this high elevation (∼720 m) land surface. Cosmogenic ^3He measurements of hematite pebbles and blocks cemented onto the plateaus at two sites, N1 and S11D, yield erosion rates as low as 0.09 and 0.08 m.Ma^(-1), respectively. Thus, these results confirm that the plateau surfaces are nearly immune to physical erosion for tens of millions of years. (U-Th)/He geochronology of ferruginous duricrusts blanketing the low elevation (250-100 m) plains surrounding the Carajás Mountains yield results consistently younger than ∼10 Ma. The geochronology results also reveal that the low elevation plain is diachronous, becoming progressively younger towards the receding plateaus. The spatial distribution of (U-Th)/He ages permits reconstruction of the history of scarp retreat for the Carajás landscape, showing that scarp retreat along major river valleys may have been as fast as 20 km.Ma^(-1) during tectonically active and humid periods in the Cenozoic. The cessation of scarp retreat at some sites suggests that metamorphosed banded iron-formations and quartzites provide effective barriers to retreating escarpments, helping to preserve some of the oldest continuously exposed land surfaces on Earth.

Item Type:Article
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URLURL TypeDescription
Monteiro, H. S.0000-0002-3797-1869
Farley, K. A.0000-0002-7846-7546
Additional Information:© 2018 Published by Elsevier Ltd. Received 24 July 2017, Accepted 28 February 2018, Available online 8 March 2018. We thank present and past colleagues from Vale, particularly Carlos Monte Lopes, Luzimar Rego, Clovis Maurity, Paulo Sérgio Machado, Fernando Greco, Fernando Martins, Henrique Meireles, Carlos Augusto de Medeiros Filho, Augusto Kishida, and Felipe Porto for field support and heated discussions on the evolution of Carajás region. This project was funded by the Australian Research Council (ARC Discovery Grant DP160104988), Australian Research Council (ARC Linkage Grant LP4001008005), and the Brazilian Research Council (CNPq), which sponsored Hevelyn Monteiro’s PhD studies. Electronic appendices are available at doi: 10.17632/fgtdnjw3mn.2
Funding AgencyGrant Number
Australian Research CouncilDP160104988
Australian Research CouncilLP4001008005
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)UNSPECIFIED
Record Number:CaltechAUTHORS:20180308-091037841
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Official Citation:H.S. Monteiro, P.M.P. Vasconcelos, K.A. Farley, C.A.M. Lopes, Age and evolution of diachronous erosion surfaces in the Amazon: Combining (U-Th)/He and cosmogenic 3He records, Geochimica et Cosmochimica Acta, Volume 229, 2018, Pages 162-183, ISSN 0016-7037, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:85197
Deposited By: Tony Diaz
Deposited On:08 Mar 2018 17:27
Last Modified:15 Nov 2021 20:26

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