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Goethite (U–Th)/He geochronology and precipitation mechanisms during weathering of basalts

Riffel, Silvana B. and Vasconcelos, Paulo M. and Carmo, Isabela O. and Farley, Kenneth A. (2016) Goethite (U–Th)/He geochronology and precipitation mechanisms during weathering of basalts. Chemical Geology, 446 . pp. 18-32. ISSN 0009-2541. doi:10.1016/j.chemgeo.2016.03.033.

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(U–Th)/He geochronology of 33 goethite grains from in situ ferruginous duricrusts overlying the Paraná flood basalt in the Guarapuava region, Paraná, Brazil, reveals ages ranging from 3.6 ± 0.4 to 0.4 ± 0.1 Ma. Thirty-one grains from detrital fragments of ferruginous duricrust yield ages in the 6.2 ± 0.6 to 0.7 ± 0.1 Ma range. The results show that goethites from detrital blocks are generally older than those from the in situ ferruginous layers and that all the goethites from the Guarapuava sites are relatively young (≤ 6.2 ± 0.6 Ma). Goethites show variable U and Th contents depending on the mode of precipitation. Goethite that forms by progressive ferrugization and pseudomorphic replacement of basalts are rich in Th, U-poor, contain various mineral inclusions (e.g., kaolinite, rutile, ilmenite) and display a distinct “checkered” appearance. Colloform goethite precipitated within cavities and desiccation cracks contain higher U, show low Th/U values, and are free of mineral contaminants, suggesting direct precipitation from solution. The geochronological results reveal a dynamic evolution for the soils overlying the Paraná basalt, where recurrent duricrust formation and dismantling lead to the evolution of regional colluvial soil profiles while simultaneously preventing the evolution of chemically stratified lateritic weathering profiles. The modes of formation and U, Th, and He contents of goethite at Guarapuava provide useful constraints on the expected compositions and modes of formation of goethite formed on basaltic soils on Mars.

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Farley, Kenneth A.0000-0002-7846-7546
Additional Information:© 2016 Elsevier B.V. Received in revised form 30 March 2016; Accepted 31 March 2016; Available online 11 April 2016. The authors are grateful for the financial support from CAPES (PhD scholarship 4862-06-6) and CNPq (postdoctoral fellowship), and the logistic and financial support for fieldwork from PETROBRAS/CENPES. We thank ANSTO grants to A. Seeber and P. Vasconcelos for access to the Tsukuba and Australian synchrotrons; A. Seeber for the synchrotron analysis and A. Mostert for the Rietveld refinement of the synchrotron results. This work benefited from editorial comments from Prof. Francois Chaboux and in-depth reviews by H. Handley, P. Reiners, and the anonymous reviewer, whose corrections and suggestions greatly helped to improve the final version of the manuscript.
Funding AgencyGrant Number
Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)4862-06-6
Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)UNSPECIFIED
Australian Nuclear Science and Technology Organisation (ANSTO)UNSPECIFIED
Subject Keywords:Weathering geochronology; (U–Th)/He; Goethite; Paraná Continental Flood Basalts; Landscape evolution
Record Number:CaltechAUTHORS:20170103-091501350
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Official Citation:Silvana B. Riffel, Paulo M. Vasconcelos, Isabela O. Carmo, Kenneth A. Farley, Goethite (U–Th)/He geochronology and precipitation mechanisms during weathering of basalts, Chemical Geology, Volume 446, 23 December 2016, Pages 18-32, ISSN 0009-2541, (
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:73168
Deposited By: Tony Diaz
Deposited On:03 Jan 2017 19:11
Last Modified:11 Nov 2021 05:12

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