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Geochemistry of late quaternary sediments from Tecocomulco lake, central Mexico: Implication to chemical weathering and provenance |
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| Authors: | PD Roy M Caballero W Smykatz-Kloss |
| Institution: | a Departamento de Geomagnetismo y Exploración, Instituto de Geofisica, Universidad Nacional Autónoma de México, 04510 Mexico City, Mexico b Centro de Investigaciones en Ciencias de la Tierra, Universidad Autónoma del Estado de Hidalgo, 42184 Pachuca, Mexico c Instituto de Geología, Universidad Nacional Autónoma de México, 04510 México City, Mexico d Institut fuer Mineralogie und Geochemie, Universitaet Karlsruhe, 76131 Karlsruhe, Germany |
| Abstract: | This paper presents the first detailed multi-element geochemical data from the late Quaternary sediments of the Tecocomulco lake basin (central Mexico) and rocks exposed in the basin catchments to understand the extents of chemical weathering and provenance of the siliciclastic fractions. Ternary diagrams of A-CN-K, A-C-N and A-CNK-FM and elemental ratios suggest that most of the lacustrine sediments were derived from mafic volcanic deposits comprising the Chichicuatla and the Apan-Peñon andesites and the Apan-Tezontepec basaltic-andesites. The felsic tephra layers have chemical compositions comparable to the Acoculco volcanic sequences. The calculated indices of chemical weathering such as chemical index of alteration (CIA), plagioclase index of alteration (PIA) and chemical index of weathering (CIW) indicate low to extreme chemical weathering for the lacustrine sediments and low chemical weathering for tephra layers. The varying degree of chemical weathering in lacustrine sediments is related to the fluctuating average annual precipitation during the late Quaternary. However, the low weathering of tephra layers are due to their higher rate of deposition. The dacite-rhyolitic tephra layers of ca. 31,000 14C yr BP are relatively more weathered compared to the unweathered rhyolitic tephra of ca. 50,000 14C yr BP. This could be due to the rapid deposition of ca. 200 cm of tephra layers during the ca. 50,000 14C yr BP volcanic eruption that might have prevented the interaction between tephra layers and weathering agents. |
| Keywords: | Chemical weathering Provenance Geochemistry Tecocomulco lake Mexico |
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