Geochemical tracers of source rocks in a Cretaceous to Quaternary sedimentary sequence (Eastern Sierras Pampeanas, Argentina)

Metamorphic rocks, granitic rocks, and sediments from the Eastern Sierras P ampanas: Argentina, were analyzed for major and trace element concentration s, including rare earth elements (REE). Parental rocks exhibit distinctive REE normalized diagram patterns and elemental ratios, and some elemental ra tios reveal significant differences between rock sources. For example, rati os such as Th/Sc, Cr/Th, and La/Cr have a mean value of 0.7, 8.4 and 0.4 in metamorphic rocks, whereas granitic rocks exhibit means of 1.4, 0.7 and 4. 9, respectively. These ratios are also useful in linking detrital materials with the corresponding parental rocks. Metamorphic sources yield sediments with lower Th/Sc and La/Cr, and higher Cr/Th ratios than sediments derived from granitic sources. REE and other elements are enriched in the silt-siz e fraction, whereas they are diluted by quartz in the sand-size fraction. The size of the Eu/Eu* anomaly can be used as a stratigraphical correlation tool in the sedimentary record: Cretaceous rocks show a mean value of 0.9 +/- 0.1, whereas Tertiary rocks have a mean value of 2.9 +/- 0.3. The Eu an omaly in Quaternary and modern sediments ranges from 0.5 to 0.8. (C) 1999 E lsevier Science Ltd. All rights reserved.