REE Characteristics and REE Mixing Modeling of the Proterozoic Quartzites and Sandstones

摘要

Rare earth elements (REE) in sedimentary rocks are most suitable for source rock characterization. Rare earth element data of the sandstones of the unmetamorphosed Meso-Neoproterozoic Chhattisgarh and Indravati basins and the metamorphosed Paleoproterozoic Sakoli and Saucer basins of the Bastar craton have been studied for source rock characterization. The quartzites have higher ∑R EE mean value (145 ppm) compared to the sandstones (34 ppm). The REE patterns of all the three formations of the Chandarpur Group of the Chhattisgarh basin and the Tiratgarh Formation of the Indravati basin are uniform and there are no systematic differences in REE patterns among different formations of the Chandarpur Group and the Tiratgarh Formation. The REE patterns of the quartzites are similar to the REE patterns of the sandstones. Chondrite-normalized REE patterns with LREE enrichment and a strong negative Eu anomaly of the sandstones and quartzites gives a broad hint about felsic source rocks. The source rocks are identified as Archean granite and gneiss of the Bastar craton. The REE mixing modeling of the sandstones and quartzites suggest that the exposed the Proterozoic upper crust of the Bastar craton during the sedimentation of the Paleoproterozoic Sakoli and saucerand the Meso-Neoproterozoic Chhattisgarh and Indravati basins of the Bastar craton was largely consisted of gneissic rocks (70%), with a little contribution (20%) from Late Archean (2.5 Ga) granites. The present study does not suggest any significant change in the upper crustal composition during Proterozoic in the Bastar craton.