Geochemistry of Proterozoic Delhi Quartzites: Implications for the Provenance and Source Area Weathering

Mineralogy and geochemistry, including REE, of the Proterozoic Delhi quartzites have been studied to understand the processes and provenance involved in the origin of supermature quartzites. Post Archaean Australian Shale (PAAS) like chondrite normalised REE patterns, including negative Eu anomalies but with low abundance, show that the source for the quartzites was dominanted by evolved granitic rocks. High weathering indices (CIA) and strong negative Eu anomaly suggest that the source area had gone through intensive chemical weathering. We infer that the PAAS like pattern for the quartzites was inherited from the granitic source rocks through quantitative transfer of REE bearing heavy minerals. These heavy minerals (-0.7%) supplied nearly 60% of the total REE. The quantitative transfer of heavy minerals and conservation of REE patterns with respect to the source are likely due to the lack of any selective sorting of heavy minerals indicating a very low degree of recycling. One possible explanation for this type of transfer is the formation of mature weathering profiles. Mature weathering profiles on the stable craton could give rise to mature upper silica rich horizons and lower horizons rich in fine-grained clays due to illuviation and downward transport. The upper horizons could have acted as source for the quartzose sands and resistant REE bearing heavy minerals for the quartzites. The lower horizons could become a likely source for the argillaceous material overlying the quartzites during subsequent sedimentation.