A041-0016
Loess Geochemistry and Upper Crustal Composition of India : Comparison with Global loess and Global UCC

Tuesday, 8 December 2020
Poster
Esha Ray, Indian Institute of Technology Kanpur, Kanpur, India, Debajyoti Paul, Indian Institute of Technology Kanpur, Department of Earth Sciences, Kanpur 208016, India, Jitendra K Dash, Project Emplyoee, Department of Earth Sciences Pondicherry University, Puducherry, India and Rajneesh Bhutani, Professor & H.O.D, Department of Earth Sciences, Puducherry, India
Abstract:
Loess is a silt-dominated yellowish-brown colored glacial or aeolian deposit of Pleistocene age, which covers almost 10% of Earth’s surface. In this study, we obtained major, trace elements including REEs, and Sr and Nd isotope composition of eleven different loess and dune deposits from Kashmir, Rajasthan, Uttarakhand, and Son valley in India. Although the major element composition of Indian loess deposits are compositionally slightly different (contains low SiO2 and Al2O3 but high CaO), from other global loess (such as China, Argentina, Europe, USA, Norway, New Zealand, Tajikistan etc.) and UCC, the chondrite-normalized REE patterns exhibit remarkable similarity suggesting thorough mixing and recycling of upper crustal sources. The average La/YbN~12 in Indian loess is similar to the granodioritic upper continental crust (La/YbN ~10). The La/Th ratio of 3.2±0.1 in Indian loess is similar to that in the global loess, UCC and other global post-Archean shales. Indian loess show fractionated REE (La/YbN=11.2-14.8), relatively flat HREE pattern (Gd/YbN=1.9–2.3), and a conspicuous negative Eu-anomaly (Eu/Eu*: 0.65-0.80), suggesting an origin from upper crustal granitoids. The average Chemical Index of Alteration (CIA) values of 68±3 (n=17) in Indian loess is similar to that in the global loess as well as in the Indian shales, indicating moderate chemical alteration. The 87Sr/86Sr and 143Nd/144Nd ratios in the Indian loess vary in ranges 0.71457±3‒0.72727±12 and 0.511908±5‒0.512091±6 (ꜫNd = ‒10.51 to ‒14.08), respectively whereas the present-day 87Sr/86Sr and 143Nd/144Nd composition of global loess show a wide range of variation (0.70956±3‒0.71850±7 and 0.511573±24‒0.511061±21, ꜫNd = ‒5.1 to ‒15.1 respectively). The Nd-Sr isotopic compositions of Indian as well as global loess suggest contribution from the upper continental crustal source. The new data along with previously published data on Indian loess can be used as a proxy for the composition of the Indian upper continental crust.
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