<p>The Kamthai carbonatites form part of the Sarnu-Dandali alkaline complex (SDAC) of Rajasthan, western India. The SDAC is one of several alkaline intrusive complexes emplaced prior to the Deccan continental flood basalt eruptions. Considered as one of the earliest Deccan-Reunion plume related magmatic activities, the rocks of the complex hold clues to many tectonomagmatic processes such as plume-lithosphere interaction, mantle melting prior to flood basalt volcanism, and carbonatite-plume relationship, apart from the outstanding questions pertaining to the origin of carbonatites themselves, and their association with alkaline silicate rocks. To understand some of these processes vis-&#224;-vis the evolution of the complex, we have carried out a detailed field, petrographic, geochronological (<sup>40</sup>Ar/<sup>39</sup>Ar), geochemical, and Sr-Nd-Pb-C-O isotopic investigation. Phlogopites from carbonatites yield an age of 68.6 Ma, identical to the ages determined for the three associated phonolite dykes. Interestingly, an earlier study reports the presence of older (89-86 Ma) subvolcanic and volcanic bodies in the complex, thus suggesting recurrent alkaline magmatism. Carbonatites of Kamthai occur as veins, dykes, and small plugs, along with dykes/plugs of ijolite, nephelinite, syenite and phonolite etc. The SDAC intrudes into the basement made up of Malani Rhyolites. The stable C-O isotopic compositions of unaltered carbonatites (&#948;<sup>13</sup>C<sub>PDB</sub>= -6.6 to -4.6 &#8240;; &#948;<sup>18</sup>O<sub>SMOW</sub>=5.5 to 9.5 &#8240;), which are predominantly calcite carbonatites, not only confirm the magmatic nature of the rocks but also show evidence of fractional crystallization. The chondrite-normalized rare-earth element patterns of the carbonatites and alkaline silicate rocks show LREE enriched patterns, with the former possessing abnormally high contents of LREE. The average (<sup>87</sup>Sr/<sup>86</sup>Sr)<sub>i</sub> and &#949;<sub>Nd</sub>(t=68.5 Ma) for carbonatites are 0.7043&#177;0.0001 and 2.4&#177;0.2, respectively, which are indistinguishable from those for the alkaline silicate rocks (<sup>87</sup>Sr/<sup>86</sup>Sr)<sub>i</sub>= 0.7045&#177;0.0003; &#949;<sub>Nd</sub>(t)=2.4&#177;0.4), which suggests common parentage. All these data point towards a petrogenetic link between the 68.6 Ma carbonatites and alkaline silicate rocks of the SDAC, either through liquid immiscibility or fractional crystallization of a common parental magma. Overlapping initial Sr-Nd isotopic ratios of these rocks with those of the least contaminated Deccan lava flows and the Reunion island rocks suggest a possible genetic link between the SDAC and the Deccan-Reunion plume.&#160;</p>
Sediment transfer from the interiors of the Himalaya is complex because the archives are influenced by both glacial and monsoonal cycles. To deconvolve the coupling of glacial and monsoonal effects on sediment transfer processes, we investigate the Late Pleistocene–Holocene sediment archive in the Upper Chenab valley. Optically stimulated luminescence (OSL) ages from the archive indicate major aggradation during ca. 20–10 ka. Isotopic fingerprinting using Sr-Nd isotopes in silt fractions together with clast counts in boulder-pebble fractions indicate a decreasing Higher Himalayan sediment flux in the archive with time. Decreasing clast size, increasing clast roundness, increasing matrix to clast ratio, and dominance of the Higher Himalayan sourcing unequivocally suggest strong glacial influence during the initial stages of the archive formation. This evidence also agrees with the existing retreat ages of glaciers in the Upper Chenab valley. Results of our study also show that the upper parts of the archive contain significant fluvial sediment contribution from the Lesser Himalaya, which suggests an active role of the stronger Indian Summer Monsoon (ISM) in the region during the Early Holocene. The apparent decrease in sediment supply from the Higher Himalayan sources could have been due to longer source-to-sink transport in the Early Holocene and/or increased hillslope flux from Lesser Himalayan sources.
India is one of the oldest maritime nations in the world, and the overseas contacts date back to the third millennium BCE. Besides several archaeological vestiges, numerous stone anchors of various types have been documented during maritime archaeological explorations along the Indian littoral. During a recent maritime archaeological exploration, a broken Indo-Arabian stone anchor, of the Medieval period, was discovered along the Manikapatna coast of Odisha, Indian eastern littoral. In an attempt to determine the provenance of the anchor, we carried out a detailed petrographic, geochemical (major/trace elements) and Sr-Nd isotopic investigation. The results of our study reveal that the stone of the anchor had been cut out of a geologically young, vesicular, alkali basalt lava flow. Source fingerprinting done using petrographic, geochemical and isotopic data, suggests that contrary to the general perception, the anchor rock did not come from any local rock formations. All data point to the most likely scenario that it was sourced from one of the Deccan Traps lava flows of Palitana in the Saurashtra region of Gujarat, western India. This confirms the Medieval maritime trading between western and eastern Indian states.
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