T36 Advances in Non-Traditional Stable Isotope Measurements and Utility as Proxies in Modern and Paleo-Settings (Posters)

Sunday, 15 October 2023
8:00 AM - 5:30 PM
Hall B

MOLYBDENUM ISOTOPE COMPOSITION OF SIBERIAN TRAPS BASALTS: IMPLICATIONS FOR SOURCE CONTRIBUTIONS

Paper number: T36-5
Program: Technical Sessions
Time: 8:00 AM – 5:30 PM

Authors

Abstract

The Siberian Traps Large Igneous Province (STLIP) is the most voluminous continental magmatic event of the Phanerozoic. The STLIP has been linked to the Permian–Triassic mass extinction, and has produced the world-class Norilsk and Talnakh Cu–Ni–PGE magmatic sulphide ore deposits. Despite the numerous studies that have characterized the petrogenesis of the STLIP, questions surrounding the mantle source remain. To address this knowledge gap, we report new Sr, Nd, and Hf radiogenic isotopes, and Mo stable isotopes to characterize the mantle source of the STLIP. We characterized eleven volcanic formations (approximately 2 km of lava thickness), two sills, and three potential contaminants — anhydrite, coal, and black shale from the Norilsk region. The 87Sr/86Sr(i) and 143Nd/144Nd(i) data are consistent with previous work from the STLIP basalts, and can be interpreted as magma–crust interaction between a melt from a relatively depleted mantle source (εNd(i) of ~4), and granitic and/or metasedimentary rock (εNd(i) <- 15). In εNd–εHf space, the STLIP basalts plot along the terrestrial array.

The δ98Mo (values normalized to NIST SRM3134) in the STLIP basalts range from -0.6‰ to 0.07‰ (mean=-0.17, 2sd=0.21, n=37). The Norilsk ore body has δ98Mo ~ 0.0. The coupled Mo-Sr-Nd-Hf isotope compositions are inconsistent with assimilation of anhydrite (δ98Mo = 0.35‰), coal (δ98Mo = 0.06‰ to -0.15‰) or black shale (δ98Mo= -0.08‰) due to the relatively low Mo concentrations of the later. δ98Mo shows a weak correlation with crustal assimilation, assuming a continental crust with δ98Mo = 0.15‰. However, the most radiogenic, high-Mg Gudchinchinski lavas, with high Gd/Yb ratios ~ 2.6 that imply a source within garnet stability field (>80 km depth), show a large range of δ98Mo (-0.4 to 0.05‰), compared to the upper mantle (~-0.21 +/-0.06 ‰). When combined with the low Mo/Ce (<0.01-0.03) ratios of these lavas, we infer a subduction-modified source for the plume, that comprises a dehydrated eclogite with low δ98Mo and Mo/Ce.

Geological Society of America Abstracts with Programs. Vol. 55, No. 6

doi: 10.1130/abs/2023AM-392448

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