From Volcanic Source to Sedimentary Sink - Tellurium as a proxy for LIP volcanism

Tellurium is a highly volatile, chalcophile and moderately siderophile trace element that is strongly enriched in volcanic gases relative to crustal rocks. Like mercury, tellurium concentrations in sediments can therefore represent a proxy for past volcanic activity, allowing the timing of LIP volcanism relative to environmental and biotic change during mass extinction events to be determined. Previous studies reported high Te contents in sedimentary rocks at the Permian-Triassic, Cretaceous-Paleogene and Paleocene-Eocene boundaries, which may be linked to eruption of the Siberian, Deccan, and North Atlantic flood basalts, respectively.

Due to the low abundance of Te in most geological materials, and the relatively high ionization energy of Te, this element is rarely analyzed and its geochemical behavior is poorly understood. We have developed methods for analysis of nanogram amounts of Te (and other trace elements) using desolvating nebulizer ICP-MS. Addition of a single-step cationic exchange preconcentration allows analysis of samples containing ppt levels of Te. Using these methods, we carried out analyses of different geological materials, in order to advance our understanding of the behavior of Te in volcanic and sedimentary systems and assess its potential as a proxy for volcanic activity.

Glacial diamictite composites, previously used to estimate the average composition of the Upper Continental Crust (UCC), yield an average Te concentration of 36.7 ± 0.5 ng/g. Assuming this is representative of average UCC, this enrichment in Te relative to estimates of the primitive mantle (silicate Earth) of about 12 ng/g, despite tellurium’s moderately compatible behavior during mantle melting, may indicate that Te has been concentrated in the UCC due to volcanic and hydrothermal processes.

Deccan flood basalts that have not fractionated sulfide, have low Te concentrations (average 0.94 ppb, n=12) relative to MORB (3 – 5 ppb), suggesting that Te was largely degassed during emplacement of the subaerial Deccan lavas at 66.5 – 65.5 Ma. By contrast, the red boles (fossil soil horizons) interbedded with Deccan lavas, have high Te concentrations of up to 2200 ppb, indicating that significant amounts of Te were released during volcanism, some of which was deposited close to the site of volcanism. This observation agrees with data of several thousand sedimentary rocks from profiles across the K-Pg boundary in Italy, Egypt, Morocco, Turkey and Spain, thus supporting the use of Te as a geochemical proxy for LIP volcanism.