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Much of the Mid-European basement has been consolidated during the Variscan Orogeny and includes large volumes of granitic intrusions. Gamma radiation spectroscopic measurements in three study areas along the western margin of the Bohemian Massif give a record of radiogenic element concentrations in the Variscan granites. Most intrusions of the Fichtelgebirge (except for the Tin Granite) and intrusive complexes in the Bavarian Forest show Th/U ratios exceeding unity, most likely related to abundance of monazite. In contrast, some of the Oberpfalz granites located near the Saxothuringian-Moldanubian boundary (Flossenbürg, Steinwald and Friedenfels types) are characterized by higher uranium concentrations and thus Th/U < 1. The low Th/U ratios here are in agreement with a possible U mobilisation along the Saxothuringian-Moldanubian contact zone observed in previous studies. Heat production rates of granites in the three study areas vary between 3.9 and 8.9 µW/m 3 , with a mean of 4.9 µW/m 3. This classifies the intrusions as moderate-to high-heat-producing granites. Considering the huge volume of granitic bodies in the Variscan crust of the Bohemian Massif, the contribution of in situ radiogenic heat production had to have a major impact and should be considered in further thermal modeling.

In NW India, large volumes of exposed Neoproterozoic basement rocks are formed by two magmatic suites, Erinpura granites as a late thermal event with respect to the ∼1 Ga Delhi Orogeny and the younger Malani igneous suite (770-750 Ma). Average uranium and thorium equivalent concentrations (in ppm) inferred from spectroscopic gamma radiation survey are higher in Malani rocks (Th 47.33 ppm and U 6.95 ppm) as compared to the Erinpura granites (Th 33.55 ppm and U 4.77 ppm). These values are considerably above the granite world average (Th 14.8 ± 13.2 ppm; U 3.93 ± 3.27 ppm). High U (up to 19 ppm) and Th (up to 88 ppm) in some Malani granites and a constant Th-U ratio of 7 points to a high degree of fractionation of the felsic magma. Higher radioelement concentration in the east (Mirpur granite) as compared to the west (Jaswantpura granite) is substantiated by geochemical data. Areas to the west and east of the Sirohi frontal thrust show differences, most likely a consequence of anatexis in the eastern sector. A high linear correlation between inductively coupled plasma mass spectrometry and gamma-ray data underlines the suitability of in-situ measurements for the determination of U and Th concentrations during a field survey providing basic information for future petrogenetic and risk-hazard studies in this granitic terrain.

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The Permo-Triassic Mass Extinction (PTME) was the most catastrophic biocrisis of the entire Phanerozoic. About 90% of all marine species became extinct near the P-Tr boundary, including all tabulate and rugose corals, trilobites and several brachiopod types, and many other groups including conodonts and ammonoids were severely affected (e.g., Bond & Grasby, 2017; Bond & Wignall, 2014; Erwin, 1994). The main phase of extinction occurred over a short time interval in the latest Permian (e.g., Bond & Grasby, 2017), this Late Permian Extinction (LPE) phase is recorded immediately below bed 25 in the Meishan stratotype section, with a second phase recorded in the basal Triassic at the bed 28/29 boundary at this location (Song et al., 2013). The absolute ages of these horizons are constrained by U-Pb zircon ages of 251.941 ± 0.037 and 251.880 ± 0.031 Ma for beds 25 and 28 respectively (Burgess et al., 2014), a period of 61 ± 48 kyr. These ages overlap with the ages of flood basalt volcanism in Siberia (251 Ma), at which time >2 × 10 6 km 3 of lava were erupted within a few 100 kyr (

The timing and mechanisms of the climatic and environmental perturbations induced by the emplacement of the Deccan Traps large igneous province (India) and their contribution to the Cretaceous-Paleogene (K-Pg) mass extinction are still debated. In many marine sediment archives, mercury (Hg) enrichments straddling the K-Pg boundary have been interpreted as the signature of Deccan Traps volcanism, but Hg may also have been derived from the Chicxulub (Mexico) impact. We investigated the Hg isotope composition, as well as the behavior of iridium (Ir) and other trace elements, in K-Pg sediments from the Bidart section in southwest France. Above the K-Pg boundary, Ir content gradually decreases to background values in the Danian carbonates, which is interpreted to indicate the erosion and redistribution of Ir-rich fallouts. No significant enrichment in Ir and W, or Zn and Cu, is observed just below the K-Pg boundary, excluding the hypothesis of downward remobilization of Hg from the boundary clay layer. Positive Δ199Hg and slightly negative values in the upper Maastrichtian and lower part of the early Danian are consistent with the signature of sediments supplied by atmospheric Hg2+ deposition and volcanic emissions. Up section, large shifts to strongly negative mass-dependent fractionation values (δ202Hg) result from the remobilization of Hg formerly sourced by the impactor or by a mixture of different sources including biomass burning, volcanic eruption, and asteroid impact, requiring further investigation. Our results provide additional support for the interpretation that the largest eruptions of the Deccan Traps began just before, and encompassed, the K-Pg boundary and therefore may have contributed to the K-Pg mass extinction.

The origin and evolution of granites remain a matter of debate and several approaches have been made to distinguish between different granite types. Overall, granite classification schemes based on element concentrations and ratios, tectonic settings or the source rocks (I-, A-, S-type) are widely used, but so far, no systematic large-scale study on Th/U ratio variations in granites based on their source or tectonic setting has been carried out, even though these elements show very similar behavior during melting and subsequent processes. We therefore present a compiled study, demonstrating an easy approach to differentiate between S-, A- and I-type granites using Th and U concentrations and ratios measured with a portable gamma ray spectrometer. Th and U concentrations from 472 measurements in S- and I-type granites from the Variscan West-Bohemian Massif, Germany, and 78 measurements from Neoproterozoic A-type Malani granites, India, are evaluated. Our compendium shows significant differences in the average Th/U ratios of A-, I- and S-type granites and thus gives information about the source rock and can be used as an easy classification scheme. Considering all data from the studied A-, I- and S-type granites, Th/U ratios increase with rising Th concentrations. A-type granites have the highest Th/U ratios and high Th concentrations, followed by I-type granites. Th/U ratios in S- to I-type granites are lower than in A-type and I-type granites, but higher than in S-type granites. The variation of Th/U ratios in all three types of granite cannot be explained by fractional crystallization of monazite, zircon and other Th and U bearing minerals alone, but are mainly due to source heterogeneities and uranium mobilization processes.

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