Radiogenic heat production of Variscan granites from the Western Bohemian Massif, Germany

Abstract

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.

Origin of S-, A- and I-Type Granites: Petrogenetic Evidence from Whole Rock Th/U Ratio Variations

“…It uses a bismuth germinate (BGO) scintillation detector. Individual data (550 samples) and coordinates of locations are all recorded in our previous published papers [74,75], but can also be found in Table S1. We provide statistical evaluation in Table S2 and statistical analysis using the Mann-Whitney pairwise U-test with Bonferroni correction (Past 4.01) in Table S3 (see Supplementary Materials).…”

“…Compared with the granites from the worldwide granite database GRAN-ITE2017 [23], the studied granites are typical for S-, I-and S-to I-type granites. Data on radioelement concentration have been obtained from in situ gamma radiation measurements, reported in previous studies [74,75].…”

“…The following are available online at https://www.mdpi.com/article/ 10.3390/min11070672/s1, Table S1: Th and U concentrations of the A-type, S-type, I-type and S-I-type granites from the Fichtelgebirge, Oberpfalz, Bavarian Forest and India (550 samples). All measurements and coordinates of locations are recorded in our previous published papers [74,75], Table S2: Statistical evaluation of the data. Shown here the mean, standard deviation (1 sigma) and the mean square error, Table S3: Statistical analysis using the Mann-Whitney U pairwise test with Bonferroni correction (Past 4.01).…”

“…Measured samples are from within the frame.Geological map after[81]. Coordinates of the sample locations can be found in[74,75].…”

“…However, A-type granites tend to have higher Th concentrations, I-type granites have moderate concentrations (marked with the ellipse) and S-type granites tend to have higher U concentrations. Abbreviations: FG: Fichtelgebirge (Region 1), OPf: Oberpfalz (Region 2), BF: Bavarian Forest (Region 3), HB: Hauzenberg, MIS: Malani Igneous Suite, gamma-ray data from in situ measurements of gamma radiation[75]; MIS A-type geochemical data: U and Th values from geochemical analyses from the Mt. Abu batholith[79,86].…”