Crustal Contamination of Tertiary Volcanic Rocks: Evidence from K, U, Th and Radiogenic Heat Production Data in Eastern Pontides (NE Turkey)

Abstract

Herein, we present new U-238, Th-232, and K-40 radionuclide concentrations, density and radiogenic heat production (RHP) data on the Tertiary volcanic rocks outcropping in Borcka, Gumushane and Trabzon regions within the Eastern Pon-tide Orogenic Belt (EPOB). The mean K values for Trabzon, Borcka and Gumushane regions were 2.19 +/- 0.87%, 0.90 +/- 0.70% and 0.59 +/- 0.25%, respectively, the mean U values for Trabzon, Borcka and Gumushane regions were 2.12 +/- 0.76 ppm and 1.29 +/- 0.68 ppm and 0.90 +/- 0.32 ppm, and the average Th values were calculated as 6.54 +/- 2.32 ppm, 2.49 +/- 1.93 ppm and 1.33 +/- 0.60 ppm for Trabzon, Borcka and Gumushane regions, respectively. The average Th/U values are 3.38 +/- 1.48 for the Trabzon region, 2.01 +/- 1.22 for the Borcka region, and 1.69 +/- 1.09 for the Gumushane region. Average U/Th values were calculated as 0.35 +/- 0.14, 0.71 +/- 0.52 and 0.89 +/- 0.72 for the Trabzon, Borcka and Gumushane regions, respectively. The RHP values were determined as 1.16 +/- 0.35 mu Wm(-3), 0.58 +/- 0.33 mu Wm(-3) and 0.37 +/- 0.10 mu Wm(-3) for Trabzon, Borcka and Gumushane regions, respectively. The Tertiary aged rocks in the EPOB that we have examined within this study scope have been derived from an enriched mantle, previously metasomatized by fluids derived from subducted slab. The parental magma of Eocene basaltic rocks was contaminated with crustal material during the ascension of the magma through the crust or in the shallow-level crustal magma chambers.