A review for genesis of continental arc magmas: U, Th, K and radiogenic heat production data from the Gümüşhane Pluton in the Eastern Pontides (NE Türkiye)

Abstract

In this study, in situ radioelemental (238U, 232Th and 40K) measurements and heat production rate evaluation have been conducted at 132 sites in the Gümüşhane Pluton of the Eastern Pontides Orogenic Belt (EPOG) of Northern Türkiye. The average K, U and Th values for granites are 4.35±0.71%, 5.85±2.74ppm, 22.13±5.55ppm, respectively; microgranites 4.33±1.37%, 7.12±2.23ppm, 24.11±9.59ppm; metagranite 3.93±0.68%, 6.24±2.75ppm, 12.87±3.92ppm; andesite/basalt 1.75±0.74%, 3.22±1.07ppm, 9.01±5.14ppm. Based on the abundances of K, U and Th, the radiogenic heat production (RHP) values, which is a reflection of the geological rock types, are estimated as 3.52±1.03μWm−3, 3.86±1.31μWm−3, 2.93±0.89μWm−3, and 1.68±0.63μWm−3 for granites, microgranites, metagranites and andesite/basalt, respectively. The average heat production value for the study area is estimated as 2.83±1.39μWm−3, which is closer to the upper continental crustal value; contrary to the highest heat production value of granitic basement and the lowest heat production values of the sedimentary rocks.The study region is depicted with very high level of Th/U value ranging from 0.11 to 23.19 with mean value of 3.53±2.5, which is comparatively close to the upper continental crustal estimate of 3.8. The numerical results verify that mantle-derived magmas are subjected to contamination with both middle and lower crustal material constituted by fragments of southerly dipping subduction of Tethys Ocean during the late Mesozoic–Cenozoic.