Trace Elements of Pegmatitic Quartz and Their Regional Distribution in two Pegmatite Fields of Southern Norway

Abstract

In this article, we analyzed the trace elements Li, Ge, Al, and Ti in quartz of 155 granitic pegmatites from the Froland and Evje-Iveland pegmatite fields by laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS). These elements are the most common trace elements in quartz, and their concentrations can be utilized to determine the degree of melt fractionation (Al, Li, and Ge) and the crystallization temperature of pegmatites applying the Ti-in-quartz geothermometer. Both pegmatite fields are part of the south Norwegian pegmatite province which was formed during the Sveconorwegian orogenesis at the western margin of the Fennoscandian shield, when the Bamble Complex was thrust over the Telemark Block along the Porsgrunn-Kristiansand Fault Zone (PKFZ).Quartz of the Froland pegmatites has relative homogeneous compositions with 11.8±6.7 ppm Li, 1.5±0.8 ppm Ge, 44.7±22.7 ppm Al, and 7.7±3.3 ppm Ti. The low Ti corresponds to crystallization temperatures of 535±31 °C. The temperatures are highest along the NW margin of the pegmatite field (>550 °C), close to the PKFZ. The most differentiated pegmatites occur along the northeastern margin of the field, away from the PKFZ.Quartz of the Evje-Iveland pegmatites has more variable compositions with 7.3±4.5 ppm Li, 3.0±2.9 ppm Ge, 81.7±58 ppm Al, and 21.4±11.4 ppm Ti. The high Ti indicates crystallization temperatures of 582±48 °C. The highest crystallization temperatures were detected along the northern margin of the EvjeIveland field and in a 12-km long, 2-km wide, N-S striking belt in the center of the field. Low crystallization temperatures were detected in the central east and southwest part of the Evje-Iveland field. Keywords: quartz, pegmatite, LA-ICP-MS, Evje, Froland INTRODUCTIONStudies of the chemistry of pegmatite quartz are relatively rare [1] due to the low contents of trace elements and consequent difficulty in obtaining reliable analytical results. More recently, with the development of microbeam techniques enabling the precise in situ determination of trace element in quartz [2,3], studies of pegmatite quartz have become more frequent [4][5][6]. These studies showed that the trace element signature of quartz in pegmatites reflects the composition and pressure-temperature (P-T) conditions of the melt from which the quartz crystallized. For example, the Ti concentration in quartz is a function of the crystallization temperature [7], and concentrations of Al, Li, and Ge reflect the abundance of these elements in the melt and, thus, the degree of melt fractionation [6].

Trace element composition of quartz from different types of pegmatites: A case study from the Moldanubian Zone of the Bohemian Massif (Czech Republic)

“…After several pioneering studies from the 1960s to the 1980s (Dennen, 1967;Lyakhovich, 1972;Suttner and Leininger, 1972;Schrön et al, 1988), further investigations addressing the composition of igneous quartz were published during the last decade as a result of the improvement in microanalytical methods. Apart from numerous studies of quartz from granites (Jacamon and Larsen, 2009;Müller and Koch-Müller, 2009;Breiter and Müller, 2009;Deans, 2010;Breiter et al, 2012bBreiter et al, , 2013, several authors focused their interest on quartz from granitic pegmatites (Larsen et al, 2000(Larsen et al, , 2004Götze et al, 2004Götze et al, , 2005Müller et al, 2008a;Beurlen et al, 2011;Müller and Ihlen, 2012). Unfortunately, the majority of these studies characterized each pegmatite body by investigating only one representative sample without any data regarding the internal structure of the pegmatite.…”