Trace element chemistry and textures of quartz during the magmatic hydrothermal transition of Oslo Rift granites

Abstract

This study documents the textures and chemical evolution of igneous quartz (Qz) in granite from the Oslo Rift (Norway) during the magmatic-hydrothermal transition. Contrary to the other major igneous phases, primary quartz is well preserved. SEM-CL imaging documents four types of quartz (Qz1— Qz4). Qz1: bright primary magmatic quartz that grew under H2O-undersaturated conditions and developed a conspicuous sector zoning. Qz2: light grey luminescent secondary quartz that surrounds Qz1 and altered Qz1 in a ‘non-destructive’ process. Qz3: is usually darker than Qz2 and intersects Qz1 and Qz2. It is formed by dissolution/recrystallization processes involving saline deuteric fluids. Qz4: found in narrow cracks and patches of black quartz intersecting all the other types. EPMA in situ analyses of the different quartz generations confirm that the intensity of luminescence of quartz is positively correlated with the Ti content of the quartz. Aluminium and K are mostly incorporated in quartz in the form of [AlO4/K+]0 centre defects. In the Drammen granite, the Ti and Al contents of Qz1 averages 200 ppm and 80 ppm respectively. Titanium in Qz1 varies from 50 to 95 ppm in the peralkaline granite known as ekerite, whereas Al is irregular and ranges between 100 ppm and values below the limit of detection (LODAl at 2σ = 14 ppm). In all samples, Qz2 and Qz3 are strongly depleted in Ti and Al compared to Qz1. Either the Ti content in Qz2 is falling gradually towards Qz1 or more abruptly, whereas it is sharp from Qz3 towards Qz1 and Qz2. Potassium is variable in all four quartz types and samples, and ranges from values below the detection limit (LODk, at 2σ = 8 ppm) to 120 ppm. Grains in Qz4, being only 1–2µm wide, could not be resolved with the EPMA beam. In all granites, quartz crystallized from haplogranitic melts at P ~1.5 kbar and T = 700—750°C. SEM-CL and EPMA studies of igneous Oslo Rift quartz illustrate vividly the complex chemical and physical processes that characterize the magmatic-hydrothermal transition in shallow granitic systems and show that the chemistry of primary aqueous fluids is strongly modified from its primary igneous composition before eventually being expelled from the granitic system and perhaps incorporated in ore-forming hydrothermal convection systems.

Contact Metamorphism of Precambrian Gneiss by the Skaergaard Intrusion

“…Ghiorso & Gualda, 2013), assuming that equilibrium can be achieved (see Huang & Audetat, 2012;Morgan et al, 2013). For melt-present crystallization, several studies demonstrate that in silicic volcanic systems, aTiO 2 typically varies by 50·5 between compositionally similar samples from the same location (Leeman et al, 2012;Aude¤ tat, 2013;Ghiorso & Gualda, 2013;Kularatne & Aude¤ tat, 2014). These studies are not directly applicable to a contact metamorphic setting where melt fractions are significantly smaller.…”

“…A prominent peak at 415 nm is positively correlated with Ti concentration (Mu« ller et al, 2002(Mu« ller et al, , 2005Rusk et al, 2006Rusk et al, , 2008Spear & Wark, 2009), and this luminescence is expected to dominate parachromatic images at Ti contents 440^50 ppm (Mu« ller et al, 2000(Mu« ller et al, , 2002Larsen et al, 2009). The Ti content of quartz is proportional to the crystallization temperature (Wark & Watson, 2006;Thomas et al, 2010).…”

“…The two different calibrations by Thomas et al (2010) and Huang & Aude¤ tat (2012) yield temperatures that can differ by more than 2008C at pressures of 0·2 GPa. Studies supporting both calibrations exist (Leeman et al, 2012;Wilson et al, 2012;Ashley et al, 2013;Aude¤ tat, 2013;Morgan et al, 2013;Kularatne & Aude¤ tat, 2014), suggesting that the two calibrations might be appropriate in different geological settings or that their success might be dependent on aTiO 2 (Leeman et al, 2012; Thomas & Watson, 2012;Wilson et al, 2012;Morgan et al, 2013;Kularatne & Aude¤ tat, 2014). It should be noted that an alternative TitaniQ calibration by Kawasaki & Osanai (2008), as well as the calibration by Wark & Watson (2006), does not include a pressure dependence and will not be included in the following discussion.…”

“…However, it is easy to qualitatively assess the brightness of the quartz across images by comparing it with different minerals with a more uniform luminescence in the same image. To test the relationship between quartz luminescence and Ti content (see Mu« ller et al, 2000Mu« ller et al, , 2002Larsen et al, 2009), we compared trace element concentrations in quartz with the greyscale in the CL images within $5 mm of the sampled point. The results of this comparison in nine SEM-CL images from four samples are shown in Fig.…”

A Study of Cathodoluminescence and Trace Element Compositional Zoning in Natural Quartz from Volcanic Rocks: Mapping Titanium Content in Quartz

“…For example, hydrothermal "vein" quartz associated with various types of ore deposits often has distinctive ranges of Ti, Al, and other elements reflecting specific compositions and temperatures of associated mineralizing or metamorphic fluids~Holness & Watt, 2001;Monecke et al, 2002;Müller et al, 2003aMüller et al, , 2003bMüller et al, , 2010Götze et al, 2004;Landtwing & Pettke, 2005;Rusk et al, 2006Rusk et al, , 2008Rusk et al, , 2011Lehmann et al, 2009!. Ti contents in metamorphic and igneous quartz samples also display significant ranges and vary with inferred crystallization temperature or other factors~Suttner & Leininger, 1972;Watt et al, 1997;Müller et al, 2002Müller et al, , 2003aGötze et al, 2005;Student et al, 2006;Sato & Santosh, 2007;Wark et al, 2007;Wiebe et al, 2007;Leeman & Lee, 2008;Shane et al, 2008;Campbell et al, 2009;Kohn & Northrup, 2009;Larsen et al, 2009;Spear & Wark, 2009;Storm & Spear, 2009;Vazquez et al, 2009;Girard & Stix, 2010;Huang & Audétat, 2012;Matthews et al, 2012!. Numerous workers have demonstrated the efficacy of cathodoluminescence~CL!…”