Textural and compositional evidence for a polyphase saturation of tourmaline in granitic rocks from the Třebíč Pluton (Bohemian Massif)

Abstract

Crystallization of granite melts produced several textural types of granites and pegmatites in the Třebíč Pluton: dykes of volumetrically dominant muscovite-biotite granite (MBG) locally containing tourmaline nodules with leucocratic halos, minor oval pods to dykes of tourmaline granite and veins of tourmaline pegmatite, both enclosed in the MBG. An aplitic zone with comb textures, locally developed in MBG along the contact with surrounding durbachites, suggests high degree of undercooling. Evidence for polyphase saturation of tourmaline was observed within MBG and related granitic rocks including the following textural and compositional types of tourmaline: (i) nodules surrounded by leucocratic halos; (ii) euhedral to subhedral grains randomly distributed within tourmaline granite and tourmaline-quartz accumulations with leucocratic halos in the marginal part of granite dykes; (iii) rare columnar crystals of black tourmaline occurring locally in central parts of pegmatite; (iv) dravite-rich rims and late dravite veinlets in tourmaline grains from nodules, suggesting crystallization from hydrothermal fluids in the system open to host rocks as supported also by fluid inclusions study.

Tourmalines as a Tool in Provenance Studies of Terrigenous Material in Extra-Carpathian Albian (Uppermost Lower Cretaceous) Sands of Miechów Synclinorium, Southern Poland

“…The XMg ratio of all the examined tourmaline grains ranges from 0.57 to 0.64, which fits well to the composition of tourmaline that crystallized in rocks experiencing low-to medium-grade metamorphism. The tourmalines from Tourmaline is stable under very diverse pressure-temperature (P-T) conditions from diagenetic [61,62,97], hydrothermal epigenetic [98][99][100][101] and through wide range of metamorphic grades [91,102], up to ultra-high pressure (UHP) and high-temperatures [66,103,104]. The thermal stability of the dravite structure was experimentally established up to 3-5 GPa and a temperature close to 950 °C [103].…”

Tourmaline as a Tracer of Late-Magmatic to Hydrothermal Fluid Evolution: The World-Class San Rafael Tin (-Copper) Deposit, Peru

“…The San Rafael megacrystic granite has a moderately fractionated peraluminous S-type composition (ASI = 1.1-1.5), as indicated by whole-rock and mineral chemistry data (Kontak and Clark, 2002;Mlynarczyk, 2005;Corthay, 2014;Prado, 2015). Its whole-rock boron content (B = 60-160 ppm, avg = 115 ppm; Mlynarczyk, 2005) falls in the same range of peraluminous granites hosting tourmaline nodules elsewhere (B = 10-500 ppm; Dini et al, 2007;Balen and Broska, 2011;Pesquera et al, 2013;Drivenes et al, 2015;Burianek et al, 2016) as well as quartz-hosted melt inclusions from Bolivian tin porphyries (B = 35-640 ppm; Dietrich et al, 2000;Lehmann et al, 2000;Wittenbrink et al, 2009). This suggests that the boron content of the San Rafael granitic melt may have been initially much higher owing to the preferential partitioning of boron into a fluid phase relative to the silicate melt during water saturation (e.g., Pichavant, 1981;London et al, 1988;Hervig et al, 2002;Thomas et al, 2003;Schatz et al, 2004).…”

“…3 and 4) are typical of magmatic tourmaline in evolved peraluminous granites (e.g., London and Manning, 1995;London et al, 1996;Balen and Broska, 2011;Balen and Petrinec, 2011;Drivenes et al, 2015). The formation of tourmaline nodules has been widely discussed in the literature and three main hypotheses have been proposed for their origin: (i) post-magmatic hydrothermal alteration of granitic bodies by externally derived boron-rich fluids (e.g., Rozendaal and Bruwer, 1995); (ii) crystallization from immiscible, hydrous, boron-aluminosilicate melts or boron-rich aqueous fluids that separated from coexisting silicate melt (e.g., Dini et al, 2007;Balen and Broska, 2011;Drivenes et al, 2015;Burianek et al, 2016); and (iii) products of magmatic crystallization on the liquid line of descent of boron-rich granitic melts (e.g., Perugini and Poli, 2007;Balen and Petrinec, 2011;Valentini et al, 2015). The Tur 1 nodules observed in the San Rafael granites are devoid of alteration features (i.e., absence of veins, dissolution-reprecipitation texture, and pervasive alteration), thus arguing against a hydrothermal origin related to post-magmatic alteration.…”

Rutile Mineral Chemistry and Zr-in-Rutile Thermometry in Provenance Study of Albian (Uppermost Lower Cretaceous) Terrigenous Quartz Sands and Sandstones in Southern Extra-Carpathian Poland

“…The Bohemian Massif comprises a large variety of igneous and metamorphic rocks [100,101]. Therefore, it is possible to indicate potential source rocks for detrital rutile crystallized under amphibolite-LT eclogite facies (e.g., mica schists, gneisses) conditions [100,102,103], as well as in high-grade granulite-HT eclogite facies rocks, namely granulites and gneisses [101,104,105]. During the Albian, the Bohemian Massif was neighboring to the western and central zones (Figure 2).…”