Non-invasive assessment of the formation of tourmaline nodules by X-ray microtomography and computer modeling

Abstract

Tourmaline nodules occurring in the Capo Bianco (Elba Island, Italy) aplitic rocks are here investigated by X‑ray microtomography 3D imaging. This non-invasive technique provides 3D images of the tourmaline nodules, revealing an irregular morphology consisting of branches that extend radially from the cores. The nodules present scale-invariant features that can be described by a box-counting fractal dimension. The value of the fractal dimension is proportional to the size of the nodules and tends asymptotically to a value of 2.5, in agreement with the results obtained from the simulation of virtual nodules, by means of a diffusion-limited aggregation model based on a Monte Carlo Metropolis algorithm, in which the growth probability at the tips of the nodule is an inverse function of the diffusion coefficient. The results support the hypothesis that tourmaline formed by a disequilibrium magmatic process, in which diffusion represents the rate-limiting step, inducing the formation of nodules with irregular shapes. This study shows the potential of X‑ray microtomography, in combination with numerical modeling, as a probe for accessing the 3D microstructural information of complex mineral morphologies with a non-invasive approach. The combination of numerical and experimental, non-invasive, 3D techniques represents a fundamental step forward in bridging the gap between the observation of microstructures and the interpretation of the associated processes

Volcanic ash aggregation enhanced by seawater interaction: the case of Secche di Lazzaro phreatomagmatic deposit (Stromboli)

“…Although X-ray computed microtomography (X-CT) is becoming increasingly valuable in the geosciences [Ketcham and Carlson, 2001;Mees et al, 2003;Ketcham, 2005;Carlson, 2006;Gualda et al, 2010;Polacci et al, 2010;Voltolini et al, 2011;Baker et al, 2012a,b;Iglauer et al, 2012;Blunt et al, 2013;Fusseis et al, 2014;Wiesmaier et al, 2015;Valentini et al, 2015;Arzilli et al, 2016;Morgavi et al, 2016;Paredes-Mariño et al, 2017], so far the application of this method to the study of accretionary lapilli is limited to a single study [Van Eaton et., 2012]. In this study, X-CT scans were performed using a Skyscan 1172 (Bruker, Billerica, US) at the Geosciences Department (University of Padova, Italy) equipped with a W X-ray source.…”

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

“…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.…”

Three-dimensional distribution of primary melt inclusions in garnets by X-ray microtomography

“…In the geosciences, one of the first reported application of computed X-ray tomography is the 143 pioneering work by Carlson and Denison (1992) microstructural analysis of ore-bearing rocks (Godel 2013), identification of mineral inclusions in 151 diamonds (Nestola et al 2012), and morphological analysis of mineral nodules (Valentini et al 2015). 152…”