Fernanda Gervasoni

Zircon saturation in silicate melts: a new and improved model for aluminous and alkaline melts

The importance of zircon in geochemical and geochronological studies, and its presence not only in aluminous but also in alkaline rocks, prompted us to think about a new zircon saturation model that can be applied in a wide range of compositions. Therefore, we performed zircon crystallization experiments in a range of compositions and at high temperatures, extending the original zircon saturation model proposed by Watson and Harrison (Earth Planet Sci Lett 64:295–304, 1983) and Boehnke et al. (Chem Geol 351:324–334, 2013). We used our new data and the data from previous studies in peraluminous melts, to describe the solubility of zircon in alkaline and aluminous melts. To this effect, we devised a new compositional parameter called G

The role of F-clinohumite in volatile recycling processes in subduction zones

\left[ {\left( {3 \cdot {\text{Al}}_{2} {\text{O}}_{3} + {\text{SiO}}_{2} )/({\text{Na}}_{2} {\text{O}} + {\text{K}}_{2} {\text{O}} + {\text{CaO}} + {\text{MgO}} + {\text{FeO}}} \right)} \right]

Experimental constraints on mantle metasomatism caused by silicate and carbonate melts

3·Al2O3+SiO2)/(Na2O+K2O+CaO+MgO+FeO (molar proportions), which enables to describe the zircon saturation behaviour in a wide range of rock compositions. Furthermore, we propose a new zircon saturation model, which depends basically on temperature and melt composition, given by (with 1σ errors):

The origin of Patagonia revealed by Re-Os systematics of mantle xenoliths

\ln \left[ {\text{Zr}} \right] = \left( {4.29 \pm 0.34} \right) - \left( {1.35 \pm 0.10} \right) \cdot \ln G + \left( {0.0056 \pm 0.0002} \right) \cdot T\left( {^\circ C} \right)

Slab-derived components in the subcontinental lithospheric mantle beneath Chilean Patagonia: Geochemistry and Sr–Nd–Pb isotopes of mantle xenoliths and host basalt

lnZr=4.29±0.34-1.35±0.10·lnG+0.0056±0.0002·T∘C where [Zr] is the Zr concentration of the melt in µg/g, G is the new parameter representing melt composition and T is the temperature in degrees Celsius. The advantages of the new model are its straightforward use, with the G parameter being calculated directly from the molar proportions converted from electron microprobe measurements, the temperature calculated given in degrees Celsius and its applicability in a wider range of rocks compositions. Our results confirm the high zircon solubility in peralkaline rocks and its dependence on composition and temperature. Our new model may be applied in all intermediate to felsic melts from peraluminous to peralkaline compositions.

Phlogopite-bearing fossil plume and EM II component evidences in Patagonia, registered in alkaline basalts from Southern Argentine (36°S - 44°S)

The purpose of this study is to assess the composition of wet precipitation in three sites of the metropolitan area of Porto Alegre. Besides the variables usually considered, such as pH, conductivity, major ions (Cl(-), NO(3)(-), F(-), SO(4)(2-), Na(+), K(+), Mg(2+), NH(4)(+) and Ca(2+)) and metallic elements (Cd, Co, Cr, Cu, Fe, Mn and Ni), the suspended matter was examined by X-ray diffraction (XRD) and scanning electron microscopy (SEM), with energy dispersive system (EDS), for better identification of possible anthropogenic material in this wet precipitation. Results showed an alkaline pH in the samples analyzed and higher concentrations for Na(+), Cl(-) and SO(4)(2-). The acidification and neutralization potential between anions (SO(4)(2-)+NO(3)(-)) and cations (Ca(2+)+Mg(2+)+K(+)+NH(4)(+)) showed a good correlation (0.922). The metallic elements with highest values were Zn, Fe and Mn. Results of XRD identified the presence of some minerals such as quartz, feldspar, mica, clay, carbonates and sulfates. In samples analyzed with SEM, we detected pyroxene, biotite, amphibole and oxides. Cluster analysis (CA) was applied to the data matrix to identify potential pollution sources of metals (natural or anthropogenic) and the association with minerals found in the analysis of SEM.