Fonction : Maître de conférences, Université de Lorraine
Thème(s) :
Coordonnées :
CRPG UMR 7358 CNRS-UL
15 rue Notre Dame des Pauvres
54500 Vandœuvre les Nancy – France
Email : karine.devineau@univ-lorraine.fr
Téléphone : +33 (0)3 83 59 42 08
Bureau : 301
2021 |
Martel, C., Pichavant, M., Carlo, I. Di, Champallier, R., Wille, G., Castro, J. M., Devineau, K., Davydova, V. O., Kushnir, A. R. L. Experimental constraints on the crystallization of silica phases in silicic magmas (Article de journal) Dans: Journal of Petrology, p. 1–18, 2021. @article{Martel_etal2021,Low-pressure silica polymorphs, e.g. quartz (Qtz), tridymite (Trd), and cristobalite (Crs), are common in silicic magmas, but the conditions of their formation are still unclear. The stability fields of these polymorphs have been determined in the SiO2, SiO2--H2O, and haplogranite systems, but these simple systems are not directly applicable to silica polymorph crystallization in natural silicic magmas. The present study compiles an experimental database of new and previously-published data documenting the crystallization of silica phases in natural silicic magmas and simple synthetic systems. Silica polymorphs are identified using Raman spectroscopy and their pressure temperature domains of occurrence and chemical compositions are determined at pressures between 0.1 and 200 MPa, temperatures between 685 to 1200 textdegreeC, and under H2O-saturated and H2O-undersaturated conditions. Qtz is the stable silica polymorph at pressures higher than 25--30 MPa, temperatures between 700 and 950textdegree C, and occurs for a narrow range of melt SiO2 contents ( 79--81 wt %). Constraints on Qtz stability derived from simple systems are mutually compatible with, and thus applicable to natural compositions. This is consistent with Qtz compositions being close to textquoteleftpuretextquoteright SiO2, both in experiments and nature. In volcanic systems, Qtz crystallization may occur in magmatic reservoirs and deep volcanic conduits. Trd did not crystallize in the experiments conducted as part of this study despite several experiments having been performed in the Trd stability field. This is consistent with results from the literature which show that Trd crystallization is kinetically inhibited in particular relative to Crs. Natural Trd have compositions deviating substantially from textquoteleftpuretextquoteright SiO2, so that stability limits determined in simple systems should not be applied directly to natural cases. Crs was encountered at pressures below 20--30MPa (or H2O contents < 1.5wt %), from subsolidus ( 800.C) to near-liquidus (up to 1040. C), and coexisting with melts having a large range of SiO2 contents (70--81 wt %). The Crs stability field is much larger in natural magmas compared to pure SiO2 systems. Crs is a metastable phase stabilized by components (Al, Na, K ; about 3wt %) present in the silicic melt. In volcanic systems, Crs crystallization may thus be restricted to subsurface manifestations such as lava domes. |
2020 |
Devineau, K., Champallier, R., Pichavant, M. Dynamic crystallization of a haplogranitic melt : Application to pegmatites (Article de journal) Dans: Journal of Petrology, vol. 61, no. 5, p. egaa054, 2020. @article{Devineau_etal2020,Both equilibrium and dynamic crystallization experiments have been performed on a hydrous haplogranitic melt at 200 MPa to model nucleation and growth mechanisms and simulate pegmatite textures. The equilibrium results provide a reference frame (phase assemblages and compositions, liquidus and solidus temperatures and dependence with the melt H2O concentration) to parametrize the kinetic experiments. The seven H2O-saturated dynamic crystallization experiments followed a specific time-temperature path. After a pre-conditioning step at 800textdegreeC, charges were cooled between 3.5 and 7textdegreeC/min to 700, 660 and 600textdegreeC corresponding to DT of 20, 60 and 120textdegreeC. Dwell times ranged from 42 up to 1440h. Variable mineral assemblages and textures, and two types of polymineralic assemblages were obtained depending on DT and t. For DT textonequarter 120textdegreeC, crystallization is sequential and includes graphic quartz--alkali-feldspar intergrowths characteristic of pegmatite textures. The crystallization sequence reflects nucleation and growth of kinetically favoured metastable phases and solid solution compositions from the supercooled melt. Early alkali-feldspars are more K-rich than expected at equilibrium and late albites more Na-rich. The Krich graphic texture progressively evolves to a Na-rich intergrowth texture. Melts also follow a progressive though limited sodic evolution with time. At the interface of growing alkali-feldspars, melts are enriched in SiO2 and depleted in Al2O3, Na2O and, to a lesser extent, K2O. H2O accumulates at the interface reaching concentration levels higher (by 1--2 wt %) than the saturation. Rejection of SiO2 and H2O at the interface controls the effective undercooling in the local melt and promotes rapid textural changes toward larger grain sizes at the front of graphic zones. Textural ripening takes place contemporaneously to sequential crystallization. Growth rates for quartz and alkali-feldspar are tightly grouped, between 7.3 x 10-11 and 1.6 x 10-12 m s-1. Textures from the dynamic crystallization experiments closely resemble natural pegmatites, but layered aplite units have not been reproduced. Our results confirm and strengthen the importance of liquidus undercooling to generate pegmatite textures. |
2017 |
Faure, F., Tissandier, L., Florentin, L., Devineau, K. A magmatic origin for silica-rich glass inclusions hosted in porphyritic magnesian olivines in chondrules: An experimental study (Article de journal) Dans: Geochimica et Cosmochimica Acta, vol. 204, p. 19–31, 2017. @article{Faure_etal2017,Rare silica-rich glass inclusions (69 < SiO2 < 82 wt.%) are described within magnesian olivines of porphyritic Type IA chondrules. These glass inclusion compositions are clearly out of equilibrium with their host Mg-olivines and their presence within the olivines is generally attributed to an unclear secondary process such as a late interaction with nebular gases. We performed dynamic crystallisation experiments that demonstrate that these Si-rich glass inclusions are actually magmatic in origin and were trapped inside olivines that crystallized slowly from a magma with a CI, i.e. solar, composition. Their silicarichcompositions are the consequence of the small volumes of inclusions, which inhibit the nucleation of secondary crystalline phase (Ca-poor pyroxene) but allow olivine to continue to crystallize metastably on the walls of the inclusions. We suggestthat Si-rich glass inclusions could be the only reliable relicts of what were the first magmas of the solar system, exhibiting a CI, i.e. non-fractionated, composition. |
2013 |
Devineau, K., Devouard, B., Leroux, H., Tissandier, L. Incorporation of Zn in the destabilization products of muscovite at 1175 textdegreeC under disequilibrium conditions, and implications for heavy metal sequestration (Article de journal) Dans: American Mineralogist, vol. 98, p. 932–945, 2013. @article{Devineau_etal2013,This work reports on the thermal decomposition of muscovite within a granite powder doped with 8.5 wt% ZnO and heated during 10 min to 68 h at 1175 textdegreeC, and the implications for the sequestration of Zn, and other heavy metalts in such decomposition products. Samples were characterized using analytical scanning and transmission electron microscopy. After 10 min, muscovite is completely pseudomorphosed by Si-rich glass, spinel structure phases, and minor mullite. Spinel phases incorporate Zn, but their compositions depend on their position within the muscovite pseudomorphs. Al-rich oxides crystallize at the core of the pseudomorphs while Zn-Al spinels are located at the rims. The most Al-rich spinels have compositions close to $gamma$-Al2O3, a metastable transition alumina, with up to 5 wt% MgO, 2 wt% Fe2O3, 4 wt% ZnO, and 9 wt% SiO2. The most Zn-rich spinels show compositions intermediate between Al2O3 and gahnite (ZnAl2O4), with up to 31 wt% ZnO and significant contents of MgO (3 wt%), Fe2O3 (5 wt%), and SiO2 (10 wt%). After 68 h, stable spinels are gahnite close to the end-member composition with MgO and Fe2O3 contents below ca. 5 wt%, and SiO2 contents ca. 1 wt%. These results support the existence of a metastable solid solution between $gamma$-Al2O3 and gahnite. This experimental work shows that Zn can be incorporated in spinel structures after heating at 1175 textdegreeC during short durations and Zn is preferentially incorporated in the muscovite pseudomorphs as opposed to the Qtz-Fds glass. Consequently, the thermal breakdown of phyllosilicates can be a viable process to immobilize heavy metals such as Zn. |