Abstract
Chromite from Los Congos and Los Guanacos in the Eastern Pampean Ranges of Córdoba (Argentinian Central Andes) shows homogenous and exsolution textures. The composition of the exsolved phases in chromite approaches the end-members of spinel (MgAl2O4; Spl) and magnetite (Fe2+
Special collection papers can be found online at http://www.minsocam.org/MSA/AmMin/special-collections.html.
Acknowledgments
This research was supported by the project CGL2010-15171 and F.P.I. grant BES-2011-045423 of the Ministerio de Econonía y Competitividad (Spain). Support for this study has also been provided by the FONDECYT #11140005 and “Millenium Nucleus for Metal Tracing Along Subduction NC130065” to José María González-Jiménez. We thank Steve Barnes and an anonymous reviewer for their careful and constructive comments and Ferdinando Bosi for his proficient editorial handling of this manuscript. The analytical data were obtained using instrumentation funded by DEST Systemic Infrastructure Grants, ARC LIEF, NCRIS, industry partners and Macquarie University. This is a contribution 701 from the ARC Centre of Excellence for Core to Crust Fluid Systems (www.ccfs.mq.edu.au) and 1055 in the GEMOC Key Centre (www.gemoc.mq.edu.au).
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Appendix
Data sources for calculated crystal-crystal partition coefficients
The crystal-crystal partition coefficients of exsolved phases in chromite from previously published data sets were calculated using reported EMPA data for minor elements. Chromite with exsolution textures come from the layered complexes of Carr Boyd Rocks Complex (Western Australia, Purvis et al. 1972), Giant Nickel Mine (British Columbia, Muir and Naldrett 1973), Red Lodge district (Montana, U.S.A., Loferski and Lipin 1983), Kuså (Sweden, Zakrzewski 1989), Chilas (Pakistan, Jan et al. 1992), Isua Greenstone Belt (Greenland, Appel et al. 2002) and the Eastern Desert (Egypt, Ahmed et al. 2008); from the Uralian-Alaskan-type complexes of Staré Ransko (Czech Republic, van der Veen and Maaskant 1995), Uktus (Russia, Garuti et al. 2003) and the Central Ural Mountains (Krause et al. 2007); and from the peridotite complex of Iwanai-dake (Japan, Tamura and Arai 2005).
Data source for minor and trace elements in chromite
The data sources for minor and trace elements in chromite used in this study consist of previously published and new data sets. Chromite samples are classified based on magmatic setting (ophiolitic peridotites, lavas, and layered intrusions) and by metamorphic assemblage (chromite and Fe3+-rich chromite in equilibrium with chlorite).
Reported minor and trace element compositions of chromite in ophiolitic peridotites come from the Thetford Mine Ophiolite (Canada, Pagé and Barnes 2009), Ouen Island and Dyne (New Caledonia, González-Jiménez et al. 2011; Colás et al. 2014), Mercedita, Tres Amigos and Rupertina (Cuba, Colás et al. 2014; González-Jiménez et al. 2015), and Luobusa (Tibet, Zhou et al. 2014). Chromite samples of lavas are taken from the East Pacific Rise, Bonin Island (Japan), Thetford Mine Ophiolite (Canada) (Pagé and Barnes 2009), and Solomon Island (Yao 1999); and those of layered intrusions from the Bushveld Complex (South Africa) and the Great Dike (Zimbabwe) (Yao 1999). Data for the metamorphosed chromite come from ophiolitic chromitites of Los Congos and Los Guanacos (Argentina), Central and Eastern Rhodope (Bulgaria, González-Jiménez et al. 2015; Colás et al. 2014), Ouen Island (New Caledonia, González-Jiménez et al. 2011) and Southeastern Turkey (Akmaz et al. 2014); and those from the greenstone belt of Nuggihalli (India, Mukherjee et al. 2015).
Matlab script to plot spinel prism in 3D
The following is a simple Matlab script to plot the spinel prism that reads an input csv file consisting in four columns (without headers) as follow Cr/R3+, Al/R3+, Cr/R3+, and XMg in mole proportions.
clear all
data = importdata(’CongosExs.csv’);
λ = data(:,1:3);
points_x = transpose(1-data(:,4));
% Cartesian components of the triangle vertices r1, r2, r3;
% ri = (yi, zi), i = 1:3
% r1 r2 r3
vertex = [0 1 0.5; % y
0 0 1]; % z
% transformation to cartesian coordinates
points_y = zeros(1,length(λ));
points_z = zeros(1,length(λ));
for i = 1:length(λ)
points_y(i) = λ(i,1)*vertex(1,1)...
+λ(i,2)*vertex(1,2)...
+λ(i,3)*vertex(1,3);
points_z(i) = λ(i,1)*vertex(2,1)...
+λ(i,2)*vertex(2,2)...
+λ(i,3)*vertex(2,3);
end
scatter3(points_x,points_y,points_z)
xlabel(‘x’), ylabel(‘y’), zlabel(‘z’),
xlim([0 1]), zlim([0 1])
text(-0.05,-0.15,0,[‘Pc’],‘FontSize’,14)
text(-0.05,1.15,-0.1,[‘Sp’],‘FontSize’,14)
text(1,-0.15,0,[‘Chr’],‘FontSize’,14)
text(0,0.5,1.1,[‘Mf’],‘FontSize’,14)
text(1,0.5,1.1,[‘Mt’],‘FontSize’,14)
text(1.15,1.25,-0.1,[‘Her’],‘FontSize’,14)
hold on
daspect([1.7 1 1.1753])
% Prism
plot3([0 0 0 0 1 1 1 1 1 0 0 1],...
[0 1 0.5 0 0 1 0.5 0 0.5 0.5 1 1],...
[0 0 1 0 0 0 1 0 1 1 0 0])
© 2016 by Walter de Gruyter Berlin/Boston