000165650 001__ 165650 000165650 005__ 20260113234334.0 000165650 0247_ $$2doi$$a10.1016/j.oregeorev.2017.02.025 000165650 0248_ $$2sideral$$a104323 000165650 037__ $$aART-2017-104323 000165650 041__ $$aeng 000165650 100__ $$0(orcid)0000-0002-9615-9168$$aColás, V. 000165650 245__ $$aThe role of silica in the hydrous metamorphism of chromite 000165650 260__ $$c2017 000165650 5060_ $$aAccess copy available to the general public$$fUnrestricted 000165650 5203_ $$aRetrograde hydrous metamorphism has produced three types of microstructures in chromite grains from chromitites and enclosing rocks of the Tapo Ultramafic Massif (Central Peruvian Andes). In semi-massive chromitites (60–80 vol% chromite), (i) partly altered chromite with homogeneous cores surrounded by lower Al2O3 and MgO but higher Cr2O3 and FeO porous chromite with chlorite filling the pores. In serpentinites (ii) zoned chromite with homogeneous cores surrounded by extremely higher Fe2O3 non-porous chromite and magnetite rims, and (iii) non-porous chromite grains. The different patterns of zoning in chromite grains are the consequences of the infiltration of reducing and SiO2-rich fluids and the subsequent heterogeneous interaction with more oxidizing and Fe-bearing fluids. During the first stage of alteration under reduced conditions magmatic chromite is dissolved meanwhile new metamorphogenic porous chromite crystallizes in equilibrium with chlorite. This reaction that involves dissolution and precipitation of minerals is here modeled thermodynamically for the first time. µSiO2-µMgO pseudosection calculated for unaltered semi-massive chromitites at 2 kbar and 300 °C, the lowest P-T conditions inferred from the Tapo Ultramafic Massif and Marañón Complex, predicts that chromite + chlorite (i.e., partly altered chromite) is stable instead of chromite + chlorite + brucite at progressive higher µSiO2 but lower µMgO. Our observation is twofold as it reveals that the important role of SiO2 and MgO and the open-nature of this process. P-T-X diagrams computed using the different P-T pathways estimated for the enclosing Tapo Ultramafic Massif reproduce well the partial equilibrium sequence of mineral assemblages preserved in the chromitites. Nevertheless, it is restricted only to the P-T conditions of the metamorphic peak and that of the latest overprint. Our estimations reveal that a high fluid/rock ratio (1:40 ratio) is required to produce the microstructures and compositional changes observed in the chromitites from the Tapo Ultramafic Massif. The circulation of SiO2-rich fluids and the mobilization of MgO from the chromitite bodies are linked with the formation of garnet amphibolites and carbonate-silica hydrothermalites (i.e., listwaenites and birbirites) in the ultramafic massif. The origin of these fluids is interpreted as a result of the dissolution of orthopyroxene and/or olivine from the metaharzburgites and metagabbros enclosed in the Tapo Ultramafic Massif. 000165650 536__ $$9info:eu-repo/grantAgreement/ES/MINECO/BES-2011-045423$$9info:eu-repo/grantAgreement/ES/MINECO/CGL2010-15171 000165650 540__ $$9info:eu-repo/semantics/openAccess$$aby-nc-nd$$uhttps://creativecommons.org/licenses/by-nc-nd/4.0/deed.es 000165650 590__ $$a3.993$$b2017 000165650 591__ $$aGEOLOGY$$b3 / 47 = 0.064$$c2017$$dQ1$$eT1 000165650 591__ $$aMINING & MINERAL PROCESSING$$b1 / 20 = 0.05$$c2017$$dQ1$$eT1 000165650 591__ $$aMINERALOGY$$b3 / 29 = 0.103$$c2017$$dQ1$$eT1 000165650 592__ $$a1.707$$b2017 000165650 593__ $$aEconomic Geology$$c2017$$dQ1 000165650 593__ $$aGeology$$c2017$$dQ1 000165650 593__ $$aGeochemistry and Petrology$$c2017$$dQ1 000165650 655_4 $$ainfo:eu-repo/semantics/article$$vinfo:eu-repo/semantics/acceptedVersion 000165650 700__ $$aPadrón-Navarta, J.A. 000165650 700__ $$aGonzález-Jiménez, J.M. 000165650 700__ $$0(orcid)0000-0002-0302-2737$$aFanlo, I.$$uUniversidad de Zaragoza 000165650 700__ $$aLópez Sánchez-Vizcaíno, V. 000165650 700__ $$aGervilla, F. 000165650 700__ $$aCastroviejo, R. 000165650 7102_ $$12000$$2120$$aUniversidad de Zaragoza$$bDpto. Ciencias de la Tierra$$cÁrea Cristalografía Mineralog. 000165650 773__ $$g90 (2017), 274-286$$pOre geol. rev.$$tORE GEOLOGY REVIEWS$$x0169-1368 000165650 8564_ $$s9290169$$uhttps://zaguan.unizar.es/record/165650/files/texto_completo.pdf$$yPostprint 000165650 8564_ $$s1099394$$uhttps://zaguan.unizar.es/record/165650/files/texto_completo.jpg?subformat=icon$$xicon$$yPostprint 000165650 909CO $$ooai:zaguan.unizar.es:165650$$particulos$$pdriver 000165650 951__ $$a2026-01-13-22:05:02 000165650 980__ $$aARTICLE