000136014 001__ 136014
000136014 005__ 20240704095850.0
000136014 0247_ $$2doi$$a10.1016/j.oregeorev.2024.106109
000136014 0248_ $$2sideral$$a139014
000136014 037__ $$aART-2024-139014
000136014 041__ $$aeng
000136014 100__ $$aGarcía-Tudela, Matías
000136014 245__ $$aThe chromitites of the Herbeira massif (Cabo Ortegal Complex, Spain) revisited
000136014 260__ $$c2024
000136014 5060_ $$aAccess copy available to the general public$$fUnrestricted
000136014 5203_ $$aThe ultramafic rocks of the Herbeira Massif in the Cabo Ortegal Complex (NW Iberia) host chromitite bodies. The textural and compositional study of the host rocks and the chromitites classified them into: (1) Type-I chromitites, forming massive pods of intermediate-Cr chromite (Cr# = 0.60–0.66) within dunites; and (2) Type-II chromitites forming semi-massive horizons of high-Cr chromite (Cr# = 0.75–0.82) interlayered with dunites and pyroxenites. Minor and trace elements (Ga, Ti, Ni, Zn, Co, Mn, V and Sc) contents in the unaltered chromite cores from both types show patterns very similar to fore-arc chromitites, mimicked by the host dunites and pyroxenites. Calculated parental melt compositions suggest that Type-I chromitites crystallized from a melt akin to fore-arc basalt (FAB), while Type-II chromitites originated from a boninite-like parental melt. Both melts are characteristic of a fore-arc setting affected by extension during rollback subduction and have been related to the development of a Cambrian-Ordovician arc. These chromitites are extremely enriched in platinum-group elements (PGE), with bulk-rock PGE contents between 2,460 and 3,600 ppb. Also, the host dunites and pyroxenites exhibit high PGE contents (167 and 324 ppb, respectively), which are higher than those from the primitive mantle and global ophiolitic mantle peridotites. The PGE enrichment is expressed in positively-sloped chondrite-normalized PGE patterns, characterized by an enrichment in Pd-group PGE (PPGE: Rh, Pt and Pd) over the Ir-group PGE (IPGE: Os, Ir and Ru) and abundant platinum-group minerals (PGM) dominated by Rh-Pt-Pd phases (i.e. Rh-Ir-Pt-bearing arsenides and sulfarsenides, Pt-Ir-Pd-base-metal-bearing alloys, and Pt-Pd-bearing sulfides). The PGM assemblage is associated with base-metal sulfides (mostly pentlandite and chalcopyrite) and occurs at the edges of chromite or embedded within the interstitial (serpentinized) silicate groundmass. Their origin has been linked to direct crystallization from a S-As-rich melt(s), segregated by immiscibility from evolved volatile-rich small volume melts during subduction. At c. 380 Ma, retrograde amphibolite-facies metamorphism occurred during the exhumation of the HP-HT rocks of the Capelada Unit, which affected chromitites and their host rocks but preserved the primary composition of chromite cores of the chromitites. This event contributed to local remobilization of PGE as suggested by the negative slope between Pt and Pd and high Pt/Pd ratios in the studied chromitites, and host dunites and pyroxenites. In addition, it promoted the alteration of primary PGM assemblage and the formation of secondary PGM. Nanoscale observations made by focused ion beam high-resolution transmission electron microscopy (FIB/HRTEM) analysis of a composite grain of Rh-bearing arsenide with PGE-base-metal bearing alloys suggest the mobilization and accumulation of small nanoparticles of PGE and base-metals that precipitated from metamorphic fluids forming PGE-alloys. Finally, we offer a comparison of the Cabo Ortegal chromitites with other ophiolitic chromitites involved in the Variscan orogeny, from the Iberian Peninsula to the Polish Sudetes. The studied Cabo Ortegal chromitites are similar to the Variscan chromitites documented in the Bragança (northern Portugal) and Kraubath (Styria, Austria) ophiolitic massifs.
000136014 540__ $$9info:eu-repo/semantics/openAccess$$aby$$uhttp://creativecommons.org/licenses/by/3.0/es/
000136014 655_4 $$ainfo:eu-repo/semantics/article$$vinfo:eu-repo/semantics/publishedVersion
000136014 700__ $$aProenza, Joaquín A.
000136014 700__ $$aFarré-de-Pablo, Júlia
000136014 700__ $$aPujol-Solà, Núria
000136014 700__ $$aAiglsperger, Thomas
000136014 700__ $$aCastillo-Oliver, Montgarri
000136014 700__ $$0(orcid)0000-0002-9615-9168$$aColás, Vanessa$$uUniversidad de Zaragoza
000136014 700__ $$aArenas, Ricardo
000136014 700__ $$aGarcia-Casco, Antonio
000136014 7102_ $$12000$$2120$$aUniversidad de Zaragoza$$bDpto. Ciencias de la Tierra$$cÁrea Cristalografía Mineralog.
000136014 773__ $$g170 (2024), 106109 [30 pp.]$$pOre geol. rev.$$tORE GEOLOGY REVIEWS$$x0169-1368
000136014 8564_ $$s3090735$$uhttps://zaguan.unizar.es/record/136014/files/texto_completo.pdf$$yVersión publicada
000136014 8564_ $$s2379330$$uhttps://zaguan.unizar.es/record/136014/files/texto_completo.jpg?subformat=icon$$xicon$$yVersión publicada
000136014 909CO $$ooai:zaguan.unizar.es:136014$$particulos$$pdriver
000136014 951__ $$a2024-07-04-08:00:10
000136014 980__ $$aARTICLE