Geodynamic implications of ophiolitic chromitites in the La Cabaña ultramafic bodies, Central Chile

González-Jiménez, José María; Barra, Fernando; Walker, Richard J.; Reich, Martin; Gervilla, Fernando

Geodynamic implications of ophiolitic chromitites in the La Cabaña ultramafic bodies, Central Chile

dc.contributor.author	González-Jiménez, José María
dc.contributor.author	Barra, Fernando
dc.contributor.author	Walker, Richard J.
dc.contributor.author	Reich, Martin
dc.contributor.author	Gervilla, Fernando
dc.date.accessioned	2024-05-31T18:27:16Z
dc.date.available	2024-05-31T18:27:16Z
dc.date.issued	2014-07-18
dc.description.abstract	Chromitites (>80% volume chromite) hosted in two ultramafic bodies (Lavanderos and Centinela Bajo) from the Palaeozoic metamorphic basement of the Chilean Coastal Cordillera were studied in terms of their chromite composition, platinum group element (PGE) abundances, and Re-Os isotopic systematics. Primary chromite (Cr# = 0.64–0.66; Mg# = 48.71–51.81) is only preserved in some massive chromitites from the Centinela Bajo ultramafic body. This chemical fingerprint is similar to other high-Cr chromitites from ophiolite complexes, suggesting that they crystallized from arc-type melt similar to high-Mg island-arc tholeiites (IAT) and boninites in supra-subduction mantle. The chromitites display enrichment in IPGE (Os, Ir, Ru) over PPGE (Rh, Pt, Pd), with PGE concentrations between 180 and 347 ppb, as is typical of chromitites hosted in the mantle of supra-subduction zone (SSZ) ophiolites. Laurite (RuS2)-erlichmanite (OsS2) phases are the most abundant inclusions of platinum-group minerals (PGM) in chromite, indicating crystallization from S-undersaturated melts in the subarc mantle. The metamorphism associated with the emplacement of the ultramafic bodies in the La Cabaña has been determined to be ca. 300 Ma, based on K-Ar dating of fuchsite. Initial 187Os/188Os ratios for four chromitite samples, calculated for this age, range from 0.1248 to 0.1271. These isotopic compositions are well within the range of chromitites hosted in the mantle section of other Phanaerozoic ophiolites. Collectively, these mineralogical and geochemical features are interpreted in terms of chromite crystallization in dunite channels beneath a spreading centre that opened a marginal basin above a supra-subduction zone. This implies that chromitite-bearing serpentinites in the metamorphic basement of the Coastal Cordillera are of oceanic-mantle origin and not oceanic crust as previously suggested. We suggest that old subcontinental mantle underlying the hypothetical Chilenia micro-continent was unroofed and later altered during the opening of the marginal basin. This defined the compositional and structural framework in which the protoliths of the meta-igneous and meta-sedimentary rocks of the Eastern and Western Series of the Chilean Coastal Cordillera basement were formed.
dc.description.sponsorship	This research was funded by FONDECYT project #1110345 and the project CGL2010-15171 funded by the Spanish Ministry of Education and Science
dc.description.uri	http://dx.doi.org/10.1080/00206814.2014.947334
dc.identifier	https://doi.org/10.13016/sn1t-mmrj
dc.identifier.uri	http://hdl.handle.net/1903/32580
dc.language.iso	en_US
dc.publisher	Taylor & Francis
dc.relation.isAvailableAt	College of Computer, Mathematical & Natural Sciences	en_us
dc.relation.isAvailableAt	Geology	en_us
dc.relation.isAvailableAt	Digital Repository at the University of Maryland	en_us
dc.relation.isAvailableAt	University of Maryland (College Park, MD)	en_us
dc.rights	CC0 1.0 Universal	en
dc.rights.uri	http://creativecommons.org/publicdomain/zero/1.0/
dc.subject	chromite
dc.subject	ophiolite
dc.subject	marginal basin
dc.subject	Chile
dc.subject	Chilenia
dc.title	Geodynamic implications of ophiolitic chromitites in the La Cabaña ultramafic bodies, Central Chile
dc.type	Article
local.equitableAccessSubmission	Yes