Chromite-bearing serpentinite bodies within an arc–backarc metamorphic complex near La Cabaña, south Chilean Coastal Cordillera

Hofer, Christine; Kraus, Stefan; Miller, Hubert; Alfaro, Guillermo; Barra, Fernando

doi:10.1016/s0895-9811(01)00011-6

Cited by 17 publications

(9 citation statements)

References 10 publications

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“…Frutos and Alfaro (1987) proposed a model of ophiolite formation in a backarc setting, and Vivallo et al (1988) assigned a marginal basin setting for the Coastal Cordillera ophiolite complex. The latter model has been supported by further works by Schirra (1991), Rabbia et al (1994), and Höfer et al (2001). More recent studies suggest that the rocks of the Western and Eastern Series were emplaced onto the margin of Gondwana during the Late Paleozoic by basal and frontal accretion processes, respectively Glodny et al 2006Glodny et al , 2008.…”

Section: Geological Settingmentioning

confidence: 68%

“…1; Barra et al 1998;Höfer et al 2001). These rocks are part of a large number of poorly studied meta-ultramafic (mainly serpentinites) bodies, scattered within the Western Series.…”

Section: Geological Settingmentioning

confidence: 99%

“…Previous studies have suggested a fault-controlled emplacement for the smaller Lavanderos serpentinite and diapiric emplacement for the large (6×3 km) Centinela Bajo lobate peridotite body (Alfaro 1980;Barra et al 1998). The contact zones between the ultramafic bodies and micaschists are characterized by decimeter-thick layers of mostly monomineralic rocks composed of large (<4 cm) tremolite crystals, Mg-rich chlorite, and talc (Höfer et al 2001). The Centinela Bajo body has been affected by post-emplacement faulting (Fig.…”

Section: Geological Settingmentioning

confidence: 99%

“…2). Adjacent to these faults the degree of serpentinization is higher (>80 %) and the rocks have a schistose texture (Höfer et al Höfer et al (2001) 2001). Preliminary studies using chlorine stable isotopes (δ 37 Cl) indicate that the fluids responsible for the serpentinization of the Lavanderos serpentinite are sedimentary pore-fluids released during the regional metamorphic event (Barra et al 2012).…”

Section: Geological Settingmentioning

confidence: 99%

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Alteration patterns of chromian spinels from La Cabaña peridotite, south-central Chile

et al. 2014

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La Cabaña peridotite is part of a dismembered ophiolite complex located within the metamorphic basement of the Coastal Cordillera of south-central Chile, and is the only location in Chile were Cr-spinels have been described so far. The La Cabaña peridotite is part of the Western Series unit, which comprises meta-sedimentary rocks, metabasites, and serpentinized ultramafic rocks. This unit has been affected by greenschist-facies metamorphism with reported peak PT conditions of 7.0-9.3 kbar and 380°-420°C. Within La Cabaña peridotite Cr-spinels are present in two localities: Lavanderos and Centinela Bajo. In Lavanderos, Cr-spinel occurs in small chromitite pods and as accessory/disseminated grains with a porous or spongy texture in serpentinite, whereas in Centinela Bajo Cr-spinel is present as accessory zoned grains in partly serpentinized dunites, and in chromitite blocks. All Cr-spinels display variable degrees of alteration to Fe 2+ -rich chromite with a variation trend of major elements from chromite to Fe 2+ -rich chromite similar to those observed in other locations, i.e., an increase in Fe 2 O 3 and FeO, a decrease in Al 2 O 3 and MgO. Cr 2 O 3 content increases from chromite to Fe 2+ -rich chromite in chromitite pods from Lavanderos and chromitite blocks from Centinela Bajo, but decreases in ferrian chromite zones in accessory grains from Centinela Bajo. The minor element (Ti, V, Zn, Ni) content is mostly low and does not exceed 0.4 wt.%, with the exception of MnO (<0.9 wt.%), which shows a correspondence with increasing degree of alteration. Cr# (Cr/Cr+ Al) versus Mg# (Mg/Mg+Fe 2+ ) and Fe 3+ /Fe 3+ +Fe 2+ versus Mg# plots are used to illustrate the Cr-spinel alteration process. Overall, the Cr-spinels from Lavanderos (chromitite pods and disseminated grains) exhibit Cr# values ranging from 0.6 to 1.0, Mg# (Mg/Mg+Fe 2+ ) below 0.5, and (Fe 3+ /Fe 3+ +Fe 2+ ) <0.4. Cr-spinels from chromitites in Centinela Bajo have Cr# and Mg# values that range from 0.65 to 1.0, and 0.7-0.3, respectively, and (Fe 3+ /Fe 3+ +Fe 2+ )<0.4. Accessory Cr-spinels from Centinela Bajo have Cr# and Mg# values that range from 0.55 to 1.0, and 0.6-<0.1, respectively. The (Fe 3+ /Fe 3+ +Fe 2+ ) ratio is less than 0.4 in chromite cores and Fe 2+ -rich chromite, and >0.5 in ferrian chromite and Cr-magnetite. Interpretation of the data obtained and Cr-spinel textures indicate that the alteration of Cr-spinel is a progressive process that involves in its initial stages the reaction of chromite with olivine under watersaturated conditions to produce clinochlore and Fe 2+ -rich chromite. During this stage the chromite can also incorporate Ni, Mn, and/or Zn from the serpentinization fluids. As alteration progresses, Fe 2+ -rich chromite loses mass resulting in the development of a spongy texture. In a later stage and under more oxidizing conditions Fe 3+ is incorporated in chromite/Fe 2+ -rich chromite shifting its composition to an Fe 3+ -rich chromite (i.e., ferrian chromite). Depending on the fluid/rock and Cr-spinel/ silicate ratios, Cr-...

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Section: Geological Settingmentioning

confidence: 68%

“…1; Barra et al 1998;Höfer et al 2001). These rocks are part of a large number of poorly studied meta-ultramafic (mainly serpentinites) bodies, scattered within the Western Series.…”

Section: Geological Settingmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

Section: Geological Settingmentioning

confidence: 99%

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Alteration patterns of chromian spinels from La Cabaña peridotite, south-central Chile

et al. 2014

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“…Heavily serpentinized ultramafic bodies occur sparsely in the Western Series of the paleo-accretionary wedge represented by the Coast Range metamorphic complexes of south-central Chile (Vergara, 1970;Ojeda, 1976;Alfaro, 1980;Hervé, 1988;Godoy and Kato, 1990;Crignola et al, 1997;Duhart et al, 2001). They have been considered as emplaced in a Late Paleozoic supra-subduction zone environment (Barra et al, 1998;Höfer et al, 2001;González-Jiménez et al, 2014). Peridotites form part of a banded layered mafic intrusion, mainly composed of troctolites and gabbro, in the Pennsylvanian Coastal Batholith of Central Chile (Hervé and del Campo, 1975;Hernández, 2006).…”

Section: Introductionmentioning

confidence: 99%

Ultramafic rocks in the North Patagonian Andes: is their emplacement associated with the Neogene tectonics of the Liquiñe–Ofqui Fault Zone?

Hervé

Fuentes

Calderón

et al. 2017

andgeo

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ABSTRACT. Serpentinites and fresh or partially serpentinized harzburgite crop out in the western slope of the North Patagonian Andes of continental Chiloé (41°44'-42°12'S). These rocks are spatially associated with low-grade metamorphic rocks containing Cenozoic detrital zircons. The metamorphic rocks, together with Devonian metasediments, have been mapped previously as Late Paleozoic-Triassic metamorfic complex, an age no longer tenable for at least part of the complex. Transpressional tectonic emplacement of the ultramafic body or bodies is thought to have been related to activity on the Liquiñe-Ofqui Fault Zone, following a late Oligocene-Early Miocene extensional phase in the forearc region of the present Andes. This fault zone occurs immediately east of the outcrops of the ultramafic rocks and has been interpreted previously as generating a hemi-flower or flower structure. RESUMEN. Rocas ultramáficas en los Andes norpatagónicos: ¿está su emplazamiento asociado a la actividad tectónica Neógena de la Zona de Falla Liquiñe-Ofqui? En la vertiente occidental de los Andes norpatagonicos deChiloé continental (41°44'-42°12' S) af loran serpentinitas y harzburgitas frescas o parcialmente serpentinizadas. Estas rocas están espacialmente asociadas con rocas metamórficas de bajo grado que contienen circones detríticos Cenozoicos. Estas rocas metamórficas, junto a metasedimentos Devónicos, han sido mapeados previamente como del Paleozoico superior-Triásico, una edad que no es sostenible para al menos una parte de ellos. El emplazamiento tectónico transpresivo del o de los cuerpos ultramáficos, se supone relacionado a la actividad de la Zona de Fallas Liquiñe-Ofqui, después de una fase extensional del Oligoceno tardío-Mioceno temprano en la región de antearco de los Andes actuales. La mencionada zona de fallas aparece inmediatamente al este de los afloramientos de rocas ultramáficas, y ha sido previamente interpretada como causante de una estructura de flor o hemiflor.

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Platinum-group element and gold enrichment in soils monitored by chromium stable isotopes during weathering of ultramafic rocks

et al. 2018

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Chromite-bearing serpentinite bodies within an arc–backarc metamorphic complex near La Cabaña, south Chilean Coastal Cordillera

Cited by 17 publications

References 10 publications

Alteration patterns of chromian spinels from La Cabaña peridotite, south-central Chile

Alteration patterns of chromian spinels from La Cabaña peridotite, south-central Chile

Ultramafic rocks in the North Patagonian Andes: is their emplacement associated with the Neogene tectonics of the Liquiñe–Ofqui Fault Zone?

Platinum-group element and gold enrichment in soils monitored by chromium stable isotopes during weathering of ultramafic rocks

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