Serpentinitas y cromititas de La Cabaña, Cordillera de la Costa, Chile central

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

doi:10.4067/s0716-02081998000100003

Cited by 11 publications

(5 citation statements)

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“…Furthermore, the presence of talc suggests a postserpentinization hydrothermal event in Lavanderos. Additionally, preliminary chlorine isotope studies indicate that the fluids responsible for the serpentinization of the Lavanderos ultramafic body are sedimentary pore-fluids possibly released and heated during the metamorphic event (Barra et al 2012). Both areas have Cr-spinels present as accessory grains and forming small pods (Lavanderos) or large chromitite blocks (Centinela Bajo).…”

Section: Discussionmentioning

confidence: 98%

“…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: 97%

“…3c). 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).…”

Section: Geological Settingmentioning

confidence: 98%

“…These rocks are part of a large number of poorly studied meta-ultramafic (mainly serpentinites) bodies, scattered within the Western Series. Preliminary chemical analysis on unaltered Cr-spinels from La Cabaña indicate an arc related setting for the ultramafic rocks and associated chromitite bodies (Barra et al 1998); however, the alteration processes that have affected these rocks remain poorly understood.…”

Section: Geological Settingmentioning

confidence: 98%

“…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: Discussionmentioning

confidence: 98%

“…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: 97%