Garnet-chloritoid-kyanite metapelites from the Raspas Complex (SW Ecuador): a key eclogite-facies assemblage

The assemblage garnet-chloritoid-kyanite is shown to be quite common in high-pressure eclogite facies metapelites from orogenic belts around the world, and occurs over a narrowly restricted range of temperature 550-600°C, between 20 and 25 kbar. This assemblage is favoured particularly by large Al 2 O 3 :K 2 O ratios allowing the development of kyanite in addition to garnet and chloritoid. Additionally, ferric iron and manganese also help stabilize chloritoid in this assemblage. Pseudosections for several bulk compositions illustrate these high-pressure assemblages, and a new thermodynamic model for white mica to include calcium and ferric iron was required to complete the calculations. It is extraordinary that so many orogenic eclogite facies rocks, both mafic eclogites sensu stricto as well as metapelites with the above assemblage, all yield temperatures within the range of 520-600°C and peak pressures 23±3 kbar. Subduction of oceanic crust and its entrained associated sedimentary material must involve the top of the slab, where mafic and pelitic rocks may easily coexist, passing through these P-T conditions, such that rocks, if they proceed to further depths, are generally not returned to the surface. This, together with the tightly constrained range in peak temperatures which such eclogites experience, suggests thermal weakening being a major control on the depths at which crustal material is decoupled from the downgoing slab.

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“…Despite previous studies claiming the rare nature of this assemblage (Gabriele et al. , 2003; Negulescu et al.…”

Section: The Garnet–chloritoid–kyanite Assemblage In Metapelitesmentioning

confidence: 69%

Garnet–chloritoid–kyanite assemblages: eclogite facies indicators of subduction constraints in orogenic belts

Smye

Greenwood

Holland

2010

Journal Metamorphic Geology

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“…Peak P-T conditions for eclogites and garnet-chloritoid-kyanite metapelites are very similar at about 2 GPa and 550-600°C (Gabriele et al, 2003;John et al, 2010). The partially serpentinized peridotites of the El Toro Formation locally host mafic dikes that have preserved eclogitic mineral assemblages, indicating subduction depths similar to those of the associated Raspas Formation (Gabriele, 2002).…”

Section: Geological Settingmentioning

confidence: 94%

“…It represents an exhumed terrane fragment of oceanic lithosphere (Arculus et al, 1999), which can be interpreted as a highpressure ophiolite . The complex is subdivided into the Raspas Formation, which comprises eclogites, blueschists and metasediments, and the El Toro Formation, which consists of eclogite-facies, serpentinized peridotites (Feininger, 1980;Gabriele et al, 2003).…”

Section: Geological Settingmentioning

confidence: 99%

A stable (Li, O) and radiogenic (Sr, Nd) isotope perspective on metasomatic processes in a subducting slab

et al. 2011

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Two distinct types of eclogites from the Raspas Complex (Ecuador), which can be distinguished based on petrography and trace element geochemistry, were analyzed for their stable (Li, O) and radiogenic (Sr, Nd) isotope signature to constrain metasomatic changes due to fluid-overprinting in metabasaltic rocks at high-pressure conditions and to identify fluid sources. MORB-type eclogites are characterized by a relative LREE depletion similar to MORB. High-pressure (HP) minerals from this type of eclogite have highly variable oxygen isotope compositions (garnet: +4.1 to +9.

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“…Within this complex, mafic eclogites and garnet-chloritoid-kyanite metapelites record very similar peak metamorphic conditions of about 2 GPa and 550-600°C (Gabriele et al, 2003;John et al, 2010). The age of metamorphism in the Raspas Complex has been dated by Lu-Hf methods, yielding ages of $130 Ma (John et al, 2010).…”

Section: Raspas Complex Ecuadormentioning

confidence: 98%

“…Peak P-T conditions for the metamorphic suites discussed in this paper and for some additional suites relevant to this study (modified after Hacker, 2006 andBebout, 2007a). Data sources for the peak P-T conditions: Raspas Complex: Gabriele et al (2003) and John et al (2010), Lago di Cignana: Reinecke (1998), Zambezi Belt: John et al (2003), Cabo Ortegal: Gil Ibarguchi et al (1990), Erzgebirge (Micaschist-Eclogite unit): Massonne and Kopp (2005), Erro Tobbio: Messiga et al (1995), Catalina Schist: Grove and Bebout (1995). For the Schistes Lustrés, the multiple fields are for individual units showing a wide range in metamorphic grade (from Agard et al (2002)).…”

Section: Zambezi Belt Zambiamentioning

confidence: 99%

Nitrogen recycling in subducted oceanic lithosphere: The record in high- and ultrahigh-pressure metabasaltic rocks

Halama

Bebout

John

et al. 2010

Geochimica et Cosmochimica Acta

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Garnet-chloritoid-kyanite metapelites from the Raspas Complex (SW Ecuador): a key eclogite-facies assemblage

Cited by 27 publications

References 53 publications

Garnet–chloritoid–kyanite assemblages: eclogite facies indicators of subduction constraints in orogenic belts

Garnet–chloritoid–kyanite assemblages: eclogite facies indicators of subduction constraints in orogenic belts

A stable (Li, O) and radiogenic (Sr, Nd) isotope perspective on metasomatic processes in a subducting slab

Nitrogen recycling in subducted oceanic lithosphere: The record in high- and ultrahigh-pressure metabasaltic rocks

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