Crustal make-up of the northern Andes: evidence based on deep crustal xenolith suites, Mercaderes, SW Colombia

Weber, Marion; Tarney, J.; Kempton, Pamela D.; Kent, Raymond William.

doi:10.1016/s0040-1951(01)00206-2

Cited by 80 publications

(87 citation statements)

References 68 publications

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“…The effect of H 2 O on garnet compositions is not dramatic, but results in a tendency of increasing grossular content with increasing amounts of dissolved H 2 O in the liquid. Garnet compositions of our study resemble those of ''group C'' (Coleman et al 1965, garnets present in granulites) and are similar to granulite garnets commonly found, but not restricted to, subduction environments, such as those in Northern Fiordland, New Zealand (Schröter et al 2004), deep-crustal xenoliths form the Northern Andes (Weber et al 2002) or garnet cumulates from the Jijal complex, Kohistan arc (Ringuette et al 1999, Müntener et al unpublished data). Variations of garnet Mg# expressed as the molar Mg/(Mg ?…”

Section: Garnetsupporting

confidence: 79%

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Igneous garnet and amphibole fractionation in the roots of island arcs: experimental constraints on andesitic liquids

Alonso-Perez

Müntener

Ulmer

2008

Contrib Mineral Petrol

464

231

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To evaluate the role of garnet and amphibole fractionation at conditions relevant for the crystallization of magmas in the roots of island arcs, a series of experiments were performed on a synthetic andesite at conditions ranging from 0.8 to 1.2 GPa, 800-1,000°C and variable H 2 O contents. At water undersaturated conditions and fO 2 established around QFM, garnet has a wide stability field. At 1.2 GPa garnet ? amphibole are the high-temperature liquidus phases followed by plagioclase at lower temperature. Clinopyroxene reaches its maximal stability at H 2 Ocontents B9 wt% at 950°C and is replaced by amphibole at lower temperature. The slopes of the plagioclase-in boundaries are moderately negative in T-X H 2 O space. At 0.8 GPa, garnet is stable at magmatic H 2 O contents exceeding 8 wt% and is replaced by spinel at decreasing dissolved H 2 O. The liquids formed by crystallization evolve through continuous silica increase from andesite to dacite and rhyolite for the 1.2 GPa series, but show substantial enrichment in FeO/MgO for the 0.8 GPa series related to the contrasting roles of garnet and amphibole in fractionating Fe-Mg in derivative liquids. Our experiments indicate that the stability of igneous garnet increases with increasing dissolved H 2 O in silicate liquids and is thus likely to affect trace element compositions of H 2 O-rich derivative arc volcanic rocks by fractionation. Garnetcontrolled trace element ratios cannot be used as a proxy for 'slab melting', or dehydration melting in the deep arc. Garnet fractionation, either in the deep crust via formation of garnet gabbros, or in the upper mantle via formation of garnet pyroxenites remains an important alternative, despite the rare occurrence of magmatic garnet in volcanic rocks.

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Section: Garnetsupporting

confidence: 79%

“…5b), in agreement with Sisson and Grove (1993a). Moreover, no Müntener et al 2001) and to natural occurrences from island arc systems (Schroter et al 2004;Ringuette et al 1999;Weber et al 2002). Garnet end-member compositions are calculated based on X-site occupancy (Ca, Fe 2?…”

Section: Garnetmentioning

confidence: 72%

Igneous garnet and amphibole fractionation in the roots of island arcs: experimental constraints on andesitic liquids

Alonso-Perez

Müntener

Ulmer

2008

Contrib Mineral Petrol

464

231

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“…As for most Late Cretaceous -Paleogene accretions in Ecuador (Jaillard et al, 1997;Reynaud et al, 1999), the accretion of the Raspas oceanic plateau occurred without obduction. In this model, underthrusting of parts of accreted oceanic terranes might contribute to the crustal thickening of the upper plate in this part of the Andes, as already suggested by Megard (1987Megard ( , 1989 in Ecuador and further documented in Colombia by Weber et al (2002).…”

Section: Discussionsupporting

confidence: 64%

Geodynamic significance of the Raspas Metamorphic Complex (SW Ecuador): geochemical and isotopic constraints

et al. 2002

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The Raspas Metamorphic Complex of southwestern Ecuador is regarded as the southernmost remnant of oceanic and continental terranes accreted in the latest Jurassic -Early Cretaceous. It consists of variably metamorphosed rock types. (1) Mafic and ultramafic rocks metamorphosed under high-pressure (HP) conditions (eclogite facies) show oceanic plateau affinities with flat REE chondrite-normalized patterns, eNd 150 Ma ranging from + 4.6 to 9.8 and initial Pb isotopic ratios intermediate between MORB and OIB. (2) Sedimentary rocks metamorphosed under eclogitic conditions exhibit LREE enriched patterns, strong negative Eu anomalies, Rb, Nb, U, Th, Pb enrichments, low eNd 150 Ma values (from À 6.4 to À 9.5), and high initial 87 Sr/ 86 Sr and 206,207,208 Pb/ 204 Pb isotopic ratios suggesting they were originally sediments derived from the erosion of an old continental crust. (3) Epidote-bearing amphibolites show N-MORB affinities with LREE depleted patterns, LILE, Zr, Hf and Th depletion, high eNd 150 Ma (> + 10) and low initial Pb isotopic ratios. The present-day well defined internal structure of the Raspas Metamorphic Complex seems to be inconsistent with the formerly proposed interpretation of a ''tectonic mélange''. The association of oceanic plateau rocks and continent-derived sediments both metamorphosed in HP conditions suggests that the thin edge of the oceanic plateau first entered the subduction zone and dragged sediments downward of the accretionary wedge along the Wadatti -Benioff zone. Subsequently, when its thickest part arrived into the subduction zone, the oceanic plateau jammed the subduction processes, due to its high buoyancy. In Ecuador and Colombia, the latest Jurassic -Early Cretaceous suture involves HP oceanic plateau rocks and N-MORB rocks metamorphosed under lower grades, suggesting a composite or polyphase nature for the latest Jurassic -Early Cretaceous accretionary event. D

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“…However, the lower continental crust consists mainly of granulite-or eclogite-facies rocks (Rudnick and Gao, 2003;Weber et al, 2002), which are generally much dryer than subducted oceanic crust. With systematic geochemical investigation, Liu et al (2010) suggested that the Cu-Au ore deposits in the Lower Yangtze River belt could be not due to the ancient LCC-derived magmas, regardless of having interacted with the mantle or not.…”

Section: Metallogenic Significancementioning

confidence: 99%

Early Cretaceous dioritic rocks in the Tongling region, eastern China: Implications for the tectonic settings

Xie

Yang

Sun

et al. 2012

Lithos

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Crustal make-up of the northern Andes: evidence based on deep crustal xenolith suites, Mercaderes, SW Colombia

Cited by 80 publications

References 68 publications

Igneous garnet and amphibole fractionation in the roots of island arcs: experimental constraints on andesitic liquids

Igneous garnet and amphibole fractionation in the roots of island arcs: experimental constraints on andesitic liquids

Geodynamic significance of the Raspas Metamorphic Complex (SW Ecuador): geochemical and isotopic constraints

Early Cretaceous dioritic rocks in the Tongling region, eastern China: Implications for the tectonic settings

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