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- W2059003440 abstract "Lower Cretaceous volcanism in the Coastal Range (29°20′–30°S) of Chile is mainly represented by highly porphyritic (20–30% phenocrysts) lavas with unzoned Ca-rich plagioclase (An57–54Ab40–42Or3–4), clinopyroxene (Wo40En43Fs17), magnetite, and minor idiomorphic, altered olivines. Geochemically, these lavas are characterized by a relative homogeneity with high Al2O3 and low MgO contents, and classified as high-K to shoshonitic basaltic andesites to andesites generated in an intra-arc extensional setting due to oblique subduction. Their isotopic geochemistry is characterized by highly homogeneous low initial Sr ratios ((87Sr/86Sr)0∼0.7036) and positive εNd values (εNd=+2.9 to +4.7 (143Nd/144Nd)0∼0.5127) that are very different from those proposed as representative of ‘Andean-type’ magmatism. A non-Andean modern setting dominated by subduction associated with intra-arc extension is proposed. On a (87Sr/86Sr)0 versus εNd diagram, these lavas fit a model mixing curve for which the end members are Pacific MORB and Jurassic plutonic rocks from the Coastal Range. Coeval granitoids from the Coastal Range and lavas from the High Andes plot on the same field. Isotopically depleted mafic magmas could be metasomatized by the subducted sediments, which would increase their LILE content, and then partially contaminated by Jurassic plutonic rocks. The genesis of this magmatism may be related to a global low-spreading rate of 5 cm yr−1 in the southeast Pacific during 125–110 Ma. El volcanismo del Cretácico Inferior en la Cordillera de la Costa de Chile (29°20′–30°S) está representado principalmente por lavas altamente porfı́dicas (20–30% fenocristales), con plagioclasa cálcica no zonada (An57–54Ab40–42Or3–4), clinopiroxeno (Wo40En43Fs17), magnetita, y menores proporciones de cristales idomórficos de olivino completamente alterados. Geoquı́micamente, estas lavas se clasifican como andesitas basálticas y andesitas altas en potasio a shoshonı́ticas, y están caracterizadas por contenidos de Al2O3 relativamente altos y homogéneos, y bajos valores de MgO. La génesis de estas lavas se interpreta en relación con un régimen extensional intra-arco, generado como consecuencia de una subducción oblı́cua. Isotópicamente son lavas con bajos valores iniciales en las relaciones de Sr ((87Sr/86Sr)0≈0.7036) y valores positivos del εNd (εNd=+2.9 a +4.7 (143Nd/144Nd)0≈0.5127). Se propone un contexto geotectónico diferente al del magmatismo andino reciente, controlado no sólo por la subducción sino también por una extensión intra-arco. En un diagrama (87Sr/86Sr)0 vs εNd, las lavas cretácicas se proyectan a lo largo de una curva de mezcla entre el MORB del Pacı́fico y las rocas plutónicas del Jurásico de la Cordillera de la Costa. Además, rocas granı́ticas del Cretácico de la Cordillera de la Costa, ası́ como lavas cretácicas de la Cordillera de los Andes, se proyectan en el mismo campo que el de las lavas cretácicas. Este modelo petrogenético involucra a magmas máficos, isotópicamente empobrecidos, que serı́an metasomatizados por sedimentos subducidos, aumentando sus contenidos en LILE, y posteriormente contaminados parcialmente por las rocas plutónicas del Jurásico. Este magmatismo podrı́a estar relacionado con una baja tasa de expansión oceánica de 5 cm yr−1 en el SE del Pacı́fico durante el intervalo 125–110 Ma." @default.
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- W2059003440 date "2003-12-01" @default.
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- W2059003440 title "Extensional Lower Cretaceous volcanism in the Coastal Range (29°20′–30°S), Chile: geochemistry and petrogenesis" @default.
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