Geochemical and petrological constraints on rear-arc magma genesis processes in Ecuador; the Puyo cones and Mera lavas volcanic formations

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doi: 10.1016/j.jvolgeores.2008.05.023
Authors:Hoffer, Géraldine; Eissen, Jean-Philippe; Beate, Bernardo; Bourdon, Erwan; Fornari, Michel; Cotten, Joseph
Author Affiliations:Primary:
Université Blaise Pascal, Laboratoire Magmas et Volcans, Clermont-Ferrand, France
Other:
Escuela Politécnica Nacional, Ecuador
Université Blaise Pascal, France
Escuela Politécnica Nacional, France
Université de Neuchâtel, Switzerland
Université de Nice, France
Université de Bretagne Occidentale, France
Volume Title:Recent and active volcanism in the Ecuadorian Andes
Volume Authors:Johnson, Jeffrey B., editor; Samaniego, Pablo; Hall, Minard L.; Le Pennec, Jean-Luc; Wilson, L.
Source:Recent and active volcanism in the Ecuadorian Andes, edited by Jeffrey B. Johnson, Pablo Samaniego, Minard L. Hall, Jean-Luc Le Pennec, Jean-Philippe Eissen and L. Wilson. Journal of Volcanology and Geothermal Research, 176(1), p.107-118. Publisher: Elsevier, Amsterdam, Netherlands. ISSN: 0377-0273
Publication Date:2008
Note:In English. Includes appendices. 73 refs.; illus., incl. 3 tables, geol. sketch maps
Summary:The Puyo scoria cones and the Mera lava flows, two newly recognized volcanic formations dated between Late Pliocene to Middle Pleistocene, extend the limits of the Ecuadorian rear-arc volcanic province some 100 km to the south. The Puyo scoria cones have erupted K-rich absarokites containing olivine, diopside and phlogopite, whereas the Mera lava flows display a basic andesite composition, with olivine and minor augite phenocrysts. In addition to high contents in LILE, LREE and HFSE, the Puyo absarokites exhibit many characteristics of primitive melts, namely high Cr (590-310 ppm) and Ni (330-154 ppm) contents, high Mg# (64-70) and they contain forsteritic olivine (Fo82-89). The composition of the most primary Puyo absarokite was used in petrogenetic models, in order to constrain the genesis of these high-K magmas. Major and trace elements models, as well as isotopic data, indicate that the source of Puyo magmas is a hydrated phlogopite- and garnet-bearing lherzolite. Phlogopite crystallization in the mantle wedge is triggered by the metasomatism by 3-5% of a SiO2-, H2O-rich liquid generated by slab melting. Partial melting of the subducted oceanic crust beneath Ecuador is allowed by the subduction of the young and warm Carnegie Ridge, which modifies the thermal regime of the Benioff zone. A low degree (1-4%) of partial melting of the metasomatized mantle wedge, leaving a variable garnet (4-7%)±phlogopite (0-4%) lherzolitic residual assemblage, leads to the compositions of the entire Puyo absarokite series and is consistent with previous petrogenetic models developed for the Ecuadorian volcanic arc. Indeed, the homogeneity of isotopic data across the arc suggests a similar source for the whole Ecuadorian magmas. [G.L.B.]
Sections:Petrology
Subsections:Volcanology
Subjects:Absarokite; Andesites; Cenozoic; Cinder cones; Crystallization; Geochemistry; Harzburgite; Igneous rocks; Isotopes; Lava flows; Lherzolite; Magmas; Major elements; Mica group; Neogene; Partial melting; Peridotites; Phenocrysts; Phlogopite; Plate tectonics; Pleistocene; Pliocene; Plutonic rocks; Pyroclastics; Quaternary; Scoria; Sheet silicates; Silicates; Stable isotopes; Subduction; Tertiary; Trace elements; Trachyandesites; Ultramafics; Upper Pliocene; Volcanic features; Volcanic rocks; Andes; Carnegie Ridge; East Pacific; Ecuador; Pacific Ocean; South America; Mera Formation; Puyo Ecuador
Coordinates:S012300 S012100 W0775300 W0775600
Abstract Numbers:08M/3883
Record ID:2009044048
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from CAPCAS, Elsevier Scientific Publishers, Amsterdam, Netherlands
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