Deep crustal melting in the Peruvian Andes: Felsic magma generation during delamination and uplift

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dc.contributor.authorColdwell B.
dc.contributor.authorClemens J.
dc.contributor.authorPetford N.
dc.date.accessioned2011-10-13T16:58:34Z
dc.date.available2011-10-13T16:58:34Z
dc.date.issued2011
dc.description.abstractThe Miocene-aged Yungay and Fortaleza ignimbrites (YFI), 9° S, Cordillera Blanca, Peru, share geochemical affinities typical of Phanerozoic adakite-like rocks and Archaean tonalite-trondhjemite-granodiorite (TTG) suites. In this contribution, we will investigate the melt source region(s) of the adakitic ignimbrites and their relationship to the dynamic tectonic regime in Peru at the time of eruption. The geochemistry of the YFI differs significantly from spatially related lavas in western Peru, which are characterised by classic calc-alkaline arc signatures. The YFI were erupted along crustal-scale normal faults at the culmination of major tectonic changes affecting the western Peruvian margin, where they represent the last volcanic activity recorded in the area. These regional changes included crustal thickening, shallowing of the Nazca Plate from c. 30° to c. 5°, the arrival and subduction of the Nazca Ridge and rapid crustal uplift and exhumation. The previously unstudied adakitic YFI are examined, then a series of high-pressure piston-cylinder experiments are detailed. Synplutonic mafic-intermediate dyke material is used as an analogous source, and direct experiments are performed on ignimbrite samples. These show that the geochemical signature and mineralogy of the YFI can be produced at pressures > 2.2. GPa and temperatures > 1025 °C. These data support an origin for both ignimbrites as partial melts of juvenile, garnet-bearing, hydrous, mafic lower crust (granulite to eclogite), modified by ~. 20% contamination by igneous crust. A slab source is considered highly improbable. Eclogite and granulite at > 2. GPa (> 65. km depth) are absent within the modern lithospheric architecture of the Peruvian margin, requiring removal of this source region syn- or post-eruption. A likely mechanism for removal is crustal delamination in an east-relative motion, associated with shortening caused by progressive shallowing of the Nazca Plate subducting slab. Due to the restricted mantle flow through the thinned mantle wedge, there have been no further magmatic episodes since the eruption of the Yungay and Fortaleza ignimbrites. © 2011.
dc.description.versionArticle
dc.identifier.citationLithos
dc.identifier.citation125
dc.identifier.citation02-Jan
dc.identifier.citationhttp://www.scopus.com/inward/record.url?eid=2-s2.0-79958806210&partnerID=40&md5=19ff81d7eac3363a08f38d4fc60ec829
dc.identifier.issn244937
dc.identifier.other10.1016/j.lithos.2011.02.011
dc.identifier.urihttp://hdl.handle.net/10019.1/16774
dc.subjectAdakite
dc.subjectDelamination
dc.subjectExperimental petrology
dc.subjectLower-crustal melting
dc.subjectUnderplate
dc.subjectadakite
dc.subjectcrustal structure
dc.subjectcrustal thickening
dc.subjectdelamination
dc.subjectfelsic rock
dc.subjectigneous geochemistry
dc.subjectignimbrite
dc.subjectmagma assimilation
dc.subjectmagmatism
dc.subjectmantle source
dc.subjectmelting
dc.subjectMiocene
dc.subjectNazca plate
dc.subjectuplift
dc.subjectvolcanic eruption
dc.subjectAncash
dc.subjectAndes
dc.subjectCordillera Blanca
dc.subjectCordillera Occidental [Peru]
dc.subjectPeru
dc.titleDeep crustal melting in the Peruvian Andes: Felsic magma generation during delamination and uplift
dc.typeArticle
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