Na-rich partial melts from newly underplated basaltic crust: The Cordillera Blanca Batholith, Peru

Nick Petford, Michael Atherton

Research output: Contribution to Book/Report typesChapterResearchpeer-review

Abstract

The late Miocene Cordillera Blanca Batholith lies directly over thick (50 km) crust, inboard of the older Cretaceous Coastal Batholith. Its peraluminous ‘S’ type mineralogy and its position suggest recycling of continental crust, which is commonly thought to be an increasingly important component in magmas inboard of continental margins. However, the peraluminous, apparent ‘S’ type character of the batholith is an artefact of deformation and uplift along a major crustal lineament. The batholith is a metaluminous ‘I’ type and the dominant high-silica rocks (>70%) are Na rich with many of the characteristics of subducted oceanic slab melts. However, the position of the batholith and age of the oceanic crust at the trench during the Miocene preclude slab melting. Instead, partial melting of newly underplated Miocene crust is proposed. In this dynamic model newly underplated basaltic material is melted to produce high-Na, low HREE, high-Al ‘trondhjemitic’ type melts with residues of garnet, clinopyroxene and amphibole. Such Na-rich magmas are characteristic of thick Andean crust; they are significantly different from typical cole-alkaline, tonalite-grano-diorite magmas, and their presence along the spine of the Andes provokes questions about models of trondhjemite genesis by melting of subducted oceanic crust, as well as any generalized, circum-Pacific model involving consistent isotopic or chemical changes inboard from the trench.
Original languageEnglish
Title of host publicationJournal of Petrology
PublisherOxford University Press
Pages1491-1521
Number of pages31
ISBN (Print)0022-3530
DOIs
Publication statusPublished - 1996

Publication series

NameJournal of Petrology
Volume37

Fingerprint

batholith
cordillera
melt
crust
Miocene
oceanic crust
trench
slab
melting
trondhjemite
tonalite
diorite
lineament
amphibole
clinopyroxene
continental crust
partial melting
artifact
continental margin
garnet

Keywords

  • Batholith
  • Modified 'I' type granite
  • Na-rich magma
  • Thick crust

Cite this

Petford, N., & Atherton, M. (1996). Na-rich partial melts from newly underplated basaltic crust: The Cordillera Blanca Batholith, Peru. In Journal of Petrology (pp. 1491-1521). (Journal of Petrology; Vol. 37). Oxford University Press. https://doi.org/10.1093/petrology/37.6.1491
Petford, Nick ; Atherton, Michael. / Na-rich partial melts from newly underplated basaltic crust: The Cordillera Blanca Batholith, Peru. Journal of Petrology. Oxford University Press, 1996. pp. 1491-1521 (Journal of Petrology).
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Petford, N & Atherton, M 1996, Na-rich partial melts from newly underplated basaltic crust: The Cordillera Blanca Batholith, Peru. in Journal of Petrology. Journal of Petrology, vol. 37, Oxford University Press, pp. 1491-1521. https://doi.org/10.1093/petrology/37.6.1491

Na-rich partial melts from newly underplated basaltic crust: The Cordillera Blanca Batholith, Peru. / Petford, Nick; Atherton, Michael.

Journal of Petrology. Oxford University Press, 1996. p. 1491-1521 (Journal of Petrology; Vol. 37).

Research output: Contribution to Book/Report typesChapterResearchpeer-review

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T1 - Na-rich partial melts from newly underplated basaltic crust: The Cordillera Blanca Batholith, Peru

AU - Petford, Nick

AU - Atherton, Michael

PY - 1996

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N2 - The late Miocene Cordillera Blanca Batholith lies directly over thick (50 km) crust, inboard of the older Cretaceous Coastal Batholith. Its peraluminous ‘S’ type mineralogy and its position suggest recycling of continental crust, which is commonly thought to be an increasingly important component in magmas inboard of continental margins. However, the peraluminous, apparent ‘S’ type character of the batholith is an artefact of deformation and uplift along a major crustal lineament. The batholith is a metaluminous ‘I’ type and the dominant high-silica rocks (>70%) are Na rich with many of the characteristics of subducted oceanic slab melts. However, the position of the batholith and age of the oceanic crust at the trench during the Miocene preclude slab melting. Instead, partial melting of newly underplated Miocene crust is proposed. In this dynamic model newly underplated basaltic material is melted to produce high-Na, low HREE, high-Al ‘trondhjemitic’ type melts with residues of garnet, clinopyroxene and amphibole. Such Na-rich magmas are characteristic of thick Andean crust; they are significantly different from typical cole-alkaline, tonalite-grano-diorite magmas, and their presence along the spine of the Andes provokes questions about models of trondhjemite genesis by melting of subducted oceanic crust, as well as any generalized, circum-Pacific model involving consistent isotopic or chemical changes inboard from the trench.

AB - The late Miocene Cordillera Blanca Batholith lies directly over thick (50 km) crust, inboard of the older Cretaceous Coastal Batholith. Its peraluminous ‘S’ type mineralogy and its position suggest recycling of continental crust, which is commonly thought to be an increasingly important component in magmas inboard of continental margins. However, the peraluminous, apparent ‘S’ type character of the batholith is an artefact of deformation and uplift along a major crustal lineament. The batholith is a metaluminous ‘I’ type and the dominant high-silica rocks (>70%) are Na rich with many of the characteristics of subducted oceanic slab melts. However, the position of the batholith and age of the oceanic crust at the trench during the Miocene preclude slab melting. Instead, partial melting of newly underplated Miocene crust is proposed. In this dynamic model newly underplated basaltic material is melted to produce high-Na, low HREE, high-Al ‘trondhjemitic’ type melts with residues of garnet, clinopyroxene and amphibole. Such Na-rich magmas are characteristic of thick Andean crust; they are significantly different from typical cole-alkaline, tonalite-grano-diorite magmas, and their presence along the spine of the Andes provokes questions about models of trondhjemite genesis by melting of subducted oceanic crust, as well as any generalized, circum-Pacific model involving consistent isotopic or chemical changes inboard from the trench.

KW - Batholith

KW - Modified 'I' type granite

KW - Na-rich magma

KW - Thick crust

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U2 - 10.1093/petrology/37.6.1491

DO - 10.1093/petrology/37.6.1491

M3 - Chapter

SN - 0022-3530

T3 - Journal of Petrology

SP - 1491

EP - 1521

BT - Journal of Petrology

PB - Oxford University Press

ER -

Petford N, Atherton M. Na-rich partial melts from newly underplated basaltic crust: The Cordillera Blanca Batholith, Peru. In Journal of Petrology. Oxford University Press. 1996. p. 1491-1521. (Journal of Petrology). https://doi.org/10.1093/petrology/37.6.1491