Magnesian andesite in the western Aleutian Komandorsky region: Implications for slab melting and processes in the mantle wedge

Abstract

Research Article| May 01, 1995 Magnesian andesite in the western Aleutian Komandorsky region: Implications for slab melting and processes in the mantle wedge G. M. Yogodzinski; G. M. Yogodzinski 1Institute for the Study of the Continents and Department of Geological Sciences, Cornell University, Ithaca, New York 14850 Search for other works by this author on: GSW Google Scholar R. W. Kay; R. W. Kay 1Institute for the Study of the Continents and Department of Geological Sciences, Cornell University, Ithaca, New York 14850 Search for other works by this author on: GSW Google Scholar O. N. Volynets; O. N. Volynets 2Institute of Volcanic Geology and Geochemistry, Petropavlovsk, Kamchatka 683006, Russia Search for other works by this author on: GSW Google Scholar A. V. Koloskov; A. V. Koloskov 2Institute of Volcanic Geology and Geochemistry, Petropavlovsk, Kamchatka 683006, Russia Search for other works by this author on: GSW Google Scholar S. M. Kay S. M. Kay 3Institute for the Study of the Continents and Department of Geological Sciences, Cornell University, Ithaca, New York 14850 Search for other works by this author on: GSW Google Scholar GSA Bulletin (1995) 107 (5): 505–519. https://doi.org/10.1130/0016-7606(1995)107<0505:MAITWA>2.3.CO;2 Article history first online: 01 Jun 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation G. M. Yogodzinski, R. W. Kay, O. N. Volynets, A. V. Koloskov, S. M. Kay; Magnesian andesite in the western Aleutian Komandorsky region: Implications for slab melting and processes in the mantle wedge. GSA Bulletin 1995;; 107 (5): 505–519. doi: https://doi.org/10.1130/0016-7606(1995)107<0505:MAITWA>2.3.CO;2 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGSA Bulletin Search Advanced Search Abstract The role of the subducting lithospheric slab in the genesis of mantle-derived (primitive) magmas is investigated through a study of volcanic rocks formed in the tectonically strike-slip–dominated western Aleutian arc. Two types of chemically and petrologically distinctive primitive andesites have been found among the Miocene–late Pleistocene–age volcanic rocks in the western Aleutians. These are termed the “Adak-type” and “Piip-type” magnesian andesites. Trace element and isotopic characteristics indicate that Adak-type magnesian andesites (adakites) formed principally as small percentage melts of the basaltic portion of the subducting oceanic crust, leaving a clinopyroxene-garnet-rutile residual mineralogy. The resulting slab melt signature (high La/Yb, Sr) distinguishes Adak-type magnesian andesites from all other Aleutian volcanic rocks. Primitive characteristics (high Mg#, Cr, Ni) and intermediate compositions (∼59% SiO2) of Adak-type magnesian andesites were acquired by interaction with peridotite and/or basalt in the mantle wedge. The absence of olivine phenocrysts from Adak-type magnesian andesites indicates that they were not equilibrated with peridotite and so are unlike Piip-type magnesian andesites, which appear to have equilibrated under low pressure and hydrous conditions in the subarc mantle. Piip-type magnesian andesites also contain a slab melt component, but reaction-equilibration with peridotite has lowered La/Yb and Sr to levels like those of common Aleutian volcanic rocks.Miocene-age calc-alkaline rocks of the Komandorsky Islands have chemical characteristics transitional between those of Adak-type magnesian andesites and common Aleutian volcanic rocks from the central and eastern arc. In a source mixture of depleted mantle wedge, slab melt, and sediment, the Komandorsky rocks have a relatively large contribution from the slab melt endmember. The strong slab melt signature among western Aleutian rocks is attributed to highly oblique convergence that produced a slow subduction path into the subarc mantle. Geochemically, the slab melt provided a high Sr, La/Yb, La/Ta, and low Ti/Hf endmember to the western Aleutian source mixture. The enhanced role for slab melting in the western Aleutians may be like that predicted for Archean systems and for modern systems where the subduction zone is warm. In this regard, Adak-type magnesian andesites are probably the appropriate analog to sanukitoids and other primitive andesitic rocks of Archean age. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.