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TitlePaleozoic magmatism and crustal recycling along the ancient Pacific margin of North America, northern Cordillera
 
AuthorPiercey, S J; Nelson, J L; Colpron, M; Dusel-Bacon, C; Simard, R -L; Roots, C F
SourcePaleozoic evolution and metallogeny of pericratonic terranes at the Ancient Pacific Margin of North America, Canadian and Alaskan Cordillera; by Colrpon, M (ed.); Nelson, J L (ed.); Geological Association of Canada, Special Paper 45, 2006 p. 281-322; 1 CD-ROM
Image
Year2006
Alt SeriesGeological Survey of Canada, Contribution Series 2004058
Documentserial
Lang.English
Mediapaper; CD-ROM; digital
File formatxls (Microsoft Excel)
ProvinceBritish Columbia; Yukon
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AreaCordillera; Alaska; United States of America
Lat/Long WENS-164.0000 -123.0000 70.0000 54.0000
Subjectsgeneral geology; geochemistry; geochronology; igneous and metamorphic petrology; mineralogy; regional geology; magmatic arcs; magmatic deposits; magmatic rocks; magmatism; mafic intrusive rocks; mafic volcanic rocks; mafic rocks; magmatic arcs; tholeiites; felsic intrusive rocks; felsic rocks; felsic volcanic rocks; igneous rocks; downgoing slab; craton; metamorphism; Yukon-Tanana terrane; pericratonic province; Large Igneous Province; Mantle plume; Paleozoic; Devonian
Illustrationslocation maps; geological maps; geochemical plots; tables; schematic diagrams
ProgramNSERC Natural Sciences and Engineering Research Council of Canada
ProgramAncient Pacific Margin NATMAP Project
ProgramYukon Geological Survey, Funding Program
AbstractDevonian to Permian igneous rocks in the Yukon-Tanana terrane (YTT) record six cycles of arc, arc-rift, continental rift and back-arc basin magmatism, each set apart from the others by changes in the locus and/or character of igneous activity, as well as deformational episodes and unconformities. The first four cycles, from mid-Devonian to Late Mississippian, record largely bimodal arc magmatism above a west-facing (east-dipping) subduction zone, with or without accompanying back-arc basin magmatism and continental margin rifting. The fifth, Pennsylvanian-Early Permian cycle, involved more primitive, mafic to intermediate volcanism in a west-facing arc with a corresponding marginal back-arc basin to the east. The sixth, Late Permian cycle reflects subduction reversal, and continental-arc magmatism associated with an east-facing (west-dipping) subduction zone. Mafic rocks in all cycles of both arc and nonarc character were derived from variably enriched sources, with contributions from depleted mantle wedge or back-arc asthenosphere, and enriched lithospheric mantle, with or without a subducted slab component. Felsic rocks in arc, arc-rift and back-arc geodynamic settings were derived predominantly from melting and recycling of upper continental crustal material (UCC; La/SmUCN = 1). Arc felsic rocks have calc-alkalic and tholeiitic signatures, whereas non-arc rocks are enriched in high field strength elements and rare earth elements (A-type or peralkaline signatures). Notably, throughout the late Paleozoic magmatic history of the YTT that spanned over 150 m.y., there are no systematic temporal variations in the composition of most mafic and felsic rocks. Igneous source regions and igneous processes were essentially unchanged throughout the tectonic history of the YTT.
An important aspect of many mafic rocks from YTT intra-arc rifts and back-arc basins is their high Nb/Thmn and Nb/Lamn > 1 (mn = primitive mantle normalized), implying excess Nb relative to Th and La compared to primitive mantle ratios. Excess Nb in these rocks implies a recycled oceanic crustal component in their genesis, and is a common feature of plumederived magmas and magmatic rocks from large igneous provinces. The recurrence of this recycled component over the extended magmatic history in YTT, and the common occurrence as low volume eruptions, argues against a direct plume or large-igneous province origin; however, it is possible that this signature reflects the reactivation of recycled plume or large igneous province components in the YTT lithospheric mantle that were originally derived via lithospheric fertilization by magmatism associated with Neoproterozoic breakup of Rodinia.
GEOSCAN ID215569

 
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