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Oceanic mafic magmatism in the Siletz terrane, NW North America: fragments of an Eocene oceanic plateau?

Phillips, Bethan A., Kerr, Andrew Craig, Mullen, Emily and Weis, Dominique 2017. Oceanic mafic magmatism in the Siletz terrane, NW North America: fragments of an Eocene oceanic plateau? Lithos 274/5 , pp. 291-303. 10.1016/j.lithos.2017.01.005

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Abstract

The Siletz terrane, a predominantly mafic accreted oceanic terrane, is located in the Cascadia Forearc region of Oregon, Washington and Vancouver Island. The terrane represents a late Paleocene – Eocene large igneous province that consists of pillow lavas, massive flows and intrusive sheets. Previously it has been proposed that the Siletz terrane represents either an accreted oceanic plateau, hotspot island chain, backarc basin, island arc, or a sequence of slab window volcanics. A province-wide geochemical reassessment of the terrane, including new high precision Sr-Pb-Nd-Hf isotope, has been used to assess the validity of the proposed tectonomagmatic models for the Siletz terrane. The trace element data show little evidence of crustal contamination, or an arc signature, and the samples have rare earth element (REE) patterns that are flat to light REE enriched. These features are similar to other oceanic plateaus such as the Ontong Java and the Caribbean. Initial isotope ratios range from 206Pb/204 Pb: 18.751 to 19.668, 207Pb/204Pb: 15.507–15.661, 207Pb/204Pb: 38.294–39.2128, 176Hf/177Hf: 0.28300–0.28316 (εHf: 9.0 to 14.5), 143Nd/144Nd: 0.51282–0.51299 (εNd: 5.0 to 8.1) and 87Sr/86Sr: 0.70302–0.70380. These data are consistent with a mantle source of the Siletz terrane that appears to have been heterogeneous and slightly enriched. The enriched signature has characteristics of both EM2 and HIMU components and this, combined with a calculated mantle potential temperature well above ambient mantle, indicates derivation of the Siletz magmatism from a mantle plume, possibly the Yellowstone Hotspot. We therefore conclude that the Siletz terrane represents an accreted oceanic plateau.

Item Type: Article
Date Type: Publication
Status: Published
Schools: Earth and Ocean Sciences
Subjects: Q Science > QE Geology
Uncontrolled Keywords: Oceanic plateau; Siletz terrane; Large igneous province; NW United Sates; Mantle plume
Publisher: Elsevier
ISSN: 0024-4937
Funders: Natural Environmental Research Council (NERC)
Date of First Compliant Deposit: 11 January 2017
Date of Acceptance: 5 January 2017
Last Modified: 18 Oct 2019 02:43
URI: http://orca-mwe.cf.ac.uk/id/eprint/98487

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