Journal
CANADIAN JOURNAL OF EARTH SCIENCES
Volume 56, Issue 7, Pages 738-755Publisher
CANADIAN SCIENCE PUBLISHING, NRC RESEARCH PRESS
DOI: 10.1139/cjes-2018-0083
Keywords
Neoproterozoic; Gunbarrel Large Igneous Province; Large Igneous Province; geochemistry; isotopic composition; mantle sources
Categories
Funding
- NSERC-CRD grant
- Large Igneous Province Reconstruction Group
- Mega-Grant of the Russian Federation [14.Y26.31.0012]
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Spanning 2500 km along the western margin of North America are 780 Ma dykes, sills, and minor volcanic packages of the Gunbarrel Large Igneous Province. This study focuses on southern (northwestern United States) and central (northern British Columbia) Gunbarrel intrusions and metavolcanics rocks of the Irene and Huckleberry formation (Washington State). Southern Gunbarrel U-Pb ages range from 780 to 769 Ma and new U-Pb zircon dates for the Turah and Rogers Pass sills are 778.6 +/- 0.7 and 778.7 +/- 0.9 Ma, respectively. Southern Gunbarrel intrusions are medium- to coarse-grained diabases that are moderately evolved basaltic, continental tholeiites. Intrusions display negative Nb-Ta and positive Pb anomalies in normalized multielement plots, and epsilon(78)(0)(Nd) values vary from +3.6 to +1.5. The Irene and Huckleberry volcanic rocks are E-MORB in composition with higher epsilon(780)(Nd) (+5 to +6) and likely represent partial melts of a mantle plume responsible for the Gunbarrel event. Assuming an Irene and Huckleberry parental magma, mixing models indicate that the southern Gunbarrel magmas were crustally contaminated, but local host rocks are not appropriate crustal contaminants. The modeling points to average upper crust as the crustal contaminant, with an epsilon(780)(Nd) of approximately -2. This crustal contaminant likely resides on the craton impinged upon by the mantle plume. The remarkable geochemical homogeneity of Gunbarrel intrusions from the Yukon to Wyoming is best explained if primary, plume-derived E-MORB magmas were contaminated in large magma reservoirs near the plume centre and were then injected laterally into the crust 100s to 1000s of kilometres from the reservoir.
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