3 Continental Mafic Volcanism I: Honoring the Career of Vic Camp

Wednesday, 15 May 2024
8:00 AM - 12:00 PM
Meeting Room 1

A SEVERED HEAD: CHEMICAL LINKS BETWEEN SILETZIA AND THE COLUMBIA RIVER FLOOD BASALTS

Paper number: 3-4
Program: Theme Sessions
Time: 8:45 AM – 9:05 AM

Authors

Abstract

Mafic large igneous provinces (LIPs), oceanic plateaus and continental flood basalts, are produced from the convecting heads of deep-seated mantle plumes, and related hotspots tracking away from individual LIPs are created by the plume tails [1]. The late Cenozoic Yellowstone hotspot (YHS) trace along the Snake River plain is related to the Columbia River flood basalt (CRFB) LIP, however the latter is a small province (2.1 x 105 km3) with a lower eruption rate than other mafic LIPS. An alternative candidate for the YHS plume head volcanic accumulation is the much larger Siletzia oceanic plateau (2 x 106 km3), accreted to the western margin of North America while still active during the Eocene [2,3]. In this model, the plume head was cut off by Siletzia accretion and the establishment of an eastward-dipping subduction zone to its west. The CRFB lavas are then melts from a secondary head, fed by the plume tail, that accumulated beneath the subducting slab after Siletzia accretion, and broke through during the Miocene [4]. If so, it should be possible to trace some affinity between Siletzia and CRFB lavas, despite the well-documented chemical heterogeneity of mantle plumes globally [5]. Siletzia rocks fall into two distinct areas in Pb-Pb isotope space. The dominant population lies on the Northern Hemisphere Reference Line (NHRL), while a second group has high delta-7/4. The most primitive main-phase CRFB lavas belong exclusively to the high delta-7/4 group, with which they share affinities in key trace element ratios. These relations are consistent with production of both Siletzia and the CRFB from a single heterogeneous plume. Siletzia is dominated by melts of convectively-entrained NHRL upper mantle in the plume head, plus a small contribution from the high delta-7/4 plume tail. In contrast, the CRFB are dominated by melting products of the plume tail, which conforms to the EM II type ocean island basalt mantle source [6]. Chemical data therefore provide support for the single plume Siletzia–CRFB–YHS model.

[1] Richards et al., Science 246, 103–107 (1989) [2] Wells et al., Geosphere 10, 692–719 (2014) [3] Camp & Wells, GSA Today 31, 4–10 (2021) [4] Coble & Mahood, Geology 40, 655–658 (2012) [5] Koppers et al., Nature Rev. Earth Env. 2, 382–401 (2021) [6] Wolff & Ramos, GSA Spec. Pap. 497, 273–291 (2013)

Geological Society of America Abstracts with Programs. Vol. 56, No. 4

doi: 10.1130/abs/2024CD-399081

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