Physics
Scientific paper
Dec 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agufm.v51b0576c&link_type=abstract
American Geophysical Union, Fall Meeting 2004, abstract #V51B-0576
Physics
8450 Planetary Volcanism (5480), 8109 Continental Tectonics: Extensional (0905), 8121 Dynamics, Convection Currents And Mantle Plumes, 8145 Physics Of Magma And Magma Bodies, 8164 Stresses: Crust And Lithosphere
Scientific paper
The ongoing debate on the nature of hotspots has led many to consider alternative, tectonic models for the origin of hotspot tracks. These linear volcanic migrations, thought by most to form above supposed plume tails, have received much attention in the geological literature. In contrast, radial volcanic migrations forming above supposed plume heads have gone largely unrecognized. Two such examples are described here in the harrat volcanic province of Yemen and Saudi Arabia, and in the Columbia River Basalt (CRB) Province of the western U.S. Although most models of plume impingement predict a period of thermal uplift followed by basalt volcanism, the opposite appears to be true at the Afar triple junction, where the peak of flood basalt eruption, from ˜31-19 Ma, was followed by uplift and exhumation which began at ˜20 Ma, but accelerated at ˜14 Ma. Uplift here was contemporaneous with the eruption of widely scattered basaltic lava fields which form the Miocene-to-Holocene harrat province in Yemen and Saudi Arabia. The Yemeni harrats become progressively younger and more alkalic away from the Afar region, prompting Orihashi et al. (1998) to suggest that they formed by the outward dispersion of a mantle plume, consistent with high 3He/4He ratios (Ra. 21.6) from the easternmost of the harrats. Age-equivalent harrats in Saudi Arabia erupted in a similar fashion, from linear vent systems that become progressively younger away from the Afar triple junction. As a group, the Arabian vent systems form a fan-shaped radial pattern consistent with the outward progression of a hot mantle source. One striking similarity between the Arabian harrats and the CRB Province is that both erupted from vents located on a basement of accreted oceanic terranes, adjacent to an older cratonic margin. Like the Arabian harrats, the CRB Province also erupted from a radial system of dikes concentrated along three, age-progressive trends - the Chief Joseph, Steens-Picture Gorge, and Northern Nevada Rift trends. These three trends emanate from a focal point in southeastern Oregon which is thought to be the Miocene site of plume impingement associated with the Yellowstone hotspot. Two younger volcanic migrations emanate from the same region - the eastward-younging Snake River Plain and the westward-younging Oregon High Lava Plains. The former is thought to have formed as a hotspot track above the plume tail, and the latter by asthenospheric drag of the plume head after it was sheared off against the westward moving cratonic margin. The recognition of radial, age-progressive volcanic migrations adds support to the argument that giant radiating dike systems propagate outward with advancing time. Such spatial and temporal volcanic and plutonic trends are consistent with a mantle plume origin, but difficult to reconcile by nonplume alternatives.
Camp V. E.
Orihashi Yuji
Ross M. E.
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