Paper No. 7
Presentation Time: 10:40 AM
GEOLOGIC EVIDENCE FOR A MANTLE PLUME ORIGIN FOR YELLOWSTONE: THE HISTORICAL PATTERN AND SCALE OF VOLCANISM, FAULTING, AND UPLIFT ALONG THE YELLOWSTONE HOTSPOT TRACK
A NE-migrating pattern of volcanism, faulting, and uplift define the 750-km-long Yellowstone hotspot track (YHT). Based on the geology associated with the YHT, we favor formation of the YHT by mantle plume (active mantle, deep-sourced) over that by lithospheric-tectonics (a passive mantle responding to lithospheric tectonics, particularly extension). A plume mechanism is supported by (1) youthful uplift and dissection of as much as 1 km NE of Yellowstone that precedes volcanism, (2) tilting away from Yellowstone on leading margin of Yellowstone hotspot, and (3) the highest geoid anomaly in the US centers on and extends NE (ahead) of Yellowstone. The following large-scale processes associated with Yellowstone are more directly explained by an active, deep-sourced, rather than passive, mantle upwelling: 1) the scale of uplift and faulting extending south and west from Yellowstone span a width of ~400 km, 2) Yellowstone has the largest concentration of geysers and other geothermal features in the world and heat flow 50 times normal, and 3) large-volume volcanism and intrusions occur with Yellowstone and the YHT. For the eastern Snake River Plain (ESRP), forming the younger part of the YHT, active faults on its margin and volcanic rift zones across the ESRP are at high angles to its trend, inconsistent with formation of the ESRP by lithospheric rifting driving mantle upwelling. After 10 Ma, both caldera-forming volcanism and high rates of faulting have migrated NE along the YHT at the same rate and direction as predicted by North American plate motion over a mantle plume. The YHT is parallel to but failed to follow a major crustal flaw (Madison mylonite zone) even though the flaw is only 40 km N of the YHT, favoring a fixed mantle plume rather the lithospheric pull apart (rift) origin. The YHT started ~16 Ma with widespread flood basalt volcanism (Columbia River Basalts and correlative flood basalts in Oregon and N California) and formation of the N-S, 1,100-km-long Nevada-Washington rift zone, similar to other plume-head events. Modeled asthenosphere parallel to this N-S rift is buoyant and consistent with a relict plume head. The simultaneous NW progression of rhyolite volcanism across southern Oregon may involve plume-head spreading, slab subduction, and strike-slip faulting and not necessarily negate a plume origin of the YHT.