Imaging Yellowstone Plume-Lithosphere Interactions from Inversion of Ballistic and Diffusive Rayleigh Wave Dispersion and Crustal Thickness Data
journal contributionposted on 14.06.2008, 00:00 by J. C. Stachnik, Ken Dueker, D. L. Schutt, H. Yuan
Diffusive and ballistic Rayleigh wave dispersion data from three PASSCAL seismic deployments are combined with crustal thickness constraints from receiver function analysis to produce a high-resolution shear velocity image of the Yellowstone hot spot track crust and uppermost mantle. This synoptic image shows the following crustal features: the eastern Snake River Plain (ESRP) high-velocity midcrustal layer, low-velocity lower crust beneath the 4.0-6.6 Ma Heise caldera field, high-velocity lower crust beneath the < 2.1 Ma Yellowstone Calderas, and low-velocity upper crustal volume beneath the < 2.1 Ma Yellowstone caldera fields. The low-velocity lower crust beneath the 4.0-6.6 Ma Heise caldera field is found to extend outward 50-80 km from the ESRP margins, consistent with outflow of the magmatically heated and thickened ESRP lower crust. In addition, the lack of 10 km of crustal thickening of the ESRP crust, associated with the estimated 10 km of magmatic thickening, requires that the ESRP lower crust has flowed outward in a complex fashion governed by preexisting lower crustal strength heterogeneity. Within the northern Wyoming province, the so-called 7.x km/s lower crustal magmatic layer is found to extend westward to the N-S oriented pre-Cambrian rift margin. The high-velocity, hence high-density, 7.x layer beneath the < 2.1 Ma Yellowstone caldera fields has apparently inhibited heating of the subcaldera lower crust and instead magmatic heat and fluids are exchanged with the country rock above 13 km depth. The narrow 80 km diameter plume imaged by body wave tomograms, after being sheared to horizontal by plate drift, is manifest as a very low velocity (3.9 km/s) layer that is only about 110 km wide. The ESRP mantle lithosphere has been thinned to about 28 km thickness by the plume's transport of heat and magma upward, lateral advection of the lower lithosphere by plume shear, and ongoing lithospheric dilatation.