HR: 11:50h
AN: T12A-07    [Abstracts]
TI: Delamination Origin for Columbia River Flood Basalts and Wallowa Mountain Uplift in NE Oregon
AU: * Humphreys, E D
EM: ghump@uoregon.edu
AF: Dept. of Geological Sciences, University of Oregon, Eugene, OR 97403 United States
AU: Hales, T C
EM: thales@darkwing.uoregon.edu
AF: Dept. of Geological Sciences, University of Oregon, Eugene, OR 97403 United States
AU: Abt, D A
EM: David_Abt@brown.edu
AF: Dept. of Geological Sciences, Brown University, Providence, RI 02912 United States
AU: Roering, J J
EM: jroering@darkwing.edu
AF: Dept. of Geological Sciences, University of Oregon, Eugene, OR 97403 United States
AB: The Wallowa Mountains define the high center to a 200-km diameter circular ``bulls eye'' pattern of oscillating uplifts and sags, and they are comprised of the largest of the few granitic plutons in the area. The bulls eye region is the source area for most Columbia River Basalt (CRB) eruptions. Elevation maps of CRB flow interfaces are used to quantify magnitude, timing and distribution of surface uplift, and teleseismic data are used to tomographically image the underlying mantle. The bulls eye area is characterized by mild pre-eruptive subsidence, syn-eruptive uplift of several hundred meters, and a persistent km-scale uplift of the Wallowa Mountains, and it overlies an anomalous volume of mantle that is devoid of partial melt compared with adjacent areas. Predictions of hotspot plume models and passive magmatic processes are inconsistent with the history, spatial pattern and magnitude of uplift. Within the context of current geological understanding, only a convective removal (``delamination'') of compositionally dense plutonic roots can explain the uplift timing and magnitude and the imaged upper mantle structure. This suggests that CRB magmatism is a consequence of lithospheric processes rather than arrival of a mantle plume; it is possible that delamination was triggered by the arrival of hot mantle, and that the local intensity of CRB magmatism resulted from the combined effects of anomalously hot mantle and lithospheric delamination.
DE: 1211 Non-tectonic deformation
DE: 8499 General or miscellaneous
SC: Tectonophysics [T]
MN: Fall Meeting 2005