Date of Award:


Document Type:


Degree Name:

Master of Science (MS)



Committee Chair(s)

John Shervais


John Shervais


Anthony Lowry


Dennis Newell


The Snake River Plain (SRP) in southern Idaho is one of the best preserved examples of continental hotspot tracks. A layered mafic intrusion has been seismically imaged in the mid-crust, however, few geochemical studies have investigated the midcrustal sill complex’s importance in the evolution of SRP magmas. This thesis investigates the geochemistry of 3 xenoliths from a mid-to-lower crustal sill complex sampled from core taken from Kimama, ID, and 3 xenoliths from a shallow sub-volcanic magma chamber beneath the SRP sampled from Sid Butte, ID. Forward modeling and partition coefficient calculations estimate the parent melt of the Sid Butte xenoliths was a Snake River Plain olivine tholeiite magma and the parent melt of the Kimama xenoliths was an evolved Craters of the Moon (COM) type S magma. Geobarometic estimates constrain the Sid Butte xenoliths origin to a shallow magma chamber at ~3.3 km and the Kimama xenoliths in a mid-to-lower crustal sill complex at ~22 km. Kimama xenoliths have average δ18O of 5.42, indicating mantle origin and little-to-no assimilation of felsic country rock. The presence of COM-type magmas in a mid-to-lower crustal sill complex that have assimilated little-to-no crustal material indicate that fractionation processes alone can produce evolved basaltic magmas in the subsurface of the SRP. This is in contrast with theories that require a substantial amount of assimilation of felsic material for the generation of evolved COM-type magmas in the SRP. This thesis not only provides a better understanding of the crustal architecture of the SRP, it provides evidence for the importance of crustal sill complexes and shallow subvolcanic magma chambers in the evolution of SRP basalts.



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