Abstract Title: Constraints on Mantle Melting from Inversion of Basalt 
Compositions

Abstract Author(s): Plank, Terry (Boston University)  

Abstract: Like a genetic code, the chemical composition of continental basalts 
record their conditions of formation. For example, basalt compositions can be 
used to infer the shape of the mantle melting regime and the location of the 
lithosphere/asthenosphere boundary. Thus, petrologic observations complement 
seismic observations on the in situ state of the sub-continental mantle, and 
geological observations of the tectonic history of a region. Study of the 
isotopic, trace element and major element composition of continental basalts of 
different ages is an important parallel activity accompanying the seismic 
component of EARTHSCOPE (USArray). Prior geochemical studies on Cenozoic Great 
Basin volcanics constrain mantle lithosphere evolution, geological terrane 
boundaries, and potential temperature of the asthenosphere. Our own work (Wang 
et al., JGR, 2002) modeling the major element composition of young basalts (< 
10 Ma) finds evidence for deep melting of unusually hot asthenosphere beneath 
the northern and central Basin and Range. Future work will be aimed at the 
volatile content of these magmas, as water in particular has a dramatic effect 
on mantle melting and rheology. Systematic efforts to map, date and analyze 
volcanic rocks would revolutionize the way regional geochemistry is done, and 
provide fresh constraints on continental growth and evolution to test with 
seismic imaging.