Evolution of magma source regions in the Rio Grande rift, southern New Mexico

Early magmatism of the southern Rio Grande rift was strongly controlled by the thermal history of the lithosphere. The compositions of igneous rocks in southern New Mexico record a general shift in magma source regions through the Cenozoic from lithosphere to asthenosphere and from upper crust to lower crust and, finally, to little crustal involvement. Extension began as early as 36 Ma, coincident with the onset of bimodal volcanism of the …