what is currently happening in the rio grande rift zone
Rio Grande rift The rift is presently nearly tectonically quiescent,[clarification needed][citation needed] but significant deformation and faulting with offsets of many kilometers were responsible for its formation starting about 35 Ma.[7] The largest-scale manifestation of rifting involves a pure-shear rifting mechanism, in which both sides of the rift pull apart evenly and slowly, with the lower crust and upper mantle (the lithosphere) stretching like taffy.[8][9][10] This extension is associated with very low seismic velocities in the upper mantle above approximately 400 km depth associated with relatively hot mantle and low degrees of partial melting.[11] This intrusion of the asthenosphere into the lithosphere and continental crust is thought to be responsible for nearly all of the volcanism associated with the Rio Grande rift.