Locating the Laramide Flat Slab
By: Christopher Harig
Isotope Geochemistry
While I shortly summarize isotope geochemistry here, more detailed discussion, particularly about the Nd-Sm, Rb-Sr, and Rh-Os systems, can be found by authors Heidi Reeg, Tanya Unger, and Eric Cannon.

The focus of the studies in this article are of radiogenic isotope geochemistry. This is built upon the idea that specific radioactive isotopes of an element, and the isotopes they decay to, will prefer to be in different sections of the upper sections of the Earth. Depending on the isotope system, one will usually prefer to reside in the upper mantle, while the other will prefer to reside in the crust/mantle lithosphere. So, due to fractionation during previous melting events, we would expect the mantle lithosphere and upper mantle to have different compositions of these isotopes because the mantle has been continuously mixing while mantle lithosphere has been removed from convective mixing. Thus by examining Cenozoic magmatism, we can determine whether the magma was sourced in the mantle or in mantle lithosphere. In the Isotope Studies page I will discuss the results of several studies of this nature and their implications for flat slab geometry.