What is the Cause of the Thick Crust Geochemical Signature of Convergent Margin Volcanics?

9614782 Langmuir Convergent plate margins play a key role in the solid earth geochemical cycle, as the setting where new continental crust is created and oceanic lithosphere is recycled into the mantle. The petrogenetic processes involved in the origin of magmas in oceanic arcs, where the overlying crust is thin, are better understood than those in continental arcs where the overlying crust is much thicker. The primary goal of this proposal will be to identify the processes responsible for the thick crust geochemical signature that is often seen in convergent plate margin magmatism. It is proposed to use the eastern Mexican volcanic belt as a test locality because the lavas in this continental arc have thick crust characteristics and contain a large number and range of mafic compositions. The analytical approach will include high-precision trace element and isotope analyses (Sr, Nd, Pb and He) of the mafic rocks in order to obtain the combination of geochemical parameters that are most sensitive to the addition of subducted sediments, melting of the mantle wedge and crustal processing. This approach will hopefully allow the distinction between the various hypotheses currently invoked for the thick crust signature in continental arcs.