The East Pacific Rise (EPR) north of the Orozco transform fault off the coast of Mexico provides unique opportunities to further our understanding of the origin of the ocean crust and the nature of the upper mantle. This region is the shallowest, most-inflated portion of the northern EPR, and extends the range of axial morphology that has been examined in detail by a factor of two, which allows the test of a number of models relating axial morphology to magma chambers, volcanic behavior, and hydrothermal activity. Second, this region allows a clarification of the nature and origin of the chemical characteristics of the Pacific upper mantle. Basalts recovered from the EPR differ fundamentally in their distribution of chemical compositions from those recovered along the mid-Atlantic Ridge. There are two hypotheses for these differences: (1) that the mantle beneath the EPR is ubiquitously "veined" by small scale heterogeneities that are a natural consequence of plate recirculation in the upper mantle; (2) that hot spots under the EPR are smeared out and mixed in to the upper mantle more efficiently than along the MAR. The Orozco anomaly is a potential small hot spot track near the EPR. If we find that it is a hot spot, and that its chemical characteristics can explain the enriched MORB along the EPR, then the second model will be supported. If not, then model (1) is more likely.
