Mentor: Dr. Lynne Elkins
Mid-ocean ridge basalts (MORB) are extruded on the ocean floor at divergent tectonic plate boundaries, where they interact with seawater as they cool. This interaction can cause chemical changes to occur that weather and alter the rocks. Understanding the composition of the MORB and determining which samples have been altered helps us to determine primary melt chemistry and better understand the origins of those basalts. We also hope to better constrain the complexities of the seawater alteration process. We are specifically looking at a suite of variably altered MORB from the Kolbeinsey Ridge in the Artic. This ridge is particularly interesting because it is a shallow, slow spreading ridge that thus represents near-end member mid-ocean ridge conditions, and because it is adjacent to Iceland and thus may reflect dynamics of plume-ridge interaction. To explore the extent of alteration, we will examine the Cl concentrations and Cl/K ratios within the rocks. With increased chemical exchange with seawater, the rocks develop higher concentrations of Cl. However, the original rocks can have varying levels of Cl, while seawater alterations does not affect K levels, so Cl/K ratios are commonly used to indicate the degree of seawater alteration that has occurred. Increased exposure time to seawater will increase the Cl/K ratios. We will conduct analyses of major element concentrations and Cl/K ratios using electron probe microanalysis. If results show high levels of Cl concentrations, which would indicate that there has been a more chemical interaction with seawater, we will compare Cl abundance and Cl/K results to other measures of alteration and look for systematic variations. We hope to place new chemical constraints on the nature of the alteration of MORB.