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Benjamin is a rising junior undergraduate at Tufts University this year, currently pursuing a bachelor’s degree in Physics with a minor in Mathematics. After he completes his B.S, he will continue to a Ph.D. program in Geophysics with a focus on planetary science. This summer, he will examine the effects of crustal assimilation and mantle composition on trace element ratios in arc magma and construct a geochemical model to predict the behavior of young arc systems. Benjamin is interesting in increasing the accessibility of science to the general public and hopes to become a professor in the future.
Geochemical consequences of Pressure and Temperature in arc magma formation: Modeled partitioning of Sr/Y and La/Yb in primary arc magmas.
‘Pseudobarometers’ are a methodology for the reconstruction of ancient arc crustal thickness in continental collision zones. Making use of recently observed empirical correlations between the depth of the Mohorovičić discontinuity and Sr/Y and La/Yb ratios, ‘pseudobarometers’ have risen in popularity among geochemists due to their relatively simple application compared to thermobarometers, a reliable but complex way to estimate crustal thickness. However, when compared to natural data from sampled sites spread across the world, there is significant deviance found between the crustal thickness values generated from Sr/Y and La/Yb ratios and the actual values experimentally observed for the same samples. Factors aside from Moho depth must impact the trace element ratios of surface arc magmas, negatively affecting the reliability of ‘pseudobarometers’. Therefore, in this study, we investigate the initial conditions at which arc magmas form and their impact on post-melt trace element composition. We use ideal solid solution models and a standardized bulk composition to simulate the evolution of a general arc magma and to isolate the effect of formation depth on Sr/Y and La/Yb ratios. The trace element ratios gathered through this model were substantially lower than those from the natural data, indicating that while there is a positive correlation between Moho depth and both Sr/Y and La/Yb, alternate factors have a significant impact on these ratios. From this data, we can better identify areas of research that are necessary for reliable application of ‘pseudobarometers’ as proxies for crustal thickness reconstruction.