How does the 
Continental Crust form?











Earth is unique in our solar system having a bimodal distribution of crust: a basaltic oceanic crust and a more silicic continental crust. The buoyant continental crust, not found on planets of similar bulk composition (Mars, Venus), floats above the oceanic crust, providing an important aspect to plate tectonics and leading to the development of complex life on Earth. How this silicic crust form is not well understood but its clear that many of the chemical signatures of CC can be tied to the origin of convergent margin granitoids.
Over the past 5 years, our group has produced a number of papers which lead to a very different view of how convergent margin plutons like the Tuolumne Intrusive Suite (shown above) form. First, we performed laboratory experiments in which we placed andesite with 4 wt. % water into a large temperature gradient (950 down to 350°C in a 2 cm long capsule) at upper crustal pressures for 2 months; in a major discovery, granite formed at temperatures below 400°C (Huang et al. GCA 2009). By connecting this result to models of plutons forming incrementally, Lundstrom (GCA 2009) then hypothesized that plutons formed top down by a process termed thermal migration zone refining with a directly testable aspect related to isotopic signatures formed by temperature gradients (see Huang et al. Nature 2010, Lacks et al Phys Rev Lett 2012). Indeed further work has documented the incredible unrealized behavior of water dissolved in magma in a temperature gradient (Bindeman et al. EPSL 2013). Our most recent work has been testing for isotopic signatures in natural differentiation suites; Zambardi et al. (EPSL 2014) provide changes in Fe and Si isotope ratios consistent with a temperature gradient based differentiation process.
Future work seeks to understand the enigmatic relationship between granitoids and silicic volcanic rocks. Until we understand the origin of silicic magmas in general, our ability to predict how silicic volcanoes erupt is severely hampered. If you are passionate about solving geological problems through geochemistry, we welcome your application to our graduate program!