Crustal Evolution during Continental Collision – The Western Anatolian Laboratory
Despite the growing awareness that collisional settings have likely played an important role in the production of preserved continental crust since 0.75 Ga, there has been relatively little attempt to evaluate the nature of this process; especially when compared to the many studies of the role of arc processes. While evaluating the correspondence between the composition of arc igneous rocks and continental crust is not without its complications, the controls over arc rock compositions are reasonably well understood and relatively consistent between different arcs. For example, there is a consistent bimodal distribution of SiO2 concentrations in arc magmas worldwide centred round peaks at ~75 wt% and 55 wt%, and (largely) consistent fractionation trends between the major elements and between major and trace elements. In comparison, collisional settings contain a far wider range of igneous rocks that includes arc-style rocks, but also Na-alkaline, potassic, ultrapotassic rocks, and other types and also show greater variability along a collisional zone. Here, we use Western Anatolia as a natural laboratory to address this problem in more detail. Specifically, can we identify a “life-cycle” for collisional zone magmatism that will allow us to better evaluate the role of collisional magmatism in formation of continental crust?