Detrital rutile ages can deduce the tectonic setting of sedimentary basins

Abstract

Sedimentary sequences contain a detailed record of the evolution of the Earth's surface. Detrital mineral grains provide, for example, evidence of source redox conditions, insights into the age, geochemistry and petrology of basement sources and can also be used to elucidate tectonic environments. Detrital zircon has been used as a means of analysing the tectonic setting of host sedimentary successions, but with potentially ambiguous results. It is important to find additional ways to discriminate depositional settings, particularly in Precambrian sequences where other proxies are either not available or have been lost. In this contribution we provide a new way to discriminate between different sedimentary tectonic environments using the mineral rutile. We present a large compilation of detrital rutile data to show that the U-Pb age distribution is sensitive to the tectonic setting of the basin in which the host sediments were deposited. We then apply this new approach to two case studies, where the depositional setting and age are well-constrained: siliciclastic units of NW Scotland which were deposited in the Neoproterozoic foreland of the Grenville Orogen and on the Cambrian passive margin of the Iapetus Ocean, and the Brazilian Sabará basin located within the Palaeoproterozoic foreland of the Minas orogen. We compare the detrital rutile and zircon age distributions of these successions, showing that in some cases they are different, and that rutile is most sensitive to the youngest metamorphic events affecting the sources, reinforcing the applicability of this tool. By testing this new method on polyphasally-deformed successions (Sabará basin) we show that detrital rutile can still inform the tectonic setting even at medium grades of metamorphism.