Extensive Sills in the Crust from Deep Seismic Reflection Profiling

Abstract:

Crustal seismic reflection profiling has revealed the presence of extensive, coherent reflections with anomalously high amplitudes in the crystalline continental crust at a number of locations around the world. In some cases these seismic “bright spots” have been interpreted as fluid magma at depth. At other sites they are identified or inferred to mark interfaces between solid mafic intrusions and felsic to intermediate country rock. These latter examples most commonly appear as thin, sub horizontal sheets at middle to upper crustal depths that can be traced for tens to hundreds of kilometers. Their frequency among seismic profiles suggest that they may be more common than widely realized. These intrusions constrain crustal rheology at the time of their emplacement and post emplacement deformation. They represent a significant mode of transfer of mantle material and heat into the crust, with important implications overlying basin evolution and ore deposition