New Techniques That Add to Decades-old Disputes in the Snake Range Metamorphic Core Complex
One of the notable disagreements about the evolution of the western U.S. Cordillera centers on how thick its underlying continental crust became during regional folding and thrusting in the Mesozoic. Some think it became 60-70 km thick like the crust beneath the Andes, bringing up the questions of how, where and why it was thinned to its present 30 km. Metamorphic core complexes (rare exposures of the deep crust exhumed during stretching of the crust) are one of the places that provide evidence for a very thick crust. Late Cretaceous metamorphic mineral assemblages suggest thermodynamic equilibration at 35 km depths while geologic mapping and field relationships suggest these same rocks were never buried more than 15 km. When disagreements such as these exist between data sets provided by different disciplines, we usually get to work to try to understand what the problem is.