Beyond a general scientific curiosity about the nature of the continental crust and its formation, detailed information on its lower and middle parts is a prerequisite for mineral and geothermal exploration and the assessment of earthquake hazards. For example, some of the most damaging earthquakes such as in Nepal (2015; Mw 7.8) and Sichuan (2008; Mw 7.9) occur in continental collision zones (Hubbard et al., 2016; Lin et al., 2009). Continental crust is up to 70 km thick. Thus, the lower crustal processes in active continental collision zones (e.g., formation of mafic or ultramafic cumulate rocks and emplacement of magma from the mantle) occur at too great depth to be studied directly (Arndt & Goldstein, 1989; Hacker et al., 2015), far beyond the reach of boreholes, for example, the deepest borehole on Kola peninsula was 12 km deep