Proterozoic rocks in northern and central New Mexico originated in at least six tectonostratigraphic terranes, which can be distinguished by differences in lithology, age, and/or metamorphic grade. Boundaries between some terranes have the geometry of bedding parallel, north-verging ductile thrusts. These were active during metamorphism, but prior to the thermal peak. One terrane boundary is a south-verging ductile shear zone that has placed medium-grade on top of high-grade metamorphic rocks. It was active at and after the peak of metamorphism and may be extensional in origin. We interpret that terrane assembly occurred by ductile deformation in the middle levels of the continental crust. We do not know the original geographic relations among terranes, but the possibility exists of significant horizontal translation.

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