The Proterozoic history of the Idaho Springs-Ralston shear zone : evidence for a widespread ca. 1.4 Ga orogenic event in central Colorado
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The Idaho Springs-Ralston shear zone (IRSZ) is one of several Proterozoic NE-trending zones within the central-eastern Colorado Front Range. The zone is composed of multiple mylonitic strands of a few meters to several kilometers in width and is mapped from ~16 km NNW of Denver, CO to ~26 km to the SW (near Idaho Springs, CO). The IRSZ and other NE-trending zones have previously been interpreted as ~1.45 Ga reactivated shear zones, following a pre-existing crustal-scale weakness, such as a suture zone that formed at ~1.7 Ga. The interpreted suture zone was based on the presence of tectonic mélange ...