Evidence for the Neoproterozoic Rifting of Rodinia in the Rocky Mountain Front Range

Abstract

Recent advances in low‐temperature thermochronology enable the recovery of deep‐time thermal histories from Precambrian crystalline rocks shaped by multiple tectonic events, offering unprecedented opportunities to test tectonic hypotheses and links to significant biologic and climatic episodes. In particular, the late Neoproterozoic breakup of supercontinent Rodinia profoundly shaped the western margin of Laurentia, leaving a geologic record along the Cordilleran hingeline that temporally associates continental rifting with biological change at the Ediacaran‐Cambrian transition and may explain the unusual eastern extent of the Laramide orogeny. However, sedimentary evidence east of the Cordilleran hingeline is lacking, leaving postulated links untested. Here we interpret Neoproterozoic to recent tectonic histories from the Colorado Front Range using thermal history modeling of zircon (U‐Th)/He (ZHe) ages (50–607 Ma), which vary with grain U‐Th composition. These models are constrained by geologic records that place basement rocks near Earth's surface at ca. 700, 500, and 300 Ma, and they resolve late Neoproterozoic heating to 240–285°C followed by cooling. Sensitivity tests confirm this heating signal depends on fitting Mesoproterozoic ⁴⁰Ar/³⁹Ar ages and a ZHe data set that includes high‐U‐Th grains with reproducible 61 ± 7.5 Ma ages that correspond to Colorado Mineral Belt magmatism and Laramide exhumation. We interpret the Neoproterozoic heating as direct evidence that intracontinental rifting in the Front Range region drove kilometer‐scale burial coeval with global glaciation and the fragmentation of Rodinia. The magnitude and duration of reheating are well constrained, but resolving subsequent cooling during Neoproterozoic‐Paleozoic time strongly depends on surface constraints from the geologic record.