Abstract

The “Colorado Lineament” is the name herein assigned to a northeast-trending belt of Precambrian faults that traverses the Rocky Mountains of Colorado and the Colorado Plateau and is followed along much of its trend by the Colorado River. It has been established that northeast faults in the Colorado Mineral Belt have a Precambrian ancestry; other faults in the system have been identified in north-central Colorado. Similar faults in the Grand Canyon region have been traced across the Colorado Plateau into Utah, defining an extension of the zone in Colorado. The entire belt constitutes a fault lineament more than 1,100 km long and 160 km wide.

The northern margin of the belt is the Mullen Creek–Nash Fork shear zone, which traverses southeastern Wyoming, separating an ancient basement terrain (⩾2,400 m.y. old) in central Wyoming from younger rocks (⩽1,750 m.y. old) in Colorado. Gravity and aeromagnetic data, together with radiometric ages obtained for deep-well samples, suggest an extension of this boundary beneath the high plains and into the northern midcontinent region.

The pattern that emerges resembles a fault system of the San Andreas type. Although the record is fragmentary, the sum of the evidence suggests that the system formed adjacent to the southeastern margin of the ancestral North American continent in connection with Penokean orogeny 2000 to 1700 m.y. B.P. It appears to represent a Precambrian counterpart of Phanerozoic wrench fault systems that have formed commonly along continental plate margins during episodes of mountain building.

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