Laramide structures in the Matchless Mountain area, central Colorado

Conference · Wed Jan 01 04:00:00 EST 1992 · Geological Society of America, Abstracts with Programs; (United States)

OSTI ID:5770551

Taylor, N W ^[1]

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1. Univ. of Southern California, Los Angeles, CA (United States). Dept. of Geosciences

The Paleozoic strata and Precambrian crystalline rocks of the Matchless Mountain area northeast of Gunnison in Central Colorado, show deformation unique among Laramide structures in Colorado. These structures are part of a northeast-striking belt of deformed crystalline and sedimentary rocks recognizable for 25 miles along strike in the West Elk, and eastern Sawatch Ranges. Field and geometric studies show the area contains at least five southwest verging thrust faults which root into Precambrian rocks, separated by basement cored, shallowly plunging, northeast-trending recumbent folds. Folding shows a roughly east-west gradient with intensity increasing towards the east. Within the overturned limbs of these folds, Paleozoic strata show up to 70% shortening. Microstructural studies show some small cataclastic shear zones and some evidence for pressure solution in the quartzite samples examined. However, the observed mechanisms cannot account for the stratigraphic attenuation. Field relationships indicate that recumbent folding was followed by and probably coeval with thrusting and associated drag folding, followed by extensional faulting. Deformed 72 Ma andesitic porphyries define a probable minimum age for initiation of contraction while cross-cutting Tertiary rhyolite porphyries define a minimum age for deformation. These observations are consistent with the localized involvement of upper Cretaceous Dakota Formation in the structurally highest thrust sheet of the area. These data indicate that the rocks of the Matchless Mountain area were complexly deformed by southwest-northeast contraction during Laramide times. The nature of the roughly west to east gradient of increasing deformation indicates that this area is transitional from typical Laramide drape fold deformation to the west.

• OSTI ID: 5770551
• Report Number(s): CONF-921058--
• Conference Information: Journal Name: Geological Society of America, Abstracts with Programs; (United States) Journal Volume: 24:7
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
COLORADO
DEFORMATION
DEVELOPED COUNTRIES
GEOLOGIC FAULTS
GEOLOGIC FORMATIONS
GEOLOGIC FRACTURES
GEOLOGIC STRUCTURES
MOUNTAINS
NORTH AMERICA
ROCKS
SEDIMENTARY ROCKS
TECTONICS
USA