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Deformation along the northeast side of Blacktail Mountains salient, southwestern Montana

By
Russell G. Tysdal
Russell G. Tysdal
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Published:
January 01, 1988

The Blacktail Mountains salient is a convex-eastward area of stacked Laramide-age thrust faults that trend north and dip west at moderate angles. The thrusts occur in Mississippian to Cretaceous strata above a basement of Archean metamorphic rocks. The northern margin of the salient is delimited by the Jake Canyon fault, a northwest-trending, northeast-dipping Laramide reverse fault. During the Laramide orogeny, the fault formed a common boundary of the present-day Blacktail Mountains and a structural high that existed in the area of the present-day valley of Blacktail Deer Creek. The fault juxtaposed Archean metamorphic rocks upon Phanerozoic strata in the northwest-era half of its extent, and against other Archean metamorphic rocks in the southeastern half. General structural relationships and study of small-scale structures in local areas show that movement along the Jake Canyon fault caused deformation of the north-trending thrust faults and associated folds. During Cenozoic extensional faulting, the Blacktail fault developed northeast of the Jake Canyon fault, and generally delimits the southwestern side of the basin of sedimentary rocks that lies beneath the valley of Blacktail Deer Creek.

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GSA Memoirs

Interaction of the Rocky Mountain Foreland and the Cordilleran Thrust Belt

Christopher J. Schmidt
Christopher J. Schmidt
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William J. Perry, Jr.
William J. Perry, Jr.
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Geological Society of America
Volume
171
ISBN print:
9780813711713
Publication date:
January 01, 1988

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