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Late Cretaceous stratigraphy, deformation and intrusion in the Madison Range of southwestern Montana ( USA).

Geological Society of America Bulletin

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Abstract

Dating of orogenic rock units in the central part of the Madison Range shows that Laramide deformation was virtually completed by the end of the Cretaceous. Early Campanian K-Ar dates of about 79 m.y. were obtained from welded tuffs in the basal part of the Livingston Formation, a volcanic and volcaniclastic assemblage that is conformable with underlying Cretaceous clastic rocks and with the overlying Sphinx Conglomerate. The Sphinx and the Livingston were deformed by the Hilgard fault system which extends along the western side of the southern two-thirds of the range. This north-trending fault system represents the culmination of Laramide shortening within the range. Dating of hornblende indicates an approximate date of 68-69 m.y. B.P. for emplacement of the igneous suite. The dacite postdates movement along faults of the Hilgard fault system, and postdates the synorogenic Sphinx Conglomerate. -from Authors

Additional Publication Details

Publication type:
Article
Publication Subtype:
Journal Article
Title:
Late Cretaceous stratigraphy, deformation and intrusion in the Madison Range of southwestern Montana ( USA).
Series title:
Geological Society of America Bulletin
Volume
97
Issue:
7
Year Published:
1986
Language:
English
Larger Work Type:
Article
Larger Work Subtype:
Journal Article
Larger Work Title:
Geological Society of America Bulletin
First page:
859
Last page:
868