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Geophysical interpretations of the Libby thrust belt, northwestern Montana

Professional Paper 1546

By:
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Abstract

Interpretations of gravity and aeromagnetic anomaly data, supplemented by results from two seismic reflection profiles and five magnetotelluric soundings, were used to study buried structure and lithology of the Libby thrust belt of northwestern Montana. The gravity anomaly data show a marked correlation with major structures. The Purcell anticlinorium and the Sylvanite anticline are very likely cored by stacks of thrust slices of dense crystalline basement rocks that account for the large gravity highs across these two structures. Gravity anomaly data for the Cabinet Mountains Wilderness show a string of four broad highs. The principal magnetic anomaly sources are igneous intrusive rocks, major fault zones, and magnetite-bearing sedimentary rocks of the Ravalli Group. The most important magnetic anomalies in the principal study area are five distinct positive anomalies associated with Cretaceous or younger cupolas and stocks.

Additional Publication Details

Publication type:
Report
Publication Subtype:
USGS Numbered Series
Title:
Geophysical interpretations of the Libby thrust belt, northwestern Montana
Series title:
Professional Paper
Series number:
1546
Edition:
-
Year Published:
1997
Language:
ENGLISH
Publisher:
U.S. G.P.O.,
Description:
22 p.; 2 plates in pocket