Libby thrust belt and adjacent structures - new factors to consider in thrust tectonics of northwestern Montana

Harrison, J E; Cressman, E R

Title: Libby thrust belt and adjacent structures - new factors to consider in thrust tectonics of northwestern Montana

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Abstract

About 40 mi (65 km) west of the Rocky Mountain trench and at least 9 mi (15 km) above the sole detachment of the Rocky Mountain thrust belt is a zone of Cretaceous-Tertiary thrust faults up to 25 mi (40 km) wide in middle Proterozoic and Cambrian rocks. This zone (the Libby thrust belt) extends northward from the Lewis and Clark line to the northwest corner of Montana. Within the Libby thrust belt is a series of complex ramps, horsts, splays, and folds that accommodate a tectonic shortening of about 6.2 mi (10 km). Backsliding has occurred on some listric thrust faults, and middle Tertiary(.) extensional horst-and-graben faults offset or join most thrust faults. On the east, the lead thrust ramps up onto the broad open Purcell anticlinorium. On the west, the Libby thrust belt is overridden in the north by the lead thrust of the Yaak plate (whose central part is the broad, open Sylvanite anticline), and in the south, it is overridden by the Moyie thrust (which trends northwest and also overrides the west edge of the Yaak plate). Geologic cross sections suggest that the Belt rocks have overridden the Cambrian at shallow depths only and that Cambrianmore »« less

Authors:: Harrison, J E; Cressman, E R

Publication Date:: Wed May 01 00:00:00 EDT 1985

Research Org.:: Geological Survey, Denver, CO

OSTI Identifier:: 6146108

Report Number(s):: CONF-8506201-
Journal ID: CODEN: AAPGB

Resource Type:: Conference

Journal Name:: Am. Assoc. Pet. Geol., Bull.; (United States)

Additional Journal Information:: Journal Volume: 69:5; Conference: AAPG Rocky Mountain Section meeting, Denver, CO, USA, 2 Jun 1985

Country of Publication:: United States

Language:: English

Subject:: 02 PETROLEUM; MONTANA; GEOLOGIC HISTORY; GEOLOGIC STRUCTURES; TECTONICS; ANTICLINES; CAMBRIAN PERIOD; GEOLOGIC FAULTS; PETROLEUM GEOLOGY; TERTIARY PERIOD; CENOZOIC ERA; FEDERAL REGION VIII; GEOLOGIC AGES; GEOLOGIC FRACTURES; GEOLOGY; NORTH AMERICA; PALEOZOIC ERA; USA; 020200* - Petroleum- Reserves, Geology, & Exploration

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                    Harrison, J E, and Cressman, E R. Libby thrust belt and adjacent structures - new factors to consider in thrust tectonics of northwestern Montana.  United States: N. p., 1985. 
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                    Harrison, J E, & Cressman, E R. Libby thrust belt and adjacent structures - new factors to consider in thrust tectonics of northwestern Montana.  United States.

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                    Harrison, J E, and Cressman, E R. 1985.  
        "Libby thrust belt and adjacent structures - new factors to consider in thrust tectonics of northwestern Montana".  United States.

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@article{osti_6146108,

  title        = {Libby thrust belt and adjacent structures - new factors to consider in thrust tectonics of northwestern Montana},

  author       = {Harrison, J E and Cressman, E R},

  abstractNote = {About 40 mi (65 km) west of the Rocky Mountain trench and at least 9 mi (15 km) above the sole detachment of the Rocky Mountain thrust belt is a zone of Cretaceous-Tertiary thrust faults up to 25 mi (40 km) wide in middle Proterozoic and Cambrian rocks. This zone (the Libby thrust belt) extends northward from the Lewis and Clark line to the northwest corner of Montana. Within the Libby thrust belt is a series of complex ramps, horsts, splays, and folds that accommodate a tectonic shortening of about 6.2 mi (10 km). Backsliding has occurred on some listric thrust faults, and middle Tertiary(.) extensional horst-and-graben faults offset or join most thrust faults. On the east, the lead thrust ramps up onto the broad open Purcell anticlinorium. On the west, the Libby thrust belt is overridden in the north by the lead thrust of the Yaak plate (whose central part is the broad, open Sylvanite anticline), and in the south, it is overridden by the Moyie thrust (which trends northwest and also overrides the west edge of the Yaak plate). Geologic cross sections suggest that the Belt rocks have overridden the Cambrian at shallow depths only and that Cambrian and younger Phanerozoic strata probably do not occur at greater depths beneath and west of the Purcell anticlinorium. This interpretation differs significantly from interpretations that suggest intercalation of major wedges of Paleozoic and Belt rocks at depth in this same area.},

  doi          = {},

  url          = {https://www.osti.gov/biblio/6146108},
  journal      = {Am. Assoc. Pet. Geol., Bull.; (United States)},
number       = ,

  volume       = 69:5,

  place        = {United States},

  year         = {Wed May 01 00:00:00 EDT 1985},

  month        = {Wed May 01 00:00:00 EDT 1985}

}

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