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The AAPG/Datapages Combined Publications Database

AAPG Bulletin

Abstract


Volume: 64 (1980)

Issue: 5. (May)

First Page: 700

Last Page: 700

Title: Status of Antler Orogeny in Central Idaho--Clarifications and Constraints from Pioneer Mountains: ABSTRACT

Author(s): James H. Dover

Article Type: Meeting abstract

Abstract:

Structural telescoping of argillaceous lower Paleozoic sequences with coeval calcareous and quartzitic rocks in central Idaho has commonly been presumed to be analogous to the Roberts Mountains thrust in Nevada. However, all datable thrusts in the Pioneer Mountains are post-middle Permian to pre-Eocene in age; if Antler age thrust existed, they were reactivated or obscured by major post-Antler movement. Furthermore, differences in fabric or structural style between thrusted argillaceous pre-Mississippian sequences and calcareous-arenaceous Pennsylvanian-Permian sequences, which have been cited in support of Antler orogenesis, are equivocal. These differences more likely resulted from disharmonic response to entirely later thrusting in rocks of different competencies or at different structural levels.

The Copper Basin Formation, a dominantly clastic deposit requiring an argillite-chert-quartzite western highland source in Mississippian time, remains the only evidence in central Idaho for an Antler highland. The Copper Basin now occurs in two superimposed allochthons which, when palinspastically restored, require that their original depositional basin extended at least 50 to 75 km west from the present Pioneer Mountains. Thus, in Mississippian time, the Antler highland reached no farther east than westernmost Idaho.

Emplacement of the Pioneer Mountains allochthons during mainly Mesozoic time involved (1) tectonic slices of high-grade metamorphic rocks and Precambrian crystalline basement, (2) eastward movement and imbrication of Antler detritus, and (3) thrusting of argillaceous facies lower Paleozoic rocks from the Antler highland over the tectonic remnants of its own debris. At least 100 km of post-Antler eastward translation is estimated; a comparable amount of earlier facies telescoping could be accommodated within the Antler highland based on reasonable facies reconstructions, but thrusting has not yet been demonstrated to have accompanied Antler highland development in Idaho.

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