scholarly journals Timing and deformation conditions of the western Idaho shear zone, West Mountain, west-central Idaho

Lithosphere ◽  
2016 ◽  
Vol 9 (2) ◽  
pp. 157-183 ◽  
Author(s):  
N. Braudy ◽  
R.M. Gaschnig ◽  
D. Wilford ◽  
J.D. Vervoort ◽  
C.L. Nelson ◽  
...  
Keyword(s):  
Shear Zone ◽  
West Central ◽  
Mountain West ◽  
Central Idaho

Age and structure of the Crevice pluton: overlapping orogens in west-central Idaho?

2012 ◽  
Vol 49 (6) ◽  
pp. 709-731 ◽  
Author(s):  
Keith D. Gray ◽  
A. John Watkinson ◽  
Richard M. Gaschnig ◽  
Vincent H. Isakson
Keyword(s):  
Shear Zone ◽  
Inductively Coupled Plasma ◽  
Shear Zones ◽  
Ductile Deformation ◽  
North American Cordillera ◽  
Salmon River ◽  
The North ◽  
West Central ◽  
Salmon River Suture Zone ◽  
Central Idaho

New U–Pb zircon geochronology from the Riggins region of west-central Idaho refines the timing of contractional deformation across the Salmon River suture zone (SRSZ), a broad north- to northeast-striking belt (>25 km wide) of high strain recording Jura-Cretaceous island-arc–continent collision. Laser ablation – inductively coupled plasma – mass spectrometry (LA–ICP–MS) yields mid-Cretaceous crystallization ages on formerly undated plutonic rocks sampled from the Salmon River canyon. In the Crevice pluton (∼105 Ma), the development of steep to moderate northerly striking gneissic foliation (S1) was followed by tops-to-the-west slip on shallow mylonitic shear zones (S2) and brittle overprinting via systematic joints (Jn) of regional extent. Together, these structures form the pluton’s internal architecture. Subvertical gneissic foliation in the adjacent Looking Glass pluton (∼92 Ma) indicates ductile deformation was ongoing in the Late Cretaceous. Prior to this investigation, penetrative fabrics in local arc volcanogenic, plutonic, and continental rocks have been unequivocally linked to post-collisional dextral transpression on the narrow (<10 km wide) western Idaho shear zone (WISZ). As an alternative to this model which requires spatially overlapping but temporally distinct orogenic belts (WISZ–SRSZ), we consider a protracted history whereby regional synmetamorphic structures accumulated over a pre-118 Ma to post-92 Ma interval without an overprinting orogen-scale ductile shear zone. In our view, a progressive deformation history more accurately accounts for the time-transgressive nature and structural continuity of fabrics observed across the arc–continent transition. This tectonic history proposed for western Idaho may be analogous to other long-lived accretionary margins in the North American Cordillera (e.g., Omineca Belt of southeastern British Columbia).

The milliped genus Isaphe Cook (Polydesmida: Xystodesmidae)

1993 ◽  
Vol 71 (6) ◽  
pp. 1161-1168 ◽  
Author(s):  
Rowland M. Shelley
Keyword(s):  
River Basins ◽  
Strong Convexity ◽  
Distribution Map ◽  
Montane Forests ◽  
West Central ◽  
Riparian Woodlands ◽  
Northern Idaho ◽  
Caudal Margin ◽  
Central Idaho

The harpaphine xystodesmid milliped genus Isaphe, characterized by two telopodal branches and a prefemoral process that angles across the medial face of the telopodite, comprises two species. Isaphe convexa Cook occurs in montane forests of northern Idaho and Montana, and I. tersa (Cook) is known from riparian woodlands in canyons of the Snake, Salmon, and Palouse river basins in southeastern Washington and west-central Idaho. They are distinguished by the degree of dorsal convexity, strong in I. convexa and weak in I. tersa, and by the length of the prefemoral process, which is long and slender and extends well beyond the caudal margin of the telopodite stem in I. convexa, and is short and broad and terminates well before the margin in I. tersa. The strong convexity in I. convexa results from greater expression of the dorsal curvature than is the case in most xystodesmids because of a lower than usual origin of the paranota, rather than from depression of the latter. The following new synonymies are proposed: Hybaphe Cook under Isaphe Cook, H. curtipes Cook under I. tersa, and Leptodesmus (Isaphe) simplex Chamberlin under Harpaphe haydeniana haydeniana (Wood). Modern descriptions are provided for the genus and species, and anatomical illustrations and a distribution map are presented.

Sign in / Sign up

Export Citation Format

Share Document