Journal article
Proterozoic Farwell Mountain-Lester Mountain suture zone, northern Colorado; subduction flip and progressive assembly of arcs
Geology (Boulder), Vol.30(10), pp.943-946
10/2002
DOI: 10.1130/0091-7613(2002)030<0943:PFMLMS>2.0.CO;2
Abstract
This paper considers the amalgamation of arc and oceanic terranes to be the main mechanism of ca. 1.8-1.6 Ga continental crustal growth in southwestern Laurentia. On the basis of geologic and seismic reflection data and teleseismic images, we propose the Farwell Mountain-Lester Mountain suture zone as the northernmost Paleoproterozoic arc-arc suture. North-dipping (Farwell Mountain) seismic reflections project from 18 km depths to the surface and are interpreted to represent conjugate thrusting as the 1.79-1.77 Ga Green Mountain arc was partially underthrust beneath the Archean craton. We speculate that a north-dipping high-velocity mantle "slab" in the teleseismic image is a continuation of this thrust zone. South-dipping (Lester Mountain) reflections project from 22 km depths to the surface and are interpreted to be a thrust zone between the Green Mountain arc and the 1.76-1.72 Ga Rawah block. Surface features of the Farwell Mountain-Lester Mountain suture zone are (1) marble, chert, rock with sillimanite pods, ultramafic rocks, sulfide deposits, and pillow basalts, which we interpret to be a dismembered accretionary complex; (2) an axial-planar fabric to north-verging isoclinal folds (F (sub 2) ), which we interpret to be part of a north-vergent fold-and-thrust system; and (3) a metamorphic break between approximately 500 degrees C rocks to the north and approximately 610 degrees C rocks to the south, which we attribute to reactivation of the zone. Movement on the Farwell Mountain backthrust is inferred to relate to Cheyenne belt suturing at 1.78-1.75 Ga. We correlate suturing in the Farwell Mountain-Lester Mountain suture zone to S (sub 1) /D (sub 1) (1.746-1.74 Ga) in the Soda Creek-Fish Creek shear zone. We attribute the complexity of this broad suture zone to initial conjugate thrusting, plus overprinting and steepening of accretionary structures by subsequent tectonism.
Details
- Title: Subtitle
- Proterozoic Farwell Mountain-Lester Mountain suture zone, northern Colorado; subduction flip and progressive assembly of arcs
- Creators
- A. R Tyson - University of New MexicoE. A Morozova - University of WyomingK. E Karlstrom - University of New MexicoK. R ChamberlainS. B SmithsonK. G DuekerC. T Foster - University of Iowa
- Resource Type
- Journal article
- Publication Details
- Geology (Boulder), Vol.30(10), pp.943-946
- Publisher
- Geological Society of America (GSA)
- DOI
- 10.1130/0091-7613(2002)030<0943:PFMLMS>2.0.CO;2
- ISSN
- 0091-7613
- eISSN
- 1943-2682
- Language
- English
- Date published
- 10/2002
- Academic Unit
- Earth and Environmental Sciences
- Record Identifier
- 9984229291002771
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