The Geology And Blueschist Petrology Of The Western Ambler Schist Belt, Southwestern Brooks Range, Alaska

• Main Author: Nelsen, Craig Joseph
• Format: Text
• Language: English
• Published: UNM Digital Repository 1979
• Subjects: Geology; Mull; Brooks Range; Alaska
• Online Access: https://digitalrepository.unm.edu/eps_etds/394; https://digitalrepository.unm.edu/context/eps_etds/article/1414/viewcontent/NELSEN_GEOLOGY_BLUESCHIST_ALASKA_opt.pdf

The western Ambler Schist Belt is located in the southern Brooks Range of Alaska and is defined in this study as that part of the Brooks Range schist belt which contains abundant bimodal volcanic, volcaniclastic and related carbonate sediments. The schist belt appears to be the basinal part of Middle Devonian through Mississippian shelf-slope-basin sequence. To the south of the schist belt are upper Paleozoic-Mesozoic (?) ophiolite overlain by Cretaceous greywackes and calc-alkalic intrusives and related extrusives. These two distinct terrains are juxtaposed along a suspected continental suture, the Angayucham-Cosmos Hills-Jade Mountain belt, on with a minimum of 115 km of crustal shortening by obduction has been postulated (Roeder and Mull, 1978). Lithologies in the western Ambler Schist Belt appear to be related to the development of submarine felsic volcanic centers. Laterally equivalent to Felsic Domes are Proximal Deposits consisting of metabasalts and (or) felsic metavolcanics. Farther removed are Distal Deposits which appear to have resulted from clastic contamination of metavolcanics. The most prominent structure in the schist belt is the Kalurivik Arch, the surface expression of an asymmetric, northward yielding nappe. The study area is located along the south limb of this structure and is dominated by at least three large northward vergent thrusts and related folds. Three episodes of folding are recognized, an initial isoclinal episode followed by a thrust-related episode which culminated around 98 m.y. Post-metamorphic, open, gentle folds may be related to strike-slip motion on the Kobuk and related faults. Greenstones in the western Ambler Schist Belt were initially metamorphosed to the blueschist facies and have been prograded to the greenschist facies. An amphibole geobarometer developed by Brown (1976) was employed to estimate the physical condition of these two events. The blueschist event took place at 6.5-7.0 kb and 300-350â—¦ C while the environment of the greenschist event was 1.5-3.5 kb and ...