[PDF] Bedrock Geology Of The Conconully Quadrangle Okanogan County Washington eBook

Author : United States. Superintendent of Documents
Publisher :
Page : 1092 pages
File Size : 13,65 MB
Release : 1977
Category : Government publications
ISBN :

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February issue includes Appendix entitled Directory of United States Government periodicals and subscription publications; September issue includes List of depository libraries; June and December issues include semiannual index

Author : Charles Wyckoff Gulick
Publisher :
Page : 110 pages
File Size : 33,77 MB
Release : 1985
Category : Geology
ISBN :

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"Bedrock in the southwest quarter of the Aeneas Valley 15' quadrangle includes portions of the Colville batholith and the Okanogan gneiss dome. These rocks are the southern extension of a huge plutonic and high-grade metamorphic terrane known, in Canada as the Shuswap terrane, which is a major component of the Omineca crystalline belt. Three gneissic units and two plutonic units were recognized in the study area. From oldest to youngest , these are the Tonasket Gneiss, the Crawfish Lake gneiss, the Tunk Mountain gneiss, the Moses pluton, and the Swimptkin Creek pluton. The Tonasket Gneiss is the dominant unit in the study area, where it is further subdivided into five subunits. These include the cataclastic gneiss unit, the crystalloblastic gneiss unit, the leucogneiss and pegmatite unit, the heterogeneous gneiss and hornfels unit, and the quartzofeldspathic biotite gneiss unit. The Crawfish Lake and Tunk Mountain gneisses are distinct from the Tonasket Gneiss. The Crawfish Lake is an alkali feldspar megacrystic gneiss, which is in part mylonitic. The Tunk Mountain gneiss is a homogeneous quartz monzodiorite gneiss which appears to grade into the petrographically and chemically similar Swimptkin Creek pluton. The Swimptkin Creek quartz monzodiorite and the Moses leucogranite have been assigned to regionally extensive plutonic suites of the Eocene Colville batholith. They have ambiguous contact relationships with each other, but both clearly intrude the older gneisses in the study area. Field relationships suggest that the Tonasket Gneiss was intruded by both the Crawfish Lake and Tunk Mountain ortho gneisses. All three were subsequently subjected to regional amphibolite facies metamorphism accompanied by mylonitic deformation along ductile shear zones parallel to the plane of regional foliation. The gneisses were then regionally folded and intruded by the Eocene plutons, which are only weakly foliated and lineated. Structural elements within the plutons are parallel to those within the gneisses. Folding of the Tonasket, Crawfish Lake, and Tunk Mountain gneisses formed a series of broad northwest--trending synforms and antiforms within the Okanogan dome. Most of the study area lies along the southwest limb of one of these major synforms; the axis of this synform is located in the northeast corner of the study area. Along the hinge of the synform, the cataclastic gneiss unit of the Tonasket Gneiss is comprised of intensely sheared gneisses, schists, and pegmatites which include augen gneisses and mylonite. Structurally lower within the Tonasket Gneiss, the gneisses are less deformed and characterized by textures of metamorphic recrystallization"--Document.