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Regional Significance Of The Tonga Formation, North Cascades, Washington, Kathleen (Kathleen Maura) Duggan
Regional Significance Of The Tonga Formation, North Cascades, Washington, Kathleen (Kathleen Maura) Duggan
WWU Graduate School Collection
The Tonga Formation of the North Cascades, Washington, is spatially situated between rocks of the crystalline core and those of the Northwest Cascades System. Its affinity to one or the other, or both, of these flanking units has been uncertain but is of importance to orogenic models for the region.
The Tonga Formation consists of weakly-deformed bedded feldspathic graywackes and shale metamorphosed at chlorite to staurolite grade. Comparison of protolith lithologic assemblage and Rb/Sr isotopic signature in addition to plutonic, metamorphic, and deformational histories suggests that the Tonga Formation is correlative with the Chiwaukum Schist and is not equivalent to …