The Coquihalla volcanic complex, Southernwestern British Columbia
Berman, Robert G. (Creator)
The Coquihalla Volcanic Complex consists of calc-alkaline acid to intermediate extrusive and intrusive rocks which have an areal extent of roughly 30 km2, near Hope, British Columbia. The oldest and most voluminous members of the complex are rhyclitic pyroclastic rocks (variably welded lithic-crystal lapilli tuff, vitric tuff, and crystal-lithic lapilli tuff) , that have an overall thickness of approximately 1600 m. Later igneous activity produced numerous andesite to dacite domes, dykes, and sills- A late stage diorite to quartz-diorite stock forms the core of Coquihalla Mountain. Most pyroclastic rocks rest unconformably en the Jurassic to Cretaceous Eagle pluton. Monolithologic avalanche breccias formed in the southern portion of the map area, where pyroclastic recks were deposited against a fault scarp with uplifted Lower Cretaceous Pasayten Group rocks. In the southeastern part of the area, monolithologic avalanche breccias formed in response to tilting and uplift of the underlying Eagle pluton as the basin subsided. All tuffaceous rocks are characterized by vitroclastic textures, and contain phenocrysts of plagicclase (An 40-20), biotite, quartz, and minor potassium feldspar and titanomagnetite. Andesites are porphyritic with phenocrysts of plagioclase (An 76-30), calcic augite, magnesic- to tschermakitic hornblende, and titanomagnetite. Glomeroporphyritic clots consist of plagioclase, aluminous augite, and titancmagnetite. Porphyritic dacites contain phenocrysts of plagioclase(An 60-35), hornblende, titanomagnetite, and minor apatite. The diorite stock consists of orthopyroxene^ clinopyroxene, plagioclase, titanomagnetite, and ilmenite, with interstitial quartz and potassium feldspar. Three K-Ar dates average 21.4±0.7 Ma, and are concordant with a Eb-Sr isochron (22.3±4 Ma with initial 87Sr/86Sr = 0.70370±0.00008) based on seven whole rock sauries which span the entire compositional range of the suite. These results indicate that the Coquihalla Volcanic Compl
Downloadable Archival Material, English, 2010-03-04T20:33:18Z