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Iliamna Volcano and its basement

1955; United States Department of the Interior; Linguagem: Inglês

10.3133/ofr5577

2332-4899

Werner Juhle,

Seismology and Earthquake Studies

v Iliamna volcano liea near the continental end of the 1500 mile long belt ol Aleutian volcano a.It erupted near the border oi the quart* diorite bathoiith competing the core of the Alaakaa Pea* insula.Hyper sthene*augite andeaite and basaltic andeaite flow* inter* bedded with coarse tuff breccias comprise thia strato volcano.Blocky lava fuaed into a slaggy matrix underlies moat flows.These baaal breccias seem to originate at the encrusting enda of moving flowa which are continually overridden by the still advancing fluid lava* Glaaa inclusions sealed in plagioclaae crystals are oxidized aa well aa the groundmaaa glaaa at the surface of lavaa indicating that the hematite producing the red color of the glaaa may have received ita oxygea from the glaaa rather than front the atmosphere.Crater fillings of porous aadesite tuff have been replaced by hydrous opal.Acid water a » producta of the hydratioa and oxidation of solfataric gases have leached out the metal cationa from the silicate minerals leaving only the opaline pseudomorph*.Propylitimed 1-ower Juraasic aadesite and dacite tuffs, tuff breccias* volcanic conglomerates, and mud flows make up a aectioa approximately 8, 000 feet thick.They grade conformably into 15» 000 feet of Middle and Upper Juraaaie silt stones, tuffaeeoua graywackes (/ aad conglomerate* dipping gently toward Cook Inlet.Pink graaophy* ric quarts moasoaite stock* occur along tha iatruaiva border of the quart* diorita batholith* They cut both the quarts diorite aad the ad* jacent sedimentary rock*.The hornblende quarts diorite gradea into a local muacovite-rich graaodiorite ia the interior of the batholith* Perhaps thia ia the deep "root11 of a former volcano where e*capiag fluid* altered the aade*iae to albita aad replaced the hornblende first by biotite aa£ secondly by muscovite.Ia places along the border of the plutoa the quart* diorite ha* been upthrust over the sedimentary rock* for very short distances aloag marginal reverse fault* add thrust fault*.