In contrast, the OPA magmas crystallized at depths between 7–9 km (∼2–2.5 kbar) at 1,250–1,150☌ prior to eruption.
We use thermodynamic modeling (Rhyolite-MELTS) to show that the OP suite derives from magma stored at depths <6 km (< 2 kbar) and temperatures of 1240–1155☌. The two magmas have similar rare earth (REE) trace element signatures, suggesting the same mantle source. The major-element geochemical compositions of the two petrographic suites vary slightly, with OPA samples higher in SiO 2 and total-alkali contents than OP. The first mineral assemblage is an olivine-and-plagioclase phyric (OP) suite, and the second is an olivine-plagioclase-and-augite phyric (OPA) suite.
#Diffrent landform in the northern cascadea cracked#
We establish that the Cracked Mountain volcano was fed by two separate crustally-stored magmas (i.e., polymagmatic), each characterized by a unique phenocryst assemblage indicative of different pre-eruptive storage conditions. The paleomagnetic signature of all volcanic lithofacies records a single-pole direction and, in conjunction with stratigraphic evidence, implies a monogenetic eruption. The volcano covers an area of ∼1.5 km 2, has an eruptive volume of ∼0.18 km 3, and comprises lapilli tuff, breccia, peperite, pillow and sheet lava, and dykes with no erosional surfaces present between the stratigraphic successions. Here we investigate Cracked Mountain (CM), a 401 ± 38 ka glaciovolcanic basaltic landform in southwest, British Columbia, Canada. However, recent studies on monogenetic systems have started to recover evidence of complexities within the magma-crustal dynamics.
Monogenetic volcanoes are characterized as having no temporal break in eruptive activity and are often assumed to have a simple (singular) magmatic plumbing system. Department of Earth Ocean and Atmospheric Sciences, Volcanology and Petrology Laboratory, University of British Columbia, Vancouver, BC, Canada.
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