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| Titel |
The 12.4 ka Upper Apoyeque Tephra, Nicaragua: stratigraphy, dispersal, composition, magma reservoir conditions and trigger of the plinian eruption |
| VerfasserIn |
Heidi Wehrmann, Armin Freundt, Steffen Kutterolf |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250133498
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| Publikation (Nr.) |
 EGU/EGU2016-14113.pdf |
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| Zusammenfassung |
| Highly-explosive plinian eruptions belong to the most devastating phenomena of volcanic
activity. Upper Apoyeque Tephra (UAq), erupted in close vicinity of the Managua city
region in west-central Nicaragua with two million inhabitants, was formed by a
rhyodacitic plinian eruption at 12.4 ka BP. The fallout tephra was dispersed from
a progressively rising plinian eruption column that became exposed to different
wind speeds and directions at different heights in the stratosphere, leading to an
asymmetric tephra fan with different facies in the western and southern sector. Tephra
dispersal data integrated with geochemical compositions of lava flows in the area
facilitate to delimit the source vent to the south of Chiltepe Peninsula. UAq, Lower
Apoyeque Tephra, Apoyeque Ignimbrite, and two lithic clasts in San Isidro Tephra
together form a trend distinct from that of the younger tephras and lavas at Chiltepe
Volcanic Complex in a TiO2 versus K2O diagram, compositionally precluding a
genetic relationship of UAq with the present-day Apoyeque Volcano. Apoyeque
Volcano in its present shape did not exist at the time of the UAq eruption. The surface
expression of the UAq vent is now obscured by younger eruption products and lake
water.
Pressure-temperature constraints based on mineral-melt equilibria indicate at least two
magma storage levels. Clinopyroxenes crystallised in a deep crustal reservoir at ∼24 km
depth as inferred from clinopyroxene-melt inclusion pairs. Chemical disequilibrium between
clinopyroxenes and matrix glasses indicate rapid magma ascent to the shallower reservoir
at ∼5.4 km depth, where magnesiohornblendes and plagioclase fractionated at a
temperature of ∼830∘C. Water concentrations ranged at ∼5.5 wt. % as derived from
congruent results of amphibole and plagioclase-melt hygrometry. The eruption was
triggered through injection of a hotter, more primitive melt into a water-supersaturated
reservoir. |
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