On-shore and off-shore tephrostratigraphy: Mass budgets, Time series, and Implications for geological processes

Kutterolf, Steffen (2013) On-shore and off-shore tephrostratigraphy: Mass budgets, Time series, and Implications for geological processes (Professorial dissertation), Christian-Albrechts-Universität, Kiel, 48 pp

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Abstract

This cumulative work summarizes seven manuscripts published between 2007 and 2012. These
studies use marine and on-shore tephrostratigraphy as a tool to quantify and identify the timing, extent,
and causes of geological processes taken place at subductions zones.
In many subduction-related regions on Earth, highly explosive plinian volcanic eruptions generate
buoyant, tephra bearing eruption columns capable of penetrating up to 40 km into the stratosphere,
where they reach a neutral level of buoyancy and spread laterally. Such eruption clouds drift with the
prevailing wind over nearby oceans, gradually dropping their ash load over areas that sometimes can
be larger than 106 km2. The resulting ash layers are best preserved in non-erosive marine environments
and thus provide the most complete record of volcanic activity. Wide aerial distribution across sedimentary
facies boundaries, near-instantaneous emplacement, correlative chemical signatures, and the
presence of minerals suitable for radiometric dating make ash layers an excellent stratigraphic marker
in marine sediments and provide constraints on the temporal evolution of both, the volcanic source
region and the ash-containing sediment facies.
On-shore stratigraphic successions of tephra layers are generally based on the distinct composition
of tephras. In west-central Nicaragua for example (section 2.1), late Pleistocene to Holocene
tephras were emplaced by highly explosive eruptions, with a combined erupted mass of 184 Gt (DRE),
that are distributed into 9 dacitic to rhyolitic eruptions (84%) and 4 basaltic to basaltic-andesitic eruptions
(16%). Widespread eruptive masses from explosive volcanism are usually underestimated, even
when the most distal parts of the on-shore distribution fans, normally not preserved in terrestrial environments,
are included. If on-shore tephras can be correlated to offshore deposits like those in Central
America (sections 2.2 and 2.3), the revised erupted magma mass show that the tephras account for
65% of the total arc magma output. This enables the minimum estimation of long-term average magma
production rate at each volcano and over whole arcs. Using their unique compositional signatures,
tephras facilitate the determination of provenance as well as the reconstruction of emplacement processes
of volcanoclastic marine sediments, in accordance with regional geotectonic settings (section
2.4). Ash layers in marine sediments offshore Central America can provide time constraints for submarine
landslides at the continental slope, as they probably act as weak layers where sliding initiates
(section 2.5). Variations in the sedimentation rates on the slope, constrained by bracketing tephras of known age, can be attributed to periods of intense erosion on land likely triggered by tectonic processes.
In the case of the incoming plate these changes can be due to changes in bend-faulting activity
across the outer rise, which elicit erosion and re-sedimentation. Additionally, ash layers in Central
America can help determine the duration of active and inactive periods in the multi-stage growth history
of fluid venting sites (section 2.6). Cyclicity in the marine tephra record along the Pacific Ring of
Fire yields a statistically significant detection of a spectral peak at the obliquity period, which is related
to crustal stress changes associated with ice age mass redistribution and therefore supports the presence
of a causal link between variations in ice age climate, continental stress field, and volcanism
(section 2.7).
To summarize, the seven manuscripts presented here highlight the benefit of tephrostratigraphy as
a major tool in geology, and show that the tephra record on-shore and, especially in the marine environment,
have a spectrum of possible applications to decipher the causes and temporal variability of
geological processes.

Document Type: Thesis (Professorial dissertation)
Thesis Advisors: Hoernle, Kaj
Additional Information: Kumulative Habilitationsschrift
Keywords: Volcanology, Marine and terrestrial tephrostratigraphy, Provenance, eruption parameter, IODP
Research affiliation: OceanRep > SFB 574
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems
Projects: SFB574
Date Deposited: 09 Mar 2017 07:58
Last Modified: 09 Mar 2017 08:07
URI: http://eprints.uni-kiel.de/id/eprint/36847

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