Dispersed Volcanic Ash in Sediment entering NW Pacific Ocean Subduction Zones: Towards a Regional Perspective..

Scudder, R.P., Murray, R.W., Underwood,, M.B., Kutterolf, Steffen and Plank, T. (2012) Dispersed Volcanic Ash in Sediment entering NW Pacific Ocean Subduction Zones: Towards a Regional Perspective.. [Poster] In: The Lübeck Retreat, Collaborative Research SFB 574 Volatiles and Fluids in Subduction Zones: Climate Feedback and Trigger Mechanisms for Natural Disasters. , 23.-25.05.2012, Lübeck . The Lübeck Retreat: final colloquium of SFB 574; May 23-25, 2012: program & abstracts. ; p. 29 .

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Volcanic ash has long been recognized to be an important component of the global sedimentary
system. Ash figures prominently in a number of sedimentary and petrophysical investigations,
including how the fluid budget of subducting sediment will be affected by hydration/dehydration
reactions. Additionally, many studies focus on discrete ash layers, and how to link their presence with
volcanism, climate, arc evolution, biological productivity, and other processes. Less widely recognized
is the ash that is mixed into the bulk sediment, or “dispersed” ash. Dispersed ash is quantitatively
significant and is an under-utilized source of critical geochemical and tectonic information.
Based on geochemical studies of ODP Site 1149, a composite of DSDP Sites 579 & 581, as well as
IODP Sites C0011 & C0012 drilled during Expedition 322, we will show the importance of dispersed
ash to the Izu-Bonin-Marianas, Kurile-Kamchatka and Nankai subduction zones. Initial geochemical
analyses of the bulk sediment, as related to dispersed ash entering these subduction systems are
presented here. Geochemical analysis shows that the characteristics of the three sites exhibit some
variability consistent with observed lithological variations. For example, the average SiO2/Al2O3 ratios
at Site 1149, Site C0011 and Site C0012 average 3.7. The composite of Sites 579 & 581 exhibits a
higher average of 4.6. There are contrasts between other key major elemental indicators as well
(e.g., Fe2O3). Ternary diagrams such as K2O-Na2O-CaO show that there are at least two distinct
geochemical fields with Sites 1149, C0011 and C0012 clustering in one and Sites 579 & 581 in the
other. Q-mode Factor Analysis was performed on the bulk sediment chemical data in order to
determine the composition of potential end members of these sites. The multivariate statistics indicate
that Site 1149 has 3-4 end members, consistent with the results of Scudder et al. (2009, EPSL, v.
284, pp 639), while each of the other sites has 4-5 end members. These geochemical signatures
(e.g., K2O) of the dispersed ash can be exploited to provide insight into the importance of clay
mineralogy (i.e., smectite). Additional results from trace and REE analyses, combined with additional
statistical treatments, will also be presented.

Document Type: Conference or Workshop Item (Poster)
Keywords: Geodynamics
Research affiliation: OceanRep > SFB 574 > C4
OceanRep > SFB 574
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS
Related URLs:
Date Deposited: 21 Sep 2012 10:59
Last Modified: 21 Sep 2012 10:59
URI: http://oceanrep.geomar.de/id/eprint/15332

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