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| Titel |
Reduced carbonic fluid and possible nature of high K magmas of Kamchatka. |
| VerfasserIn |
Alexander Simakin, Michael Zelensky, Tamara Salova |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250088884
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| Publikation (Nr.) |
 EGU/EGU2014-3061.pdf |
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| Zusammenfassung |
| High potassium magmatism in Kamchatka is usually interpreted as reflection of the small
degree mantle melting in back arc environment. Strong eruption of Tolbachik volcano located
in typical subduction magmatism setting and lasted for several months in 2012-2013 argues
against such interpretation. Erupted basaltic magmas contain up to 2.5-3.5 wt.% of K2O.
They bear all attributes of high-K magmas such as high Ba (600 ppm) and Zr (250 ppm)
contents [Volynets et al., 2013]. Moreover recent [Ponamareva et al., 2013] estimates of the
volume of the compositionally similar early Holocene pyroclastics from located nearby
Plosky volcano give significant value of ca 10 km3. Syneruptive probing of the
fluid on Tolbachik [Zelensky, in preparation] yields high CO2 and SO2content and
reveals micro-inclusions of elemental carbon and native alloys of Ni-Fe, Pt and
Pt-Ag. These observations stay for the intrinsic reduced carbon-bearing nature of this
fluid.
We suggest that nature of the fluid plays decisive role in the potassium magma
specialization. New experimental data on the melting with reduced carbon bearing fluid
supports this suggestion. Experiments have been performed in IHPV at P=2-5 kbar and
T=900-1000oC. Initial content of CO in the dry CO2-CO mixture was about 14
wt.%, maximum final water content of H2O in the final fluid was about 13 wt.%. At
dehydration melting through CO2-CO fluid transport of the spilitized basaltic andesite we
get melt with up to 330 ppm of ZrO2 and 9 wt.% of K2O (source rock contains
only 1 wt.% K2O). With oxidized carbonic fluid normal sodium bearing melt was
produced.
Carbon enrichment of the mantle fluid can be explained as follows. Current geodynamic
regime and volcanism in Kamchatka are affected by geologically recent accretion of
Kronotsky paleoarc approximately 5 Myrs ago (northern part). In the new geodynamic model
[Simakin, 2013] at the certain rheologic parameters accreted terrains are overstepped by
subduction zone with temporary inversion of the subduction direction. At such regime large
blocks of the accreted arc are pushed under the mantle edge. Krontsky paleoarc was formed
at the latitudes close to the equator in Cretaceous time being enriched in organic and silicified
carbonates rocks. Large masses of such rocks may ascend in the form of the sedimentary
plumes or dykes in the mantle wedge and provide source for the reduced carbonic fluids
at certain depth. By the slow circulation in the mantle wedge carbonatized zones
would shift trench-ward with time and now reach position of CKD under Tolbachik
volcano.
Literature.
Ponamareva V., Portnyagin M. et al., 2013. Geol Rundsch 102:1673–1699.
Simakin A.G. 2013. Terra Nova. Published online.
Volynets A.O., Melnikov D.V., Yakushev A.I. 2013. Proceedings of RAS, v.452,
p.303-307 (in Russian). |
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