On the fluid-mobility of molybdenum and tungsten in subduction zone volcanics: a comparative study of the Chilean Southern Volcanic Zone and the Central American Volcanic Arc.

Wehrmann, Heidi, Garbe-Schönberg, Dieter, Hoernle, Kaj , Jacques, Guillaume, Mahlke, Julia, Schumann, Kai and van den Bogaard, Paul (2010) On the fluid-mobility of molybdenum and tungsten in subduction zone volcanics: a comparative study of the Chilean Southern Volcanic Zone and the Central American Volcanic Arc. [Poster] In: SFB 574 Subduction Workshop. , 04.-07.11.2010, Pucon, Chile .

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Abstract

57 samples of young, predominantly mafic to intermediate tephra and lava samples taken along the active arc of the Chilean Southern Volcanic Zone (SVZ), and 12 mafic tephra samples from the Argentinian back-arc were characterised for their molybdenum and tungsten concentrations in bulk rock, along with a comprehensive set of other trace elements. The results are compared to the well-studied Central American arc (CAVA) with the aim to constrain the behaviour of those two elements in subduction zones. Both Mo
and W have long been classified as relatively immobile elements; only recently advances were made revealing that they can be affected by subduction fluids.
Typical trace element ratios used to derive the involvement of subduction fluids in magma generation, such as e.g. Ba/La or U/Th, show highest values in the highest-degree melts, the latter being indicated by low La/Yb ratios.
Mo/Th plotted vs. La/Yb mimics this trend, suggesting that Mo behaves more mobile than Th in both arc systems. Mo/Th also positively co-varies directly with Ba/La in the arc rocks of the SVZ, Costa Rica, and Nicaragua, which
underlines this inference. Low Ce/Pb, particularly pronounced at the SVZ and resulting from either a strong direct subduction signal or assimilation of crustal material that has enriched Pb over Ce by subduction processes on a long time scale, is associated with the highest W/Mo values, while back-arc rocks of both arcs
trend towards mantle ratios. This points to subduction fluids promoting enrichment of W over Mo.

Document Type: Conference or Workshop Item (Poster)
Keywords: Geodynamics; subduction zone volcanology; Chilean Southern Volcanic Zone; Central American Volcanic Arc
Research affiliation: OceanRep > GEOMAR
OceanRep > SFB 574
Kiel University
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-MUHS Magmatic and Hydrothermal Systems
OceanRep > SFB 574 > C2
OceanRep > GEOMAR > FB4 Dynamics of the Ocean Floor > FB4-GDY Marine Geodynamics
Date Deposited: 13 Dec 2010 12:32
Last Modified: 23 Sep 2019 19:30
URI: http://oceanrep.geomar.de/id/eprint/10480

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