HR: 10:35h
AN: V12A-02    [Abstracts]
TI: High Pressure Granitic Melt in Eclogite: Is it Internally Derived?
AU: * LeVay, B J
EM: blevay@geosc.psu.edu
AF: Department of Geosciences, Penn State University, University Park, PA 16802, United States
AU: Feineman, M D
EM: mdf12@psu.edu
AF: Department of Geosciences, Penn State University, University Park, PA 16802, United States
AU: Zack, T
EM: tzack@min.uni-heidelberg.de
AF: Mineralogisches Institut, Universitat Heidelberg, INF 236, Heidelberg, 69120, Germany
AU: Kerrick, D M
EM: kerrick@geosc.psu.edu
AF: Department of Geosciences, Penn State University, University Park, PA 16802, United States
AB: The Erzgebirge region of Southeast Germany is a dome-shaped structure that contains metamorphic rocks ranging from low-gade units at the periphery to eclogites and diamond-bearing granulites at the center. This study focuses on an eclogite locality on the shore of the Saidenbach reservoir, part of the highest-grade metamorphic core. The eclogites contain abundant K-feldspar-rich quartzofeldspathic material which we interpret to be a former melt. The quartzofeldspathic material is finely dispersed at the grain scale. However, the material commonly forms segregations, lenses, and veins up to several centimeters in diameter with no preferred orientation. The quartzofeldspathic material was in equilibrium with an upper amphibolite assemblage (overprinting the peak eclogite assemblage) that occurred around 800°C and 18 kbar (a pressure minimum for melt formation). The most noteworthy feature of this migmatitic eclogite is the granite composition of the segregations. Despite experiments which show that high pressure eclogite melting forms granites at low melt volumes (e.g., Schmidt et al, 2004), field observations associate eclogite melting with the formation of trondhjemites and tonalites. Thus, by understanding why granite and not trondhjemite formed within these eclogites, we can learn more about what variables control the composition of eclogite melts at high pressures. The origin of the melt can be attributed to one or more of the following processes: 1) it could have formed in the surrounding country rocks and pervasively infiltrated the eclogite; 2) it could have formed within the eclogite as a closed system, requiring a high potassium basaltic protolith; or 3) it could have formed within the eclogite as the result of an infiltrating potassium-rich fluid. The dispersal of small volumes of feldspathic material throughout the host rock strongly supports an internal origin for the granitic melt, and the divergence of trace element trends from expected eclogite-derived melt compositions suggests at least some degree of externally driven metasomatism. Isotope and trace element data will identify common end-members, enabling us to pinpoint which of the abve processes were responsible for the melt generation. By extension we hope to elucidate the nature of fluid and melt transport in high pressure metamorphic systems such as subduction zones.
DE: 1041 Stable isotope geochemistry (0454, 4870)
DE: 1065 Major and trace element geochemistry
DE: 3613 Subduction zone processes (1031, 3060, 8170, 8413)
DE: 3653 Fluid flow
DE: 3660 Metamorphic petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting