HR: 10:50h
AN: V12A-03    [Abstracts]
TI: Fluid evolution of the Varberg-Torpa charnockite-granite intrusion, SW Sweden: Magmatism and metamorphism on a regional scale
AU: * Harlov, D E
EM: dharlov@gfz-potsdam.de
AF: GeoForschungsZentrum, Telegrafenberg, Potsdam, D-14473, Germany
AU: Van den Kerkhof, A
EM: akerkho@gwdg.de
AF: Geowissenschaftliches Zentrum der Georg-August-Universität Göttingen, Goldschmidtstrasse 3, Göttingen, D-37077, Germany
AU: Johansson, L
EM: Leif.Johansson@geol.lu.se
AF: Department of Geology, University of Lund Sölvegatan 12, Lund, S-22362, Sweden
AB: The 1.4 Ga Varberg-Torpa charnockite-granite intrusion (Varberg, SW Sweden) consists of the magmatic Varberg charnockite (Opx-Cpx-Bt-Amph-Gt-Plg-Kfs-Qtz; accessory FAp, Zrn, Mt, Ilm, Py, Cp, ±Po, ±Rt), with granitic inlyers, accompanied by in-situ, patchy, fluid-induced, dehydration of local, amphibolite-facies granitic gneisses to charnockite in the vicinity of the intrusion, and the Torpa granite that is both continuous and synmagmatic with the Varberg charnockite, has a similar whole rock chemistry and mineral assemblage (minus the pyroxenes), and contains several charnockite enclaves. P-T estimation, using Gt-Opx Fe-Mg exchange thermometry and Gt-Opx- Plg-Qtz barometry of both the igneous and metasomatically derived charnockite, indicates temperatures of 650 to 700 ^oC and pressures of 750 MPa during emplacement and crystallization of the charnockite-granite intrusion. The earliest recognized fluid inclusions in both the granite and charnockite consist of H₂O- CO₂ mixtures (DF = 0.2 to 0.7). Fluid inclusions in the charnockite are characterized by high partial CO₂ densities (up to 1.0 g/cm³ for DF=0.7; 40 to 90 % bulk CO₂ with minor/no CH₄ and/or N₂); are of possible magmatic origin; and are best preserved in garnet, plagioclase, and fluorapatite (in order of decreasing CO₂ densities). Fluid inclusions with the highest CO₂ densities (1.08 to 1.10 g/cm³) are found in quartz (Th -31 to -36 ^oC) and may have originated under granulite-facies conditions. Magmatic fluids in the granite correspond to aqueous-carbonic inclusions with an estimated bulk composition (mol%) of H₂O(73)CO₂(25)NaCl(2). The salinity of solutes in the granite is generally higher than for the charnockite (typically 14 to 20 wt% NaCl-eq.). Field, petrographic, mineralogic, geochemical, and fluid inclusion evidence suggests that charnockite vs. granite crystallisation is more a function of relative H₂O activity as opposed to relative depth. In those regions of the magma, which crystallized out as charnockite, a preponderance of CO₂ lowered the H₂O activity thereby allowing for the formation of Opx and Cpx.
DE: 3610 Geochemical modeling (1009, 8410)
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 3640 Igneous petrology
DE: 3653 Fluid flow
DE: 3660 Metamorphic petrology
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2007 Fall Meeting