HR: 1340h
AN: MR23C-0081    [Abstracts]
TI: Influence of Melt on Seismic Properties of Lower Crustal Xenoliths From SE Spain
AU: * Ferri, F
EM: fabio.ferri@unipd.it
AF: Dipartimento di Mineralogia e Petrologia, University of Padova, Corso Garibaldi 37, Padova, I-35137 Italy
AU: Burlini, L
EM: luigi.burlini@erdw.ethz.ch
AF: Rock Deformation Lab, ETH, Sonneggstrasse 5 , Zurich, 8092 Switzerland
AU: Cesare, B
EM: bernardo.cesare@unipd.it
AF: Dipartimento di Mineralogia e Petrologia, University of Padova, Corso Garibaldi 37, Padova, I-35137 Italy
AU: Cesare, B
EM: bernardo.cesare@unipd.it
AF: C.N.R.-I.G.G., Corso Garibaldi 37, Padova, I-35137 Italy
AB: The present study is focused on compressional wave velocities of five garnet + biotite + sillimanite + plagioclase + graphite ± cordierite ± spinel ± Kfeldspar metapelitic xenoliths recovered from the Neogene dacites of El Hoyazo and Mazarrón (SE Spain). They represent the best example of partially molten lower crust in the Alborán Domain and preserve widespread interstitial ryolitic glass as evidence of primary melt extraction. Measurements were carried out with the pulse transmission technique (Birch, 1961) in an internally heated gas apparatus (Paterson rig). For each sample three mutually orthogonal cores (x, y, z) were drilled parallel to the macroscopic fabric elements: x was parallel to lineation and z normal to foliation. Dealy time was calibrated using a sapphire single cristal cut parallel to [0001]. Measurements were conducted at pressures up to 0.5 GPa and temperatures up to 700°C on 22 mm diameter cores and up to 950°C on 15 mm diameter samples. The influence of glass on Vp is first reflected by anomalous positive dVp/dT. The velocity increases with temperature till all the grain boundaries and all the pores within the glass are closed. After that, the velocity can start to decrease. We reached that point when the melt has gone through the glass transition and was liquid again. At these high temperatures, interestingly, the velocities are remarkably high, 6.21 km/s, corresponding to 10% decrement from room T value (6.91 km/s). Anisotropy = (Vp_max-Vp_min)/Vp_mean strong increases with temperature and suggests a textural control on melt distribution. Experiments reveal that in the presence of intergranular melt, reliable data are achieved above the glass transition temperature where glass rheology changes and residual porosity is closed. As a consequence, room T measurements cannot be extrapolated to geological conditions. At melting Vp values are in agreement with deep seismic refraction data and tomography in the area and validate the hypothesis that partial melts are actually present in Alborán lower crust. REFERENCES Birch A. F., J. Geoph. Res., 66 (7): 2199-2224, 1961
DE: 5102 Acoustic properties
DE: 5112 Microstructure
DE: 7205 Continental crust (1219)
DE: 8159 Rheology: crust and lithosphere (8031)
SC: Mineral and Rock Physics [MR]
MN: Fall Meeting 2005