In this paper the elastic properties of amphibolites from the Serie dei Laghi and the Ivrea zone (Southern Alps, N-Italy) were investigated as a function of their mineralogical composition, microfabric and density. Three orthogonal cores were cut parallel and normal to foliation and lineation; from those, bulk and grain density were measured and the interconnected porosity was calculated. Bulk density varies from 2.75 to 3.07 g/cm(3) and calculated porosity ranges from 0.02 to 0.88%. The same cores were also used to measure seismic velocity of ultrasonic waves at room temperature and at increasing confining pressure up to 300 MPa. At high pressure the matrix properties are separated from the crack-induced properties. P-wave velocity varies with respect to the direction of propagation: the slowest direction is always normal to foliation and the fastest parallel to the mineral lineation. The mineral lineation is typically defined by the elongation of amphibole crystals, in which the fastest Vp direction is parallel to the c axis, that is also the elongation axis. The Vp ranges between 6.76 and 7.54 km/s in the direction parallel to lineation and between 6.32 and 7.06 km/s in the direction normal to foliation. This defines a Vp anisotropy of up to 14%, whose shape varies from orthorhombic to axially symmetric (either prolate or flattened). It was observed that both Vp and Vp anisotropy increase with the amount of amphibole and decrease with the amount of plagioclase. Moreover, the c axis distribution of amphiboles is responsible of the Vp anisotropy intensity and shape, in agreement with observations from previous studies. The seismic properties calculated with the approach of Mainprice (1990), using the fabric data, the elastic constants and the modal composition, gave results in good agreement with the measurements. Exposed rocks in the Ivrea and Serie dei Laghi zones show that amphibolites are interlayered with metapelites on a scale from I to 100 m. Because of the very large acoustic impedance contrast (20.34 +/- 1.75 for amphibolites, 17.16 +/- 0.4 for metapelites), they represent a very reflective portion in the middle-lower crust

Barberini, V., Burlini, L., Zappone, A. (2007). Elastic properties, fabric and seismic anisotropy of amphibolites and their contribution to the lower crust reflectivity. TECTONOPHYSICS, 445(3-4), 227-244 [10.1016/j.tecto.2007.08.017].

Elastic properties, fabric and seismic anisotropy of amphibolites and their contribution to the lower crust reflectivity

BARBERINI, VALENTINA
;
2007

Abstract

In this paper the elastic properties of amphibolites from the Serie dei Laghi and the Ivrea zone (Southern Alps, N-Italy) were investigated as a function of their mineralogical composition, microfabric and density. Three orthogonal cores were cut parallel and normal to foliation and lineation; from those, bulk and grain density were measured and the interconnected porosity was calculated. Bulk density varies from 2.75 to 3.07 g/cm(3) and calculated porosity ranges from 0.02 to 0.88%. The same cores were also used to measure seismic velocity of ultrasonic waves at room temperature and at increasing confining pressure up to 300 MPa. At high pressure the matrix properties are separated from the crack-induced properties. P-wave velocity varies with respect to the direction of propagation: the slowest direction is always normal to foliation and the fastest parallel to the mineral lineation. The mineral lineation is typically defined by the elongation of amphibole crystals, in which the fastest Vp direction is parallel to the c axis, that is also the elongation axis. The Vp ranges between 6.76 and 7.54 km/s in the direction parallel to lineation and between 6.32 and 7.06 km/s in the direction normal to foliation. This defines a Vp anisotropy of up to 14%, whose shape varies from orthorhombic to axially symmetric (either prolate or flattened). It was observed that both Vp and Vp anisotropy increase with the amount of amphibole and decrease with the amount of plagioclase. Moreover, the c axis distribution of amphiboles is responsible of the Vp anisotropy intensity and shape, in agreement with observations from previous studies. The seismic properties calculated with the approach of Mainprice (1990), using the fabric data, the elastic constants and the modal composition, gave results in good agreement with the measurements. Exposed rocks in the Ivrea and Serie dei Laghi zones show that amphibolites are interlayered with metapelites on a scale from I to 100 m. Because of the very large acoustic impedance contrast (20.34 +/- 1.75 for amphibolites, 17.16 +/- 0.4 for metapelites), they represent a very reflective portion in the middle-lower crust
Articolo in rivista - Articolo scientifico
Amphibolites; Seismic properties; Anisotropy; Fabric; Ivrea zone; Serie dei Laghi
English
227
244
18
Barberini, V., Burlini, L., Zappone, A. (2007). Elastic properties, fabric and seismic anisotropy of amphibolites and their contribution to the lower crust reflectivity. TECTONOPHYSICS, 445(3-4), 227-244 [10.1016/j.tecto.2007.08.017].
Barberini, V; Burlini, L; Zappone, A
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/2285
Citazioni
  • Scopus 38
  • ???jsp.display-item.citation.isi??? 39
Social impact