Fluid inclusions are known to be formed at pressures reaching some tens of kilobars. The solid matrix encompassing the fluid filled cavity experiences decompression as a consequence of uplift processes such as eruptions. This event may prompt the mechanical failure of the host-mineral matrix through either decrepitation or stretching, depending on a brittle or ductile mechanism of matrix failure, respectively (Bodnar, 2003). Laboratory experiments performed on synthetic inclusions show that the decrepitation temperature is strongly size dependent, with smaller cavities observed to decrepitate at higher temperatures. On the other hand, natural inclusions which undergo migration through a pressure gradient are always found intact below a critical size (Roedder, 1984). In this paper, we model fluid inclusions as spherical cavities in a continuous elastic-plastic medium. Under these conditions, the differential stress applied in the matrix has a cubic dependence on 1/r, where r is the radius of the cavity. The maximum differential stress concentrates at the cavity/matrix interface. For a matrix with a brittle response, if a non-local stress approach to fracturing is adopted, we demonstrated the fundamental prediction that the decrepitation phenomenon is characterized by a threshold size, and a threshold internal pressure of the cavity, below which decrepitation would not be allowed. The order of magnitude of the decrepitation threshold size is 1 µm for the analysed datasets of quartz and olivine inclusions (Campione et al., 2015). For a matrix with a ductile behaviour, plastic yield prevents critical differential stresses to be reached during uplift. However, substantial volumetric expansion starts if a threshold overpressure is reached. This overpressure influences the maximum value of the inclusion pressure one might expect for a specific matrix, and the inferred depth of magma storage levels (Campione, 2018). Bodnar, R. J. (2003), Re-equilibration of fluid inclusions, in Fluid inclusions: Analysis and interpretation, vol. 32, pp. 213–230, I. Samson, A. Anderson, and D. Marshall. Campione, M., Malaspina, N. & Frezzotti, M. L. (2015), Threshold size for fluid inclusion decrepitation. J. Geophys. Res., 120, 7396–7402. Campione, M. (2018), Threshold effects for the decrepitation and stretching of fluid inclusions. J. Geophys. Res., in press. Roedder, E. (1984), Fluid inclusions. Reviews in Mineralogy, Paul H. Ribbe.

Campione, M. (2018). The smaller the stronger – The more yielding the more obstinate: Guidelines to identify preserved mineral inclusions. In Congresso congiunto SGI-SIMP 2018 - 'Geosciences for the environment, natural hazards and cultural heritage'. Abstract book (pp.474-474).

The smaller the stronger – The more yielding the more obstinate: Guidelines to identify preserved mineral inclusions

Campione, M
2018

Abstract

Fluid inclusions are known to be formed at pressures reaching some tens of kilobars. The solid matrix encompassing the fluid filled cavity experiences decompression as a consequence of uplift processes such as eruptions. This event may prompt the mechanical failure of the host-mineral matrix through either decrepitation or stretching, depending on a brittle or ductile mechanism of matrix failure, respectively (Bodnar, 2003). Laboratory experiments performed on synthetic inclusions show that the decrepitation temperature is strongly size dependent, with smaller cavities observed to decrepitate at higher temperatures. On the other hand, natural inclusions which undergo migration through a pressure gradient are always found intact below a critical size (Roedder, 1984). In this paper, we model fluid inclusions as spherical cavities in a continuous elastic-plastic medium. Under these conditions, the differential stress applied in the matrix has a cubic dependence on 1/r, where r is the radius of the cavity. The maximum differential stress concentrates at the cavity/matrix interface. For a matrix with a brittle response, if a non-local stress approach to fracturing is adopted, we demonstrated the fundamental prediction that the decrepitation phenomenon is characterized by a threshold size, and a threshold internal pressure of the cavity, below which decrepitation would not be allowed. The order of magnitude of the decrepitation threshold size is 1 µm for the analysed datasets of quartz and olivine inclusions (Campione et al., 2015). For a matrix with a ductile behaviour, plastic yield prevents critical differential stresses to be reached during uplift. However, substantial volumetric expansion starts if a threshold overpressure is reached. This overpressure influences the maximum value of the inclusion pressure one might expect for a specific matrix, and the inferred depth of magma storage levels (Campione, 2018). Bodnar, R. J. (2003), Re-equilibration of fluid inclusions, in Fluid inclusions: Analysis and interpretation, vol. 32, pp. 213–230, I. Samson, A. Anderson, and D. Marshall. Campione, M., Malaspina, N. & Frezzotti, M. L. (2015), Threshold size for fluid inclusion decrepitation. J. Geophys. Res., 120, 7396–7402. Campione, M. (2018), Threshold effects for the decrepitation and stretching of fluid inclusions. J. Geophys. Res., in press. Roedder, E. (1984), Fluid inclusions. Reviews in Mineralogy, Paul H. Ribbe.
No
abstract + slide
Brittle and ductile failure, decrepitation and stretching, elastic-plastic behaviour, brittle fracture, yield strength
English
Congresso congiunto SIMP-SGI 2018 "Geosciences for the environment, natural hazards and cultural heritage"
9788894269642
Campione, M. (2018). The smaller the stronger – The more yielding the more obstinate: Guidelines to identify preserved mineral inclusions. In Congresso congiunto SGI-SIMP 2018 - 'Geosciences for the environment, natural hazards and cultural heritage'. Abstract book (pp.474-474).
Campione, M
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Utilizza questo identificativo per citare o creare un link a questo documento: https://hdl.handle.net/10281/206278
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