Threshold Effects for the Decrepitation and Stretching of Fluid Inclusions

Minerals embedding fluids in the form of microinclusions are recurrent in xenoliths and exploited for inferring the characteristics of magma dynamics in relation to volcanism. Xenolith migration from mantle conditions to Earth surface might trigger failure transformations known as decrepitation and stretching. The former is a fairly recognizable transformation, corresponding to the brittle failure of the host mineral nearby the inclusion. The latter is a more intriguing transformation, corresponding to the plastic expansion of the cavity, that is, without fracture formation. Both transformations bring about a decrease of the fluid inclusion density, preventing to assess the original depth level of the xenolith. Here decrepitation and stretching are analyzed in the framework of an elastic-plastic model providing a thorough tool to interpret experimental density data. Both phenomena are shown to be governed by threshold effects, establishing a net boundary between preserved and failed matrixes in terms of cavity size, internal, and confining pressure. A common feature of stretched systems emerges in the concept of the limiting pressure, influencing the maximum value of the inclusion pressure one might expect for a specific matrix, and the inferred depth of magma storage levels.