Experimental shock metamorphism of maximum microcline

Abstract

Single-crystal perthitic maximum microcline was shocked to a peak pressure of 417 kbar in a series of 15 recovery experiments. Shock-induced cleavagelike lamellar features parallel to and form above 50 kbar and contain diaplectic glass at higher shock pressures. Sets of planar deformation features parallel to specific crystallographic planes are developed above 150 kbar; some orientations transform to deformation twins above 200 kbar. With increasing pressure, bulk density, refractive indices, and birefringence of the recovered material decrease and approach diaplectic glass values; disappearance and weakening of reflections in Debye-Scherrer patterns are due to disordering of the feldspar lattice. In experiments above 300 kbar the X ray pattern is that of a previously unrecorded disordered phase which possibly inverted from a compressed phase on pressure release. Weak indications of jadeite and stishovite may be remnants of the high-pressure breakdown of albite stringers.