Abstract
Shock recovery experiments using ALH-78084 H3 and Y-793375 L3 chondrites
are conducted in the shock pressure range of 11–43 GPa to reproduce
shock-induced melting and chondrule flattening. Shock experiments prove
that shock-induced melting occurs beyond 11 GPa at least. The melting
occurs at the boundaries between chondrules and matrices. The melts
include fine-grained silicate minerals, glasses, and amoeba or spherical
metallic Fe-Ni or metallic Fe-Ni–iron-sulfide with a eutectic texture,
which coincides with shock-induced melts in shocked natural chondrites.
Shock experiments also prove that shock-induced flattening of chondrules
occurs and the flattening degree increases with increasing shock
pressure. Taking account of not only the shock experiments of ordinary
chondrites but also carbonaceous chondrites, the flattening degree does
not depend significantly on the densities, porosities, and
chondrule/matrix ratios of chondrites. Considering the shock experiments
of the Allende CV3 and Murchison CM2 carbonaceous chondrites along with
present shock experiments using H/L3 ordinary chondrites, the aspect
ratios of chondrules in unequilibrated chondrites (Rcho)
can be expressed as follows: Rcho = 0.011 (±1) ×
Pressure (GPa) + 1.18 (±3). The long axes of chondrules in shocked
ALH-78084 H3 and Y-793375 L3 chondrites have preferred orientations and
the degree increases with increasing shock pressure. Natural L/LL3
ordinary chondrites with shock-induced melts have higher aspect ratios
and preferred orientations than those without shock-induced melts
although it is difficult to determine quantitatively shock pressure
using the empirical formula between the aspect ratios of chondrules and
shock pressure.