Lingunite-a high-pressure plagioclase polymorph at mineral interfaces in doleritic rock of the Lockne impact structure (Sweden)

Lingunite nanocrystals and amorphous plagioclase (maskelynite) are identified at the contacts
between augite and labradorite wedge-shaped interfaces in the doleritic rocks of the Lockne impact
structure in Sweden. The occurrence of lingunite suggests that the local pressure was above 19 GPa
and the local temperature overwhelmed 1000 °C. These values are up to 10 times higher than previous
values estimated numerically for bulk pressure and temperature. High shock-induced temperatures
are manifested by maskelynite injections into microfractures in augite located next to the wedges.
We discuss a possible model of shock heterogeneity at mineral interfaces, which may lead to longer
duration of the same shock pressure and a concentration of high temperature thus triggering the
kinetics of labradorite transformation into lingunite and maskelynite.