Crystal chemistry of clinopyroxene and spinel from mantle xenoliths hosted in Late Mesozoic lamprophyres (Villany Mts, S Hungary)

摘要

The pre-Neogene subcontinental lithosphere beneath the Carpathian-Pannonian region is poorly studied and the mantle beneath the Tisza Unit (S Hungary) is known only from the rare occurrence of mantle xenoliths in Late Cretaceous lamprophyre dykes in the Villany Mts. This paper presents clinopyroxene and spinel single-crystal X-ray diffraction studies from spinel lherzo-lite xenoliths from this locality. Clinopyroxene unit cell volumes are significantly high (up to 437 A~3) and show final equilibrium pressures near to the plagioclase stability field. Unit cell parameters of the spinel crystals range from 8.1479 to 8.1541 A, and are directly related with their low cr#. Oxygen atomic coordinates u are equal to 0.2628 and suggest slow cooling of the samples related to the subvolcanic character of the host rock. Crystal structure and thermobarometrical data of the xenoliths, together with a detailed petrographical study, indicate recrystallization and re-equilibration of the sampled mantle section under low PT conditions.