Dynamic crystallization experiments on the Angra dos Reis achondritic meteorite

Abstract

The types of cooling histories necessary to produce the porphyritic texture and the observed mineral assemblage in Angra dos Reis (ADOR) achondritic meteorite, which, on the basis of its trace element characteristics was considered to be a cumulate with a recrystallized texture, while a recent model suggested that ADOR is a porphyry. Dynamic crystallization experiments were conducted with nucleation conditions varied by melting the starting material at different degrees of superheat. The results show that, at low pressure, a volcanic or hypabyssal history of ADOR is possible. The most likely history involved cooling from a slightly subliquidus temperature with a relatively high and irregular nucleation density resulting in a granular texture with the poikilitic fassaite growing late; accumulation of some crystal is tought to be probable.