The Grand Brûlé exploration drilling: New data on the deep framework of the Piton de la Fournaise volcano. Part 2: Secondary minerals

The Grand Brûlé borehole intersects a thick pile of basaltic lavas, down to 1010 m, and a basic-ultrabasic intrusive complex, from 1010 to 3003.50 m.The lavas are, in general, unaltered except in two fractured zones, where hydrothermal fluids circulated at temperatures not exceeding 350 ° C. The main secondary minerals there are pyroxene, feldspar, epidote, actinolite and chlorite.The entire thickness of the intrusive body intersected contains secondary minerals representing three stages of cooling:

1. 1. A late magmatic episode (600–900°C) characterized by biotite, kaersutite, edenite and pargasite.

2. 2. A hydrothermal episode (T<- 350°C) characterized by epidote, albite, biotite, actinolite and chlorite.

3. 3. A phase of serpentinization (T≤ 350°C).

It is very likely that the two later events occurred simultaneously, with physical and chemical interference.