""The mantle is not involved; at this location it is much deeper.
Temperatures are high, however, also leading to high gas pressures.""

Did you get that GfS. Given the averages involved, it was a racing certainty that such would be the case, since the thinnest parts of the crust would be concentrated at the edges of the emerging tectonic plates, none of which are anywhere near the drilling sites, being concentrated in the Pacific "Ring of Fire", and the Atlantic "Mid Ocean Ridge". The Carribean and the Gulf of Mexico would presumably be closer to the subduction zone at the other edge of the plate, where the crust would be thicker.

Don T.