Methane hydrate in crystalline bedrock and explosive methane venting tectonics

摘要

Methane hydrate (clathrate, ice) does not only form in shelf environments, but may also accumulate in voids and fractures in continental crystalline rocks. This has turned out to be the case in formerly glaciated areas where the waxing and waning of thick ice caps following the Quaternary alterations between Ice Ages and Interglacial implied very large changes both in temperature and pressure in the bedrock below. The Swedish situation is highlighted. Seepage of methane gas from the crystalline bedrock is recorded. Methane accumulated as ice in fractures and voids in the rock. In postglacial time, such accumulations vented explosively, generating "methane venting tectonics". This occurred both spontaneously as a function of changes in temperature and load-pressure, and partly as violent deformational events as a function of earthquake events. Whilst most venting events refer to the time of deglaciation, three major deformational events occurred shortly after the uplift induced land emergence in Late Holocene time. A possible analogous event in association with the 1988 Saguenay earthquake in Canada is revisited.