Phreatomagmatic eruption during the buildup of a Triassic carbonate platform (Oman Exotics): eruptive style, associated deformations, and implications on CO2 release by volcanism

Christophe Basile (1) , François Chauvet (1)

1 LGCA - Laboratoire de Géodynamique des Chaines Alpines

Oman exotics represent remnants of a Triassic carbonate platform (Misfah Formation). Within these carbonates, and coeval with the sedimentation, several basaltic magmatic events occurred mainly as intrusions, also as lava flows and projections. We describe one of these events, that produced a phreatomagmatic eruption along a volcanic fissure. The initial ascent of magma probably occurred along on a normal fault related to gravity-driven sliding of the carbonates towards the platform edge. Magma first emplaced in a saucer-shaped sill few tens of meters below the surface. This intrusion provided a decollement layer, that may have speed up the gravity-driven sliding, opening fractures that brought sea-water in contact with the magma, hence triggering the phreatomagmatic eruption. Eruption was followed by the collapse of the limestones in a megabreccia infilling the eruptive line and prohibiting further contact between sea water and magma. The main magma volume emplaced at depth in two superposed magma chambers that replaced the host sediments and uplifted the overlying eruptive line. These magma chambers fossilized the substratum of the carbonate platform, that consists in uplifted sediments from the distal Hawasina basin. Replacing limestones by magma chambers may have release huge volumes of Carbon dioxide, estimated to be two to three hundred times higher than CO2 release by volcanic gases. CO2 release by decarbonating sediments may be an important mechanism to explain climatic changes associated to some large igneous provinces such as Siberia, Central Atlantic Magmatic Province, or Karoo, where very large magmatic volumes where intruded in sedimentary basins.

Mots clés: Phreatomagmatic eruptions; sills; magma chambers; megabreccia; carbonate platforms; Carbon dioxide

Domaines: Tectonique; Volcanologie

Christophe Basile, François Chauvet. Phreatomagmatic eruption during the buildup of a Triassic carbonate platform (Oman Exotics): eruptive style, associated deformations, and implications on CO2 release by volcanism. 2006. ⟨hal-00116078⟩