Combustion metamorphism in southern california

Area of Science:

• Geology
• Mineralogy
• Petrology

Background:

• Bituminous sediments of the Monterey Formation in Southern California contain organic matter.
• These sediments include siliceous shales, phosphatic rocks, dolomites, and arkoses.

Purpose of the Study:

• To investigate the effects of spontaneous subsurface combustion on these rock formations.
• To characterize the resulting metamorphic processes and mineralogical changes.

Main Methods:

• Analysis of rock complexes affected by combustion metamorphism.
• Determination of mineral assemblages formed at high temperatures and lower temperatures.

Main Results:

• Spontaneous combustion reached temperatures up to 1600°C, causing recrystallization and partial melting.
• Formation of immiscible siliceous and phosphatic pseudomagmas intruding country rocks.
• Identification of high-temperature minerals (e.g., cristobalite, pyroxene) and lower-temperature minerals (e.g., calcite, gypsum).

Conclusions:

• Combustion metamorphism significantly alters rock complexes, forming unique pseudomagmas.
• The chemical composition of these melts differs from typical igneous magmas.
• These processes provide insights into natural high-temperature geological events.