Metamorphism in Louisiana - Who are you kidding?

Yes, it is true - there are metamorphic rocks in the subsurface of northern Louisiana and there was relatively vigorous metasomatic system that probably contributed to the generation of gas in this area.

The metamorphism is associated with Late Cretaceous alkaline igneous dikes that intrude the Jurassic Smackover Formation at depths of about 2 km in northeastern Louisiana. A typical 11 m dike produces a contact aureole that affects organic-rich interlayered carbonate mudstones and siltstones out to 4-6 m from the dike. The metamorphic mineral assemblages are rich in alkali and alkaline earth elements as well as fluorine and include development of local isograds producing analcite, grossular garnet, fluorite, pectolite, and diopside. The heating due to igneous intrusion locally results in overmaturation of hydrocarbons that may control or contribute to the gas field developed immediately above the dikes. 

Papers and abstracts on metamorphism in Louisiana

Dutrow, B. L., Henry, D. J., Gable, C. and Travis, B. (1998) Thermal evolution and fluid infiltration adjacent to an alkalic dike: Development of metasomatic mineralogy and implications for hydrocarbon maturation. IGPP Annual Meeting Abstracts.

Dutrow, B. L., Henry, D. J., Gable, C. and Travis, B. (1998) Thermal evolution and fluid infiltration: Development of metasomatic mineralogy adjacent to an alkalic dike. Abstracts of the 17^th International Mineralogical Association, A77.

Dutrow, B., Henry, D. J., Christensen, C., Gable, C. W., Travis, B. J. and Heydari, E. (1997) Blackened Smackover: Thermal evolution and mass transfer adjacent to a subsurface alkalic igneous dike in northern Louisiana. Gulf Coast Association of Geological Societies Transactions, Vol. XLVII, 131-139.

Heydari, E., Byerly, G. R. and Henry, D. J. (1997) Contact metamorphism and over maturation of organic matter associated with an igneous intrusion in the Smackover Formation, Northeastern Louisiana. . Gulf Coast Association of Geological Societies Transactions, Vol. XLVII, 201-213.

Christensen, C., Dutrow, B. L., Henry, D. and Heydari, E. (1996) Contact metamorphism in subsurface northeastern Louisiana: metasomatism in a hydrocarbon source rock. Geological Society of America Abstracts with Program, 28, A101.

Heydari, E., Byerly, G., Henry, D. and Dutrow, B. (1994) Enhanced hydrocarbon maturation by igneous intrusions, Smackover Formation, Northeast Louisiana. Geological Society of America Abstracts with Program, v. 26, p. A231.