300-Myr-old magmatic CO sub(2) in natural gas reservoirs of the west Texas Permian basin

Except in regions of recent crustal extension, the dominant origin of carbon dioxide in fluids in sedimentary basins has been assumed to be from crustal organic matter or mineral reactions. Here we show, by contrast, that Rayleigh fractionation caused by partial degassing of a magma body can explain...

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Bibliographic Details
Published in:Nature (London) 2001-01, Vol.409 (6818), p.327-331
Main Authors: Ballentine, Chris J, Schoell, Martin, Coleman, Dennis, Cain, Bruce A
Format: Article
Language:English
Online Access:Get full text
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Summary:Except in regions of recent crustal extension, the dominant origin of carbon dioxide in fluids in sedimentary basins has been assumed to be from crustal organic matter or mineral reactions. Here we show, by contrast, that Rayleigh fractionation caused by partial degassing of a magma body can explain the CO sub(2)/ super(3)He ratios and delta super(13)C(CO sub(2)) values observed in CO sub(2)-rich natural gases in the west Texas Val Verde basin and also the mantle super(3)He/ super(22)Ne ratios observed in other basin systems. Regional changes in CO sub(2)/ super(3)He and CO sub(2)/CH sub(4) ratios can be explained if the CO sub(2) input pre-dates methane generation in the basin, which occurred about 280Myr ago. Uplift to the north of the Val Verde basin between 310 and 280Myr ago appears to be the only tectonic event with appropriate timing and location to be the source of the magmatic CO sub(2). Our identification of magmatic CO sub(2) in a foreland basin indicates that the origin of CO sub(2) in other mid-continent basin systems should be re-evaluated. Also, the inferred closed-system preservation of natural gas in a trapping structure for similar to 300Myr is far longer than the residence time predicted by diffusion models.
ISSN:0028-0836
DOI:10.1038/35053046