Hiemstra, Erik J.1, Robert H. Goldstein1
(1) The University of Kansas, Lawrence, KS
ABSTRACT: The Indian Basin, New Mexico: A Tectonically Valved Hydrothermal Dolomite Reservoir
The Cisco-Canyon (Virgilian-Missourian) reservoir within the Indian basin (Eddy County, New Mexico) was affected by hydrothermal processes linked to tectonic history. The reservoir consists of dolomitized clean carbonate. Cathodoluminescence was used to correlate replacement dolomite and six xenotopic dolomite cements (DC1-6). Dolomites postdate some stylolitization and pervasive fracturing. Abundant vugs and molds formed after the replacement dolomite. Later saddle dolomite and anhydrite cementation was associated with multiple events of fracturing.
Consistent assemblages of primary fluid inclusions within xenotopic dolomite yield homogenization temperatures (Th) of 90-170° C. These temperatures commonly exceed the expected maximum burial temperature (<100° C). Low-temperature microthermometric data indicate salinities from 6 wt. % to greater than 30 wt. % NaCl eq. Inclusions measured in transect across successive growth subzones record recurring fluctuations in temperature as great as 20° C and fluctuations in salinity as great as 17 wt. % NaCl eq.
Dolomite 18O ranges from -4.08o/oo to -9.18o/oo and 13C ranges from -2.44o/oo to 4.48o/oo (VPDB). Dolomite 87Sr/86Sr ranges from 0.70798 to 0.70901. Both dolomite 18O and 87Sr/86Sr show spatial variability related to distance from faults. Dolomite samples close to faults commonly have more negative 18O than samples farther from faults, indicating higher temperatures in fault zones.
These data suggest that dolomite and associated secondary porosity formed during tectonically valved, episodic injection of hydrothermal brines through faults and fractures. Convection-driven, hydrothermal flow was likely initiated following 40-30 Ma (Eocene-Oligocene) intrusive activity and continued after some Basin and Range uplift and unroofing.
AAPG Search and Discovery Article #90026©2004 AAPG Annual Meeting, Dallas, Texas, April 18-21, 2004.