Wellbore heat flow from the Toa Baja scientific drillhole, Puerto Rico

Journal Article · Fri Mar 01 00:00:00 EST 1991 · Geophysical Research Letters (American Geophysical Union); (United States)

DOI:https://doi.org/10.1029/91GL00391· OSTI ID:5536692

Anderson, R N ^[1]; Larue, D K ^[2]

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1. Columbia Univ., Palisades, NY (United States)
2. Univ. of Puerto Rico, Mayaguez (Puerto Rico)

Heat flow values, determined from temperature logs and estimates of thermal conductivity from geophysical logs range from 23 to 37 mW/m{sup 2} from 800 to 2,500 m depth in the Toa Baja scientific drillhole on the north, central coast of Puerto Rico. Near the target seismic reflector at the base of the well, an active hydrothermal system was encountered in which heat flow of up to 90 mW/m{sup 2} was found in a mineralized zone beneath a volcanic sill or flow. The heat flow then dropped to 50 mW/m{sub 2} beneath this subhorizontal flow zone. The mining of heat from downdip is proposed to account for this thermal anomaly, as well as the scatter in the heat flow determined from the few other wells drilled into Puerto Rico. The time-temperature history of the well indicates that Eocene volcaniclastics of the lower 2 km were deposited into a geothermal gradient of 60C/km north of an active arc (heat flow estimated to have been 120-180 mW/m{sup 2}). Uplift, erosion and cooling occurred between 40 and 30 Ma. Reburial and deposition of Oligocene-Miocene Limestones produced the present-day geothermal gradient of 15C/km (heat flow of 30-50 mW/m{sup 2}). Based upon comparisons with slab cooling models, the crustal thickness beneath Puerto Rico is estimated to be closer to continental then oceanic.

• OSTI ID: 5536692
• Journal Information: Geophysical Research Letters (American Geophysical Union); (United States), Vol. 18:3; ISSN 0094-8276
• Country of Publication: United States
• Language: English

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