Effects of subduction parameters on geothermal gradients in forearcs with an application to Franciscan subduction in California

Journal Article · Thu Jan 10 00:00:00 EST 1991 · Journal of Geophysical Research; (United States)

DOI:https://doi.org/10.1029/90JB01913· OSTI ID:5589805

Dumitru, T A ^[1]

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1. La Trobe Univ., Bundoora, Victoria (Australia)

Geothermal gradients in forearcs are often suppressed below normal values because of the cooling effect of the relatively cold downgoing plate. In this paper, finite difference thermal modeling is used to evaluate the influence on forearc gradients of variations in six potentially important subduction zone parameters: radiogenic heat production; thermal conductivity of forearc rocks; subduction angle; subduction rate; frictional heat production; and presubduction geothermal gradients. Pressure-temperature conditions of blueschist-facies metamorphism in the Franciscan subduction complex of California are easily explained with typical subduction rates and slab ages with plate contact shear stresses of the order of 10 MPa, but stresses within the range zero to a few tens of megapascals are probably permitted by the thermal constraints. Speculative application of the modeling results assuming a shear stress of 4% of lithostatic pressure to plate motion reconstructions for the Franciscan forearc suggests that forearc gradients were about 8C/km around 85 Ma when the subducting slab was perhaps 145 m.y. old and the subduction rate was perhaps 95 km/m.y. Gradients increased moderately through the latest Cretaceous to middle Tertiary as subduction became slower and the subducting slab became younger, reaching about 16C/km at 28 Ma when the slab age was about 11 m.y. and the subduction rate was about 48 km/m.y. The slab age, subduction rate, and forearc gradient then remained fairly constant until 5 Ma, when subduction slowed to about 32 km/m.y. and the slab age decreased to about 8 m.y., causing gradients to rise to about 20C/km.

• OSTI ID: 5589805
• Journal Information: Journal of Geophysical Research; (United States), Vol. 96:B1; ISSN 0148-0227
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
CALIFORNIA
SUBDUCTION ZONES
GEOTHERMAL GRADIENTS
AGE ESTIMATION
COOLING
CRETACEOUS PERIOD
FINITE DIFFERENCE METHOD
FRICTION
GEOLOGIC HISTORY
INCLINATION
MASS TRANSFER
MATHEMATICAL MODELS
METAMORPHISM
PLATE TECTONICS
RADIOACTIVITY
RESERVOIR PRESSURE
RESERVOIR ROCK
RESERVOIR TEMPERATURE
SHEAR
TERTIARY PERIOD
THERMAL CONDUCTIVITY
CENOZOIC ERA
DEVELOPED COUNTRIES
FEDERAL REGION IX
GEOLOGIC AGES
ITERATIVE METHODS
MESOZOIC ERA
NORTH AMERICA
NUMERICAL SOLUTION
PHYSICAL PROPERTIES
TECTONICS
TEMPERATURE GRADIENTS
THERMODYNAMIC PROPERTIES
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580000* - Geosciences