Thermal Maturity in the Gulf of Cadiz Due to Mantle Plumes, Triple Junctions, and Plate Tectonics

摘要

Petroleum exploration in the Gulf of Cadiz began in the 1970's, and by 1999, 26 commercial wells have been drilled. Several 2-D, multi-channel seismic grids at spacings of approximately 4 and 6.5 km have been shot across the continental shelf, upper and middle slope in waters depths up to 1000 m (Fig. 1). Recent drilling by Repsol (1996 - 1998) on the continental shelf off the city of Cadiz are producing natural gas, much of it biogenic. The gas is being transported to nearby Cadiz. The geothermal gradient measured in these few wells on the central and inner shelf is 2.4 degrees C/100 m. If that value should characterize the entire Gulf of Cadiz and adjacent continental margin, then it is likely, given observed sediment thicknesses, that the area might not be commercially petroliferous. In this article, geologic arguments are presented that the regional geothermal gradient, especially along the shelf-break and continental slope, may be appreciably higher, locally up to 3.1 degrees C/100 m.