Towards determining the thermal state of old ocean lithosphere: heat-flow measurements from the Blake--Bahama outer ridge, north-western Atlantic

• Published in: Geophysical Journal International
• Main Authors: Davis, Earl E., Lister, Clive R. B., Sclater, John G.
• Format: Text
• Language: English
• Published: Oxford University Press 1984
• Subjects: Articles; North West Atlantic
• Online Access: http://gji.oxfordjournals.org/cgi/content/short/78/2/507; https://doi.org/10.1111/j.1365-246X.1984.tb01962.x

Detailed suites of heat-flow measurements have been completed at four sites on and to the east of the southern end of the Blake-Bahama outer ridge in the north-west Atlantic on ocean crust which ranges in age from roughly 115 to 155 Ma. The principal purpose of these measurements was to compare instrumental techniques and to examine the decay of heat flow with age on old ocean floor. Multi-penetration gradient measurements were made at the youngest site with a 2.5 m outrigger probe, and multipenetration heat flow measurements at the other three sites with a new 3.5 m violin-bow type instrument. In addition, at all four sites the gradient was measured using outriggers on a 9 m piston or gravity corer, and conductivities were measured on the sediment recovered. The average of thermal conductivities measured on cored sediments agreed to better than 2 per cent with the average of conductivities measured in situ at the oldest three sites. Such good agreement is surprising given the problems associated with making measurements on sediments recovered in cores. The greatest measurement errors in determining heat flow were found to be caused by temperature disturbances generated by the piston coring process. Gravity coring reduced these disturbances but provided a less representative section for measuring thermal conductivity. The violin-bow probe, which measures average interval conductivities in situ , provided the most reliable heat flow determinations. The accuracy of these determinations was limited primarily by the presence of thermal disturbances due to bottom water temperature variations. The heat flow averages at all four sites are virtually identical: they range from 47mW m-2 (1.12 μcal cm-2s-1) to 49mW m-2(1.17μcal cm-2s-1) with standard errors of less than 2 mW m-2 (0.05 μcal cm-2s-1). The constancy and the value of heat flow over lithosphere of this age, and the local shallowing of depth with increasing age in the region containing the heat flow sites cannot be explained by either a simple plate or a ...