The heat flow pattern from the deep sea across the Queen Charlotte Terrace to the west coast of the Queen Charlotte Islands has been determined through 20 marine heat flow measurements and by 11 borehole measurements at one land site. There is a continuous transition from very high deep sea heat flow, through intermediate values on the terrace, to low continental heat flow. The deep sea values are scattered, probably reflecting hydrothermal circulation in the crust, but their mean is in agreement with the theoretical value for the 7 Ma deep sea oceanic crust. The mean heat flow at the land site of 47 mW m−2 is similar to the average for the coast Insular Belt to the south and east. The measurements on the 30 km wide 2 km deep terrace are less scattered and much lower than those on the deep sea floor. The main thermal contrast is at the seaward edge of the terrace rather than near the coast where the earthquakes of the main plate boundary are located. Numerical models suggest that no reasonable steady state ocean–continent boundary can explain the observed heat flow transition. The data are consistent with a model of oblique underthrusting of the deep sea floor beneath the terrace. The continental margin heat flow transition will tend to mask any thermal anomaly generated by fault motion, but the results imply that there is no large frictional heat generated by motion on the Queen Charlotte fault.Nine marine heat flow measurements were made at the southwestern end of Queen Charlotte Sound south of the Queen Charlotte fault zone to test the hypothesis that the sound is a zone of recent crustal extension or rifting. The measurements were limited to isolated pockets of soft sediment and to sea floor depths greater than 800 m where bottom water temperature transients are negligible. The heat flow values are fairly uniform with an average of 86 mW m−2, which is about double the mean of other Insular Belt values. The Queen Charlotte Sound values could be affected by a nearby ocean spreading centre or by sediment erosion, but they are consistent with the rift hypothesis.

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