Abstract
Detailed magnetic measurements were made on specimens from profiles across the contact zones of two unmetamorphosed Miocene diabase dikes. The dikes cut Cretaceous plutonic rocks of the Coast Crystalline Complex near Bella Bella, British Columbia. The dikes feed flat-lying basalts that outcrop nearby. This indicates post-Miocene uplift is less than 1 km in the area. Alternating field demagnetization, magnetic susceptibility, thermal demagnetization, and magnetic force balance measurements were made on the specimens. From them, the distance from the contact and the maximum reheated temperature of the magnetic hybrid zone were determined. Results are reported for the Thorburne Island contact only because the other contact had unsuitable remanence characteristics. Using standard conduction heat flow equations the ambient temperature of the host rock at the time of intrusion was found to be 18 ± 5 °C giving a determined depth for the present erosion surface at the time of intrusion of 0.3 ± 0.1 km. This is the first positive test of the magnetic paleogeobarometric method.
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