Constraining the post-emplacement evolution of the Hebridean Igneous Province (HIP) using low-temperature thermochronology: how long has the HIP been cool?

Abstract

The thermal history of the Hebridean Igneous Province has been determined through the application of low-temperature thermochronology to the four central complexes in the province. The zircon (U–Th)/He age (59.4 ± 3.3 Ma, 1σ, n = 18) and the ages from each complex (60.7 ± 2.3 Ma for Skye; 58.0 ± 0.4 Ma for Mull; 55.9 ± 3.2 Ma for Ardnamurchan; 55.6 ± 2.7 Ma for Rum) are indistinguishable from the crystallization ages. Apatite fission-track ages (61.2–57.2 Ma, mean of 59.3 ± 3.4 Ma) from the major plutonic units also overlap crystallization ages, implying that on a regional scale the Hebridean Igneous Province cooled rapidly to near-surface temperatures immediately after emplacement. However, apatite fission-track ages and track lengths and apatite (U–Th)/He ages from some small-volume intrusions in the Skye and Rum central complexes identify localized mid-Eocene (45–47 Ma) cooling. Forward and inverse modelling suggests a discrete heating–cooling event at c. 47 Ma, which may have been caused by structurally controlled localized advection of heat above shallow emplacement. This is the first suggestion of Eocene magmatism in the Hebridean Igneous Province.