Constraints on early Cenozoic underplating-driven uplift and denudation of western Scotland from low temperature thermochronometry

摘要

Apatite (U-Th)/He and fission track data from profiles in western Scotland constrain the timing and magnitude of denudation during the early Cenozoic when the north Atlantic region was the site of intense magmatic activity related to the proto-Icelandic plume. Apatite helium ages vary from 77 +/- 8 to 265 +/- 27 Ma ( +/- 2 sigma) at Sgorr Dhonuill, Ballachulish, and from 104 +/- 10 Ma to 166 +/- 17 Ma at Clisham, Outer Hebrides. At both locations apatite fission track (AFT) ages are older than the correspon 257 +/- 12 Ma at Sgorr Dhonuill. Apatite He ages increase linearly with elevation suggesting that the cooling rate remained constant in the late Mesozoic. However, the apatite He age profile requires a period of rapid cooling after similar to 100 Ma. Apatite He ages predicted from the AFT-derived thermal histories are indistinguishable from measured He ages for a rapid cooling event of I to 10 Myr duration between 61 and 47 Ma at Sgorr Dhonuill and 65 to 49 Ma at Clisham. The combined apatite FT- and He-derived thermal histories constrain the early Cenozoic geothermal gradient at 39 +/- 9 degrees C/km at Sgorr Dhonuill and 19 +/- 6 degrees C/km at Clisham. Amounts of denudation related to the rapid cooling event vary from 1330 +/- 230 m at Sgorr Dhonuill to 2250 +/- 750 in at Clisham, in agreement with models that predict greater amounts of denudation where magmatic underplating is thicker. However, the direct correlation between underplating-driven surface uplift and denudation may only be apparent and a more complex link between spatial variation of surface uplift and denudation is suggested. The integration of results from multiple low-temperature thermochronometers, combined with inverse and forward modelling, provides a convincing and quantitative method to deduce onshore erosional histories, and provides critical information about the spatial distribution of erosion that cannot be derived from the offshore record. (c) 2007 Elsevier B.V. All rights reserved.