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SUMMARY:The post-Variscan evolution of Ireland – a case study in constr
 aining shallow crustal exhumation and deformation - David Chew\, Trinity C
 ollege Dublin
DTSTART:20241112T120000Z
DTEND:20241112T130000Z
UID:TALK220480@talks.cam.ac.uk
CONTACT:Dr Rachael Rhodes
DESCRIPTION:The Cenozoic uplift and exhumation history of the British Isle
 s has been attributed to epeirogenic exhumation driven by the proto-Icelan
 d plume\, or multiple phases of Cenozoic compression driven by far-field s
 tresses. This talk focusses on the post-Variscan exhumation and shallow cr
 ustal deformation history of Ireland and western Britain\, which in Irelan
 d is particularly challenging to constrain given the near-complete absence
  of post-Variscan sediments.\n\nHigh-resolution thermal history models (fr
 om inverse modelling of apatite fission track and (U–Th–Sm)/He data fr
 om vertical bedrock profiles) clearly show rapid Paleocene exhumation (1 
 – 2.5 km) focused on the Irish Sea. Paleocene exhumation is greatest in 
 the north of the Irish Sea and decreases to the south and west.  Its spati
 al distribution agrees with the extent of magmatic underplating inferred f
 rom receiver function data and lithospheric thickness estimates derived fr
 om surface wave tomography. Earlier (Mesozoic) exhumation onshore is linke
 d to hinterland exhumation during the complex and long-lived rifting histo
 ry of neighbouring offshore basins. The extent of Neogene exhumation is di
 fficult to constrain due to the poor sensitivity of the thermochronometers
  at low temperatures but appears most signifcant on the western Atlantic c
 oast. The Cenozoic topographic evolution of a significant portion of Briti
 sh Isles thus appears to be the result of plume-driven uplift and exhumati
 on\, with inversion playing a secondary role.\n\nEven so\, Cenozoic shorte
 ning has affected onshore Ireland. The Carboniferous North Dublin Basin (1
 50 km north of the supposed Variscan “front”) exhibits tight chevron f
 olds and kinematically linked calcite vein sets\, along with bedding-paral
 lel veins with slickenfibres. Late Eocene LA-ICP-MS U-Pb ages were obtaine
 d from many calcite veins\, including fold hinge breccias and bedding-para
 llel slickenfibre veins clearly associated with N-S shortening (flexural s
 lip). This late Eocene fold reactivation is attributed to far-field\, N-di
 rected shortening associated with the Alpine/Pyrenean orogenies\, but was 
 not of sufficient magnitiude to manifest in the low-temperature thermochro
 nology record.
LOCATION:Department of Earth Sciences\, Tilley Lecture Theatre
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