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SUMMARY:A Dual Rift Model for the Opening of the NE Atlantic - Richard Wal
 ker\, University of Leicester
DTSTART:20141118T160000Z
DTEND:20141118T170000Z
UID:TALK54485@talks.cam.ac.uk
CONTACT:John Maclennan
DESCRIPTION:Existing models for the opening of the NE-SW oriented NE Atlan
 tic invoke a near instantaneous rotation in extension direction\, from E-W
  to NW-SE associated with eventual break-up during the Early Eocene. The i
 mplication of this model is that NW-SE extension is accommodated on margin
 -parallel normal faults and margin-oblique (NW-SE) strike-slip “transfer
  zone” faults\, acting contemporaneously\, and resulting in basin segmen
 tation along the margin. Recent studies of fault kinematics in the Faroe I
 slands and Faroe-Shetland Basin\, indicate that the extension vector rotat
 ion was prolonged (>10 My) and rift-oblique structures accommodate minor e
 xtension as relatively small dykes and normal faults (sub-basin-scale late
 ral continuity)\, rather than basin-scale strike-slip systems. Tectonostra
 tigraphic mapping in the Faroe Shetland basin indicates a younging-directi
 on for margin-oblique structures throughout the Palaeogene\, from the NE t
 o the SW along the margin\, related to propagation of the newly forming At
 lantic.\nHere we use high-resolution structural mapping and paleostress an
 alysis from the Faroe Islands and Kangerlussuaq region of East Greenland\,
  and compare this with an analogous study of ancillary deformation surroun
 ding the tips of two NE-SW trending rift-fault segments in the Krafla Fiss
 ure Swarm\, NE Iceland\, to constrain the relative timing\, distribution\,
  and kinematics\, of propagating rift systems. In the Faroes\, extension v
 ector rotation involves: (1) NE-SW extension accommodated by NW-SE normal 
 faults and dykes\, which are cut by (2) ENE-WSW and ESE-WNW striking dykes
  and strike-slip faults accommodating N-S extension\, which in turn are cu
 t by (3) NE-SW striking (margin-parallel) oblique-slip faults. Structural 
 mapping of fault sets in Krafla reveals multiple fault sets associated wit
 h the main rift faults: (1) ESE-WNW striking mode I fractures\, (2) NNW-SS
 E striking normal faults and mixed-mode fractures\, and (3) NE-SW trending
  normal faults and mode I fractures\, which form the final hard linkage be
 tween the bounding fault segments. Comparison between the margin datasets\
 , and the Krafla system shows that relative timings and relative kinematic
 s are the same for both systems. We find no evidence for rift segmentation
  across transfer zone faults in either setting. The distribution and scale
  of rift-oblique structures in Krafla indicates they are laterally discont
 inuous\, rather than forming a rift-scale structure. Comparison between th
 e Krafla dataset\, and numerical models for ancilliary fault development a
 head of propagating tips\, shows a positive correlation\, suggesting the e
 volution of structural sets in the Krafla system reflects an evolving loca
 l stress field ahead of the main bounding faults. We infer therefore that 
 “transfer” structures interpreted along the Atlantic margins\, instead
  represent ancilliary faults and dykes associated with tip-zone stress per
 turbations in the overlap zone of two active rift systems: in this instanc
 e\, a dual rift system involving the NE-propagating Reykjanes ridge from t
 he SW\, and a SW-propagating Aegir ridge from the NE.\n\nReferences\nEllis
  D\, Stoker MS. 2014. The Faroe–Shetland Basin: a regional perspective f
 rom the Paleocene to the present day and its relationship to the opening o
 f the North Atlantic Ocean. Geological Society\, London\, Special Publicat
 ions 397.\nMoy DJ\, Imber J. 2009. A critical analysis of the structure an
 d tectonic significance of rift-oblique lineaments (‘transfer zones’) 
 in the Mesozoic–Cenozoic succession of the Faeroe–Shetland Basin\, NE 
 Atlantic margin. Journal of the Geological Society\, London\, 166\, 1-14\n
 Walker RJ\, Holdsworth RE\, Imber J\, Ellis D. 2011. Onshore evidence for 
 progressive changes in rifting directions during continental break-up in t
 he NE Atlantic: Journal of the Geological Society\, v. 168\, p. 27-48.\n
LOCATION:Harker 1 seminar room\, Department of Earth Sciences
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