Deformation In Nature

 

Field mapping the Ivrea-Verbano zone, N. Italy

As part of our programme of field mapping in the lower and mid crustal section of the Ivrea-Verbano zone, mapping of the central part of the upper Ivrea-Verbano zone has been completed, and all of the data from all groups has been compiled onto a GIS using Arc-Info (Tony James (PhD graduate), Ernie Rutter and Kate Brodie, collaboration with Prof A. Boriani, Drs L. Burlini and A. Zappone, Univ. Milan and ETH Zurich). A complex pattern of very large fold structures has been found to dominate the geology of this part of the section.

  • Rutter, E. H., Khazanehdari, J., Brodie, K. H., Blundell, D. J. & Waltham, D. A. 1999. Synthetic seismic reflection profile through the Ivrea zone Serie dei Laghi continental crustal section, northwestern Italy. Geology 27(1), 79-82.
  • Khazanehdari, J., Rutter, E. H. & Brodie, K. H. 2000. High-pressure-high-temperature seismic velocity structure of the midcrustal and lower crustal rocks of the Ivrea-Verbano zone and Serie dei Laghi, NW Italy. Journal of Geophysical Research-Solid Earth 105(B6), 13843-13858.
  • Rutter, E.H., Brodie, K.H., James, T. and Burlini, L. 2007. Large scale folding in the upper part of the Ivrea-Verbano lower crustal section, NW Italy. Journal of Structural Geology, 29. 1-17.

For more information contact: Ernie Rutter or Kate Brodie

Lidar survey of Mam Tor landslide

Lidar survey of Mam Tor landslide

We have annually monitored creep movements on this slump-earthflow landslide since 1995 and have been able to analyze the 3D strain pattern within the slip using the methods of geodetic strain analysis (Ernie Rutter, Chris Arkwright, Rob Holloway). The slip is presently moving faster (up to 0.5 m/yr) than over most of its previous history. This is attributed to increased frequency of severe winter storms. We have recently installed automatic monitoring equipment to measure continuously creep motions, pore fluid pressure and tilt (in 2 boreholes), automatic rain gauging and 2 seismometers. Data collected to date spectacularly shows the relationship between rainfall and groundwater infiltration to creep events. Accompanying small earthquakes have also been detected. Annual LiDAR measurements of parts of the creeping mass have also been initiated.

  • Rutter, E. H., Arkwright, J. C., Holloway, R. F. & Waghorn, D. 2003. Strains and displacements in the Mam Tor Landslip, Derbyshire, England. Journal of the Geological Society 160, 735-744.

For more information contact: Ernie Rutter or Sam Green

Strain and Fabric Variations in Rocks

Theoretical modelling and field-based studies of cleavage patterns, folds, multiphase systems and conglomerates conducted by Sue Treagus reveal subtly small viscosity ratios among many common rock types and suggest quasi-Newtonian rheology. Deformed non-ellipsoidal geological objects provide a new indicator of strain and viscosity contrasts in rocks. In current research, Sue is revisiting theory of fold initiation in multilayers and stratified rocks.

  • Treagus S. H. 1999. Are viscosity ratios of rocks measurable from cleavage refraction? Journal of Structural Geology 21(8-9), 895-901.
  • Treagus S. H. and Treagus J. E. 2001. Effects of object ellipticity on strain, and implications for clast-matrix rocks. Journal of Structural Geology 23(4), 601-608
  • Treagus S. H. and Treagus J. E. 2002. Studies of strain and rheology of conglomerates. Journal of Structural Geology 24(10), 1541-1567.
  • Treagus S. H. 2002. Modelling the bulk viscosity of two-phase mixtures in terms of clast shape. Journal of Structural Geology 24(1), 57-76.
  • Treagus S. H. 2003. Viscous anisotropy of two-phase composites, and applications to rocks and structures. Tectonophysics 372(3-4), 121-133.
  • Treagus S. H. and Lan L. 2003. Simple shear of deformable square objects. Journal of Structural Geology 25(12), 1993-2003.
  • Treagus, S.H. and Lan, L. 2004. Deformation of square objects and boudins. Journal of Structural Geology 26, 1361-1376.

For more information contact: Sue Treagus

Naturally deformed clastic rocks such as breccias and conglomerates provide a useful way to study strain and, indirectly, the rheology of rocks. This Ph.D. study aims to complement the approaches that have been developed to extract information from naturally deformed rocks by means of an experimental study using synthetic breccias and conglomerates deformed at elevated temperatures and pressures, so that the relative viscosities of clasts and matrix can be controlled. To complement the experimental aspect of the project, comparative field studies will be undertaken of Carboniferous conglomerates in the Western Alps. Here, conglomerates of the same age can be found deformed over a range of pressure temperature conditions from the external to the internal parts of the orogen. Strains in clasts of different lithologies can thus be related to the rheological behaviour of particular rock types under different P/T conditions. Conducted by Alex Edwards.

For more information contact: Alex Edwards, Steve Covey-Crump, Sue Treagus, or Ernie Rutter

Structural Mapping of Classical Areas of British Geology

  • Treagus, S. H., Treagus, J. E. & Droop, G. T. R. 2003. Superposed deformations and their hybrid effects: the Rhoscolyn Anticline unravelled. Journal of the Geological Society 160, 117-136.
  • Hassani, H., Covey-Crump, S. J. & Rutter, E. H. 2004. On the structural age of the Rhoscolyn antiform, Anglesey, North Wales. Geological Journal 39(2), 141-156.

For more information contact: Sue Treagus or Steve Covey-Crump

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