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Geoscience Conference & Exhibition
Innovative Geoscience Solutions – Meeting Hydrocarbon Demand in Changing Times
March 7-10, 2010 – Manama, Bahrain
Fractures as Indicators to 4D Fold Development within the Zagros Fold-and-Thrust Belt, Iran
(1) Geology, Fugro-NPA, Edenbridge, United Kingdom.
(2) Midland Valley, Glasgow, United Kingdom.
The Zagros fold and thrust belt represents progressive deformation of Palaeozoic to Cenozoic sediments above a salt detachment, which in turn overlays inverted extensional faults in the metamorphic basement. The Cenozoic sediments of the Zagros contain some fine examples of exposed fractured carbonate sequences.
Using Landsat 7 ETM+ imagery data, regional scale fracture sets have been interpreted across the anticlines of Kuh-e Khurgu, Kuh-e Devin, Kuh-e Finu and Kuh-e Ginau in the Laristan domain, SE Zagros. Using Quickbird imagery data, field-scale fracture sets have also been interpreted across Kuh-e Khurgu. The results of the regional and field-scale fracture analysis show dominant fold axis-parallel, fold axis-orthogonal, and conjugate NW-SE and NE-SW fold axis-oblique orientations.
Utilising the 0.67m resolution of the Quickbird data allows rapid, field-scale identification of fracture patterns. Mapping the fracture and joint sets alongside fold aspect ratio analysis illustrates the deformation evolution of the folds, including the presence of, and disturbance by, reactivated basement faults.
NW-SE orientated fracture patterns dominate anticlinal rose diagrams regardless of fold size, axial orientation or shape. This abundance confirms a local underlying basement trend striking roughly NW-SE. A balanced cross-section of the area was constructed, using the Landsat 7 ETM+ imagery and the newly released 30m Global ASTER DEM data, showing salt-cored detachment folds above a series of reactivated basement thrusts that indicate both thin and thick-skinned deformation.
The results of the satellite image interpretation are then integrated in 3-D Move and a geological model built. The restoration tools are used to validate the geological model and suggest alternatives where appropriate. Once a “best fit” structural history has been identified, the data are then used to capture the geometric strain history through time in 3-D Move. The strain information and other attributes (e.g. curvature) are used to generate a discrete fracture network that is controlled by the observed data.
A multi-stage, 4-dimensional fracture model is proposed for all four folds of the area. This takes into account the incremental and progressive development of fractures as strain indicators within the fold.