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AAPG Bulletin


AAPG Bulletin, V. 96, No. 12 (December 2012), P. 22452274.

Copyright copy2012. The American Association of Petroleum Geologists. All rights reserved.


An integrated model of the structural evolution of the central Brooks Range foothills, Alaska, using structural geometry, fracture distribution, geochronology, and microthermometry

Alec Duncan,1 Catherine Hanks,2 Wesley K. Wallace,3 Paul B. O'Sullivan,4 Thomas M. Parris5

1Department of Geology and Geophysics, University of Alaska, Fairbanks, Alaska: present address: Anadarko Petroleum, 1099 18th Street Suite 1800, Denver, Colorado; [email protected]
2Geophysical Institute and Department of Petroleum Engineering, University of Alaska, Fairbanks, Alaska; [email protected]
3Geophysical Institute and Department of Geology and Geophysics, University of Alaska, Fairbanks, Alaska; [email protected]
4Apatite to Zircon, Inc., 1521 Pine Cone Road Moscow, Idaho; [email protected]
5Petro-Fluid Solutions LLC, Lexington, Kentucky; present address: Kentucky Geological Survey, 228 Mining and Mineral Resources Building, University of Kentucky, Lexington, Kentucky; [email protected]


Episodic deformation, triangle zone development, and related back thrusting in the central Brooks Range foothills are major factors in the distribution of fractures and the thermal history of rocks involved in the deformation. Structural reconstructions suggest that the rocks forming the Endicott Mountains allochthon, the youngest and northernmost part of the orogen during its first phase, were emplaced during the Early Cretaceous (Valanginian) at temperatures approximately 150degC. Fractures associated with that deformation are filled with synkinematic calcite cement, indicating that they formed in the presence of fluids. After a period of quiescence during the Late Cretaceous, renewed deformation involved the shortening of the existing orogenic wedge and the development of a triangle zone and overlying back thrust in adjacent mid- to Late Cretaceous rocks of the foreland basin. This later deformational event and subsequent uplift resulted in two sets of uncemented barren fractures that formed in all parts of the fold and thrust belt. Restriction of cement-filled fractures to the older and structurally deeper parts of the orogen implies that the youngest and most obvious fractures visible at the surface developed at shallow depths and temperatures and thus may not have been an important factor in petroleum migration.

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