AAPG Bulletin; January 2006; v. 90; no. 1;
p. 1-20; DOI: 10.1306/08090504134
© 2006 American Association of Petroleum Geologists (AAPG)
Fracture paragenesis and microthermometry in Lisburne Group detachment folds: Implications for the thermal and structural evolution of the northeastern Brooks Range, Alaska
C. L. Hanks1,
T. M. Parris2 and
W. K. Wallace3
1 Geophysical Institute, University of Alaska, Fairbanks, Alaska 99775;
chanks{at}gi.alaska.edu
2 Petro-Fluid Solutions, LLC, 236 Shady Lane, Lexington, Kentucky 40503
3 Department of Geology and Geophysics and Geophysical Institute, University of Alaska, Fairbanks, Alaska 99775
After receiving her M.S. degree from the University of Washington, Catherine Hanks worked for ARCO Exploration in Anchorage, Alaska. She received her Ph.D. from the University of Alaska–Fairbanks in 1991 and joined the Geophysical Institute as a research faculty in 1994. Her recent research has focused on fracturing in detachment folds and the implications for reservoir behavior.Marty is a research geologist at the Kentucky Geological Survey and is the founder of Petro-Fluid Solutions. Previously, he held positions at the U.S. Geological Survey (postdoctorate, 1999–2002) and ARCO's research lab (1997–1999). Marty received degrees from the University of California–Santa Barbara (Ph.D.), Texas Christian University (M.S.) and Tennessee Tech University (B.S.).
Wesley Wallace received his B.A. degree in geology from Rice University and his Ph.D. from the University of Washington. After several years working for ARCO Exploration, he joined the faculty at the University of Alaska–Fairbanks, where his research interests include the tectonic evolution of Alaska and the structure of mountain belts. His current research focuses on the geometry and kinematics of detachment folds and duplexes in the northeastern and central Brooks Range.
The distribution, character, and relative age of fractures in detachment folded Mississippian–Pennsylvanian Lisburne Group carbonates and overlying Permian–Triassic clastic rocks in the northeastern Brooks Range of northern Alaska provide important clues to the thermal and deformational sequence experienced by these rocks. Although paleothermal indices in the host rock limit the conditions of folding to temperatures equal to or less than 280°C, field and petrographic relationships suggest that different fracture sets formed at different times during the deformational history of the rocks, providing a record of deformation under changing temperature and pressure conditions. These rocks probably initially entered the oil-generation window (80–140°C) during the Early Cretaceous formation of the Colville basin via thrust loading by the Brooks Range to the south. Regional fractures formed during this time as a result of high pore pressures and low in-situ differential stresses. Shortening in these rocks related to the advancing northeastern Brooks Range fold and thrust belt began during the Late Cretaceous to early Tertiary. Early phases of detachment folding were via flexural slip, with associated fracturing. With continued shortening and growth of detachment folds, structural thickening resulted in deeper burial of the bottom part of the deforming wedge. Early fold-related fractures were subsequently overprinted by penetrative strain during peak folding at temperatures of approximately 280°C. Continued shortening resulted in uplift and erosional unroofing at approximately 60 Ma. Late fold-related fractures formed at about 150°C. Subsequent uplift of the thickened wedge through 60°C occurred after about 25 Ma. Late pervasive extension fractures related to unroofing and/or regional stresses formed at relatively shallow depths and low temperatures, overprinting all the earlier fractures and penetrative structures.
Copyright © 2009 by American Association of Petroleum Geologists (AAPG)
