Invited Speakers

 Education:
1983
Columbia University (Lamont-Doherty Earth Observatory), PhD - The thermo-mechanical properties of the continental lithosphere.
1979
Canberra College of Advanced Education, Grad. Dipl (Statistics)
1974
Flinders University, BSc (Hons) – Marine Geology & Geophysics

Experience:
1975
Mount Isa Mines; Computer programmer
1975-1978
Bureau of Mineral Resources; Science 1 (Marine Group)
1979-1983
Bureau of Mineral Resources; Science 2 (Gravity Group)
1983
Bureau of Mineral Resources; Senior Research Scientist
1984-1986
University of Durham, Elf-Aquitaine Research Fellow
1986-1993
Lamont-Doherty Geological Observatory of Columbia University; Associate Research Scientist
1993-1996
Lamont-Doherty Earth Observatory of Columbia University; Research Scientist
1996-2006
Lamont-Doherty Earth Observatory of Columbia University; Senior Research Scientist
2006-Present
ExxonMobil URC; Senior Research Associate (New Play Concepts)

Professional Interests:
The integration of geological, geophysical, geochemical, petrological, gravity and magnetic data to map and quantify the geological and tectonic development of extensional, compressional, and intracratonic basins, their environments of deposition, crustal structure, subsidence and uplift histories, and their tectonic-related spatial and temporal heat flow histories.

Develop company workflows for the use of process-oriented gravity modeling to extract information about basin-forming processes, such as rifting, thrusting, sedimentation, compaction, erosion, eustasy, lithospheric flexure, magmatic underplating, crustal intrusions, and volcanic flows, from observed gravity anomalies across sedimentary basins and passive margin systems.

Publications and Awards:
Over 90 publications in various scientific journals, including the AAPG Bulletin, Marine & Petroleum Geology, NATURE, GEOLOGY, Journal of Geophysical Research, Tectonophysics, and Earth & Planetary Science Letters.

Recent papers include:
Karner, G.D., N.W. Driscoll and D.H.N. Barker, 2003. Syn-rift regional subsidence across the west African continental margin: The role of lower plate ductile extension. In: "Petroleum systems and evolving technologies in African exploration and production", T. Arthur, D. MacGregor and N.R. Cameron (eds), Spec. Publ. Geol. Soc. Lond., 207, 105-129.

John, C.M., Karner, G.D., and Mutti, M., 2004. 18O and Marion Plateau backstripping: Combining two approaches to constrain late middle Miocene eustatic amplitude. Geology, 32, 829-832.

Karner, G.D., M. Studinger, and R.E. Bell, 2005. Gravity anomalies of sedimentary basins and their mechanical implications: Application to the Ross Sea basins, West Antarctica. Earth Planet. Sci. Letts., 235, 577-596.

Cathro, D.L., and G.D. Karner, 2006. Cretaceous-Tertiary inversion history of the Dampier sub-basin, northwest Australia: Insights from quantitative basin modeling. Marine Petrol. Geol., 23, 503-526.

1989
Storke Research Award (Columbia University)
1992-1993
DuPont Educational Aid program - Science & Engineering award
1993-1994
DuPont Educational Aid program - Science & Engineering award
1997
Wallace E. Pratt Memorial Award for best paper published in the AAPG Bulletin during 1996 (Development of sediment overpressure and its effect on thermal maturation: Application to the Gulf of Mexico basin. AAPG Bulletin, Vol. 80, No. 9, 1367-1396. Mello, U.T., & G.D. Karner)
1999
2000-2001 Ocean Drilling Program Distinguished Lecturer

Professional Affiliations:
American Geophysical Union
Geological Society of Australia
Geological Society of London
American Association of Petroleum Geologists

ABSTRACT

DEPTH-DEPENDENT EXTENSION AND MANTLE EXHUMATION: AN EXTREME PASSIVE MARGIN END-MEMBER OR A NEW PARADIGM?

Karner, Garry D.¹

¹ExxonMobil URC P.O. Box 2189, Houston, TX, 77251-2189, United States

The discovery of exhumed continental mantle rocks and lack of magmas in ocean continent transitions, the existence of top-basement detachments, and the recognition of an “extension discrepancy” across many passive continental margins, as exhibited by preferential thinning of lower crust and the rapid thinning of continental crust in the absence of obvious faulting, have seriously challenged the accepted paradigms for the formation of passive continental margins and the way in which continental lithosphere is deformed in extension. Recent studies have clearly demonstrated that rifting, that is, the offset across high-angle basin bounding normal faults, is only a minor component in the thinning of continental lithosphere. During extension, early fault controlled subsidence tends to be limited to the proximal regions of passive margins while later brittle deformation dominates the distal regions. Kinematic considerations of passive margin subsidence require preferential bulk thinning of the lower crust and lithospheric mantle relative to the upper crust, an observation supported by seismic refraction results across the West African margin and the Exmouth Plateau, northwest Australia. Age considerations indicate that this depth-dependent extension (DDE) of the lithosphere is the significant process for thinning continental crust from its 30-40 km pre-rift thickness to a thickness of ~10 km, but surprisingly, depositional environments seem to be characterized by shallow water and quiescent conditions, as evidenced by Tithonian carbonates of the Iberian margin now at abyssal depths. Such extension partitioning requires a lateral strain balance, which may take the following form: 1) a counterbalancing of upper crustal extension leading to late-stage brittle deformation in the vicinity of the ocean-continent transition zone (e.g., the low angle detachment systems of the distal Iberian margin), and/or 2) the lateral emplacement and exposure of serpentinized and magmatically modified continental mantle and lower crust out from under the adjacent continental lithosphere.

While isostatic considerations of DDE allow the distribution and amplitude of syn- and post-extension accommodation to be calculated, a geological understanding of the thinning process and the modes of crustal and mantle deformation cannot be addressed. Thus, the fundamental question remains: what mechanism(s) allow the continental lithosphere to be thinned from ~30 km to ~10 km and thence to the point of rupture? Lavier and Manatschal (2006), using field observations from the exposed Tethyan margin in the Swiss Alps and geodynamic modeling, have suggested that the Iberia-Newfoundland system is the result of a complex rifting history that can be described as a sequence of different modes of extension. This sequence initiates with a broadly-distributed brittle deformation (stretching phase) and is followed by strain localization and crustal thinning along upper crustal and mantle ductile shear zones decoupled along a mid-crustal decollement, localized and controlled by a relatively weak middle crustal rheology (thinning phase). If and when coupling of the thinned upper and lower crust occurs (i.e., once the crust has reached a thickness of ~10 km), crustal embrittlement and continued extension leads to the formation of crustal-scale detachments along downward-concave faults that are conducive to mantle exhumation (exhumation phase). While this sequencing is a working hypothesis for how continental lithosphere extends, the view is that the final crustal architecture of at least the Iberia-Newfoundland margin is controlled by the stacking of these different modes of extension. Thus, given the field and drilling observations from the Iberia-Newfoundland and Tethyan margins, the proxy for extensional strain partitioning in the crust is the existence of syn-extensional sags and the exhumation of lower crust and continental mantle. The width of these exhumed zones may be 100’s km wide and contain organized magnetic anomalies. However, these magnetic anomalies are likely a consequence of mantle exhumation and serpentinization rather than mid-ocean ridge basalt production at the spreading center, a review of which was recently published by Sibuet et al., (2007).

Many passive continental margins are characterized by such observations, for example, Galicia Bank and the Iberian margin, the Exmouth, Queensland and Marion Plateaus, the Woodlark basin, the West African margin, and the Norwegian margin. While the geological details and sedimentary facies differ between the various margins, the style of deformation is remarkably similar. It would appear that what was once considered an extreme end-member of passive margin formation (viz., the Iberian-Newfoundland margin) may instead be a template for the development of many hyperextended margins around the world, that is, continental lithosphere that has undergone 100’s of percent of extension to the point of rupture. The modes of extension discussed above have immense implications for the heat flow history, environments of deposition, syn-extensional stratigraphy, and basin architecture of passive margin systems. A goal of this presentation is to show examples of depth-dependent extension and changing modes of crustal deformation. Our future challenge is to understand exactly how to link crustal deformation with lithospheric mantle thinning in a predictive way.

References

Lavier, L., and G. Manatschal, 2006. A mechanism to thin the continental lithosphere at magma-poor margins, Nature, 440, 324-328.

Sibuet, J.C., S. Srivastava, and G. Manatschal, 2007. Exhumed mantle forming transitional crust in the Newfoundland-Iberia rift and associated magnetic anomalies, Journal of Geophysical Research, 112, B06105, doi:10.1029/2005JB003856.