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Tectonic Development of the Amerasia Basin
Banff Centre, Alberta, Canada
4–9 October 2009
- Lawrence Lawver
- University of Texas at Austin, Institute for Geophysics, 10100 Burnet Road, R2200, Austin, TX 78758-4445
- Victoria Pease
- PetroTectonics Centre, Dept. of Geology & Geochemistry, Stockholm University, SE-106 91 Stockholm, Sweden
- Ruth Jackson
- Natural Resources Canada, 1 Challenger Drive, Room H-507 Dartmouth, Nova Scotia B2Y 4A2, Canada
- Sergey Drachev
- ExxonMobil Russia, Inc., 31 Novinsky Boulevard, 5th floor, 123242 Moscow, Russia
A sequel to the 1995 Penrose meeting, “The Tectonic Development of the Canada Basin and Surrounding Basins,” also held in Banff, this conference turned out to be much more than a simple update. In October 2009, 59 scientists from the U.S., Canada, Russia, England, Sweden, Norway, Australia, Germany, and Denmark came together to present new data and new ideas concerning the tectonic development of the Amerasia Basin. Fifteen participants attended the original 1995 meeting, including three of the conveners, and nine of the attendees were graduate students. As with the 1995 meeting, generous sponsorship was much appreciated from industry; 2009 contributors included BHP, BP, ConocoPhillips, ExxonMobil, Shell, and ION GX Technology. Because of this support, registration fees for graduate students were waived and were substantially reduced for all other participants.
The amount of new data from the Amerasia Basin is staggering, yet there is still no clear-cut answer to how or when the Amerasia Basin developed. Looming United Nations Convention on Law of the Sea [UNCLOS] claims for additional Arctic territory have spurred a substantial amount of new and ongoing research, including the spectacular new multibeam data presented by Larry Mayer and brand-new seismic reflection data presented by Ruth Jackson, Debbie Hutchinson, and others.
Different aspects of the Amerasia Basin were emphasized each day—Monday: ridges and highs; Tuesday: the continental margins; Thursday: shelves and basins; and Friday: resource perspectives, including some extremely interesting but differing views from industry participants. A one-day field trip on Wednesday, exploring the folding and thrusting of the Canadian Rockies, was ably led by Clint Tippett of Shell Canada Ltd.
- New multibeam bathymetry from around the Chukchi Borderland and along the eastern side of the Mendeleev Ridge;
- Long seismic reflection lines collected by joint Geological Survey of Canada and USCGC Healy surveys;
- Intra-plate lavas recently dredged from the Chukchi Borderland region;
- Spectacular deep seismic reflection lines collected on the shelves, particularly the lines in the Mackenzie Delta region shown by Menno Dinkelman of ION GX Technology;
- Seismic reflection and refraction data bearing on the crustal structure of the junction between the Lomonosov Ridge and Ellesmere Island collected by a joint Canadian-Danish operation;
- Multichannel seismic reflection and sonobuoy seismic refraction results from the Amerasia Basin collected by a joint U.S.-Norwegian operation in 2005;
- Sea-ice seismometer data from Chukchi Cap and the Mendeleev Ridge collected in 2006;
- Seismic reflection and refraction data from the Mendeleev Ridge that suggests it is contemporaneous with the oceanic crust on which it sits and therefore oceanic in nature;
- The Cretaceous age of the Makarov-Podvodnikov Basin between the Mendeleev and Lomonosov Ridges;
- Mapping and structural analysis constraining field relationships;
- Heavy mineral and detrital zircon data constraining sediment depocenters and pathways;
- Floral, faunal, and paleomagnetic constraints on Arctic paleogeography;
- Terrane correlations;
- Aerogeophysical data from the Canada Basin; and
- New and improved tectonic reconstructions.
The resource perspectives session included Steve Bergman of Shell, who reprised his presentation from 1995 with new insights into the evolution of the region. It was very clear that his ideas had changed substantially. He was followed by quite different interpretations of the tectonics and the evolution of the Arctic by Steve Matthews of BP, Steve Creaney of ExxonMobil, and Jim Dietrich of the Geological Survey of Canada. The meeting ended with an update from Bernie Coakley on future Arctic drilling targets and possibilities. He made the point that many of the unanswered questions about the tectonic evolution of the Amerasia Basin will only be decided with targeted drilling.
In the early 1990s, there were a number of differing models concerning the tectonic evolution of the Arctic. The intervening years have actually resulted in less agreement as to the nature and age of the Arctic Ocean crust. The Chukchi Borderland and the major trans-basin ridges, the Alpha and Mendeleev ridges, present obstacles to a simple rotational opening of the Canada Basin as originally proposed by Warren Hamilton and Irv Tailleur. It is generally agreed, and new seismic refraction and gravity data confirm, that at least parts of the Chukchi Borderland are continental, but there is still major disagreement concerning the nature of the Alpha and Mendeleev ridges. Previously, there was not much question concerning the oceanic nature of the deeper parts of the Amerasia Basin even if there had been little agreement concerning the age of the seafloor. Now, there are several theories regarding the nature of the deeper seafloor, ranging from oceanic, to transitional, to continental for more than just the shallower parts of the Alpha and Mendeleev ridges. The gravity signature of a probable abandoned spreading center in the Canada Basin trending toward the Mackenzie Delta region is asymmetric, based on new seismic profiles, with greater depth-to-basement toward the Canadian margin. The regional distribution of these new profiles, combined with over 90% of 82 sonobuoys recording converted crustal shear waves, will produce a regional distribution of the continental, transitional, and oceanic crustal affinities, and these new data will undoubtedly provide constraints for the various plate tectonic scenarios.
Even though a great deal of fundamental work has been accomplished since 1995, it has not provided the expected easy answers. The 2009 Penrose Conference focused thoughts on tectonic models and exposed some areas of basic knowledge that need work. Offshore, this includes the nature of the plate boundary between the Lomonosov Ridge continental fragment and the Amerasia Basin, the nature of the other basin margins (is the North Greenland margin strike-slip?), the age of the oldest sediment in the Canada Basin, ages and sources of intrusives both in the basin itself and along its margins, and the true nature of the Alpha and Mendeleev ridges, a subject still controversial after all these years and now even more important given pending UNCLOS claims. There was universal agreement that more data of all types are needed, including seismic and denser coverage of the aeromagnetic data. Onshore, circum-Arctic margins require more detailed mapping and sampling. These vast, remote, and consequently poorly studied regions often provide real “value for money” since the field investigations needed to understand age-relationships, to identify piercing points and sutures, to link on-shore with off-shore geology, etc., are often less costly than their marine counterparts.
The conference also provided a forum to develop new ideas and to coordinate future work and joint investigations. New investigations are planned for the Brooks Range and Yukon regions, Ellesmere Island, northeast Greenland and Baffin Bay in North America, and for Taimyr and Chukotka in the Russian Arctic. A clear need was expressed for more data from the Arctic Islands (e.g., Wrangel, New Siberian, and DeLong Islands). Seismic data over the shelf regions are necessary to connect on-shore with shelf and island geology, and to link this to the deep basin—critical to unraveling the mysteries of the Amerasia Basin. New initiatives, such as the Circum-Arctic Lithosphere Evolution (CALE) project being coordinated by V. Pease, will specifically address this topic over the coming five-year period. It was also clear that many of the unanswered questions about the tectonic evolution of the Amerasia Basin will only be decided with targeted sampling cruises—the need for sample material means that future Arctic drilling initiatives are a definite priority.
Although we may be close to a breakthrough in understanding the tectonic development of the Amerasia Basin with the integration of geological, geophysical, and geochronological observations combined with modeling and interpretation, we are not there yet. Mikhail Kos’ko does not think he can wait another 14 years for the next meeting and hopes that we can reconvene in perhaps eight years from now. As we know, the Amerasia Basin and the surrounding region will not give up their secrets easily.