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The Belt Association promotes and co-ordinates geologic study of the Proterozoic Belt Supergroup of the northwestern U.S.A. and the equivalent Purcell Group in southwestern Canada. A principal objective of the Association is to provide funds for geologic research by senior undergraduate students and graduate students working in Belt terrane.
The Association is comprised of a 9-member board of directors, elected for three-year terms. There is no general membership. The Association holds a Belt Symposium every decade. A Field Trip Guide and Proceedings are published for each symposium. Informal sessions are held each year at the Northwest Mining Association convention, to discuss results of on-going research in the Belt.
The current board of directors:
Larry Appelgate: appelgateexp@icehouse.net
Jim Browne: barbnjim@icehouse.net
Lisa Hardy: basalt@earthlink.net
Reed Lewis: reedl@uidaho.edu (Secretary)
Paul Karl Link: linkpaul@isu.edu (Treasurer)
Mark McFaddan: mcfaddan@usamedia.tv
Jeff Lonn: jefflonn@lycos.com
Brian White: revett@nidlink.com (President)
Don Winston: winston@selway.umt.edu
The Belt/Purcell Supergroup is a package of sedimentary rocks deposited in a Proterozoic basin over what are now portions of Alberta, British Columbia, Montana, Idaho and Washington. The low metamorphic grade of Belt rocks in much of their outcrop area allows a rare opportunity to study Proterozoic sedimentation processes.
The Belt sediments accumulated to perhaps 50,000 feet in thickness near the Washington-Idaho line, and thin eastward to the vanishing point in central Montana. The sediments are not seen to thin to the west; instead they are abruptly truncated by an 800 m.y.a. rift which split the basin. The western portion of the basin is now thought to be part of either Australia or Asia.
Convergent tectonism along the west margin of the North American plate started in the Mesozoic and continues to the present day. This convergence resulted in the accretion of the "exotic" terranes that make up most of Oregon and Washington, and the attendant compression and plutonism caused widespread disruption of the Belt rocks.
The study of Belt rocks has focused on three primary goals. First is an understanding of Proterozoic sedimentation processes. Second is the correlation of faulted and folded blocks to allow piecing together the history of tectonic adjustments. Third is the locating of economic ore deposits. These goals are interdependent.
Proterozoic sedimentation processes have only poor modern analogues. The land was bare of vegetation and the air contained less oxygen than it does today. No burrowing organisms were present to disrupt the sediments once they were deposited. Thus, sedimentary structures such as mudcracks, ripple marks, and salt casts are extremely well preserved. The weather and even plate tectonics appear to have operated under different rules. The best modern analogue we have for Proterozoic sediment deposition is alluvial outwash fans in sparsely vegetated desert terrains. These do not approach the vast scale of deposition in the Belt basin. In addition, no modern analogue exists for a basin with the size and geometry of the Belt basin, suggesting that the mechanisms of Proterozoic plate tectonics differed from those of the Phanerozoic.
Belt rocks host world-class ore deposits, most notably the Sullivan volcanogenic massive-sulfide deposit, and the Coeur d'Alene Ag-Pb-Zn district.
Annual meeting
| This year's annual meeting will again be held during the Northwest Mining Association convention in December in Spokane, WA. |
The Belt Association, incorporated for the purpose of encouraging research on the economically significant and intellectually challenging Mesoproterozoic Belt-Purcell Supergroup, holds its annual review of new work. This is an informal session where anyone with an interest in the Belt is invited to listen or share new data, observations, and conjectures.""
Belt Symposium IV
Belt Symposium IV is scheduled for August 7-12, 2003, in Salmon, ID. The meeting will be held jointly with the Tobacco Root Geological Society. A guidebook will be available at the meeting (Northwest Geology Volume). Field trip guides need to be completed by April 1, 2003. Visit the Tobacco Root Geological Society Website (http://trgs.org) for details.
Mapping
Revett compilation
Stratigraphic standardization
Marker beds and zircons
Volcanic ash units have been identified from the Belt basin. Further identification and correlation of ash layers presents a significant opportunity to establish "snapshots" of the basin’s appearance, thereby elucidating the mechanics of the basin development. This area of research is being pursued sporadically by several investigators, and would be an excellent subject for a graduate-level thesis.
The Association offers $500 to $1000 research grants each year to one or more graduate students whose theses deal with Belt-Purcell rocks.
2003 Research Grants are Available
Geologic Guidebook to the Belt-Purcell Supergroup, Glacier National Park and Vicinity, Montana and Adjacent Canada, edited by Paul Karl Link, 1997, (2nd edition), 173 p.
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