View from base camp at Agate Fiord.
1996 University of Rochester
expedition to Axel Heiberg Island, Canadian High Arctic
Large igneous provinces are massive accumulations of mafic rocks
that are often associated with mantle plume activity. Because of
the large volumes of new crust created, these provinces are intimately
related to the tectonic development of both cratons and ocean basins in
which they are found. Some provinces show a striking coincidence with
extinction and/or climatic events and their emplacement has been
invoked as an agent of global change.
The mid-Cretaceous appears to have marked an extremely active
period for the emplacement of large igneous provinces, especially
the giant oceanic plateaus in the Pacific and Indian Oceans.
Other phenomena also characterize the mid-Cretaceous, including
episodes of oceanic anoxia, a geomagnetic superchron and the
recently defined rapid motion between Atlantic and Pacific hotspot
groups (see
Tarduno and Gee, 1995).
All of these phenomena may be related, directly or indirectly,
to an unusually vigorous episode of mantle plume activity.
Similar magmatism is also present in the Cretaceous on-land record
exposed throughout the High Arctic. In particular, flood basalts, dikes and
sills of Cretaceous age are well-represented in the Canadian Arctic islands.
These flood basalts may be part of a greater large igneous province
that includes major tectonic elements of the Arctic Ocean such as
Alpha Ridge. If so, the entire province would be one of the
largest in the world.
During the summer of 1996, the paleomagnetic group at the University of Rochester
investigated these flood basalts on western Axel Heiberg
Island. Ours is a multidisciplinary study linked through a common
sampling scheme: the flow-by-flow sampling of continuous sequences
for paleomagnetic and geochemical analyses. Ultimately we hope to
determine the age and duration of the volcanism, place paleomagnetic
and geochemical constraints on its origin and obtain high-latitude
paleomagnetic data for geomagnetic studies.
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First explored at the turn of the century by members of Otto Sverdrup's
expedition, many of the fiords of western Axel Heiberg Island are
bounded by ridges and peaks composed of the flood basalts.
We chose the area near Expedition and Agate Fiords
(79.5 degrees N, 93 degrees W) because here the entire
volcanic sequence is preserved. However, this area is probably the distal
part of what was once a much more extensive on-land exposure that has
been lost to erosion.
Eurekan deformation has resulted in broad folding of the volcanic rocks and
bounding strata, while rapid uplift has produced
spectacular exposure. Although accessibility is often challenging,
with care one can sample the entire stratigraphic succession
of volcanic flows in continuous stream cuts. The sections we
examined are 100-300 m thick and contain individual flows
of up to 60 m, with well developed columnar
jointing
Among the more surprising finds in these sections were volcanic tuffs
and a small bed containing fossil bones of
potential climatic significance.
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The other major challenge in this effort is that of paleomagnetic sample
orientation, given the proximity of the north magnetic pole,
which is actually located to the southwest of our field area.
The large daily variation, combined with
deflections caused by the magnetism of the basalt renders orientation by
magnetic compass nearly useless. Instead samples must be oriented by the sun,
requiring a certain degree of cooperation from the weather.
Of our 39 days in the field, our group experienced 10 days of rain and
8 days of snow (which is unusual even for
this region). Nevertheless, we were
able to complete several flow-by-flow stratigraphic sections,
with all samples oriented by sun compasses. Analyses of these rocks
is presently underway at the Paleomagnetic Laboratory at the
University of Rochester.
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Our work is supported by the Arctic Natural Sciences
Program (Office of Polar Programs, National Science
Foundation) and by the Canadian Polar Continental Shelf
Project. For more information about our work, please contact
John Tarduno at
john@skyline.earth.rochester.edu.
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To see more pictures of Axel Heiberg Island and students and faculty in the Arctic, click HERE.
Pictures from the Arctic '97 Expedition! Click
HERE.
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