The Geology of The Juneau Icefields Research Programs Camp 26 Nunatak, northeastern Coast Mountains, nortwestern British Columbia

Deron T. Carter

Department of Geology, Whitman College, Walla Walla, WA 99362

The Juneau Icefield Research Program's Camp 26 lies on a previously unmapped nunatak, located ~2 km north of 59 degree North latitude, within the Llewellyn Glacier of the Juneau Icefield, northeastern Coast Mountains, northwestern British Columbia. It is underlain by metamorphic rocks that are covered by volcaniclastic rocks, including minor ignimbrite, that are correlated with the Eocene Sloko Group. The metamorphic and volcaniclastic rocks are intruded by granitic-dioritic plutons. If the plutons are coeval with Sloko Group volcanism, they may be related to the Eocene portion of the Coast Range Batholith.

The metamorphic rocks include pelites, semi-pelites, marble and minor amphibole rich gneiss and quartzite. They are considered part of the Jurassic or older Florence Range Suite of the Tracy Arm terrane, in part equivalent to the Nisling terrane based on comparable rock types and lack of a significant igneous component. This correlation extends the known extent of the Tracy Arm terrane in this area.

The nunatak is located west of the Llewellyn Fault Zone, a steep, north-northwest striking fault zone that is at least 150 km long, and was active ~100 m.y. ago and possibly earlier. The oldest structures are folds in the Florence Range Suite, while the youngest structure is an east-west striking fault that cuts metamorphic, volcaniclastic and andesitic rocks. This fault is almost perpendicular to the Llewellyn Fault Zone, but it is not clear which fault is older because they intersect beneath the Llewellyn Glacier.


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