Beloit College Field Excursions - Fall 2001

Northern Minnesota Field Trip Itinerary

Fall Break 2001

October 14 - Sunday

8:00 AM Pack all personal items and food chests into the van.

8:10 AM Leave Chamberlin Hall.

12:00 Lunch -buy stuff at a store, or eat out.

5:00 PM Jay Cooke State Park, Thomson, MN. Set up camp. Jay Cooke has a continuation of the lithologies and structures seen at Thomson Dam.

Thomson Dam, Cloquet. Here we will see the type locality of the Middle pC Thomson Formation composed of volcanoclastic sediments deformed by folding and plastic flow and intruded by dikes. Look for primary structures to aid in your interpretation of structural features. Cleavage-bedding relationships are important. Some sulfides are present with massive quartz, which often marks extension fractures. Good cleavage-bedding relationships are exposed.

7:00 PM Kill a deer and eat it, or eat out at a local diner.

October 15 - Monday

7:00 a.m. Eat breakfast and break camp.

West on Skyline Drive from Visitors’ Center on I-35. Park in cleared area on dirt road just beyond pathway over outcrop. Layered gabbro and overview of rift. There will be a steep descent to a railroad cut with gabbro and peridotite. Layering in the cut is spectacular. Continue a short way west along grade to second outcrop and less mafic phase of gabbro.

North Shore volcanic group along North Shore Scenic Drive, 2.1 miles beyond turnoff on 61. Examples of Keweenawan (1100 Ma) plateau basalts showing pahoehoe structures and vesicle fillings of calcite and fluorite. Gas pipes (vents) can be seen in places.

Gooseberry Falls: Steps lead down to a series of olivine tholeiite basalt flows. Up river is an example of colonade structure in the upper falls. Park in parking lot at visitor’s center along main highway just north of bridge.

Split Rock Light House: The rock forming the base of the lighthouse is made of anorthosite. The anorthosite is probably a xenolith in troctolitic rocks. At this stop you will be able to observe excellent layering in the anorthosite, and textures that may reflect rapid crystallization outward from centers.

Anorthosite at Reserve Taconite plant: Across from the plant is a beautiful exposure of anorthosite. Be very careful in this area. Traffic is heavy. Silver Bay is a good place to shop (Zupps Super Market) and fill up with gas.

Palisade Head (about 2.5 miles north of Silver Bay): Excellent view from a topographic high supported by rhyolite flows.

Finland (optional): About two miles out of Finland on 7 is and road leading to an abandoned air force base. Along this road are exposures of what are called "ferrogranite," with quartz, orthoclase, some euhedral plagioclase, hedenbergite, titanomagnetite, and minor ilmenite. There are some diabase dikes, and inclusions of amygdaloidal basalt up to several meters.

Drive to Ely and stay at the ACM Wilderness Field Station.

October 16 - Tuesday

2.6 miles south of Ely on highway 1: Giants Range Batholith, medium-grained porphyritic hornblende-biotite ademellite. Hornblende and K-spar often show flow structure. Note the evidence for faulting and epidotization that has developed along the fracture surfaces. Also note the displaced character of large blocks, rendering structural measurements unreliable.

Hwy 21 south, go 2.2 miles from 169. Harry Homer’s auto graveyard is on the right. Next to the small office building is an excellent exposure of glacially polished pillow basalt. Determine the upward direction. Further west are more deformed pillows. Toward the north is an exposure of porphyritic rhyolite, which HHW thinks may have originally been an obsidian. Can you find any contacts? Return to 169.

Hwy 169 west of Ely, 2.5 miles: Pillow basalts of the Ely Greenstone belt. Test your skills to determine which way is up. These were once thought to be a part of the oldest rock sequence in the world.

West on 169 to Soudan: Take Main street along base of hill to east past the post-office and up the hill along Stuntz Bay road. At the top of the Soudan Hill is an outcrop of the Soudan Iron Formation - good example of BIF. Note the different styles of folding in the hematite and jasper layered-sequence. Is the folding soft-sediment deformation or multiple stages of tectonism? Note the open pits just over the hill left from ore extraction.

Hwy 169 west of Tower: Metagreywacke and dike.

Pike River: Bedded greywacke and faults.

Highway 53 at Confusion Hill: Cross-cutting relationships in migmatite; dikes

We will try to stop at an overlook of one of the open-pits which made the Messabi Range one of the major suppliers of our nation’s iron.

Virginia-Eveleth: Knife Lake Conglomerate, angular unconformity with BIF

Return to Ely and stay at the ACM Wilderness Field Station.

October 17 - Wednesday

7:00 am Head for home.

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