GEOLOGICAL  SOCIETY
OF
MINNESOTA

 

 

FIELD TRIP
TO
NORTHEASTERN WISCONSIN
AND
NORTHERN MICHIGAN

 

Sunday and Monday, AUGUST 3-4, 2008

 

 

BY

 

GENE AND SALLY LABERGE

 

GENERAL INFORMATION FOR THE TRIP

(Day One, Sunday, Aug 3)

Lodging:  Iron Mountain, MI is 5.5 to 6 hours from St Paul, so staying there Saturday night may be the choice of most folks.  There is no lodging available in Pembine or Niagara, Wisconsin for Saturday night.  However, there are numerous motels available in Iron Mountain, Michigan, a few miles away.  There are about half a dozen motels along Hwy 2-141 at the east end of Iron Mountain, having various prices and with restaurants nearby. There are also some motels in Norway, Michigan.  The Sunday morning assembly point is about 6 miles from Iron Mountain.

Assembly Point:  Restaurants for breakfast are readily available in Iron Mountain and Norway.  We will meet at the Wayside about 0.1 mi east of Niagara, WI on the US-141, at 8:30 AM.  The wayside is on the south side of US-141.  We will need to bring food and water (drinks) along with us, since we will not be near restaurants during the day.

Bathroom facilities are scarce, but we will try to accommodate folks on the trip (We WILL be passing gas stations).

 

Several locations have quite limited parking, so we should take as few vehicles as possible.  Vans would be ideal, and ride pooling will be valuable.  A maximum of about 30 participants are all that some outcrops can accommodate, so this might limit the size of the group.  Additionally, several stops will require fairly strenuous walking, sometimes in distance, other times by rugged hiking through the woods.

 

(Day Two, Monday, Aug 4)

 

Lodging:  Lodging is quite abundant in Marquette for Sunday evening; restaurants are also available.  The leaders probably will be staying Holiday Inn in Marquette, (Phone 1-800-HOLIDAY); some folks may want the Econolodge, perhaps a half-mile away (Phone 1-800-435-2502).

Assembly Point.  We will assemble at the Holiday Inn on Hwy-41 on the west side of Marquette at 8:30 AM.

 

We will have a Pasty Lunch in Negaunee for those who are interested, getting these from Grandma-T’s Pasty shop.  They will have hot pasties available for those who choose this delicacy, if we plan ahead.  Optionally, one may plan for a bag lunch.  Bathroom facilities are not as limited as they were on day one since we will pass more gas stations.   Day two will not be as strenuous as day one.  The Trip will end at the Champion Mine in mid-to-late afternoon.  Participants can return to Iron Mountain and proceed home from there, OR drive west on M-28 through Ironwood toward Duluth, etc, if they desire.

The cost will be $50/person, and lodging, food and gas would be the responsibility of each person.     Be prepared for any type of weather.

                                     GENERAL GEOLOGICAL BACKGROUND

By Gene L. LaBerge

The Precambrian rocks of the Lake Superior region have been studied by geologists for well over 150 years, yet new interpretations of the geological environment in which the rock sequences formed continue to be presented.  In addition, new discoveries have helped geologists understand the rocks – and the geological events that formed them.  On this trip we will examine rocks and structural features that illustrate some of the relatively recent new understandings of the rocks in the region.

One of the major “new” concepts applied to the Lake Superior region is that of Plate Tectonics which has revolutionized the field of geology since the late 1960’s.  According to this concept the Earth’s crust consists of a number of large plates that are moving — some toward other plates, some away from neighboring plates, yet others sliding past neighboring plates.  When plates move apart new crust is formed, typically on the ocean floor, and we call the concept “sea-floor spreading”.  When the plates move toward one another, one of the plates bends down and is carried several hundred miles down into the Earth’s mantle, where it partially melts, producing batches of molten rocks that move up toward the surface and cool to form bodies of granite.  If the molten rock reaches the surface volcanic rocks are formed.  This convergent process is called “subduction” and the boundary between the converging plates is called a “subduction zone”.  Subduction zones are also characterized by intense deformation, usually forming mountain ranges.

The concept of Plate Tectonics has been proposed as an explanation of many of the major features in the Lake Superior region.  The work of many geologists, utilizing a wide variety of scientific studies (such as various methods of determining the age of the rocks, the chemistry of the rocks, geophysical techniques – such as magnetic, electrical and gravity studies, and structural patterns within the rocks) have shown quite conclusively that that several plate boundaries, with plates moving in different directions have occurred during the immense span of Precambrian time in this region.

The Michigan-Wisconsin border in the general Iron Mountain area contains abundant exposures of rocks that formed when two plates were moving toward one another, or “colliding” around 1,875-million to 1,850-million years ago.  An older (Archean) continental crust about 2,650-million years old, containing a thick cover of 2,200-million year old sedimentary rocks on it was moving slowly toward an ocean area now occupied by Wisconsin.  The older continental crust was gradually moving down beneath the oceanic crust, forming a series of volcanic islands that developed on the oceanic crust.  The older continent ultimately collided with the volcanic islands, producing much folding and faulting of the rocks on the continent and those forming the ocean floor crust.  The deformation resulted in the formation of an east-west trending mountain range –the “Penokean Mountains“, now almost completely eroded away. It was during this collisional event that the great iron-formations, the source rocks of the extensive iron ores of the region were deposited.

Elsewhere in the Lake Superior region a much younger event (about 1,000 million years ago) during which two plates were moving apart produced the rocks and the event that we call the “Keweenawan”.   Huge quantities of basaltic lava were brought to the surface. These rocks are the host of the rich copper-silver deposits on the Keweenaw Peninsula were formed.  Keweenawan lava flows, mainly basalts, and associated sedimentary rocks were deposited almost entirely on a land surface in an arid environment similar to that in Death Valley today. These rocks are well exposed in Minnesota, as well as in northern Wisconsin and Michigan and in Ontario.

These events occurred over many millions of years.  However, some geologic events, such as the impact of a large meteorite are very sudden, catastrophic events, and one of these, too, is represented in the region.  An exceptionally large meteorite struck the Earth at the site of present-day Sudbury, Ontario, 1,850 million years ago.  This may have been the second largest meteorite impact in the last 3-billion years of Earth history, producing unique deposits that may well have spread over most, if not all, the Earth.  It is quite possible that the major copper-nickel-platinum deposits in the Sudbury area are a result of this meteorite impact.  Deposits produced by this event have been recognized only in the past few years and are currently being mapped and studied.  Highly shattered fragments of rocks from the Sudbury area blanketed most of the Lake Superior region.

The stops on this trip will illustrate examples of some of the rock types formed and some of the folding and faulting (structural features) produced by the plate tectonic events as well as a site showing the nature of some of the ejecta from the “Sudbury Meteorite”

END DESCRIPTIONS

 

(Day One)

STOP – 1  Quiver Falls on the Menominee River.

 

At the NE outskirts of Pembine, WI (near the Catholic Church) turn east on Kremlin Rd (County Road R) and go east about 9.5 miles.  About 0.5 miles past the entrance to the ISP Kremlin Mine take the gravel road that angles off to the right.  Cross the RR tracks and turn left and follow the road about 0.6 miles to a parking area near the river on the right.  At Quiver Falls there is a wooded island in the Menominee River.  Follow the fishing trail down to the outcrops along the river’s edge.

The rocks are part of the Quinnesec Volcanics, an extensive area of volcanic rocks along the Wisconsin side of the river.  The rocks here are basaltic lavas about 1,850 million years old that were part of the ocean floor.  Pillow structures are present locally, indicating that the basalt was extruded under water, and spherical knobs called variolites are visible in many of the pillows showing that they were glassy. 

STOP – 2  Timm’s Lake Road

Return to the blacktop Kremlin Road and proceed west about 2 miles to Timm’s Lake Rd (the road to Morgan Park).  Turn right and go several hundred feet from the intersection to a steep hill in the woods just off the road on the right.  The hill is very steep, but has a gentler slope on the north side.

The rock is composed mainly of the mineral serpentine and is called a serpentinite.  It formed by the alteration of a rock composed originally of olivine (adunite).  These serpentine-rich rocks are fairly common in the Quinnesec Volcanics along the Wisconsin border.  They are typical of basaltic rocks that form oceanic crust.  Incidentally asbestos deposits occur in some of the serpentine bodies, and these were examined as possible sources of asbestos during World War II.

STOP – 3  Junction of Hwy 141-8 and Morgan Park Rd.

Continue on Timm’s Lake Road through Morgan Park and follow it on to the main highway between Pembine and Niagara, Wisconsin.  Turn right on the main highway and stop just after entering the highway.  Please park well off the highway and watch traffic!  (NOTE:  Bathroom facilities are available in Morgan Park for those in need!!)

The outcrop here consists of basalts of the Quinnesec Volcanics intruded by a number of granitic dikes.  The granite was produced by the partial melting of the older continental crust as it was subducted beneath the oceanic crust with volcanic islands to the south.  We will pass a number of similar outcrops as we continue toward the next stop.

STOP – 4.  Piers Gorge on the Menominee River.

Continue toward Niagara on Hwy 141-8.  Turn right (north) on Hwy 8 toward Norway, Michigan and follow Hwy 8 across the Menominee River into Michigan.  Proceed about 0.25 mile and turn left (west) at the sign for Piers Gorge on the blacktop road.  Follow the main road to the parking area at the end, generally keeping left.  However, several roads to the left lead to the Menominee River short of the end of the road.  From the parking area a well maintained trail about 0.3 miles long (approximately a 20-minute walk) that leads to the waterfalls at the gorge.  However, the trail involves walking up over several rock ridges.

(Note:  There are no bathroom facilities here!  However, this might be a good lunch stop.)

We could make a bathroom stop in Norway, Michigan after the lunch stop!

The rocks here consist of mica and chlorite schists with prominent nearly vertical layering (foliation).  The rocks were formed by intense deformation of the volcanic rocks of the Quinnesec Volcanics along a major fault zone that separates the volcanic and granitic rocks in Wisconsin from the sedimentary rocks we will see in Michigan.  The fault is part of the “Niagara Fault Zone” that marks the subduction zone between the two crustal plates that collided in this area about 1,850 million years ago.

STOP – 5.  Sturgeon River Dam northeast of Loretto, Michigan.

Return to Hwy 8 from the parking area, turn left (north) on Hwy 8 and proceed to US Hwy 2 in  Norway, Michigan.  (Hwy 8 ends here.)  Turn right (east) on Hwy 2 and proceed east about 4.5 miles through Vulcan to Loretto, Michigan.  Turn left (north) on County Rd – 573 near the east edge of town and proceed about 0.5 miles to Swede Settlement Rd.  Turn right (east) and go about 1.2 miles.  Turn left (north) on a smaller road that leads to the dam.  Continue about 0.5 mile and park in the parking lot at the gate.  Park and walk about 0.25 miles on the road past the gate to the dam site. (Note that the dam has recently been removed.)

Exposed here is the Archean (2,700 million year old) Carney Lake Gneiss intruded by several basaltic dikes.  The Fern Creek Tillite, a Precambrian glacial deposit about 2,200 million years old, unconformably overlies the gneiss.  The glacial deposits are overlain by the ~2,000 foot thick Sturgeon Quartzite, which grades upward into a thick dolomite unit (the Randville Dolomite).  The contact between the Carney Lake Gneiss and the Fern Creek Tillite is exposed at the former dam site.  Although it is difficult to see, the bedding in the Sturgeon Quartzite dips steeply north, but the beds “face” south, indicating that the layers are overturned due to the north-south compression along the Niagara Fault Zone.  (We are now on the older continent plate that collided with the volcanic rocks in Wisconsin.)

STOP – 6.  Quinnesec Iron Mine just northwest of Quinnesec, Michigan.

Return to the cars and return to Swede Settlement Road.  Turn right (west) and proceed to County Rd – 573 and turn left (south).  Continue to Hwy–2 in Loretto and turn right (west).  Continue west on Hwy-2 about 8.0 miles, through Vulcan and Norway to Quinnesec, Michigan.  At the traffic light in Quinnesec, turn right (north) and proceed about 0.25 mile up the hill and turn left (west) on the blacktop road that curves around to the left.  A locked gate marks the entrance into the Quinnesec mine property.  Continue south several hundred feet to a locked gate in the chain link fence along the right side of the road.  Park near the gate through the chain link fence.  After passing through the gate follow the trail west in the narrow valley about 1,000 feet to the mine. (NOTE; recent windstorms have blown down many trees across the trail, making walking rather difficult!!  However, this unique view of an iron mine makes the effort worthwhile!!)

The Quinnesec Mine is within the Vulcan Iron-formation, and was mined from the late 1800’s to about 1950.  The iron-formation is about 1,850 million years old, the same age as the volcanic rocks in Wisconsin, and about 350 million years younger than the Sturgeon Quartzite. The rocks here are dipping about 60 degrees north, but are “facing” south (so, like the Sturgeon Quartzite, the iron-formation is overturned, however the structure is much more obvious).  The rock on the south side of the mine is the Briar Slate, a shaly unit within the Iron-formation.  Perhaps the most unique feature at this locality is the Paleozoic (Cambrian) sandstone that forms the “cap” on the hill and the exposures on the north side of the workings.  We are looking UP at the unconformity! Interestingly, several of the “pillars” in the mine have collapsed within the last few years, making this mine a much more dangerous locality to walk under.

(NOTE; WE WILL NOT BE WALKING UNDER, OR NEAR, THE DANGER AREA)

STOP – 7  Randville Dolomite outcrop on Lake Antoine

Return to the vehicles and return to Quinnesec and turn right (west) on Hwy-2.

Proceed west through the business section of Iron Mountain, Michigan.  We will re-join Hwy-141 just before we enter Iron Mountain.  After we cross the causeway across the lake formed by collapse of the Chapin iron mine, turn right (east) on Margaret Street one block after a stop light, and a block before the A&W Root Beer stand on the left.  Continue east on Margaret Street to where the street makes a sharp right turn along the south shore of Lake Antoine.  The outcrop is on the north side of the street so park along the street as you can.

Walk (climb) up onto the glacially smoothed outcrop.  The dolomite here is dipping almost vertically, so the top surface is a cross-section of the layers.  Note that the dolomite is thinly bedded, and note that some layers contain abundant stromatolites, produced by micro-organisms.   Stromatolites used to be called  “algal structures” because they were believed to have been formed by blue-green algae.  However, biologists have re-classified the organisms, and now call them Cyanobacteria.  Therefore, we now call the structures “stromatolites”.  The stromatolites here are unusual in that they all appear to be “leaning” to the west!  This unusual shape is, again, due to the collision zone a few miles south of here.  The dolomite is rather “plastic” and has ”flowed” westward by re-crystallizing during the collision of the crustal plates.  The shape of the stromatolites here indicates that Michigan was sliding east and Wisconsin was sliding west during the collision.

END OF DAY ONE.

Return to Hwy US-2/141 and turn right and continue northwest out of Iron Mountain.  At Hwy-M-95, turn right (north) and proceed north about 52 miles, through Sagola, Channing and Republic to Hwy – 41/ M-28.  Turn right (east) and go 19 miles to Ishpeming then 8 more miles to Marquette).

(Day Two)

STOP – 1.  Presque Isle Park on Lake Superior north of Marquette, Michigan.

From the assembly point, follow the road north along the east (lake) side of Presque Isle Park to the parking area at the north end of the park.  Walk to the low ledge near the shore.   Exposed here is an unconformity between an Archean age (~2,700 million year old) peridotite overlain by the Keweenawan age (~1,000 billion year old) Jacobsville Sandstone.  The peridotite is composed mainly of serpentine, and is associated with pillow basalts.  The Jacobsville Sandstone has the mottled brown iron staining characteristic of this formation.  Like the other Keweenawan rocks it was deposited in an arid climate.

STOP – 2.  Sudbury Impact Layer at McClure Basin.

Continue on the road around Presque Isle Park and exit where we entered the park near the iron ore dock.   Drive south along the lakeshore to Washington Street (Business Hwy-41) and go west out of town toward Negaunee on Hwy-41/M-M28.  Continue west approximately 5 miles.  Shortly after going under the railroad overpass turn right (north) on County Rd 502 and go about 0.5 mile to County Rd. 510.  Turn right (east) on County 510 and follow it for approximately 2.4 miles to the new road construction site. Park along the road BEFORE the bridge and walk into the site on the left side of the road.

This is a short walk, but requires crossing a small creek on a plank “bridge”.

The rocks exposed here are debris formed as a result of a huge meteorite that struck the Earth at the present site of Sudbury, Ontario, about 240 miles to the east.  The impact occurred 1,850 million years ago.  Much of the debris is intensely shattered rock.

STOP – 3.   Archean Pillow basalts along Hwy-41/28.

Turn around and follow Hwy 510 about 2.4 miles to Hwy 502, Turn left and go 0.5 miles to Hwy-41/M-28.  Turn right (west) and proceed about 0.25 miles to the glacially polished outcrop on the north side of the Hwy.  There is limited parking space here, so park as far off the road as possible,

These basalts are probably the most photographed pillow lavas in the Lake Superior region.  They are part of the Archean rocks in the Marquette Iron district, and were named the “Mona Schists” by C. R.Van Hise and W. S. Bayley, the US Geological Survey geologists who mapped the district nearly 100 years ago. Like the pillow lavas near Pembine, WI, a number of serpentine bodies are present in these ocean floor basalts.  In addition, several gold deposits were discovered in the serpentine bodies north of Ishpeming in the late 1800”s.

STOP-4  Iron-formation pyramid in the Teal Lake Park in Negaunee. (LUNCH-REST).

                (Grandma-T’s Pasty Shop is a few blocks away for those interested!!)

Continue west on Hwy-41/M-28 for approximately 6 miles to Negaunee.  Shortly after passing through a road cut of white rocks (quartzite), exit right (north) and park along the street on the east edge of the park.

A large pyramid made of blocks of jaspilite (interlayered jasper and hematite) commemorating the first discovery of iron-formation, and iron ORE, in the Lake Superior region in 1844 stands near the highway.

STOP – 5. Jasper Knob exposure in Ishpeming.

Continue west of Hwy-41/M-28 about 5 miles to the stoplight at 3^rd Street in Ishpeming.  Turn left (south) and proceed about 12 blocks to Ready Street.  Turn left (east) on Division St. and continue just past the CCIC (Cleveland Cliffs Iron Company) Research Lab (brick building on the right).  Turn right (south) on Jasper Street and follow it around up the hill.  Park near a stone wall along the left side of the street.  A narrow set of steps within the wall marks the beginning of the trail up to Jasper Knob.  This is a moderately long walk up hill, but the trail is good.

This exposure of highly deformed jaspilite is at the top of the ~2,000-foot thick Negaunee Iron-formation.  It is NOT typical of most of the iron-formation, which consists of gray-black chert, interlayered with various iron minerals (siderite, magnetite, minnesotaite and stilpnomelane).  It is, however, a famous outcrop visited by most people who wish to see the iron-formation on the Marquette Iron Range.

STOP-6. The Champion Iron Mine in Champion, Michigan.

Return down the hill and turn left (west) on Ready Street, then turn right (north) onto third Street and continue on to Hwy-41/M-28.  Turn left (west) at the stoplight and continue west approximately 16 miles to Champion, Michigan.  Turn left (south) at the blinking traffic light and go up the hill toward Beacon. Go past the old school on the left and turn left (east) onto AJ Rd just past Dr. Van Riper’s house.  Turn right on AK Rd at the pale green house and continue to a side road to the right marked with a red U.S. Steel NO TRESPASSING sign, continue on this un-named road to the waste piles.

The Champion Mine produced magnetite and specular hematite ore (the “hard ore” of the Marquette district.  The rocks here are metamorphosed to a much higher degree than those around Negaunee and Ishpeming.  The Champion Mine is noted for the wide variety of minerals (such as tourmaline, molybdenite, etc.) found in the ore here.

END OF THE TRIP