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19 hours to Altona

It all started in 2018 with an email. Todd Braun wrote me that he was a stonemason, interested in erratics, and had found an orbicular rock in a gravel pit. Todd lives in Altona. Altona in Manitoba, Canada.

orbicular rock, erratic in southern Manitoba
Figure 1: It all started with this orbicular rock.

While doing research on orbicular rocks, Todd had found my site. His inquiry sparked a lively exchange and soon emails were going back and forth daily. The following year we made initial travel plans, but then Canada was closed in the spring of 2020. It took a year and a half before entry became possible again in September 2021, if one met a long list of conditions.
It's a long way to Manitoba. It takes three flights to get to Winnipeg via Frankfurt, Montreal. That alone takes over 19 hours, plus the drive from Winnipeg to Altona.
When we faced each other at the airport in Winnipeg, Todd and his wife Lisa were at least as excited as I was. After more than two years of planning and anticipation, it took a few days for me to really arrive.

Contents:

  • Canada, and Altona in Manitoba
  • Geology
  • Erratics
  • Gravel pit near Miniota, Jasper
  • Plagioclase rocks and greenstone belts
  • Whiteshell Provincial Park
  • West Hawk Lake
  • Anorthosite
  • Open questions
  •  

    Canada

    North America belongs to the continents with an ancient core, the "Canadian Shield". There, the rocks are more than 2.6 billion years old and extend over a vast area.
    In eastern Canada are the rocks of the Grenville Mountain Formation, which are about 1 billion years old. They form the western continuation of the Svekonorwegian rocks of southern Norway and southwestern Sweden.
    The mountains to the far west are young and still growing. The collision of North America with the Pacific plate is ongoing, which is associated with violent earthquakes and volcanism.

    Altona, MB

    Altona is in the middle of Canada, just north of the 49th parallel, the border with the United States. All around stretches the former prairie, which is now farmland. It is an almost empty landscape, treeless, flat as a table, with very straight roads to the horizon and a wide sky. The starry night sky is breathtaking on a clear day. The Milky Way reaches to the horizon and the Andromeda Galaxy can be seen with the naked eye.

    Canada was fundamentally surveyed starting in 1871 - at least where agriculture was possible. A system of right-angled roads was laid out, forming squares with an edge length of one mile (1.6 km). (See also "Dominion Land Survey")

    Map of Altona and surroundings
    Figure 2: Altona and the surrounding area.
    (Section width approx. 30 kilometers.)

    From about 1876, Mennonites originally from northern Germany settled in the area. They brought with them their traditional Low German ("Plautdietsch") and German place names. That is why in southern Manitoba there are places like Altona, Neubergthal, Sommerfeld, Halbstadt, Blumenfeld and Steinbach.
    Colloquial language is English and so the place names sound unfamiliar. "Altona" is pronounced on the "o", which takes some getting used to for Hamburg ears.
    Orientation is very easy. Almost all streets run straight from east to west or from north to south. If you have to drive a longer distance, you pay more attention to the road condition than to the route. There are "Provincial Roads", which are nothing provincial, but well developed highways with allowed 100 km/h, which in practice are 110 to 115 km/h. Canadians need less time for long distances than we do in Germany.
    Secondary roads are mostly gravel roads on which you can drive quickly as long as you don't steer abruptly or brake sharply. However, a huge plume of dust in the rearview mirror is then unavoidable.

    an almost empty landscape
    Figure 3: The former prairie is flat and mostly treeless.

    The close range for everyday errands is large. A distance of 100 kilometers and more is easily driven. In Canada, everything is a lot of farther away than here in Germany.

    Geology

    The south and west of Manitoba consists of sedimentary rocks. This is mostly limestone and also dolomite from the Ordovician to the Jurassic.
    The much older crystalline rocks of the Canadian Shield are found in the east, along the Ontario border and farther north. On the map the crystalline is light brown.

    Geology of Mantitoba, simplified
    Figure 4: Geology of southern Manitoba, simplified.
    Courtesy of MGS

    Canada experienced the same ice ages as Europe. The European glaciations (Elster-, Saale- and Weichsel) here are called Kansas, Illinois, and Wisconsin glaciations. At that time, glaciers covered almost all of Canada and reached far into the United States. Frozen in this ice a lot of rock was moved and these rocks are called erratics. Because the ice in Manitoba moved primarily from northeast to southwest, a lot of erratics from the Canadian Shield lie on the limestone in southern and southwestern Manitoba today.
    At the end of the cold periods, a huge lake covered southern Manitoba, called "Lake Agassiz". It formed on the southern edge of the glacier that covered central Canada. Because this landscape drained to Hudson Bay, but the ice lay there, the meltwater dammed up at the southern edge and so the probably largest freshwater lake of all times was formed. It was several times larger than the four great lakes in North America. This lake emptied several times into the Atlantic Ocean and the Arctic Ocean, which probably caused considerable climatic disturbance, because so much fresh water interferes with the Gulf Stream.
    The four great lakes in the northern United States are remnants of Lake Agassiz, as is "Lake Winnipeg" in Manitoba. It alone is over 400 kilometers long.

    Just as northern Germany was completely covered by ice, so was it here in Manitoba. That's why there are a lot of ice-age deposits, which are mined as sand and gravel in various gravel pits. In the process, large boulders are also found. Unfortunately, they all end up in the crusher and are processed into gravel. This hurts, because among them are beautiful and rare pieces, which every museum would exhibit immediately.

    Boulder from Manitoba
    Figure 5: Boulder with large zoned plagioclases.

    Old acquaintances

    The gravel pits look familiar to a visitor from Europe: a lot of granites, quartz syenites and some monzonites. In addition granodiorites and tonalites - but a lot more than in Europe. The whole crystalline is rather gray and black-white and altogether somewhat finer-grained than the Scandinavian erratics. Intense red granites are also found, but less frequently than in Germany.

    Canadian erratics
    Figure 6: Canadian erratics.

    Gneisses are abundant, including garnet-bearing paragneisses that resemble the Sörmland-gneisses of southern Sweden. (See all figures on page 2.)
    Most of the igneous and metamorphic rocks were delivered by the ice from a northeasterly direction and are older than 2.6 billion years.
    Unlike Scandinavia, the Canadian glacier, the "Laurentian Ice," formed on a flat landscape. There are no mountains in the middle of Canada that could significantly influence the flow direction of the ice. From the glacial striations and the position of the terminal moraines, it can be seen that the center of the ice sheet was approximately over Hudson Bay, and from there the ice moved in all directions.

    visited places
    Figure 7: Visited outcrops.
    source: openstreetmap.org

    However, there were glaciers that moved differently than most. This is evidenced by some erratics in western Manitoba that came in a straight line from the north.

    The first gravel pit I visit with Todd is near Blumenort, southeast of Winnipeg. The first thing I notice is a lot of limestone. This is no surprise because the bedrock all around consists of just such limestone. But it looks different from the limestone at the Baltic Sea

    Tyndall rock
    Figure 8: "Tyndall stone" - fossil-rich limestone with burrows.

    This fossil-rich limestone with burrows is called "Tyndall stone" and dates from the Ordovician. "Tyndall" lime is quarried as ashlar east of Winnipeg and is a valued ashlar throughout Canada because of its hardness. It is used as masonry stone and also in interior work, often polished.

    The following figure shows how much lime there is. The arrows point to some of the Tyndall limestones.

    A pile of erratics at Blumenort
    Figure 9: Erratics in Blumenort.
    (picture without annotation)

    The crystalline rocks at Blumenort are a rich mix. Among them are "granoblastic amphibolites" which look exactly like those from Scandinavia. The amphiboles in them are deep black and some of them have nice edges, thus showing their crystal form.

    Amphibolite
    Figure 10: Granoblastic amphibolite as erratic.

    Completely black amphibolites are rare and garnet amphibolites I don't find at all.

    Wet and dry

    Also in Canada gravel pits are operated either wet or dry. In wet cutting, a dredge bucket is used to remove the bottom of a lake. This bucket is pulled by rope over a pulley to the other shore and then dragged forward again over the lake bottom. In the process, it scrapes sand and gravel from the bottom of the lake.

    dredge bucket
    Figure 11: This bucket is used for dredging.
    Dredging in action
    Figure 12: Dredging in Blumenort.
    Photo Todd Braun

    For dry mining, one simply uses a wheel loader.

    The gravel pits near Miniota

    Already on the first weekend we undertake the longest excursion. We drive to the west, to the gravel pits near Miniota, which are located in the valley of the Assiniboine River. The journey is quite long, almost 400 kilometers. Why so far? Because there are very special erratics.
    We set off while it is still dark and at sunrise we reach a long step that runs right across the entire landscape. This is the "Manitoba Escarpment"

    A step in the landscape - Manitoba Escarpement
    Figure 13: "Manitoba Escarpment" at sunrise.

    This ridge forms the western end of the flat and level prairie. The formation of this elevation is again connected with Lake Agassiz at the end of the last ice age. Its shore was located here and wave action contributed to the formation of this step in the landscape.
    Further to the west the terrain becomes more hilly and we pass rivers with such sounding names as "Cypress River".

    early morning
    Figure 14: Morning atmosphere.

    After 4 hours we reach the Assiniboine.

    the valley of the Assiniboine River
    Figure 15: View over the valley of the Assiniboine River.

    The valley is flat and wide. Here the first trees are already turning yellow, although it is only early September.

    The gravel pit we are looking for is located north of the river and, to my surprise, is almost empty.

    The almost empty gravel pit near Miniota
    Figure 16: Gravel pit in the valley of the Assiniboine near Miniota.

    There is only one pile of stones, but it turns out to be quite rich. Above all, there is a typical Canadian rock that I am determined to find, the "Omarolluk". Mostly it is simply called "Omar". Omars are fine-grained graywackes with bright round spots. In these patches, the graywacke contains calcite, which weathers easily and leaves round holes.

    Omarolluk (Omar)
    Figure 17: Omars contain bright calcitic spots.

    Todd shows me the first Omar after only a few minutes and from then on one after the other. I don't find a single one. When I complain and tell him to leave them so I can find them myself, he bursts out laughing. It takes me a while to realize that I'm standing on one right now. How embarrassing. But now at least I know how such an Omar looks between the other erratics and from then on I also find my own. The only striking feature are their round spots.

    Omarolluk (Omar) with pits
    Figure 18: Weathered calcite.

    Such stratification is rather rare in the Omars.

    Omar with Stratification
    Figure 19: Stratification in the Omar.

    The Omars come from the "Belcher-Islands" in the Hudson-Bay. There really are a lot of Omars in this gravel pit. You can pick one up every few steps. Whether they really all come from Hudson Bay seems a little questionable to me at over 1500 kilometers away.

    close up of Graywacke, Omar
    Figure 20: Graywacke, the calcite-rich spot on the right.

    You can find Omars everywhere else in southern Manitoba, but their quantity varies from sparse to common depending on the gravel pit.

    Back to the gravel pit. Since we are here in a deepened river valley, I wonder whether the stones are rather river gravel or glacial till. This is not obvious at first glance, but the very varied composition suggests that everything here was moved by ice. The omars, for example, come from an area much too far away and in the wrong direction. These stones have not been brought here by any river.
    At the vertical edge of the gravel pit, one can see that the river was also involved, because only fast-flowing water can sort fist-sized stones and then pile them up at an angle. Thus, the stones in this gravel pit were first transported by the ice and then redeposited by the river.

    gravel
    Figure 21: Diagonally deposited gravel at the edge of the pit.

    The undisturbed sediment contains inclined layers of coarse gravel. This gravel was deposited either on the inside of a river bend (glide slope) or when flowing over an obstruction. Sediment may be deposited in inclined layers on its back side. The size of the stones indicates a high flow velocity.

    What exactly are we looking for here? On the one hand there are small brown-red pebbles and on the other hand pale red granite and quartz porphyry. Although we are here mainly for the granite porphyries, it takes more than two hours until we find the first one. It is a ring quartz porphyry, as it can hardly be more beautiful.

    Granite porphyry with black rimmed quartz
    Figure 22: Granite porphyry with black rimmed quartz.

    I could not distinguish this piece from one of the Åland granite porphyry. Just as in the Finnish rocks, there is a ground mass full of graphic intergrowths, individual larger alkali feldspars and also larger, greened plagioclase in addition to the black-rimmed quartz.

    black rimmed quartz
    Figure 23: The arrows point to the rims around the quartz.
    (Picture without annotation)

    For such a texture to be the result of, a granite melt must incorporate a dark, plagioclase- and pyroxene-rich magma. In this process, the black rims form as a reaction of the quartz with the pyroxene from the dark melt.

    These granite porphyries are from the Nueltin Rapakivi, which lies far to the north of Manitoba (map). It is one of the few rapakiwis in Canada and belongs to the "Dubawnt Supergroup". With an age of 1.75 billion years it is younger than the surrounding rocks. Also in this it resembles the Rapakiwis in Scandinavia.

    And there are also the matching quartz porphyries here, which also look like the ones from Åland. They also probably come from the Nueltin Rapakivi or the neighboring Pitz Formation.

    Quartz porphyry erratic in Manitoba
    Figure 24: Quartz porphyry erratics in Miniota.

    Jasper

    The second rock Todd looks out for is only available here as small brown-red pebbles. When he shows me the first one, I am a bit disillusioned, because it looks rather boring. This changes when I examine the wet stone with a magnifying glass. Suddenly you look at a really exciting surface full of tiny little spheres. These round formations are ooids.

    Oolitic Jasper in Manitoba
    Figure 25: Oolitic Jasper, wet (erratic, Miniota).

    The rock is called "Oolitic Jasper". The small spheres consist of quartz, which is colored by reddish and silver-gray hematite.
    Because this jasper is made almost entirely of quartz, it is particularly hard and was used by indigenous people to make arrowheads and other stone tools.
    Alternatively, they used chert, which we also find in this gravel pit. My pieces are yellow, yellow-reddish, black and gray and have the typical conchoidal fracture.

    Chert in Canada
    Figure 26: Yellow chert from Miniota.

    They are exceedingly hard and some resemble flints from the Baltic Sea, including the small parabolic cracks on the surface.
    "Chert" I use here as a generic term for hard and very fine-grained rocks. Whether they are radiolarites (lydite) or fine-grained volcanics cannot be determined without a microscope.

    Black chert from Canada
    Figure 27: Black chert from Miniota.

    Stone Age tools and arrowheads made from such rocks are found throughout Canada, especially at former settlement sites. Over the years, Todd has found a lot of such arrow points. The ones on his hand are called "Oxbow points", named after the archaeological site at Oxbow, Saskatchewan.

    arrowheads
    Figure 28: Oxbow points. (Photo Todd Braun)
    arrowhead, type Scottsbluff
    Figure 29: Arrowhead, type Scottsbluff.
    (Photo Todd Braun)

    Another light green rock from which tools were made is called "West Patricia Recrystallized Chert" (WPRC) by archaeologists. The name refers to a site found near "West Patricia Lake" in western Ontario.
    Shortly after I left, Todd found a really large erratic of it.

    erratic, green chert
    Figure 30: "West Patricia Recrystallized Chert" as erratic.
    Photo Todd Braun

    Especially the sharp-edged, conchoidal fracture surfaces are striking. They show how hard this rock is, because erratics are usually a lot more rounded. A chert boulder of this size is really rare.

    erratic, green chert
    Figure 31: Front view. Photo Todd Braun.

    But back to our gravel pit near Miniota. One thing bothers us all the time, and that is the thick crust of limestone that covers a lot of the rocks. This crust is sometimes so thick that one cannot recognize the actual rock at all.

    Lime crusts with imprints of the neighboring stones.
    Figure 32: Lime crusts with imprints of the neighboring stones.
    Lime crusts with imprints of the neighboring stones.
    Figure 33: Lime crusts with imprints of the neighboring stones.

    We bathe such pieces first in hydrochloric acid (= muriatic acid), so that we can see something at all.

    Because I have never encountered so much subsequently deposited lime, I take a closer look.
    Again, the edge of the gravel pit is interesting because it shows that each individual stone has a thick crust of lime on its underside.

    Lime crusts
    Figure 34: Every stone in the sediment has a lime crust at the bottom.
    (without annotation)

    I have no idea what is different here compared to other gravel deposits. The only certainty is that all the lime was precipitated from solutions that seeped through the sediment here from top to bottom.

    With so much lime, it is not surprising that we also find abundant ironstone nodules and septaria.

    ironstone
    Figure 35: Ironstone nodule.

    Two of the lot of clay iron stone nodules.

    ironstone
    Figure 36: Ironstone nodule.
    Septaria
    Figure 37: Septaria - result of calciferous clay.

    Unfortunately, all septaria are crumbly and disintegrate almost by themselves. There is not one among them that could be taken away. Too bad.

    Sandstones are also found, but really beautiful ones are rare and red ones very special.

    red sandstone
    Figure 38: Sandstone erratic in western Manitoba.

    At the end of the day we even find an ignimbrite, which we hardly recognize at first because of its lime coating. After an acid bath a really nice piece comes to light.

    Ignimbrite erratic, Manitoba
    Figure 39: Ignimbrite erratic from Miniota.
    Ignimbrite erratic, Manitoba
    Figure 40: Ignimbrite erratic from Miniota.

    Further finds are some cone-in-cone, a lapilli stone, a conglomerate similar to the Digerberg from Sweden and others.

    Plants

    Away from the gravel pit, the meadows smell like a herb garden. Among others, sage, wormwood and a lot of flowering asters grow in the prairie.

    Canadian Aster
    Figure 41: Asters in the Canadian prairie.
    Canadian Aster
    Figure 42: Asters in the Canadian prairie.

    Until we are at home, it takes a long time again and it gets late. That was a long day full of new impressions and completely new rocks.

    Plagioclase rocks and greenstone belts

    In the gravel pits of southern Manitoba, all rocks that are not limestone are from the Canadian Shield. They are of archaic age, i.e. more than 2.5 billion years old. Rocks this old form the cores of ancient continents worldwide. These archaic cores regularly consist of plagioclase-rich rocks, especially tonalite, trondhjemite and granodiorite. Because these three often occur together, they are called "TTG" and the whole group "TTG suite".
    Tonalite contains a lot of quartz, a lot of plagioclase, and no (or almost no) alkali feldspar.
    Trondhjemite is a particularly bright and quartz-rich tonalite with only a little biotite as a dark mineral. Granodiorite, like tonalite, consists of a lot of quartz and a lot of plagioclase, but contains slightly more alkali feldspar.
    Because these TTGs occur throughout the Canadian Shield, there are so many plagioclase-rich erratics in the gravel pits.

    The second common feature of the Archean areas is greenstone belts. These are elongated, narrow zones of volcanic deposits, basaltic lavas, and sedimentary rocks.
    They were all formed at the Earth's surface or in shallow water and have collectively undergone greenschist metamorphism, which is responsible for the green coloration of the rocks. (Amphibolite facies are also occasionally reached).
    The coexistence of weakly metamorphosed surface rocks and plagioclase-rich plutonic rocks (TTG) is both striking and in need of explanation. At the core of this is the question of how continental crust formed in early Earth. This has not yet been clarified in all details, but it is considered certain that TTGs and greenstone belts were the result of subduction at island arcs.
    When these rocks were formed, the Earth was young and a lot of hotter. Therefore more mantle rock was melted during the subduction and the oceanic crust was a lot of thicker than today.

    For us, in the gravel pit, it's a lot more interesting to see what the tonalites, granodiorites, and the other members of the greenstone belts look like. Later, I will also try to find these rocks in the Canadian Shield.
    Let's start with the erratics. Most impressive are pillow lavas, which with their greenish hue indicate that they originate from a greenstone belt. A look at the geological map proves this. (Or this one.)

    Pillow lava, erratic
    Figure 43: Pillow lava as erratic.
    Photo Todd Braun

    A pillow lava forms only when molten lava flows into water. (Since only basalt lava is so mobile, pillow lavas are always basalts).
    The outer layer of molten lava is instantly quenched by the water, resulting in a rounded structure. As lava continues to flow inside, it bursts laterally and elongates in a few seconds to form a tube-like structure that can be several meters long. The diameter is approximately between 30 cm and 1 m. Because this tube is still soft at the beginning, it can adhere to uneven ground without any gaps. In cross-section, these tubes then look like cushions.

    It is remarkable that the outer layer of quenched basalt is still easily recognizable even after a very long time. Although over time this thin rim of rock glass converts, because no glass is permanently stable, the rim remains recognizable.

    Pillow lava, erratic
    Figure 44: Individual pillows of a pillow lava.

    These pillow lavas come from the neighborhood greenstone belts - close by Canadian standards.
    Over the years, Todd has found quite a few pillow lavas. Most are from gravel pits near Morden, a larger town west of Altona.

    Another member of the greenstone belts are conglomerates. Here in Manitoba, these often contain gray or black and white clasts. This suggests a mountain range of plagioclase-dominated rocks, i.e. andesites and dacites or diorites, tonalites and granodiorites.

    Conglomerate
    Figure 45: Conglomerate in Todd's boulder collection.

    Back side of this rock:

    Conglomerate
    Figure 46: Almost only black and white rocks.

    A mountain range can be inferred because such large rocks are rounded only in fast flowing water, that is, in steep terrain. This means mountains. Therefore, these conglomerates are the erosion deposits of mountains over island arcs.

    Most greenstone belts experienced only weak metamorphism. From time to time, however, strongly deformed rocks occur, especially metaconglomerates. However, they are rare as erratics.

    Metaconglomerate
    Figure 47: Section through a greened metaconglomerate.

    Banded iron ores

    The old continental shields are known for this particular rock. Banded iron ores (BIF) are sedimentary rocks consisting of alternating layers of quartz and hematite or magnetite.

    Banded iron ore (BIF)
    Figure 48: Banded iron ore, erratic.

    Such erratics are rare. It took Todd several years to get a small collection of them.

    Banded iron ore with layers of manetite and quartz (BIF)
    Figure 49: Polished surface with layers of quartz and magnetite.
    (image without annotation)

     

    Whiteshell Provincial Park

    Besides all the erratics, of course, I really wanted to see the bedrock. This is two hours drive east of Altona as a flat undulating landscape with shrubs and trees. There lies the "Whiteshell Provincial Park", a nature reserve where you can hike, fish and paddle. For geologically interested people there are nature trails and in the net also some videos of the Geological Survey of Manitoba - MGS.
    At the road, a large sign points to the "Falcon Creek Self-guiding Trail".

    Information board at Falcon Creek Self-guiding Trail
    Figure 50: "Falcon Creek Self-guiding Trail" with information board

    At the parking lot is an information board with a geology brochure and a request to stow all food well and use the bear-proof garbage cans because of the bears. This is bear country.

    geological brochure at the left
    Figure 51: Information board with brochure.
    (Copyright Park Canada)

    The brochure is aimed at laymen, but it contains information about plate tectonics, volcanism and ice ages. This is really well done. In addition a hint to the former search for gold, because there are single quartz veins here. But probably no gold.

    Boreal forest like in northern Europe
    Figure 52: Boreal forest

    The circular trail leads over two kilometers through a forest that hardly differs from one in Sweden or Finland. It is the typical boreal primeval forest on rocky ground with pines, spruces, single birches, a lot of moss and plenty of blueberries. But this forest here sounds different, because it rustles above my head all the time. That's the lot of aspens. Their leaves have long thin stems and move at the slightest breeze. If you look only fleetingly, you can confuse them with birch trees, because the trunk of the aspens is light gray to almost white. Their sound, however, is unmistakable.
    The trail crosses Falcon Creek - a tiny stream - and then winds through hilly terrain.

    The rock at the bottom is fine-grained, black and dull with no sparkle. The geological map says "basalt" - that fits. A magnet is not attracted, so no magnetite in it.

    basalt from a greenstone belt
    Figure 53: The basalt at the Falcon Creek Trail.

    Then the dense forest divides and one stands abruptly in front of a mighty boulder. Over two meters high and at least 8 meters long, it is too big to photograph it completely. The forest is too close and so I can only take a picture from the front.

    boulder
    Figure 54: Large boulder.

    I cannot recognize the rock, the boulder is too dirty.

    Leccinum versipelle
    Figure 55: Orange Birch Bolete (Leccinum versipelle).

    Behind it the terrain rises slightly, the forest becomes light and the ground more and more rocky. Then I see them: pillow lavas. Everywhere. They are the highlight of this trail.

    Pillow lava along the Falcon Creek Trail
    Figure 56: Pillow lava along the Falcon Creek Trail.

    The outer rim of each pillow is often still well preserved, despite a slight deformation that can be seen in the elongated outlines of the pillows.

    Pillow lava along the Falcon Creek Trail
    Figure 57: Perfect pillows.

    This here is a gorgeous outcrop, the kind you don't see every day. Especially not with a pillow lava from the Archean.

    At the edge of the forest a mullein is blooming, which also grows wild here in Germany.

    Mullein
    Figure 58: Mullein.

    But the red dogwood, which I find shortly after, is not native to Europe.

    Red Dogwood
    Figure 59: Red Dogwood.

    As a garden shrub, it probably originated here, in North America. To read that some of our garden plants come from overseas is one thing. But to find such a plant unexpectedly in the forest more than 6000 kilometers away makes even more of an impression.
    Next to the path is another small, very pretty plant. Only later it becomes clear that this is also a dogwood, a particularly small one: Cornus canadensis.

    On the way back, something small and furry flits across the forest floor. Too big for a mouse, too much bushy tail, but so fast that I can't see anything. What was that?

    I continue east on a side road to West Hawk Lake. On the way, I again encounter outcropping rock, which this time is not pillow lava, but fine-grained, black, and full of tiny, glittering minerals.

    Amphibolite in a greenstone belt
    Figure 60: Road outcrop.

    Since it is a dark rock, I am still in the greenstone belt. But this is not basalt anymore, because it would not glitter. This looks like amphibolite, because intensely reflecting minerals mean good cleavage, and with this black color it can only be amphibole. This is an example of amphibolite facies in a greenstone belt.

    Amphibolite in a greenstone belt
    Bild 61: Amphibolite.

    The bridge in the background of figure 60 is the eastbound lane of the Trans-Canada Highway.

    Whiteshell Provincial Park
    Figure 62: The southwest of Whiteshell Provincial Park.
    (map from openstreetmap.org)

    Sketches of the surroundings off the "Falcon Creek Trail".

    Sketch Falcon Creek Trail
    Figure 63: Pillow lava and boulder on Falcon Creek Trail.
    (map from openstreetmap.org)

    For a closer look at the bedrock, use the map "Kenora" from the Manitoba Geological Survey. In the upper part of the map runs as a narrow green band the part of the greenstone belt we are concerned with here.

    West Hawk Lake

    There is a lake and a small town by that name: West Hawk Lake. When I arrive, it's summer weather, but the season is over. The boats are winterized, the kiosks are closed and on the campground I see only three people. Nevertheless, it is beautiful.

    West Hawk Lake
    Figure 64: West Hawk Lake.

    At the main road a sign welcomes the visitors.

    West Hawk Lake
    Figure 65: This bird is a loon.

    Everyone in Canada knows this bird, it is a "loon". It can dive for minutes and is known for its special wail. To me it sounds more like a wolf than a bird, but it is really impressive.

    The common loon also decorates the front of the 1-dollar coin, which is therefore called "Loonie". Fittingly, the $2 coin is a "Toonie."

    Loonie and Toonie
    Figure 66: Canadian dollar coins: Loonie and Toonie.

    I take a walk along the shore of the campground and see that the people there are divers who are taking a break. This fits perfectly, because until just now they were walking around on another nice pillow lava. So I can get a photo without any wet footprints.

    Pillow lava
    Figure 67: Lake shore with basalt.

    The pillow in the center is about 50 cm wide

    Pillow lava
    Figure 68: Perfect pillow lava.

    During the Cretaceous period, a meteorite struck here at West Hawk Lake. There is an impact breccia on the shore, geological information boards and a video on the web. I skip that because it is already afternoon and drive further north, through a landscape that is not different from Scandinavia. Here, too, the glaciers have smoothed the rocks, rounded the hills and left behind a flat landscape on which a sparse forest fights for survival.

    Archaic bedrock in Whiteshell Park
    Figure 69: Archaic bedrock in Whiteshell Park

    From now on, I drive slowly, stopping often and looking closely at everything, because this is the first time I see the Archaean granites and granodiorites of the Canadian Shield up close. The determination of the feldspars is partly laborious. I can easily recognize the plagioclase, but what is alkali feldspar and what is not is often difficult to decide.

    Archaic gneiss in Whiteshell Park
    Figure 70: Archaic gneiss in Whiteshell Park.

    After more than two hours I find a quarry west of Big Whiteshell Lake. Here I can take a few specimens without hesitation. The rock is colorful. It contains a lot of quartz and plenty of gray to colorless plagioclase.

    Granodiorite at Big Whiteshell Lake
    Figure 71: Granodiorite, west of Big Whiteshell Lake.

    In addition there is some brown alkali feldspar. Since the plagioclase clearly outweighs the alkali feldspar, this is a granodiorite, a pretty one. Another specimen of the same rock below.

    Granodiorite at Big Whiteshell Lake
    Figure 72: Granodiorite, west of Big Whiteshell Lake.

    A second, light brown rock has much more alkali feldspar than plagioclase, plus again lots of quartz. This is a granite.

    Granite from Big Whiteshell Lake
    Figure 73: Granite from the same quarry.

    The fresh plagioclase in this area is almost uniformly colorless, but turns brownish red when altered.

    Reddish brown plagioclase
    Figure 74: The arrow points to a reddish brown plagioclase.
    (Animation)

    The enlarged animation shows that at the lower left end the plagioclase is still transparent. Only its core is altered.
    Such reddish-brown plagioclase is also found in several granites of southwestern Finland as well as occasionally in southern Norway.

    While I am formatting my samples, something moves in front of me. There is one of these small furry animals again!

    there is something
    Figure 75: There is something between the rocks.

    But this fellow is completely relaxed and walks over the stones. Then he climbs around in the scrawny plants and feeds on seeds.

    Chipmunk
    Picture 76: This little fellow is not afraid.

    This is a chipmunk, as Todd explains to me in the evening.

    It is getting dark, I have to go back. A few miles down the road, I'm driving all in thought, suddenly there are two turkeys on the side of the road. I am so stunned that I don't even brake. Turkeys!

     

    Anorthosite

    Todd has been collecting boulders for many years and now has an impressive collection. Among them are quite a few anorthosites - magmatic rocks consisting of more than 90 % plagioclase.
    In contrast to Scandinavia, Canada has a lot of anorthosites with porphyritic textures, often with individual rounded plagioclases. The size of these feldspars ranges from a few millimeters to a lot of centimeters.

    Porphyritic anorthosite, erratic, Manitoba
    Figure 77: Porphyritic anorthosite, erratic, Manitoba.

    This anorthosite contains relatively small crystals with angular outlines and a size between 1 and 2 cm.

    Porphyritic anorthosite, erratic, Manitoba
    Figure 78: Porphyritic anorthosite, erratic, Manitoba.

    However, there are also coarser grained anorthosites:

    Porphyritic anorthosite, erratic, Manitoba
    Figure 79: Porphyritic anorthosite, erratic, Manitoba.

    In this anorthosite are a lot of intergrown plagioclase, which are grouped to "heaps". Such textures are also called "glomerophyric".

    Glomerophyric anorthosite, erratic, Manitoba
    Figure 80: Porphyritic anorthosite, erratic, Manitoba.

    In addition, there are single large crystals, which can be recognized by their angular-regular outlines.

     Porphyritic anorthosite
    Figure 81: Large plagioclase crystal, same stone.

    Other anorthosites contain rather roundish plagioclase.
    There are variants of erratics found several times, probably from the same occurrence.

    Porphyritic anorthosite
    Figure 82: Porphyritic anorthosite, erratic, Manitoba.

    The porphyritic anorthosites of figures 82 to 85 belong to such a group. Todd has found several identical erratics of it, always containing single roundish plagioclase about 2-3 cm in size, embedded in a greenish ground mass.

    Porphyritic anorthosite, close up
    Figure 83: Same rock, close up, wet.

    The next erratic belongs to this group too.

    Porphyritic anorthosite
    Figure 84: Porphyritic Anorthosite, erratic, Manitoba.

    Up close you can see that there are also fragments besides the roundish feldspars.

    Porphyritic anorthosite
    Figure 85: Close-up of the Anorthosite from figure 82 and 83.

    Another common feature is the somewhat dull looking feldspars. Presumably they have been altered by fluids, but this needs clarification by thin section.

    A class of its own are so called "megacrystic" anorthosites. They contain extremely large plagioclase as roundish structures.

    Megacrystic anorthosite
    Figure 86: Megacrystic anorthosite. This boulder from Mora, Minnesota (USA) is more than 1.5 m (5 ft) wide.

    Such anorthosites were found several times as erratics and similar occurrences are also known in the bedrock. (There is a text worth reading about this.)
    All these anorthosites originate from the Archean.

    Megacrystic anorthosite
    Figure 87: Megacrystic anorthosite, same like above.

    Their formation is most likely the result of the higher temperature of the earth's crust at that time. Because the crust and mantle were a lot hotter than today, a lot more melt was formed over subduction zones and particularly large magma chambers were the result of this. In these, the light minerals could separate from the heavy ones, because due to its low density, plagioclase moves upward in a melt and accumulates at the very top. Because the cooling of a large magma chamber takes a particularly long time, good conditions for long-lasting crystal growth are given.

    In addition, there was very likely an effect called Ostwald ripening. In this process, large crystals grow at the expense of smaller ones, because it is energetically more efficient to form a few large crystals than a lot of small ones. Given sufficient time, only a few large crystals are left in the end and all the small ones are dissolved. This mechanism is probably involved in the formation of the giant-grained anorthosites.

    So far we have not found any erratics from these anorthosites. Of course, it would be best to see such a rock in the bedrock. In Manitoba alone, at least two such deposits are known, although the plagioclase may not be quite as large as in the images above. However, it is still unclear whether an excursion to one of these anorthosites can be realized at all.

    Besides the porphyritic ones there are also massive anorthosites in Canada.

    Anorthosite with garnet
    Figure 88: Garnet-bearing anorthosite, erratic, Manitoba.

    This erratic contains garnet which is not found in the Scandinavian anorthosites.

    Anorthosite with garnet
    Figure 89: Brown-red garnet in massive anorthosite (erratic).

    Since we have another garnet-bearing specimen from a quarry in Ontario, this rock is not exotic. Therefore my request to the readers: If someone finds an erratic of a garnet-bearing anorthosite in northern Germany, please send me a message. Of course it would be even better to know such an occurrence in the bedrock of Norway or Sweden. (Next to the garnet bearing anorthosite from Bergen, Norway.)

    Open questions

    Of course there are also rocks which raise questions. For example this sedimentary rock which seems to be related to oolitic iron ores.

    Unknown sedimentary rock
    Figure 90: Sedimentary rock from near Morden.

    We do not know what this rock is. Unfortunately, an inquiry to the Geological Survey of Manitoba did not help us either. The only certainty is that it is a sedimentary rock consisting of ooids. It occurs only in a gravel pit near Morden, MB and is almost always decomposed and friable. It is not a carbonate rock.

    Unknown sedimentary rock
    Figure 91: Close up of the sedimentary rock from near Morden.
    Unknown sedimentary rock in the gravel pit
    Figure 92: Sedimentary rock in the gravel pit.

    The large block in figure 92 is still intact, while figure 93 shows several fragments. One to the left of center, two others at the bottom left at 7 o'clock.

    Unknown sedimentary rock in the gravel pit
    Bild 93: Several large fragments of this rock in the gravel pit.

    Other erratics are completely disintegrated.

    Unknown sedimentary rock in the gravel pit - disintegrated
    Figure 94: This pitiful remnant was once an erratic.

    It is very rare to find this sedimentary rock in a solid, non-weathering form.

    The same rock - solid
    Figure 95: This is the solid version of the same rock.

    Close up:

    The same rock - solid
    Figure 96: The same rock.

     

    A second rock with open questions has already been microscoped and determined to be basalt. However, we do not yet know what the striking pattern is all about.

    Basalt with pattern
    Figure 97: Basalt with patterning.

    The bright structures are part of the rock and not only superficial.

    Basalt with pattern
    Figure 98: The pattern of this basalt up close.

    Todd also found several pieces of this type that look quite similar.

    Basalt with pattern - erratic in Todd's collection
    Figures 99: Erratic of this kind in Todd's collection. Photo Todd Braun.

    The large erratics are slightly coarser, but otherwise the various pieces are similar. It seems certain that they originate from the same place.

    Basalt with pattern - erratic in Todd's collection
    Figure 100: Another one of this kind in Todd's collection. Photo Todd Braun.

     

    End

     

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    Coordinates:

    The Orbicular rock was found in a gravel pit near Ste-Geneviève.
    The pillow lava at Falcon Creek Trail is located at N 49.69624, W95.33988
    Road outcrop in amphibolite, SW of West Hawk Lake, is at N49.73030 W95.24327
    Pillow lava at campsite at approximately N49.74562 W95.20905

    Rocks from Todd Braun's collection: 1, 5, 10, 18, 19, 22, 23, 24, 28, 29, 30, 31, 39, 40, 43-49, 77-85, 88, 89, 95, 96, 99, 100

     

    Literature:

    BEST M G 2003 Igneous and metamorphic petrology Blackwell Science Ltd.

    FRISCH W, MESCHEDE M. 2013: Plattentektonik, Wissenschaftliche Buchgesellschaft Darmstadt, 5th ed.

    H.P. Gilbert, M.G. Houlé, X.M. Yang, J.S. Scoates, R.F.J. Scoates, C.A. Mealin, V. Bécu, V.J. McNicoll and C.R. Galeschuk. Field Trip Guidebook FT-C2: Mafic and ultramafic intrusive rocks and associated Ni-Cu-(PGE) and Cr-(PGE) mineralization in the Bird River greenstone belt, southeast Manitoba. Geological Association of Canada-Mineralogical Association of Canada Joint Annual Meeting, Winnipeg, May, 2013.

    LE MAITRE RW (ed.), STRECKEISEN A, et al: 2004 Igneous rocks: a classification and glossary of terms, Cambridge University Press.

    OKRUSCH, MATTHES: Mineralogie. Eine Einführung in die spezielle Mineralogie, Petrologie und Lagerstättenkunde, 8. Auflage, Springer Verlag

    Polat, Ali. (2018). An overview of anorthosite-bearing layered intrusions in the Archaean Craton of southern West Greenland and the Superior Province of Canada: Implications for Archaean tectonics and the origin of megacrystic plagioclase. Geodinamica Acta, 30 (1), 84-99. DOI:10.1080/09853111.2018.1427408
    (https://ir.lib.uwo.ca/cgi/viewcontent.cgi?article=1027&context=earthpub or
    Here: https://scholar.uwindsor.ca/environmentalsciencepub/104

    Manitoba Geological Survey:
    https://www.manitoba.ca/iem/info/library/downloads/precambrian.html

    Kenora bedrock map:
    https://www.manitoba.ca/iem/info/libmin/bgcms/bgcms_kenora.pdf

    Bedrock map Pointe Du Bois:
    https://www.manitoba.ca/iem/info/libmin/bgcms/bgcms_pointe_du_bois.pdf

    Rapakiwis in Manitoba (Nueltin Granite and Pitz Formation):
    http://www.largeigneousprovinces.org/10dec

    Boreal forest: https://www.spektrum.de/lexikon/geographie/borealer-nadelwald/1197

    Call of the common loon: https://youtube.com/watch?v=4ENNzjy8QjU

     

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    Matthias Bräunlich, January 2022