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The Archean Superior Province is surrounded
on all sides by the shallow water clastic sequences of (in anti-clockwise
order):
the Huronian (2.5-2.2 Ga) and Animikie (2.2-1.8
Ga, see Appendix A below) Supergroups
of the Southern Province;
the Kaniapiskau Supergroup (2.3 - 1.88 Ga,
volcanism) of the Labrador trough;
the Povungnituk
Group of the Cape Smith Thrust belt (2.0-1.84 Ga) of Ungava;
and the Richmond Gulf-Nastapoka-Belcher Groups
(2.025 - 1.8 Ga) of the Belcher Islands region.
To the west of the early Proterozoic Churchill ocean, passive margin and intracontinental arenaceous sedimentary sequences ssociated with the Wyoming, Hearne, Rae, and Slave Archean cratons are represented by the Hurwitz Group (2.45 - 2.11 Ga) of northern Saskatchewan and the Medicine Bow Group (2.3 Ga) of Wyoming; the Foxe Group located within the Archean Rae Province; and, to the northwest, northeast, and southeast, respectively, of the Slave Craton Province, the Coronation (1.98 - 1.84 Ga), Goulburn (2.02-1.91 Ga). and Great Slave (1.93 Ga) Supergroups. The stratigraphic sequences of the Hurwitz and Medicine Bow Groups bear considerable resemblance to that of the Huronian of the Southern Province. Corresponding sandstone dominated terranes are also found in the Ketilidian and Jatulian terranes of the Greenland and Baltic shields, respectively (see Appendix B below), as well as in South America, Africa, and Western Australia.
The early Proterozoic extension of Archean crust, leading in some cases to the formation of passive margins, is recorded by the intrusion of dike swarms at the following times:
Mafic intrusives in the Huronian
2.491+5 Ga; Huronian volcanism 2450+25 Ma
Volcanics EpNd = 0 to -6
East Bull Lake
2.490-2450 Ga EpNd = chondritic
Hearst/Matachewan
2.454+2 Ga
Murray-Creighton granites
2.39-2.33 Ga
Nipissing
2.219+4 Ga; EpNd = -2 to -6
Fort Francis
2.120+67 Ga; Rb-Sr
Kapuskasing
2.014 Ga
Biscotasing
c. 2.1 Ga
Marathon
2.1 Ga
Preissac
2. 04 Ga
Sudbury norite
1.85 Ga; EpNd = -8
Wanapitei complex
1.74 Ga; EpNd = 0 to -8
The oldest early Proterozoic
sedimentary basins are represented by the Huronian, Hurwitz and Snowy
Pass Supergroups, all of which are characterized by the presence of very
similar lithologies, including lower clastic units containing detrital
pyrite and uraninite, diamictites of glacial origin (Gowganda), aluminous
quartzites, chromiferous green quartzites (Lorrain), and iron bearing
sediment (see Appendix C below)
at the very highest levels. Although very similar successions, the
Huronian and the Hurwitz-Medicine Bow Mountain rocks are located on opposite
sides of the Churchill ocean, and this fact has led to the suggestion
that the Medicine Bow rocks represent the southern margin of the
Huronian basin rifted at c. 2.1 Ga and transposed across the Churchill
ocean. Such an explanation however does not explain the similarity
of the Huronian and the Hurwitz. Furthermore, similar lower Proterozoic
sequences are also found as shelf sequences in Africa, Brazil, India, and
Scandinavia.
Comparative
stratigraphy of the Huronian and Medicine Bow (Snowy Pass Supergroup) Early Protoerozoic successions
- lprotmedbow1.jpg
Major
Precambrian geological elements of central North America - lprotmedbow2.jpg
Organisation
of the Archean Superior and Wyoming provinces during the Early Proterozoic
- lprotmedbow3.jpg
Stratigraphic
succession of the Hurwitz Group - lprothurwitz.jpg
The progressive appearance
of a negative Eu anomaly in the the REE
patterns of Huronian sedimentary rocks witnesses the progressive emergence
and subjection to erosion of Eu-depleted K-granite terranes formed during
the last stages in the collisional cratonization of the Archean Abitibi
belt to the north.
Variation
in REE abundances in Archean and Huronian rocks - lprothurree.jpg
Plots
of Sm-Nd versus sedimentation and provenance age for sediments deposited
since the Archean - lprotsmnd.jpg
The principles involved
in the generation of Eu-depleted granitoids by the partial melting of Archean
tonalite are illustrated in the following data diagrams (Condie et al,
1985):
Generalized
geologic map of southern India - lprotmysore.jpg
Chondrite-normalized
REE patterns for Archean tonalites and granites - lprotmysoreree.jpg
Similar changes occur in
the Th/Sc and Sm/Nd chemical characteristics of early Proterozoic sediments.
Plots
of Th/Sc versus sedimentation age for sediments deposited since the Archean
- lprotthsc.jpg
Oceanic
terranes are represented by the Kisseynew-La Ronge arc volcanic
(including boninite) complexes of the Churchill Province, the Wisconsin-Yavapai-Mazatzal
volcanic provinces, the obducted Purtiniq ophiolite of the Cape Smith
fold belt of Ungava, the Wopmay arcs west of the Coronation 'miogeosyncline',
and the Taltson magmatic plutonic arc of the North West Territories.
Within the Cape Smith fold
belt of Ungava, the oldest rocks (Povungnituk Group) include shales,
quartzite, carbonate and iron formations overlain by rift volcanic rocks
clearly of WP character. This unit is structurally overlain by a
pyroxene- and plagioclase-phyric basalts and rocks with komatiitic affinity
(Chukotat) and MORB chemistry marking the development of an oceanic
rift. This rift sequence is structurally overlain by a deep water
turbidite facies (Spartan Group) and at the top of the structural sequence
by the primitive low-Ti Purtiniq ophiolite klippe. Arc rocks
are potentially represented by the Parent Group of basic to intermediate
flows and pyroclastic rocks locally present below the ophiolite, but they
may also represent fractionated rift volcanic rocks. Similar komatiitic
rocks and associated ultramafic material also occurs along the Superior
margin (Thompson-Fox River belts) of the Churchill ocean.
Geological map of the
Cape Smith fold and thrust belt, Ungava Peninsula - lprotungava.jpg
Discrimination diagrams
for rocks of the Cape Smith fold and thrust belt - lprotungfinger.jpg
The best documented collisional complex in the Lower Proterozoic is that of the Trans-Hudsonian system of Manitoba- Saskatchewen (NATMAP Shield Margin Project: Canadian Journal of Earth Science, 1999, volumes 36, numbers 2 and 11; Zwanzig, H.E., 1999). The Trans-Hudson, which extends from south Dakota, through Saskatchewan and Manitoba to northern Quebec, is a 400 km wide collage of juvenile oceanic terranes (Reindeer zone) and re-worked parts of the bounding Archean cratons. Collision of opposing Archean terranes at 1.84-1.8 Ga has caused the intervening oceanic terranes to be thrust stacked over the basal metaplutonic rocks and paragneisses of the 3.2-2.4 Ga Sask craton. The oceanic terranes of the lower part of the thrust stack are composed of 1.92-1.87 juvenile arc rocks, including boninites, 1.88-1.84 Ga stitching plutons, 1.87-1.85 Ga volcano-sedimentary units, and 1.85-1.84 Ga alluvial-fluvial sandstones, whereas the upper part of the stack is composed of marine turbidites (1.85-1.84 Ga) and coeval distal facies of alluvial-fluvial sandstones. Collision of the amalgamated arc terranes with the Superior craton took place at about 1.81 Ga and led to sinistral transpression of the eastern Trans-Hudson.
Diagram of interactive crustal blocks in Trans-Hudson Orogen (Zwanzig, 1999, Fig 11).
According to Zwanzig (1999) the tectonic history
of the south flank of the Flin Flon and Kisseynew Domains representing
the southern margin of the Trans-Hudson Orogen involved the following sequence
of events:
1) 1.85-1.825 Reindeer Zone collision with the Sask
craton in the southwest, provoking southerly directed overthrusting of
the Flin Flon - Glennie Complex (1.92-1.87 Ga Amisk collage) over the Sask
Craton; this potentially represents an early D0 phase of obduction accretion.
Rocks to the north of the accretionary complex are dominantly sedimentary
and represented by the Burntwood Group turbidites
overlain by or as a facies of the continental
arenites, conglomerates, quartzites, and continental arc-volcanic
rocks, of the Missi Group. Burntwood
sediments coeval with and to the north of the Missi arc volcanics would
have been deposited in a fore-arc basin of the arc system. They were
ultimately involved in F1 folding and thrusting towards the northeast
(in present-day coordinates), commensurate with their sense of subduction
beneath the Missi arc.
N-S section through the Trans-Hudson orogen between the Lynn Lake and Flin Flon arcs (Zwanzig, 1999).
2) 1.82 collision with the Superior
Craton in the southeast, and overturning on the margin of the
Flin
Flon - Glennie Complex during overriding by the Burntwood
Group and possibly by the rocks in the Snow Lake area; formation
of large F2 folds, now recumbent but originally west verging, the File
River nappe; doming; and formation of associated foliation.
3) 1.81-1.79 overriding by the northern part of
the Reindeer Zoneattached to the Hearne
Craton, with south and southwesterly mid-crustal flow in the
central Kisseynew Domain, driving the
Flin
Flon - Glennie Lake Complex farther over the SaskCraton:
F3 folds with associated S3 foliation co-planar with S2; northeast stretching;
folding is upright at the Flin Flon Beltmargin.
4) 1.8-1.77 intracontinental convergence of the
Kisseynew
DomainandSuperior
Craton; final overthrusting by the northeast part of the Reindeer
Zone; formation of upright folds, steep shears, and retrograde
folation S4.
5) development of north northeast-trending
and east to northeast- trending faults.
Geologic map of and N-S section through part of the south flank of the Flin Flon Belt (Zwanzig, 1999, Fig 4)
East-west sections drawn as downplunge
projections, in segments with relatively uniform plunge (Zwanzig,
1999, Fig. 5).
APPENDIX A
On the south side of the Superior Province, arc rocks are represented by the Wisconsin magmatic terranes south of the Niagara fault of Michigan/Wisconsin. North of the fault occurs a continental margin represented by the following assemblages: NORTHWEST SOUTHEAST Locality: Cuyuna Gogebic Marquette Crystal Rabbit Lake Range Falls Allochthon? Northern Virginia G ANIMIKIE GP Biwabik IF 1873 +/-3 Ma | Pokegama Q | -------------------------------------------- | (Rabbit Lake S,IF,V)? = (Trommald IF)? (U. Paint River)| | (Mahnomen G)? (Riverton IF) | | <<<<<< Thrust U. Michigammee* (L. Paint River)| ?Allochthonous? | Trout Lake C Bijiki IF (Badwater V) | Southern Little Falls G,S,V L. Michigammee S Michigammee*S MILLE LAC GP Glentown IF, V. BARAGAR GP Clarksburg V. Hemlock V. 1874+/-9 Ma Rabbit Lake S,IF,V)? Greenwood IF Denham Q Goodrich Q Tyler G Ironwood IF Negaunee IF Vulcan IF (Trommald IF)? MENOMINEE GP Siamo S Palms Q Ajibik Q Felch Q (Mahnomen G)? ----------Unconformity?---Unconformity?-----------Unconformity? CHOCOLAY GP Chocolay Gp Chocolay Gp Chocolay GpTable 1. Tentative correlation of the Lower Proterozoic rocks of Michigan, Wisconsin, and Minnesota. Q = quartzite; C = carbonate; S = shale; G = Greywacke (foreland turbidite); IF = iron formation ('starved basin'); V = volcanic; * = 'Province 1' southerly derived Michigammee Formation;
The locally developed Chocolay
Group includes Gowganda-like tillites (Fern Creek Fm) overlain by aluminous
quartzites (Sturgeon Fm) and carbonates, and is potentially equivalent
to the Huronian Gowganda-Lorrain shelf sequence. If so, the succeeding
rocks of the Menominee Group are likely unconformable on the Chocolay.
The Menominee, Baragar, Mille Lac, and Animikie Groups are characterized
by the presence of sedimentary iron-formations (IF).
Rocks of the Lower Michigammee
turbidite succession have Nd/Nd characteristics indicating that
they were derived from the Superior crust, whereas the Upper Michigammee
rocks have Nd/Nd (epsilonNd -0.8 to +1.5) characteristics indicating
that they were being fed by debris from the colliding Wisconsin arc to
the south at about 1860 Ma. Similarly in the Medicine Bow Mountain section
of Wyoming, paragneisses of the Cheyenne Belt separating the
Huronian-like Snow Pass Supergroup rocks from arc rocks of the early Proterozoic
Colorado Province (Yavapai) also have Nd/Nd characteristics indicating
derivation from a mixed provenance. As such the Cheyenne and Michigammee
rocks represent foreland basin sediments laid down in advance of the overriding
Wisconsin and Colorado arcs.
Comparative sections of the
Lower Proterozoic geology of Michigan and Wyoming
Early Protoerozoic plate
tectonic development of Wisconsin and northern Michigan - lprotmichigan.jpg
NNE-SSW (Lake Michagan)
seismic profile across the Penokean orogen of northern Michigan - lprotseis.jpg
Distribution of Early
Proterozoic structural provinces of the southern and southwestern United
States - lprotmazat1.jpg
Other younger Lower Proterozic
systems such as the Coronation, Thelon, and Labrador Trough, also
contain sedimentary sequences exhibiting the change from rift to shelf
to foreland basin to molasse reflecting changes in tectonics from rift
to drift to arc accretion to continent collision. It would therefore seem
that Lower Proterozoic tectonic settings resemble those of younger Paleozoic
orogenic systems.
The Early Proterozoic of the Fennoscandian Shield
The Archean of the Fennoscandian Shield is composed of:
tonalite terranes older than
2843 Ma;
greenstone belts
2790-2750 Ma old;
granodiorites
2740-2690 Ma;
granodiorites
2676
pegmatites
2642
The earliest Proterozoic
activity at 2450 Ma led to the formation of structurally controlled basins
filled with volcano-sedimentary sequences of granitoid breccias,
arkoses , basalts, andesites, and conglomerates (Sariola).
The activity was coeval with basic
magmatism at 2440 Ma (20 bodies) and focussed along rift zones within areas
of the Archean as layered mafic intrusions with pseudo boninitic affinities
(E-W Tornio-Narankavaara and Kuhmo-Suomussalmi belts of Finland).
The mafic magmatism was accompanied by potassic rapakivi-type granite
intrusion dated at 2435+12. The mafic complexes were faulted, uplifted
and eroded before the extrusion of the Perapohja and Lapponian volcanic
rocks at 2330 Ma. Further rifting involving the deposition of clastics,
including quartzites, and volcanics, in a narrow inland sea led to
the formation of the Kainuu basin. Intrusion of low-Al tholeiitic sills
and Fe-tholeiitic dikes along listric shear zones took place at 2200 Ma,
with dikes serving as feeders to the Jatulian mafic volcanic suite. The
intracratonic Hoytianinen basin system devloped at about 2100 Ma as a result
of extensional tectonics of a passive margin in an asymmetrical rift
or half graben above a major detachment fault extending deep into the lithosphere.
In the sedimentary sequence, there is ab abrupt change in facies from psammites
and dolostones to carbonaceous rocks, accompanied by a dramatic change
in C isotope ratios in the carbonates, interpreted ato reflect the change
in concentration of atmospheric oxygen at 2200-2100 Ma.
At 2040 Ma the Otanmaki
layered mafic complex with its Fe-T-V oxide deposits and associated rapakivi
anorogenic intrusions was formed at the same time as the sulphide-bearing
Keivitsa layered complex and the ultramafic Kummitsoiva - Sattasvaara
- Karasjokk komatiitic volcanic belt of Lapland.
Further rifting was marked
by the ultramafic Outokumpu assemblage and the 1970 Ma Jormu ophiolite
of the Kainuu basin.
The crust at the Sveccofennian
- Archean boundary is very thick (46-65 km). Most of the thickness
variation is in the high velocity lower crust. Thermal resetting of K-Ar
ages to 1850-1800 Ma and fluid mediated resetting of Rb-Sr ages to
1800-1760 Ma has taken place in Archean rocks marginal to the Sveccofennian
system.
The early Proterozoic tectonic
activity of the Sveccofennian system shows clear parallels with the early
Proterozoic development of the Southern Province of the Canadian Shield.
Lower Proterozoic Iron Formations
Banded
Iron formations (BIFs) are thought to be chemical sediments
containing relatively little detrital material. Consequently it is
believed that the positive Eu anomalies of Archean BIFs reflects
the greater mobility of divalent Eu under conditions of relatively
low oxygen fugacity, and/or the preponderance of higher temperature oceanic
hydrothermal systems. Within a reducing environment Eu would
participate as a divalent ion and would be uncoupled from the other
trivalent REE ions. High temperature hydrothermal fluids would preferentially
remove Eu into oceanic solution relative to the other REE,
and chemical sediments of iron and silica would therefore show relative
Eu-enrichment.
Such a process would be advantaged by oceanic water itself having
a low oxygen (sulphate) content.
In the case of Lower Proterozoic
BIFs,
sustained periods of volcanicity caused production of chert - carbonate
- silicate BIF rather than the normal and dominant hematite - magnetite
- chert BIF. During volcanic periods, the normally high capacity
of sunlight to precipitate ferric iron directly by photolytic oxidation
of ferrous iron, and indirectly by reaction of ferrous iron with
photosynthetic oxygen, was modified by turbidity in the atmosphere,
by dust, and, in the water, by the formation of colloids from the reactive
ash. Surface-precipitated ferric hydroxyoxide redissolved in the
presence of decaying organic material in the subphotic zone, were precipitated
as ferrous carbonates and silicates when solubilities
were exceeded. Despite decreased sunlight, an increase in volcanic activity
would increase the availability of nutrients and therefore the production
of biogenic matter, consequently cutting off the deposition of ferric
oxide deposits. Conditions favourable for the formation of early Proterozoic
BIF
deposits included a high level of ocean floor formation and concommitant
hydrothermal
activity, relatively elevated deep
sea water temperatures (higher than 20 degrees C), the
existence of photosynthetic plankton,
the absence of silica secreting organisms,
and a low oxygen to anoxic atmosphere
allowing the build up of high iron in oceanic waters.
APPENDIX D
The Early Proterozoic of the Hamersley Province of Western Australia
Martin, D. McB., 1999. Depositional
setting and implications of Paleoproterozoic glaciomarine sedimentation
in the Hamersley Province, Western Australia. BGSA, 111, 2, 189-203.
Powell, C. McA., et al.,
1999. Synorogenic hydrothermal origin for giant Hamerslay iron oxide ore
bodies. Geology, 27, 2, 175-178.
Powell, C. McA. and Horwitz,
R.C., 1994. Late Archean and Early Protoerozoic tectonics and basin formation
of the Hamersley Ranges. Geol. Soc. Australia (WA Division) Excursion Guidebook
No. 4, 53 p.
Parker, A.K. et al. Mafic
dyke swards of Austalia, in Mafic dyke swarms, eds., Halls, H.C. and Fahrig,
W.F., Geol. Assoc. Canada Spec. paper 34, p. 401-417.
Geological
map and schematic evolution of the Early Proterozoic Hamersley Province
- lprotaustham1.jpg
Magnetic
anomaly map of Australia - austmag.jpg
Simplified
map of mafic dike swarms in the Yilgarn and Hamersley blocks - austhamdikes.jpg
Kimberley Block
Map
of the Archean Kimberley block, Western Australia - austkimb.jpg
Lachlan - Tasman orogen
Map
of Tasmania and the southern Lachlan orogenic belt - austtasman.jpg
Structural Provinces of North America.
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