Precambrian terrane of north-central Wisconsin: an aeromagnetic perspective

1990 ◽  
Vol 27 (11) ◽  
pp. 1472-1477 ◽  
Author(s):  
Elizabeth R. King
Keyword(s):  
Shear Zones ◽  
Superior Province ◽  
Large Area ◽  
Midcontinent Rift ◽  
North Central ◽  
The North ◽  
Magnetic Signatures ◽  
Granitoid Rocks ◽  
Western Side ◽  
Shaded Relief

A shaded relief magnetic map covering most of the region of exposed Precambrian rocks of north-central Wisconsin shows the structural grain and many lithologic units with clarity and comprehensive detail. The area includes part of the volcanic sequence of the Keweenawan Supergroup south of Lake Superior, the southern margin of the Archean Superior Province, the accreted island-arc terranes of the Penokean Orogen, and the Wolf River batholith. Numerous dikes are evident in the shaded relief, some being more than 200 km in length. Many of the longer dikes are reversely magnetized Keweenawan diabase associated with early extension of the Midcontinent Rift; some apparently were intruded along preexisting faults. A northwest system of dikes and faults indicated by the shaded relief map may be related to later stages of Keweenawan rifting. The Wolf River batholith is characterized by low magnetic relief associated with the predominant granitoids but includes circular plutons of highly magnetic anorthosite and a large area of magnetic rock having a signature different from the mapped anorthosite bodies. A fault bounding the western side of the batholith is paralleled by an apparent system of faults or dikes in the older terrane to the west. The magnetic map covering the Wisconsin magmatic terranes and the Archean Superior Province margin to the north is dominated by east-northeast-trending Penokean rocks. Large units of magnetic mafic rocks and less magnetic granitoid rocks are cut by a system of well-defined northeast shear zones and a more easterly trending, possibly younger set of faults, some of which contain dikes along parts of their lengths. Although the sutures bounding the magmatic terranes generally follow the magnetic trends, they do not have distinctive magnetic signatures.

Geological evolution of the northwestern Superior Province: Clues from geology, kinematics, and geochronology in the Gods Lake Narrows area, Oxford–Stull terrane, Manitoba

2006 ◽  
Vol 43 (7) ◽  
pp. 749-765 ◽  
Author(s):  
S Lin ◽  
D W Davis ◽  
E Rotenberg ◽  
M T Corkery ◽  
A H Bailes
Keyword(s):  
Large Scale ◽  
Volcanic Rocks ◽  
Shear Zones ◽  
Superior Province ◽  
Continental Margins ◽  
The North ◽  
Geological Evolution ◽  
Southern Half ◽  
Andean Type ◽  
Tectonic Interpretation

The study of lithology, geochronology, and structure in the Oxford–Stull terrane, in particular in the Gods Lake Narrows area, has led to the recognition of three distinct supracrustal sequences: ~2.8–2.9 Ga volcanic rocks; a ~2720 Ma fault-bounded package of volcanics and sandstones; and ~2705 Ma conglomerate and alkaline volcanic rocks of the Oxford Lake Group. Detrital zircon as old as 3647 Ma is present in the Oxford Lake Group. An early generation of folding and shearing occurred prior to deposition of the Oxford Lake Group and was probably synchronous with emplace ment of 2721 Ma tonalite dykes. The second generation of deformation caused south-over-north thrusting of volcanic rocks over the Oxford Lake Group. The youngest fabric resulted from east-southeast-trending, dextral, south-over-north shearing. The youngest rock dated in the area is the 2668 ± 1 Ma Magill Lake pluton, which records crustal melting following deformation. The pattern of sedimentation and deformation in this area is similar to but slightly older than that found in the southern half of the Superior Province, which shows a southward-younging diachroneity. The south-dipping north-vergent shear zones observed in the area contrast with dominantly north-dipping south-vergent structures observed and interpreted south of the North Caribou superterrane (NCS). The limited size of the study area precludes any strongly based large-scale tectonic interpretation; however, data and observations from the Gods Lake Narrows area are most easily accommodated in a model where the NCS served as a nucleus onto which other terranes were accreted and both the northern and southern margins of the NCS were Andean-type continental margins with opposite subduction polarities.

Stratigraphy, structure, and geochronology of the 3.0–2.7 Ga Wallace Lake greenstone belt, western Superior Province, southeast Manitoba, Canada

2006 ◽  
Vol 43 (7) ◽  
pp. 929-945 ◽  
Author(s):  
C Sasseville ◽  
K Y Tomlinson ◽  
A Hynes ◽  
V McNicoll
Keyword(s):  
Greenstone Belt ◽  
Volcanic Rocks ◽  
Crustal Contamination ◽  
Shear Zones ◽  
Iron Formation ◽  
Superior Province ◽  
Lake Winnipeg ◽  
The North ◽  
Southern Margin ◽  
Plume Magmatism

In western Superior province, the North Caribou terrane (NCT) constitutes a Mesoarchean proto-continent heavily overprinted by Neoarchean magmatism and deformation resulting from the western Superior Province accretion. Locally, along the southern margin of the NCT, Mesoarchean (~3.0 Ga) rift sequences are preserved. These sequences are of key importance to our understanding of the early tectonic evolution of continental crust. The Wallace Lake greenstone belt is located at the southern margin of the NCT and includes the Wallace Lake assemblage, the Big Island assemblage, the Siderock Lake assemblage, and the French Man Bay assemblage. The Wallace Lake assemblage exposes one of the best-preserved Mesoarchean rift sequences along the southern margin of the NCT. The volcano-sedimentary assemblage (3.0–2.92 Ga) exposes arkoses derived from the uplift of a tonalite basement in a subaqueous environment, capped by carbonate and iron formation. Mafic to ultramafic volcanic rocks exhibiting crustal contamination and derived from plume magmatism cap this rift sequence. The Wallace Lake assemblage exhibits D1 Mesoarchean deformation. The Big Island assemblage comprises mafic volcanic rocks of oceanic affinity that were docked to the Wallace Lake assemblage along northwest-trending D2 shear zones. The timing of volcanism and docking of the Big Island assemblage remain uncertain. The Siderock Lake and French Man Bay assemblages were deposited in strike-slip basins related to D3 and D4 stages of movement of the transcurrent Wanipigow fault (<2.709 Ga). Regionally, the Wallace Lake assemblage correlates with the Lewis–Story Rift assemblage observed in Lake Winnipeg, whereas the Big Island assemblage appears to correlate with the Black Island assemblage observed in the Lake Winnipeg area. Thus, the North Caribou terrane appears to preserve vestiges of a Mesoarchean rifted succession together with overlying Neoarchean allochthonous, juvenile, volcanic successions over a considerable distance along its present-day southern margin.

Proterozoic reactivation of the southern Superior Province and its role in the evolution of the Midcontinent rift

1997 ◽  
Vol 34 (4) ◽  
pp. 562-575 ◽  
Author(s):  
Matthew L. Manson ◽  
Henry C. Halls
Keyword(s):  
Lake Superior ◽  
Dyke Swarm ◽  
Superior Province ◽  
Midcontinent Rift ◽  
Potential Field Data ◽  
Major Activity ◽  
The North ◽  
Western Lake ◽  
Narrow Belt ◽  
Radiometric Data

Major reverse faults associated with the late compressional phase of the 1.1 Ga Midcontinent rift in the western Lake Superior region appear to cut across the rift at the eastern end of the lake and join with reverse faults on the eastern shoreline, defined on the basis of geological and potential field data. The continuation of the faults across eastern Lake Superior is inferred on evidence drawn from nearshore shipborne magnetic surveys together with new interpretations of published bathymetric and GLIMPCE aeromagnetic data. In the Archean Superior Province about 100 km east of Lake Superior, paleomagnetic and petrographic data from the 2.45 Ga Matachewan dyke swarm show that the Kapuskasing Zone, a narrow belt of uplifted crust, can be extended to within 50 km of the Lake Superior shoreline and has bounding reverse faults that are almost continuous with two faults of similar dip and sense of displacement that define the inversion of the Midcontinent rift in the central and western parts of the lake. Since the Kapuskasing Zone is dominantly a Paleoproterozoic (about 1.9 Ga) structure, the continuity suggests that the Lake Superior faults, whose last major activity was during the Grenville Orogen, may represent reactivation of much older faults that were part of an extended Kapuskasing structure. Within the Superior Province to the north and east of Lake Superior, published radiometric data on biotites suggest a series of alternating crustal blocks of varying tectonic stability, separated by northeast-trending faults. The Lake Superior segment of the Midcontinent rift developed within the most unstable block, bounded by the Gravel River fault to the northwest and the Ivanhoe Lake fault (the eastern margin of the Kapuskasing Zone) to the southeast.

Block and shear-zone architecture of the Minnesota River Valley subprovince: implications for late Archean accretionary tectonics

1996 ◽  
Vol 33 (6) ◽  
pp. 831-847 ◽  
Author(s):  
D. L. Southwick ◽  
Val W. Chandler
Keyword(s):  
Regional Scale ◽  
Shear Zones ◽  
River Valley ◽  
Superior Province ◽  
Tectonic Zone ◽  
Minnesota River ◽  
The North ◽  
Geophysical Anomalies ◽  
Superior Craton ◽  
Minnesota River Valley

The Minnesota River Valley subprovince of the Superior Province is an Archean gneiss terrane composed internally of four crustal blocks bounded by three zones of east-northeast-trending linear geophysical anomalies. Two of the block-bounding zones are verified regional-scale shears. The geological nature of the third boundary has not been established. Potential-field geophysical models portray the boundary zones as moderately north-dipping surfaces or thin slabs similar in strike and dip to the Morris fault segment of the Great Lakes tectonic zone at the north margin of the subprovince. The central two blocks of the subprovince (Morton and Montevideo) are predominantly high-grade quartzofeldspathic gneiss, some as old as 3.6 Ga, and late-tectonic granite. The northern and southern blocks (Benson and Jeffers, respectively) are judged to contain less gneiss than the central blocks and a larger diversity of syntectonic and late-tectonic plutons. A belt of moderately metamorphosed mafic and ultramafic rocks having some attributes of a dismembered ophiolite is partly within the boundary zone between the Morton and Montevideo blocks. This and the other block boundaries are interpreted as late Archean structures that were reactivated in the Early Proterozoic. The Minnesota River Valley subprovince is interpreted as a late accretionary addition to the Superior Province. Because it was continental crust, it was not subductible when it impinged on the convergent southern margin of the Superior Craton in late Archean time, and it may have accommodated to convergent-margin stresses by dividing into blocks and shear zones capable of independent movement.

Geochemical and radiogenic isotope (Sr-Nd) characteristics of Paleoproterozoic anorthositic and granitoid rocks in the Umiakoviarusek Lake region, Labrador, Canada.

1999 ◽  
Vol 36 (12) ◽  
pp. 1957-1972 ◽  
Author(s):  
Stephen J Piercey ◽  
Derek HC Wilton
Keyword(s):  
Crustal Contamination ◽  
Isotopic Data ◽  
North Central ◽  
Radiogenic Isotope ◽  
The North ◽  
Lake Region ◽  
Intrusive Rocks ◽  
Mantle Component ◽  
Granitoid Rocks ◽  
Source Materials

Recent work in the north-central Labrador has identified Paleoproterozoic anorthositic and granitoid rocks that are spatially associated with, yet temporally distinct from, younger Mesoproterozoic intrusions of the Nain Plutonic Suite. The Umiakoviarusek Lake (UL) region of Labrador contains several of these Paleoproterozoic intrusions and provides an opportunity to study their geochemical and radiogenic isotope (Sr-Nd) characteristics. Geochemically, the anorthositic and granitoid rocks have features consistent with contemporary anorthositic and granitoid rocks from other anorthosite-mangerite-charnockite-granite complexes. The anorthositic rocks contain elevated contents of Al2O3, CaO, Sr, and Eu with low Ba, Rb, K, Zr, total rare earth elements (REE), and light REE. The granitoid rocks, on the other hand, contain lower concentrations of these elements along with elevated SiO2 and K2O. Isotopic data at 2050 Ma for the anorthositic rocks (ISr = 0.7048-0.7082; εNd = -4.1 to -15.9) and granitoid rocks (ISr = 0.7036-0.7094, εNd = -5.1 to -9.7) are consistent with variable crustal and mantle contributions to their genesis. The relatively unradiogenic Sr and slightly evolved Nd isotopic data from the UL granitoid rocks is consistent with a significant juvenile mantle component, possibly derived from an underplating mantle plume; this component may also be present in the anorthositic rocks. The Nd and Sr isotopic data are also consistent with crustal contamination from Archean source materials; however, based on the existing isotopic database for the Nain Province gneisses, it is not possible to delineate a specific gneiss component. Furthermore, it is also quite possible that an Archean source, unlike any described at present, was a crustal source component in the UL intrusive rocks.

scholarly journals Sinistral transpression and hydrothermal activity during emplacement of the Early Proterozoic Julianehåb batholith, Ketilidian orogenic belt, South Greenland

1994 ◽  
Vol 163 ◽  
pp. 5-22
Author(s):  
B Chadwick ◽  
P Erfurt ◽  
T Frisch ◽  
R.A Frith ◽  
A.A Garde ◽  
...  
Keyword(s):  
Shear Zones ◽  
Field Work ◽  
Hydrothermal Activity ◽  
Vertical Shear ◽  
Early Proterozoic ◽  
North West ◽  
North East ◽  
The North ◽  
Granitoid Rocks ◽  
Quartz Veining

The first systematic investigations of the central part of the Early Proterozoic Ketilidian orogen in the vicinity of Søndre Sermilik in the early 1960s suggested that this part of the orogen comprised a mixture of the Julianehåb granite, altered supracrustal rocks and older orthogneisses. Recent field work has shown that the area consists only of a variably deformed suite of granitic to dioritic plutonic rocks and a range of hornblende-bearing dykes of the appinite suite which all belong to the Julianehåb batholith. Steep to vertical shear zones with widths from a few centimetres to more than one kilometre are a significant element of the structure. The principal shear zones trend north-east and they are parallel to the schistosity and subhorizontal linear structures in the granitoid rocks. Kinematic indicators in many of the shear zones indicate sinistral transcurrent displacements. The relationships between granite fabrics, shear zones and mafic dykes suggest that the Julianehåb batholith was emplaced during subduction from the south towards the Archaean craton in the north-west in a sinistral transpressional system. Effects of hydrothermal alteration, mainly in the form of quartz veining, silicification, chloritisation, epidotisation and pyritisation, are common within and adjacent to the largest shear zones. These effects are believed to be related to late stages of the evolution of the batholith. Gold anomalies appear to be closely tied to the hydrothermal phenomena.

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