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1
Sexton, John L., and Harvey Henson Jr. "Interpretation of seismic reflection and gravity profile data in western Lake Superior." Canadian Journal of Earth Sciences 31, no. 4 (1994): 652–60. http://dx.doi.org/10.1139/e94-058.
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The interpretation of 1047 km of seismic reflection data collected in western Lake Superior is presented along with reflection traveltime contour maps and gravity models to understand the overall geometry of the Midcontinent Rift System beneath the lake. The Douglas, Isle Royale, and Keweenaw fault zones, clearly imaged on the seismic profiles, are interpreted to be large offset detachment faults associated with initial rifting. These faults have been reactivated as reverse faults with 3–5 km of throw. The Douglas Fault Zone is not directly connected with the Isle Royale Fault Zone. The seismic data has imaged two large basins filled with more than 22 km of middle Keweenawan pre-Portage Lake and Portage Lake volcanic rocks and up to 8 km of upper Keweenawan Oronto and Bayfield sedimentary rocks. These basins persisted throughout Keweenawan time and are separated by a ridge of Archean rocks and a narrow trough bounded by the Keweenaw Fault Zone to the south. Another fault zone, herein named the Ojibwa fault zone, previously interpreted as the northeastern extension of the Douglas Fault Zone, has been reinterpreted as a reverse fault that closely follows the ridge of Archean rocks. Previous researchers have stated that neighboring segments of the rift display alternating polarity of basins associated with large detachment faults. Accommodation zones have been previously interpreted to exist between rift segments; however, the seismic data do not image a clearly identifiable accommodation zone separating the two basins in western Lake Superior. Thus, the seismic profile may lie directly above the pivot of a scissors-type accommodation fault zone, there is no vertical offset associated with the zone, or the zone does not exist. Seismic data interpretations indicate that application of a simple alternating polarity basin – accommodation zone model is an oversimplification of the complex geological structures associated with the Midcontinent Rift System.
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Manson, Matthew L., and Henry C. Halls. "Post-Keweenawan compressional faults in the eastern Lake Superior region and their tectonic significance." Canadian Journal of Earth Sciences 31, no. 4 (1994): 640–51. http://dx.doi.org/10.1139/e94-057.
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GLIMPCE aeromagnetic data in eastern Lake Superior are characterized by a series of strong easterly- and northeasterly-oriented gradients that relate to mapped post-Keweenawan faults occurring along the eastern shore. The reversed nature of three of the faults is established through field observations and potential field modelling. Middle Keweenawan volcanic rocks at Mamainse Point are in fault contact on their south side with upper Keweenawan sandstone of Bayfield–Jacobsville type. Gravity modelling suggests that the fault is a low angle thrust dipping to the north. Field observations and high-resolution aeromagnetic data show that it extends inland along the southern margin of the Batchawana Greenstone Belt for at least 17 km. To the west, the Mamainse Point fault may extend across eastern Lake Superior to the Keweenaw Peninsula, linking several offsets in the seismic data that are consistent with the same attitude and sense of displacement. Along the south side of Batchawana Bay at Havilland, sandstones of Bayfield–Jacobsville type are isoclinally folded against a package of upthrust older rocks that include drag-folded middle Keweenawan volcanics. At Grindstone Point, north of Cape Gargantua, a reverse fault separating isoclinally-folded upper Keweenawan sandstones from Archean basement may, on aeromagnetic evidence, be an eastward extension of the Michipicoten Island fault.These faults mark a significant change in the style of late compressional tectonism observed within the Midcontinent Rift. All cut Keweenawan rocks across strike. The inference is that broad north–south or northwest–southeast compression, consistent in timing and orientation with the Grenville Orogeny, led to a reversal of movement along the major graben faults in western Lake Superior and was taken up in the eastern region by reverse faults oriented normal to the extensional axis of the rift.
3
Thomas, M. D., and D. J. Teskey. "An interpretation of gravity anomalies over the Midcontinent Rift, Lake Superior, constrained by GLIMPCE seismic and aeromagnetic data." Canadian Journal of Earth Sciences 31, no. 4 (1994): 682–97. http://dx.doi.org/10.1139/e94-061.
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Cross sections of the Midcontinent Rift in Lake Superior, derived from GLIMPCE seismic reflection images, provide unprecedented structural details of the rift and a new constraint for modelling associated gravity anomalies. In turn, gravity modelling, constrained also by new high-resolution aeromagnetic data, has permitted critical examination of the seismic models. The latter generate gravity anomalies having limited agreement with observed anomalies when appropriate rock densities are assigned. Good agreement may be achieved, generally, by making comparatively local changes to the models, while retaining their larger-scale attributes. Gravity modelling thus enhances and supports GLIMPCE seismic models.Modifications to seismic models include revisions of initial densities within the geometrical framework of the models, leading to a redefinition of lithologies. For example, in some segments of the rift, mafic volcanics are substituted for Keweenawan sedimentary and sedimentary–volcanic sequences and for Lower Proterozoic sediments, and a felsic igneous body is modelled within a mafic volcanic unit. Positions of some unit boundaries and faults, or segments thereof, have also been modified.Gravity modelling traces the paths of the Keweenaw, Isle Royale, Thiel, Douglas, and Michipicoten Island faults deep into the crust, generally supporting the configurations outlined by seismic images and, thereby, arguments for rift development controlled by growth faults. Modelling also indicates a requirement for large, buried masses of mafic (plutonic?) igneous rocks of presumed Keweenawan age along the northern margin of the rift. This imparts an asymmetry to the rift, with northern and southern margins dominated by plutonic and volcanic igneous rocks, respectively.
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Klewin, Kenneth W., and Jonathan H. Berg. "Geochemistry of the Mamainse Point volcanics, Ontario, and implications for the Keweenawan paleomagnetic record." Canadian Journal of Earth Sciences 27, no. 9 (1990): 1194–99. http://dx.doi.org/10.1139/e90-126.
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The Keweenawan (1100 Ma) Mamainse Point volcanics, located along the eastern shore of Lake Superior in Ontario, formed in the Midcontinent Rift of North America. They are a 5250 m thick sequence of over 350 predominantly basaltic lava flows. The Mamainse Point section is the most continuous Keweenawan volcanic sequence and spans nearly the entire igneous history of the rift. The lower part of the section consists of high-MgO picrites and basalts, but the upper part of the section is composed of olivine tholeiites intercalated with numerous conglomerate layers. Major- and trace-element data reveal that the section consists of numerous stratigraphically constrained, geochemically distinct groups of lava flows. The comprehensive geochemical data on the entire sequence indicate that the section has no repetition due to faulting, as has been suggested by other workers on the basis of paleomagnetic studies. Evidently, the three paleomagnetic reversals previously found in the Mamainse Point section are real, and therefore there were multiple paleomagnetic reversals during Keweenawan time.
5
Halls, H. C., and E. G. Shaw. "Paleomagnetism and orientation of Precambrian dykes, eastern Lake Superior region, and their use in estimates of crustal tilting." Canadian Journal of Earth Sciences 25, no. 5 (1988): 732–43. http://dx.doi.org/10.1139/e88-069.
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Archean rocks form the eastern margin of the 1.1 Ga old Central North American rift along the eastern shore of Lake Superior and have been tilted westwards in response to rifting. Paleomagnetic and structural data from 2.6 Ga old Matachewan dykes suggest a westward crustal tilt of about 60°, which agrees well with dips recorded in nearby Keweenawan volcanics that rest directly on basement rocks. The Matachewan dyke swarm occurs throughout the east shore region of Lake Superior, whereas Keweenawan supracrustal sequences, which give a more precise estimate of tilt, are restricted to a few isolated shoreline patches. Estimates of crustal tilt can be obtained from the dykes on a regional basis, thus generating a more complete picture of basement deformation adjacent to a major intracratonic rift.
6
Shirey, Steven B. "Re-Os isotopic compositions of Midcontinent rift system picrites: implications for plume – lithosphere interaction and enriched mantle sources." Canadian Journal of Earth Sciences 34, no. 4 (1997): 489–503. http://dx.doi.org/10.1139/e17-040.
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Picrites and tholeiites from the Mamainse Point Formation, a 5.3 km thick section of Keweenawan (1100 Ma) volcanic and sedimentary fill on the eastern flank of the central portion of the Midcontinent rift system, contain a nearly continuous record of rift magmatic activity. Picrites occur primarily in the lowermost two units of the formation. In this study, they are compared to rarely exposed, slightly older Keweenawan basalts from the North Shore Volcanic Group and the Powder Mill Group to constrain mantle source compositions during early phases of rift magmatic activity. The most primitive picrites analyzed have low Re content (0.069–0.18 ppb), high Os content (0.8–2.1 ppb), and low 187Re/188Os (0.28–1.18). A Re–Os isochron with an age of 1128 ± 54 Ma and an initial 187Os/188Os of 0.1267 ± 0.0013 (γOs = +5.7) was obtained from a 24-point isochron on all but two analyzed samples. The Re–Os data, regressed separately for the older basalts, and the groups 1 and 2 samples from the Mamainse Point Formation, have barely resolvable initial 187Os/188Os that decrease up-stratigraphy from initial γOs(1100) of +12.2 to +6.2 and +4.2, respectively, and couple with changes in initial Nd isotopic composition. These data can be explained by mixing of melts of an enriched mantle plume and unradiogenic continental lithospheric mantle. A radiogenic initial Os isotopic composition (γOs of +8 or higher) for the Keweenawan plume marks the first known appearance of demonstrably radiogenic plume-derived magmas on Earth. Plume-derived magmas with radiogenic Os signatures are more common later. The radiogenic Os signatures of Keweenawan plume magmas may mark the appearance of melts derived from mantle containing recycled slab components from late Archean subduction.
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Manson, Matthew L., and Henry C. Halls. "An investigation of Superior Shoal, central Lake Superior, with a manned submersible." Canadian Journal of Earth Sciences 28, no. 1 (1991): 145–50. http://dx.doi.org/10.1139/e91-013.
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A Johnson-Sea-Link submersible was used to examine the geology of Superior Shoal in central Lake Superior. Here, glacially scoured, vertical cliffs, some more than 100 m high, are formed of 1.1 Ga middle Keweenawan basaltic lava flows displaying ophitic interiors and red amygdaloidal tops. Flat-lying sandstones, lithologically similar to the upper Keweenawan Bayfield–Jacobsville sequences, occur to the north of the volcanic rocks. These are inferred to have been downthrown along an eastward extension of the Isle Royale fault, a major boundary fault of the Midcontinent rift. The volcanic rocks are normally magnetized, supporting lithological evidence that they correlate with the middle Keweenawan sequence on Isle Royale. Paleomagnetic data suggest that the volcanics have a complex structure, possibly involving drag folding along the Isle Royale fault.
8
Mariano, John, and William J. Hinze. "Gravity and magnetic models of the Midcontinent Rift in eastern Lake Superior." Canadian Journal of Earth Sciences 31, no. 4 (1994): 661–74. http://dx.doi.org/10.1139/e94-059.
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Gravity and magnetic models of the Midcontinent Rift (MCR) in eastern Lake Superior supplement recent structural and stratigraphic interpretations based on the seismic reflection method. An algorithm developed to accommodate spatially varying direction and magnitude of magnetization within a magnetic source is used in both forward and inverse modeling procedures. Structural attitudes of rift-filling basalts derived from seismic reflection sections are used to rotate the Keweenawan remanent magnetization vectors in the direction of deformation. An iterative linear inversion routine calculates magnitudes of induced and remanent magnetizations, as well as normal and reversed polarity basalt flow distributions. The results indicate that the Koenigsberger ratios of these basalts generally range from 1 to 3, which is in agreement with values obtained from rock property measurements. The models also suggest that the greater volume of the Keweenawan basalt section in eastern Lake Superior is reversely polarized and that remanent magnetizations persist to depths of up to 20 km. Our results, supplemented by isotopic and paleomagnetic data, suggest that the vast majority of the basalts predate 1097 ± 1 Ma. A prominent positive magnetic anomaly and a corresponding gravity low strike west across the trend of the rift from the vicinity of Michipicoten Island. These anomalies may reflect a relatively strongly magnetized, felsic igneous body of late-middle to upper Keweenawan in age. Forward gravity models suggest clastic sedimentary rocks up to several kilometers thick overlay the volcanic rocks in localized depressions. Deep crustal seismic data used to constrain gravity models provide evidence of anomalously dense lower crust beneath the MCR.
9
MITCHELL, R., and N. SHELDON. "Weathering and paleosol formation in the 1.1Ga Keweenawan Rift." Precambrian Research 168, no. 3-4 (2009): 271–83. http://dx.doi.org/10.1016/j.precamres.2008.09.013.
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Symons, David T. A., Kazuo Kawasaki, and Jimmy F. Diehl. "Magnetization age from paleomagnetism of the Copper Harbor red beds, Northern Michigan, USA, and its Keweenawan geologic consequences." Canadian Journal of Earth Sciences 56, no. 1 (2019): 1–15. http://dx.doi.org/10.1139/cjes-2017-0094.
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The Copper Harbor Formation on Lake Superior’s Keweenaw Peninsula records the transition from volcanic to sedimentary infilling of North America’s 1.1 Ga Keweenawan rift. Radiometric dating shows that the formation’s primary mafic sediments and interbedded “Lake Shore” flows were deposited between ∼1092 and ∼1082 Ma. Our regional paleomagnetic results for the Copper Harbor’s red beds yield a dominantly prefolding normal-polarity secondary chemical characteristic remanent magnetization in hematite at 18 of 21 sites with a mean direction of declination = 274.9°, inclination = +10.9° (k = 69.5, α95= 4.2°), and a paleopole at 7.4°N, 181.7°E (A95= 3.3°). Using paleopoles from Keweenawan volcanic rocks with U–Pb zircon age dates, an apparent polar wander path is constructed from 1106 ± 2 to 1087 ± 2 Ma. Extrapolation of this path dates oxidation of the Copper Harbor’s primary gray beds to red beds at 1060 ± 5 Ma. The path implies an apparent polar wander rate of ∼18 cm per year from ∼1108 to 1096 Ma and of 6.8 cm per year from 1096 to 1087 Ma, along with a consistent clockwise rotation of 0.30 ± 0.05°per million years for the Laurentian Shield from ∼1108 to ∼1160 Ma. Further, most Keweenawan volcanic rocks around the Lake Superior region carry an endemic ∼1060 Ma normal-polarity hematite remanence overprint, acquired during the initial stages of Grenvillian tectonic uplift, that has caused asymmetry in a unit’s normal and reverse paleopoles. Also, the Copper Harbor paleopole dates emplacement of the White Pine stratiform sedimentary copper mineralization more precisely at 1060 ± 5 Ma.
11
Klewin, Kenneth W. "Polybaric Fractionation in an Evolving Continental Rift: Evidence from the Keweenawan Mid-Continent Rift." Journal of Geology 97, no. 1 (1989): 65–76. http://dx.doi.org/10.1086/629281.
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Hart, S. R., J. S. Steinhart, and T. J. Smith. "Terrestrial heat flow in Lake Superior." Canadian Journal of Earth Sciences 31, no. 4 (1994): 698–708. http://dx.doi.org/10.1139/e94-062.
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Using oceanographic heat-flow techniques, 162 measurements of heat flow were made in Lake Superior during the summers of 1966 and 1967. These data are of high quality, with precisions with respect to intercomparisons typically in the 3–5% range. The data define two very clear features. One is a trough of low heat-flow values, which runs continuously for 650 km along the northern edge of the lake, with values ranging between 0.46 and 0.98 heat-flow units (HFU) (19.2–41.0 mW/m2). This feature correlates with surface exposure of Keweenawan mafic volcanics; it is believed to delineate a major crustal separation associated with the Midcontinent Rift and is filled to crustal thicknesses with mafic intrusives and extrusives. This feature has not been imaged with the seismic reflection profiling of GLIMPCE. The other heat-flow feature is an arcuate ridge of high heat-flow values (1.0–1.45 HFU; 41.8–60.7 mW/m2), parallel to and south of the heat-flow trough. The highest areas of this ridge correspond to areas of thick rift-filling Keweenawan sediments. The high heat flow is modulated to lower values in areas where the thick sediments overlie highly thinned crust now containing large thicknesses of mafic volcanic rock. The heat-flow features show very good correlation with the magnetic anomaly map of Lake Superior, but only spotty correlation with the Bouguer gravity anomaly features.
13
Berg, Jonathan H., and Kenneth W. Klewin. "High-MgO lavas from the Keweenawan midcontinent rift near Mamainse Point, Ontario." Geology 16, no. 11 (1988): 1003. http://dx.doi.org/10.1130/0091-7613(1988)016<1003:hmlftk>2.3.co;2.
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Taylor, Ian E., and Gerard V. Middleton. "Aeolian sandstones in the Copper Harbor Formation, Late Proterozoic, Lake Superior basin." Canadian Journal of Earth Sciences 27, no. 10 (1990): 1339–47. http://dx.doi.org/10.1139/e90-144.
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Sandstones with cross-sets up to 1.5 m thick occur within the Copper Harbor Formation, most prominently at Five Mile Point. In contrast to intercalated sandstones with smaller scale cross-stratification or horizontal lamination, pebbles are very scarce in the large-scale cross-stratified sandstones and, where present, are restricted to set bases. The large-scale cross-stratified sandstones are better sorted than intercalated sandstones and show a mean palaeocurrent direction at 90° to the mean for the interbedded sandstones.The large-scale cross-stratified sandstones are interpreted as the product of fields of small transverse aeolian dunes that formed on dry parts of alluvial fans bordering the Keweenawan rift. The aeolian palaeocurrent mean is along the rift valley, and tentatively may be interpreted as the result of topographically constrained palaeo-tradewinds.
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Klewin, Kenneth W., and Jonathan H. Berg. "Petrology of the Keweenawan Mamainse Point lavas, Ontario: Petrogenesis and continental rift evolution." Journal of Geophysical Research 96, B1 (1991): 457. http://dx.doi.org/10.1029/90jb02089.
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Gordon, Mark B., and Mark R. Hempton. "Collision-induced rifting: The Grenville Orogeny and the Keweenawan Rift of North America." Tectonophysics 127, no. 1-2 (1986): 1–25. http://dx.doi.org/10.1016/0040-1951(86)90076-4.
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Hart, Thomas Robert, and Carole Anne MacDonald. "Proterozoic and Archean geology of the Nipigon Embayment: implications for emplacement of the Mesoproterozoic Nipigon diabase sills and mafic to ultramafic intrusions." Canadian Journal of Earth Sciences 44, no. 8 (2007): 1021–40. http://dx.doi.org/10.1139/e07-026.
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The Nipigon Embayment is underlain by Archean rocks of the English River, Wabigoon, and Quetico subprovinces, and intruded along the west side by late- to post-tectonic mafic to ultramafic intrusions. The early Mesoproterozoic ultramafic to felsic Badwater intrusion and felsic English Bay Complex are located in the northwest corner of the Nipigon Embayment. Three mafic to ultramafic intrusions, the Disraeli, Seagull, and Hele intrusions, are located south of Lake Nipigon, and the Kitto intrusion is located east of the lake. A number of mafic to ultramafic bodies (Jackfish (Island), Shillabeer, Kama Hill, Nipigon Bay) have only limited outcrops. The gabbroic Nipigon diabase sills intrude all other rocks in the Nipigon Embayment and generally have a consistent mineralogy and geochemistry, except for the Inspiration sill(s) and the McIntyre Sill. Geological and geophysical data suggest emplacement of the ultramafic intrusions by mechanisms similar to those controlling emplacement of the saucer-shaped diabase sills. These mechanisms are partially dependent on a series of pre-existing north-, northwest-, and northeast-trending faults formed prior to Keweenawan magmatism. The presence of sills, rather than dykes, indicates that the Nipigon Embayment was not extensional during the Keweenawan Midcontinent Rift, suggesting that the Nipigon Embayment is not a classic failed arm.
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King, Elizabeth R. "Precambrian terrane of north-central Wisconsin: an aeromagnetic perspective." Canadian Journal of Earth Sciences 27, no. 11 (1990): 1472–77. http://dx.doi.org/10.1139/e90-156.
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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.
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Cheadle, Burns A. "Alluvial–playa sedimentation in the lower Keweenawan Sibley Group, Thunder Bay District, Ontario." Canadian Journal of Earth Sciences 23, no. 4 (1986): 527–42. http://dx.doi.org/10.1139/e86-053.
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The Middle Proterozoic Sibley Group is a mixed clastic–carbonate red bed sequence located in the Thunder Bay – Nipigon area on the north shore of Lake Superior. The lowest unit, the Pass Lake Formation, consists of a basal paraconglomerate member, of probable alluvial debris-flow origin, overlain by 20–80 m of plane-bedded and cross-bedded quartz arenites, which were probably deposited by sheetfloods and eolian processes on alluvial outwash sand flats. The overlying Rossport Formation is dominated by red and buff dolomicritic mudstone. The association of these mudstones with relatively pure massive carbonate beds and sheetflood sandstone units is strongly suggestive of a playa lake depositional environment. Fluctuations in playa lake levels may have resulted in oscillations between carbonate-dominated and clastic-dominated sedimentation. The upper unit, the Kama Hill Formation, consists of horizontally laminated purple shales and ripple cross-laminated buff siltstones to fine sandstones. The presence of stacked "powering-down" sequences and abundant dessiccation features is suggestive of sheetflood deposition on a distal alluvial floodplain.The sequence of depositional environments suggests that the Sibley Basin formed by stretching and sagging of the Middle Proterozoic crust preceding the main period of volcanic activity along the Keweenawan Midcontinent Rift Zone. In this sense, the Sibley Group red beds represent the earliest products of Keweenawan rifting. They were not, however, deposited in a classical aulacogen or "failed arm."
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Zartman, Robert E., Suzanne W. Nicholson, William F. Cannon, and G. B. Morey. "U – Th – Pb zircon ages of some Keweenawan Supergroup rocks from the south shore of Lake Superior." Canadian Journal of Earth Sciences 34, no. 4 (1997): 549–61. http://dx.doi.org/10.1139/e17-044.
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New single-crystal zircon U–Th–Pb ages for plutonic and rhyolitic Keweenawan Supergroup rocks from the south shore of Lake Superior provide geochronological constraints on magmatic evolution associated with the 1.1 Ga Midcontinent rift. Analyses of a granophyric phase of the Mineral Lake intrusion and the Mellen granite, both parts of the Mellen Intrusive Complex, and a laterally extensive rhyolite from the top of the Kallander Creek Volcanics have weighted average 207Pb/206Pb ages of 1102.0 ± 2.8 Ma (N = 2), 1100.9 ± 1.4 Ma (N = 5), and 1098.8 ± 1.9 Ma (N = 4), respectively. Analyses of a pyroclastic rhyolite flow at the top of the Porcupine Volcanics result in variable 207Pb/206Pb ages that range from 1080 to 1137 Ma. This rhyolite exhibits a continuum between morphologically complex and simpler prismatic zircon crystals, the latter yielding concordant analyses having a weighted average 207Pb/206Pb age of 1093.6 ± 1.8 Ma (N = 2). Four prismatic zircons from an aphyric rhyolite of the Chengwatana Volcanics in the Ashland syncline form a linear array intersecting concordia at 1094.6 ± 2.1 Ma (MSWD = 1.3). Another presumed Chengwatana rhyolite recovered from drill core intersecting the Hudson–Afton horst in southeast Minnesota yielded only ~20 morphologically indistinguishable zircons. Six analyses give 207Pb/206Pb ages ranging from 1112 to 1136 Ma, including one analysis with a virtually concordant age of 1130 Ma. This age, however, is considerably older than that obtained for the Chengwatana Volcanics in the Ashland syncline or any other precisely dated rock from the Midcontinent rift.
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White, Robert S. "Mantle temperature and lithospheric thinning beneath the Midcontinent rift system: evidence from magmatism and subsidence." Canadian Journal of Earth Sciences 34, no. 4 (1997): 464–75. http://dx.doi.org/10.1139/e17-038.
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The tectono-magmatic history of the Midcontinent rift system can be explained by the presence of a mantle plume bringing elevated-temperature mantle beneath the rift system at about 1110 Ma. Huge volumes of extrusive and intrusive igneous rocks were generated as abnormally hot mantle decompressed beneath the lithospheric rift. Geochemical and isotopic data from the Keweenawan volcanics show that the earliest melts were derived from small-degree melting of primitive plume mantle, coupled with enriched metasomatic melts derived from the continental lithosphere. As rifting progressed, the main bulk of the volcanics was generated primarily from the plume mantle, with the melting starting at depths of about 120 km and extending to as shallow as the base of the stretched lithosphère at 45 km depth. Elevated mantle temperatures of 1500–1560 °C, approximately 150–200 °C above normal, are inferred from the rare earth element concentrations in the volcanic rocks. Further constraints on the mantle temperature come from combined subsidence and melt-generation modelling. I assume that rifting occurred in two main periods, during 1110–1105 and 1100–1094 Ma, with a reduced rate of stretching and greatly decreased melt production during the intervening period, 1105–1100 Ma. At the centre of the rift, production of more than 15 km of volcanic rocks close to, or above, sea level was followed by the accumulation of up to 8 km of mainly coarse terrigenous sediments in the postrift subsidence phase. This can be explained by lithospheric thinning by a factor of approximately 6 above mantle with a potential temperature of about 1550 °C. Subsequently, the mantle cooled to a normal potential temperature of 1350 °C as the plume thermal anomaly died away.
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Green, John C., and Thomas J. Fitz. "Extensive felsic lavas and rheoignimbrites in the Keweenawan Midcontinent Rift plateau volcanics, Minnesota: petrographic and field recognition." Journal of Volcanology and Geothermal Research 54, no. 3-4 (1993): 177–96. http://dx.doi.org/10.1016/0377-0273(93)90063-w.
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Symons, D. T. A., M. T. Lewchuk, D. J. Dunlop, et al. "Synopsis of paleomagnetic studies in the Kapuskasing structural zone." Canadian Journal of Earth Sciences 31, no. 7 (1994): 1206–17. http://dx.doi.org/10.1139/e94-106.
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This paper summarizes results from paleomagnetic studies sponsored by Lithoprobe on the Kapuskasing structural zone (KSZ). Data from Archean rocks outside the KSZ indicate that the Wawa Subprovince has not been significantly rotated or translated (< 5°) relative to the Abitibi Subprovince. Results from the granulites and amphibolites indicate that the KSZ underwent several kilometres of uplift at ca. 2.51 Ga and then 10 ± 5° west-northwest tilt with several kilometres of further uplift between 2.04 and 1.88 Ga from thrust faulting on the Ivanhoe Lake fault zone. Localized chemical remagnetization occurred at 1.1 Ga along the west side of the Shawmere anorthosite. Paleomagnetic data from the 2.45 Ga Matachewan diabase dike swarm indicate that it was emplaced within one reversed to normal polarity interval of less than 5 Ma. Their polarity pattern indicates major north-trending faults with several kilometres of dip-slip displacement. Their remanence confirms that the Superior Province was deformed around the KSZ into an oroclinal flexure with 40° changes in trend between 2.04 and 1.88 Ga. Results from eight 1.1 Ga alkali syenite–carbonatite complexes show that the KSZ and adjacent subprovinces have undergone only minor uplift (< 6 ± 2 km) since emplacement. Also, these data refine the radiometric ages of some complexes, demonstrate that the use of superchrons to correlate Keweenawan units in the Midcontinental Rift is unsound, and show that Keweenawan magnetic field was symmetrical. Many specific conclusions that relate to a given unit or limited area were drawn in the KSZ paleomagnetic studies.
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Swanson-Hysell, Nicholas L., Joshua M. Feinberg, Thelma S. Berquó, and Adam C. Maloof. "Self-reversed magnetization held by martite in basalt flows from the 1.1-billion-year-old Keweenawan rift, Canada." Earth and Planetary Science Letters 305, no. 1-2 (2011): 171–84. http://dx.doi.org/10.1016/j.epsl.2011.02.053.
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Jerde, Eric A. "Geochemistry of Hypabyssal Rocks of the Midcontinent Rift System in Minnesota, and Implications for a Keweenawan Magmatic “Family Tree”." International Geology Review 40, no. 11 (1998): 963–80. http://dx.doi.org/10.1080/00206819809465248.
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Windley, Brian F. "Anorogenic magmatism and the Grenvillian Orogeny." Canadian Journal of Earth Sciences 26, no. 3 (1989): 479–89. http://dx.doi.org/10.1139/e89-041.
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The Grenvillian Orogeny was preceded by extensive anorogenic volcanism and plutonism in the period 1500–1300 Ma in the form of rhyolites, epizonal granites, anorthosites, gabbros, alkaline complexes, and basic dykes. An analogue for the mid-Proterozoic anorogenic complexes is provided by the 2000 km by 200 km belt of anorogenic complexes in the Hoggar, Niger, and Nigeria, which contain anorthosites, gabbros, and peralkaline granites and were generated in a Cambrian to Jurassic rift that farther south led to the formation of the South Atlantic. An analogue for the 1 × 106 km2 area of 1500–1350 Ma rhyolites (and associated epizonal granites) that underlie the mid-continental United States is provided by the 1.7 × 106 km2 area of Jurassic Tobifera rhyolites in Argentina, which were extruded on the stretched continental margin of South America immediately preceding the opening of the South Atlantic. The mid-Proterozoic complexes were intruded close to the continental margin of the Grenvillian ocean and were commonly superimposed by the craton-directed thrusts that characterized the final stages of the Grenvillian Orogeny. The bulk of the Keweenawan rift and associated anorogenic magmatism formed about 1100 Ma at the same time as the Ottawan Orogeny in Ontario, which probably resulted from the collision of the island arc of the Central Metasedimentary Belt attached to the continental block in the east with the continental block to the west. The most appropriate modern equivalent would be the Rhine Graben, which formed at the same time as the main Alpine compression.
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Harlan, Steve S. "Paleomagnetism of Middle Proterozoic diabase sheets from central Arizona." Canadian Journal of Earth Sciences 30, no. 7 (1993): 1415–26. http://dx.doi.org/10.1139/e93-122.
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Paleomagnetic results from 1090 Ma diabase sheets of the southwestern U.S.A. diabase province exposed in central Arizona yield two distinct remanent magnetizations (herein termed ADn and ADr), in accordance with the findings of previous investigations. Magnetization ADn is well-defined and has an in situ mean direction of D = 283.3°, I = 45.1° (k = 17.7, α95 = 8.7°, n = 17 independent observations). A mean pole, after correction of paleomagnetic site means for a net 5° clockwise rotation of the Colorado Plateau and transition zone, is located at 22.7°N, 179.3°E (K = 21.9, A95 = 7.8°). The second magnetization (ADr) gives an in situ mean direction of D = 161.1°, I = −87.5° (k = 22.2, α95 = 19.9°, n = 4 independent observations) with a poorly defined pole at 37.6°N, 247.6°E (K = 6.5, A95 = 38.9°). Rock magnetic and alternating field and thermal demagnetization characteristics indicate the ADn and ADr magnetizations are both carried by low-Ti titanomagnetite. Both magnetizations are interpreted to be primary thermoremanent magnetizations acquired during emplacement and cooling of the diabase sheets at about 1090 – 1100 Ma. Comparison of the ADn pole and published geochronologic data from the Arizona diabase with the well-dated normal polarity poles of the Keweenawan region indicates that mafic magmatism in the southwestern U.S.A. diabase province and in the midcontinent rift was essentially synchronous.
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Speece, Marvin A., Timothy D. Bowen, James L. Folcik, and Henry N. Pollack. "Analysis of temperatures in sedimentary basins: the Michigan Basin." GEOPHYSICS 50, no. 8 (1985): 1318–34. http://dx.doi.org/10.1190/1.1442003.
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We develop an analytical and numerical methodology for the analysis of large bottom‐hole temperature (BHT) data sets from sedimentary basins, and test the methodology using temperature, stratigraphic, and lithologic data from 411 boreholes in the Michigan Basin. Least‐squares estimates of temperature gradients in the formations and lithologies present are calculated as solutions to a large system of linear equations. At each borehole the temperature difference between the bottom and top of the hole is represented as a sum of temperature increments through the various formations or lithologies penetrated by the borehole. Quadratic programming techniques enable bounds to be placed on the gradient solutions in order to suppress or exclude improbable gradient estimates. Numerical experiments with synthetic data reveal that the estimates of temperature gradients for a given formation or lithology are sensitive to the degree of representation of that unit; well represented units have more stable gradient estimates in the presence of noise than do poorly represented units. The estimates of temperature gradients obtained for lithologies are more stable than those for formations and are believed to be good estimates of actual lithologic temperature gradients in the Michigan Basin. Formation temperature gradients obtained as a weighted sum of the estimates of the component lithologic temperature gradients appear to be good estimates of the average temperature gradients for the formations of the basin. At each borehole a temperature residual exists corresponding to the difference between the observed BHT and the BHT predicted by the estimated interval temperature gradients. Residuals are far more stable than estimated temperature gradients. The values of residuals change little regardless of whether lithology, formation, bounded, or unbounded gradient estimates are used to calculate them. Maps of residuals indicate well‐defined and spatially coherent patterns of positive and negative temperature residuals. Filtered subsets of large‐magnitude residuals alone show a pattern of negative residuals coinciding with the mid‐Michigan gravity high, a geophysical feature thought to delineate a Precambrian (Keweenawan) rift zone in the crust beneath the basin. Thermal models of the Michigan Basin and the crust and upper mantle beneath the basin indicate that the suspected rift beneath the basin can cause a variation in basement heat flow sufficient to produce temperature residuals of the magnitude observed in the sediments, with negative temperature residuals over the area of the rift.
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Keays, R. R., and P. C. Lightfoot. "Geochemical Stratigraphy of the Keweenawan Midcontinent Rift Volcanic Rocks with Regional Implications for the Genesis of Associated Ni, Cu, Co, and Platinum Group Element Sulfide Mineralization." Economic Geology 110, no. 5 (2015): 1235–67. http://dx.doi.org/10.2113/econgeo.110.5.1235.
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Mariano, John, and William J. Hinze. "Structural interpretation of the Midcontinent Rift in eastern Lake Superior from seismic reflection and potential-field studies." Canadian Journal of Earth Sciences 31, no. 4 (1994): 619–28. http://dx.doi.org/10.1139/e94-055.
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Integrated interpretations of potential-field and GLIMPCE and industry seismic reflection data in eastern Lake Superior reveal the structural and stratigraphic complexity of the Midcontinent Rift in this region. Projection of the Keweenaw fault into southeastern Lake Superior suggested by early potential-field studies is confirmed by seismic reflection data. Analysis of seismic data in conjunction with aeromagnetic anomalies and regional gravity data also reveals a continuous section of basalt in the footwall of the Keweenaw fault. The lateral dimensions of this section vary along the strike of the rift from the center of the basin towards the southern flank. Spatially extensive anticlinal and synclinal features, reverse faults and related drag folds imaged by the reflection and enhanced potential-field data attest to the influence of a late-stage compressional event in this region. East-northeast trending gradients and displacements associated with observed potential-field anomalies and fault traces mapped at the surface also indicate a degree of accommodation perpendicular to the strike of the rift. These trends parallel the prevalent tectonic grain in the adjacent Archean basement rocks, perhaps suggesting that structures within the rift were in part controlled by preexisting crustal features.
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Clowes, R. M., F. A. Cook, A. G. Green, et al. "Lithoprobe: new perspectives on crustal evolution." Canadian Journal of Earth Sciences 29, no. 9 (1992): 1813–64. http://dx.doi.org/10.1139/e92-145.
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Lithoprobe is Canada's national, collaborative, multidisciplinary earth science research program directed toward an enhanced understanding of how the North American continent evolved. Research in its eight transects or study areas, which span the country from Vancouver Island to Newfoundland and geological time from 4 Ga to the present, is spearheaded by seismic reflection surveys. These, combined with many other studies, are providing new insight into the varied tectonic processes that have been active in forming the continent. Results from the Southern Cordillera transect show that Mesozoic crustal growth occurred in the central and eastern Cordillera by the accretion and amalgamation of exotic terranes, the collision of which resulted in the generation of crustal-scale antiforms and duplexes. After the principal periods of compression, this area was affected by a major episode of extension that led to the unroofing of the metamorphic core complexes. Farther to the west, past and present subduction processes have eroded the lower lithosphere of accreted terranes and left underplated sediments and oceanic lithosphere. The Lithoprobe East transect, covering the Paleozoic Newfoundland Appalachians and Mesozoic rifted Atlantic margin, reveals three lower crustal blocks, each with distinctive reflection signatures on marine seismic data. Structures of the geologically established tectono-stratigraphic domains, imaged clearly by new onshore reflection data, sole at upper crustal to mid-crustal levels, suggesting that much of the surface stratigraphy is allochthonous to the lower crustal blocks. At the ocean–continent transition, interpretations suggest underplating of thinned continental crust by basaltic melt during the rifting process.In Lake Superior, data from the Great Lakes International Multidisciplinary Program on Crustal Evolution (GLIMPCE) transect reveal the complex structures of the late Middle Proterozoic Keweenawan rift, which is up to 35 km deep, that almost split North America. The GLIMPCE data in Lake Huron show a spectacular series of east-dipping crustal-scale reflections that coincide with the Grenville front tectonic zone. These and other data have led to a two-stage model involving collision of an exotic terrane with the southern Superior cratonic margin in the late Early Proterozoic followed by stacking–crustal penetrating imbrication and ramping associated with the Middle Proterozoic Grenvillian orogeny. The Archean Kapuskasing structural zone, a prominent northeast-trending feature that cuts obliquely across the dominant east-west structures of the Superior Province, is interpreted as a thin thrust sheet, soled by a variably reflective décollement, above which about 70 km of crustal shortening has occurred to bring mid-crustal to lower crustal rocks to the surface, and below which the Moho deepens. The shortening may have been accomplished by brittle faulting and erosion at levels above 20 km and ductile folding or faulting in the lower crust. Preliminary studies in the Archean Abitibi greenstone belt indicate that two major fault zones, the Larder Lake–Cadillac and Porcupine–Destor, which host significant mineralization, were generated by crustal-scale thrust and (or) strike-slip tectonics. Archean crustal sections are as structurally diverse and complex as their Proterozoic and Phanerozoic counterparts. The reflection Moho has highly variable characteristics as imaged within transects and among different transects. Crustal and Moho reflectivity observed in the various transects is caused by a wide range of features, including fault–shear zones, lithologic contacts, compositional layering, fluids in zones of high porosity, and anisotropy.
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Hutchinson, D. R., R. S. White, W. F. Cannon, and K. J. Schulz. "Keweenaw hot spot: Geophysical evidence for a 1.1 Ga mantle plume beneath the Midcontinent Rift System." Journal of Geophysical Research 95, B7 (1990): 10869. http://dx.doi.org/10.1029/jb095ib07p10869.
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Samson, C., and G. F. West. "Crustal structure of the Midcontinent rift system in eastern Lake Superior from controlled-amplitude analysis of GLIMPCE deep reflection seismic data." Canadian Journal of Earth Sciences 29, no. 4 (1992): 636–49. http://dx.doi.org/10.1139/e92-055.
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The reprocessing of line F of the GLIMPCE deep marine reflection seismic survey according to controlled-amplitude principles provides new insights on the crustal structure of the Midcontinent rift system in eastern Lake Superior. The insertion of refraction static corrections in the processing sequence was crucial to recover the lateral continuity and amplitude strength of reflectors under rough lake-bottom topography. Coherent noise consisting mainly of waves scattered by irregularities on die lake bottom and first-order water reverberations was best attenuated by use of multiple passes of velocity filtering in different seismic domains rather than by trace editing. Overall, the variations in reflection style and strength on our final stacked and trace envelope sections allow for the identification of broad geological domains. Lava flows and postrift sediments can be traced uninterrupted across most of the rift basin, which is bounded to the north by a complex region of secondary sagging, felsic volcanism, and (or) intrusives, and to the south by the Keweenaw fault. The crust–mantle transition zone is characterized by both a smooth amplitude anomaly and by discontinuous packages of diffractions and reflections. It is overlain by an anomalous transparent lower crustal domain beneath the central basin. These observations suggest that, during rifting, magma rose from a layer of underplated material located at the base of the crust to the surface through numerous small feeders. They do not, however, fully exclude die possibility of complete crustal separation.
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Mitchell, Ria L., and Nathan D. Sheldon. "Sedimentary provenance and weathering processes in the 1.1 Ga Midcontinental Rift of the Keweenaw Peninsula, Michigan, USA." Precambrian Research 275 (April 2016): 225–40. http://dx.doi.org/10.1016/j.precamres.2016.01.017.
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Davis, D. W., and J. B. Paces. "Time resolution of geologic events on the Keweenaw Peninsula and implications for development of the Midcontinent Rift system." Earth and Planetary Science Letters 97, no. 1-2 (1990): 54–64. http://dx.doi.org/10.1016/0012-821x(90)90098-i.
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Kulakov, Evgeniy V., Aleksey V. Smirnov, and Jimmy F. Diehl. "Paleomagnetism of ∼1.09 Ga Lake Shore Traps (Keweenaw Peninsula, Michigan): new results and implications." Canadian Journal of Earth Sciences 50, no. 11 (2013): 1085–96. http://dx.doi.org/10.1139/cjes-2013-0003.
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We report paleomagnetic data from a new section of the ∼1.09 Ga Lake Shore Traps exposed on Silver Island (10 flows) and on the adjacent mainland (two flows) along the northwestern coastline of the Keweenaw Peninsula in Michigan. We also present new data from nine additional lava flows, sampled from the tip of the peninsula previously studied by Diehl and Haig in 1994. Samples from all these lava flows yield well-defined characteristic magnetization directions upon thermal demagnetization. After structural tilt correction, the directions from Silver Island (site-mean declination, D = 276.9°; site-mean inclination, I = 44.4°; 95% radius of confidence for site mean, α95 = 2.6°; number of samples, N = 10) and mainland (D = 298.7°, I = 36.0°, α95 = 10.1°, N = 2) flows are close to the directions from equivalent lava flows from the upper (D = 277.8°, I = 41.0°, α95 = 2.3°, N = 17) and lower (D = 300.0°, I = 34.9°, α95 = 2.3°, N = 10) sections of the middle Lake Shore Traps exposed at the eastern tip of the Peninsula, respectively. Testing the paleomagnetic directions for serial correlation shows that some of the sequential lava flows on Silver Island and from the middle Lake Shore Traps at the tip of the Peninsula record the same vector of the geomagnetic field. Combining these correlated directions yielded new mean directions for Silver Island (D = 277.2°, I = 44.1°, α95 = 3.1°, N = 8), and the upper (D = 277.0°, I = 40.4°, α95 = 3.7°, N = 10) and lower (D = 298.6°, I = 33.3°, α95 = 4.3°, N = 5) middle Lake Shore Traps at the tip of the Peninsula. The statistical similarity of paleomagnetic directions obtained from these two locations with significantly different structural trends supports the conclusions of prior studies that the curvature of the Midcontinent Rift is primary. The new paleomagnetic pole for the Lake Shore Traps is located at 23.1°N, 186.4°E (95% confidence for the paleomagnetic pole, Α95 = 4.0°; N = 31) and merits a nearly perfect six-point classification on the paleomagnetic reliability scale.
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Jeffrey M. Yarus, Jay E. Leonard, M. "Lithostratigraphy and Source Potential of Keweenawan Rocks in Mid-Continent Rift: ABSTRACT." AAPG Bulletin 73 (1989). http://dx.doi.org/10.1306/44b49fa6-170a-11d7-8645000102c1865d.
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"About this title." Geological Society, London, Memoirs 24, no. 1 (2002): NP.1—NP. http://dx.doi.org/10.1144/gsl.mem.2002.024.01.08.
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The Torridonian sandstones form one of the principal elements of British stratigraphy. They form the majestic mountains of NW Scotland and also extend westwards under the Minch basin. The sediments were deposited in a Proterozoic rift nearly contemporaneous with the Keweenawan Supergroup of North America.This book contains the first complete field description of the rocks and the sedimentary environments in which they formed, together with a comprehensive examination of their tectonic and palaeoclimatic significance, geochemistry, palaeomagnetism and diagenesis. It includes the result of over forty years' work by the author, most of it previously unpublished.
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Perry, H. K. C. "Heat flow in the Nipigon arm of the Keweenawan rift, northwestern Ontario, Canada." Geophysical Research Letters 31, no. 15 (2004). http://dx.doi.org/10.1029/2004gl020159.
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Good, David J., Pete Hollings, Greg Dunning, et al. "A New Model for the Coldwell Complex and Associated Dykes of the Midcontinent Rift, Canada." Journal of Petrology 62, no. 7 (2021). http://dx.doi.org/10.1093/petrology/egab036.
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Abstract Mafic intrusions on the NE shoulder of the Midcontinent Rift (Keweenawan LIP), including Cu–PGE mineralized gabbros within the Coldwell Complex (CC), and rift parallel or radial dykes outside the CC are correlated based on characteristic trace element patterns. In the Coldwell Complex, mafic rocks are subdivided into four groups: (1) early metabasalt; (2) Marathon Series; (3) Layered Series; (4) Geordie–Wolfcamp Series. The Marathon Series are correlated with the rift radial Abitibi dykes (1140 Ma), and the Geordie–Wolfcamp Series with the rift parallel Pukaskwa and Copper Island dykes. U–Pb ages determined for five gabbros from the Layered and Marathon Series are between 1107·7 and 1106·0 Ma. Radiogenic isotope ratios show near chondritic (CHUR) εNd(1106 Ma) and 87Sr/86Sri values that range from –0·38 to +1·13 and 0·702537 to 0·703944, respectively. Distinctive geochemical properties of the Marathon Series and Abitibi dykes, such as Ba/La (14–37), Th/Nb (0·06–0·12), La/Sm (3·8–7·7), Sr/Nd (21–96) and Zr/Sm (9–19), are very different from those of the Geordie–Wolfcamp Series and a subset of Copper Island and Pukaskwa dykes with Ba/La (8·7–11), Th/Nb (0·12–0·13), La/Sm (6·7–7·9), Sr/Nd (5–7·8) and Zr/Sm (18–24). Each unit exhibits covariation between incompatible element ratios such as Zr/Sm and Nb/La or Gd/Yb, Sr/Nd and Ba/La, and Nb/Y and Zr/Y, which are consistent with mixing relationship between two or more mantle domains. These characteristics are unlike those of intrusions on the NW shoulder of the MCR, but resemble those of mafic rocks occurring in the East Kenya Rift. The results imply that an unusual and long-lived mantle source was present in the NE MCR for at least 34 Myr (spanning the 1140 Ma Abitibi dykes and the 1106 Ma Marathon series) and indicate potential for Cu–PGE mineralization in an area much larger than was previously recognized.
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Davis, W. R., M. A. Collins, T. O. Rooney, et al. "Geochemical, petrographic, and stratigraphic analyses of the Portage Lake Volcanics of the Keweenawan CFBP: implications for the evolution of Main stage volcanism in Continental Flood Basalt Provinces." Geological Society, London, Special Publications, May 17, 2021, SP518–2020–221. http://dx.doi.org/10.1144/sp518-2020-221.
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AbstractContinental Flood Basalt Provinces (CFBPs) are large igneous features formed by the extrusion of massive amounts of lavas that require significant evolution within the lithosphere. Although sequential lava flows are effective probes of magmatic systems, CFBPs are typically poorly preserved. We focus on lava flows from the well-preserved 1.1 Ga Keweenawan CFBP that erupted within the Midcontinent Rift System. We present a new geochemical, petrographic, and stratigraphic synthesis from the Main stage Portage Lake Volcanics (PLV). Flow-by-flow analysis of the PLV reveals that major element behavior is decoupled from trace element behavior; MgO exhibits limited variability, while compatible and incompatible trace elements deviate from high to low concentrations throughout the sequence. The concentrations of incompatible trace elements slightly decrease from the base of the sequence to the top. We investigate these observations by applying a recharge, evacuation, assimilation, and fractional crystallization model to geochemical and petrographic data. Our modelling demonstrates a magmatic system experiencing increased evacuation rates while fractionation and assimilation rates decrease, indicating an increase in magmatic flux. The outcome of this modelling is a progressively more efficient magma system within the PLV. This study highlights the utility of joint petrographic and geochemical interpretation in constraining CFBP magma evolution.Supplementary material at https://doi.org/10.6084/m9.figshare.c.5424758