Synopsis of paleomagnetic studies in the Kapuskasing structural zone

Symons, D. T. A.; Lewchuk, Michael T.; Dunlop, David J.; Costanzo-Alvarez, V.; Halls, H. C.; Bates, Martin; Palmer, H. C.; Vandall, T. A.

doi:10.1139/e94-106

Cited by 28 publications

(15 citation statements)

References 60 publications

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“…Their antipodal equivalent positions that would have been generated in reverse fields (B1R, B2R) lie near the start of track 1 but their ages would be greater than that of the A components. The B1N and B2N paleopoles lie near the Proterozoic “Keewanawan” APWP in the northern Pacific region at ∼1100 Ma, as discussed elsewhere [e.g., Symons et al , 1994]. In that case, it may be difficult to propose an energy source that would trigger a widespread CRM or TVRM resulting in demagnetization temperatures as high as 450°C.…”

Section: Discussionmentioning

confidence: 96%

“…That lower precision geochronology is still useful for regional tectonic studies because K‐Ar closure temperatures and paleomagnetic blocking temperatures both broadly respond to slow, plutonic, postmetamorphic cooling. The latter part of track 1 from late Archean and Paleo‐Proterozoic rocks is much better defined by more recent studies, some of which used high‐precision geochronology from Proterozoic rocks, or associated with Proterozoic events such as uplift of the Kapuskasing Structural Zone [e.g., Constanzo‐Alverez and Dunlop , 1988; Symons et al , 1994; Symons and Vandall , 1990; Vandall and Symons , 1990]. …”

Section: Discussionmentioning

confidence: 99%

“…Unfortunately, as we will show, our dikes are late syntectonic and a different and necessarily less precise APWP is used. It was obtained from plutonic rocks and mostly uses low‐precision K‐Ar geochronology [ Constanzo‐Alvarez and Dunlop , 1988; Constanzo‐Alvarez et al , 1993; Dunlop , 1979, 1983, 1984a, 1984b, 1985; Irving , 1979; Symons et al , 1994] (Figure 1a, track 1). Whereas the geochronological data are much less precise than for track 2, paleopole positions have been repeatedly confirmed along these tracks from thermochemical remanences acquired during postmetamorphic cooling at the close of Archean deformation in this region (2700–2600 Ma).…”

Section: Introductionmentioning

confidence: 99%

“…Using new cores from the same specimens, here we distinguish successfully between consistently oriented vector components by using low‐temperature demagnetization (LTD) before thermal demagnetization. Although the paleopoles appear well defined, comparisons with published APWPs for the Superior Province from late Archean [ Irving , 1979; Dunlop , 1983; Symons et al , 1994] to early Proterozoic [ Buchan et al , 2000] are difficult. Moreover, the earlier parts of the paths are progressively less precise and complete.…”

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confidence: 99%

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Apparent polar wander paths and the close of late Archean crustal transpression, northern Ontario

2003

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Lamprophyre dikes of the southern Superior Province of the Canadian Shield crosscut Archean structures, including a late Archean unconformity and its overlying younger Archean Timiskaming sedimentary and volcanic rocks. The dikes also cut the single schistosity that formed in these rocks. Nevertheless, the lamprophyre dikes show a weak internal tectonic fabric that is approximately parallel to the schistosity in the bedrock and oblique to dike walls. The consistent orientation of this internal tectonic fabric has been recognized in every lamprophyre dike using anisotropy of magnetic susceptibility (AMS). Thus the lamprophyre dikes provide a useful chronological marker, trapping the last pulse of Archean tectonism. Unfortunately, our previous attempts to compare the lamprophyre paleopoles with those of the age‐calibrated apparent polar wander path (APWP) failed because it was not possible to isolate separate young and old components of magnetization. That failure occurred due to the overlap of blocking temperatures or coercivities for the different characteristic vector components [Borradaile et al., 1994a]. Using new cores from the same specimens, here we distinguish successfully between consistently oriented vector components by using low‐temperature demagnetization (LTD) before thermal demagnetization. Although the paleopoles appear well defined, comparisons with published APWPs for the Superior Province from late Archean [Irving, 1979; Dunlop, 1983; Symons et al., 1994] to early Proterozoic [Buchan et al., 2000] are difficult. Moreover, the earlier parts of the paths are progressively less precise and complete. Nevertheless, A component remanences for the dikes give a paleopole near the path at ∼2650 Ma. For a Timiskaming volcanic breccia with a U‐Pb age of 2696 Ma the A component paleopole may lie between 2600 and 2650 Ma. B component remanences yield paleopoles in the NW Pacific region, incompatible with any proposed Archean path but perhaps representing some much younger Proterozoic remagnetization event (e.g., Keweenawan, ∼1100 Ma).

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Section: Discussionmentioning

confidence: 96%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Apparent polar wander paths and the close of late Archean crustal transpression, northern Ontario

2003

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“…(a) Apparent polar wander path of the late Proterozoic rocks of northern Ontario [ Costanzo‐Alvarez and Dunlop , 1988, Pesonen and Halls , 1979; Symons et al , 1994; Palmer et al , 1981]. (b) Virtual geomagnetic poles (VGPs) determined from sites in the Logan diabase sills.…”

Section: Discussionmentioning

confidence: 99%

Proterozoic diabase sills of northern Ontario: Magnetic properties and history

Middleton¹,

Borradaile

Baker

et al. 2004

J. Geophys. Res.

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Magnetic fabrics show that a series of massive diabase sills (“Logan sills”) possess flow fabrics away from the midcontinental Proterozoic rift system, near its triple junction on the north shore of Lake Superior. Their intense remanences are commonly antiparallel to the geomagnetic field, requiring some knowledge of natural remanent magnetization in order to interpret of ground magnetic surveys. Thermal demagnetization, low‐temperature demagnetization, and the combined techniques yield differently oriented characteristic remanence vectors in some of these sills. Although the commonly reported “Keweenawan” reversed paleofield direction is verified by most A components, the orientation of vectors within sites and through the thickness of sills is large and may be attributed to reversals, excursions, and secular variation. B components are mostly down, but their orientation distribution is poorly concentrated. Low‐temperature demagnetization, prior to thermal demagnetization, tends to improve the consistency of vectors defined in subsequent thermal demagnetization. Moreover, in some cases, three to five cycles of low‐temperature demagnetization alone produces the same result as the more time‐consuming thermal demagnetization. Some within‐site scatter of the A components is large, and some anomalous specimen directions and alternate polarities may be associated with platinum group mineralization. Whereas the grand mean direction for all sites lies on the available apparent polar wander path between 1100 and 1300 Ma, the mean paleopole locations differ at the 95% level for different demagnetization treatments of specimens from the same sites.

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