- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
- Abstract
- Affiliation
- All
- Authors
- Book Series
- DOI
- EISBN
- EISSN
- Full Text
- GeoRef ID
- ISBN
- ISSN
- Issue
- Keyword (GeoRef Descriptor)
- Meeting Information
- Report #
- Title
- Volume
NARROW
GeoRef Subject
-
all geography including DSDP/ODP Sites and Legs
-
Canada
-
Eastern Canada
-
Ontario
-
Algoma District Ontario
-
Mamainse Point (1)
-
-
-
-
-
North America
-
Great Lakes region (1)
-
-
United States
-
Michigan
-
Michigan Upper Peninsula
-
Keweenaw County Michigan (1)
-
Keweenaw Peninsula (1)
-
-
-
-
-
geochronology methods
-
paleomagnetism (1)
-
-
geologic age
-
Precambrian
-
upper Precambrian
-
Proterozoic
-
Keweenawan (1)
-
Neoproterozoic (1)
-
-
-
-
-
Primary terms
-
Canada
-
Eastern Canada
-
Ontario
-
Algoma District Ontario
-
Mamainse Point (1)
-
-
-
-
-
North America
-
Great Lakes region (1)
-
-
paleomagnetism (1)
-
Precambrian
-
upper Precambrian
-
Proterozoic
-
Keweenawan (1)
-
Neoproterozoic (1)
-
-
-
-
sedimentary rocks
-
clastic rocks
-
conglomerate (1)
-
-
-
stratigraphy (1)
-
United States
-
Michigan
-
Michigan Upper Peninsula
-
Keweenaw County Michigan (1)
-
Keweenaw Peninsula (1)
-
-
-
-
-
sedimentary rocks
-
sedimentary rocks
-
clastic rocks
-
conglomerate (1)
-
-
-
Abstract New palaeomagnetic and rock magnetic results are presented for the 1122±7 Ma Salla Diabase Dyke in NE Finland. A positive baked-contact test proves that the dyke has a primary natural remanent magnetization carried by magnetite. The characteristic remanent magnetization direction (D=42.2°, I=73.9°, k=75.7°, α 95 =4.8°) of 13 sites along the large single dyke provides a virtual geomagnetic pole (VGP) position of Plat=71°N, Plon=113°E (A 95 =8.1°). Although secular variation may not have been fully averaged out, the new VGP provides an important result to define the late Mesoproterozoic position of Baltica. The VGP is not close to any known Proterozoic palaeopoles of Baltica, and therefore the pre-Sveconorwegian apparent polar wander path (APWP) of Baltica must be modified. The pre-Sveconorwegian ( c . 1.3–1.0 Ga) APW swathes of Baltica, Laurentia (including the Logan Loop) and Kalahari cratons show similar shape, but new well-dated palaeomagnetic poles for c . 1.25–1.12 Ga interval from these continents are required to test the similarity. The Salla dyke VGP provides hints that the Mesoproterozoic Baltica–Laurentia connection in the Hudsonland supercontinent assembly lasted until 1.12 Ga.
More than 60 individual paleomagnetic poles have been obtained by various workers in the last 20 years from late Precambrian Keweenawan rocks of the Lake Superior region. Nearly all major formations and intrusive units have been subject to at least one paleomagnetic study. Keweenawan rocks thus represent paleomagnetically the world’s most intensely studied rock sequence, one that may span a time interval from about 1.2 to 1.0 b.y. ago. The large amount of paleomagnetic data coupled with locally excellent stratigraphic and structural control allows an examination of the extent to which factors other than continental displacement determine the distribution of Precambrian paleopoles. Keweenawan paleomagnetic poles of both normal and reversed polarity plot along a northeast-southwest trending band in the North Central pacific. Stratigraphic and radiometric evidence suggests that within this polar distribution there is a hairpin-shaped path open to the southwest (the so-called Logan Loop) along which there appears to be an anticlockwise polar movement with time. After filtering of the pole population using certain reliability criteria, the width of the better documented western arm of the loop decreases from 20 to 10 degrees of arc along an arc length of about 70 degrees. A smooth narrow polar path is thus produced by selecting those poles for which errors due to sampling density, structural correction, and unremoved secondary components are considered to be a minimum. Although much of the dispersion in pole position may be caused by uncertainties in the paleomagnetic data and associated geological constraints, the gross form of the loop appears to result from two superimposed effects: an apparent movement of the pole relative to the North American continent and a fictitious one arising from a violation in the assumption of a geocentric axial dipole to calculate pole positions. The latter effect is revealed by successive asymmetric reversals that can be explained neither by the presence of an unremoved secondary component nor by continental motion. The Keweenawan apparent polar wander path and that for a contemporaneous sequence from the Grand Canyon, Arizona, agree closely if only normal poles are used. In this case both paths have a similar form to the Logan Loop but are more subdued. While the Keweenawan reversed data also appear to follow an arcuate path, the arc is displaced to the northeast of the normal one as a possible consequence of non-geocentric dipole field behavior. However, both paleointensity and paleosecular variation results from Keweenawan igneous rocks are compatible with the usual assumption of a geocentric dipole and with a change to higher paleolatitudes during times of reversed polarity, but it is possible that some non-geocentric dipole model could also explain these data. Although a regional secondary component can be discounted as the cause of Keweenawan reversal asymmetry, other generally minor components are present with different directions and origins. They may be due to late Keweenawan igneous activity, burial of the Keweenawan sequence, Grenville tectonism, emplacement of copper-bearing ores, and in one instance, possible meteorite impact. Some of these magnetic overprints appear to have formed within a time period of about 1.0 to 0.8 b.y. ago and are thus important as they lie in an age interval poorly represented in North American paleomagnetic data.