Paleomagnetic poles from the Upper Proterozoic Mackenzie Mountains supergroup (MMs) of northwestern Canada define an apparent polar wander path lying to the west of the Grenville Loop. This path is suggested from an analysis of the quartzitic Katherine Group, whose probable primary pole lies at the beginning of the sequence, near the younger end of the Grenville Track (0.88 Ga). The end of the apparent polar wander (APW) sequence may be defined by a primary pole from sills intruding the Tsezotene Formation below the Katherine. We relate the sills, dated at about 0.77 Ga, to the rifting event that led to "Copper cycle" and Rapitan sediments above the MMs, and we suggest that the exposed part of the MMs has an age between 0.88 and 0.77 Ga. The APW path is apparently not affected by rotations: pole evidence indicates little if any relative rotation between thrust sheets of the fold belt or between the fold belt and the craton.Paleomagnetic analysis of the Katherine Group data, obtained by alternating field, thermal, and chemical methods, revealed three magnetizations. The probable primary remanence, K A , carried by mainly detrital hematite grains, has a direction of D, I = 267°, +21 °(N = 13 specimens, k = 33, α 95 = 7°) and a pole at 9°N, 210°W (δ p , δ m = 4°, 8°). A secondary component, K B , carried by hematite pigment, has a direction of D, I = 258°, +42 °(N = 4 sites, k = 326, α 95 = 5°) and a pole at 17°N, 196°W (δ p , δ m = 4°, 6°). It documents further a pervasive overprint magnetization found in most MMs rocks. A similar hematite magnetization is probably primary in the overlying Copper cycle rocks. The youngest component, K C , is found partly in a second, probably largely post-folding pigment phase (post-Late Cretaceous or Paleocene) and has a direction of D, I = 007°, +84 °(N = 9 sites, k = 77, α 95 = 6°) and a pole at 77°N, 122°W (δ p , δ m = 11°, 12°).
The most common primary tumors of the human brain are thought to be of glial cell origin. However, glial cell neoplasms cannot be fully classified by cellular morphology or with conventional markers for astrocytes, oligodendrocytes, or their progenitors. Recent insights into central nervous system tumorigenesis suggest that novel molecular markers might be found among factors that have roles in glial development. Oligodendrocyte lineage genes ( Olig1/2 ) encode basic helix–loop–helix transcription factors. In the rodent central nervous system, they are expressed exclusively in oligodendrocytes and oligodendrocyte progenitors, and Olig1 can promote formation of an chondroitin sulfate proteoglycon-positive glial progenitor. Here we show that human OLIG genes are expressed strongly in oligodendroglioma, contrasting absent or low expression in astrocytoma. Our data provide evidence that neoplastic cells of oligodendroglioma resemble oligodendrocytes or their progenitor cells and may derive from cells of this lineage. They further suggest the diagnostic potential of OLIG markers to augment identification of oligodendroglial tumors.
A paleomagnetic study of mafic plutonic rocks in the northeast Grenville Province found five magnetizations, interpreted as Grenvillian and later overprints. Components A, B, and C, with the highest unblocking temperatures and distinct regional distributions, have paleopoles that appear to lie on the Grenville Track. Component C, with pole at 348°E, 11°S (δp, δm = 2°, 4°) and mostly distributed in lower-grade mafic rocks in the Groswater Bay terrane near the Grenville Front, is interpreted as a post ca. 970 Ma Grenville overprint, predating components A and B. The latter components, nearly coextensive in distribution in the Groswater Bay and Sandwich Bay regions farther south, have respective poles at 326°E, 02°N (N = 9 sites; δp, δm = 8°, 11°) and 348°E, 13°N (N = 13 sites; δp, δm = 6°, 8°). Component B could be interpreted either as a Grenville overprint or, more likely, as a later overprint of late Neoproterozoic (615 Ma) to Cambrian age due to rifting in the Lake Melville region. If so, many other so-called "Grenville" overprints from rock units within or near the St. Lawrence rift system may have been erroneously attributed to Grenvillian thermal effects and, in fact, be younger. If component B is post-Grenville and component C, a Grenville overprint, then component A is probably latest Grenvillian or later Neoproterozoic in age. These results strongly suggest that the Grenville Track needs reinterpretation.
Analysis of paleomagnetic data obtained from 1966 alternating-field treatment and from recent thermal demagnetization of the same samples of Late Proterozoic (770 Ma) diabase sills and dykes distributed about the Mackenzie Arc from northeastern British Columbia to the Alaskan border has revealed a primary magnetization in seven sites that is similar to existing data from 10 sites confined to the central Mackenzie Mountains region (N = 17 site poles; 222.2°W, 01.6°N; R = 16.73; K = 60; A 95 = 5°). The diabases are confined to the dominantly clastic Late Proterozoic Tsezotene Formation and Katherine Group of the Mackenzie Mountains Supergroup. Tests of Carey's orocline hypothesis for the arc using linear regression and a plan-view application of the fold test suggest, in line with earlier structural studies, that the arc is largely nonrotational and that it is not an orocline resulting from the Cretaceous and early Tertiary Laramide Orogeny. Rather, it conforms to the arcuate foreland margin predating deposition of the Late Proterozoic Mackenzie Mountains Supergroup.
Paleomagnetic analysis of the Risky and underlying Blueflower formations at the top of the Neoproterozoic Windermere Supergroup in the northern Cordillera of Canada revealed several magnetic components of geological significance. Rock strata of the Blueflower locality in the Mackenzie Mountains yielded no primary remanence due to extensive "pyritization" and weathering. However, dolomitic rocks of the Risky locality in the eastern Wernecke Mountains, 250 km to the north, yielded a probable primary remanence. The remanence has a direction at D, I = 055°, −64° (N = 11 samples from 4 sites, k = 18, α 95 = 11°) and pole at 007°E, 29°S (δp, δm = 14°, 18°), and indicates a paleolatitude of 46 ± 14°S. Comparison between poles from the Risky and the overlying Backbone Ranges and Ingta formations suggests a profound post-Risky unconformity. Three secondary components are also present. Component B in both the Blueflower and Risky units appears to be a thermal overprint, possibly related to Vendian rifting. Its respective direction in each unit is D, I = 062°, +77° (N = 4 sites, k = 143, α 95 = 8°) and D, I = 064°, +56° (N = 6 sites, k = 21, α 95 = 15°), yielding poles of 110°E, 64°S (δp, δm = 13°, 14°) and 142°E, 44°S (δp, δm = 15°, 21°). Component C, only found in the Risky, is attributed to Late Cambrian to Middle Ordovician extension and magmatism. Component D, which predominates in both formations, relates to late Mesozoic compression and to weathering.
Paleomagnetic evidence from 37 sites of the partly red‐pigmented siliciclastic Tsezotene Formation supports a recently proposed apparent polar wander path for the Hadrynian Mackenzie Mountains supergroup (MMs). The probable primary remanence has a direction at D°, I° = 271, +24 ( k = 15; α 95 ° = 8) with an associated pole T A (12°N, 214°W; N = 23 specimens; δ p °, δ m ° = 5, 9). T A becomes the oldest pole from the MMS. It helps bridge the gap between the apparently youngest poles of the Grenville Loop (about 0.88 Ga) and the suggested younger poles from the MMs. A secondary pole T B (23°N, 198°W; N = 18 sites; δ p °, δ m ° = 3, 5), derived from a magnetic direction in hematite pigment ( D °, I° = 263, +48; k = 73; α 95 ° = 4), supports a magnetization found in the overlying “Copper cycle” and in younger units of the MMs as a pervasive overprint. Another secondary pole T c (63°N, 141°W; N = 29 sites; δ p °, δ m ° = 6, 6), derived from a magnetization (D°, I° = 317, +87; k = 89; α 95 ° = 3) partly residing in another phase of hematite pigment, is of postfolding age (post‐Paleocene). This study demonstrates the importance of using several treatment methods, singly and in combination, when analyzing complex magnetizations.
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