A Paleomagnetic Traverse of the Frontenac, Sharbot Lake, Mazinaw and Elsevir Terranes, Grenville Province, Ontario

Details A Paleomagnetic Traverse of the Frontenac, Sharbot Lake, Mazinaw and Elsevir Terranes, Grenville Province, Ontario A Paleomagnetic Traverse of the Frontenac, Sharbot Lake, Mazinaw and Elsevir Terranes, Grenville Province, Ontario

May 2004

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004agusmgp33b..04b&link_type=abstract

American Geophysical Union, Spring Meeting 2004, abstract #GP33B-04

Physics

1525 Paleomagnetism Applied To Tectonics (Regional, Global), 1533 Remagnetization

Scientific paper

A paleomagnetic traverse has been carried out across the Ontario section of the Central Metasedimentary Belt (CMB) of the Precambrian Grenville Province, between the St. Lawrence and Ottawa Rivers in the east and extending west as far as the Bancroft Terrane, where it links with an earlier traverse of the Central Gneiss Belt (CGB) and the CMB Boundary Zone (CMBBZ). 54 sites were sampled, 11 in the Frontenac (F) Terrane, 12 in the Sharbot Lake (SL) Terrane, 12 in the Mazinaw (M) Terrane, 3 in the Bancroft (B) Terrane, and 16 in the Elsevir Terrane, mainly in the Belmont Domain. Ar/Ar thermochronometric work across the CMB by Cosca et al. (Tectonics 10, 959-77, 1991; Contrib. Min. Petr. 110, 211-25, 1992) documented differential unroofing of different terranes and slow cooling (1.0-1.5 oC /Ma) along parallel T-t paths offset by 50-100 Ma for the Frontenac, the western and eastern Elsevir (Ew, Ee) and the CMBBZ. Around 1000 Ma, inferred burial depths were 20 km for the CMBBZ, 15 km for Ew, >20 km for Ee (or M), 10 km for F, and transitional (12-16 km) in SL between F and Ee/M. The very different hornblende, phlogopite, muscovite and biotite Ar/Ar ages between neighboring terranes should have a counterpart in the paleomagnetic results of the terranes because the interval 1100-850 Ma was a time of rapid paleolatitude shift. However our results and previous data from B, CMBBZ and the adjacent CGB (Costanzo-Alvarez & Dunlop, Earth Planet. Sci. Lett. 157, 89-103, 1998) do not bear this out. F, SL and M have very similar R-polarity poles in the central part of the Grenville Track, while F and SL N-polarity poles are typical 980 Ma Grenville A poles. Cooling through 500oC occurred around 1100 Ma for F but the F poles do not resemble Keweenawan poles of this age. Cooling through 500oC occurred around 950 Ma for Ee/M but the M pole does not match this age. Our Ew mean pole, like that of the Tudor Gabbro, falls off the Grenville Track on a possible pre-Grenvillian track.

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