Publication Type:

Book Chapter


Geological Society of America, 1998 annual meeting, Geological Society of America (GSA), Boulder, CO, United States, Volume 30, p.215 (1998)




absolute age, Canada, dates, eastern canada, Grenville Front, Huronian, mesoproterozoic, Metamorphic rocks, metamorphism, monazite, nesosilicates, North America, Ontario, orthosilicates, P-T conditions, Penokean Orogeny, phosphates, polymetamorphism, Precambrian, proterozoic, silicates, Sudbury District Ontario, titanite, titanite group, U/Pb, upper Precambrian, zircon, zircon group


U-Pb geochronology was carried out in conjunction with mapping and metamorphic petrology to examine the timing of metamorphism along the Grenville Front (GF) in Street Township, east of Sudbury. The area is underlain by metasedimentary and intrusive rocks of the Paleoproterozoic Huronian Supergroup. Metamorphic assemblages in rocks within 1.5 km south of the Grenville Front near Crerar indicate a progressive southward increase in peak metamorphic conditions. A ms-bi-ky-gt-st gneiss yields PT conditions of 685 degrees C and 8.1 kb (TWEEQU). This metamorphic event is dated by monazite and zircon at 990-985 Ma. Besides coexisting Archean detrital zircon the gneiss also contains zircon tips formed during an earlier Mesoproterozoic metamorphism. A gt-bi-st-(trace ky) schist slightly to the north yields 660 degrees C and 7. 3 kb and a monazite age of about 986 Ma. This event did not completely reset titanite in an adjacent Huronian-age granite. In another area, about 8 km farther south, zircon (and titanite) date folded leucosome veins at 995 Ma and cross-cutting late pegmatites at 989 Ma. In contrast, titanite in the host granite underwent strong Pb loss but no new growth at 990 Ma; this titanite was formed during an earlier 1.7 Ga metamorphism. The 1.7 Ma event and possibly an earlier Penokean (1.9 Ga) event left an imprint on the Pb loss pattern of the coexisting primary 2475 Ma zircon. An opx-hornblendite at the GF contains primary magmatic 2468 Ma zircon, coexisting with two distinct metamorphic zircon generations formed at 1471 Ma and subordinately at about 1052 Ma. Together, these data demonstrate that subdomains of the Street Tp. area were variously affected by all the major events known in the region prior to the intense but short-lived metamorphism related to the terminal Grenvillian collisional phase. The study emphasizes the importance of combining multi-mineral isotopic work with a well documented geological framework in order to properly understand complex geological histories.


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