Publication Type:
Book ChapterSource:
Geological Society of America, 1998 annual meeting, Geological Society of America (GSA), Boulder, CO, United States, Volume 30, p.95 (1998)ISBN:
0016-7592Keywords:
absolute age, alteration, Arkansas River valley, Canada, dates, eastern canada, faults, gouge, Grenville Front, leucosomes, Metamorphic rocks, metamorphism, migmatites, monazite, nesosilicates, North America, Ontario, orthosilicates, P-T conditions, partial melting, phosphates, Precambrian, schists, silicates, Sudbury District Ontario, U/Pb, United States, zircon, zircon groupAbstract:
In the Timmins Creek area, located in Street Twp., roughly 30 km ENE of Sudbury, Ontario, a 750-1000 m wide Transitional zone (TZ) of metasedimentary and metavolcanic schists occurs between the Southern Province (SP) (marked by the Ess Creek Fault) and the Grenville Province (GP) (marked by the Grenville Fault Boundary Fault (GFBF)). Structural, petrographic, metamorphic and geochronological data suggest that the boundary between the two provinces occurs at the Ess Creek Fault, rather than the GFBF; the former is marked by mylonites, the latter by hematitic, chlorite alteration and fault gouge. This places the Grenville Front 1 to 1. 5 km further north than previously indicated in a 25 km long stretch between Timmins Creek and River Valley. Our data show (1) that fold patterns in the GP and TZ are similar and are distinct from those in the SP. (2) Mineral chemistry and whole rock geochemistry indicate that rocks in the TZ and GP have a similar origin and metamorphic history. (3) the presence of migmatites in the GP are the key feature that distinguishes TZ from GP rocks. (4) Thermobarometry using a variety of calibrations ,as well as TWEEQU and INVEQ, using staurolite-kyanite-garnet-biotite-muscovite assemblages indicate conditions of 7-8 kb, 630-680 degrees C in the TZ and 8-9 kb, 685-725 degrees C in the GP. For the SP, mineral paragenesses indicate T approximately 350 degrees C. Pressures are not well constrained, but are likely 2-5 kb. (5) Best estimates of timing of partial melting and closure through 700 degrees C is 995+ or -2 Ma from zircon (U-Pb) in folded leucosome of metagranites in the GP. D2 is constrained between 995-990 Ma based on U-Pb zircon ages of folded and unfolded leucosome in the GP. U-Pb dates of metamorphic monazite from pelites in both the GP and TZ give an age of 986+ or -2 Ma, representing closure through 700 degrees C, and confirm that the GP and TZ have had similar tectonic histories. CHIME microprobe dates of monazite from the matrix of the metapelites in both the GP and TZ yield ages of ca. 989 Ma, however, monazites included within garnet and kyanite in metapelites within the GP yield CHIME ages of ca. 1060-1070 Ma, suggesting either a protracted period of metamorphism, or incomplete resetting of an earlier metamorphic event.
Notes:
GeoRef, Copyright 2018, American Geological Institute.<br/>1999-017274<br/>Ess Creek Fault<br/>Grenville Fault<br/>Street Ontario<br/>Timmins Creek
