Geology, metamorphism, and geochemistry of Southern and Grenville Province rocks in the vicinity of the Grenville Front, Timmins Creek area, near Sudbury, Ontario

The Timmins Creek area is located in Street Township, roughly 30 kin ENE of Sudbury, Ontario. A 750--1000 in 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 Front Boundary Fault (GFBF)). Structural, petrographic, metamorphic and geochronological data suggest that the boundary between these 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. This study shows that: (1) the geology, geochemistry and geochronology indicate that the rocks forming the TZ can be correlated with units of the lower Huronian Supergroup; (2) old patterns in the GP and TZ are similar to but distinct from those in the SP; (3) mineral chemistry and whole rock geochemistry indicate that rocks in the TZ and GP domains have a simil origin and metamorphic history; (4) the presence of migmatites in the GP is the key feature that distinguishes TZ from GP rocks; (5) thermobarometry using a variety of calibrations, as well as TWEEQU and INVEQ, using staurolite-kyanite-garnet-biotite-muscovite bearing assemblages indicates conditions of 7--8 kbar and 630--680°C in the TZ and 8--9 kbar and 685--725°C in the GP. For the SP, mineral parageneses indicate T∼ 350°C. Pressures are not well constrained, but are likely 2--5 kbar; (6) the estimated P-T-t path for the TC area is clockwise; (7) best estimates of timing of partial melting and closure through 700°C are 995 +/- 2 Ma from zircon (U-Pb) in folded leucosome of metagranites in the GP terrain. U-Pb dates of metamorphic monazite from pelites in both GP and TZ domains give an age of 986 +/- 3 Ma and represent closure through 700°C, confirming the suggestion that the GP and TZ had similar tectonic histories; (8) relatively rapid cooling in the TC area is constrained between 995--990 Ma based on U-Pb zircon ages of folded and unfolded leucosome in the GP (average cooling rate = 7.5°C/Ma). These data we comparable to the cooling histories along the GF in the Temagami and Killarney areas; (9) tectonic modeling suggests compression from the SE resulted in the formation of an asymmetric structural and metamorphic antiforin that can explain the present distribution of the metamorphic isograds across GF and GFBF in the TC area.