SYNOROGENIC METAMORPHIC AND MAGMATIC PATTERNS IN THE CENTRAL GRENVILLE PROVINCE (QUEBEC)
Anatectic aluminous rocks from contrasting crustal levels record biotite dehydration melting and partial melt loss at different P-ranges, and distinctive P–T patterns: 13–14 kbar, 850°C with moderate-gradient P–T paths in the high-P portion of the Parautochthonous belt; 15–16 kbar, 875°C with steeper P–T paths in the HPh; 8–9 kbar, ~850°C and moderate P–T paths in the MPh; and 4–5 kbar at ~700 in the LPh. Monazite U–Pb ages in the HPh young from 1.05 to 1.02 Ga towards the structural top, and they cover a wide range at the sample scale (1.08–1.05 to 1.02 Ga) in the MPh, where in addition, Rigolet ages (1.0–0.98 Ga) are recorded by a texturally distinct generation of monazite.
Ottawan magmatisn is mostly in the ~1.07 – 1.05 Ga range including I-type granitoids scattered throughout the MET, with the largest bodies aligned SSE of the SFDZ. Rigolet-age magmatism (~1.0 to 9.8 Ga) is represented by mafic sills and swarms of ultrapotassic dykes (0.98 Ga) and felsic pegmatite (1.00–0.99 Ga) in MPh, and leucogranite in the amphibolite-grade LPh. In addition, 1.015 Ga granite in the HPh, and 1.017 – 1.015 Ga mangerite in the MPh fall in the time interval between the two orogenic phases. The large majority of the plutonic units represent high-T magmas, mantle-derived, or involving melting of intermediate crust. It is suggested that in the central Grenville the base of the crust remained hot throughout the orogeny and that mantle-derived heat was important during metamorphism.