High‐temperature cordierite migmatites in the north‐eastern Grenville Province

Abstract

In the northeastern part of the Grenville Province, along the gulf of St Lawrence, cordierite is widespread in the migmatites of Baie Jacques Cartier (BJC) and Baie des Ha! Ha! (BHH). In the BJC area, rafts of mesosome occur in a pervasive network of leucosome consisting of cordierite-bearing pegmatite. In BHH, however, the mesosome and leucosome are well segregated and locally separated by thin biotite -hornblende melanosomes.Leucosomes in the BJC area record the highest temperatures (oxide thermometry =900"C), whereas leucosomes of BHH and mesosomes of both areas indicate peak temperatures around 800°C (oxide thermometry; biotite-garnet thermometry with fluorine-rich biotite). Peak pressures were constrained at 720 MPa using the IlrnSil-Qtz-Grt-Rt (GRAIL) equilibrium.The area is thought to have undergone extensive melting under relatively modest pressures. The highest temperatures recorded in the BJC area are probably related to a pervasive impregnation of this terrane by aluminous granitic melts.Most post-peak P-T estimates for the mesosomes fall on a nearly isobaric, clockwise, P-T path (0.6 MPaPC) with the exception of the high-temperature leucosomes of BJC. which fall about 100°C away from this path; this is additional evidence for the external origin of these leucosomes. The ultimate source of heat that generated the migmatites is thus though to be an underlying plutonic complex (anorthosite?). List of abbreviations used in the text andfiguresAlm And Andr Bt Crd Grt Grs Hem Hc Ilm Kfs Hog KY Mag PI PrP Qtz Sil SPS Rt USP

Petrology of spinel granulites from Araku, Eastern Ghats, India, and a petrogenetic grid for sapphirine‐free rocks in the system FMAS

“…The presence of two types of ilmenite lamellae suggests that such unmixing proceeded in at least two stages during the cooling of the complex (cf. Perrault & Martignole, 1988). Sillimanite rimming the Fe-Ti oxides is enriched in Fe20, compared to that in association (i).…”

Controls on intrusion of near-trench magmas of the Sanak-Baranof Belt, Alaska, during Paleogene ridge subduction, and consequences for forearc evolution

“…However, kyanite megacrysts are very rare in granitic magmas. Examples of granitic rocks bearing other aluminosilicate megacrysts are known from several places, including the Blue Mountains of northeastern Oregon (Johnson et al, 1997), and in the Grenville province (Perreault and Martignole, 1988). There are at least three possible origins for the large kyanite and other aluminosilicate megacrysts in the plutons of the Sanak-Baranof belt.…”