Table 2.

Metamorphic ages recorded in rims to zircon grains and associated PT conditions and tectonic styles found in the tectonic domains

Craton/Belt/ComplexArea/UnitApproximate metamorphic ages (Ma)Pan-African PT conditions (based on mineral chemistries; BGS-USGS-GLW 2008)Terminal Pan-African tectonic style
AntongilNorthern area (Mananara Group)537–526600–750 °C; 8–10 kb These conditions may relate to an Archaean metamorphism and most samples did not record Pan-African eventsWeakly affected by Pan-African events with relatively open NNW– and north–NE-trending folds
MasoraSouthern area530–515650–700 °C; 6–7 kb Samples from the central part of this domain did not record a Pan-African metamorphic eventCentral area preserves an open SSW-plunging synform that is transposed and cut by ductile thrusts around the margins of the Craton
AntananarivoMangoro713, 560–537650–750 °C; 4–6 kbDome and basin interference folds aligned c. north–south, and the discordant Antananarivo Virgation Zone
Ambatolampy560–540
Imorona-Itsindro807–801, 767–763, 550–516
TsaratananaAndriamena819, 779, 750, 535750–820 °C; 5.5 kbStrong c. north–south to NNW–SSE structural grain with tight interference fold patterns
BemarivoNorth526–511There are very few thermobarometric determinations and mineral assemblages suggest greenschist to upper amphibolite conditionsSouth-directed horizontal translation and formation of a thrust-imbricated fan. Subsequent shearing and open folding after c. 520 Ma (Buchwaldt et al. 2003)
South540–520500–600 °C; 6–8 kb Higher temperatures up to 850 °C were recorded by the two-feldspar thermometer (previous studies give 800–970 °C, 6.5–9 kb)
Anaboriana-Manampotsy Belt (‘Betsimisaraka Suture Zone’)Anaboriana540–520West to east decrease in temperature but increase in pressure across the Manampotsy Belt. The south-westernmost part of the belt shows similar PT values to the Antananarivo Craton but slightly higher pressures in the north where 7–8 kb was recorded. Central parts of the Manampotsy Belt record temperatures of 700–750 °C but with higher pressure of 7.5–10 kb, while in the east temperatures of 600–650 °C and higher pressures of 10–12 kb were recordedSouth: Strong north–south structural grain with transposed fabrics and dominated by anastomosing ductile shears and the Angavo–Ifanadiana Shear Zone North: NW–SE structural grain within the Anaboriana Belt
Ampasary551–520
Manampotsy560