Delineating crustal domains in Peninsular India: Age and chemistry of orthopyroxene-bearing felsic gneisses in the Madurai Block

摘要: Abstract The Madurai Block of southern India is rich in granitic orthogneiss, much which orthopyroxene-bearing (charnockite). This study has identified that orthogneiss from the northwest (broadly defined as north and west Karur–Kambam–Painavu–Trichur lineament) a very different origin south-eastern Block. To north-west Block, charnockites record Neoarchaean (∼2.7–2.5 Ga) crystallization ages with metamorphic overprinting at ∼535 Ma. Their Archaean Nd depleted mantle model (2.51–3.01 Ga), high ɛNd(T) values (between −3.28 +4.55) low to moderate initial 87Sr/86Sr ratios (0.7017–0.7106) indicate primarily mantle-derived variable involvement crustal material. south-east samples have younger 1007 ± 23 Ma 784 ± 18 Ma range between 1.38 1.69 Ga, suggesting significantly isotopic evolution this terrane. signature these (ɛNd(T) = +2.58 −3.28, 87Sr/86Sr = 0.7054–0.7084) suggests source input contemporary crust. All show subsequent zircon growth, or disturbance, due Ediacaran–Cambrian metamorphism (∼535 Ma). sharply contrasting primary igneous U–Pb orthogneisses identify two distinct terranes; an basement terrane Proterozoic dominated by metasedimentary rocks south east boundary here broad zone (KKPT) lineament appears southerly dipping series seismic reflectors. A correlation made central Madagascar where metsedimentary are thrust over Antananarivo