Geochemistry and geochronology of proterozoic tholeiite dykes of east antarctica: evidence for mantle metasomatism

Rb–Sr whole-rock studies of tonalitic gneiss within the Grenville Province on the eastern extension of the Abitibi fold belt may indicate an age greater than 3000 m.y. The gneiss samples were collected up to 32 miles (52 km) from the Grenville Front. Rocks beyond this generally show the effects of the Grenvillian orogeny about 1100 m.y. ago which raised the 87 Rb/ 86 Sr initial ratio from about 0.7025 to 0.7148. Rocks more than 40 miles (64 km) from the Grenville Front show retrograde metamorphism from the granulite facies that is considered to be related to the metamorphism associated with the intrusion of anorthosite still farther to the southeast (ca. 1500 m.y.). The Archean tonalitic gneisses exhibit E–W and NE–SW aeromagnetic trends but similar rocks to the southeast exhibit aeromagnetic patterns that are chiefly N–S and may be a result of Hudsonian deformation. A small granitic body in this zone of N–S aeromagnetic pattern was intruded 1745 ± 23 m.y. ago( 87 Rb λ = 1.39 × 10 −11 y −1 ).

Orogeny

Anorthosite

Charnockite

10.1139/e75-073

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Citations (24)

Multistage metamorphic evolution and nature of the amphibolite–granulite facies transition in Lofoten–Vesterålen, Norway, revealed by U–Pb in accessory minerals

Chemical Geology (2007)

Fernando Corfú

Migmatite

Charnockite

10.1016/j.chemgeo.2007.01.028

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Citations (40)

Ion probe U–Th–Pb zircon dating of polymetamorphic orthogneisses from northern Labrador, Canada

Canadian Journal of Earth Sciences (1989)

L. Schiøtte W. Compston D. Bridgwater

Rounded zircons included within igneous zircons from the Uivak I gneisses, northern Labrador, have ages of up to 3863 ± 12 Ma (2σ), showing the (former) existence of rocks that predate the Uivak gneisses by more than 100 Ma. The igneous zircons themselves have experienced varying amounts of early Pb loss, but age estimates based on maximum 207 Pb/ 206 Pb from three separate gneiss samples agree to within error at 3732 ± 6 Ma (2σ), which is taken as the age of emplacement of the igneous precursor to the dominant component of the Uivak gneisses. A new generation of zircons was formed during migmatization at ca. 3620 Ma. The volumetrically less important Lister gneiss was emplaced at 3235 ± 8 Ma (2σ). In the late Archaean, different parts of the gneiss complex were subjected to different grades of metamorphic overprinting. The zircon chronology of gneisses affected by granulite facies metamorphism suggests a rapid sequence of events, with simultaneous recrystallization of old zircons and growth of new U-poor zircons at 2766 ± 17 Ma (2σ), followed by partial melting at 2744 ± 4 Ma (2σ), and further recrystallization and growth of U-poor zircons afterwards. No late Archaean zircon growth has been recorded from orthogneisses unaffected by granulite fades metamorphism.

Recrystallization (geology)

Migmatite

Anatexis

10.1139/e89-131

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Citations (108)

Rb-Sr isotopic dating and metamorphism of a suite of migmatite and granites from Sandmata Granulite complex, Rajasthan: An evidence of mesoproterozoic thermal event

Journal of the Geological Society of India (2015)

Krishnapriya Basak Subhasish Ghosh

Migmatite

10.1007/s12594-015-0349-6

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