U-Pb isotopic systematics of zircons from prograde and retrograde transition zones in high-grade orthogneisses, Sri Lanka

Journal Article · Mon Jul 01 04:00:00 EDT 1991 · Journal of Geology; (United States)

DOI:https://doi.org/10.1086/629515· OSTI ID:5616833

Baur, N; Liew, T C; Todt, W; Hofmann, A W ^[1]; Kroener, A ^[2]; Williams, I S ^[3]

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1. Max-Planck-Institut fuer Chemie, Mainz (West Germany)
2. Univ. Mainz (West Germany)
3. Australian National Univ., Canberra (Australia)

The authors present U-Pb zircon isotopic data from locally restricted prograde (arrested in situ charnockitization) and retrograde metamorphic transition zones, which are well exposed in Proterozoic orthogneisses tectonically interbanded with granulite facies supracrustal rocks of the Highland Group in Sri Lanka. These granitoid rocks yield apparent ages of 1942 {plus minus} 22 Ma, {approximately} 770 Ma, {approximately} 660 Ma, and {approximately} 560 Ma. All samples show severe Pb-loss some 550-560 Ma ago. The main phase of granulite-formation could not be dated unambiguously but is bracketed between {approximately} 660 Ma and {approximately} 550 Ma. The pervasive Pb-loss event around 550-560 Ma reflects the end of this period of high-grade metamorphism and was associated with widespread igneous activity and retrogression. This is constrained by the 550 {plus minus} 3 Ma intrusion age for a post-tectonic granite. They relate this late phase of thermal activity to crustal uplift of the Sri Lankan granulites. This data unambiguously prove the high-grade history of the Sri Lanka gneisses to be a late Precambrian event that may be related to the Pan-African evolution along the eastern part of Africa.

• OSTI ID: 5616833
• Journal Information: Journal of Geology; (United States), Journal Name: Journal of Geology; (United States) Journal Issue: 4 Vol. 99:4; ISSN JGEOA; ISSN 0022-1376
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
ACTINIDE ISOTOPES
AGE ESTIMATION
ASIA
CHEMISTRY
DEVELOPING COUNTRIES
ELEMENTS
GEOCHEMISTRY
GEOLOGIC AGES
GEOLOGIC FORMATIONS
GEOLOGIC HISTORY
GNEISSES
GRANULITES
IGNEOUS ROCKS
ISLANDS
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
LEAD
LEAD ISOTOPES
LOSSES
METALS
METAMORPHIC ROCKS
METAMORPHISM
MINERALS
PLATE TECTONICS
PLUTONIC ROCKS
PRECAMBRIAN ERA
ROCKS
SILICATE MINERALS
SRI LANKA
TECTONICS
URANIUM ISOTOPES
ZIRCON