U-Pb isotopic systematics of zircons from prograde and retrograde transition zones in high-grade orthogneisses, Sri Lanka
- Max-Planck-Institut fuer Chemie, Mainz (West Germany)
- Univ. Mainz (West Germany)
- 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), Vol. 99:4, Issue 4; ISSN 0022-1376
- Country of Publication:
- United States
- Language:
- English
Similar Records
Rubidium-strontium whole-rock ages of Kataragama and Pottuvil charnockites and East Vijayan gneiss: Indication of a 2 Ga metamorphism in the highlands of southeast Sri Lanka
Timing of Early Proterozoic collisional and extensional events in the granulite-gneiss-charnockite-granite complex, Lake Baikal, USSR: A U-Pb, Rb-Sr, and Sm-Nd isotopic study
Related Subjects
GEOLOGIC FORMATIONS
AGE ESTIMATION
SRI LANKA
ZIRCON
ISOTOPE RATIO
GEOCHEMISTRY
GEOLOGIC HISTORY
GNEISSES
GRANULITES
ISOTOPE DATING
LEAD
LEAD ISOTOPES
LOSSES
METAMORPHISM
PLATE TECTONICS
PLUTONIC ROCKS
PRECAMBRIAN ERA
URANIUM ISOTOPES
ACTINIDE ISOTOPES
ASIA
CHEMISTRY
DEVELOPING COUNTRIES
ELEMENTS
GEOLOGIC AGES
IGNEOUS ROCKS
ISLANDS
ISOTOPES
METALS
METAMORPHIC ROCKS
MINERALS
ROCKS
SILICATE MINERALS
TECTONICS
580000* - Geosciences