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

Journal Article · Sat Sep 01 04:00:00 EDT 1990 · Journal of Geology; (USA)

DOI:https://doi.org/10.1086/629440· OSTI ID:6033478

De Maesschalck, A A; Oen, I S ^[1]; Hebeda, E H; Verschure, R H ^[2]; Arps, C E.S. ^[3]

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1. Vrije Universiteit, Amsterdam (Netherlands)
2. NWO Laboratorium voor Isotopen Geologie, Amsterdam (Netherlands)
3. RGM, Leiden (Netherlands)

Highland Group granulite-facies rocks of the Kataragama klippe in southeast Sri Lanka yield a Rb-Sr whole-rock apparent age of 1,930 {plus minus} 130 Ma, MSWD = 39, and a {sup 87}Sr/{sup 86}Sr intercept of 0.715 {plus minus} 0.005, indicating a Highlandian metamorphism about 2.0 Ga ago. A charnockitic gneiss at Komari near Pottuvil, east Sri Lanka, gives a Rb-Sr whole-rock isochron age of 820 {plus minus} 70 Ma, MSWD = 0.78, initial {sup 87}Sr/{sup 86}Sr = 0.725 {plus minus} 0.007, suggesting a metamorphic resetting at about 0.8 Ga. The Rb-Sr whole-rock data of an East Vijayan biotite-hornblende gneiss fit a reference isochron of 800 Ma with a {sup 87}Sr/{sup 86}Sr intercept of 0.705; the low {sup 87}Sr/{sup 86}Sr intercept may be explained by a juvenile addition to the older crust. A review of available data from various isotopic dating methods suggests that the Highland Group supracrustals were deposited 2.5-2.0 Ga ago, metamorphosed in the granulite-facies about 2.0 Ga (M1) ago, and disturbed by resetting events about 1.1 Ga (M2), 0.8 Ga (M3), and 0.55 Ga (M4) ago. The East Vijayan supracrustals were deposited 2.0-1.1 Ga ago, invaded by granites and metamorphosed in the amphibolite-facies about 1.1 Ga (M2) ago, and disturbed by resetting events about 0.8 (M3) and 0.55 Ga (M4) ago. Overthrusting of the Kataragama granulites over the East Vijayan gneisses occurred post-M3.

• OSTI ID: 6033478
• Journal Information: Journal of Geology; (USA), Journal Name: Journal of Geology; (USA) Vol. 98:5; ISSN JGEOA; ISSN 0022-1376
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
580000* -- Geosciences
AGE ESTIMATION
ALKALI METAL ISOTOPES
ALKALINE EARTH ISOTOPES
AMPHIBOLE
ASIA
BETA DECAY RADIOISOTOPES
BIOTITE
CONTINENTAL CRUST
DEPOSITION
DEVELOPING COUNTRIES
EARTH CRUST
ELECTRON CAPTURE RADIOISOTOPES
EVEN-EVEN NUCLEI
EVEN-ODD NUCLEI
GEOLOGIC HISTORY
GEOLOGIC STRUCTURES
GNEISSES
HORNBLENDE
HOURS LIVING RADIOISOTOPES
INTERMEDIATE MASS NUCLEI
ISLANDS
ISOMERIC TRANSITION ISOTOPES
ISOTOPE DATING
ISOTOPE RATIO
ISOTOPES
METAMORPHIC ROCKS
METAMORPHISM
MICA
MINERALS
NUCLEI
RADIOISOTOPES
ROCKS
RUBIDIUM ISOTOPES
SEDIMENTARY BASINS
SILICATE MINERALS
SRI LANKA
STABLE ISOTOPES
STRONTIUM 86
STRONTIUM 87
STRONTIUM ISOTOPES
TECTONICS