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Title: Zircon ion microprobe dating of high-grade rocks in Sri Lanka

Abstract

The high-grade gneisses of Sri Lanka display spectacular in-situ granulitization phenomena similar to those observed in southern India and of current interest for evolutionary models of the lower continental crust. The absolute ages of these rocks are poorly constrained and so, using the SHRIMP ion microprobe, the authors have analyzed small spots on zircons from upper amphibolite to granulite grade quartzitic and pelitic metasediments. Detrital grains from a metaquartzite of the Highland Group preserve premetamorphic U-Pb ages of between 3.17 and 2.4 Ga and indicate derivation of the sediment from an unidentified Archean source terrain. The Pb-loss patterns of these zircons and the other samples suggest severe disturbance at ca 1100 Ma ago, which the authors attribute to high-grade regional metamorphism. Two pelitic gneisses contain detrital zircons with ages up to 2.04 Ga and also record an approx. = 1100 Ma event that is also apparent from metamorphic rims around old cores and new zircon growth. A granite intrusive into the Highland Group granulites records an emplacement age of 1000-1100 Ma as well as metamorphic disturbance some 550 Ma ago but also contains older, crustally derived xenocrysts. Zircons from a metaquartzite xenolith within the granitoid Vijayan Complex are not oldermore » than approx. 1100 Ma; therefore the Vijayan is neither Archean in age nor acted as basement to the Highland Group, as previously proposed. The authors suggest that the Vijayan Complex formed significantly later than the Highland Group and that the two units were brought into contact through post-1.1 Ga thrusting. Although the granulitization phenomena in India and Sri Lanka are similar, the granulite event in Sri Lanka is not Archean in age but took place in the late Proterozoic.« less

Authors:
; ; ; ; ;
Publication Date:
Research Org.:
Universitaet Mainz, West Germany
OSTI Identifier:
5718360
Resource Type:
Journal Article
Journal Name:
J. Geol.; (United States)
Additional Journal Information:
Journal Volume: 95:6
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; GEOLOGIC DEPOSITS; AGE ESTIMATION; SRI LANKA; CONTINENTAL CRUST; GEOLOGIC HISTORY; GEOLOGIC MODELS; GNEISSES; ION MICROPROBE ANALYSIS; ISOTOPE DATING; LEAD ISOTOPES; METAMORPHISM; ORIGIN; URANIUM ISOTOPES; ZIRCON; ACTINIDE ISOTOPES; ASIA; CHEMICAL ANALYSIS; DEVELOPING COUNTRIES; EARTH CRUST; ISLANDS; ISOTOPES; METAMORPHIC ROCKS; MICROANALYSIS; MINERALS; NONDESTRUCTIVE ANALYSIS; OXYGEN COMPOUNDS; ROCKS; SILICATE MINERALS; SILICATES; SILICON COMPOUNDS; TRANSITION ELEMENT COMPOUNDS; ZIRCONIUM COMPOUNDS; ZIRCONIUM SILICATES; 580100* - Geology & Hydrology- (-1989)

Citation Formats

Kroener, A, Williams, I S, Compston, W, Baur, N, Vitanage, P W, and Perera, L R.K. Zircon ion microprobe dating of high-grade rocks in Sri Lanka. United States: N. p., 1987. Web. doi:10.1086/629177.
Kroener, A, Williams, I S, Compston, W, Baur, N, Vitanage, P W, & Perera, L R.K. Zircon ion microprobe dating of high-grade rocks in Sri Lanka. United States. https://doi.org/10.1086/629177
Kroener, A, Williams, I S, Compston, W, Baur, N, Vitanage, P W, and Perera, L R.K. 1987. "Zircon ion microprobe dating of high-grade rocks in Sri Lanka". United States. https://doi.org/10.1086/629177.
@article{osti_5718360,
title = {Zircon ion microprobe dating of high-grade rocks in Sri Lanka},
author = {Kroener, A and Williams, I S and Compston, W and Baur, N and Vitanage, P W and Perera, L R.K.},
abstractNote = {The high-grade gneisses of Sri Lanka display spectacular in-situ granulitization phenomena similar to those observed in southern India and of current interest for evolutionary models of the lower continental crust. The absolute ages of these rocks are poorly constrained and so, using the SHRIMP ion microprobe, the authors have analyzed small spots on zircons from upper amphibolite to granulite grade quartzitic and pelitic metasediments. Detrital grains from a metaquartzite of the Highland Group preserve premetamorphic U-Pb ages of between 3.17 and 2.4 Ga and indicate derivation of the sediment from an unidentified Archean source terrain. The Pb-loss patterns of these zircons and the other samples suggest severe disturbance at ca 1100 Ma ago, which the authors attribute to high-grade regional metamorphism. Two pelitic gneisses contain detrital zircons with ages up to 2.04 Ga and also record an approx. = 1100 Ma event that is also apparent from metamorphic rims around old cores and new zircon growth. A granite intrusive into the Highland Group granulites records an emplacement age of 1000-1100 Ma as well as metamorphic disturbance some 550 Ma ago but also contains older, crustally derived xenocrysts. Zircons from a metaquartzite xenolith within the granitoid Vijayan Complex are not older than approx. 1100 Ma; therefore the Vijayan is neither Archean in age nor acted as basement to the Highland Group, as previously proposed. The authors suggest that the Vijayan Complex formed significantly later than the Highland Group and that the two units were brought into contact through post-1.1 Ga thrusting. Although the granulitization phenomena in India and Sri Lanka are similar, the granulite event in Sri Lanka is not Archean in age but took place in the late Proterozoic.},
doi = {10.1086/629177},
url = {https://www.osti.gov/biblio/5718360}, journal = {J. Geol.; (United States)},
number = ,
volume = 95:6,
place = {United States},
year = {1987},
month = {11}
}