Post Tectonic Granites in Sri Lanka

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290 North China craton was mainly formed during the Mesoarchaean and Neoarcliaean ages. The widely exposed rocks in tlie North China were strongly metamorphosed and deformed by Neoarchaean event. References UNESCO-IUGS-IGCP-368 (1 998) International Seminar on Precambi ian Crust in Eastern and Central India. October 29-30, 1998. Bhubanesliwar, Geological Survey of India, Calcutta, 24913 Geological Survey of lndia (19%) Guide Book Irc~-Seniinar I : d d Workshop i n pal I\ o f Wc,\l kmg29 I References Crawford, A. R. and Oliver, R. L. (1969) The precainbrian geoclironology o f Ceylon. Spec. Publ. Geol. Soc. Australia, v.2, pp.283 -306. Geological Survey Department, Sri Lanka, Gcological Map of Kroner,A., Cooray, P.G.and Vitanage,P.W. (3991) Lithotectonic subdivision of the Precambrian basement in Sri Lanka. In: Kroner, A. (Ed.) The crystalline crust of Sri Lanka, Part 1. Geological Survey of Sri Lanka, Professional Paper 5 pp.69-88. Santosh, M. and Drury, S. A. (1988) Alkali granite with Pan- African affinities from Kerala, S. India. Jour. Geol., v.96, Sri Lanka. (1982) pp.616-626. CORRESPONDENCE Latest Neoproterozoie Gondwana Eastern Margin T.Watanabel, Y. Oriliaslii2 and C.M.Fanning3 lDivisiori of Earth aiid Planetary Sciences, Holcknido University, Sapporo, Inpan 2Dcpt. of Enrtlz arid Plaiietavy Scieiices, Tokyo lrzstitzife of Techtzologj, Tokcyo, Japatz iResearcli Scliool of Earth Scierice, Azistraliaiz National Uizivenity, Canberra, ACT, Aiistralin Rodinia Breakup and Eastern Australia Reconstruction of the Rodinia supercontinent, especially palaeogeographical position of the south China block, has been one of the disputable problems. It is debated whether the parts of south China block were situated between Australia and Laurentia prior to the break up of Rodinia or not (c.f. Hoffman,1991; Dalziel, 1992; Li et al., 1995, among others). If Laurentia was in direct contact with Australia, radial dyke swarm activity proposed by Park (1995) was the first testament of the initiation of rifting of the supercontinent. Subsequent breakup and the timing of initiation of compressive regime along Australia and Antarctica formed constructive tectonism for passive western margin of Laurentia (Goodge, 1997). However, recent study on eastern Australia leads us to a new scenario. Late Neoproterozoic Basaltic Magmatism in South - Central Australia Prior to the breakup of Rodinia at ca.700Ma along the eastern Gondwana margin giant dike swarm activity derived from upwelling plumes have been recognized at 1600-1800Ma and ca.800Ma in central and south Australia (Zhao and McCulloch,l993; Zhao et a1.,1994). Recent chronological study reveals that Neoproterozoic basaltic magmatism in south - central Australia for ca. 800 Ma dyke activity is at least 40Ma before the mafic intrusion in western North America. Precise ion-microprobe U-Th-Pb analyses of baddeleyite and zircon yield 827Ma for emplacement of the dyke swarm. Hence a hypothesis of radiating dyke swarm (Park et al., 1995) would not be accepted. They support roughly coeval magmatism in Australia and south China block. Hypothetical paleogeographic position of the south China block between Australia and Laurentia (Li et al., 1995) must be positively examined. Neoproterozic Ages in the Tasman Fold System The Tasman Fold System comprises four fold belts. They are the Kanmantoo, Lachlan/Thomson and New England from west to east. Crawford et al. (1997) reported ca.580Ma riftogenic greenstones in the Mt Wright area in the Kanmantoo Fold Belt. Recently Watanabe et a1.(1998) found ca.570Ma eclogite (Attunga eclogite) from the serpentinite melange in the New England Fold Belt. From the Thomson Fold Belt high temperature metamorphic rocks of Neoproterozoic age (ca.580Ma) was reported (Fergusson et al., 1998). Eclogite in the New England Fold Belt In 1970s, occurrence of eclogite in the serpentinite zone was reported by Shaw and Flood (1974) at Attunga, and Goridrvnnn Iiesenrcli (Goiidrvniin Nerrislel ter Section) V. 2, No. 2, p p . 291-293. 0 7 999 lriterrintionnl Associntioll for Gondrunnn l-k?senrcli, 1npnnrl