CAMBRIAN OROGENIC BELT IN EAST ANTARCTICA AND SRI-LANKA - IMPLICATIONS FOR GONDWANA ASSEMBLY

Ion microprobe U-Pb dating of zircons from the Lutzow-Holm Complex (LHC) and the Yamato-Belgica Complex (YBC), East Antarctica indicate high-grade regional metamorphism and associated folding of LHC occurred between 521 +/- 9 and 553 +/- 6 Ma. This shows, for the first time, the existence of a Cambrian orogenic belt within the East Antarctic Shield. Many zircons from the LHC contain cores that record inherited ages from approximately 2900 to approximately 1500 Ma. Components of approximately 1000 Ma zircon have been identified in three locations. This may indicate the maximum age of the deposition of LHC. One metasedimentary gneiss from the YBC records a well-defined age at about 600 Ma, whereas another yields a dispersion of ages interpreted as the result of varied radiogenic Pb loss in approximately 1000 Ma zircons at about 500-600 Ma. These gneisses have inherited ages of up to approximately 2500 Ma. Our work enables an improved fit to the once contiguous fragments of Gondwana. The Highland/Southwestern Complex (HSWC) of Sri Lanka has remarkable petrological similarities to the LHC. This is now supported by the identification of approximately 500 Ma metamorphic age for both complexes. The presence of approximately 500 and approximately 1000 Ma metamorphic ages for the Vijayan Complex and the Wanni Complex of Sri Lanka correlate respectively with the YBC and the Rayner Complex, Antarctica. Moreover, integrating the recent geochronological and petrological data from Sri Lanka enable us to reinterpret the deep crustal evolution of Sri Lankan complexes defined on the basis of the Sm-Nd model age mapping. Once contiguous, LHC in East Antarctica and HSWC of Sri Lanka developed in the suture zone at the very last phase of Gondwana construction during the Pan-African orogeny. We contend this implies that the Late Proterozoic supercontinent was separated by a missing ocean at the position of the LHC, and that this might continue to the ''Mozambique Ocean'' through Sri Lanka and the southernmost tip of India.