Cambrian Orogenic Belt in East Antarctica and Sri Lanka: Implications for Gondwana Assembly: A Discussion

The paper by Shiraishi et al. (1994) provided evidence for a Pan-African event in Lutzow-Holm Bay (LHB) of East Antarctica but dismisses evidence that the Pan-African event overprints rocks with a long prior history of tectonothermal activity in both LHB and adjoining areas; thus the conclusion that LHB lies in a Pan-African suture between exotic blocks may be erroneous. 1) Shiraishi et al. (1994, p. 57) state that "extensive petrological study has not elucidated a polymetamorphic history in the Lutzow-Holm Complex." However, amphibolite-facies metamorphism overprinting an earlier granulite facies event has been well characterized (e.g., Yoshida 1994 and references therein). For example, alteration of anhydrous minerals such as orthopyroxene by hydrous minerals such as amphibole or biotite has been widely recognized, and clear structural evidence of superposition of later upright fold over the major fold which resulted in the development of inclined mineral lineation and schistosity from hinges and axial surface of the major fold has been documented. Earlier and later folds in the Prince Olav Coast, and first (fl), second (f2) and third (f3) folds in the LHB area have been recognized. Shiraishi et al. (1994, p. 49) hold that "the D1 folds [referred to as the earlier folds in the Prince Olav Coast and fl folds in LHB] are contemporaneous with the main metamorphism, since mineral lineations are parallel to the D1 axes," in support of their scheme of monometamorphic history. Their view on the relationship of D1 folds and the main metamorphism is based totally on a few observations in the Prince Olav Coast, which are neither supplemented by detailed structural elements, nor strengthened by structural comparison of folds and lineations in the