Monazite and zircon dating by the chemical Th-U-total Pb isochron method (CHIME) from Alasheyev Bight to the Sor Rondane Mountains, East Antarctica: A reconnaissance study of the Mozambique suture in Eastern Queen Maud land

Ages based on electron microprobe analysis using the chemical Th-U-total Pb isochron method ( CHIME) were determined for monazite and zircon in 12 granulite-facies paragneiss samples from four exposures on or near the coast of East Antarctica: Mt. Vechernyaya (Alasheyev Bight; 46degreesE, Rayner Complex), East Ongul Island (39degrees35' E, Lutzow-Holm Complex), the southernmost Yamato Mountains (36degreesE, Yamato-Belgica Complex), and the Sor Rondane Mountains (23degrees-28degrees E). Monazite occurs in textural equilibrium with silicate minerals in all samples and as inclusions in garnet in three of these and is presumed to have crystallized under granulite-facies conditions. Most of the analyzed monazite grains appear to be chronologically homogeneous, but many others are markedly zoned. The CHIME ages on rims of the latter range from 514 +/- 27 to 553 +/- 11 Ma, consistent with ages on the apparently homogeneous grains, 517 +/- 14 to 544 +/- 5 Ma. Apparent ages on cores of the zoned grains range from 620 to 760 Ma, and in a few cases, CHIME ages can be extracted, the youngest of which are 628 +/- 32 and 622 +/- 11 Ma. Ages obtained on the rims of zircons texturally coexisting with monazite range from 485 +/- 58 to 530 +/- 17 Ma, whereas ages of the cores show bimodal distribution with peaks at about 730 and 1100 Ma. The CHIME ages clustering around similar to530 Ma are interpreted to date the granulite-facies events in the four study areas, an interpretation supported by SHRIMP data on zircon from these areas. The Neoproterozoic ages on monazite cores suggest the intriguing possibility that the area between 45degrees E (west of Alasheyev Bight) and 25degrees E (within the Sor Rondane Mountains) constitutes a Cambrian monometamorphic belt in which sediments were deposited during the Neoproterozoic or early Cambrian with much less involvement of older rocks; i.e., the Mozambique suture could pass between 45degrees E and 25degrees E.