PALEOMAGNETIC DATA AND U-PB ISOTOPIC AGE-DETERMINATIONS FROM COATS-LAND, ANTARCTICA - IMPLICATIONS FOR LATE PROTEROZOIC PLATE RECONSTRUCTIONS

Paleomagnetic results and isotopic age determinations for granophyre a nd rhyolite from small, isolated nunataks in southern Coats Land, Anta rctica, are used to evaluate late Proterozoic plate reconstructions. U -Pb zircon dates for the two rock types indicate coeval crystallizatio n at 1112 +/- 4 Ma. A concordant 1106 +/- 3 Ma titanite date from the granophyre overlaps the crystallization age, implying rapid cooling, a nd is consistent with field and petrographic evidence of no subsequent penetrative deformation, metamorphism, or hydrothermal disturbance. T he mean direction of magnetization of the rhyolite at Littlewood Nunat aks is statistically indistinguishable from the mean directions of fiv e sites in the granophyre and crosscutting rhyolite dikes at Bertrab N unataks. The group mean virtual geomagnetic pole of 22.9 degrees N, 80 .3 degrees E (N=6, A(95)=6.8 degrees) compares favorably with the only other extant Precambrian paleomagnetic poles for the East Antarctic c raton, two poles from western Dronning Maud Land. The East Antarctic a nd Laurentian poles of 1.1 Ga do not coincide after restoration of the continents to a position suggested by the SWEAT hypothesis juxtaposin g the Pacific margins of East Antarctica-Australia and Laurentia, indi cating either that the hypothesis is incorrect or that Coats Land and parts of western Dronning Maud Land (herein the CMG province) were not part of the East Antarctic craton at 1.1 Ga. In support of the latter , there is reasonable agreement of the 1.1 Ga CMG poles and approximat ely coeval poles from the Kalahari craton of West Gondwana when the CM G is restored to a position adjacent the Kalahari craton. Such a recon struction places the CMG in West Gondwana rather than East Gondwana, a s originally implied in Rodinia reconstructions, and is consistent wit h previously recognized links between the geology of the Kalahari crat on and western Dronning Maud Land. It further implies that the CMG did not become part of East Antarctica until latest Precambrian to Cambri an time. A new reconstruction places a partially assembled West Gondwa na off the present southeastern margin of Laurentia at 1.1 Ga such tha t poles of the CMG and Kalahari fall on the Laurentian polar wander pa th for this time period.