ZIRCON AGE LINKS BETWEEN PROTEROZOIC LAURENTIA AND EAST ANTARCTICA: COMPARISON OF ~1.7 AND ~1.4 GA SIGNATURES

Paleogeographic models of Rodinia commonly link western Laurentia with eastern Australia and East Antarctica, yet the precise fit and breakup age(s) are highly debated. Zircon U-Pb ages from the East Antarctic shield and adjacent Neoproterozoic to Ordovician sediments support the general Rodinia model, and they highlight similarity between the central Ross margin of Antarctica and southwest Laurentia. Gneissic East Antarctic shield rocks preserve evidence of deep-crustal metamorphism, eclogite formation, and magmatism between ~1730-1720 Ma. This ~1.7 Ga record of crustal thickening is similar in age to deep-seated events in the Mojave province of eastern California and Arizona. Although ~1.7 Ga events are well-known from East Antarctica and Australia, the shared deep-crustal signature overprinted on Archean protoliths suggests that a collisional belt of this age transected the Antarctic-Laurentian region of Rodinia. Siliciclastic rocks of Neoproterozoic to early Paleozoic age along the Ross margin include narrow rift-margin deposits (ca. 1000-650 Ma) and a widely-distributed succession of younger (ca. 515-475 Ma) syn- to post-orogenic molasse deposits. Offshore transport to the east is inferred for both assemblages based on paleoslope and paleocurrent indicators, depositional facies geometry, and populations of Precambrian detrital zircons. Detrital populations in both assemblages, however, show persistent first-cycle ~1.4 Ga igneous zircon, suggesting erosion of a Mesoproterozoic magmatic province like the trans-Laurentian granite belt. We know of no cratonic sources for detritus of this age in present-day Antarctica or Australia. Because East Antarctica and Laurentia were widely separated by Cambrian time, a direct source in Laurentia for ~1.4 Ga components in the outboard deposits is unlikely. Allowing for longshore drift, a western source can be explained if the trans-Laurentian granite province extends into East Antarctica, but is now ice-covered. Age components of 1.8-1.6 Ga, predicted by extension of Mojave-Yavapai-Mazatzal crust into East Antarctica, are also abundant in the detrital populations. The ~1.7 and ~1.4 Ga signatures, unlike ubiquitous Grenville-age belts, may thus provide unique geologic ties between East Antarctica and Laurentia in the Rodinian supercontinent.