Early to middle Proterozoic dykes in the Mt. Riiser-Larsen area of the Napier Complex, East Antarctica: tectonic implications as deduced from geochemical studies
Satoko Suzuki, Hideo Ishizuka, Hiroo Kagami, 2008. "Early to middle Proterozoic dykes in the Mt. Riiser-Larsen area of the Napier Complex, East Antarctica: tectonic implications as deduced from geochemical studies", Geodynamic Evolution of East Antarctica: A Key to the East–West Gondwana Connection, M. Satish-Kumar, Y. Motoyoshi, Y. Osanai, Y. Hiroi, K. Shiraishi
Download citation file:
NE–SW- and north–south-striking dykes were emplaced into ultrahigh-temperature (UHT) granulites apparently after UHT metamorphism in the Mt. Riiser-Larsen area of the Archaean Napier Complex, East Antarctica, of which the north–south-striking dykes interrupt the NE–SW-striking ones. The NE–SW-striking dykes are tholeiite basalt (THB) and high-magnesian andesite (HMA) in composition. The THB dykes display relict doleritic textures, whereas the HMA dykes shows blastoporphyritic textures characterized by phenocrysts of clinopyroxene and plagioclase. Both sets of dykes exhibit large ion lithophile element and light rare earth element enrichment and negative anomalies of Nb, Ti and/or P in a spider diagram normalized to primitive mantle, which is reminiscent of modern subduction-related arc volcanism or continental flood volcanism. The isotope ratios of the THB dykes define isochron ages of 2.0–1.9 Ga: 1979±80 Ma in the Rb–Sr system (initial ratio (I0): 0.70239±0.00035) and 2078±104 Ma in the Sm–Nd system (I0: 0.50964±0.00012). Such moderate 87Sr/86Sr and low 143Nd/144Nd initial ratios may represent source materials closely related to the mantle wedge of a subduction zone. The north–south-striking dykes are compositionally divided into two basalt types. One is an alkaline basalt (AL) showing intergranular texture and characterized by high concentrations of incompatible elements, similar to those of ocean island basalt. They yield an isochron age of c. 1.2 Ga: 1161±238 Ma in the Rb–Sr system (I0: 0.7047±0.0012). The other type (THB-m) is doleritic (ophitic) in texture, and has a tholeiitic affinity with a flat chondrite-normalized REE pattern, which is comparable with that of enriched mid-ocean ridge basalt. A comparison with dykes reported from other areas of the Napier Complex suggests that the north–south-striking dykes occur in restricted areas, whereas the NE–SW-striking dykes are more regional in occurrence. The 2.0–1.9 Ga magmatism of the NE–SW-striking dykes may have been related to the formation of continental crust of the Rayner Complex.
Figures & Tables
Geodynamic Evolution of East Antarctica: A Key to the East–West Gondwana Connection
Geological correlations of East Antarctica with adjoining continents have been puzzling geologists ever since the concept of a Gondwana supercontinent surfaced. Despite the paucity of outcrops because of ice cover, difficulty of access and extreme weather, the past 50 years of Japanese Antarctic Research Expeditions (JARE) has successfully revealed vital elements of the geology of East Antarctica. This volume presents reviews and new research from localities across East Antarctica, especially from Dronning Maud Land to Enderby Land, where the geological record preserves a history that spans the Archaean and Proterozoic. The reviews include extensive bibliographies of results obtained by geologists who participated in the JARE. Comprehensive geological, petrological and geochemical studies, form a platform for future research on the formation and dispersion of Rodinia in the Mesoproterozoic and subsequent assembly of Gondwana in the Neoproterozoic to Early Palaeozoic.