Search

Recognition of Late Archean and Early Proterozoic tonalite-trondhjemite-granodiorite crust in the Mount Isa block, northwest Queensland, Australia, has important implications for Proterozoic crustal evolutionary models in the North Australian craton. Protoliths of the Black Angel Gneiss Complex formed 2.42-2.50 Ga (Black Angel Gneisses) and 1.97-2.00 Ga (Pothole Creek Gneisses). Both groups have Nd model ages of 2.42 to 2.58 Ga. Supracrustal components within the gneiss complex have Nd model ages of 2.75 to 2.83 Ga. These data, and inherited components in zircons, indicate the presence of even older Archean crust. Crystallization of 1.84-1.87 Ga rims record a thermal event during a subsequent period of granitic (Kalkadoon-Leichhardt) magmatism. Both the Black Angel Gneiss Complex and Kalkadoon-Leichhardt magmatic suite have strong arc geochemical signatures and have components that are compositionally similar to Archean tonalite-trondhjemite-granodiorite lithologies. A seismically defined, crustal-scale, west-dipping feature in the Mount Isa block may be a Proterozoic cryptic suture. Subduction-zone magmatism may be related to this feature. Late Archean and Early Proterozoic crust formation in this segment of the North Australian craton was subduction driven, involving assembly of microcontinental terranes similar to other Early Proterozoic belts. This observation is significant, because paleomagnetic data indicate that the North Australian craton and Laurentia were juxtaposed during Early to Middle Proterozoic time.

Mass spectrometric U-series dating of speleothems from Tangshan Cave, combined with ecological and paleoclimatic evidence, indicates that Nanjing Man, a typical Homo erectus morphologically correlated with Peking Man at Zhoukoudian, should be at least 580 k.y. old, or more likely lived during the glacial oxygen isotope stage 16 (~620 ka). Such an age estimate, which is ~270 ka older than previous electron spin resonance and alpha-counting U-series dates, has significant implications for the evolution of Asian H. erectus. Dentine and enamel samples from the coexisting fossil layer yield significantly younger apparent ages, that of the enamel sample being only less than one-fourth of the minimum age of Nanjing Man. This suggests that U uptake history is far more complex than existing models can handle. As a result, great care must be taken in the interpretation of electron spin resonance and U-series dates of fossil teeth. Keywords: H. erectus, U-series, TIMS, speleothem, tooth.