Halpin et al. investigate rock fragments dredged from escarpments on the Indian Ocean floor off southwestern Australia and find evidence that a large submarine mountain range, the Naturaliste Plateau, is a fragment of an older supercontinent called Rodinia. This piece of crust formed over a billion years ago and is probably related to similarly aged rocks now exposed in parts of East Antarctica and southwestern Australia; it was then deformed when India collided with Australia and Antarctica to form the supercontinent Gondwana during Cambrian time (around 520 million years ago). This slice of crust, currently the Naturaliste Plateau, was exhumed to Earth's surface and left stranded underwater between India and Australia when Gondwana broke apart during Cretaceous time (around 83 million years ago). Evidence for all of these colossal events can be found preserved in tiny crystals from rocks dredged off the seabed, where they have been resting since the time of the dinosaurs.
Modeling of gold scavenging by bismuth melts coexisting with hydrothermal fluids
Blake Tooth et al., Geology and Geophysics, School of Earth and Environmental Sciences, The University of Adelaide, North Terrace, Adelaide 5005, Australia. Pages 815-818.
Native bismuth is molten down to 271 degrees Celsius, and polymetallic melts can occur at even lower temperatures if bismuth is combined with elements such as gold or tellurium. Such metallic melts are observed in many magmatic-hydrothermal gold deposits. Tooth et al. illustrate the importance of this additional liquid phase during ore deposit formation by presenting equilibrium thermodynamic modeling of a coexisting aqueous fluid and a bismuth-rich melt. The model's predictions match observations in a modern seafloor volcanogenic massive-sulphide (VMS) deposit (Escanaba Tough, Sou
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Geological Society of America