Field occurrence, geochemistry and petrogenesis of the Archean Mid-Oceanic Ridge Basalts (AMORBs) of the Cleaverville area, Pilbara Craton, Western Australia

The geochemistry and petrogenesis of the Paleoproterozoic du Chef dyke swarm, Québec, Canada

“…Again, using a simplistic, linear cooling model between 1480 °C at 3.8 Ga and 1350 °C today, the temperature of the upper mantle at 2.46 Ga can be estimated at 1432 °C. These three estimates of upper mantle temperature at ~2.4 Ga using the work of Ohta et al (1996), Galer and Mezger (1998) and Komiya et al (2004) are all significantly lower than the T P recorded by sample DC011 (180 °C, 135 °C and 145 °C respectively). This reinforces the evidence presented by Fig.…”

“…In summary, secular cooling models of the Earth's mantle suggest that the du Chef dykes originated from anomalously hot early-Proterozoic mantle according to the models of Davies (2009) and Richter (1988) as well as other estimates derived from studies of Archaean mantle rocks (Ohta et al 1996;Galer and Mezger 1998;Komiya et al 2004). This evidence, along with consistent trace element geochemistry suggests that the du Chef dykes are be the product of mantle plume-driven magmatism as proposed by Buchan (2004) andSöderlund et al (2010).…”

“…10 is beyond the scope of this study. However, the model of Other studies have estimated the temperature of the upper mantle at various points during the Archaean (Ohta et al 1996;Galer and Mezger 1998;Komiya et al 2004). Galer and Mezger (1998) examined the regional metamorphic grade of ten undisturbed Archaean granitegreenstone segments and showed that metamorphic facies exposed at the surface today are indicative of burial pressures of ~1.5 kbar.…”

“…Using a linear cooling rate of 30 °C Gy -1 (which is comparable to estimates of the present day cooling rate of the Earth), the temperature of the upper mantle at 2.4 Ga can be estimated as 1422 °C. Ohta et al (1996) used the geochemistry of Archaean MORB rocks preserved in a 3.1-3.3 Ga accretionary complex in Pilbara, Western Australia to constrain the ambient temperature of the upper mantle at 3.1-3.3 Ga to be 1400 °C. Using this temperature of 1400 °C as an estimate for T P at 3.2 Ga and a simplistic, linear cooling modelling between 1400 °C at 3.2…”

Experimental Hydrogen Production in Hydrothermal and Fault Systems: Significance for Habitability of Subseafloor H2 Chemoautotroph Microbial Ecosystems

“…On this basis, it has been hypothesized that hydrothermal fluids with H 2 , sufficiently abundant to sustain methanogens, existed in the early Earth (Takai et al 2006). In contrast to the modern ocean, in the Hadean and early Archean ocean, peridotite was probably scarce beneath the crust of the ocean floor, because at that time the oceanic crust may have been two to three times the thickness of the modern oceanic crust (Ohta et al 1996;Moores 2002;Takai et al 2006). In this tectonic setting, komatiite, a distinctive ultramafic volcanic rock, was most likely the main component of ultramafic rocks on the floor of Hadean and Archean oceans.…”