Melting temperature measurements of six minerals (stishovite (SiO2), corundum(Al2O3), diopside (CaMgSi2O6), and three perovskites (MgSiO3, CaSiO3, Mg3Al2Si3O12)) at high pressures were carried out in a YAG laser‐heated diamond anvil cell with rhenium metal as an absorber of the laser light. A polished or compressed disc of the sample was in contact with rhenium foil and heated by conduction. Melting was determined by plotting laser power/sample temperature function and looking for the thermal anomaly associated with the fusion of materials. All these solids were found to be highly refractory, requiring quite high temperatures for melting at the lower mantle pressures. The experimental melting results showed that for these minerals, melting temperatures increased with increasing pressure. Our results at low pressures are consistent with the data determined by other techniques (piston‐cylinder, multianvils). The high‐pressure melting of MgSiO3 perovskite agreed with the recent measurements by Zerr and Boehler (1993) within experimental uncertainties. Melting temperatures and melting slopes of CaSiO3 and Mg3Al2Si3O12 perovskites were found to be less than those of MgSiO3 perovskite, indicating that the presence of Ca and Al would decrease the melting temperatures of MgSiO3 perovskite in the Earth's lower mantle and that this effect will increase with increasing pressures. Melting temperature measurements on stishovite and corundum to pressures of 36 GPa and 25 GPa, respectively, are reported.
We have after half a century of coordinated scientific drilling gained insight into Earth´s largest microbial habitat, the subseafloor igneous crust, but still lack substantial understanding regarding its abundance, diversity and ecology. Here we describe a fossilized microbial consortium of prokaryotes and fungi at the basalt-zeolite interface of fractured subseafloor basalts from a depth of 240 m below seafloor (mbsf). The microbial consortium and its relationship with the surrounding physical environment are revealed by synchrotron-based X-ray tomographic microscopy (SRXTM), environmental scanning electron microscopy (ESEM), and Raman spectroscopy. The base of the consortium is represented by microstromatolites—remains of bacterial communities that oxidized reduced iron directly from the basalt. The microstromatolites and the surrounding basalt were overlaid by fungal cells and hyphae. The consortium was overgrown by hydrothermally formed zeolites but remained alive and active during this event. After its formation, fungal hyphae bored in the zeolite, producing millimetre-long tunnels through the mineral substrate. The dissolution could either serve to extract metals like Ca, Na and K essential for fungal growth and metabolism, or be a response to environmental stress owing to the mineral overgrowth. Our results show how microbial life may be maintained in a nutrient-poor and extreme environment by close ecological interplay and reveal an effective strategy for nutrient extraction from minerals. The prokaryotic portion of the consortium served as a carbon source for the eukaryotic portion. Such an approach may be a prerequisite for prokaryotic-eukaryotic colonisation of, and persistence in, subseafloor igneous crust.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.