Hydrothermal experiment was carried out reacting vermiculite with K- and Si-bearing solutions in a Teflon vessel at 150°C for 14, 51, and 71 days to demonstrate biotitization of vermiculite. Our results revealed that biotite is formed within 71 days. High-resolution transmission microscopy and energy dispersive X-ray spectrometry showed that biotite is formed by precipitation directly from solution, domain formation in vermiculite, layer-by-layer transformation of vermiculite, or combination of the three. Our results clearly indicate that biotitization of vermiculite occurs under hydrothermal condition when K is available. Our study suggests that vermiculite formed during weathering is altered progressively to biotite by diagenesis as well as metamorphism after burial.
2.7 Ga shoshonites occur in the Upper Keewatin Assemblage of the Shoal Lake-Lake of the Woods area in the northwestern part of the late Archean Wabigoon Belt, Superior Province, Canada. They are enriched both in large-ion lithophile elements (K, Rb, Sr, Ba and Th) and compatible elements (Mg, Ni and Cr). Their incompatible element abundance patterns exhibit a negative Ta anomaly and high La/Yb and Sr/Y ratios, similar to adakitic volcanic rocks in the same area. We suggest that the shoshonite magmas were formed by partial melting of a mantle source enriched by contemporaneous adakitic magmas derived by melting of subducted oceanic crust. We further speculate on the origin of Timiskaming alkaline volcanic rocks, located 1100 km to the east in the Abitibi Greenstone Belt, Superior Province, the archetypal example of late Archean alkaline magmatism. It seems probable that the mantle sources of Timiskaming alkaline rocks also were metasomatized by adakitic magmas, but that this source enrichment occurred 20-30 m.y. prior to the Timiskaming magmatism.
Photoluminescence (PL) properties of halite from Salton Sea, California, USA, are investigated at 10, 80, and 295 K. The color of clear part of this halite is transparent under daylight, and the fluorescence under UV light at 253.7 nm is orange-red. The orange-red emission band at 640 nm is assigned to the electronic transitions within the 3d5 configuration of Mn2+ in halite (NaCl). The excitation spectrum of the orange-red fluorescence consists of unefficient excitation bands due to Mn2+ and efficient excitation bands due to Pb2+. The existence of the Pb2+ bands in the excitation spectrum of the Mn2+ fluorescence suggests that there is an excitation process due to the energy transfer with the resonance type from Pb2+ to Mn2+. Thermal quenching of the specimen is undertaken, and it is clarified that the clusters of the Pb2+-vacancy pairs play an important part in the orange-red fluorescence from the halite. Analysis by inductively coupled plasma-mass spectrometry (ICP-MS) reveals that this halite includes Mn (98 μg/g) and Pb (640 μg/g).
Synthesis of minerals and the phase equilibrium relations in the systems MgO-B2O3 and MgO-B2O3-H2O were studied. A new result shows that the phase MgO·B2O3 is absent at 930°C in air and the phase assemblage 2MgO·B2O3 + MgO·2B2O3 is stable in stead of the 1:1 compound. Hydrothermal experiments showed that among 13 known ternary phases, only two, 2MgO·B2O3·H2O (szaibelyite) and 2MgO·6B2O3·15H2O (mcallisterite), exist at 300°C and 400°C under 100 MPa. The possible phase diagram of the system MgO-B2O3-H2O at 400°C and 100 MPa is proposed.