Understanding argon release mechanisms in K-bearing minerals is essential in interpreting the ArrAr data and their application to geological studies. The release mechanisms of argon in vacuo have been examined in a series of ArrAr Ž . Ž a. isothermal heating experiments on two biotite specimens with Fer FeqMg Fe s0.50 and 0.87 respectively. The crystal structure of the biotite was also monitore...

A comparison was made between single-crystal structure refinements, electron microprobe analyses and octahedral site populations of seven biotite crystals and data obtained previously for coexisting muscovite in peraluminous granites using the same methods. Both micas, from several plutons of Northern Victoria Land (Antarctica) and Sardinia (Italy), show significant octahedral substitutions: bi...

Mineral compositions and reaction textures found in migmatitic gneisses from near Gilsum, New Hampshire, constrain both peak metamorphic pressure (P) and temperature (T) conditions and the PT path. Large K-feldspar porphyroblasts indicate isobaric heating of the samples at P < 4 kb (Spear et al. 1999), and relict cordierite + garnet assemblages record the occurrence of biotite vapor-absent melt...

In the mountainous Rio Icacos watershed in northeastern Puerto Rico, quartz diorite bedrock weathers spheroidally, producing a 0.2–2 m thick zone of partially weathered rock layers ( 2.5 cm thickness each) called rindlets, which form concentric layers around corestones. Spheroidal fracturing has been modeled to occur when a weathering reaction with a positive DV of reaction builds up elastic st...

Temperature estimates obtained with various biotite-garnet thermometers are inconsistent in granulite facies rocks. Although the inconsistency lies partly in the lack of definition of equilibrium criteria, it still remains after rigorous selection of analyzed mineral pairs (isolated biotite and garnet cores for peak equilibrium conditions) and originate from minor element effects in garnet and ...

Dyella jiangningensis strain SBZ3-12 can weather biotite and release Al and Fe from biotite under nutrient-poor conditions. Here, we report the first complete genome sequence of D. jiangningensis strain SBZ3-12, which may facilitate a better understanding of the molecular mechanism behind mineral weathering.

Rocks from the Valhalla metamorphic core complex, British Columbia, Canada, have experienced granulite Jades metamorphism at conditions of 820±30°C, 8±1 kbar. Peak metamorphism was accompanied by dehydration melting of muscovite, but not biotite, followed by minor back reaction of garnet + K-feldspar + H20sillimanite + biotite+plagio close.' At conditions very near those of the peak, extensive ...

The TCG consists of a basal pebble-conglomerate with distinctive black chert clasts overlain by sandstones interlayered with white-purple volcanic ash. All lithologies have experience an episode of post-deposition silicification. Petrographic analysis reveals sandstones are compositionally mature with high abundances of quartz and minor amounts of feldspar and muscovite or biotite mica. Most gr...

-A vermiculite (Libby, Montana) sample obtained from the Zonolite company contained mostly coarse-grained separates with only 8.7 per cent clay. The 2-50 #m fraction was used for particle-size reduction studies by wet and dry grinding, and size-fractionated into < 2, 2-5, 5-20 and 20--50 #m sizes. About 18 per cent of the sample was attrited to clay after 64 hr of wet grinding, but as much as 5...

of Wallowa terrane crust, as the Blue Mountains terrane assemblage The Cornucopia stock, in the Blue Mountains of northeastern collided with the continental margin during Early Cretaceous time. Oregon, is a small composite intrusion comprising five distinct Results of this study suggest that deformation and crustal melting intrusive units: a hornblende biotite tonalite, a biotite trondhjemite, ...