Search results for "Andalusite"

Time-scale of deformation and intertectonic phases revealed by P-T-D-t relationships in the orogenic middle crust of the Orlica-Śnieżnik Dome, Polish…

2014

A section of the orogenic middle crust (Orlica-nienik Dome, Polish/Czech Central Sudetes) was examined to constrain the duration and significance of deformation (D) and intertectonic (I) phases. In the studied metasedimentary synform, three deformation events produced an initial subhorizontal foliation S1 (D-1), a subsequent subvertical foliation S2 (D-2) and a late subhorizontal axial planar cleavage S3 (D-3). The synform was intruded by pre-, syn- and post-D-2 granitoid sheets. Crystallization-deformation relationships in mica schist samples document I1-2 garnet-staurolite growth, syn-D-2 staurolite breakdown to garnet-biotite-sillimanite/andalusite, I2-3 cordierite blastesis and late-D-3…

Experimental study on the solubility of the “model”-pelite mineral assemblage albite + K-feldspar + andalusite + quartz in supercritical chloride-ric…

2001

A total of 34 solubility experiments using the “model”-pelite mineral assemblage microcline + low albite + andalusite + quartz were performed at 600°C and 0.2 GPa over a total chloride range of 0.03–2.9 molal. The concentrations of sodium, potassium, aluminum, and silica were measured and the results are compared with four different thermodynamic datasets. The K/Na ratio was approached from below and above for the thermodynamically buffered mineral assemblage microcline + low albite + andalusite + quartz. Tight brackets were obtained for experiments performed in up to 1 molal chloride concentration. From 0.03 to ∼1 molal chloride concentration, a constant K/Na ratio of 0.33 was obtained. At…

Structure and polarized absorption spectra of Mn3+-substituted andalusites (viridines)

1977

The state of iron in andalusite

1990

Iron in andalusite (Al2SiO5) with concentrations of 1.5 … 4.3 wt-% has been reported in the literature to occupy mainly Al1 sites as Fe3+, and only small portions occupy Al2 sites as Fe3+ and Fe2+. In no case a magnetic hyperfine splitting has been found at temperatures above 77 K.

Solubility of the assemblage albite+K-feldspar+andalusite+quartz in supercritical aqueous chloride solutions at 650 °C and 2 kbar

2003

Abstract The solubility of the high grade pelite assemblage albite+K-feldspar+andalusite+quartz at 650 °C and 2 kbar was determined in aqueous solutions over a total chloride range of 0.01–3 mCltot using rapid-quench hydrothermal technique. The concentration of Na, K, Si, and Al was determined in the fluid phase after quench. The K/Na ratio was determined by approaching the equilibrium from below and above. It is 0.34 at low chloride concentrations and decreases slightly to 0.31 with increasing total chloride. Silica and aluminum concentrations were determined only from undersaturation. The silica solubility is found to be independent of chloride concentration and is ∼0.13 molal. Aluminum i…

Clockwise, low- metamorphism of the Aus granulite terrain, southern Namibia, during the Mesoproterozoic Namaqua Orogeny

2013

Abstract The Aus granulite terrain forms part of the Mesoproterozoic Namaqua Metamorphic Complex (NMC) of southern Africa. The terrain consists of pre- to syn-tectonic granitoid gneisses containing subordinate aluminous metasediments, metapsammites, mafic granulite and calc-silicate, all of which have been metamorphosed and migmatised to varying degrees. Pseudosection modelling of garnet–sillimanite–cordierite–biotite aluminous metapelitic samples constrain peak metamorphic conditions at 5.5 kbar and 825  ° C. Pseudomorphs of sillimanite after andalusite constrain early prograde conditions of ∼ 550–600  ° C at below 4 kbar, whereas the replacement of sillimanite by garnet–cordierite and sub…

Metastable staurolite-cordierite asemblage of the Bossòst dome: Late variscan decompression and polyphase metamorphism in the Axial Zone of the centr…

2004

Abstract A kilometre-scale shear zone is recognized in the Cambro–Ordovician schist of the Bossost dome, a Variscan metamorphic and structural dome in the Axial Zone of the central Pyrenees. Non-coaxial deformation is recorded by rotated garnet and staurolite porphyroblasts following regional metamorphism M 1 , while coaxial conditions prevailed during later contact metamorphic M 2 growth of andalusite and cordierite. Mineral compositions and bulk rock analyses show that garnet–staurolite–andalusite–cordierite assemblages are significantly enriched in Mg and Mn over the garnet–staurolite assemblage, which lacks sufficient Mg for cordierite to form. The garnet–staurolite assemblage preserves…