In thin section tourmaline (0.5-1 mm) exhibits olive green to tan pleochroism and is zoned with blue-green cores. Sillimanite needles in lenses within the tourmaline matrix were deformed by an earlier zonal crenulation cleavage. Deformation took place after peak metamorphism, and at least two...
US $15.56 US $31.43 Sillimanite Chemical Formula Al2SiO5 Species Silicates Crystal System Orthorhombic Mohs Scale 6-7 Specific Gravity 3.24 Color Colorless or white to gray, also brown, yellow, yellow-green, gray-green, blue-green, blue; colorless in thin section ...
It is natural, therefore, that a geologist will endeavour to have the largest garnets exposed within the thin section area, as these have best chance of preserving early prograde history in high-grade rocks; but what if garnet is only a minor constituent and comprises <1 vol.% of the ...
Mineral modes wereestimated from thin sections (e.g., Table 1), X-ray mapping, andimage analyses. Relative diffusion coefficients were taken fromFoster (1981), with the exception of those for B and SiO2, whichare estimated in this study.The above observations and analyses suggest that the...
Section snippets The Tandilia belt This belt (Fig. 1a) is the southernmost exposure of a 2.2 - 2.0 Ga old orogen, which extends to Uruguay (Piedra Alta Terrane) to form a considerable part of the Rio de la Plata craton (e.g. Oyhantçabal et al., 2011; Rapela et al., 2011),...
The expected volume of rutile in kyanite created by replacing biotite is 3%, comparable to the ~5% seen in thin section and supporting replacement of biotite by kyanite and rutile: Bt = Ky + Ru (DeltaVrxn= -68%). Similarly, biotite interfingered with sillimanite and ilmenite suggests a ...
Magnetic modeling results suggest a consistent average magnetization direction before and after demagnetization at both the grain and thin section scale, with a decrease in the magnetization intensity of ≈30%. Results are consistent with previous bulk magnetic measurements and the likelihood to use ...