Mica history

A popular method used to date rocks is the potassium-argon method. Potassium is abundant in rocks such as feldspars, hornblendes, and micas. The K-Ar method has been used to date the Earth and its geologic formations. It has also been applied to determine magnetic reversals that have taken place throughout the Earth s history. Another method used in geologic dating is the rubidium-strontium, Rb-Sr, method. Some of the oldest rocks on Earth have been dated with this method, providing evidence that the Earth is approximately 5 billion years old. The method has also been used to date moon rocks and meteorites. 

With the advent of stable isotope paleoaltimetry towards the turn of the millennium the stable isotope and tectonics communities have witnessed an increasing number of isotopic mineral proxies developed to address the long-term topographic histories of orogenic belts and continental plateaus. These proxies include calcite from paleosols (see for example Quade et al. 2007, this volume and references therein), fluvial and lacustrine rocks the phosphate and carbonate component of mammal teeth (Kohn and Dettman 2007, this volume and references therein), smectite and kaolinite from paleosols, weathered sediments and volcanic ashes (e.g., Chamberlain et al. 1999 Takeuchi and Larson 2005 Mulch et al. 2006a) as well as white mica from extensional shear zones and fluid inclusions in hydrothermal veins (e.g., Mulch et al. 

The long time scales (104 to 10s m.y.) involved in deformation and synkinematic isotope exchange in white mica provide a robust, long-term average of meteoric water-rock interaction, characteristic for the time scales of major readjustments in surface elevation. Thus the hydrogen isotope record in recrystallized muscovite provides a direct link between the tectonic and fluid flow history in the shear zone and temporal variations in meteoric water composition due to changing surface elevation. 

It is worth noting that, if the chitosan-mica system that has experienced the history of step-wise increasing pH is returned to pH 3.8 and the forces are remeasured, then it is found that the forces are very similar to those originally observed at this pH value (Fig. 11). Hence, it is concluded that only very few chitosan molecules may have desorbed and the layer is pratically intact. This is very important since it points to the possibility of using chitosan for surface coating and modification in a broad range of environmental conditions. 

Reddy S. M., Kelley S. P., and Wheeler J. (1996) A AtP At laser probe study of micas from the Sesia zone, Italian Alps implications for metamorphic and deformational histories. J. Metamorph. Geol. 14, 493-508. 

Stuart F. M. (2002) The exhumation history of orogenic belts from Ar/ Ar ages of detrital micas. Min. Mag. 66, 121-135. 

Wagner G. A., Reimer G. M., and Jager E. (1977) Cooling ages derived by apatite fission track, mica Rb-Sr, and K-Ar dating the uplift and cooling history of the Central Alps. Mem. Univ. Padova 30, 1-27. 

Hiyagon, H., Ozima, M., Marty, B., Zashu, S. Sakai, H. 1992. Noble gases in submarine glasses from mid-oceanic ridge and Loihi Seamount constraints on early history of the Earth. Geochi-mica et Cosmochimica Acta, 56, 1301-1316. 

C) Plasma-treatment variables In all of the above comparisons, the various mica samples had been exposed to plasmas under arbitrarily selected, constant conditions of monomer pressure, plasma duration and applied power. It is very probable (2, that these variables and possibly others, such as reactor geometry and post-treatment history, may influence strongly the magnitude of surface modification effects attained by the present route. For this reason the performance modifications of polymer composites will also depend on the exact selection of treatment variables. 

An English translation of Cronstedfs book (1788) contained the same list of species and varieties cited previously, but also reported the chemical analysis of Kirwan as well as an observation by Fabroni, deputy-director of the Museum of Physics and Natural History of Florence. Fabroni observed that colored mica was dissolved by acqua regia or muriatic acid to produce a liquid that is yellow on account of iron. 

Another growing field of work has been dating detrital minerals in sediments as a provenance tool, but also in order to study the sedimentary systems supplying basins and uplift or thermal history of the source. Clauer (1981) and Adams and Kelley (1998) have shown that while biotite is often quickly altered in the sedimentary environment, white micas survive and retain ages even in second cycle sediments (those which were originally deposited and then re-excavated during later basin inversions e.g., Sherlock... 

Reddy SM, Kelley SP, Wheeler J (1996) A " °Ar/ Ar laser probe study of micas from the Sesia Zone, Italian Alps Implications for metamorphic and deformation histories. J Metamorph Geol 14 493-508 Reddy SM, Kelley SP, Magennis L (1997) A microstractural and argon laserprobe study of shear zone development at the western margin of the Nanga Paibat-Haramosh Massif, western Himalaya. Contrib Mineral Petrol 128 16-29... 

When a nematic is put in contact with a crystalline substrate, tbe surface of wbicb possesses the A-fold rotational symmetry (e.g., IV = 6 for mica, A7 = 4 for NaCl), the director is free to choose any of those N easy axes. In experiments, the orientation depends on the pre-history of the sample. A director field n(r) in a nematic drop put on the surface of a crystal acquires the same N-fold symmetry. In a sandwich cell, when crystalline axes of the opposite interfaces coincide, different domains are observed, with uniform structure or twisted through an angle 2k/N [20]. Using a properly oriented external in-plane field one can switch domains from one of the possible N orientations to another. Thus we have multistable alignment. When the crystalline axes of the opposite interfaces do not coincide, many domains with different twist angles are possible. 

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