Visualization of elastic strain fields by the spatial distribution of the blue luminescence in a twinned microcline crystal



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Sanchez Muñoz, L. and Correcher Delgado, Virgilio and Turrero Jiménez, María Jesús and Cremades Rodríguez, Ana Isabel and García Guinea, Javier (2006) Visualization of elastic strain fields by the spatial distribution of the blue luminescence in a twinned microcline crystal. Physics and Chemistry of Minerals, 33 (8 sep). pp. 639-650. ISSN 0342-1791

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This paper correlates the mineralogical characteristics of twinning and exsolutions of a microcline giant crystal with macroscopic twin-domains and perthitic texture, taken from the Golconda III granitic pegmatite ( Minas Gerais, Brazil), with the spatial distribution of the blue luminescence from radiation-induced O- defects. The twinning macrostructure and the Na distribution of the microcline have been studied by optical microscopy, backscattered electron scanning electron microscopy (SEM), chemical mapping and quantitative chemical analyses with electron microprobe. Spectra luminescence data were recorded by high sensitivity thermoluminescence, X-ray radioluminescence, cathodoluminescence ( CL) and also CL-imaging under optical microscope at room temperature, and under SEM at liquid nitrogen temperature. The crystal recorded three different stages of re-equilibration during the geological cooling: ( 1) building up of regular macrostructures, formed mainly by only two Albite-twin law orientation variants, by solid-state domain self-assembly; ( 2) coarsening of one orientation variant at the expenses of the other by dissolution - reprecipitation reactions and ( 3) later degradation of regular twins into irregular domains. The spatial distribution of the blue luminescence in microcline can be used for two practical applications: ( 1) to mark water-rich fluid-flow channelways at low temperatures in which these light emissions are absent and ( 2) to visualize elastic strain fields across twin patterns, with maxima emission from the Na-rich ( 0 1 0) boundaries and remnants Pericline twin cores and minima from the Na-poor ( 0 1 0) twin cores and residual Pericline boundaries. Elastic strain must be the physical factor determining the radiation sensitivity of the lattice, i.e. radiation damage is not random in twinned lattices and defect formation occurs preferentially at the sites with high local elastic strain. Environmental ionizing radiation could involve a twofold effect during subsolidus microcline re-equilibration, i.e. Si/Al re-ordering, mainly acting on coherent twin boundaries, and also producing reactive H center dot and OH center dot radicals as radiolytic products of water.

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© Springer-Verlag 2006.
Acknowledgments We are grateful to P.D. Townsend for the analyses in the high-sensitivity TL spectrometer of Sussex (UK), to M.L. Clarke for recording the 3D-plot TL measurements, to Olivier Rouer for the EMPA analyses and the X-ray map for
sodium. The experiment was supported by the C.I.C.Y.T. CGL2004-03564/BTE and Comunidad Autónoma de Madrid S-0505/MAT/0094 (MATERNAS) projects. The present study was benefited from discussion with Adrian Finch (University of St Andrews, UK) and Masanori Kurosawa (University of Tsukuba, Japan). Thanks are also due to Odulio José Marensi de Moura (Governador Valadares, Minas Gerais, Brazil) for the valuable help in sample collection in the Golconda III pegmatite in 1989.

Uncontrolled Keywords:Alkali Feldspars, Cathodoluminescence, Pegmatites, Rocks, Spectroscopy, Microscopy, Evolution, Emissions, Minerals, Centers
Subjects:Sciences > Physics > Materials
ID Code:23168
Deposited On:15 Oct 2013 18:15
Last Modified:09 May 2016 14:32

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