Mathematics – Logic
Scientific paper
Jul 1993
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1993gecoa..57.3421k&link_type=abstract
Geochimica et Cosmochimica Acta, vol. 57, Issue 14, pp.3421-3426
Mathematics
Logic
5
Scientific paper
Oxygen-isotope equilibration temperatures of coexisting quartz, muscovite, illite, chlorite, and biotite from a variety of geologic environments have been used in conjunction with the 18 O and D values of associated tourmaline to formulate empirical quartz-tourmaline and tourmaline-water isotope fractionation factors over temperatures from 200 to 600°C. The fractionation factors determined using this method are as follows: 1. (1) 1000 In ( quartz tourmaline ) = 1.0 ± 0.17 (10 6 / T 2 ) + 0.39 ± 0.44 (oxygen); 2. (2) 1000 In ( tourmaline - water ) = -27.2 ± 4.4 (10 6 / T 2 ) + 28.1 ± 9.8 (hydrogen; 350-600°C). The isotopic properties of tourmaline are nearly identical to those of muscovite and illite, despite the significant differences in their crystal structures. Similarities in the oxygen- and hydrogen-isotope systematics of tourmalines and micas imply that the dominant controls on the isotopic properties of these minerals are the vibrational energies of the Al-Si-O and Si-O bonds. However, the BO 3 groups in the tourmalines may have some effect on oxygen isotopic properties as there are minor differences between the 18 O values of coexisting tourmalines and micas. D values of coexisting tourmalines and micas are generally concordant to within 10 . Chemical compositions indicate that varying Fe/Mg ratios in the tourmalines appear to have only a minor control on their D values. There is a discontinuity in the 1000 In (tourmaline-water) values for hydrogen at temperatures between 200°C and 300°C, suggesting that the hydroxl groups in tourmaline are affected by hydrogen bonding and changes in the properties of water near its critical point, as are some other hydrous minerals.
Kerrich Rob
King Robert W.
Kotzer T. G.
Kyser Kurt T.
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