NEW IMPROVED EQUATIONS FOR NA K, NA/LI AND SIO2 GEOTHERMOMETERS BY OUTLIER DETECTION AND REJECTION/

We present new improved equations for three still widely used Na/K, Na /Li and SiO2 geothermometers (obtained by statistical treatment of the data and application of outlier detection and rejection as well as th eory of error propagation) and compare them with those by Fournier and others. New equations are also developed for estimating errors associ ated with the use of these new geothermometric equations and comparing them with the performance of the original equations. The errors in th e use of the new Na/K equation for temperatures ranging from 80 to 350 degrees C vary from about 19 to 34%, which is lower than the correspo nding errors (24-43%) for the original Fournier equation. Similarly, f or temperatures ranging from about 50 to 320 degrees C, our new equati on for Na/Li geothermometer for Cl < 0.3 m shows errors of about 13-34 % as compared to 15-39% for the original equation, and for Cl greater than or equal to 0.3 m, from 10 to 44%, much lower than 26-106% estima ted for the corresponding original equation. Finally, for temperatures ranging from 20 to 210 degrees C our results show that the total prop agated errors of the new geothermometric equation for SiO2 < 295 ppm a re about 1-9%, smaller than 3-12% for the original SiO2 geothermometer . We have proposed a linear equation for the temperature range of 210 to 310 degrees C (SiO2 greater than or equal to 295 ppm), which shows considerably smaller total propagated errors (2-3%) than for the origi nal equation (5-29%). (C) 1997 Elsevier Science B.V.