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UBC Theses and Dissertations

K[40] - Ar[40] isotopic age determination of the Nelson batholith, B.C. Nguyeh, Kim-Khanh


The purposes of this thesis are to examine ages of the Nelson batholith and its satellites because of the wide range of biotite model ages previously published in the literature, and to test hornblende and pyroxene further for their application in K⁴⁰ - Ar⁴⁰ dating as reliable minerals. K⁴⁰ - Ar⁴⁰ model ages obtained on biotite, hornblende and clinopyroxene from the present study indicate with certainty that the various phases of the Nelson batholith were emplaced during a short span of time, centered around 156 m.y. corresponding to the Upper-Middle Jurassic boundary of the Kulp’s time scale. At least a period of hydrothermal alteration has occurred in this area since that time. It is evident that these phases cannot be distinguished on the basis of their K⁴⁰ - Ar⁴⁰ model ages. It is also evident that hornblende gives reliable model ages. Clinopyroxene contains significant excess of radiogenic argon and should not be used for K⁴⁰ - Ar⁴⁰ dating. Biotite may occasionally contain excess of radiogenic argon, particularly under high temperature and high argon pressure environmental conditions. Analytical techniques used and descriptions of the samples analyzed are given as appendixes.

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