The age problem of apophyllite in late hydrothermal mineral associations

Apophyllite 40Ar/39Ar and Rb‐Sr geochronology: Potential utility and application to the timing of secondary mineralization of the Kirkpatrick Basalt, Antarctica

“…Only limited geochronological data for apophyllite have been previously published. Chukhrov et al [1973] reported conventional K-Ar and Rb-Sr dates for apophyllite samples from ore deposits, as well as some basalt sequences. Their K-Ar results for apophyllite from Middle Eocene volcanic rocks from the Republic of Georgia yielded dates of 47 to 13 Ma (Middle Eocene to Miocene), which they considered as possible ages of mineralization.…”

“…Their K-Ar results for apophyllite from Middle Eocene volcanic rocks from the Republic of Georgia yielded dates of 47 to 13 Ma (Middle Eocene to Miocene), which they considered as possible ages of mineralization. Single samples of apophyllite from several continental flood basalt sequences were also analyzed by Chukhrov et al [1973] using conventional K-Ar methods: Siberia (198 +8 Ma), Nova Scotia (148 _+6 Ma), and Brazil (93 _+8 Ma). In all cases the apophyllite dates are younger than the eruption age of the flood basalts by 40-50 Ma; however, there are few geologic constraints on the actual timing of the secondary mineralization to evaluate the validity of the ages.…”

“…In all cases the apophyllite dates are younger than the eruption age of the flood basalts by 40-50 Ma; however, there are few geologic constraints on the actual timing of the secondary mineralization to evaluate the validity of the ages. Because of difficulties in measuring small quantities of radiogenic Sr, the Rb-Sr results of Chukhrov et al [1973] were restricted to "older" (210-745 Ma) apophyllites from ore deposits in Kazakhstan and Ukraine; where Rb-Sr dates were obtained, they were older than their K-Ar counterparts by 60 to 215 m.y. These authors concluded that the Rb-Sr dates probably represent the true crystallization age of the apophyllites and that the Ar dates were likely to be unreliable due to 4øAr loss.…”

“…As a mineral of high potassium content, it may be a suitable material for geochronology by the K-Ar and Rb-Sr methods for a number of low-temperature geologic events. However, previous geochronologic work on apophyllite [Chukhrov et al, 1973] Other than Upper Cenozoic glacial deposits, the only rocks younger than the Ferrar Group in the Transantarctic Mountains are sparsely distributed Upper Cenozoic (<25 Ma) alkaline volcanic and plutonic rocks [Kyle, 1990]. Uplift and denudation in the Transantarctic Mountains has been episodic at least since the Early Cretaceous [Fitzgerald and Stump, 1997].…”

Absolute age of volcanogenic formations of the central Siberian Platform

“…The faunal remains from these sediments consist either of Permian species (with the exception of a phyllopod fauna from the upper horizons of thVtuffogenic sequence) or of local forms, which make an objective dating of the rocks impossible (Sadovnikov, 1964). In addition, new palynological (Odintsova, 1969), geological (Kuznetsov and Naumov, 1971), and the first radiometric data ( Chukhrov et al, 1973;Dmitriyev, 1975) have been provided, which indicate a broader age range for the volcanogenic formations of this region. The absolute-age data for the volcanics of the central part of the Siberian Platform may turn out to be useful in controlling the stratigraphy of the volcanics themselves.…”