Geochemical and Sr and Nd isotopic constraints on the origin of late Proterozoic volcanics and associated tin-bearing granites from the Franklin Mountains, west Texas (USA)

D. I. Norman, K. C. Condie, R. W. Smith, W. F. Thomann

Research output: Contribution to journalArticle

15 Citations (Scopus)

Abstract

Late Proterozoic volcanic and granitic rocks from the Franklin Mountains in W Texas define a continuous tholeiitic trend from rhyolite (granite) to trachyte with a small compositional gap between trachyte and basalt. Volcanics and granitic rocks have immobile-element geochemical affinities with volcanics from continental-margin-arc systems and associated back-arc basins. Felsic volcanics and granitic rocks appear to have formed by fractional crystallization of basalt during which REE and high-field-strength elements were stabilized as fluoride complexes and concentrated in late or post-magmatic fluids. A Rb-Sr isochron from nonhematized samples (1064 + or - 5 Ma, i = 0.7034) falls within the error of reported U-Pb zircon dates and probably dates a period of hydrothermal alteration. epsilonNd values (0.7-2.5 at 1065 Ma) fall below a depleted mantle growth curve and probably reflect contamination of the fractionating magmas with older continental crust. Changes in the isotopic composition of Nd during hydrothermal alteration may also contribute to the spread in epsilonNd values.-Authors

Original languageEnglish
Pages (from-to)830-839
Number of pages10
JournalCanadian journal of earth sciences
Volume24
Issue number4
Publication statusPublished - 1987
Externally publishedYes

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