کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
---|---|---|---|---|
5784171 | 1638632 | 2017 | 51 صفحه PDF | دانلود رایگان |
عنوان انگلیسی مقاله ISI
Variscan metagranitoids in the central Tauern Window (Eastern Alps, Austria) and their role in the formation of the Felbertal scheelite deposit
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کلمات کلیدی
موضوعات مرتبط
مهندسی و علوم پایه
علوم زمین و سیارات
ژئوشیمی و پترولوژی
پیش نمایش صفحه اول مقاله
![عکس صفحه اول مقاله: Variscan metagranitoids in the central Tauern Window (Eastern Alps, Austria) and their role in the formation of the Felbertal scheelite deposit Variscan metagranitoids in the central Tauern Window (Eastern Alps, Austria) and their role in the formation of the Felbertal scheelite deposit](/preview/png/5784171.png)
چکیده انگلیسی
The W mineralised Early Carboniferous orthogneisses (K1 and K3 orthogneiss) in the Felbertal scheelite deposit represent a chemically evolved metagranitoid series. Some of its characteristics are high concentrations of F (< 4438 ppm), Nb (< 86 ppm), Ta (< 13 ppm), and U (< 74 ppm) and REE patterns with distinct negative Eu-anomalies (Eu/Eu* = 0.24-0.48) and increasing HREE concentrations (LuN/HoN = 1.93-2.81). The systematic chemical trends documented for a multitude of elements (e.g., SiO2, TiO2, P2O5, Ba, Nb, Ta) and their respective ratios (e.g., 1/TiO2, Nb/Ta, Zr/Hf) indicate that crystal-melt fractionation controlled the evolution of the granitic melts. The higher differentiated, peraluminous light-coloured K1-K3 variety (ASI = 0.99-1.08, Nb/Ta = 5-7, Zr/Hf = 13-18) evolved from the less differentiated, metaluminous dark-coloured variety (ASI = 0.93-1.03; Nb/Ta = 6-10, Zr/Hf = 18-24). Peraluminous holo-leucocratic aplite gneiss represents the most evolved member of the series (ASI = 1.11-1.12, Nb/Ta = 4, Zr/Hf = 9-10). Modelling of magmatic differentiation assuming Rayleigh fractionation shows that c. 70-90% of the residual granitic magma had crystallised at the time of the emplacement of the aplites. When compared to barren metagranitoids in the central Tauern Window (“Zentralgneis”), the metaluminous dark-coloured K1-K3 orthogneiss shows some geochemical similarities with the peraluminous Felbertauern augengneiss, one of the regional orthogneisses exposed near the W deposit. Elevated concentrations of Nb (< 36 ppm), Ta (< 5.3 ppm) and U (< 30 ppm) distinguish it from other regional Zentralgneis types and illustrate its genetic relation with the K1-K3 orthogneiss. We propose that the Felbertauern augengneiss represents a peraluminous granitic melt, generated by melting of a source assemblage containing hydrous F-bearing minerals (i.e., biotite). Progressive dehydration melting of the same (or a similar source) at higher temperature involving a Ca-phase (i.e., hornblende) produced melt batches of metaluminous composition; i.e., dark-coloured K1-K3 orthogneiss. An alternative model for explaining the unusual chemical characteristics of the latter would be entrainment and separation of a peritectic and restitic accessory mineral assemblage co-existing with the granitic melt. Higher contents of fluxing elements such as F in the melt may have been responsible for lowering the solidus temperature of the granitic melts allowing concentration of W and other elements in the residual melts and later on in the exsolved magmatic hydrothermal fluids. These processes were a pre-requisite for the development of highly specialised W-rich granitic melts and formation of the world-class Felbertal scheelite deposit.
ناشر
Database: Elsevier - ScienceDirect (ساینس دایرکت)
Journal: Lithos - Volumes 278â281, May 2017, Pages 303-320
Journal: Lithos - Volumes 278â281, May 2017, Pages 303-320
نویسندگان
Michael Kozlik, Johann G. Raith,