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|Title: ||The multistage crystallization of zircon in calc‑alkaline|
|Authors: ||Pereira, M. Francisco|
Santos, J. Francisco
Sola, A.M. Rita
Williams, Ian S.
Silva, Jose B.
Armstrong, Richard A.
|Issue Date: ||4-Feb-2015|
|Citation: ||Pereira, M.F., Chichorro, M., Moita, P., Santos, J.F., Solá, A.M.R., Williams, I.S., Silva, J.B., Armsrong, R.A. (2015).The multistage crystallization of zircon in calc‑alkaline granitoids: U–Pb age constraints on the timing of Variscan
tectonic activity in SW Iberia. International Journal of Earth SciencesDOI 10.1007/s00531-015-1149-3|
|Abstract: ||CL imaging and U–Th–Pb data for a population
of zircons from two of the Évora Massif granitoids
(Ossa-Morena Zone, SW Iberia) show that both calcalkaline
granitoids have zircon populations dominated by
grains with cores and rims either showing or not showing
differences in Th/U ratio, and having ages in the range ca.
350–335 Ma (Early Carboniferous). Multistage crystallization
of zircon is revealed in two main growth stages
(ca. 344–342 Ma and ca. 336–335 Ma), well represented
by morphologically complex zircons with cores and rims
with different ages and different Th/U ratios that can be explained by: (1) crystallization from melts with different
compositions (felsic peraluminous to felsic-intermediate
metaluminous; 0.001 < Th/U ratio < 0.5) and (2) transient
temperature fluctuations in a system where anatectic felsic
melts periodically underwent injection of more mafic magmas
at higher temperatures. The two studied calc-alkaline
granitoids do not include inherited zircons (pre-Carboniferous),
probably because they were formed at the highest
grade of metamorphism (T > 837 °C; granulite facies)
and/or because they were derived from inheritance-poor
felsic and mafic rocks from a previous cycle, as suggested
by the internal structures of zircon cores. These Variscan
magmatic rocks with crystallization ages estimated at ca.
336–335 Ma are spatially and temporally related to hightemperature
metamorphism, anatexis, processes of interaction
between crustal- and mantle-derived magmas and
intra-orogenic extension that acted in SW Iberia during the
|Appears in Collections:||GEO - Publicações - Artigos em Revistas Internacionais Com Arbitragem Científica|
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