Late-Variscan emplacement and genesis of the Vieira do Minho composite pluton, Central Iberian Zone: Constraints from U-Pb zircon geochronology, AMS data and Sr-Nd-O isotope geochemistry

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• 作者：Helena C.B. Martins ; ^{hbrites@fc.up.pt} ; Helena Sant´ ; Ovaia ; Fernando Noronha
• 关键词：Peraluminous granites ; Iberian Variscan Belt ; AMS ; Sr&ndash ; Nd&ndash ; O isotopes
• 刊名：Lithos
• 出版年：2013
• 出版时间：March, 2013
• 年：2013
• 卷：162-163
• 期：Complete
• 页码：221-235
• 全文大小：2147 K

文摘

In the Central Iberian Zone synorogenic (syn- and late-D₃, the last deformation phase) composite batholiths of biotite-rich granitods with peraluminous character are well represented. We report here U-Pb zircon and monazite ages, geochemical, Sr-Nd-O isotopic data and Anisotropy of Magnetic Susceptibility (AMS) studies for the late-D₃ Vieira do Minho pluton, in northern Portugal. AMS reveals the paramagnetic behaviour of these granites and the magnetic fabric enhances the major role of NW-SE regional anisotropies on controlling the ascent and emplacement of the magmas. Magnetic anisotropy and medium temperature microstructures also point out the evolution of regional tectonics during crystallization of the magma. U-Pb zircon and monazite analyses yield consistent ages of 310 ¡À 2 Ma and 312 ¡À 2 Ma, interpreted as emplacement age.

The Vieira do Minho pluton consists of two peraluminous monzogranites, the VMG and the MRG. Both have similar ¦Å_Nd values (VMG = ? 5.2 to ? 5.7; MRG = ? 4.98 to ? 5.96) but the VMG is slightly enriched in ⁸⁷Sr/⁸⁶_i = 0.7087-0.7098 as well as in ¦Ä¹⁸O in the range of 10.6¡ë to 11.0¡ë than the MRG with ⁸⁷Sr/⁸⁶_i = 0.7064-0.7075 and ¦Ä¹⁸O = 9.9¡ë¨C10.5¡ë. These granites are associated with coeval scarce grabroic intrusions and/or mafic microgranular enclaves which are not considered as mafic precursors of the associated granitic magmatism. Instead, a lower metaigneous crustal source, at different levels, is proposed based on the available data set.