Deciphering Iberian Variscan Orogen Magmatism Using the Anisotropy of Magnetic Susceptibility from Granites
In this paper, we have synthesized the information derived from more than 20 papers and PhD theses on the anisotropy of the magnetic susceptibility (AMS) of 19 Variscan granite plutons, spanning the period between 320 Ma and 296 Ma. The AMS data are obtained from 876 sampling sites with more than 70...
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MDPI AG
2024-03-01
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| Series: | Minerals |
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| Online Access: | https://www.mdpi.com/2075-163X/14/3/309 |
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| author | Helena Sant’Ovaia Cláudia Cruz Ana Gonçalves Pedro Nogueira Fernando Noronha |
| author_facet | Helena Sant’Ovaia Cláudia Cruz Ana Gonçalves Pedro Nogueira Fernando Noronha |
| author_sort | Helena Sant’Ovaia |
| collection | DOAJ |
| description | In this paper, we have synthesized the information derived from more than 20 papers and PhD theses on the anisotropy of the magnetic susceptibility (AMS) of 19 Variscan granite plutons, spanning the period between 320 Ma and 296 Ma. The AMS data are obtained from 876 sampling sites with more than 7080 AMS measurements and a re-interpretation is proposed. The studied granites exhibit a magnetic susceptibility (Km) ranging from 30 to 10,436 × 10<sup>−6</sup> SI units. Most granites typically exhibit Km values below 1000 × 10<sup>−6</sup> SI, indicative of paramagnetic behavior. Biotite serves as the main carrier of iron (Fe), emphasizing the reduced conditions prevalent during the formation of granite melts in the Variscan orogeny. The AMS fabrics of the studied granite plutons record the magma strain, expressing the chronologic evolution of the stress field during the orogeny. This chronologic approach highlights the magmatic events between around 330 and 315 Ma, occurring in an extensional regime, in which the Borralha pluton is an example of a suite that recorded this extensional AMS fabric. Plutons with ages between 315 and 305 Ma show AMS fabrics, pointing out their emplacement in a compressional tectonic regime related to the Variscan collision. The plutons, younger than 305 Ma, record AMS fabrics indicating that the tectonic setting for emplacement changes from a wrench regime to an extensional one at the end of the collision stage. This is evident as there is a chronological overlap between the granites that exhibit AMS fabrics indicating extension and the ones that have AMS fabrics indicating a wrench regime. |
| first_indexed | 2024-04-24T17:59:12Z |
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| institution | Directory Open Access Journal |
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| language | English |
| last_indexed | 2024-04-24T17:59:12Z |
| publishDate | 2024-03-01 |
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| series | Minerals |
| spelling | doaj.art-45816258adf54c9892316a7bda7f5e042024-03-27T13:56:23ZengMDPI AGMinerals2075-163X2024-03-0114330910.3390/min14030309Deciphering Iberian Variscan Orogen Magmatism Using the Anisotropy of Magnetic Susceptibility from GranitesHelena Sant’Ovaia0Cláudia Cruz1Ana Gonçalves2Pedro Nogueira3Fernando Noronha4Departamento de Geociências, Ambiente e Ordenamento do Território, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, PortugalDepartamento de Geociências, Ambiente e Ordenamento do Território, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, PortugalInstituto de Ciências da Terra, Polo da Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, PortugalDepartamento de Geociências, Universidade de Évora, Colégio Luís António Verney, Rua Romão Ramalho, 59, 7000-671 Évora, PortugalDepartamento de Geociências, Ambiente e Ordenamento do Território, Faculdade de Ciências, Universidade do Porto, Rua do Campo Alegre, 687, 4169-007 Porto, PortugalIn this paper, we have synthesized the information derived from more than 20 papers and PhD theses on the anisotropy of the magnetic susceptibility (AMS) of 19 Variscan granite plutons, spanning the period between 320 Ma and 296 Ma. The AMS data are obtained from 876 sampling sites with more than 7080 AMS measurements and a re-interpretation is proposed. The studied granites exhibit a magnetic susceptibility (Km) ranging from 30 to 10,436 × 10<sup>−6</sup> SI units. Most granites typically exhibit Km values below 1000 × 10<sup>−6</sup> SI, indicative of paramagnetic behavior. Biotite serves as the main carrier of iron (Fe), emphasizing the reduced conditions prevalent during the formation of granite melts in the Variscan orogeny. The AMS fabrics of the studied granite plutons record the magma strain, expressing the chronologic evolution of the stress field during the orogeny. This chronologic approach highlights the magmatic events between around 330 and 315 Ma, occurring in an extensional regime, in which the Borralha pluton is an example of a suite that recorded this extensional AMS fabric. Plutons with ages between 315 and 305 Ma show AMS fabrics, pointing out their emplacement in a compressional tectonic regime related to the Variscan collision. The plutons, younger than 305 Ma, record AMS fabrics indicating that the tectonic setting for emplacement changes from a wrench regime to an extensional one at the end of the collision stage. This is evident as there is a chronological overlap between the granites that exhibit AMS fabrics indicating extension and the ones that have AMS fabrics indicating a wrench regime.https://www.mdpi.com/2075-163X/14/3/309granitesanisotropy of magnetic susceptibilityVariscan orogenymagma strain |
| spellingShingle | Helena Sant’Ovaia Cláudia Cruz Ana Gonçalves Pedro Nogueira Fernando Noronha Deciphering Iberian Variscan Orogen Magmatism Using the Anisotropy of Magnetic Susceptibility from Granites Minerals granites anisotropy of magnetic susceptibility Variscan orogeny magma strain |
| title | Deciphering Iberian Variscan Orogen Magmatism Using the Anisotropy of Magnetic Susceptibility from Granites |
| title_full | Deciphering Iberian Variscan Orogen Magmatism Using the Anisotropy of Magnetic Susceptibility from Granites |
| title_fullStr | Deciphering Iberian Variscan Orogen Magmatism Using the Anisotropy of Magnetic Susceptibility from Granites |
| title_full_unstemmed | Deciphering Iberian Variscan Orogen Magmatism Using the Anisotropy of Magnetic Susceptibility from Granites |
| title_short | Deciphering Iberian Variscan Orogen Magmatism Using the Anisotropy of Magnetic Susceptibility from Granites |
| title_sort | deciphering iberian variscan orogen magmatism using the anisotropy of magnetic susceptibility from granites |
| topic | granites anisotropy of magnetic susceptibility Variscan orogeny magma strain |
| url | https://www.mdpi.com/2075-163X/14/3/309 |
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