The importance of sequential partial melting and fractional crystallization in the generation of syn-D3 Variscan two-mica granites from the Carrazeda de Ansiães area, northern Portugal
The importance of sequential partial melting and fractional crystallization in the generation of syn-D3 Variscan two-mica granites from the Carrazeda de Ansiães area, northern Portugal
In the Carrazeda de Ansiães region, northern Portugal, a mesozonal granitic suite intruded Precambrian to Ordovician metasedimentary rocks during the late kinematic stages of the Variscan orogeny. In this multiphase granitic complex, consisting of ten granite types, the youngest group of two-mica granites (G7–G10) was emplaced between 318 ± 1 Ma and 316.2 ± 0.7 Ma, as determined by ID-TIMS U–Pb on zircon and monazite. Granite types G7–G9 were affected by the third phase of deformation (D
3) before they were completely crystallized, as indicated by their internal NW–SE magmatic foliation concordant with the regional structures. The granite type G10 shows some distinctive textural features, showing a strong brittle deformation, probably due to its preferential emplacement in late NNE-SSW fault zones. Granites G7–G9 have equal or higher amounts of muscovite than biotite and contain surmicaceous enclaves, xenoliths, “schlieren”, and, more rarely, microgranular enclaves. The muscovite-dominant granite G10 does not contain enclaves. These Variscan granites are peraluminous, with ASI ranging between 1.22 and 1.39 and normative corundum of 2.79–4.39%, having the characteristics of S-type granites. In fact, the enrichment in LREE relatively to HREE, the negative Eu anomalies, and similar mean values of (
87Sr/
86Sr)
i, εNd
t and δ
18O for G7 (0.7156 ± 0.0005; − 8.5; 11.49 ‰) and G8 (0.7155 ± 0.0007; − 8.4; 11.39 ‰) show that these two granite types resulted from sequential partial melting of the same metasedimentary material, where granite G8 would have derived from a higher degree of partial melting than G7. Granites G8–G10 and their minerals show a fractionation trend that is confirmed by modeling of major and trace elements. The subparallel REE patterns and the decreasing REE contents within the differentiation series, the Rb–Sr isochron for G8, G9 and G10 (315.5 ± 5.4 Ma; MSWD = 1.3) and the relatively uniform εNd
t and δ
18O data suggest that fractional crystallization was the main mechanism, which would have lasted less than 1 Ma. The tin-bearing granites G7 and G10 have ≥ 20 ppm Sn, but the main quartz veins containing cassiterite and wolframite cut granite G10, which contains 31 ppm Sn. Fractional crystallization was responsible for the increase in Sn content in granites from the G8–G10 series and their micas.
Fractional crystallization, Isotopic data, S-type granites, Sequential partial melting, Tin, U–Pb zircon and monazite ages
281-305
Teixeira, R. J. S.
0f819b12-b467-4dc9-9c23-47193239c8bf
Neiva, A. M. R.
5e04fd56-df56-418e-bd3e-e5ba1b5defd7
Gomes, M. E. P.
8b8c6444-3f6c-4ea4-8606-21a9341d159e
Corfu, F.
e36e7120-d221-47be-b699-3706bc8be924
Cuesta, A.
b4881d22-765d-4dea-a1ec-e1d5db01052c
Croudace, I. W.
24deb068-d096-485e-8a23-a32b7a68afaf
May 2021
Teixeira, R. J. S.
0f819b12-b467-4dc9-9c23-47193239c8bf
Neiva, A. M. R.
5e04fd56-df56-418e-bd3e-e5ba1b5defd7
Gomes, M. E. P.
8b8c6444-3f6c-4ea4-8606-21a9341d159e
Corfu, F.
e36e7120-d221-47be-b699-3706bc8be924
Cuesta, A.
b4881d22-765d-4dea-a1ec-e1d5db01052c
Croudace, I. W.
24deb068-d096-485e-8a23-a32b7a68afaf
Teixeira, R. J. S., Neiva, A. M. R., Gomes, M. E. P., Corfu, F., Cuesta, A. and Croudace, I. W.
(2021)
The importance of sequential partial melting and fractional crystallization in the generation of syn-D3 Variscan two-mica granites from the Carrazeda de Ansiães area, northern Portugal.
Journal of Iberian Geology, 47 (1-2), .
(doi:10.1007/s41513-020-00160-x).
Abstract
In the Carrazeda de Ansiães region, northern Portugal, a mesozonal granitic suite intruded Precambrian to Ordovician metasedimentary rocks during the late kinematic stages of the Variscan orogeny. In this multiphase granitic complex, consisting of ten granite types, the youngest group of two-mica granites (G7–G10) was emplaced between 318 ± 1 Ma and 316.2 ± 0.7 Ma, as determined by ID-TIMS U–Pb on zircon and monazite. Granite types G7–G9 were affected by the third phase of deformation (D
3) before they were completely crystallized, as indicated by their internal NW–SE magmatic foliation concordant with the regional structures. The granite type G10 shows some distinctive textural features, showing a strong brittle deformation, probably due to its preferential emplacement in late NNE-SSW fault zones. Granites G7–G9 have equal or higher amounts of muscovite than biotite and contain surmicaceous enclaves, xenoliths, “schlieren”, and, more rarely, microgranular enclaves. The muscovite-dominant granite G10 does not contain enclaves. These Variscan granites are peraluminous, with ASI ranging between 1.22 and 1.39 and normative corundum of 2.79–4.39%, having the characteristics of S-type granites. In fact, the enrichment in LREE relatively to HREE, the negative Eu anomalies, and similar mean values of (
87Sr/
86Sr)
i, εNd
t and δ
18O for G7 (0.7156 ± 0.0005; − 8.5; 11.49 ‰) and G8 (0.7155 ± 0.0007; − 8.4; 11.39 ‰) show that these two granite types resulted from sequential partial melting of the same metasedimentary material, where granite G8 would have derived from a higher degree of partial melting than G7. Granites G8–G10 and their minerals show a fractionation trend that is confirmed by modeling of major and trace elements. The subparallel REE patterns and the decreasing REE contents within the differentiation series, the Rb–Sr isochron for G8, G9 and G10 (315.5 ± 5.4 Ma; MSWD = 1.3) and the relatively uniform εNd
t and δ
18O data suggest that fractional crystallization was the main mechanism, which would have lasted less than 1 Ma. The tin-bearing granites G7 and G10 have ≥ 20 ppm Sn, but the main quartz veins containing cassiterite and wolframite cut granite G10, which contains 31 ppm Sn. Fractional crystallization was responsible for the increase in Sn content in granites from the G8–G10 series and their micas.
Text
Portugal Paer - Just Accepted JIBG-D-20-00067_R21
- Accepted Manuscript
More information
Accepted/In Press date: 27 December 2020
e-pub ahead of print date: 11 February 2021
Published date: May 2021
Additional Information:
Funding Information:
This paper corresponds to a part of the PhD thesis of R. J. S. Teixeira. We are grateful to Prof. Robert Nesbitt who managed the EU SOCFAC facility (HPRI-1999-CT-00108) that led to access to geochemical facilities at the University of Southampton (United Kingdom), Dr. Andy Milton (at the same institution) for the skilled assistance in the laser ablation ICP-MS laboratory, Prof. Jos? Ignacio Gil Ibarguchi, Dr. Sonia Garc?a de Madinabeitia and Dr. Maria Eugenia Sanchez Lorda for the Rb-Sr and Sm-Nd isotopic data obtained at the Geochronology and Isotope Geochemistry- SGIker Facility of the Universidad del Pa?s Vasco UPV/EHU (Spain). Prof. Fred J. Longstaffe for the oxygen-isotope analyses obtained at the Department of Earth Sciences, University of Western Ontario (Canada). R. J. S. Teixeira also thanks to ?lvaro Miranda, Dr. Alvaro Rubio, M?rcio Silva, Miguel Fern?ndez, Nelson Pinto, Sim?o Botelho and Tito Azevedo for their help in field and laboratory works. Funding was provided to R. J. S. Teixeira by the SFRH/BD/17246/2004 PhD Grant from FCT?Funda??o para a Ci?ncia e a Tecnologia, Portugal, and another grant from SOCFAC (Southampton Oceanography Centre, Facilities and Co-Operation). This research was financially supported by the Pole of the Geosciences Centre (CGeo) and projects UIDB/00073/2020 and UIDP/00073/2020 through FCT?Portuguese Foundation for Sciences and Technology. Very helpful constructive reviews and comments were provided by two anonymous referees. We are also grateful to the Guest Editors for the final comments.
Funding Information:
This paper corresponds to a part of the PhD thesis of R. J. S. Teixeira. We are grateful to Prof. Robert Nesbitt who managed the EU SOCFAC facility (HPRI-1999-CT-00108) that led to access to geochemical facilities at the University of Southampton (United Kingdom), Dr. Andy Milton (at the same institution) for the skilled assistance in the laser ablation ICP-MS laboratory, Prof. José Ignacio Gil Ibarguchi, Dr. Sonia García de Madinabeitia and Dr. Maria Eugenia Sanchez Lorda for the Rb-Sr and Sm-Nd isotopic data obtained at the Geochronology and Isotope Geochemistry- SGIker Facility of the Universidad del País Vasco UPV/EHU (Spain). Prof. Fred J. Longstaffe for the oxygen-isotope analyses obtained at the Department of Earth Sciences, University of Western Ontario (Canada). R. J. S. Teixeira also thanks to Álvaro Miranda, Dr. Alvaro Rubio, Márcio Silva, Miguel Fernández, Nelson Pinto, Simão Botelho and Tito Azevedo for their help in field and laboratory works. Funding was provided to R. J. S. Teixeira by the SFRH/BD/17246/2004 PhD Grant from FCT—Fundação para a Ciência e a Tecnologia, Portugal, and another grant from SOCFAC (Southampton Oceanography Centre, Facilities and Co-Operation). This research was financially supported by the Pole of the Geosciences Centre (CGeo) and projects UIDB/00073/2020 and UIDP/00073/2020 through FCT—Portuguese Foundation for Sciences and Technology. Very helpful constructive reviews and comments were provided by two anonymous referees. We are also grateful to the Guest Editors for the final comments.
Publisher Copyright:
© 2021, Universidad Complutense de Madrid.
Keywords:
Fractional crystallization, Isotopic data, S-type granites, Sequential partial melting, Tin, U–Pb zircon and monazite ages
Identifiers
Local EPrints ID: 448021
URI: http://eprints.soton.ac.uk/id/eprint/448021
ISSN: 1698-6180
PURE UUID: 800b9980-f7bb-4f24-a2b0-ca5546bf4118
Catalogue record
Date deposited: 30 Mar 2021 16:34
Last modified: 17 Mar 2024 06:26
Export record
Altmetrics
Contributors
Author:
R. J. S. Teixeira
Author:
A. M. R. Neiva
Author:
M. E. P. Gomes
Author:
F. Corfu
Author:
A. Cuesta
Download statistics
Downloads from ePrints over the past year. Other digital versions may also be available to download e.g. from the publisher's website.
View more statistics