LATE-VARISCAN DUCTILE BRITTLE DEFORMATION IN CENTRAL IBERIAN AUTOCHTHON (NW PORTUGAL): TECTONIC IMPLICATIONS

• Type: Article in International Conference Proceedings Book
• Date: 2016

Authors

Anjos Ribeiro (Author) FCUP; H. C. B. Martins (Author) FCUP; Sant'Ovaia, H (Author) FCUP; Doria, A (Author) Other

Conference proceedings International

Title: 16TH INTERNATIONAL MULTIDISCIPLINARY SCIENTIFIC GEOCONFERENCE, SGEM 2016: SCIENCE AND TECHNOLOGIES IN GEOLOGY, EXPLORATION AND MINING, VOL I

Pages: 313-320

16th International Multidisciplinary Scientific Geoconference (SGEM 2016)

Albena, BULGARIA, JUN 30-JUL 06, 2016

Indexing

ISI Web of Knowledge - 1 Citation

Scopus - 2 Citations

Scientific classification

FOS: Natural sciences

Other information

Authenticus ID: P-00M-6VJ

DOI: 10.5593/sgem2016/b11/s01.040

Abstract (EN): The NW sector of Porto-Viseu metamorphic belt (PVMB), in the western border of Central Iberian Zone (CIZ), is characterised by the confluence of two major variscan shear zones: the Douro-Beira shear zone (DBSZ) and the Porto-Tomar shear zone (PTSZ). In order to provide relative age constraints of the timing of deformation in these shear zones, this study aims to ascertain the area of confluence of these structures and the lithological and structural data of the area between them. The study pointed out to the metamorphic and magnetic foliations, the fluid inclusion planes (FIP), the granite radiometric ages, the geometry and the relative chronology of the ductile-brittle and brittle strutures. In the NW sector of PVMB, the Porto syn-tectonic granite is an example of a peraluminous magmatism, with small granitic bodies to the east, namely Pedregal (311 +/- 5 Ma), Gondomar and Fanzeres granites. These small granite bodies have NE-SW magnetic foliation (from N25 degrees to N55 degrees), dipping to SE. The orientation of FIP is NW SE and NE-SW in the Fanzeres and Gondomar granites, and NW-SE to W-E in Pedregal. The host-rocks of these granites are staurolite-micaschists with a NW-SE to N170 degrees, subvertical metamorphic foliation or metatexitic rocks with a compositional banding WNW-ESE to WSW-ENE. The staurolite-micaschists show intense non coaxial ductile deformation synchronous and subsequent to blastesis, with down-dip mineral lineation. The Lavadores granite (294 +/- 4Ma) is an undeformed biotite granite. However, an intense dextral ductile-brittle shear, developing a C-S fabric occurs on the NE border of this granite, in the contact with host-rocks. The magnetic foliations of Lavadores granite are consistent with the C-S geometry of the host-rock, although marked by different processes: magmatic flow inside the granitic body and ductile-brittle deformation in the border. These data point out to a late-variscan evolution (syn- to post-D-3), conditioned by the rising and emplacement of peraluminous granites, as well as upflow of the ductile adjacent solid rocks and local reactivation of the previous NW-SE foliation as dextral ductile shear zones. In the area under study, the discrete brittle-ductile shear zones have N110 degrees to N100 degrees direction and the brittle shear zones have N-S to N170 degrees direction and they are later than that with WNW-ESE to W-E direction.

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 8