Anisotropy of magnetic susceptibility as the key to understand the ascending and emplacement mechanisms of granitic plutons: a review

• Type: Article in International Scientific Journal
• Date: 2024

Authors

Goncalves, A (Author) Other; Sant'Ovaia, H (Author) FCUP; Noronha, F (Author) FCUP

Journal

Title: Journal Of Iberian Geology

ISSN: 1698-6180

Publisher: Springer Nature

Indexing

ISI Web of Knowledge - 0 Citations

Scopus - 0 Citations

Other information

Authenticus ID: P-017-K26

DOI: 10.1007/s41513-024-00272-8

Abstract (EN): The present study includes a multidisciplinary approach applied to seven ilmenite-type granite intrusions outcropping in Northern and Central Portugal, inside the so-called Gal & iacute;cia-Tr & aacute;s-os-Montes (GTMZ) and Central Iberian (CIZ) geotectonic zones. The main goals are to understand the ascent, emplacement mechanisms and deformation patterns evolution during the late stages of Variscan orogeny. To this end, different granites were studied, which currently exemplify distinct levels of the intrusion suites, as they intrude metasedimentary rocks of low metamorphic grade (namely, Freixo de Num & atilde;o granite (FNG)), or the contact of metasedimentary-granites rocks (such as, Capinha granite (CaG) and Valpa & ccedil;os granite (ValG)), or other granites (e.g., Caria-Vila da Ponte pluton (CVPP) and Esmolfe-Matan & ccedil;a pluton (EMP)). Anisotropy of magnetic susceptibility (AMS), microstructural and bulk magnetic susceptibility (Km) studies were performed. The correlation between AMS and microstructures pointed out that the studied granites exhibit magnetic fabric that mimics the magmatic fabric inherited during a passive ascent and emplacement under an extensional regime. On the other hand, ValG magnetic fabric resulted from the combination of magmatic and tectonic fabrics, being the last one less expressive. AMS data allowed to infer the trajectories drawn by the magnetic foliations providing important clues about the granite intrusions shape. Therefore, distinct 3D shapes were suggested: bell-shape intrusion for CVPP; tongue-shape intrusion for CaG; asymmetric laccolith for EMG and FNG; and, inverted flat drop-shape intrusion for ValG. The fieldwork relationships between the granite intrusions, host rocks and local/regional structures together with AMS results allowed to verify that the ascent and emplacement of studied intrusions were structural controlled using structures like shear zones (ValG, EMG and FNG) and deep strike-slip faults (CaG and CVPP). El presente estudio incluye un enfoque multidisciplinar aplicado a siete intrusiones gran & iacute;ticas de tipo ilmenita que afloran en el norte y centro de Portugal, dentro de las zonas geotect & oacute;nicas denominadas Galicia-Tr & aacute;sos- Montes (GTMZ) y Centro Ib & eacute;rica (CIZ). Los principales objetivos son comprender el ascenso, los mecanismos de emplazamiento y la evoluci & oacute;n de los patrones de deformaci & oacute;n durante las & uacute;ltimas etapas de la Orogenia Varisca. Para este fin, se estudiaron diferentes granitos, que actualmente ejemplifican distintos niveles de las intrusiones, ya que intruyen rocas metasedimentarias de bajo grado metam & oacute;rfico (a saber, el granito Freixo de Num & atilde;o (FNG)), o el contacto de rocas metasedimentarias-gran & iacute;ticas (como, el granito Capinha (CaG) y el granito Valpa & ccedil;os (ValG)), o otros granitos (por ejemplo, el plut & oacute;n Caria-Vila da Ponte (CVPP) y el plut & oacute;n Esmolfe-Matan & ccedil;a (EMP)). Se realizaron estudios de anisotrop & iacute;a de susceptibilidad magn & eacute;tica (ASM), microestructural y de susceptibilidad magn & eacute;tica volum & eacute;trica (Km). La correlaci & oacute;n entre ASM y microestructuras se & ntilde;al & oacute; que los granitos estudiados exhiben una f & aacute;brica magn & eacute;tica que imita la f & aacute;brica magm & aacute;tica heredada durante un ascenso pasivo y emplazamiento en un r & eacute;gimen extensional. Por otra parte, la f & aacute;brica magn & eacute;tica ValG result & oacute; de la combinaci & oacute;n de f & aacute;bricas magm & aacute;ticas y tect & oacute;nicas, siendo esta & uacute;ltima menos expresiva. Los datos ASM permitieron inferir las trayectorias dibujadas por las foliaciones magn & eacute;ticas proporcionando pistas importantes sobre la forma de las intrusiones gran & iacute;ticas. Por lo tanto, se sugirieron distintas formas 3D: intrusi & oacute;n en forma de campana para CVPP; intrusi & oacute;n en forma de lengua para CaG; lacolito asim & eacute;trico para EMG y FNG; y intrusi & oacute;n en forma de gota plana invertida para ValG. Las relaciones del trabajo de campo entre las intrusiones gran & iacute;ticas, rocas hospedantes y estructuras locales/regionales junto con los resultados ASM permitieron verificar que el ascenso y emplazamiento de las intrusiones estudiadas estaban controlados estructuralmente utilizando estructuras como zonas de cizalla (ValG, EMG y FNG) y fallas de desgarre profundas (CaG y CVPP).

Language: English

Type (Professor's evaluation): Scientific

No. of pages: 26