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Architecture and construction mechanisms of continental bimodal intrusions: insight from the layered pluton of Punta Falcone (Sardinia, Italy)

English title Architecture and construction mechanisms of continental bimodal intrusions: insight from the layered pluton of Punta Falcone (Sardinia, Italy)
Applicant Bussy François
Number 149423
Funding scheme Project funding (Div. I-III)
Research institution Institut de Minéralogie et Géochimie Université de Lausanne
Institution of higher education University of Lausanne - LA
Main discipline Mineralogy
Start/End 01.10.2013 - 30.09.2015
Approved amount 131'360.00
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Keywords (7)

hybrid rocks; granite; Variscan; layered intrusion; zircon geochronology; gabbro; magma chamber

Lay Summary (French)

Lead
L’emplacement des magmas pose un problème d’espace disponible dans la croûte terrestre. Un mécanisme invoqué est l’injection de pulses de magma transportés le long de filons verticaux et accumulés dans des pièges structuraux, finissant par engendrer de grands plutons. Ceux présentant des zonations sont donc des cibles de choix pour l’étude de la construction incrémentale des plutons, notamment les aspects de rhéologie des magmas, de leur rythme d’injection et de cristallisation.
Lay summary

Contenu et objectifs du travail de recherche

Les objectifs du projet sont les suivants :

(1) compléter l’acquisition de données (cartographie très détaillée, minéralogie, géochimie) débutée en octobre 2011, en particulier une étude de l’anisotropie de la susceptibilité magnétique (AMS) dans les diverses unités de refroidissement du gabbro de Punta Falcone ;

(2) comprendre les processus responsables du développement du rubanement vertical rythmique exprimé par le facies gabbroïque central, qui inclut :

(3) une investigation complémentaire sur des roches très semblables observées dans la zone racinaire du laccolite de Torres del Paine en Patagonie ;

(4) l’établissement précis de la chronologie de mise en place des unités de refroidissement par datation U-Pb sur zircon ;

(5) l’identification des sources des magmas mafiques et felsiques et leurs interactions potentielles par la géochimie isotopique sur roche totale (Nd-Sr-Pb) et zircon (Hf) ;

(6) l’établissement éventuel d’un modèle numérique de déformation d’un magma partiellement cristallisé qui sera confronté au rubanement rythmique observé sur le terrain.

Contexte scientifique du projet de recherche

Contexte scientifique du projet de recherche

Nos résultats permettront de mieux comprendre les mécanismes de ségrégation à l’œuvre dans les niveaux structuraux intermédiaires entre la source des magmas et leur mise en place finale (sub)volcanique. Punta Falcone est effectivement considérée comme un site d’accumulation et de fractionnement de magmas, dont une partie différenciée a quitté le système vers des niveaux supérieurs.

Direct link to Lay Summary Last update: 26.09.2013

Responsible applicant and co-applicants

Employees

Collaboration

Group / person Country
Types of collaboration
Prof. L. Caricchi, UNIGE Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Research Infrastructure
Prof. Othmar Müntener Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Research Infrastructure
Prof. L. Baumgartner Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Research Infrastructure
Prof. U. Schaltegger, isotope geochemistry group, UNIGE Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Research Infrastructure

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
American Geophysical Union, San Francisco Poster Construction and magmatic evolution of a vertically layered mid-crustal gabbroic complex (Punta Falcone, Sardinia) 15.12.2014 San Francisco, United States of America Hauser Anne-Cécile; Bussy François;
European Geosciences Union EGU Vienna Poster Internal structure of a mid-crustal magmatic conduit: the Punta Falcone mafic pluton (Sardinia, Italy) 27.04.2014 Vienna, Austria Bussy François; Hauser Anne-Cécile;


Associated projects

Number Title Start Funding scheme
130253 Architecture and construction mechanisms of continental bimodal intrusions: insight from the layered plutons of St-Jean-du-Doigt (Brittany, France) and Punta Falcone (Sardinia, Italy) 01.04.2010 Project funding (Div. I-III)

Abstract

Pluton emplacement in the continental crust has long been a challenging question, in particular for km-sized granite intrusions. This "space problem", which is tightly connected to magma transport issues, has been addressed in different ways. Proposed mechanisms include, among others, en masse transport through diapirs, stoping of roof country rock and multiple injection of magma through vertical dikes, ponding in structural traps and resulting in the progressive construction of large bodies. The Carboniferous Punta Falcone gabbro, northern Sardinia, is a spectacular example of layered pluton emplaced at mid- to upper crustal level. Layering is vertical and coeval felsic and hybrid rocks are hosting the gabbro stock as a whole. A decameter-scale zonation of rock facies is symmetrical to the center of the pluton and results from emplacement of about twelve major cooling units, each made of one or several magma pulses. A spectacular centimeter-scale rhythmic modal layering in gabbros at the center of the intrusion is currently interpreted as evidence for mechanical mineral sorting within a crystallizing mush in a low-strain stress field. Geochemistry documents the cumulate nature of the layered gabbros and we hypothesize the rhythmic layering to have developed concomitantly to the residual melt extraction, which escaped to higher levels. The aims of this two-year proposal are: (1) to complete the data acquisition scheme in progress, in particular an AMS study of the different cooling units; (2) to understand the processes responsible for the development of vertical rhythmic layering in the Punta Falcone gabbros, which includes (3) a complementary work on similarly layered mafic rocks from the root zone of the 12 Ma-old Torres del Paine laccolith in Patagonia; (4) to precisely establish the time and duration of the Punta Falcone mafic and felsic magmatism through high-precision U-Pb zircon dating; (5) to identify the sources of the mafic and felsic magmas and their potential interactions through whole-rock (Nd-Sr-Pb) and zircon (Hf) isotope geochemistry; (6) to perform numerical modeling of the deformation of a crystallizing mush to duplicate the observed rhythmic layering, provided preliminary tests done in Summer 2013 are conclusive.
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