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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)

English title 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)
Applicant Bussy François
Number 130253
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 01.04.2010 - 30.09.2013
Approved amount 189'036.00
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Keywords (8)

gabbro; layered intrusion; Variscan; magma chamber; thermal modelling; zircon; granite; geochronology

Lay Summary (English)

Lead
Lay summary
This project is a continuation of an earlier project entitled : "Architecture and construction mechanisms of continental bimodal intrusions: insight from the stratified, multiply recharged Devonian Saint Jean du Doigt gabbro pluton, Brittany, France". It aims to the understanding of the construction mechanisms of bimodal mafic-felsic intrusions in answering the following questions:(1) how do magmas find the necessary space in the continental crust? (2) what is the thermal evolution of incrementally built intrusions? (3) how do vertical layering develop in upper crustal intrusions? (4) How can we explain the temporal and spatial coexistence of mafic magmas of mantellic origin and granitic magmas of crustal origin? (5) What are the sources of the magmas? (6) What are the geotectonic context of the two intrusions in the Variscan belt?Pluton emplacement in the continental crust has long been a challenging question. 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 diapirism, 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 St Jean du Doigt (SJDD) and Punta Falcone (PF) plutons are rare examples in the Variscan belt of Western Europe of such layered, multiply recharged intrusions. Although essentially gabbroic, the SJDD pluton hosts volumetrically subordinate, but spatially omnipresent felsic rocks of unknown origin, which underline the sheet-like architecture of the intrusion. Spectacular rheologic features are developed at the interface of coeval mafic-felsic magma layers and hybrid rocks are common. At the other end, the PF pluton is essentially granitic, but hosts mafic and hybrid stocks, which evidence incremental pluton growth.The aims of this project are: (1) to refine our thermal models in SJDD and do oxygen ion probe measurements on antecrystic zircons; (2) to start deciphering the complex architecture of the Punta Falcone intrusion through detailed mapping and reconstitute the magma dynamics and construction mechanisms of the pluton; (3) to understand the processes responsible for the development of vertical rhythmic magmatic layering in the Punta Falcone gabbro; (4) to investigate the mineral, textural and chemical interactions between mafic and acid magmas in their contact zone; (5) to precisely establish the time and duration of the Punta Falcone magmatism through high-precision U-Pb zircon dating.
Direct link to Lay Summary Last update: 21.02.2013

Responsible applicant and co-applicants

Employees

Publications

Publication
Petrogenesis of magmatic albite granites associated to cogenetic A-type granites: Na-rich residual melt extraction from a partially crystallized A-type granite mush
barboni mélanie, bussy françois (2013), Petrogenesis of magmatic albite granites associated to cogenetic A-type granites: Na-rich residual melt extraction from a partially crystallized A-type granite mush, in Lithos, 177, 328-351.
Timing of incremental pluton construction and magmatic activity in a back-arc setting revealed by ID-TIMS U/Pb and Hf isotopes on complex zircon grains
barboni mélanie, schoene blair, ovtcharova maria, bussy françois, schaltegger urs, gerdes axel (2013), Timing of incremental pluton construction and magmatic activity in a back-arc setting revealed by ID-TIMS U/Pb and Hf isotopes on complex zircon grains, in Chemical Geology, 340, 76-93.
Origin of Early Carboniferous pseudo-adakites in Northern Brittany (France) through massive amphibole fractionation from hydrous basalt
barboni mélanie, bussy françois, chiaradia massimo (2011), Origin of Early Carboniferous pseudo-adakites in Northern Brittany (France) through massive amphibole fractionation from hydrous basalt, in Terra Nova, 23(1), 1-10.

Collaboration

Group / person Country
Types of collaboration
UNIGE Switzerland (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
University of Frankfurt Germany (Europe)
- in-depth/constructive exchanges on approaches, methods or results
- Publication
- Research Infrastructure
University of Bristol Great Britain and Northern Ireland (Europe)
- in-depth/constructive exchanges on approaches, methods or results

Scientific events

Active participation

Title Type of contribution Title of article or contribution Date Place Persons involved
Goldschmidt conference Poster 25.08.2013 Florence, Italy Hauser Anne-Cécile;
crustal melting within the European Variscan belt Talk given at a conference 20.06.2013 Orléans, France Bussy François;
Swiss geoscience meeting Poster 16.11.2012 Bern, Switzerland Hauser Anne-Cécile; Bussy François;
Seventh Hutton Symposium on Granites and Related Rocks Poster 04.07.2011 Avila, Spain, Spain Barboni Mélanie; Bussy François;
LASI IV Conference (Laccoliths, Sills and Dykes) Talk given at a conference 22.09.2010 Moab, Utah, USA, United States of America Bussy François; Barboni Mélanie;


Awards

Title Year
Prix de faculté, université de Lausanne 2011

Associated projects

Number Title Start Funding scheme
116705 Architecture and construction mechanism of continental bimodal intrusions: insight from the stratified, multiply recharged Devonian Saint Jean du Doidt gabbro pluton, Brittany, France 01.04.2007 Project funding (Div. I-III)
149423 Architecture and construction mechanisms of continental bimodal intrusions: insight from the layered pluton of Punta Falcone (Sardinia, Italy) 01.10.2013 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 diapirism, 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 Early Carboniferous St Jean du Doigt gabbro pluton is a rare example in the Variscan belt of Western Europe of such a stratified, multiply recharged intrusion. Although essentially gabbroic, this pluton hosts volumetrically subordinate, but spatially omnipresent felsic rocks of unknown origin, which underline the sheet-like architecture of the intrusion. Spectacular rheologic features are developed at the interface of coeval mafic-felsic magma layers and hybrid rocks are common. Crosscutting dykes of basaltic to hybrid composition are the feeders of the magma layers. The Carboniferous Punta Falcone gabbro, northern Sardinia, is another example of layered pluton, but in a different context. Layering is vertical and the coeval felsic rocks are hosting the gabbro stock as a whole. The layering is interpreted as evidence for incremental injection of discrete basalt pulses in a significantly warmer environment than at St-Jean. Consequently, the rheology and rock textures of individual cooling units are different from those of St-Jean. Mineral fractionation is more effective as well.The aims of this proposal are: (1) to complete the running project on St-Jean-du-Doigt, including refinement of thermal models, ion probe measurements on antecrystic zircons and interpretation of whole-rock geochemical data; (2) to start deciphering the complex architecture of the Punta Falcone intrusion through very detailed mapping and reconstitute the magma dynamics and construction mechanisms of the pluton; (3) to understand the processes responsible for the development of vertical rhythmic magmatic layering in the Punta Falcone gabbro; (4) to investigate the mineral, textural and chemical interactions between mafic and acid magmas in their contact zone; (5) to precisely establish the time and duration of the Punta Falcone magmatism through high-precision U-Pb zircon dating.
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