Emplacement of magma pulses and growth of magma bodies

Thierry Menand (1) , Michel de Saint-Blanquat (2) , Catherine Annen (1)

1 School of Earth Sciences [Bristol]
2 GET - Géosciences Environnement Toulouse

Magmatism is responsible for the formation of continental and oceanic crusts. It is the main agent of mass and heat transfers from the mantle towards the crust, the hydrosphere (oceanic and continental hydrothermalism) and the atmosphere (emissions of volcanic gas and ashes). Its expressions are the crystallization of intrusive rocks and the eruption of volcanic products. However, with a ratio between the volumes of extrusive and intrusive magmatic rocks estimated to be of the order of 1:5 for most magmatic systems (White et al., 2006), one of the main characteristics of magmatism is that magmas rarely reach the Earth's surface. This suggests that the prevailing conditions in the crust are not favourable to the arrival of magma on the Earth's surface, but instead lean heavily towards the formation of intrusive bodies in the crust. These intrusive bodies, referred to here as plutons, constitute the elementary building brick of the continental crust. An increasing number of geophyscial and geochronological data as well as geological observations is currently modifying our understanding of pluton construction. When plutons were initially envisaged as quasi-spherical bodies growing slowly and essentially by an overall inflation, they are now recognized as growing incrementally by the accretion of successive and relatively small magma pulses, over variable periods of time, from hundred to millions of years, depending on geodynamic setting and source fertility. This brings new challenges and has far-reaching implications. According to this new model of plutonism, the evolution of magma bodies is related to the processes that control the timescale and the spatial distribution of the successive pulses. Depending on their emplacement rate and on their ability to amalgamate, repeated magma pulses can either rapidly solidify or ultimately build up an active magma chamber. Thus understanding how magma bodies grow has fundamental implications for the link between volcanism and plutonism as well as for magma differentiation and ultimately for our understanding of the growth and evolution of the Earth crusts. The concept of pluton incremental growth challenges our understanding as well as our field interpretations of the processes involved during pluton construction. Indeed, these processes and how they operate in governing the emplacement and growth of plutons, both in space and time, are still debated. A state-of-the-art session on these very issues was held at the 2008 General Assembly of the European Geosciences Union. As a follow-up of this session, this special volume Emplacement of magma pulses and growth of magma bodies brings together both theoretical models and field studies that cover most aspects of the emplacement and growth of plutons.

Mots clés: Granite; Sills; Plutons; Incremental emplacement; Granite

Domaines: Volcanologie

Thierry Menand, Michel de Saint-Blanquat, Catherine Annen. Emplacement of magma pulses and growth of magma bodies. Tectonophysics, 2011, 500 (1-4), pp.1-2. ⟨10.1016/j.tecto.2010.05.014⟩. ⟨hal-01146246⟩