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Mechanical anisotropies and mechanisms of mafic magma ascent in the middle continental crust: The Sondalo magmatic system (N Italy)
- Source :
- Geological Society of America Bulletin, Geological Society of America Bulletin, Geological Society of America, 2018, 130 (1-2), pp.331-352. ⟨10.1130/B31693.1⟩
- Publication Year :
- 2017
- Publisher :
- Geological Society of America, 2017.
-
Abstract
- International audience; Magma transfer between lower and upper continental crust is a fundamental process linking the dominantly mafic composition of the lower crust with the more felsic composition of the upper crust. We explore the mechanisms of mafic magma ascent and emplacement in the middle crust by studying a mid-crustal gabbroic to dioritic magmatic system (Sondalo complex, Eastern Central Alps, N Italy). We characterize the structure and Anisotropy of Magnetic Susceptibility (AMS) fabric of concentric gabbroic to dioritic intrusions. The significance of AMS fabrics is discussed using Anisotropy of Anhysteretic Remanent Magnetization (AARM) and Crystallographic Preferred Orientation (CPO) data acquired on different test sites. The magmatic and magnetic fabrics of the pluton were acquired during its emplacement in the Permian and were not subsequently tilted: the fabrics are essentially vertical, indicating vertical magma transfer through the crust with a two-phase intrusion history. (1) The concordant orientation between the magmatic foliation and the host-rock xenoliths in the center of the pluton suggest that the first magma ascent phase occurred along pathways subparallel to the vertical fabric of the host metasedimentary rocks. (2) The second magma ascent phase was controlled by a change in the rheology of the host-rock and the mafic magma. Heat dissipation to the contact aureole induced partial melting, thereby lowering the mechanical strength of the host-rocks, whereas the viscosity of the mafic magma increased due to cooling and associated fractional crystallization. This caused an en-masse rise of the pluton resulting in the formation of a structural aureole, i.e. a vertical foliation in the contact aureole and a weaker but concordant magmatic foliation at the rim of the pluton. This ascent phase accounts for the P−T evolution recorded by metasedimentary rocks in the contact aureole of the pluton.
- Subjects :
- Fractional crystallization (geology)
Felsic
010504 meteorology & atmospheric sciences
Gabbro
Continental crust
Pluton
[SDU.STU.PE]Sciences of the Universe [physics]/Earth Sciences/Petrography
Geochemistry
Geology
Ascent mechanism
010502 geochemistry & geophysics
01 natural sciences
Magmatic water
[SDU.STU.GC]Sciences of the Universe [physics]/Earth Sciences/Geochemistry
Magma
[SDU.STU.VO]Sciences of the Universe [physics]/Earth Sciences/Volcanology
AMS
Mafic
Mid-crustal intrusion
Permian magmatism. Short title: Mid-crustal gabbro emplacement
[SDU.STU.MI]Sciences of the Universe [physics]/Earth Sciences/Mineralogy
0105 earth and related environmental sciences
Subjects
Details
- ISSN :
- 00167606
- Volume :
- 130
- Database :
- OpenAIRE
- Journal :
- GSA Bulletin
- Accession number :
- edsair.doi.dedup.....f15312ad4457937a887a1da82782bc35