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Coulomb failure of Earth's brittle crust controls growth, emplacement and shapes of igneous sills, saucer-shaped sills and laccoliths
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Mineralogy Petrology and Tectonics. Univ Oslo, Dept Geosci, NJORD Ctr, PGP, Oslo, Norway.ORCID iD: 0000-0001-9368-7494
Univ Oslo, Dept Geosci, NJORD Ctr, PGP, Oslo, Norway.
Univ Oslo, Dept Geosci, NJORD Ctr, PGP, Oslo, Norway.
Univ Oslo, Dept Geosci, NJORD Ctr, PoreLab, Oslo, Norway.
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2019 (English)In: Earth and Planetary Science Letters, ISSN 0012-821X, E-ISSN 1385-013X, Vol. 510, p. 161-172Article in journal (Refereed) Published
Abstract [en]

Tabular intrusions are common features in the Earth's brittle crust. They exhibit a broad variety of shapes, ranging from thin sheet intrusions (sills, saucer-shaped sills, cone sheets), to more massive intrusions (domed and punched laccoliths, stocks). Such a diversity of intrusion shapes reflects different emplacement mechanisms caused by contrasting host rock and magma rheologies. Most current models of tabular intrusion emplacement assume that the host rock behaves purely elastically, whereas numerous observations show that shear failure plays a major role. In this study, we investigate the effects of the host rock's Coulomb properties on magma emplacement by integrating (1) laboratory models using dry Coulomb granular model hosts of variable strength (cohesion) and (2) limit analysis numerical models. Our results show that both sheet and massive tabular intrusions initiate as a sill, which triggers shear failure of its overburden along an inclined shear damage zone at a critical sill radius, which depends on the emplacement depth and the overburden's cohesion. Two scenarios are then possible: (1) if the cohesion of the overburden is significant, opening of a planar fracture along the precursory weakened shear damage zones to accommodate magma flow, leads to the formation of inclined sheets, or (2) if the cohesion of the overburden is negligible, the sill inflates and lifts up the overburden, which is dissected by several faults that control the growth of a massive intrusion. Finally, we derive a theoretical scaling that predicts the thickness-to-radius aspect ratios of the laboratory sheet intrusions. This theoretical prediction shows how sheet intrusion morphologies are controlled by a mechanical equilibrium between the flowing viscous magma and Coulomb shear failure of the overburden. Our study suggests that the emplacement of sheet and massive tabular intrusions are parts of the same mechanical regime, in which the Coulomb behavior of the Earth's brittle crust plays an essential role.

Place, publisher, year, edition, pages
2019. Vol. 510, p. 161-172
Keywords [en]
magma emplacement, tabular intrusions, brittle shear failure, laboratory models, limit analysis
National Category
Geology
Identifiers
URN: urn:nbn:se:uu:diva-379329DOI: 10.1016/j.epsl.2019.01.011ISI: 000460069800016OAI: oai:DiVA.org:uu-379329DiVA, id: diva2:1298073
Funder
The Research Council of Norway, 244155The Research Council of Norway, 240767The Research Council of Norway, 262644European Science Foundation (ESF), 4673Available from: 2019-03-21 Created: 2019-03-21 Last updated: 2019-03-21Bibliographically approved

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Schmiedel, Tobias

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