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[Geophysical Research Letters]
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Supporting Information for
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[Anatomy of an extinct magmatic system along a divergent plate boundary: Alftafjordur,
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Iceland]
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[S. Urbani1, D. Trippanera1, M. Porreca2,3, C. Kissel4 and V. Acocella1]
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[1Dipartimento di Scienze, Università Roma Tre, Rome, Italy, 2Dipartimento di Fisica e Geologia, Università di
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Perugia, Perugia, Italy, 3Istituto Nazionale di Geofisica e Vulcanologia (INGV), L’Aquila, Italy, 4Laboratoire des
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Sciences du Climat et de l'Environnement, CEA-CNRS-UVSQ, Gif-sur-Yvette Cedex, France]
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Contents of this file
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Figures S1 to S5
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Table S1
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Introduction
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[Supplementary material about the field and AMS analysis.]
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Figure S1. Main magnetic anisotropy features and orientations of the principal axes. Mean bulk susceptibility, K m =
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(Kmax+Kint+Kmin) / 3 (10E-03 SI); magnetic lineation, L = Kmax / Kint; magnetic foliation, F = Kint / Kmin; shape parameter,
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T = [2(η2−η3)/(η1−η3)−1]; anisotropy degree, Pj = exp{2[(η1−η)2+(η2−η)2+(η3−η)2]}1/2; D = declination of the principal
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axes; I = inclination of principal axes (standard deviation values in parentheses). η1, η2, η3 and η represent the natural log
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(ln) of Kmax, Kint, Kmin and Km respectively. T and Pj defined as proposed by [Jelinek, 1981]. The dark and light gray lines
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refer to two dikes sampled in different locations. C= Number of cores. N= Number of samples.
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Figure S2. a) Location of the sections for the calculation of the along-strike dike frequency. The dotted lines indicate
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that the number of dikes has been extrapolated assuming that along a profile the dike frequency for unit length in the off
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shore portion is the same as that on shore portion of each section. Redrawn from [Paquet et al., 2007]. b): Dike number
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vs. distance from volcanic center. A,B,C,D refer to the sections in a. c): Data utilized to calculate dike frequency along
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the swarm. D= distance from volcanic center. N= number of dikes.
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Figure S3. Dike density along the Alftafjordur volcanic system based only on data from the present study. The red
and black lines show the attitude of faults and dikes respectively.
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Figure S4. a) View of a main fault plane and of the offset of the greenish ignimbrite. b) Stereographic projection of
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dikes plane and poles (red), of the secondary fault planes (green) and of the main fault plane (black). c) Zoom on the fault
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plane outcrop (the white circle in a) sketched in (d).
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Figure S5. Typical Pj profile along the dike section with low values along the margins and anomalous very high
values in the inner part.
Table S1. Data of the kinematic indicators of 7 dikes sampled for AMS analysis.