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Ultra-high pressure and ultra-reduced minerals in ophiolites may form by lightning strikes

C. Ballhaus1,

1Steinmann Institute, University of Bonn, Germany

R. Wirth2,

2Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Potsdam, Germany

R.O.C. Fonseca1,

1Steinmann Institute, University of Bonn, Germany

H. Blanchard1,

1Steinmann Institute, University of Bonn, Germany

W. Pröll3,

3Wehrtechnische Dienststelle, WTD 81, Greding, Germany

A. Bragagni4,

4Institute of Geology and Mineralogy, University of Cologne, Germany

T. Nagel5,

5Department of Geoscience, University of Århus, Denmark

A. Schreiber2,

2Helmholtz Centre Potsdam, GFZ German Research Centre for Geosciences, Potsdam, Germany

S. Dittrich6,

6Fraunhofer Institute for Building Physics Holzkirchen, Germany

V. Thome6,

6Fraunhofer Institute for Building Physics Holzkirchen, Germany

D.C. Hezel4,

4Institute of Geology and Mineralogy, University of Cologne, Germany

R. Below4,

4Institute of Geology and Mineralogy, University of Cologne, Germany

H. Cieszynski4

4Institute of Geology and Mineralogy, University of Cologne, Germany

Affiliations  |  Corresponding Author  |  Cite as  |  Funding information

Ballhaus, C., Wirth, R., Fonseca, R.O.C., Blanchard, H., Pröll, W., Bragagni, A., Nagel, T., Schreiber, A., Dittrich, S., Thome, V., Hezel, D.C., Below, R., Cieszynski, H. (2017) Ultra-high pressure and ultra-reduced minerals in ophiolites may form by lightning strikes. Geochem. Persp. Let. 5, 42–46.

German Research Council (DFG).

Geochemical Perspectives Letters v5  |  doi: 10.7185/geochemlet.1744
Received 06 July 2017  |  Accepted 31 October 2017  |  Published 20 November 2017

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Figure 1 Experimental arrangement. A basalt cuboid surrounded by a 7 mm thick steel sleeve. The epoxy resin serves as electric insulator to prevent the current from short circuiting around the sample through the steel sleeve. Current pulses are generated with a pulse generator of the type SSG 10 kV/100 kJ (Haefely). The capacity of the pulse generator is 2140 µF. It can be charged to 10 kV. The energy achievable is 100 kJ. The pulse width depends on the load and is of the order of a few hundred microseconds.
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Figure 2 Images in BSE mode of plasma deposits. (a) Cross section of a crack covered by an up to 100 µm wide porous glass rim, resting upon a cpx phenocryst from the basaltic target rock. (b) Thermally resorbed cpx covered by inclusion-free glass (in situ melt), a chain of metal beads (arrow), and porous metal-bearing silicate glasses to the upper left (see text). (c) Larger exsolved metal globule within silicate glass; in situ glass to the right of the metal chain (arrow). (d) A metal globule in detail; bright quench phases are W-Ti metal, medium grey are Fe silicides, darker grey are SIC, and dark spherules are carbon condensates.
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Figure 3 Transmission electron (TEM) images of a metal globule. (a) Overview; bright Ti bearing W metals coexisting with Fe5Si3 xifengite, SiC moissanite (darker grey), and black carbon spherules (C). (b) Dark field image of W-Ti alloy in contact with xifengite. (c) HRTEM image of xifengite and fast Fourier transform (FFT) as inset. (d) Beta-SiC intergrown with Fe silicides. (e) HRTEM image of SiC with FFT as inset. (f) Amorphous carbon surrounded by graphene layers in concentric arrangement around amorphous cores, possibly shell fullerenes; FFTs as insets.
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Figure 4 Images of plasma spherules in secondary electron (SEM) mode, sputtered with Au. (a) and (b) Oxide spherules; surfaces composed of porous Fe-O oxide platelets. (c) Silicate glass spherule. (d) and (e) Surface crystals of Fe oxide spherules (? wüstite) in detail. (f) A quench oxide crystal on edge, apparently composed of multiple layers of nano-spherules. Note that all spherules shown are from an experiment where metallic Fe metal electrodes were used instead of W metal.
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