Electrical properties of a graphite-rich quartzite from a former lower continental crust exposed in the Serre San Bruno, Calabria (southern Italy)

Jödicke, H.; Nover, G.; Kruhl, Jörn H.; Markfort, Rudolf

doi:10.1016/j.pepi.2007.08.001

Cited by 9 publications

(3 citation statements)

References 34 publications

(23 reference statements)

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“…3 is in a broad region of shearing where oceanic mafic crustal elements are highly faulted and stacked above and below the Heathcote Fault Zone 23 , 24 , representing a zone of enhanced transient permeability during tectonism. The lower resistivity observed along the Heathcote Fault Zone may represent a zone of enhanced graphite deposition from CO 2 -rich fluids 27 , 37 , 38 evolved from tectonically thickened carbon-rich sediments.…”

Section: Introductionmentioning

confidence: 93%

“…Organic carbon in sediment may be metamorphosed to flake graphite at amphibolite grade conditions at depths of ~ 20–30 km and temperatures ~ 550 °C 34 . In addition, mobilised CO 2 may be precipitated as graphite 35 , 36 either at grain boundaries 27 or along more permeable zones 37 , 38 through retrograde hydration reactions where the host-rock oxygen fugacity (fO 2 rock ) is below the upper fO 2 limit of graphite 39 . We argue, therefore, that the low resistivity imaged ~ 30 km depth may be due to graphite.…”

Section: Introductionmentioning

confidence: 99%

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Lower crustal resistivity signature of an orogenic gold system

Heinson

Duan

Kirkby

et al. 2021

Sci Rep

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Orogenic gold deposits provide a significant source of the world’s gold and form along faults over a wide range of crustal depths spanning sub-greenschist to granulite grade faces, but the source depths of the gold remains poorly understood. In this paper we compiled thirty years of long-period magnetotelluric (MT) and geomagnetic depth sounding (GDS) data across western Victoria and south-eastern South Australia that have sensitivity to the electrical resistivity of the crust and mantle, which in turn depend on past thermal and fluid processes. This region contains one of the world’s foremost and largest Phanerozoic (440 Ma) orogenic gold provinces that has produced 2% of historic worldwide gold production. Three-dimensional inversion of the long-period MT and GDS data shows a remarkable correlation between orogenic gold deposits with > 1 t production and a < 20 Ω m low-resistivity region at crustal depths > 20 km. This low-resistivity region is consistent with seismically-imaged tectonically thickened marine sediments in the Lachlan Orogen that contain organic carbon (C), sulphides such as pyrite (FeS2) and colloidal gold (Au). Additional heat sources at 440 Ma due to slab break-off after subduction have been suggested to rapidly increase the temperature of the marine sediments at mid to lower crustal depth, releasing HS− ligands for Au, and CO2. We argue that the low electrical resistivity signature of the lower crust we see today is from a combination of flake graphite produced in situ from the amphibolite grade metamorphism of organic-carbon in the marine sediments, and precipitated graphite through retrograde hydration reactions of CO2 released during the rapid heating of the sediments. Thus, these geophysical data image a fossil source and pathway zone for one of the world’s richest orogenic gold provinces.

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Section: Introductionmentioning

confidence: 93%

Section: Introductionmentioning

confidence: 99%

Lower crustal resistivity signature of an orogenic gold system

Heinson

Duan

Kirkby

et al. 2021

Sci Rep

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“…In conclusion, our obtained experimental results on the electrical conductivities of the dry hot-pressed sintering gabbro with various mineralogical proportions (CpxXPl100-X, X = 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 vol%) at high temperature and high pressure are abnormally lower than those of field magnetotelluric data of the gabbro-rich regions, which cannot explain the high conductivity anomalies for the oceanic crust and West African craton. Some potential causes need to be considered conscientiously, such as the structural water in nominally anhydrous minerals [9,28,30,50,51], dehydration (oxidation-dehydrogenation) of hydrous minerals [23,52,53], partial melting [54][55][56][57], the interconnected high conductive phases [24,28,58,59], and the salinity-bearing (or water-bearing) fluids [15,31,[60][61][62], in the future. Although the present acquired electrical conductivity results on the dry hot-pressed sintering gabbro with various mineralogical proportions cannot explain the high conductivity anomaly in the oceanic crust and West African craton, it can provide one reasonable constraint on the mineralogical composition in these representative gabbro-rich regions.…”

Section: Geophysical Implicationsmentioning

confidence: 99%

Effect of Different Mineralogical Proportions on the Electrical Conductivity of Dry Hot-Pressed Sintering Gabbro at High Temperatures and Pressures

Wang

Dai

et al. 2022

Minerals

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Electrical conductivities of the dry hot-pressed sintering gabbro with various mineralogical proportions (CpxXPl100–X, X = 0, 10, 20, 30, 40, 50, 60, 70, 80, 90, and 100 vol% (the signals of Cpx and Pl denote clinopyroxene and plagioclase, respectively) were measured in the YJ-3000t multi-anvil pressure and Solartron-1260 impedance spectroscopy analyzer at temperatures of 773–1073 K and pressures of 1.0–3.0 GPa. At the given pressure conditions, the electrical conductivity and temperature conformed to an Arrhenius relation. For the fixed mineralogical composition of Cpx50Pl50, the electrical conductivities of the samples significantly increased with the rise of temperature, but slightly decreased with increasing pressure. Furthermore, the activation energy and activation volume were determined as 1.06 ± 0.12 eV and 6.00 ± 2.00 cm3/mole, respectively. As for the various mineralogical compositions of dry gabbro, the electrical conductivities of the samples increased with the rise of volume percentage of clinopyroxene (Cpx) at 1.0 GPa. It is proposed that the main conduction mechanism is the small polaron, owing to the positive relation between the electrical conductivity and the iron content in samples. On the basis of these obtained conductivity results, laboratory-based electrical conductivity–depth profiles for the hot-pressed sintering gabbro with various mineralogical proportions and temperature gradients were successfully established. In conclusion, although the present acquired electrical conductivity results on the dry hot-pressed sintering gabbro with various mineralogical proportions cannot explain the high conductivity anomaly in the oceanic crust and West African craton, it can provide one reasonable constraint on the mineralogical composition in these representative gabbro-rich regions.

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Unstable graphite films on grain boundaries in crustal rocks

Yoshino

Noritake

2011

Earth and Planetary Science Letters

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Electrical properties of a graphite-rich quartzite from a former lower continental crust exposed in the Serre San Bruno, Calabria (southern Italy)

Cited by 9 publications

References 34 publications

Lower crustal resistivity signature of an orogenic gold system

Lower crustal resistivity signature of an orogenic gold system

Effect of Different Mineralogical Proportions on the Electrical Conductivity of Dry Hot-Pressed Sintering Gabbro at High Temperatures and Pressures

Unstable graphite films on grain boundaries in crustal rocks

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