The control of shear‐zone development and electric conductivity by graphite in granulite: An example from the Proterozoic Lofoten‐Vesterålen Complex of northern Norway

• Published in: Terra Nova
• Main Authors: Engvik, Ane K., Gautneb, Håvard, Baranwal, Vikas C., Rønning, Jan‐Steinar, Knežević Solberg, Janja, Liu, Yunhe, Austrheim, Håkon
• Other Authors: Norges Geologiske Undersøkelse
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2021
• Subjects: Lofoten; Northern Norway; Vesterålen
• Online Access: http://dx.doi.org/10.1111/ter.12545; https://onlinelibrary.wiley.com/doi/pdf/10.1111/ter.12545; https://onlinelibrary.wiley.com/doi/full-xml/10.1111/ter.12545

Abstract Graphite impacts crustal rheology and electric conductivity in the lower crust. In a combined geophysical and geological study from the Proterozoic Lofoten‐Vesterålen Complex, Norway, we show the enrichment of graphite resulted in zones with strong schistosity and a sharp strain gradient towards host massive granulite gneiss. Increased graphite content resulted in high‐conductivity zones with true resistivity values <10 Ωm compared with a resistivity of >3,000 Ωm in the low‐conductive crust. The regionally distributed graphite zones contain up to 39% graphite with variable amounts of quartz, feldspars, biotite and pyroxenes and where graphite is present in stable assemblage to orthopyroxene. High‐ordered graphite and biotite with a strong‐preferred orientation define the well‐developed foliation. Our results demonstrate that graphite accounts for the high electric conductivity of this former Proterozoic lower‐crustal segment. The presence of graphite causes strain localisation in the granulite facies crust, reducing crustal strength and may thereby influence continental architecture and evolution of collision zones.