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Oriented flow textures of magma mingling and mixing within a dyke: the basaltic-rhyolitic Streitishvarf composite dyke, Eastern Iceland

Tegan A. Havard 1, Janine L. Kavanagh1, Stefano Urbani1,2, Elisabetta Mariani1, Steffi Burchardt3

  • Affiliations: 1 Department of Earth, Ocean, and Ecological Sciences, University of Liverpool, United Kingdom 2 Department of Geological Survey of Italy, Institute for Environmental Protection and Research (ISPRA), Italy 3 Department of Earth Sciences, Uppsala University, Sweden

  • Presentation type: Poster

  • Presentation time: Tuesday 16:30 - 18:30, Room Poster Hall

  • Poster Board Number: 199

  • Programme No: 3.2.22

  • Theme 3 > Session 2

Abstract

Studying how magma flows in dykes can help with understanding how dykes transport magma vertically and laterally through the crust and up to the surface. The ~26-30 m wide Streitishvarf composite dyke (10.7 ± 0.2 Ma) in eastern Iceland exhibits macroscopic flow indicators where visually distinct, elongate mafic enclaves (<1 cm -- 1 m) are distributed through the felsic core (~10 m wide). The flow within the dyke and the magma interactions are studied at three sites along the dyke, spanning a horizontal distance of ~15 km and ~700 m of vertical distance. We collected photographs for enclave shape and distribution analyses and oriented hand samples for petrographic texture and mineralogy analyses. Our results show that in the south (deeper exposure), the enclaves in the felsic core are aligned sub-parallel to the strike of the dyke but are randomly oriented towards the dyke centre. This indicates the final preserved flow may have been more turbulent towards the centre. Towards the north (shallower depth), the enclaves are aligned sub-perpendicular to the dyke strike. At the microscale, the shape elongation of the feldspar crystals in the felsic core are of similar strike to the macroscale enclaves at each site. This indicates that the macroscale flow indicators are representative of the microscale flow texture. The mineral assemblages reveal magma mingling and mixing at the microscale throughout the samples. We discuss our results in terms of previous magnetic fabric analysis work at this dyke, magma recharge, and magma flow in dykes.