No abstract

Poppe et al. An Inside Perspective on Magma Intrusion KEYPOINTS -Cutting-edge dynamic wide beam X-ray Computed Tomography and Digital Volume Correlation allows an inside view on the temporal behavior of analog magma intrusion in granular host material in laboratory experiments. -Intrusion-induced 3D displacement and strain can be quantified over time. -Thick cryptodomes form with distributed strain and mixedmode fracturing in weak host materials. -Thin dikes form with localized strain and opening-mode fracturing in strong host materials. -A continuum of cone sheet geometries occurs in between these end-members. Frontiers in Earth Science | www.frontiersin.org

No abstract

No abstract

Two end‐member conceptual models are used to describe deformation of the Earth's crust induced by magma intrusion. “Mode I” fracturing assumes tensile or opening‐mode, elastic deformation, while “Mode II” fracturing assumes plastic shear‐mode deformation around a viscous indenter. Field observations of both mechanisms exist, but it remains unclear which mechanism dominates in which conditions. We describe intrusion geometries, host rock deformation, and geochemical magma‐host rock interactions around 53 exceptionally preserved, tephrite‐basanite Permian dike segments of 0.5‐ to 30‐cm thickness. These thin dikes, that is, “dikelets,” intruded Late‐Ordovician carbonate‐rich sedimentary rocks on Hovedøya island, Oslo Rift, Norway. Dikelets emplaced in preexisting fractures dominantly created cavities ahead of their narrow, tapering tips and are associated with bent host rock, broken bridges, and stepped segmented geometries. Other tips are blunt with dense brittle fracturing around them. Also, cross‐sectional intrusion segment opening profiles deviate from parabola‐shaped profiles typical for elastic media. The observations demonstrate that dominant opening‐mode host rock deformation can coexist with shear‐mode deformation locally. Alignment of most dikelet segments along the dominant host rock fracture directions highlights the control of local structural orientations on magma emplacement. Analysis of bulk major and trace element compositions, in situ micro‐XRF sample analysis and carbon and oxygen stable isotope compositions, suggests that thermochemical interactions between magma and the carbonate‐rich host rock produced a low‐viscosity mixture of magma, pore water, and gas. We propose that such low‐viscosity hybrid fluid may assist in the intrusion of magma in sedimentary rocks by filling the cavity ahead of propagating sheet intrusion tips.