Interaction between propagating basaltic dikes and pre-existing fractures : A case study in hyaloclastite from Dyrfjoll, Iceland

• Magma in the Earth's crust is commonly transported through dikes. Fractures and faults, which are common in the shallow crust, form structural weaknesses that can act as energy-efficient propagation pathways. Although examples of this are known from active and extinct volcanoes in varying host rocks, the conditions and mechanisms of how and when dikes are influenced by these structures are not yet fully understood. This study investigates how basaltic dikes propagating through hyaloclastite in the shallow crust interact with pre-existing fractures. Using virtual 3D-models from drone-based photogrammetry, we mapped basaltic dikes exposed in a caldera-filling hyaloclastite in the extinct Dyrfjoll volcano, NE-Iceland, to measure the orientations of fractures and dikes, and quantify their interactions. We observe 39 changes in strike among 45 dikes and found a strong control of the governing stress field on orientations and interactions. Three types of dike-fracture interaction were identified: (1) Dikes propagating along pre-existing fractures. This is most frequently observed for dikes following the tectonic stress field. (2) Dikes with an abrupt change in strike occurring near or at a crosscutting fracture, but without magma flow into the fracture. (3) Dikes arrested at a crosscutting fracture. Such dikes may develop offshoots near the dike tip, which may approach the fracture at different angles and be able to cut across. Understanding how dikes interact with pre-existing fractures in moderately fractured host rock such as hyalo-clastite is relevant for hazard assessment and monitoring of volcanically active areas.

Ämnesord

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geologi (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geology (hsv//eng)

NATURVETENSKAP  -- Geovetenskap och miljövetenskap -- Geofysik (hsv//swe)

NATURAL SCIENCES  -- Earth and Related Environmental Sciences -- Geophysics (hsv//eng)

Nyckelord

Dike propagation

Dike-fracture interaction

Volcano-tectonic interaction

Hyaloclastite

Photogrammetry

Iceland

Publikations- och innehållstyp

ref (ämneskategori)

art (ämneskategori)