Details

Autor(en) / Beteiligte

• Jamtveit, Bjørn
• Petley‐Ragan, Arianne
• Incel, Sarah
• Dunkel, Kristina G.
• Aupart, Claire
• Austrheim, Håkon
• Corfu, Fernando
• Menegon, Luca
• Renard, François

Titel

The Effects of Earthquakes and Fluids on the Metamorphism of the Lower Continental Crust

Ist Teil von

• Journal of geophysical research. Solid earth, 2019-08, Vol.124 (8), p.7725-7755

Ort / Verlag

Washington: Blackwell Publishing Ltd

Erscheinungsjahr

2019

Link zum Volltext

Quelle

Wiley Online Library - AutoHoldings Journals

Beschreibungen/Notizen

• Rock rheology and density have first‐order effects on the lithosphere's response to plate tectonic forces at plate boundaries. Changes in these rock properties are controlled by metamorphic transformation processes that are critically dependent on the presence of fluids. At the onset of a continental collision, the lower crust is in most cases dry and strong. However, if exposed to internally produced or externally supplied fluids, the thickened crust will react and be converted into a mechanically weaker lithology by fluid‐driven metamorphic reactions. Fluid introduction is often associated with deep crustal earthquakes. Microstructural evidence, suggest that in strong highly stressed rocks, seismic slip may be initiated by brittle deformation and that wall‐rock damage caused by dynamic ruptures plays a very important role in allowing fluids to enter into contact with dry and highly reactive lower crustal rocks. The resulting metamorphism produces weaker rocks which subsequently deform by viscous creep. Volumes of weak rocks contained in a highly stressed environment of strong rocks may experience significant excursions toward higher pressure without any associated burial. Slow and highly localized creep processes in a velocity strengthening regime may produce mylonitic shear zones along faults initially characterized by earthquake‐generated frictional melting and wall rock damage. However, stress pulses from earthquakes in the shallower brittle regime may kick start new episodes of seismic slip at velocity weakening conditions. These processes indicate that the evolution of the lower crust during continental collisions is controlled by the transient interplay between brittle deformation, fluid‐rock interactions, and creep flow. Plain Language Summary When continents collide, a mountain range form along the collision zone in an area referred to as an orogenic belt. The evolution of orogenic belts depends on the physical properties of the different layers in the Earth's crust and upper mantle. During a continent‐continent collision, the mechanical strength and density of these layers change. We discuss transformation processes in the lower part of the continental crust during the formation of an orogenic belt. We emphasize the critical role of fluids and show that introduction of fluids to initially dry lower crust is often associated with earthquakes. Earthquakes cause fracturing and fragmentation and allow fluids to migrate into highly reactive dry rocks. This results in the formation of weaker rocks, which subsequently deform slowly along zones where earthquakes initially occurred. Earthquakes in the upper crust may subsequently send stress pulses to the lower crust to trigger new generations of earthquakes. Key Points When continents collide, the lower crust is dry and strong and subject to high mechanical stress Introduction of fluids to the lower crust is often associated with earthquakes Fluid‐induced metamorphism may cause a transition from brittle to ductile deformation of the lower crust