Fluid-driven metamorphism of the continental crust governed by nanoscale fluid flow
Published by: Oliver Plümper, Alexandru Botan, Catharina Los, Yang Liu, Anders Malthe-Sørenssen and Bjørn Jamtveit
Massive fluid-induced feldspar replacement in the Larvik batholith, Norway. a, Geological map showing the extent of feldspar replacement across 60 km2 . Inset shows the geographic location of the study area. b, Partly replaced larvikite. c,d, Magnified views showing the partial feldspar replacement. As the replacement goes to completion the original shape remains (pseudomorphism; dashed areas in d). Unaltered feldspars are greyish to dark blue in b to d, whereas the replaced, secondary feldspars appear pink-coloured in b and ochre/greenish coloured in c and d. Scale bars, 30 cm (b); 2 cm (c,d).
The transport of fluids through the Earth’s crust controls the redistribution of elements to form mineral and hydrocarbon deposits, the release and sequestration of greenhouse gases, and facilitates metamorphic reactions that influence lithospheric rheology. In permeable systems with a well-connected porosity, fluid transport is largely driven by fluid pressure gradients. In less permeable rocks, deformation may induce permeability by creating interconnected heterogeneities, but without these perturbations, mass transport is limited along grain boundaries or relies on transformation processes that self- generate transient fluid pathways. The latter can facilitate large-scale fluid and mass transport in nominally impermeable rocks without large-scale fluid transport pathways. Here, we show that pervasive, fluid-driven metamorphism of crustal igneous rocks is directly coupled to the production of nanoscale porosity. Using multi-dimensional nano-imaging and molecular dynamics simulations, we demonstrate that in feldspar, the most abundant mineral family in the Earth’s crust, electrokinetic transport through reaction-induced nanopores (<100 nm) can potentially be significant. This suggests that metamorphic fluid flow and fluid-mediated mineral transformation reactions can be considerably influenced by nanofluidic transport phenomena.