Tracing wedge-internal deformation by means of strontium isotope systematics of vein carbonates

Abstract

Radiogenic strontium isotopes (87Sr/86Sr) of vein carbonates play a central role in the tectonometamorphic study of fold-and-thrust belts and accretionary wedges and have been used to document fluid sources and fluxes, for example, along major fault zones. In addition, the 87Sr/86Sr ratios of vein carbonates can trace the diagenetic to metamorphic evolution of pore fluids in accreted sediments. Here we present 87Sr/86Sr ratios of vein carbonates from the Infrahelvetic flysch units of the central European Alps (Glarus Alps, Switzerland), which were accreted to the North Alpine fold-and-thrust belt during the early stages of continental collision. We show that the vein carbonates trace the Sr isotopic evolution of pore fluids from an initial seawater-like signature towards the Sr isotopic composition of the host rock with increasing metamorphic grade. This relationship reflects the progressive equilibration of the pore fluid with the host rock and allows us to constrain the diagenetic to low-grade metamorphic conditions of deformation events, including bedding-parallel shearing, imbricate thrusting, folding, cleavage development, tectonic mélange formation and extension. The strontium isotope systematics of vein carbonates provides new insights into the prograde to early retrograde tectonic evolution of the Alpine fold-and-thrust belt and helps to understand the relative timing of deformation events.

The Geometry, Spatial Distribution and Texture of Slate‐Hosted Calcite Veins in the Helvetic Flysch Units—Insights in Structural and Fluid Processes Within a Paleo‐Accretionary Complex

“…Particular when being associated with layer-parallel veins, keeping in mind that we only examined samples from vein arrays, these densely spaced micron-veinlets constitute a pervasive micro-fracture network that enabled layer/foliation-perpendicular fluid transport. Note that in contrast to the cm-to dm-wide isolated G1 and G2 veins treated by Dielforder et al (2015Dielforder et al ( , 2016Dielforder et al ( , 2022 the layer-parallel veins of our study appear in layer-parallel vein arrays and vein array clusters, respectively, with characteristic spacings of 50-100 m and 400-700 m (Figures 2c and 10a). Hence, they indicate a time-integrated accumulation of layer-parallel fluid transport channelized at least at three scales.…”

“…If this hypothesis is correct, one expects that the source fluids for the steep veins are largely derived from the slate itself. This prediction has been proposed on the base of Sr-isotopes for G2 and G3 veins by Dielforder et al (2015Dielforder et al ( , 2016Dielforder et al ( , 2022. Parallel veins may also be promoted by hydraulic fracturing requiring high pore-fluid pressures for their formation.…”

How the geochemistry of syn-kinematic calcite cement depicts past fluid flow and assists structural interpretations: a review of concepts and applications in orogenic forelands

“…Indeed, calcite crystals can keep their initial chemical signature pristine at low-grade metamorphism (e.g. Dielforder et al 2022), so it is important to discard the idea that dissolution/reprecipitation or recrystallization processes affected the cement. A classical tool used for that purpose is cathodoluminescence (Fig.…”

“…Consequently, the 87 Sr/ 86 Sr value of a calcite cement has been used in numerous past fluid reconstructions, sometimes showing that fluids flowed in contact with radiogenic materials (Travé et al 2000;Beaudoin et al 2011Beaudoin et al , 2014a, and sometimes preserving a pristine seawater signature in spite of being buried to metamorphic conditions (Dielforder et al 2015(Dielforder et al , 2022. Even if the 87 Sr/ 86 Sr ratio does not vary during dissolution and precipitation, the recrystallization of calcite during diagenesis can release Sr in the fluid, altering its 87 Sr/ 86 Sr ratio (Dielforder et al 2022). Another example of misleading Sr radiogenic measurement has been documented in the vicinity of diapirs (Pichat et al 2018), where the present-day seawater yields the radiogenic signature of the underlying evaporites.…”

“…Lacroix et al 2014;de Graaf et al 2019;Smeraglia et al 2019), deformation bands (Parry et al 2004;Fossen et al 2007;Zuluaga et al 2016;del Sole et al 2020), and vein networks at the scale of the fold and at the scale of the entire FTB/BF (e.g. Ferket et al 2000;Roure et al 2005;Sibson, 2005;Fischer et al 2009;Beaudoin et al 2011Beaudoin et al , 2014aBeaudoin et al , 2015Fitz-Diaz et al 2011a;Evans & Fischer, 2012;Crognier et al 2018;de Graaf et al 2019;Dielforder et al 2022).…”