Residual stresses preserved in calcite from cave stalagmites and its impact on fluid inclusions

Stalagmites record valuable information within their crystal structure and composition about past climate and environmental changes. Stalagmite crystal fabrics reflect growth conditions: the crystallisation pathway influences the distribution of nano- to micro-particulates, crystal defects, and nano- to micro-porosities. These microstructures may act as nucleation sites for the formation of larger fluid inclusions — small cavities encapsulating relic drip water that are important climate archives. Stalagmite fluid inclusions are widely used for paleotemperature reconstructions using nucleation-assisted microthermometry and oxygen isotope thermometry. However, the influence of different crystallisation mechanisms and fabrics on fluid inclusion properties (e.g., water density and composition) and their preservation is still poorly constrained.

Here, we apply a crystallographic approach to investigate the internal crystal structure of two calcite stalagmites from Borneo and New Zealand. Our aim is to assess whether fluid inclusions are affected by post-growth deformation and/or volume changes and to quantify their impact on microthermometric data. This work seeks to identify non-thermal processes that could explain the observed scatter in microthermometry measurements from coeval fluid inclusions.

Previous electron backscatter diffraction (EBSD) analyses showed these samples exhibit columnar compact, open, and porous fabrics composed of mm- to cm-scale crystal domains, further subdivided into sub-domains characterised by rotations around the c-axis of up to 4°. Fluid inclusions are preferentially located along these sub-domain boundaries, indicating a strong relationship between fluid inclusion nucleation and crystal defects. High-angular resolution EBSD (HR-EBSD) reveals residual stresses up to 200–300 MPa located along the sub-domain boundaries. Since stalagmites form in a nominally stress-free environment, these stresses are interpreted as remnants of crystallisation energy stored in the lattice as crystallographic defects. High-resolution transmission electron microscopy (HR-TEM) confirms the presence of high densities of edge dislocations located along the sub-domain boundaries, that bend the crystal lattice and generate the observed misorientations and stress fields.

Our results demonstrate that fluid inclusions are located in mechanically fragile microstructural environments. The internal stresses stored by these microstructures may be released in response to external forces such as sample preparation or ambient temperature changes and could induce post-formation volume changes in fluid inclusions, ultimately biasing paleotemperature reconstructions. These quantified stress values provide a basis for evaluating the magnitude of this effect on microthermometric data.