Mineral inclusions are common and have been widely used to investigate complex geological history. When a rock undergoes cooling and decompression after the entrapment of an inclusion into a host mineral, residual pressure may develop within the inclusion because of the differences in thermal expansivity and compressibility between the inclusion and host. By combining laser Raman spectroscopy and experimental data relating hydrostatic pressure and Raman shift, it is possible to estimate the entrapment pressure-temperature (P-T) conditions using an isotropic elastic model. In this study, we report Raman spectroscopic data on both zircon and quartz inclusions in garnet host from the Holsnøy eclogite, Bergen Arcs, Norway.Averaged residual pressures based on different Raman peaks for zircon and quartz inclusions are obtained to be ca. 0.6GPa and ca. 0.65GPa respectively. Using the equation of state for zircon and quartz, the entrapment P-T conditions are constrained to be 1.7~1.9GPa, 680~760 o C, consistent with previous estimates based on phase equilibria. Heating/cooling experiments are performed on an entrapped zircon inclusion. A clear trend is found between the residual zircon inclusion pressure and the externally controlled temperature. We show that the residual zircon inclusion pressure sealed in garnet host is very sensitive to the entrapment temperature, and can be used as a Raman-thermometer. The effects of laser heating and the thermo-elastic anisotropy of zircon inclusion are quantified and discussed.

A novel electron backscatter diffraction (EBSD) ‐based finite‐element (FE) wave propagation simulation is presented and applied to investigate seismic anisotropy of peridotite samples. The FE model simulates the dynamic propagation of seismic waves along any chosen direction through representative 2D EBSD sections. The numerical model allows separation of the effects of crystallographic preferred orientation (CPO) and shape preferred orientation (SPO). The obtained seismic velocities with respect to specimen orientation are compared with Voigt‐Reuss‐Hill estimates and with laboratory measurements. The results of these three independent methods testify that CPO is the dominant factor controlling seismic anisotropy. Fracture fillings and minor minerals like hornblende only influence the seismic anisotropy if their volume proportion is sufficiently large (up to 23%). The SPO influence is minor compared to the other factors. The presented FE model is discussed with regard to its potential in simulating seismic wave propagation using EBSD data representing natural rock petrofabrics.

Abstract. Residual pressure can be preserved in mineral inclusions, e.g. quartz-in-garnet, after exhumation due to differential expansion between inclusion and host crystals. Raman spectroscopy has been applied to infer the residual pressure and provides information on the entrapment temperature and pressure conditions. However, the amount of residual pressure relaxation cannot be directly measured. An underestimation or overestimation of residual pressure may lead to significant errors between calculated and actual entrapment pressure. This study focuses on three mechanisms responsible for the residual pressure modification: (1) viscous creep; (2) plastic yield; (3) proximity of inclusion to the thin-section surface. Criteria are provided to quantify how much of the expected residual pressure is modified due to these three mechanisms. An analytical solution is introduced to demonstrate the effect of inclusion depth on the residual pressure field when the inclusion is close to the thin-section surface. It is shown that for a quartz-in-garnet system, the distance between the thin-section surface and inclusion centre needs to be at least 3 times the inclusion radius to avoid pressure release. In terms of viscous creep, representative case studies on a quartz-in-garnet system show that viscous relaxation may occur from temperatures as low as 600–700 ∘C depending on the particular pressure–temperature (P–T) path and various garnet compositions. For quartz entrapped along the prograde P–T path and subject to viscous relaxation at peak T above 600–700 ∘C, its residual pressure after exhumation may be higher than predicted from its true entrapment conditions. Moreover, such a viscous resetting effect may introduce apparent overstepping of garnet nucleation that is not related to reaction affinity.

The evolution of microdamage (interfacial dewetting) in highly filled elastomers under consideration of high deformation gradients is examined. The interface between hard (rigid, two-dimensional) inclusions embedded in an elastomer characterized by a three-term Ogden (rate insensitive) model, and the elastomer matrix is represented by a cohesive-zone type interfacial model to follow the whole process of interfacial dewetting and its effect on the global (multiphase) material response in a plane strain setting. The analysis is carried out through a mixed finite element formulation for hyperelasticity, incorporating interface elements. We consider the effects of particle geometry and loading conditions on the process of interfacial failure. The results indicate that the distributed failure process is highly unstable and depends heavily on the size, shape, orientation and interactions of inclusions as well as the global loading conditions. The overall material behavior of the model agrees qualitatively with experimental observation.

Tectonic forces and surface erosion lead to the exhumation of rocks from the Earth’s interior. Those rocks can be characterized by many variables including peak pressure and temperature, composition and exhumation duration. Among them, the duration of exhumation in different geological settings can vary by more than ten orders of magnitude (from hours to billion years). Constraining the duration is critical and often challenging in geological studies particularly for rapid magma ascent. Here, we show that the time information can be reconstructed using a simple combination of laser Raman spectroscopic data from mineral inclusions with mechanical solutions for viscous relaxation of the host. The application of our model to several representative geological settings yields best results for short events such as kimberlite magma ascent (less than ~4,500 hours) and a decompression lasting up to ~17 million years for high-pressure metamorphic rocks. This is the first precise time information obtained from direct microstructural observations applying a purely mechanical perspective. We show an unprecedented geological value of tiny mineral inclusions as timekeepers that contributes to a better understanding on the large-scale tectonic history and thus has significant implications for a new generation of geodynamic models.