This study examines the potential influence of deformation on the systematics of Rb-Sr geochronology in mica phases under different conditions. Biotite and muscovite porphyroclasts in deformed specimens were characterized using electron backscattered diffraction, electron probe microanalysis and laser ablation inductively coupled plasma mass spectrometry to quantify spatial variations in crystal lattice orientations, element concentrations and in situ Rb-Sr geochronology. S29, a specimen subjected to deformation at greenschist facies conditions, is characterized by a spread in in situ Rb-Sr two-point isochron spot dates, which exhibit a strong inverse correlation with lattice deformation. As such, these Rb-Sr dates are interpreted to record partial re-equilibration controlled by deformation. Rb-Sr data from white mica in a specimen (NP17-58), which was deformed at lower amphibolite facies conditions, define a single population isochron. No correlation between lattice distortion and Rb-Sr spot dates is noted. Finally, two biotite porphyroclasts and matrix grains in a specimen (AC4), deformed at upper amphibolite facies conditions, define unique, single population Rb-Sr isochrons. The Rb-Sr systematics of the older porphyroclast are interpreted to be mainly temperature-controlled. In contrast, the Rb-Sr systematics for the younger porphyroclast and matrix grains are interpreted to reflect fluid-mediated resetting. The results of this study demonstrate that the multi-faceted influences on Rb-Sr systematics make isolating the effect of deformation difficult. Due to the complexity of the Rb-Sr systematics in deformed specimens, careful consideration of the mica phase analysed, as well as the temperatures, fluids and deformation experienced throughout the rock’s history, needs to be accounted for.

In this study, we used thermo–mechanical control process (TMCP) technique to investigate the effect of arisen dislocation density and texture components on hydrogen induced cracking susceptibility in as-received API X60 pipeline steel. Dislocations and texture components appeared during cold rolling and annealing treatments. X-ray diffraction and electron backscatter diffraction measurements were used to study these phenomena. We observed that the cold rolling and annealing treatments produced higher dislocation density in deformed and recovered regions. The increase of dislocation density also caused the increased hydrogen trap density. Macro-texture studies by x-ray method indicates that initial weak texture of as-received X60 steel was changed from ζ-fiber to γ-fiber and θ-fiber in 90% cold rolled and annealed specimen. Therefore, the number of grains with 〈100〉||ND orientation which had a harmful effect on hydrogen induced cracking susceptibility increased. The {100} dominant texture and high density of hydrogen traps mitigated against any possible benefits of the other microstructural parameters such as coincidence site lattice boundaries and grain size. As a result, we could not consider this process as a suitable method to increase hydrogen induced cracking resistance in pipeline steel.