Coupled interaction between fluid and deformation mechanisms in quartz

Fluids are widely recognized to weaken quartz and to be redistributed during deformation. However, integrated constraints that link water partitioning in natural quartz (fluid inclusions, grain boundaries, and crystal defects) to the evolution of dynamic recrystallization mechanisms (from SGR-dominated recrystallization, through increasing grain-boundary involvement, to GBM-dominated recrystallization) are still limited. Three types of quartz veins that are (sub-)parallel to foliation in the Xuelongshan metamorphic complex record a progressive shift in recrystallization style, providing an ideal natural laboratory to compare deformation mechanisms and fluid reservoirs.

We integrate field observations, microstructure, electron backscatter diffraction (EBSD), fluid inclusion (FI), laser Raman microspectroscopy (LRM), and Fourier-transform infrared spectroscopy (FTIR) to constrain coupled deformation-fluid evolution. All three quartz veins display widespread grain-size reduction and strong crystallographic fabrics. EBSD indicates dominant dislocation creep, with dynamic recrystallization evolving from subgrain rotation (SGR; Type I) through a transitional regime with enhanced grain boundary processes (Type II) toward grain boundary migration (GBM; Type III).

Fluid inclusions are mainly small, irregular, and are preferentially aligned along grain boundaries. Raman spectra from Types I and II quartz reveal a multicomponent fluid system including CO₂, SO₂, CH₄, and CO₃²⁻. FTIR spectra and spatial maps of bulk H₂O and Al-related OH demonstrate a systematic, mechanism-dependent redistribution of water among microstructural reservoirs. In SGR dominant quartz, water exist mainly as inclusion H₂O concentrated along (sub)grain boundaries, and inclusion deformation and rupture promote leakage so that recrystallized grains contain more bulk H₂O than porphyroclasts. Toward GBM, crystal defect OH increases significantly and the relative contribution of inclusion water decreases. In GBM dominant quartz, however, the proportion of defect water declines again as migrating boundaries efficiently sweep out dislocations and reduce the capacity for crystal defect H, despite continued high bulk H₂O.

Overall, our results suggest quartz deformed mechanism transitions are linked not only to the bulk water budget, but more critically to the redistribution of water among microstructural reservoirs (inclusions, grain boundaries, and defects), and to the evolving capacity of the microstructure to store mechanically effective water.