Elastic Barometry and Ti‐in‐Quartz Thermometry Evidence for a Layered Lower Crust Beneath the Central Qilian Arc, NW China

ABSTRACT

This study reconstructs the pressure–temperature (P–T) structure of a deep continental arc crustal section in the western Central Qilian belt by integrating quartz‐in‐garnet elastic thermobarometry (QuiG) with Ti‐in‐quartz thermometry (TiQ). We examined lower crustal rocks from the Yemananshan and Heigou complexes, measuring residual stresses and Ti concentrations in 297 quartz inclusions using micro‐Raman spectroscopy and electron‐probe microanalysis. For 107 isotropic inclusions with a residual elastic strain anisotropy parameter (∣A∣ ≤ 0.003), the hydrostatic and Grüneisen tensor methods of QuiG yielded a pressure difference of < 0.34 GPa at 650°C. Most inclusions (101/107) have a positive Raman shift and yield metamorphic conditions of 0.90 ± 0.05–1.10 ± 0.04 GPa and 631°C ± 28°C–709°C ± 22°C for the Yemananshan Complex. The Heigou Complex yields higher pressures of 1.09 ± 0.06–1.29 ± 0.04 GPa and temperatures of 691°C ± 29°C–755°C ± 32°C. These results are consistent with P–T estimates derived from phase equilibrium modelling. The reconstructed P–T structure reveals clear vertical stratification of the lower crust with paleodepths ranging from 39.1 ± 0.3–44.2 ± 1.1 km down to 31.8 ± 0.2–38.4 ± 0.9 km. These results provide new constraints on the composition and evolution of continental arc crust and validate the utility of QuiG elastic barometry for probing deep arc systems. The strong consistency between QuiG estimates and independent phase‐equilibrium constraints further underscores their complementary roles in deciphering mineral‐equilibration histories.