Metamorphic P-T conditions and ages of garnet-biotite schists in the Dahongshan Group from the southwestern Yangtze Block

The Dahongshan Group,situated at the southwestern margin of the Yangtze Block,represents a geological unit characterized by relatively high-grade metamorphism in the region.This paper investigates the garnet-biotite schist from the Laochanghe Formation of the Dahongshan Group,employing an integrated approach that includes petrological analysis,phase equilibrium modeling,and zircon U-Pb dating.The schist is mainly composed of garnet,biotite,plagioclase,quartz,rutile,and ilmenite.Phase equilibrium modeling revealed the peak metamorphic conditions of 8-9 kbar and 635-675°C.By further integrating the prograde metamorphic profile of garnet and geothermobarometric results,a clockwise P-T metamorphic evolution path is constructed,which includes an increase in temperature and pressure during the prograde stage.LA-ICP-MS zircon U-Pb dating and zircon Ti thermometry constrains the post-peak metamorphic age of 831.2±7.2 Ma.Integrated with previously reported results,it is revealed that the southwestern margin of the Yangtze Block experienced a large-scale regional metamorphism during the Neoproterozoic(890-750 Ma),which is related to the collisional orogenic process.This may be associated with the late-stage assembly of the Rodinia supercontinent or with local compression and subduction processes during the breakup of the Rodinia supercontinent.

Influence of He ion irradiation on the microstructure and hardness of Ni-TiC_(NP)composites

In the present study,samples of a titanium carbide nanoparticle-reinforced nickel alloy(Ni-TiC_(NP)composite)were irradiated with 1 MeV He ions at 700°C.The evolution of He bubbles and nanohardness was characterized using transmission electron microscopy(TEM)and nanoindentation,respectively.TEM images showed that the size and number density of He bubbles in the grains were affected by the He ion fluence.The number density first increased significantly and then decreased with increasing ion dose,while the size exhibited an inverse trend.Moreover,the swelling induced by He bubbles continuously increased with increasing ion dose.He bubbles also formed in the grain boundaries,interior of the TiC nanoparticles,and interfaces between the TiC nanoparticles and Ni matrix.Nanoindentation measurements indicated a decrease in nanohardness after irradiation,which is attributed to the disappearance of intrinsic dislocation lines caused by He ion irradiation.