Rheology of continental lithosphere and seismic anisotropy

Rheology of rocks controls the deformation of the Earth at various space-time scales,which is crucial to understand the tectonic evolution of continental lithosphere.Researches of rock rheology are mainly conducted via high-pressure and hightemperature rheological experiments and multi-scale observations and measurements of naturally deformed rocks.At present,a large amount of data from such kinds of studies have been accumulated.This paper first provides an up-to-date comprehensive review of the rheological mechanisms,fabric types and seismic properties of the main rock-forming minerals at different depths of continental lithosphere,including olivine,orthopyroxene,clinopyroxene,amphibole,plagioclase,quartz and mica.Then,progress in high-pressure and high-temperature experiments and natural deformation observations is introduced,mainly regarding the rheological strength and behavior,seismic velocity and anisotropy of lithospheric mantle peridotite,eclogite,mafic granulite,amphibolite and felsic rocks.Finally,by taking the Tibetan Plateau as an example,the application of rock rheology for quantitative interpretation of seismic anisotropy data is discussed.The combination of mineral deformation fabrics and seismic anisotropy is expected to make an important breakthrough in understanding the rheological properties and structure of continental lithosphere.

Effect of chemical composition on zircon radiation damage dating:Implications for low-temperature thermochronology

Zircon radiation damage dating is a low-temperature thermochronological method that can reveal the cooling histories of magmatic intrusions and discriminate sedimentary provenance in combination with other dating methods.This method has broad application prospects because of its advantages of nondestructive,high efficiency,and capable of double(or multiple)dating,involving only multiple measurements by Raman spectrometer and laser ablation-inductively coupled plasma-mass spectrometry.However,several factors,such as zircon chemical composition and the non-uniformity of radiation damage annealing kinetics,can cause poor precision when using this method and thus restricts its wide application.This study examined the effect of chemical composition(P,Ti,Dy,Th,U,and Hf)on Raman spectra using synthetic zircon crystals grown in a lithium-molybdate flux.The results show that the full width at half-maximum(FWHM)of the v_(3)(SiO_(4))band has positive linear correlations with the concentrations of P,Ti,Dy,Th,and U in decreasing order of influence,while the FWHM is unaffected by Hf at concentrations<1 wt.%but increases at concentrations>10 wt.%.Furthermore,the Raman shift is negatively correlated with Th,U,and Dy concentrations,positively correlated with Hf,and shows no obvious correlation with Ti and P.Thus,our study shows that chemical composition is a non-ignorable factor for calculating zircon radiation damage age using Raman spectroscopy,especially for zircon with relatively high concentrations of P,rare earth elements(REEs),Th,U,and Hf.The obtained multiple linear regression equation provides a potential means for estimating the FWHM at zero dose and implication for improving the dating precision of this method.In addition,the observed effects of REEs,Th,U,and Hf on the Raman shift of the v_(3)(SiO_(4))band indicate that chemical composition in zircon might affect the estimation of the P-T conditions of geological processes when using entrapped zircon inclusions in host minerals or the field of zircon as an in situ pressure sensor in hydrothermal experiments.Our study suggests that zircon radiation damage dating,excluding geochemical effects,will be more accurate for addressing lower-temperature geological processes.