Deformation behavior and fluid action of quartz veins in the Xuelongshan metamorphic complex,Western Yunnan

The Xuelongshan metamorphic complex underwent Cenozoic sinistral strike-slip shearing and exhumation from deep to shallow in the southeast margin of the Tibet Plateau.We studied the deformation behavior and fluid action of quartz veins in the metamorphic complex in depth based on macroscopic observation,electron backscatter diffraction fabric,and fluid inclusion analysis.The mylonitic samples are characterized by strongly elongated and orientated porphyroclasts and a finegrained matrix with a shear strain of 2.4.The ultramylonitic samples are characterized by a strongly fine-grained matrix with a shear strain of 5.8.The{m}glide controls the quartz deformation in the mylonites and ultramylonites.As the dominant recovery mechanism,subgrain rotation dynamic recrystallization reduces the grain size and promotes rheological weakening.The porphyroclasts restrict the crystal orientation of the recrystallized quartz matrix.The mylonitic quartz veins have abundant single-phase and two-phase fluid inclusions.However,the ultramylonitic quartz veins have a few fluid inclusions,most of which are small and irregular toward the grain boundaries.The temperature and pressure of fluid activity in quartz veins are 550–500℃and 391–218 MPa for ultramylonitic quartz veins,with a depth of 14.2–7.9 km and 450–400℃and 236–91 MPa for mylonitic quartz veins,with a depth of 8.6–3.3 km.The deformation process changes the shape of fluid inclusions from mylonitization to ultramylonitization and causes fluid leakage,an increase in local fluid pressure at the boundary,and hydrolysis weakening,promoting lattice dislocation glide and recrystallization,which is directly related to regional continuous shear deformation and exhumation.

Grain-size reduction of feldspar and flow of deformed granites within the Gaoligong shear zone, southwestern Yunnan, China

Mineral deformation and rock flow mechanism in the lithosphere are related to the rheological behavior and weakening mechanism of the continent. Natural deformation behaviors of feldspars are not well understood due to the complexity of their mineral compositions, crystal structures, as well as changing deformation conditions. The refined microstructure,fabric and composition of major minerals in the deformed granitic rocks within the Gaoligong shear zone(GLGSZ), southwestern Yunnan, China, were studied. With increasing mylonitization, two fabric types of end-members have been distinguished(type-I banded granitic mylonite and type-II banded ultramylonite). The two types of deformed granitic rocks have the same mineral assemblage, but different mineral modes. The type-I banded granitic mylonite has a greater proportion of K-feldspar(mostly present as porphyroclasts)>plagioclase>quartz±biotite, however, the type-II banded ultramylonite has a greater proportion of fine-grained plagioclase>K-feldspar>quartz±biotite. The crystallographic preferred orientation(CPO) patterns of quartz combined with two-feldspar geothermometer, confirm that the quartz grains in the type-I and type-II granitic rock have undergone high-temperature dislocation creep deformation. The K-feldspar grains in the matrix of type-II banded ultramylonite show a dominant(100)[010] slip system with dislocation creep recrystallization, while the fine-grained plagioclase grains present a weak CPO pattern with superplastic flow. The K-feldspar porphyroclasts show grain-size reduction associated with mineral composition and fabric transformation. The myrmekite formation with the fine-grained neocrystallization of plagioclase and quartz significally replaced the K-feldspar porphyroclasts. Finally, the fine-grained neocrystallization plagioclases were formed further into the high strain localized ultramylonites with superplastic flow.

Metamorphic, deformation, fluids and geological significance of low-temperature retrograde mylonites of Diancangshan metamorphic massif along Ailaoshan-Red River strike-slip fault zone, Yunnan, China

Diancangshan metamorphic massif is one of the four metamorphic massifs developed along the Ailaoshan-Red River strike-slip fault zone, Yunnan, China. It has experienced multi-stage metamorphism and deformation, especially since the late Oligocene it widely suffered high-temperature ductile shear deformation and exhumation of the metamorphic rocks from the deep crust to the shallow surface. Based on the previous research and geological field work, this paper presents a detailed study on deformation and metamorphism, and exhumation of deep metamorphic rocks within the Diancangshan metamorphic massif,especially focusing on the low-temperature overprinted retrogression metamorphism and deformation of mylonitic rocks. With the combinated experimental techniques of optical microscope, electron backscatter diffraction attachmented on field-emission scanning electron microscopy and cathodoluminescence, our contribution reports the microstructure, lattice preferred orientations of the deformed minerals, and the changes of mineral composition phases of the superposition low-temperature retrograde mylonites. All these results indicate that:(1) Diancangshan deep metamorphic rock has experienced early high-temperature leftlateral shear deformation and late extension with rapid exhumation, the low-temperature retrogression metamorphism and deformation overprinted the high-temperature metamorphism, and the high-temperature microstructure and texture are in part or entirely altered by subsequent low-temperature shearing;(2) the superposition of low-temperature deformation-metamorphism occurs at the ductile-brittle transition; and(3) the fluid is quite active during the syn-tectonic shearing overprinted lowtemperature deformation and metamorphism. The dynamic recrystallization and/or fractures to micro-fractures result in the strongly fine-grained of the main minerals, and present strain localization in micro-domians, such as micro-shear zones in the mylonites. It is often accompanied by the decrease of rock strength and finally influences the rheology of the whole rock during further deformation and exhumation of the Diancangshan massif.

Stimulated Brillouin scattering induced all-optical modulation in graphene microfiber

Graphene microfibers are burgeoning modulators with great potential in all-optical communication. One of the critical issues that remains to be understood is the dynamic mechanism of light–graphene interaction. Here, we propose a power dependent modulation by using 980 nm pump light and 1064 nm signal light via graphene microfiber, and the results show a strong transmission reduction and frequency blue shift with the increase of pump power. The experimental observation is attributed to a stimulated Brillouin scattering process induced by the pump light. Power and frequency variations are a result of energy transition of the scattered phonon in the fiber. This work reveals the nonlinear effect process in the light–graphene interaction and provides a new method for power and frequency control with graphene all-optical modulation.

Single-scan polarization-resolved degenerate four-wave mixing spectroscopy using a vector optical field

We report on a new method to achieve the single-scan polarization-resolved degenerate four-wave mixing(DFWM)spectroscopy in a Rb atomic medium using a vector optical field,in which two pump beams are kept linearly polarized and a vector beam is employed as the probe beam.As the polarization and intensity of the DFWM signal are closely dependent on the polarization state of the probe beam,a vector probe beam with space-variant states of polarization is able to generate a DFWM signal with space-variant states of polarization and intensity across the DFWM image.Accordingly,the polarization-resolved spectra can be retrieved from a single DFWM image.To the best of our knowledge,this is the first time that the single-scan polarizationresolved spectrum detection has been realized experimentally with a vector beam.This work provides a simple but efficient single-scan polarization-resolved spectroscopic method,which would be of great utility for the samples of poor light stability and fast optical processes.

Deformation structure and exhumation process of the Laojunshan gneiss dome in southeastern Yunnan of China

Middle-lower crust and mantle rocks are generally widely exposed in metamorphic core complex or gneiss dome,which is an ideal place to study the exhumation process related to regional extension and rheology.The Laojunshan metamorphic complex in southeastern Yunnan is located in a special tectonic position surrounded by the Cathaysia,Yangtze and Indochina blocks.It is composed of different metamorphic-deformation rocks and granitic intrusions.There also are many economic deposits(e.g.,tin and tungsten)that are spatially and genetically associated with the formation and exhumation of the Laojunshan gneiss dome.Based on detailed analysis of macro-and microscopic structure,stress field distribution and deformation condition,the tectonic units of the Laojunshan metamorphic complex show obvious characteristics of doming,as well as of typical structural units of metamorphic core complex.It has strongly deformed metamorphic gneiss core(footwall),detachment fault system and sedimentary cover(hanging wall)with lightly metamorphism and deformation.The footwall of gneiss dome presents a strongly ductile deformation domain,accompanied by different ages of granitic intrusions.The distribution of developed foliation and lineation within granitic gneisses are arc-shaped and radial,respectively,with a nearly N-S trending from the footwall to the hanging wall.Mylonitization of deformed rocks gradually weakens and transits to orthogneiss as it moves away from the detachment fault toward the footwall.The low angle detachment fault between the footwall and the hanging wall shows an arc-like shape feature.Mylonite fabrics are preserved in the deformed rocks of the detachment fault,which are mainly composed of chloritized schist,fault breccia,cataclasite and fault gouge.A large number of normal faults are developed in detachment faults and hanging wall,and their stress fields radiate in an arc around the footwall.Zircon U-Pb ages of amphibolite and granitic gneiss from the footwall range from 445 to 420 Ma,indicating the timing of Caledonian magmatic emplacement and the main formation period of the Laojunshan gneiss dome.U-Pb ages of the zircon metamorphic rims are 241-230 Ma,representing the timing of high temperature metamorphism and shortened deformation of the Indosinian collision.In this period,the Laojunshan gneiss dome experienced the tectonic compression in association with high temperature metamorphism-deformation,which was superimposed by detachment and extensional exhumation in association with intense hydrothermal interaction and mineralization in the late stage.

Enhancement of phase conjugation degenerate four-wave mixing using a Bessel beam

We report on the enhancement of phase conjugation degenerate four-wave mixing(DFWM) in hot atomic Rb vapor by using a Bessel beam as the probe beam. The Bessel beam was generated using cross-phase modulation based on the thermal nonlinear optical effect. Our results demonstrated that the DFWM signal generated by the Bessel beam is about twice as large as that generated by the Gaussian beam, which can be attributed to the extended depth and tight focusing features of the Bessel beam. We also found that a DFWM signal with reasonable intensity can be detected even when the Bessel beam encounters an obstruction on its way, thanks to the selfhealing property of the Bessel beam. This work not only indicates that DFWM using a Bessel beam would be of great potential in the fields of high-fidelity communication, adaptive optics, and so on, but also suggests that a Bessel beam would be of significance to enhance the nonlinear process, especially in thick and scattering media.