Deformation Structures of the Madao Gneiss in South Qinling:Structural Analysis,Geochronological Constraints,and Tectonic Implications

The tectonic evolution of South Qinling, which is a main part of the Qinling orogenic belt, is still in dispute and deformation history of South Qinling is poorly studied. In this paper, detailed structural, microstructural, quartz c-axis fabric analysis, and geochronology results for the Madao gneiss in South Qinling are presented to characterize the deformation history. Results show that rocks in the northern part （Tiefodian-Laozhanggou） experience general shearing and deform at relative low temperature. The shear sense generally is south to north. In contrast, rocks in the southern part （Laozhanggou-Panjiahe） are weakly sheared with pure shear features and evidence of high- temperature deformation. Based on the analyses, we conclude that there exist two distinct deformation geometries in the Madao gneiss and accordingly we can divide the deformation into two stages. The early stage is represented by regional shortening, while the late stage features northward thrust shearing and evidence shows that it was a progressive process between them. LA-ICP MS U-Pb dating of zircons from pre-deformational migmatite veins yields age of 198.5 ±2.0 Ma. This result, in combination with the age of post-deformational granite, indicates that the northward thrust shearing of the Madao gneiss occurred in the Late Triassic. In view of these results and other reported data in South Qinling, we propose that deformation in Madao gneiss may result from the initial collision and subsequent northward accretion in Late Triassic.

Investigation of Granite Deformation Process under Axial Load Using LSTMBased Architectures

Granite is generally composed of quartz,biotite,feldspar,and cracks.The changes in digital parameters of these compositions reflect the detail of the deformation process of the rock.Therefore,the estimation of the changes in digital parameters of the compositions is much helpful to understand the deformation and failure stages of the rock.In the current study,after dividing the frames in the video images photographed during the axial compression test into four parts(or,the upper left,upper right,lower left,and lower right ones),the digital parameters of various compositions in each part were then extracted.Using these parameters as input dataset,a long short-term memory(LSTM)based neural network was then established for exploring the changes of various compositions.After dividing the deformation process into four stages based on the stress-strain curve and using the digital parameters of various compositions as the dataset,the LSTM-based neural network for estimating the rock deformation stage was also established.The root mean squared error(RMSE)and goodness of fit(R2)and the average accuracy(ACC)were used to evaluate the efficiencies of these two LSTM-based neural networks.The influences of variables(such as the number of hidden layers,maximum epoch,learning rate,minimum batch size and train ratio)on efficiencies of the LSTM-based neural networks were thereafter explored.It shows that the super parameters have a great influence on the efficiency of the established LSTM-based neural network for estimating digital parameter changes of various compositions;the estimations were relatively good if the number of hidden layers,maximum epoch,learning ratio,minimum batch size,and train ratio is 2,150,0.005,10,and 0.8,respectively;the compositions with the greater percentage have a greater accuracy using the neural network;the great-small sequence of ACC is biotite,feldspar,crack,and quartz,if the LSTM-based architecture for estimating deformation stages was used.These results may be referable both for investigating the availably of the established LSTM-based architectures and for exploring the deformation process of the rock materials.

NUMERICAL MODELING OF KELVIN-HELMHOLTZ INSTABILITY AND RAYLEIGH-TAYLOR INSTABILITY AT LARGE DEFORMATION STAGE——(Ⅰ) NUMERICAL METHOD AND NUMERICAL RESULTS OF RAYLEIGHTAYLOR INSTABILITY

This paper improves the discrete vortex method for modeling Kelvin-Helmholtz instability and Rayleigh-Tay- lor instability by proper choice of velocity weighted average coefficients, redistribution of markers and successive adding of computational points with the increase of interfacial deformation and gives the numerical results of Rayleigh-Taylor instability. The numerical results show that the first two techniques greatly enhance the ability of the discrete vortex method for modeling large interracial deformations and the last technique greatly reduces the computational amounts of the numerical modeling at large deformation stage. The numerical modeling of Rayleigh- Taylor instability not only reproduces some phenomena such as the roll up at the end part of the spike observed in experiments but also finds some new phenomena such as the splashes at the roll up parts which needs to be tested by experiment.