Effect of temperature and metallic composition on the metal silicate partitioning behaviour of the moderately siderophile and volatile element germanium

Abstract

Boudin structures form during layer parallel extension and can be subsequently rotated in later stages of deformation. In the Ambaji area of the South Delhi Terrane, Aravalli Delhi mobile belt, which is suffered by four phases of deformation. In Ambaji, both symmetric and asymmetric boudins are observed: symmetric boudins, which form during the first phase of deformation and are overprinted by the second deformational event, and asymmetric boudins, which form during the second phase of deformation. The third and fourth phases of deformation have a negligible effect on the boudin formation and rotation. We have done 1D, 2D strain analysis, vorticity analysis and calculated geometrical parameters for Ambaji boudins. We observed that the geometrically boudins have lower dimensional parameter values and higher angular parameter values that implies the dominance of simple shearing over pure shearing in the area. Angular parameters α, θ and θ’ for shearband boudins are 17.178°, 60.863°, 52.72°, for gash boudins values are 12.291°, 64.894°, 60.939°, and for domino shape boudins values are 27.985°, 82.695°, 66.845°. Dimensional parameters L/W, D/W, M/L and N/L for shearband boudins are 2.448, 1.805, 0.2922, 0.0991, for gash boudins values are 2.448, 1.805, 0.2922, 0.0991, and for domino boudins values are 1.289, 0.506, 115.613, 0.318, 0.085. Values of defined dimensional boudin parameters L/W, M/L and N/L for torn boudin is 0.21, 0.297, 0.297 and for drawn boudins values are 2.416, 0.384 and 0.384. Boudins are used to calculate the 1D, 2D strain and vorticity. For 1D strain analysis of boudins, we find that elongation varies from 0.156-0.292, stretch varies from 1.156-1.292 and quadratic elongation varies from 1.337-1.669. For 2D strain, we have taken samples from interboudin zone and the 2D strain ratio (Rs) varies from 1.74-1.84 and grains are rotated with an angle of 19.22 ± 6 to 18.91±9. For variolite samples, the 2D strain analysis was carried out on the field images and the 2D strain ratio (Rs) ranges from 1.6-3.16 and variolites are rotated with an angle of 15.36±5 to 19.64±5. The different types of boudin formation is controlled by rheology and viscosity contrasts in competent and incompetent layers present in the area. The rotation and percent of simple shear applied during boudin formation is calculated by the kinematic vorticity from different boudin type. The Kinematic vorticity (Wm) values of boudin ranges from 0.7-0.9 in the Ambaji, which indicates the boudins are formed due to simple shear dominated deformation.