Texture and fabric
The maps of identified grains and grain boundaries for DS03, BC11, BC302, and HC01 (shallowest to deepest in terms of paleodepth, least to most mafic, and highest to lowest Rb/Sr ratios) are shown in Fig. 7. The thin sections were cut along planes that were originally perpendicular to the surface (assuming a 45ยบ westward postemplacement tilt) and were striking NS but that had since been tilted (Fig. 7a). Only grains away from the edges were analyzed leading to some vacant space on certain portions of the maps. Rose diagrams (last two column of Fig. 7) show the number of particles oriented at a given angle (azimuth) with respect to the bottom edge of the image. The tan rose diagrams include all identified grains while the pink rose diagrams only include phenocryst grains (euhedral plagioclase, alkali feldspar, and biotite) for each sample. The intensity of fabric development can be described by the alignment factor (Barraud, 2006). The alignment factor (AF) can be calculated by first introducing an orientation tensor, Tn, for each grain:
\(T^{n}=\ L_{n}\par \begin{bmatrix}\operatorname{}\alpha_{n}&\cos\alpha_{n}\sin\alpha_{n}\\ \cos\alpha_{n}\sin\alpha_{n}&\operatorname{}\alpha_{n}\\ \end{bmatrix}\) (1)
Here, n , refers to a grain of interest and L is the major axis length. The bulk orientation tensor, Mij, can be related to Tn as:
\(2.\ \ M_{\text{ij}}=\frac{1}{N}\sum_{1}^{N}T_{\text{ij}}^{n}\) (2)
Finally, AF is defined as:
\(alignment\ factor\ (AF)=100\ \times\ \frac{e_{1}-e_{2}}{e_{1}}\)(3)
where e1 and e2 are eigenvalues of Mij. Conceptually speaking, AF represents the extent of agreement between orientations of individual grains.