Quantitative structural analyses and numerical modelling of ...

TEXTURES OF NATURALLY DEFORMED METAGABBROS 103progressively their cleavage planes { 110} parallelto the foliation. Small needle-like grains (0.02-0.05 x 0.1-0.3 mm in size), arranged parallelto the mylonitic foliation, are present in highstraindomains.Mylonite (E2). Within the eastern metagabbros,plagioclase porphyroclasts are recrystallized intoelongate aggregates or bands wrapped aroundhornblende clasts, and porphyroclasts representonly 5-10% of the total plagioclase volume.Elongate needle-like hornblende grains arearranged into aggregates or bands parallel to themain mylonitic foliation (Fig. 4a). Isolated hornblendeneedles scattered within plagioclase-richdomains are inclined at an angle of 20-30 ~ withrespect to the main fabric, indicating noncoaxialdeformation (Figs 4a and b). Plagioclasegrains attain 0.1-0.25 mm in size. Increase ingrain size with respect to the protomylonitestage and common optical zoning of recrystallizedgrains due to increase in anorthite contentsuggest syndeformational growth. Matrix grainsare often twin-free; the twinned grains representFig. 4. Digitized drawings and micrographs of the eastern mylonite. (a) Mylonitic foliation with alternating layers ofamphibole and plagioclase aggregates (PPL). (b) Plagioclase of subequant shapes and grain size typical for themylonitic stage (E2-pll). (c) High-strain plagioclase domain (E2-p12) adjacent to an amphibole porphyroclast ischaracterized by elongate shapes and strong SPO (XPL). (d) Amphibole porphyroclast (E2) cross-cut by microshearzones filled by small needle-like grains (XPL). Undulatory extinction documents strong internal deformation. Arrowsmark corresponding grains in the digitized drawings and micrographs.255