Quantitative structural analyses and numerical modelling of ...

TEXTURES OF NATURALLY DEFORMED METAGABBROS 115maximum eigenvector V1 is only slightlyinclined with respect to the foliation, suggestingminor component of non-coaxial deformation. Inthe western belt, ramp_am p weakens from 2.26 inthe augen mylonite (W1) to 1.96 in the bandedmylonite (W2), being still stronger than rpl-plin similar rock types. The eigenvector V~ is parallelto the foliation in both types of mylonites.Crystallographic preferred orientationFive thin sections, covering all the deformationstages, were analysed using the EBSD technique.In the eastern mylonite (E2) and the westernbanded mylonite (W2), two plagioclase domainswere investigated.Besides pole figures of [100] directions andpoles to (010) and (001) planes, inverse polefigures, calculated parallel to stretching lineationand pole to foliation, are used in the eastern belt inorder to identify orientation maxima, which couldcorrespond to less common slip systems reportedin the literature. The inverse pole figures may beemployed because the orientations of lineationand foliation follow strong SPO and CPO ofamphibole. For the description of inverse polefigures, only the slip systems previouslydescribed in the literature will be mentioned(for summary see e.g. Kruse et al. 2001 ; Sttinitzet al. 2003). The I parameters representing theintensity of CPO are shown in Table 5.PlagioclaseWithin the protomylonite of the eastern belt (El),the plagioclase CPO is not random (Figs 13 and14a). In the inverse pole figure, the lineations aredistributed subparallel to the horizontal planewith a maximum around [i 10]. Poles to foliationare arranged in a N-S girdle with maximaaround (001) and a* (100). The (001) [1 i0] slipsystem (Olsen & Kohlstedt 1984, 1985) couldTable 5. Intensity I of crystallographic preferredorientationE1 1.51tE2-pl 1E2-p12E3 2.906Wl 1.422W2-pll 0.948W2-p12HornblendePlagioclase(100) [001] {110} [1001 (010) (001)1.926 0.897 0.116 0.666 0.3190.095 0.109 0.1000.108 0.347 0.1711.591 1.454 0.083 0.033 0.1781.854 0.846 0.111 0.074 0.0201.606 0.653 0.457 0.552 0.9480.590 0.299 0.741thus be possibly active. The orientation of porphyroclastsis different from that of recrystallizedgrains, suggesting that the recrystallization wasnot host-controlled (e.g. Ji & Mainprice 1990;Kruse et al. 2001). The mylonite (E2-pll andE2-p12) shows weak CPO in both plagioclasedomains. A weak maximum of lineations is situatedaround [110] in the E2-pll _domain, and someclusters of lineation around [1_12] directions andpoles to foliation close to (201) can be observedin the high-strain domain in sample E2-p12. Theseorie_ntationsmay indicate the possible activation of(201)1/21112] (Marshall & McLaren 1977a, b) inthe high-strain fine-grained domain adjacent to thehornblende porphyroclast (Fig. 4d). The ultramyloniteCPO (E3) displays maximum for polesto foliation clustering near the (021) and maximumfor lineations near the [112] direction. SuchCPO would suggest activation of (021)1/21112]slip system (Olsen & Kohlstedt 1984; Montardi& Mainprice 1987). The I parameters attain lowervalues in more deformed stages for [100], (010),and (001), respectively.The CPO of the augen mylonite in the westernbelt (W1) (Fig. 15) is very weak and no slipsystems could be extracted even by examiningthe inverse pole figures, which are not shownhere. Within banded mylonite (W2-pll and W2-p12), both coarse-grained (pll) and fine-grained(p12) plagioclase domains exhibit strong maximaof [100] directions close to the lineation. Polesto (010) and (001) planes are distributed close tothe pole of the foliation, which is defined by compositionallayering. The domain W2-p12 representslate shear zones marked by importantgrain refinement (Fig. 7c). The 1 parameters arehigher in the banded mylonite (W2) comparedto the augen mylonite (W1), indicating strengtheningof plagioclase CPO. It is likely that thislate shearing was not entirely coaxial with respectto the main flow represented by coarse-grainedaggregate fabrics (W2-pl 1). Therefore, the differenceof (010) and (001) maxima in pole figurescould result from slightly oblique orientation oflate shear plane with respect to dominant compositionallayering. The shear zone (W2-p12) ismarked by an inclination of [100] maximum ofabout 10 ~ with respect to the lineation, whichcould be attributed to non-coaxial deformation (Jiet al. 1988). Activity of slip systems (001)[100](Marshall & McLaren 1977a, b) and (010)[100](Montardi & Mainprice 1987) may be inferredfrom such orientation patterns.AmphiboleSmall recrystallized hornblendes adjacent totheir host grain in the eastern protomylonite267