serie NOVA TERRA nº 49

137 ( 143 Nd/ 144 Nd = 0.511858; Lugmair et al., 1983 ) was run along with the samples yielding an average value of 143 Nd/ 144 Nd = 0.511847 for 7 replicas, with and internal precision of ±0.000006 (2 σ ). Analytical errors on 147 Sm/ 144 Sm and 143 Nd/ 144 Nd ratios were estimated at less than 0.1% and 0.006%, respectively, and the total procedural blanks using this procedure were always under 0.1 ng. 3.2. Rock sampling and petrography Eleven samples of metasandstones were collected from the late Edi- acaran Escoural Unit of the Évora Massif ( Fig. 3 a and c). These samples correspond to single layers of rock taken from sections of the succession richer in metasandstone beds, but yet showing a layered appearance made of grey metasandstones and metapelites ( Fig. 4 a). Monfurado and Carvalhal units were considered as not suitable for establishing correlations with the basal allochthonous units of NW Iberia (see discussion in Sections 5.1 and 5.2 ), and thus they were not sampled for geochemical analyses. All of the rock samples are albite-bearing schists with a main folia- tion (S e ) marked by quartz + biotite + white mica + plagioclase (albite-oligoclase) ±opaque minerals ± tourmaline ( Fig. 4 b). The albite porphyroblasts include an internal schistosity (S i ) that is usually oblique to the main foliation ( Fig. 4 c), and is de fi ned by quartz + white mica + chlorite + opaque minerals (ilmenite) ± garnet ( Fig. 4 d). Bio- tite, when trapped within albite, may either overprint the internal fabric or constitute a foliation de fi ned by quartz + white mica + biotite ± opaque minerals that occupies a more external position within the porphyroblasts ( Fig. 4 b – d). Occasionally, the second internal fabric continues out of the albite porphyroblasts and into the main foliation ( Fig. 4 e). In the matrix, it is also possible to observe relicts of a previous fabric made of quartz + white mica + biotite, either in the form of disrupted and crenulated microlithons surrounded by the main foliation, or as polygonal arcs in the quartz-rich bands of the gneissic banding ( Fig. 4 e). A similar folded fabric can be also observed within albite porphyroblasts ( Fig. 4 c). The orientation of albite crystals ranges be- tween subparallel and oblique to themain foliation. In fact, theseminerals are sometimes fl anked by asymmetric pressure shadows consisting of plagioclase, quartz, and mica, all of which are subconcordant with the main foliation of the surrounding matrix. The amount of opaque minerals varies from sample to sample, although it is usually moderate (samples EV-8 and EV-10) to low (rest of the samples). Opaque minerals may occur in association with any of the fabrics described in these metasedimentary rocks, but in some cases they occur preferentially as part of the internal fabric preserved in porphyroblasts. Scattered porphyroblasts of cordierite are also found parallel to the main foliation. Some calcite is found fi lling late fractures that cut across the main foliation. 3.3. Results 3.3.1. Whole-rock geochemistry The normally applied geochemical discrimination diagrams charac- terize the analyzed rocks as described below. Most of the rocks plot in the greywacke fi eld ( Herron, 1988 ), and only four samples fall close to the shale fi eld ( Fig. 5 a). Table 2 Whole rock Rare Earth Element data of the Ediacaran metagreywackes of the Escoural Unit (basal allochthonous units of SW Iberia). EV-1 EV-2 EV-3 EV-4 EV-5 EV-6 EV-7 EV-8 EV-10 EV-11 EV-17 La 39.10 61.00 58.40 51.10 62.00 53.50 49.90 34.80 44.10 31.50 42.40 Ce 76.50 117.00 114.00 100.00 121.00 104.00 97.40 69.00 86.50 63.30 80.60 Pr 8.62 12.60 12.30 11.20 13.20 11.20 10.90 7.72 9.66 7.20 9.03 Nd 32.20 46.60 45.00 41.20 47.80 39.50 40.40 29.30 37.80 28.30 33.00 Sm 6.58 8.79 8.74 8.36 9.30 7.97 7.97 6.17 7.14 5.89 6.22 Eu 1.50 1.08 1.46 1.62 1.17 1.32 1.45 1.22 1.11 1.19 1.19 Gd 5.57 6.37 6.44 6.77 7.24 6.11 6.33 4.77 5.30 5.07 4.77 Tb 0.82 1.01 1.00 1.09 1.13 0.91 0.99 0.75 0.84 0.83 0.73 Dy 4.85 5.72 6.07 6.54 6.62 5.34 5.71 4.64 5.11 4.81 4.13 Ho 0.93 1.10 1.23 1.27 1.31 1.09 1.14 0.95 1.05 1.01 0.83 Er 2.67 3.42 3.75 3.89 3.92 3.28 3.34 2.76 3.06 3.02 2.46 Tm 0.41 0.52 0.57 0.58 0.59 0.52 0.52 0.44 0.49 0.45 0.38 Yb 2.91 3.59 3.69 3.85 3.65 3.53 3.60 2.82 3.34 3.06 2.62 Lu 0.446 0.555 0.623 0.612 0.591 0.545 0.542 0.476 0.555 0.472 0.417 Σ REE 183 269 263 238 280 239 230 166 206 156 189 Eu/Eu* 0.76 0.44 0.60 0.66 0.44 0.58 0.63 0.69 0.55 0.67 0.67 (La/Sm) N 3.67 4.28 4.12 3.77 4.11 4.14 3.86 3.48 3.81 3.30 4.21 (Gd/Yb) N 1.53 1.41 1.39 1.40 1.58 1.38 1.40 1.35 1.26 1.32 1.45 (La/Yb) N 8.98 11.36 10.58 8.88 11.36 10.13 9.27 8.25 8.83 6.88 10.82 Rare earth elements data in parts per million (ppm). Table 3 Whole rock Nd isotope data of the Ediacaran metagreywackes of the Escoural Unit (basal allochthonous units of SW Iberia). Sample Sm Nd 147 Sm/ 144 Nd 143 Nd/ 144 Nd ±SErr ∗ 10 − 6 ε Nd (0) ε Nd (560) a T DM (Ma) b EV-1 6.29 31.57 0.1204 0.512065 2 − 11.2 − 5.7 1596 EV-2 11.20 60.53 0.1119 0.511804 1 − 16.3 − 10.2 1853 EV-3 6.69 35.50 0.1139 0.511909 2 − 14.2 − 8.3 1731 EV-4 9.13 46.14 0.1196 0.511958 2 − 13.3 − 7.8 1755 EV-5 7.84 41.77 0.1135 0.511874 1 − 14.9 − 9.0 1776 EV-6 7.11 38.50 0.1117 0.511850 1 − 15.4 − 9.3 1781 EV-7 7.45 38.24 0.1177 0.511967 2 − 13.1 − 7.5 1707 EV-8 5.35 27.07 0.1195 0.512075 1 − 11.0 − 5.5 1564 EV-10 5.23 26.20 0.1206 0.512051 1 − 11.4 − 6.0 1620 EV-11 5.78 28.07 0.1244 0.512168 1 − 9.2 − 4.0 1499 EV-17 5.79 31.23 0.1121 0.511890 2 − 14.6 − 8.5 1727 a ε Nd(t) calculated for 560 Ma. b Nd model ages calculated according to DePaolo (1981) . 291 R.D. Fernández et al. / Lithos 268 – 271 (2017) 285 – 301