serie NOVA TERRA nº 49

76 age range of the arc plutonic rocks of the same terrane (500 – 520 Ma). The turbiditic sequence of the Órdenes Complex was generated in a convergent setting, probably in an intra-arc sedimentary basin developed within a major, active volcanic arc located at the periphery of the West African Craton. This arc was likely built on the most external section of the Gondwanan margin, on thinned continental crust, and may incorporate remnants of the continental basement. The turbiditic sequence is intruded by numerous diabase dykes, one of which (near the village of Ares; Fig. 2 ), has now yielded a protolith age of c. 510 Ma. The structural relationships between the diabase dykes and the most important regional planar fabrics (S 1 and S 2 ) show these tectonic fabrics to be pre-Variscan and to have developed in the dynamic setting of the peri-Gondwanan volcanic arc. Moreover, the largely coeval development within the arc of plutonic activity, Table 2 Th, U, Hf (in ppm) and chondrite-normalized rare earth element data from zircon from sample GCH-06-2 (dyke Ares-1) and zircon standard R33. Spot number and description Th U Hf La Ce Pr calc Nd Sm Eu Gd Dy Er Yb Th/U Yb/Gd Ce/Sm Ce/Ce ⁎ Eu/Eu ⁎ GCH-06-2: Sada Dyke Variscan ages 25 m 792 485 9298 0.09 30.6 0.67 1.88 10.4 18.9 53.2 139 320 565 1.63 8.8 12.02 128 0.80 21 c 799 792 10,669 0.72 73.1 3.15 6.59 30.4 25.8 120.2 280 668 1170 1.01 8.1 9.87 48 0.43 20 r 246 662 10,703 0.05 42.1 0.54 1.67 12.4 12.0 69.9 194 561 1111 0.37 13.1 13.93 245 0.41 Ages <500 Ma 6 m 48 54 12,696 0.09 11.4 0.34 0.68 5.1 2.2 35.0 123 354 604 0.88 14.3 9.10 65 0.16 31 m 40 52 9877 0.08 2.6 0.79 2.46 20.7 2.2 152.2 462 1165 1781 0.77 9.7 0.50 10 0.04 13 m 34 193 11,897 0.06 1.1 0.45 1.20 17.3 1.1 184.6 1017 3200 5177 0.18 23.2 0.27 7 0.02 18 m 629 1098 11,082 0.10 83.3 1.27 4.54 42.3 10.9 343.7 1271 3338 5018 0.57 12.1 8.08 233 0.09 Dyke crystallization ages 22 m 27 34 7967 0.09 3.0 0.60 1.57 9.0 7.4 51.1 126 312 515 0.79 8.3 1.37 13 0.34 3.1 m, r 70 147 10,832 0.06 2.4 0.74 2.55 29.3 1.4 244.7 902 2452 3758 0.48 12.7 0.34 11 0.02 11 m 46 141 10,061 0.08 2.9 0.78 2.48 19.7 6.2 131.1 423 1139 1785 0.33 11.3 0.59 12 0.12 5 m 105 158 11,203 0.08 10.2 0.92 3.17 21.4 11.5 129.6 380 1009 1579 0.67 10.1 1.95 38 0.22 10 m 48 104 7650 0.18 3.4 1.53 4.44 34.4 25.2 225.1 636 1494 2239 0.47 8.2 0.40 6 0.29 1 m 64 118 7960 0.12 11.9 1.11 3.43 20.5 21.4 131.7 413 1177 2133 0.54 13.4 2.38 33 0.41 Inherited ages 510 – 600 Ma 28 m 91 142 10,155 0.09 7.5 1.24 4.57 34.0 6.6 211.8 578 1338 1876 0.64 7.3 0.90 22 0.08 29 m 78 184 10,287 0.18 7.3 0.56 0.98 5.1 9.1 25.4 73 237 532 0.42 17.3 5.92 23 0.80 17 m 69 111 10,793 0.07 21.9 0.39 0.89 8.1 6.2 57.4 197 572 1065 0.62 15.4 11.15 129 0.29 27 m 71 97 10,598 0.08 14.7 0.82 2.64 20.0 14.7 145.0 478 1372 2361 0.73 13.5 3.00 58 0.27 26 m 28 33 8565 0.11 10.5 0.85 2.41 13.0 16.6 61.4 152 426 830 0.84 11.2 3.33 35 0.59 30 m 60 158 10,159 7.50 11.7 2.71 1.63 3.4 4.9 16.8 59 234 654 0.38 32.3 14.07 3 0.65 19 m 101 248 11,034 0.05 22.1 0.32 0.82 7.6 3.4 55.0 198 606 1127 0.41 17.0 11.85 176 0.17 9 m 36 66 10,482 0.03 12.0 0.19 0.47 5.1 3.4 41.4 161 507 952 0.55 19.0 9.68 151 0.24 Inherited ages 600 – 750 Ma 32 m 86 193 11,218 0.11 24.5 0.34 0.58 5.8 3.3 46.6 189 689 1515 0.45 26.9 17.21 126 0.20 16 m 213 291 9917 0.21 39.9 0.89 1.82 11.3 14.1 68.7 223 692 1497 0.73 18.0 14.46 92 0.51 4 m 132 178 7737 0.09 23.6 0.48 1.10 7.5 13.1 44.9 142 426 883 0.74 16.3 12.84 114 0.71 7 m 72 167 10,657 0.05 34.9 0.22 0.47 4.5 2.8 33.6 142 461 981 0.43 24.2 31.67 340 0.23 3.2 c 169 234 10,643 0.05 30.9 0.44 1.31 11.2 8.1 76.9 275 795 1435 0.73 15.4 11.26 205 0.27 Inherited ages >2000 Ma 2 m 59 71 9500 0.05 28.5 0.47 1.45 9.9 5.8 58.9 170 427 688 0.83 9.7 11.75 185 0.24 23 m, r 170 448 12,322 1.51 48.6 1.17 1.02 9.2 4.7 75.2 324 1187 2469 0.38 27.2 21.59 37 0.18 24 c 74 181 12,562 0.07 46.1 0.31 0.68 6.6 4.2 53.4 222 792 1717 0.41 26.6 28.62 319 0.22 12 m 50 100 9420 0.08 26.0 0.60 1.61 10.9 7.4 60.4 181 539 1012 0.50 13.9 9.80 118 0.29 14 m 20 42 10,500 0.12 15.7 0.51 1.04 6.6 7.9 35.7 98 284 595 0.48 13.8 9.83 63 0.52 15 m 32 133 11,836 0.03 11.3 0.10 0.17 2.4 2.1 19.6 93 306 645 0.24 27.3 19.71 193 0.30 R-33 zircon standard 1 m 184 263 10,312 0.09 8.2 0.87 2.68 16.8 15.6 111.9 416 1384 2700 0.70 20.0 2.01 29 0.36 2 m 117 158 9174 0.13 8.3 1.19 3.64 23.9 18.6 166.0 592 1690 2863 0.74 14.3 1.43 21 0.30 3 m 137 199 10,025 0.06 7.7 0.56 1.76 13.4 13.9 95.0 345 1091 2150 0.69 18.7 2.37 43 0.39 4 m 150 180 8419 0.14 12.2 1.60 5.34 39.0 31.7 282.9 942 2459 3915 0.83 11.5 1.28 26 0.30 5 m 178 273 11,759 0.03 10.6 0.36 1.21 11.2 12.5 86.6 343 1138 2330 0.65 22.3 3.90 98 0.40 6 m 153 203 9262 0.12 9.5 1.30 4.27 26.5 19.8 178.1 675 2045 3520 0.75 16.4 1.47 24 0.29 7 m 129 194 10,484 0.05 7.4 0.69 2.69 18.1 15.4 115.5 427 1353 2565 0.67 18.4 1.68 42 0.34 8 m 95 136 9688 0.06 7.2 0.70 2.47 18.1 14.7 122.6 429 1259 2252 0.70 15.2 1.64 37 0.31 9 m 40 95 9074 0.04 4.6 0.19 0.44 4.3 4.0 36.3 153 542 1161 0.42 26.5 4.35 53 0.32 10 m 136 165 8709 0.05 16.0 0.61 2.13 16.4 13.1 126.8 500 1454 2490 0.83 16.2 4.00 20 0.29 11 m 122 158 8916 0.15 9.0 1.40 4.26 26.8 21.0 191.9 699 1974 3262 0.77 14.1 1.38 71 0.29 12 m 39 93 9252 0.03 6.0 0.25 0.75 6.9 6.1 55.8 232 785 1567 0.42 23.2 3.59 55 0.31 13 m 90 134 9895 0.04 6.7 0.41 1.37 11.9 11.3 90.2 324 989 1837 0.67 16.9 2.31 4 0.34 14 m 78 144 9264 2.37 9.4 2.80 3.05 9.6 9.5 37.4 123 412 918 0.54 20.3 3.99 41 0.50 15 m 12 35 9196 0.04 2.7 0.10 0.16 1.6 1.5 15.1 68 245 501 0.34 27.4 7.00 60 0.30 16 m 269 251 8445 0.08 13.7 0.65 1.84 14.8 12.2 112.0 435 1279 2193 1.07 16.2 3.82 53 0.30 17 m 33 75 9125 0.04 5.7 0.25 0.60 5.7 5.2 47.9 196 667 1322 0.44 22.8 4.07 92 0.32 Some elemental ratios cited in the text are also shown. Pr N is calculated from La N and Nd N contents (Pr=La N ^1/3 ⁎ Nd N ^2/3). Zircon description as in Table 1 . 359 F. Díaz García et al. / Gondwana Research 17 (2010) 352 – 362