serie NOVA TERRA nº 49

114 Díez Balda et al., 2004 ). These units of the Early Cambrian transgression were never found towards the S and SW of Guadarranque Syncline, therefore they do not crop out neither in the Centro-Extremeño anti- cline nor in Agudo-Valdemanco nor in the Alcudia anticline. These series accumulated following the Cadomian activity, prior to Cambro- Ordovician rifting. Finally, Ordovician quartz sands, that also constitute the Armorican Quartzite, rest discordantly over the Cambrian and Neoproterozoic sequence ( Liñán et al., 2002; Rodríguez Alonso et al., 2004a ). 3. Samples, analytical methods and geochemical tools 3.1. Samples Samples of metasedimentary rocks were selected in low grade metamorphic areas located in the southern part of the Central Iberian Zone ( Fig. 1 ). Twelve shale (slate) samples were collected in the Early Cambrian Pusa Shales Formation (Upper Unit), above the conglomerate layer referred to as “ Nivel de Fuentes ” , 70 km N of the Centro-Extremeño Dome, in the Valdelacasa Anticline (CIA-1 to CIA- 12 (UTM30/325.295/4.392.922), Figs. 2 and 3 a). These samples show a slaty cleavage de fi ned by muscovite, chlorite, quartz, and plagioclase. Sampled rocks collected are shales because of the total lack of sand- stones or greywackes in the unit. Eight samples of greywackes ( a and b layers of the Bouma sequence) were collected from the Lower Alcudian (Lower Unit), in the channel of Río Zujar, in the Alcudia Anticline, Centro-Extremeño Dome (CIA-13 to CIA-20 (UTM30/273.270/4.316.456), Late Ediacaran, Figs. 2 and 3 b). Four additional greywacke samples of this Late Ediacaran unit were col- lected in the Agudo – Valdemanco Anticline of the Centro-Extremeño Dome (CIA-21 to CIA-24 (UTM30/327.349/4.315.193) Figs .2 and 3 b). The sampled horizons correspond to full or truncated Bouma sequences in fi ne to medium grain sandy units. The quartz – micaceous matrix is oriented to de fi ne a slaty cleavage (chlorite – sericite) that wraps around clasts of quartz, chert, K-feldspar, plagioclase, muscovite, biotite and opaque minerals. Table 2 Whole rock major and trace element data of Pusa Shales (Early Cambrian). CIA-1 CIA-2 CIA-3 CIA-4 CIA-5 CIA-6 CIA-7 CIA-8 CIA-9 CIA-10 CIA-11 CIA-12 SiO 2 61.36 59.95 58.99 58.59 59.64 60.06 59.97 59.37 58.72 60.47 60.64 61.03 Al 2 O 3 18.89 18.65 19.04 19.39 19.19 18.4 18.78 19.03 19.12 18.89 18.83 18.8 Fe 2 O 3 7.17 6.66 6.95 7.63 7.23 7.1 7 6.92 6.98 7.22 7.09 7.04 MnO 0.075 0.111 0.098 0.089 0.077 0.085 0.067 0.082 0.08 0.069 0.083 0.081 MgO 2.78 2.81 2.9 3 2.8 2.72 2.51 2.89 2.93 2.67 2.78 2.76 CaO 0.25 0.93 0.66 0.43 0.45 0.64 0.27 0.36 0.51 0.24 0.28 0.47 Na 2 O 1.78 2.03 1.87 1.87 1.97 1.88 1.55 1.43 1.64 1.62 1.82 1.93 K 2 O 3.4 3.42 3.56 3.5 3.52 3.38 3.57 3.66 3.43 3.48 3.39 3.34 TiO 2 0.765 0.749 0.757 0.744 0.763 0.736 0.743 0.76 0.722 0.745 0.786 0.785 P 2 O 5 0.12 0.12 0.12 0.12 0.12 0.14 0.17 0.13 0.18 0.12 0.14 0.14 LOI a 3.77 4.5 4.2 4.06 3.98 4 3.97 4.28 4.35 4.04 3.8 3.94 Total 100.4 99.92 99.15 99.42 99.74 99.15 98.62 98.91 98.66 99.55 99.64 100.3 CIA 74 69 71 72 72 71 74 74 73 74 73 72 Sc 17 17 18 18 18 17 17 18 17 17 18 17 Be 3 4 4 4 4 4 4 4 3 4 4 4 V 115 115 117 118 118 113 115 118 115 118 116 116 Cr 90 100 100 100 100 100 100 100 90 90 100 100 Co 10 20 20 19 18 16 13 21 18 16 19 18 Ni 50 50 50 50 50 50 50 50 40 50 50 50 Cu 60 40 110 50 70 40 60 50 50 30 40 40 Zn 120 130 140 150 140 130 130 130 140 130 140 140 Ga 28 28 30 30 29 28 30 30 27 29 29 28 Rb 152 161 170 165 161 155 170 173 152 159 158 156 Sr 97 96 97 96 101 98 97 74 80 84 81 91 Y 30.9 34.9 34.1 31.8 34.1 32 34.2 34.1 32.2 31.6 34.1 32.9 Zr 156 163 155 149 155 153 158 158 144 147 167 161 Nb 16.3 15.7 15.6 15.4 15.7 15.5 15.4 15.7 13.2 14.5 14.9 15.2 Cs 7.4 8.2 8.8 8.4 8.2 7.8 7.9 9.3 7.9 8 7.9 8 Ba 595 604 630 619 630 609 644 645 610 614 606 594 Hf 4.1 4.2 4.1 3.8 4 3.9 4.2 4 3.7 4 4.3 4.1 Ta 1.08 1.04 1.07 1.1 1.34 1.09 1.15 1.12 1.05 1.04 1.09 1.1 Pb 16 19 15 11 14 16 11 10 24 12 19 10 Th 12.8 13.1 13.5 13.1 13.3 12.9 13.5 13.3 12.2 12.9 13.3 13.3 U 2.7 3.61 3.43 2.97 3.19 2.84 3.03 3.18 3.35 2.98 3.17 3.32 Al 2 O 3 /Na 2 O 10.6 9.2 10.2 10.4 9.7 9.8 12.1 13.3 11.7 11.7 10.3 9.7 Al 2 O 3 /TiO 2 24.7 24.9 25.2 26.1 25.2 25.0 25.3 25.0 26.5 25.4 24.0 23.9 SiO 2 /Al 2 O 3 3.2 3.2 3.1 3.0 3.1 3.3 3.2 3.1 3.1 3.2 3.2 3.2 K 2 O/Na 2 O 1.9 1.7 1.9 1.9 1.8 1.8 2.3 2.6 2.1 2.1 1.9 1.7 Rb/Sr 1.57 1.68 1.75 1.72 1.59 1.58 1.75 2.34 1.90 1.89 1.95 1.71 Ti/Zr 29.40 27.55 29.28 29.93 29.51 28.84 28.19 28.84 30.06 30.38 28.22 29.23 Ti/Nb 281 286 291 290 291 285 289 290 328 308 316 310 La/Sc 2.45 2.52 2.34 2.34 2.39 2.36 2.57 2.34 2.27 2.45 2.28 2.38 La/Th 3.25 3.27 3.13 3.22 3.24 3.12 3.24 3.17 3.16 3.22 3.09 3.05 Th/U 4.74 3.63 3.94 4.41 4.17 4.54 4.46 4.18 3.64 4.33 4.20 4.01 Th/Nb 0.79 0.83 0.87 0.85 0.85 0.83 0.88 0.85 0.92 0.89 0.89 0.88 Th/Sc 0.75 0.77 0.75 0.73 0.74 0.76 0.79 0.74 0.72 0.76 0.74 0.78 Zr/Sc 9.18 9.59 8.61 8.28 8.61 9.00 9.29 8.78 8.47 8.65 9.28 9.47 Co/Th 0.78 1.53 1.48 1.45 1.35 1.24 0.96 1.58 1.48 1.24 1.43 1.35 Oxides are in weight percent (wt.%). Trace elements are in parts per million (ppm). CIA: Chemical Index of Alteration ( Nesbitt and Young, 1982 ). Oxides in molar proportions. a Loss on ignition. 20 J.M. Fuenlabrada et al. / Tectonophysics 681 (2016) 15 – 30