Nova Terra 52

473 International Journal of Earth Sciences (2021) 110:467–485 13 analyses are included in Tables 1 and 2 and in the diagrams shown in Figs. 4, 5 and 7. Whole-rock Sm–Nd isotopic analysis Sm–Nd isotope analyses were performed using Isotope Dilu- tion Thermal Ionization Mass Spectrometry (ID-TIMS) at the Geochronology and Isotope Geochemistry Facility of the Universidad Complutense de Madrid. Samples were spiked with a mixed 149 Sm- 150 Nd tracer and then analysed in an IsotopX–Phoenix mass spectrometer (TIMS), follow- ing a single collection and a dynamic multicollection mode for Sm and Nd, respectively. To correct procedural and instrumental mass fractionation, the resulting 143 Nd/ 144 Nd ratios were corrected for 142 Ce and 144 Sm interferences and normalized to 146 Nd/ 144 Nd = 07219 value (O’Nions et al. 1979). To have control over the drifts from La Jolla refer- ence value (Lugmair et al. 1983), this standard was ana- lysed along with the samples, yielding an average value of 143 Nd/ 144 Nd=0.511851 for six replicates, with an internal precision of ± 0.000007 (2 σ ). The analytical error for the 147 Sm/ 144 Nd and 143 Nd/ 144 Nd ratios was estimated lower than 0.1% and 0.006%, respectively, and Nd procedural blanks were always under 0.1 ng. The results are included in Table 3 and plotted on the diagram in Figs. 6, 7 and 8. Whole-rock and isotope geochemistry results The geochemistry of major elements in siliciclastic rocks is used to describe and constrain their nature and degree of alteration, as well as to characterize their provenance and tectonic setting during sedimentation (Nesbitt and Young 1982; Bhatia 1983; Taylor and McLennan 1985; Bhatia and Crook 1986). The use of immobile trace elements such as REE, Th, Co; Cr, Nb, Ti, Sc, Y, Zr, Hf, and especially their ratios, are excellent proxies to infer the likely tectonic setting and discriminate between felsic/mafic contributions from the source area, since they remain virtually undisturbed through weathering, transport, sedimentation and metamorphic pro- cesses (Nesbitt et al. 1980; Taylor and McLennan 1985; Wronkiewicz and Condie 1987; Feng and Kerrich 1990). The distribution of REE in detrital rocks reflects the average composition of the source area and, consequently, the REE- patterns are a means to discriminate between a crustal or mantle influence in the source. In this sense, certain crustal models consider Nd model age of siliciclastic rocks as an approximation to the average resulting of the extraction of the different terrigenous components from the melt source (McCulloch and Wasserburg 1978 and others), so Nd model ages may act as tracers of the crustal/mantle evolution of the detritus reaching a particular sedimentary basin (McLennan et al. 1990; McLennan and Hemming 1992). Composition, classification and tectonic setting The Montemolín and Tentudía formations define homoge- neous series considering their major element composition (Tables 1 and 2). The SiO 2 average content for both forma- tions (65.10 and 66.23 wt%, respectively) are slightly lower than the average described by Condie (1993) for the Upper Continental Crust (UCC) (66.79 wt%), while the average value for Fe 2 O 3 (5.69 and 5.10 wt%, respectively) and Al 2 O 3 (15.75 and 15.41 wt%, respectively) are slightly higher than typical UCC values (4.51 and 14.99 wt%, respectively). In both Montemolín and Tentudía formations, the mobile ele- ments K 2 O (avg. 2.78 and 2.59 wt%, respectively) and Na 2 O (avg. 3.23 and 3.21 wt%) have an average content similar to the UCC range (3.1 and 3.35 wt%, respectively); only two samples (TE-03 and TE-10) show enriched and depleted contents, respectively, for these two elements compared to the average values of the group (Tables 1 and 2). The most significant difference between both Montemolín and Table 1 (continued) Sample MO-01 MO-02 MO-03 MO-04 MO-05 MO-07 MO-08 MO-09 MO-10 MO-11 Tm 0.30 0.32 0.31 0.29 0.35 0.31 0.31 0.32 0.36 0.32 Yb 2.04 2.1 2.1 2.04 2.33 2.24 2.09 2.21 2.43 2.13 Lu 0.32 0.32 0.31 0.32 0.35 0.35 0.32 0.34 0.38 0.33 ΣREE 160.21 175.27 160.89 164.44 145.43 159.25 139.09 152.38 181.99 165.08 Eu/Eu* 0.87 0.84 0.83 0.85 0.80 0.81 0.84 0.83 0.83 0.80 La N /Yb N 11.34 12.90 10.54 12.03 8.95 10.39 9.31 9.68 10.73 10.93 Gd N /Yb N 1.65 1.75 1.63 1.64 1.55 1.63 1.62 1.57 1.59 1.72 sumREE 160.21 175.27 160.89 164.44 145.43 159.25 139.09 152.38 181.99 165.08 LREE 318.02 357.47 314.78 331.16 290.49 317.97 274.96 301.34 361.34 326.55 HREE 76.99 80.01 76.91 74.68 84.35 81.26 78.64 79.82 88.96 83.04 LREE/HREE 4.13 4.47 4.09 4.43 3.44 3.91 3.50 3.78 4.06 3.93 L a N /Sm N 4.02 4.35 4.03 4.22 3.52 3.87 3.51 3.67 3.94 3.93 Iberian–Bohemian correlations