Isotopic analyses of samples from the study region are presented in Tables 2 and 3. All major rock units in the region were reviewed, including basement rocks, supracrustal sequences, and granitoids from the different tectonostratigraphic domains identified (Figure 3). Table 2 contains 23 analyses made by the authors, and Table 3 presents a compilation of all regional data published. TDM model age map distribution are presented in Figure 16,histograms of TDM model ages from metasedimentary rocks and granitoids in Figure 17, and the relationships between the eNd(t) values and time in Figure 18.
A new occurrence of basement rocks (Mantiqueira Complex in Table 2) was identified along the tectonic contact between the Andrelândia and Embu Domains, in the vicinities of the towns of Cruzeiro and Queluz (Figure 16), showing TDM model ages between 2.7 and 3.2 Ga (Figure 17), suggestive of an Archean source. Although absolute U-Pb zircon ages are not available, Nd isotopic signatures and characteristics of these rocks are similar to those identified by Sato (1999), a few kilometers to the southeast, indicating the existence of Archean crust remnants (Figure 3).
Figure 17. Histogram of the TDM model age
A: for supracrustal metasedimentary rocks and basement units. The Costeiro Domain has younger TDM model ages and the basement rocks yield Archean TDM model ages. The Embu Domain yields slightly younger values than the Andrelândia and São Roque Domains but with some overlap.
B: Granitoids range in value between 1.4 and 2.4 but no systematic distribution across the domain boundaries could be found. Data from tables 2 and 3.
Embu Domain. Samples from this domain have TDM model ages ranging from 1.55 to 1.95 Ga (Figure 17A), suggesting a bimodal distribution of their sources. A prevailing Paleoproterozoic source is evident in the central portion of the area, close to the southern border of the Taubaté Basin, with average TDM model ages of 1.88 Ga. Younger TDM model ages (1.55 to 1.65 Ga) are found to the south of Queluz and north of São José dos Campos (Figure 16). These results suggest a Mesoproterozoic source or, most probably, a mixture between Paleo and Neoproterozoic sources. The latter hypothesis is highlighted in the diagram plotting TDM model ages versus Nd (600) (Figure 18A) in which the analytical data points are aligned between old and young end members (basement rocks and Costeiro Domain).
Figure 18. Nd(600) versus TDM diagram
A: Samples of the Andrelândia, São Roque, Costeiro and Embu Domains and basement rocks.
B: Granitoids from all domains. Data from tables 2 and 3.
Andrelândia Domain. In the northern portion of the studied area, rocks from this unit have predominantly Paleoproterozoic model ages (TDM), with values higher (~2.0-2.3 Ga) than those of the rocks from the Embu Domain. They also display more negative Nd(600) values (Figure 18A).
Costeiro Domain. Gneiss and migmatites of this domain yielded TDM model ages between 1.27 and 1.42 Ga, defining a very homogeneous distribution of their source, with values lower than those from the Embu and Andrelândia Domains (Figure 17). This unit displays Nd(600) values between -4 and -6, less negative, therefore, than those of the Embu Domain (around -10, Figure 18A).
São Roque Domain. Data for metasedimentary and metavolcanic rocks from this domain partly overlap with those of the Andrelândia Domain and indicate provenance from Paleoproterozoic sources with a probable contribution from a younger source material. Metarhythmites have TDM model ages of 2.44 Ga whereas the phyllites yield TDM model age of 1.86 Ga, with Nd(600) of ca. -15 values (Table 3). Neoproterozoic metamafic rocks (metadiorites and amphibolites) intercalated with these metasediments display TDM model ages of 2.66 Ga. These values suggest that the igneous rocks were derived from Paleoproterozoic, and possibly Archean lithosphere.
Six different granitoid bodies of the Embu and Andrelândia Domains were analysed. TDM model ages vary between 1.8 and 2.2 Ga, and negative Nd(t) values between -20.5 to -13, suggest derivation from crustal Paleoproterozoic sources (Figure 18). However, a group of granites (Funil and Rio Branco, Table 2) shows TDM model ages between 1.7 and 1.6 Ga and Nd(t) with values close to -8, indicative of a possible involvement of younger and more juvenile source in their genesis.