Zircon Pb-Pb Geochronology of the Caruaru Area, Northeastern Brazil: Temporal Constraints on the Proterozoic Evolution of Borborema Province

Abstract

The Caruaru-Arcoverde batholith, with an outcrop area of ~2000 km 2 , is one of the largest Brasiliano plutons in Borborema Province, northeastern Brazil. The batholith intrudes orthogneisses and supracrustal rocks characterized by flat-lying foliation, and is bounded in the south by a synmagmatic, transcurrent shear zone, interpreted by some as a terrane boundary. In order to constrain the emplacement age of the batholith and the Proterozoic history of the eastern portion of Borborema Province, single zircon grains from seven samples from the Caruaru-Arcoverde batholith and nearby country rocks were analyzed by the Pb-evaporation technique.Zircons from orthogneisses immediately north of the Caruaru-Arcoverde batholith yielded ages of 2098 ± 15 Ma and 2072 ± 3 Ma. One zircon sample from an orthogneiss located south of the batholith gave an age of 2075 ± 7 Ma. Combined with existing zircon U-Pb ages in orthogneisses and Nd model ages of plutons and country rocks in eastern Borborema Province, these data indicate important crustal growth during the Middle Paleoproterozoic (2.2-2.0 Ga). In contrast, a sample from another orthogneiss southeast of the Caruaru-Arcoverde batholith gave an age of 629 ± 9 Ma. Because the flat-lying foliation in different country rocks was formed under the same high-amphibolite-facies conditions, this age suggests that the regional fabric developed during the Late Neoproterozoic. Two samples from the main phase of the Caruaru-Arcoverde batholith yielded mean ages of 591 ± 5 Ma and 587 ± 5 Ma, whereas a sample from a late facies gave an mean age of 583 ± 5 Ma. The oldest age of 591 Ma places an upper bound on the beginning of strike-slip motion, because field evidence indicates that the shear zone developed after emplacement of the Caruaru-Arcoverde batholith.Correlations of the Caruaru area with other sectors of Borborema Province and the Cameroon and Nigerian provinces of western Africa suggest that these areas: (1) were assembled during the Transamazonian/Eburnean orogeny; and (2) formed a coherent unit during the Late Neoproterozoic Brasiliano/Pan-African orogeny, when they were deformed first by a tectonic event, possibly resulting from thrust motion, and then subjected to a strike-slip regime.

Emplacement and deformation of the Cachoeirinha pluton (Borborema province, NE Brazil) inferred through petrostructural studies: Constraints on regional strain fields

“…1c), so the southern domain, at least near the studied area, consists of Paleoproterozoic-age crust. These data are similar to the dominant zircon U-Pb and Nd model ages of basement rocks north of the EPSZ (Van Schmus et al, 1995;Brito Neves et al, 2001;Mariano et al, 2001;Sá et al, 2002;Neves et al, 2004). The orthogneisses display a flat-lying foliation whose development is attributed to an early contractional event during the Brasiliano orogeny, according to a zircon Pb-evaporation age of 630 Ma in an orthogneiss south of the town of Caruaru (Fig.…”

Restraining bends in high temperature shear zones: The “Central Cameroon Shear Zone”, Central Africa

“…1a). Both the Pan-African and Brasiliano SZ show similar ages bracketed between 600 and 570 Ma (Vauchez et al, 1995;Ferré et al, 1998Ferré et al, , 2002Nguiessi Tchankam et al, 1997;Paquette et al, 1998;Neves et al, 2004;Souza et al, 2006).…”

“…1), the CCSZ likely forms a large scale fan structure with NS imbricate SZ characterized as synthetic equivalents of the sinistral N50°E-directed shear zones of northern Cameroon (Ngako, 1999; Ngako et al, 2003). This geometry which is similar to the Patos and Pernambuco networks (Vauchez et al, 1995;Neves and Mariano, 1999;Neves et al, 2000Neves et al, , 2004Souza et al, 2006) is compatible with a complex kinematic evolution including superimposition of sinistral and dextral movement parallel to the CCSZ. Likely, this shear zone does not show direct links with its Brasiliano pre-drift counterpart, and the present study has revealed that both shear zones form a complex en-echelon system including one or several intermediate relays (Fig.…”

“…1), locally designated as the ''Ngaoundéré", ''Foumban" or ''Adamawa" faults or lineaments (Browne and Fairhead, 1983;Koch, 1953a), corresponds to the SW extension of the Central African Shear Zone (Fairhead, 1988) which is outlined by a broad mylonite belt directed N70°E, and extending from Cameroon to Sudan (Cornachia and Dars, 1983;Koch, 1953b). Most pre-drift reconstructions correlate the CCSZ with the Brasiliano ductile faults (Bertrand and Jardim de Sà, 1990;Castaing et al, 1994;Davison et al, 1995;Neves et al, 2004), mainly the Patos Shear Zone in NE Brazil as illustrated (Fig. 1a) in pre-Mesozoic reconstructions (Caby, 1989;Souza et al, 2006).…”

Plates Amalgamation and Plate Destruction, the Western Gondwana History

“…Tentative correlation of NE-Brazil with its African counterpart (Caby, 1989;Trompette, 1994) shows a good structural fit between the Cearà-type and the Western Nigeria schist belts (Isseyin and Ife), in the one hand, and between the Sergipano and the Yaoundé-Oubanguide Groups, in the other hand; the Patos and Central Cameroon SZ are recognized as structural equivalents (Neves & Mariano, 1999), whereas the Cearà-type SZ are correlated with the trans-Saharan SZ (Caby, 1989). In Brazil, these shear zones are associated to early and latetectonic transcurrent plutons which ages are bracketed between 600-580 Ma, and 575-565 Ma, respectively (Neves et al, 2004;Souza et al, 2006); both age groups may be correlated with the sinistral and dextral shear evolutions in the Cameroon domain. However, NE-SW sinistral shear zones and respective NS synthetics in northern Cameroon have no equivalent in NE-Brazil.…”