Geochemical data, Nd and Hf isotopes and U–Pb geochronology of meta-mafic rocks from western Gondwana suture zone

Abstract

The West Gondwana orogen, represented in NE Brazil by Santa Quitéria continental magmatic arc and ultrahigh-pressure metamafic rocks of a suture zone, have amphibolite and coesite-bearing retro-eclogite in both margins of the magmatic arc. This research reports and discuss the geochemical and geochronological data (U–Pb and Lu–Hf in zircon and Sm–Nd whole-rock) of amphibolite and retro-eclogite from the eastern margin of a continental magmatic arc. The Santa Quitéria Complex and metasedimentary Ceará Complex hosted these rocks. The Santa Quitéria amphibolites shows evident fractionation of REE. Nb–Ta–Ce anomalies evidence magma generated in a subduction zone with contribution and recycling of crustal sedimentary material, corroborate for slightly negative εNd (−1.56) and Paleoproterozoic NdTDM value (1.80 Ga). Isotopic Lu–Hf in zircon data indicates positive εHf (+5.00 to +7.78) and Neoproterozoic model ages (HfTDM from 0.97 to 0.86 Ga) (t = 637 ± 34 Ma - sample TJF5-258) indicate their extraction from the mantle. For the amphibolite samples from the Ceará Complex, the elemental distribution suggest that these rocks place them among oceanic basalts of enriched segments of mid-ocean ridges (E-MORB) and oceanic island basalts (OIB) – intra-oceanic arc basalts (IOAB). U–Pb zircon data of Ceará Complex amphibolite points to crystallization at ca. 670 Ma (674 ± 9 Ma, sample TJJV-07) and two metamorphic events around 640 Ma (644 ± 9 Ma) and 600 Ma (591 ± 5 Ma) related to the continental collision. Positive εNd values (+1.66 to +4.16) and model ages (NdTDM from 1.26 to 1.00 Ga) suggest a protolith crystallized from juvenile material of mantle source. Our data support that the eastern edge of the Santa Quitéria magmatic arc constitutes an active margin with subduction of the Cryogenian oceanic crust.