The large layered Goias complexes are three mafic-ultramafic layered intrusions which outcrop in a -350 km, NNE-trend bel! within the Brasilia Belt (centrai Brazil). Fom N lo S, they are: Cana Brava, Niquelllndia and Barro Alto. The intrusion age and geologica! hystory of these intrusions is stili presently debated. New U-Pb SHRIMP-II zircon analyses were perforrned in samples from Cana Brava and Barro Alto, the two poorest-known complexes among them, providing fora coeval Neoproterozoic intrusion age al -790 Ma of both complexes, consistent with literature ages for the Niquelandia complex. lnherited zircons with Mesoproterozoic ages are consistent with the formation age of the metavolcanic-metasedimentary sequences in magmatic contaci with these three complexes and suggest some degree of contamination of the complexes. This contamination in Niquelandia and Cana Brava is well known in the literature as revealed by bulk-rock Rb-Sr and Sm-Nd systematics. The two complexes show enrichment of the contamination in their gabbroic sequence with local enrichment where the crustal xenoliths are more abundant. Conversely, the upper pari of Niquelandia, mainly formed by anorthosite, is almost or totally uncontaminated. The Lu-Hf analyses on zircons from the Goiés complexes were perforrned during the instrument calibration of the Lu-Hf methodology al the laboratories of Centro lnterdipartimentale Grandi Strumenti al the Università di Modena e Reggio Emilia. The measurements were carried out using a Neptune MC-ICPMS coupled with a New Wave UP-213 laser ablation. The instrument was firstly calibrated on a standard solution and successively in situ analyses on complexes zircons were carried out together with CZ3 and TEMORA2 zircon standards. Mass bias and isobaric interference were corrected offiine using the lsotopeMaker free software of Zhang et al. (2015). Preliminary Lu-Hf in situ zircon data show negative EHf(t) values which are consistent with crustal contamination of the Barro Alto and Cana Brava parental melts as show by Rb-Sr and Sm-Nd in Cana Brava. The new Lu-Hf data, togheter with a review of literature data, show, for Barro Alto, a contamination similar to Niquelandia for the Rb-Sr and Sm-Nd systematics: zircons from the gabbroic sequence are contaminated, while zircons from the upper anorthosites are poorly contaminated. lnherited zircons commonly show positive EHf(t) values, which suggest mantle-derived melts for the magmatism of the metavolcanicmetasedimentary sequence.
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|Data di pubblicazione:||2016|
|Titolo:||THE LARGE LAYERED GOIAS COMPLEXES: NEW U-Pb ANO PRELIMINARY Lu-Hf IN SITU ZIRCON ANALYSES FROM BARRO ALTO AND CANA BRAVA|
|Autori:||Giovanardi, T.; Lugli, F.; Girardi, V.A.V.; Correla, C.T.; Tassinari, C.C.G.; Sinigoi, S.; Cipriani, A.; Mazzucchelli, M.|
|Nome del convegno:||emc2016 2nd European Mineralogical Conference|
|Luogo del convegno:||Rimini (Italy)|
|Data del convegno:||11-15/09/2016|
|Appare nelle tipologie:||Abstract in Rivista|
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