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<p>The mid-to-lower crustal G1 batholith (15,000 km<sup>2</sup>) of the Araçuaí Orogen (SE Brazil) is considered a ~ 60 Myr-long event of felsic magmatism developed during three magmatic pulses between ~ 630 and ~ 570&#xa0;Ma. Initially, based on a revision of over 1000 U–Pb zircon dates, we challenge such a large spread of magmatic ages and the reality of the three magmatic pulses. Subsequently, we combined high-precision and high-spatial-resolution in situ U–Pb zircon dates with trace element and Hf isotope data to investigate the causes of age dispersion and interpret the evolution of the batholith. In situ U–Pb dating of nine granitoids revealed that the same age variability described for the whole batholith occurs within every individual sample. Conversely, chemical abrasion isotope dilution TIMS analyses of zircons selected from one sample yielded a well-defined weighted mean age at 581.35 ± 0.16&#xa0;Ma, interpreted as the final age of granitoids emplacement and crystallisation. The dates spreading along Concordia reflect the combination of crystallisation, inheritance and post-crystallisation Pb loss, which in situ dating techniques applied to untreated zircons hardly disentangle. Given the rather unradiogenic zircon Hf isotopic compositions and similar trace elements amongst zircon textures and domains, we propose that the G1 batholith formed from multiple partial melting events of the mid-to-lower crustal portions of the Araçuaí Orogen induced by thermal fluctuations during the orogenic event. This study shows the pitfalls and limitations of in situ U–Pb zircon dating, showcasing the consequences of a flawed interpretation of our understanding of magmatic timescales.</p> Graphical abstract <p>Rank-order plot of chemical abrasion, isotope-dilution, thermal ionisation mass spectrometry (CA-ID-TIMS) 206Pb/238U zircon dates for one G1 granitoid sample.</p> <p></p>

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Episodic recycling of continental crust unravelled by zircon petrochronology of the Neoproterozoic G1 batholith, Araçuaí Orogen, SE Brazil

  • 期刊论文

  • 发表日期：

    2025年9月4日

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  • Francesco Narduzzi,
  • Federico Farina,
  • Urs Schaltegger,
  • Samuel Bersan,
  • Gary Stevens,
  • Herminio Arias Nalini Jr.

摘要

The mid-to-lower crustal G1 batholith (15,000 km2) of the Araçuaí Orogen (SE Brazil) is considered a ~ 60 Myr-long event of felsic magmatism developed during three magmatic pulses between ~ 630 and ~ 570 Ma. Initially, based on a revision of over 1000 U–Pb zircon dates, we challenge such a large spread of magmatic ages and the reality of the three magmatic pulses. Subsequently, we combined high-precision and high-spatial-resolution in situ U–Pb zircon dates with trace element and Hf isotope data to investigate the causes of age dispersion and interpret the evolution of the batholith. In situ U–Pb dating of nine granitoids revealed that the same age variability described for the whole batholith occurs within every individual sample. Conversely, chemical abrasion isotope dilution TIMS analyses of zircons selected from one sample yielded a well-defined weighted mean age at 581.35 ± 0.16 Ma, interpreted as the final age of granitoids emplacement and crystallisation. The dates spreading along Concordia reflect the combination of crystallisation, inheritance and post-crystallisation Pb loss, which in situ dating techniques applied to untreated zircons hardly disentangle. Given the rather unradiogenic zircon Hf isotopic compositions and similar trace elements amongst zircon textures and domains, we propose that the G1 batholith formed from multiple partial melting events of the mid-to-lower crustal portions of the Araçuaí Orogen induced by thermal fluctuations during the orogenic event. This study shows the pitfalls and limitations of in situ U–Pb zircon dating, showcasing the consequences of a flawed interpretation of our understanding of magmatic timescales.

Graphical abstract

Rank-order plot of chemical abrasion, isotope-dilution, thermal ionisation mass spectrometry (CA-ID-TIMS) 206Pb/238U zircon dates for one G1 granitoid sample.