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<p>Granitoids and volcanic rocks of hybrid composition between mantle and crustal components are common in various tectonic settings and contribute to both the growth and differentiation of the continental crust. However, the mechanisms by which such hybrid magmas are produced are debated. We focus on a key lower crustal exposure of the Permian Sesia Magmatic System located in the Ivrea-Verbano Zone—IVZ, Italy, allowing to directly investigate the deep roots of a hybrid magmatic system. Integrating multi-scale field observations and bulk-rock data with zircon and apatite petrochronology (U–Pb dating, trace elements, Lu–Hf and Sm–Nd isotopes respectively), we show that lower-crustal orthopyroxene-bearing rocks associated to migmatites in a ‘frozen’ hybridization zone, correspond to hybrid cumulates from which melts were extracted to form upper crustal granitic plutons. Igneous zircon records at least three crystallization stages: (i) initial low-crystallinity hybridization phase at lower-crustal scale; (ii) subsequent chemical differentiation in a mush system, driven by reactive porous flow at the 10<sup>2</sup>–10<sup>3</sup>&#xa0;m scale; and (iii) final crystallization after significant melt extraction and subsequent, smaller-scale (10<sup>0</sup>–10<sup>−1</sup>&#xa0;m) chemical equilibration. Apatite, on the other hand, is fully homogenized at the sample scale but chemical differences between samples preserve the first-order hybridization trends. While crustal-scale differentiation (melt extraction, transfer and cooling) took place in a short time span (ca. 2–4&#xa0;Ma) as previously suggested in the IVZ, our zircon U–Pb data are permissive of the construction and equilibration of the lower crustal system over a longer period of ca. 15&#xa0;Myr minimum. Our study also reveals the potential of accessory minerals, in particular zircon, to preserve the successive steps involved in the complex history of the lower crust, even at high temperatures.</p>

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Hybrid granite factory in the continental lower crust: an accessory mineral perspective from the Ivrea-Verbano Zone, Northern Italy

  • 期刊论文

  • 发表日期：

    2026年5月7日

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  • Caliméria do Carmo,
  • Oscar Laurent,
  • Olivier Vanderhaeghe,
  • Andrea Galli,
  • Lorenzo Tavazzani,
  • Emilie Bruand

摘要

Granitoids and volcanic rocks of hybrid composition between mantle and crustal components are common in various tectonic settings and contribute to both the growth and differentiation of the continental crust. However, the mechanisms by which such hybrid magmas are produced are debated. We focus on a key lower crustal exposure of the Permian Sesia Magmatic System located in the Ivrea-Verbano Zone—IVZ, Italy, allowing to directly investigate the deep roots of a hybrid magmatic system. Integrating multi-scale field observations and bulk-rock data with zircon and apatite petrochronology (U–Pb dating, trace elements, Lu–Hf and Sm–Nd isotopes respectively), we show that lower-crustal orthopyroxene-bearing rocks associated to migmatites in a ‘frozen’ hybridization zone, correspond to hybrid cumulates from which melts were extracted to form upper crustal granitic plutons. Igneous zircon records at least three crystallization stages: (i) initial low-crystallinity hybridization phase at lower-crustal scale; (ii) subsequent chemical differentiation in a mush system, driven by reactive porous flow at the 102–103 m scale; and (iii) final crystallization after significant melt extraction and subsequent, smaller-scale (100–10−1 m) chemical equilibration. Apatite, on the other hand, is fully homogenized at the sample scale but chemical differences between samples preserve the first-order hybridization trends. While crustal-scale differentiation (melt extraction, transfer and cooling) took place in a short time span (ca. 2–4 Ma) as previously suggested in the IVZ, our zircon U–Pb data are permissive of the construction and equilibration of the lower crustal system over a longer period of ca. 15 Myr minimum. Our study also reveals the potential of accessory minerals, in particular zircon, to preserve the successive steps involved in the complex history of the lower crust, even at high temperatures.