Scientific article
English

Zircon Petrochronology and 40Ar/39Ar Thermochronology of the Adamello Intrusive Suite, N. Italy: Monitoring the Growth and Decay of an Incrementally Assembled Magmatic System

Published inJournal of Petrology, vol. 60, no. 4, p. 701-722
Publication date2019
Abstract

The Adamello intrusive suite is a composite batholith in Northern Italy, with an estimated 2000km3 volume, assembled incrementally over a time span of 10 to 12 million years. The history of crystallization has been studied in detail through laser ablation ICP-MS and SIMS U-Pb geochronology of zircon, which records prolonged crystallization of each of the different intrusive units at mid-crustal levels between 43.47 and 33.16 Ma. The magmas were episodically extracted from this storage area and ascended to the final intrusion level at ~6 km paleo-depth. Each batch of melt cooled very rapidly down to the ambient temperature of 250°C, evidenced by distinct cooling paths recorded by amphibole, biotite and K-feldspar 40Ar/39Ar dates. The magma source area was moving from SW to NE with time, causing increasing thermal maturity in the mid-crustal reservoir. The resulting temporal trend of higher degrees of crustal assimiliation in the course of the evolution of the magmatic system can be traced through Hf and O isotopes in zircon. Rough estimates of magma emplacement rates (‘magma flux') yield very low values in the range of 10-4km3/yr, typical of mid-to-upper crustal plutons and increase with time. Although we cannot discern a decrease of magma flux from our own data, we anticipate that a dramatic decrease of magma flux between 33 and 31Ma along the northern contact lead to cessation of magma emplacement.

Keywords
  • Isotopes
  • Magmatism
  • Trace elements
  • U–Th–Pb geochronology
  • Zircon
  • Adamello
Funding
  • Swiss National Science Foundation - The fourth dimension: resolving the time-scales of magma evolution
Citation (ISO format)
SCHALTEGGER, Urs et al. Zircon Petrochronology and 40Ar/39Ar Thermochronology of the Adamello Intrusive Suite, N. Italy: Monitoring the Growth and Decay of an Incrementally Assembled Magmatic System. In: Journal of Petrology, 2019, vol. 60, n° 4, p. 701–722. doi: 10.1093/petrology/egz010
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Identifiers
Journal ISSN0022-3530
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