Timing of incremental pluton construction and magmatic activity in a back-arc setting revealed by ID-TIMS U/Pb and Hf isotopes on complex zircon grains

Mélanie Barboni, Blair Schoene, Maria Ovtcharova, François Bussy, Urs Schaltegger, Axel Gerdes

Research output: Contribution to journalArticle

35 Scopus citations

Abstract

The lifetimes and thermal histories of upper crustal plutons are increasingly determined using geochronology, but complex growth of datable minerals in magmas impedes simple age interpretations. Careful field observation helps constrain zircon U-Pb dates in terms of timing of magma injection, for example because relative ages of successive magma pulses must be honored. We use ID-TIMS U/Pb zircon geochronology and field geology to construct timescales of incremental pluton assembly in the St-Jean-du-Doigt (SJDD) bimodal layered intrusion (Brittany, France). Field evidence suggests that early pulses were injected into a cold environment with little supersolidus interaction among successive magma pulses. Later injections occurred in a progressively hotter environment with protracted mafic and felsic magma interaction. Zircon dates show that early activity ca. 347. Ma predates the thermally mature episode by about 1. Ma, which terminated at ca. 345. Ma. Dates from samples displaying core-rim zircon overgrowths span about 5. Ma (351-346. Ma), which we interpret to represent two distinct crystallization events. Hf isotopic data from cores and rims are homogeneous, precluding zircon inheritance from basement rocks. These textures and dates could instead reflect zircon saturation fluctuations at the emplacement depth, or antecrystic zircon grains recording pre-emplacement magmatic growth.

Original languageEnglish (US)
Pages (from-to)76-93
Number of pages18
JournalChemical Geology
Volume342
DOIs
StatePublished - Mar 9 2013
Externally publishedYes

Keywords

  • Hafnium isotopes
  • U-Pb geochronology
  • Variscan
  • Zircon
  • Zircon antecryst
  • Zircon residence time

ASJC Scopus subject areas

  • Geology
  • Geochemistry and Petrology

Fingerprint Dive into the research topics of 'Timing of incremental pluton construction and magmatic activity in a back-arc setting revealed by ID-TIMS U/Pb and Hf isotopes on complex zircon grains'. Together they form a unique fingerprint.

  • Cite this