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This content will become publicly available on August 23, 2018

Title: Zircon age-temperature-compositional spectra in plutonic rocks

We present that geochronology can resolve dispersed zircon dates in plutonic rocks when magma cooling time scales exceed the temporal precision of individual U-Pb analyses; such age heterogeneity may indicate protracted crystallization between the temperatures of zircon saturation (T sat) and rock solidification (T solid). Diffusive growth models predict asymmetric distributions of zircon dates and crystallization temperatures in a cooling magma, with volumetrically abundant old, hot crystallization at T sat decreasing continuously to volumetrically minor young, cold crystallization at T solid. We present integrated geochronological and geochemical data from Bergell Intrusion tonalites (Central Alps, Europe) that document zircon compositional change over hundreds of thousands of years at the hand-sample scale, indicating melt compositional evolution during solidification. Ti-in-zircon thermometry, crystallization simulation using MELTS software, and U-Pb dates produce zircon mass-temperature-time distributions that are in excellent agreement with zircon growth models. In conclusion, these findings provide the first quantitative validation of longstanding expectations from zircon saturation theory by direct geochronological investigation, underscoring zircon’s capacity to quantify supersolidus cooling rates in magmas and resolve dynamic differentiation histories in the plutonic rock record.
Authors:
 [1] ;  [2] ;  [2] ;  [1] ;  [1]
  1. Princeton Univ., NJ (United States). Department of Geosciences
  2. Univ. of California, Los Angeles, CA (United States). Department of Earth, Planetary and Space Sciences
Publication Date:
Report Number(s):
LLNL-JRNL-747222
Journal ID: ISSN 0091-7613
Grant/Contract Number:
AC52-07NA27344
Type:
Accepted Manuscript
Journal Name:
Geology
Additional Journal Information:
Journal Volume: 45; Journal Issue: 11; Journal ID: ISSN 0091-7613
Publisher:
Geological Society of America
Research Org:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA)
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES
OSTI Identifier:
1426134