Zircon age-temperature-compositional spectra in plutonic rocks

Publication Year
2017

Type

Journal Article
Abstract

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 (Tsat) and rock solidification (Tsolid). Diffusive growth models predict asymmetric distributions of zircon dates and crystallization temperatures in a cooling magma, with volumetrically abundant old, hot crystallization at Tsat decreasing continuously to volumetrically minor young, cold crystallization at Tsolid. 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. 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.

DOWNLOAD PDF

 

Journal
geology
Volume
45
Issue
11
Pages
983 - 986
Date Published
08/2017
ISBN
0091-7613
Short Title
Geology
Full text