When can muscovite ⁴⁰Ar/³⁹Ar dating constrain the timing of metamorphic exhumation?

Warren, Clare; Hanke, Felix and Kelley, Simon (2012). When can muscovite ⁴⁰Ar/³⁹Ar dating constrain the timing of metamorphic exhumation? Chemical Geology, 291 pp. 79–86.

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DOI (Digital Object Identifier) Link:	http://dx.doi.org/doi:10.1016/j.chemgeo.2011.09.017
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Abstract

Metamorphic cooling rates determined using muscovite ⁴⁰Ar/³⁹Ar ages underpin many tectonic models, but are based on several simplifying approximations. We demonstrate that a number of these approximations, especially those relating to the assignment of a single “closure temperature”, might not hold for certain metamorphic scenarios, and particularly for metamorphism during rapid orogenic cycles. Using numerical diffusion models that include a recently reported significant pressure dependence of Ar diffusion in muscovite, we systematically interrogate the approximations associated with linking ⁴⁰Ar/³⁹Ar dates to pressure-temperature histories. The results of the simulations are presented in a simple graphic form allowing evaluation of the pressure-temperature (PT) regions in which Ar diffusion is efficient, and hence those in which the muscovite may yield true ⁴⁰Ar/³⁹Ar cooling ages. We suggest that a robust method for determining whether metamorphic muscovite ⁴⁰Ar/³⁹Ar ages relate to the timing of cooling involves: (1) the determination of the PT conditions and relative timing of muscovite crystallization during the metamorphic cycle, (2) the collection of high precision and high spatial resolution ⁴⁰Ar/³⁹Ar data from muscovite grains and (3) the comparison between analytical data and numerical diffusion models which test different post-crystallisation pressure-temperature histories.

Item Type:	Journal Article
Copyright Holders:	2011 Elsevier B.V.
ISSN:	0009-2541
Funders:	NERC
Keywords:	40Ar/39Ar geochronology; muscovite; diffusion; metamorphism; numerical modelling
Academic Unit/Department:	Science > Environment, Earth and Ecosystems Science > Physical Sciences
Interdisciplinary Research Centre:	Centre for Earth, Planetary, Space and Astronomical Research (CEPSAR)
Item ID:	29846
Depositing User:	Clare Warren
Date Deposited:	20 Oct 2011 13:23
Last Modified:	14 Nov 2012 12:03
URI:	http://oro.open.ac.uk/id/eprint/29846

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