期刊
CHEMICAL GEOLOGY
卷 291, 期 -, 页码 79-86出版社
ELSEVIER
DOI: 10.1016/j.chemgeo.2011.09.017
关键词
40Ar/39Ar geochronology; Muscovite; Diffusion; Metamorphism; Numerical modelling
资金
- NERC [NE/E0114038/1]
- Natural Environment Research Council [NE/H016279/1] Funding Source: researchfish
- NERC [NE/H016279/1] Funding Source: UKRI
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 crystallisation 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. (C) 2011 Elsevier B.V. All rights reserved.
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