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Re: Isoplot and Probability Density Plots

From:

Tectonics & structural geology discussion list <[log in to unmask]>

Date:

Mon, 25 Jul 2011 16:19:29 -0400

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 ```Peter and others, The kernel density method is available in matlab, and probably other math oriented packages as well. I would be surprised if it were not available for as a native feature in Excel, but I have not looked. Most kernel density algorithms use a Gaussian kernel for all observations. The Gaussian kernel is specified by a parameter h, which is equivalent to the standard deviation of the Gaussian kernel. The geologic community has adopted the practice to scale each grain age by the size of the standard error of the age. Hurford et al. (1984) is, to my knowledge, the first to do this, with an application for detrital zircon FT ages. I provided some statistical background for this approach and recommended as well that h should be set to 0.6 times the grain age standard error, in order avoid over smoothing (Brandon, 1996). These implimentations are easy to do in excel, matlab, etc. I would for for bandwidth, which is defined by a parameter h. It also helps to plot grain age data on a logarithmic axis given that grain ages for almost all isotopic methods have uncertainties that scale with the age. Best, Mark Hurford A. J., Fitch F. J. and Clarke A. (1984) Resolution of the age structure of the detrital zircon populations of two Lower Cretaceous sandstones from the Weald of England by fission track dating. Geol. Mag. 121, 269-277 Brandon, M., 1996, Probability density plot for fission-track grain-age samples: Radiation Measurements, v. 26, no. 5, p. 663­676.   ________________________________________________________________________ Mark Brandon, Professor, Dept. of Geology and Geophysics Yale University, P.O. Box 208109, 210 Whitney Avenue New Haven, CT 06520-8109 e-mail: [log in to unmask], skype: mark.brandon.yale wk. phone: +203-432-3135, wk. fax: +203-432-3134 cell phone: +203-650-4770 Dept. Web site: http://www.yale.edu/geology Brandon's site: http://www.geology.yale.edu/~brandon ________________________________________________________________________ -----Original Message----- From: "Clift, Peter" <[log in to unmask]> Reply-To: Tectonics & structural geology discussion list <[log in to unmask]> Date: Mon, 25 Jul 2011 16:04:25 -0400 To: "[log in to unmask]" <[log in to unmask]> Subject: Isoplot and Probability Density Plots >I have been happily using isoplot to make probability density plots for >thermochronology data for several years now but it stopped working on >Excel >2008 for the Mac and now the new Mac OS X system software prevents you >from >running the older Excel 2003. I was wondering if anyone has any >suggestions >about other ways of generating probability density plots as they are >useful >in dealing with zircon and mica age data sets in particular. > >------------------- > >Peter Clift >School of Geosciences >University of Aberdeen >United Kingdom > >Tel: +44 1224 273456 >Email: [log in to unmask] > >http://www.abdn.ac.uk/~wpg008/PChomepage.html > > > > >The University of Aberdeen is a charity registered in Scotland, No >SC013683.```