TAS plots are a graphical representation of the silica and alkali contents of a magma.\u00a0 The regions on this TAS plot are named with familiar (and unfamiliar) magma types and were defined in a report by Le Maitre et al. (2002).\u00a0 The TAS classification<\/a> page on Wikipedia has more information and links to their individual pages.<\/p>\n Example total alkali versus silica plot with the different compositional fields marked. The plot compares tephra from the Hekla 1947 eruption found in the UK (Hall and Pilcher 2002; Swindles 2006) with in Iceland (Larsen et al. 1999) and other eruptions from Hekla volcano. Click to enlarge.<\/p><\/div>\n The plot shows that the Hekla 1947 eruption<\/a> was dacite-andesite in composition.\u00a0 As you might expect for this composition, it began explosively (showering southern Iceland with pumice and ash for a few hours) before going on to produce lava flows for over a year.\u00a0 The data were downloaded from Tephrabase<\/a> and EarthChem<\/a> databases, respectively.<\/p>\n The following code was used to draw the TAS plot above.\u00a0 I wrote a module, called tasplot, with the code that draws and labels the fields via the add_LeMaitre_fields()<\/strong> function.\u00a0 All the other commands are typical for plotting with Python and Matplotlib.<\/p>\n Follow the instructions on the BitBucket repository page at https:\/\/bitbucket.org\/jsteven5\/tasplot<\/a> to install.\u00a0 You can browse the source code of tasplot.py directly by clicking here<\/a>.<\/p>\n I recently made a total alkali vs silica (TAS) plot to compare the magma of the Hekla 1947 eruption with the compositions of magmas from previous eruptions.\u00a0 This post contains the code to draw the plot, including a module that … Continue reading ![\"Example](\"http:\/\/all-geo.org\/volcan01010\/wp-content\/uploads\/2015\/01\/Tephrabase_Hekla1947_600.png\")
<\/a>\u00a0tasplot.py<\/h3>\n
\r\n# Import plotting modules\r\nimport matplotlib.pyplot as plt\r\nimport tasplot # This imports the tasplot module\r\n\r\n# Set up figure\r\nfig = plt.figure() # create figure\r\nax1 = plt.subplot(111) # create axes and store as variable\r\ntasplot.add_LeMaitre_fields(ax1) # add TAS fields to plot\r\n\r\n# Note that you can change the default colour and font size e.g.\r\n# >>> tasplot.add_LeMaitre_Fields(ax1, color='red', fontsize=8)\r\n\r\n# Plot the data (from pre-existing variables)\r\nax1.plot(hallpilcher_silica, hallpilcher_alkali, 'o', alpha=1,\r\n label='Hall and Pilcher (2002)')\r\nax1.plot(larsen_silica, larsen_alkali, 'o', alpha=1,\r\n label='Larsen et al. (1999)')\r\nax1.plot(swindles_silica, swindles_alkali, 'o', alpha=1,\r\n label='Swindles (2006)')\r\nax1.plot(earthchem_silica, earthchem_alkalis, 'o',\r\n color=(0.8, 0.8, 0.8), alpha=0.5, mec='white',\r\n label='EarthChem database', zorder=0)\r\n\r\n# Decorate the plot\r\nplt.xlabel(r'SiO$_2$ (wt%)') # Use LaTeX notation for subscript\r\nplt.ylabel(r'Na$_2$O + K$_2$O (wt%)')\r\nplt.legend(loc='upper left', numpoints=1)\r\nplt.title('Tephrabase: Hekla 1947 samples')\r\nplt.savefig('Tephrabase_Hekla1947.png', dpi=150,\r\n bbox_inches='tight')\r\n\r\n#\r\n<\/pre>\n","protected":false},"excerpt":{"rendered":"