# Lithospheric-scale dynamics during continental subduction: Evidence from a frozen-in plate interface

Kevin Mendes, Philippe Agard, Alexis Plunder, Clément Herviou

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Kevin Mendes, Philippe Agard, Alexis Plunder, Clément Herviou. Lithospheric-scale dynamics during continental subduction: Evidence from a frozen-in plate interface. Geology, 2023, 51 (12), pp.1153-1157. 10.1130/G51480.1. hal-04334700

HAL Id: hal-04334700

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Submitted on 21 Jul 2025

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<figure><img src="image_1.png" /></figure>

Distributed under a Creative Commons Attribution 4.0 International License
As explained in the text, peak temperature (Tmax) and pressure (Pmax) estimates were respectively obtained using the Raman spectroscopy of carbonaceous material method and by (1) measuring the maximum Si content of phengite, (2) calculating a P-T pseudosection using an average bulk rock composition representative of each zone of interest and (3) deriving Pmax from the intersection of the Si content isopleth for phengite and Tmax (see also Herviou et al., 2022).

## PEAK TEMPERATURE ESTIMATION

Raman spectra of carbonaceous material (RSCM), were obtained using a Renishaw inVia Spectrometer at ENS Paris. The excitation light was provided by a laser (Cobolt Fandango) at 514.5 nm and at a power of 50 mW, focused on the sample using a x100 objective (Leica). Ten to twenty-two spectra per sample were acquired in the 1000-2000 cm⁻¹ range; acquisition time was 3x10 seconds with 10% of the laser power following the spectral acquisition parameters of Beyssac et al. (2002). Peak position, baseline correction and band width were determined using Peakfit© software. Temperatures were determined using Lahfid et al. (2010) for the ~200 to 320°C temperature range and Beyssac et al. (2002) for the 330-640°C temperature range. Results are given in Table 2 of supplementary material 2.

## PEAK PRESSURE ESTIMATION

The Si content of phengite is known to be particularly dependent on pressure variations (Saliot and Velde, 1982) and can also vary depending on the rock composition. The rocks sampled in this study have been collected from areas only recording Alpine metamorphism (except for the Briançonnais sample from the RU transect). We therefore have attempted to track the most highly substituted phengite by identifying the earliest foliations and by analyzing the phengite by electron microprobe in these fabrics. Then, all the analyses have been carefully
examined in order to only keep those containing less than 15% of Xpyrophyllite, to avoid high
Si values that are not recording the highest tschermak substitution. The maximum Si content
(Simax) obtained is interpreted to represent a minimum peak pressure recorded during the
metamorphic history of the rock, as some phengite could have been partly/totally re-crystallized
during exhumation. Analyses of phengite chemical composition were performed at
CAMPARIS (Sorbonne Université, Paris) using an electron microprobe (Cameca SX-100 and
SX-Five). Point measurements were made using classical analytical conditions (15 kV
acceleration voltage and 10 nA beam current allowing ~2 µm beam size in wave-length-
dispersive spectroscopy mode) with diopside (Ca, Mg, Si), MnTiO3 (Mn, Ti), orthoclase (K,
Al), Fe2O3 (Fe), albite (Na) and Cr2O3 (Cr) as standards to measure elements indicated in
brackets. Representative electron microprobe compositions of phengite are presented in Table
3 of supplementary material 2.

In order to precisely constrain the peak pressure, we calculated P-T pseudosections
using Perple_X software (version 6.9.1; Connolly, 1990, 2005, 2009; Fig S1A, B and C).
Pseudosection modelling have been made with one consistent thermodynamic dataset for the
three zone, using an average bulk rock composition representative of each one. For our three
representative metapelites the used thermodynamic database is Holland and Powell (1998) with
its corresponding solution models (for chloritoid, garnet, carpholite, biotite, phengite) except
for chlorite (Lanari et al., 2014). Calculations were performed in a Na₂O-K₂O-FeO-MgO-
Al₂O₃-SiO₂-H₂O (NaKFMASH) chemical system. CaO is mostly restricted to carbonates and
partially in lawsonite (only 1 sample of the Briançonnais in this study) and was therefore not
considered in these calculations. MnO, TiO₂, Cr₂O₃, P₂O₅, SrO and BaO are minor and only
present in accessory phases and they were therefore also neglected. Respectively, used bulk
rocks composition (given in weight %) are 0.80 Na₂O, 1.67 K₂O, 4.48 FeO, 3.91 MgO, 8.33
Al₂O₃, 69.46 SiO₂ and 15.00 H₂O for the Briançonnais, 0.73 Na₂O, 1.49 K₂O, 3.19 FeO, 2.64
MgO, 6.59 Al₂O₃, 74.05 SiO₂ and 10.83 H₂O for the Piemont and 0.56 Na₂O, 1.56 K₂O, 6.67 FeO, 5.51 MgO, 8.91 Al₂O₃, 55.79 SiO₂ and 18.83 H₂O for the Liguro-Piemont. Pseudosections were calculated in the P-T range of 1.0-2.5 GPa and 300-600°C to cover all potentially peak P-T conditions recorded by metamorphic rocks of the Western Alps.

Finally, the minimum peak pressure conditions of each sample were determined from the intersection of Siₘₐₓ values (along Si-in-phengite isopleths) and their respective Tmax estimates using RSCM, both plotted on the pseudosections (Fig S1).

## REFERENCES CITED

* Beyssac, O., Goffé, B., Chopin, C., and Rouzaud, J.N., 2002, Raman spectra of carbonaceous material in metasediments: a new geothermometer, *Journal of Metamorphic Geology*, v. 20, p. 859–871, doi:10.1046/j.1525-1314.2002.00408.x.

* Connolly, J.A.D., 1990, Multivariable phase diagrams: an algorithm based on generalized thermodynamics: *American Journal of Science*, v. 290, p. 666-718, doi:10.2475ajs.290.6.666

* Connolly, J.A.D., 2005, Computation of phase equilibria by linear programming: A tool for geodynamic modeling and its application to subduction zone decarbonation: *Earth and Planetary Science Letters*, v. 236, p. 524–541, doi:10.1016/j.epsl.2005.04.033.

* Connolly, J.A.D., 2009, The geodynamic equation of state: What and how: *Geochemistry, Geophysics, Geosystems*, v. 10, p. n/a-n/a, doi:10.1029/2009GC002540.

* Holland, T.J.B., and Powell, R., 2004, An internally consistent thermodynamic data set for phases of petrological interest: *Journal of Metamorphic Geology*, v. 16, p. 309–343, doi:10.1111/j.1525-1314.1998.00140.x.
o Lahfid, A., Beyssac, O., Deville, E., Negro, F., Chopin, C., and Goffé, B., 2010, Evolution of the Raman spectrum of carbonaceous material in low-grade metasediments of the Glarus Alps (Switzerland): RSCM in low-grade metasediments: Terra Nova, v. 22, p. 354–360, doi:10.1111/j.1365-3121.2010.00956.x.

o Lanari, P., Wagner, T., and Vidal, O., 2014, A thermodynamic model for di-trioctahedral chlorite from experimental and natural data in the system MgO-FeO-Al2O3-SiO2-H2O: applications to P-T sections and geothermometry: Contributions to Mineralogy and Petrology, v. 167, p. 968, doi:10.1007/s00410-014-0968-8.

o Saliot, P., and Velde, B., 1982, Phengite compositions and post-nappe high-pressure metamorphism in the pennine zone of the French Alps: Earth and Planetary Science Letters, v. 57, p. 133–138, doi:10.1016/0012-821X(82)90179-0.

o Whitney, D.L., and Evans, B.W., 2010, Abbreviations for names of rock-forming minerals: American Mineralogist, v. 95, p. 185–187, doi:10.2138/am.2010.3371.
<figure><img src="image_2.png" /></figure>

Figure S1: Pseudosection showing the intersection of the Si content isopleth for phengite and Tmax. A: Briançonnais. B: Piemont. C: Liguго-Piemont. See caption of figure 2 for abbreviation of samples and Whitney and Evans (2010) for minerals. Note that all field of interest contain phengite, chlorite, mica, quartz and H₂O ± carpholite and chloritoid.
Samples data

<table><thead><tr><th>Sample</th><th>Latitude</th><th>Longitude</th><th>Lithology</th><th>Mineralogy**</th><th>Temperature [°C]</th><th>Pressure [GPa]</th></tr></thead><tbody><tr><td colspan="7">Briançonnais</td></tr><tr><td>RU</td><td>45,59724</td><td>7,03699</td><td>Quartzite</td><td>Qz-Ph-Chl-Grt</td><td>560</td><td>2.000</td></tr><tr><td>GS</td><td>45,48689</td><td>6,96117</td><td>Calcschist</td><td>Cb-Ph-Chl-Qz-Ep</td><td>459</td><td>1.380</td></tr><tr><td>GA</td><td>45,45606</td><td>7,04778</td><td>Marble</td><td>Cb-Qz</td><td>451</td><td>Ø</td></tr><tr><td>IS</td><td>45,43938</td><td>7,01126</td><td>Calcschist</td><td>Ph-Chl-Qz-Cb</td><td>419</td><td>Ø</td></tr><tr><td>PL</td><td>45,34097</td><td>6,87039</td><td>Calcschist</td><td>Ph-Chl-Qz-Cb</td><td>380</td><td>1.575</td></tr><tr><td>MC</td><td>45,22003</td><td>6,85358</td><td>Calc-schist</td><td>Ph-Chl-Qz-Cb</td><td>453</td><td>1.975</td></tr><tr><td>ETA</td><td>45,14893</td><td>6,80883</td><td>Calc-schist</td><td>Ph-Chl-Qz-Cb-Lws pseudo</td><td>412</td><td>1.800</td></tr><tr><td>NEV</td><td>45,04328</td><td>6,66367</td><td>Marble</td><td>Cb-Qz</td><td>318</td><td>1.375</td></tr><tr><td>CHA</td><td>44,95478</td><td>6,73642</td><td>Mica-schist</td><td>Ph-Qz-Chl-Grt</td><td>367</td><td>Ø</td></tr><tr><td>SV</td><td>44,68755</td><td>6,81023</td><td>Calc-schist</td><td>Ph-Chl-Qz-Cb-Lws pseudo</td><td>349</td><td>Ø</td></tr><tr><td>UB</td><td>44,60499</td><td>6,82539</td><td>Calc-schist</td><td>Cb-Ph-Chl-Qz</td><td>326</td><td>1.075</td></tr><tr><td colspan="7">Piemont</td></tr><tr><td>CHA</td><td>44,95617</td><td>6,73708</td><td>Marble</td><td>Cb-Qz</td><td>327</td><td>Ø</td></tr><tr><td>RB</td><td>44,81420</td><td>6,75754</td><td>Calc-schist</td><td>Ph-Chl-Cb-Qz</td><td>363</td><td>Ø</td></tr><tr><td>CQ</td><td>44,76394</td><td>6,79781</td><td>Calc-schist</td><td>Ph-Chl-Cb-Qz</td><td>358</td><td>Ø</td></tr><tr><td>SV</td><td>44,67625</td><td>6,85100</td><td>Calc-schist</td><td>Ph-Chl-Cb-Qz</td><td>309</td><td>Ø</td></tr><tr><td>UB</td><td>44,63957</td><td>6,86679</td><td>Calc-schist</td><td>Ph-Chl-Cb-Qz</td><td>338</td><td>1.340</td></tr><tr><td colspan="7">Liguro-Piemont</td></tr><tr><td>RU</td><td>45,62598</td><td>7,03224</td><td>Calc-schist</td><td>Ph-Chl-Cb-Qz</td><td>493</td><td>2.000</td></tr><tr><td>GS</td><td>45,49264</td><td>6,95544</td><td>Calc-schist</td><td>Ph-Chl-Cb-Qz-Ab</td><td>440</td><td>1.825</td></tr><tr><td>GA (GA2005 from Herviou et al., 2022)</td><td>45,45654</td><td>7,07285</td><td>Calc-schist</td><td>Ph-Chl-Qz-Ab-Cb-Lws pseudo</td><td>483</td><td>Ø</td></tr><tr><td>IS (49 from Gabalda et al., 2009)</td><td>45,41667</td><td>7,03333</td><td>Calc-schist</td><td>Ø</td><td>440</td><td>Ø</td></tr><tr><td>PL</td><td>45,32456</td><td>6,84919</td><td>Calc-schist</td><td>Cb-Ph-Chl-Qz</td><td>376</td><td>Ø</td></tr><tr><td>MC</td><td>45,20800</td><td>6,89917</td><td>Calc-schist</td><td>Ph-Chl-Cb-Qz</td><td>450</td><td>1.880</td></tr><tr><td>ETA</td><td>45,14940</td><td>6,80615</td><td>Calc-schist</td><td>Ph-Chl-Cb-Qz</td><td>417</td><td>1.875</td></tr><tr><td>NEV</td><td>45,07617</td><td>6,71278</td><td>Calc-schist</td><td>Cb-Qz-Ph-Chl</td><td>347</td><td>1.425</td></tr><tr><td>CHA</td><td>44,96303</td><td>6,77789</td><td>Calc-schist</td><td>Ph-Chl-Cb-Qz</td><td>358</td><td>1.375</td></tr><tr><td>RB</td><td>44,83358</td><td>6,80847</td><td>Calc-schist</td><td>Ph-Chl-Cb-Qz</td><td>370</td><td>Ø</td></tr><tr><td>CQ</td><td>44,75785</td><td>6,79218</td><td>Calc-schist</td><td>Cb-Ph-Chl-Qz</td><td>371</td><td>Ø</td></tr><tr><td>SV</td><td>44,68930</td><td>6,86560</td><td>Calc-schist</td><td>Ph-Chl-Cb-Qz</td><td>329</td><td>Ø</td></tr><tr><td>UB</td><td>44,61008</td><td>6,86842</td><td>Calc-schist</td><td>Ph-Chl-Cb-Qz</td><td>319</td><td>1.370</td></tr></tbody></table>

<footnote>** Abbreviation for minerals are from Whitney et Evans (2010).</footnote>
RSCM

<table><thead><tr><th>Sample</th><th>Number of spectra</th><th>Température [°C]</th><th>Standard deviation T°</th><th>Standard error T°</th><th>R2</th><th>Standard deviation R2</th><th>Coefficient r²</th></tr></thead><tbody><tr><td colspan="8" style="background-color: #E6B3B3; text-align: center; font-weight: bold;">Briançonnais</td></tr><tr><td>RU</td><td>10</td><td>560</td><td>46</td><td>14</td><td>0,18</td><td>0,10</td><td>0,99</td></tr><tr><td>GS</td><td>20</td><td>459</td><td>13</td><td>3</td><td>0,41</td><td>0,03</td><td>0,99</td></tr><tr><td>GA</td><td>16</td><td>451</td><td>20</td><td>5</td><td>0,43</td><td>0,05</td><td>0,98</td></tr><tr><td>IS</td><td>16</td><td>419</td><td>7</td><td>2</td><td>0,50</td><td>0,02</td><td>1,00</td></tr><tr><td>PL</td><td>13</td><td>380</td><td>8</td><td>2</td><td>0,59</td><td>0,02</td><td>0,99</td></tr><tr><td>MC</td><td>21</td><td>453</td><td>16</td><td>4</td><td>0,42</td><td>0,04</td><td>0,99</td></tr><tr><td>ETA</td><td>16</td><td>412</td><td>6</td><td>1</td><td>0,51</td><td>0,01</td><td>0,98</td></tr><tr><td>NEV</td><td>20</td><td>318</td><td>10</td><td>2</td><td>0,63</td><td>0,01</td><td>0,99</td></tr><tr><td>CHA</td><td>15</td><td>367</td><td>14</td><td>4</td><td>0,62</td><td>0,03</td><td>0,99</td></tr><tr><td>SV</td><td>12</td><td>349</td><td>38</td><td>11</td><td>0,65</td><td>0,03</td><td>0,90</td></tr><tr><td>UB</td><td>15</td><td>326</td><td>18</td><td>5</td><td>0,64</td><td>0,01</td><td>0,99</td></tr><tr><td colspan="8" style="background-color: #E6B3B3; text-align: center; font-weight: bold;">Piemont</td></tr><tr><td>CHA</td><td>14</td><td>327</td><td>20</td><td>5</td><td>0,71</td><td>0,05</td><td>0,90</td></tr><tr><td>RB</td><td>16</td><td>363</td><td>11</td><td>3</td><td>0,62</td><td>0,02</td><td>0,99</td></tr><tr><td>CQ</td><td>18</td><td>358</td><td>14</td><td>3</td><td>0,64</td><td>0,03</td><td>0,97</td></tr><tr><td>SV</td><td>16</td><td>309</td><td>34</td><td>9</td><td>0,62</td><td>0,03</td><td>0,99</td></tr><tr><td>UB</td><td>16</td><td>338</td><td>14</td><td>4</td><td>0,65</td><td>0,01</td><td>0,99</td></tr><tr><td colspan="8" style="background-color: #A9CCE3; text-align: center; font-weight: bold;">Liguro-Piemont</td></tr><tr><td>RU</td><td>16</td><td>493</td><td>26</td><td>6</td><td>0,33</td><td>0,06</td><td>0,99</td></tr><tr><td>GS</td><td>14</td><td>440</td><td>21</td><td>6</td><td>0,45</td><td>0,05</td><td>0,99</td></tr><tr><td>GA (PL2001 from Herviou et al., 2022)</td><td>15</td><td>483</td><td>19</td><td>5</td><td>Ø</td><td>Ø</td><td>Ø</td></tr><tr><td>IS (49 from Gabalda et al., 2009)</td><td>13</td><td>440</td><td>Ø</td><td>4</td><td>0,45</td><td>0,03</td><td>Ø</td></tr><tr><td>PL</td><td>16</td><td>376</td><td>7</td><td>2</td><td>0,59</td><td>0,02</td><td>1,00</td></tr><tr><td>MC</td><td>22</td><td>450</td><td>25</td><td>5</td><td>0,43</td><td>0,06</td><td>0,99</td></tr><tr><td>ETA</td><td>16</td><td>417</td><td>11</td><td>3</td><td>0,50</td><td>0,03</td><td>0,99</td></tr><tr><td>NEV</td><td>20</td><td>347</td><td>7</td><td>2</td><td>0,66</td><td>0,02</td><td>1,00</td></tr><tr><td>CHA</td><td>21</td><td>358</td><td>11</td><td>2</td><td>0,64</td><td>0,03</td><td>0,98</td></tr><tr><td>RB</td><td>20</td><td>370</td><td>6</td><td>1</td><td>0,61</td><td>0,01</td><td>0,99</td></tr><tr><td>CQ</td><td>16</td><td>371</td><td>16</td><td>4</td><td>0,61</td><td>0,04</td><td>0,98</td></tr><tr><td>SV</td><td>16</td><td>329</td><td>11</td><td>3</td><td>0,64</td><td>0,01</td><td>1,00</td></tr><tr><td>UB</td><td>13</td><td>319</td><td>11</td><td>3</td><td>0,63</td><td>0,01</td><td>0,99</td></tr></tbody></table>
Microprobe analysis

<table><thead><tr><th colspan="9">Briançonnais</th></tr><tr><th>Sample</th><th>RU</th><th>GS</th><th>PL</th><th>MC</th><th>ETA</th><th>NEV</th><th>/</th><th>UB</th></tr></thead><tbody><tr><td>SiO2</td><td>50,76</td><td>47,64</td><td>51,31</td><td>53,07</td><td>53,31</td><td>52,78</td><td>/</td><td>48,16</td></tr><tr><td>TiO2</td><td>0,10</td><td>0,22</td><td>0,06</td><td>0,13</td><td>0,11</td><td>0,15</td><td>/</td><td>0,18</td></tr><tr><td>Al2O3</td><td>27,82</td><td>30,39</td><td>27,47</td><td>26,20</td><td>25,67</td><td>26,31</td><td>/</td><td>32,67</td></tr><tr><td>Cr2O3</td><td>0,04</td><td>0,01</td><td>0,03</td><td>0,03</td><td>0,02</td><td>0,03</td><td>/</td><td>0,00</td></tr><tr><td>FeOtot</td><td>3,11</td><td>2,82</td><td>3,30</td><td>4,20</td><td>2,74</td><td>0,56</td><td>/</td><td>1,31</td></tr><tr><td>MnO</td><td>0,04</td><td>0,03</td><td>0,00</td><td>0,02</td><td>0,07</td><td>0,00</td><td>/</td><td>0,01</td></tr><tr><td>MgO</td><td>2,52</td><td>2,71</td><td>2,85</td><td>1,94</td><td>3,89</td><td>6,21</td><td>/</td><td>1,88</td></tr><tr><td>CaO</td><td>0,03</td><td>0,00</td><td>0,03</td><td>0,06</td><td>0,03</td><td>0,04</td><td>/</td><td>0,08</td></tr><tr><td>Na2O</td><td>0,33</td><td>0,39</td><td>0,13</td><td>1,41</td><td>0,06</td><td>0,29</td><td>/</td><td>0,78</td></tr><tr><td>K2O</td><td>10,37</td><td>9,58</td><td>10,11</td><td>8,88</td><td>10,25</td><td>9,88</td><td>/</td><td>8,73</td></tr><tr><td>total</td><td>95,12</td><td>93,79</td><td>95,29</td><td>95,92</td><td>96,15</td><td>96,24</td><td>/</td><td>93,79</td></tr><tr><td>Si</td><td>3,40</td><td>3,23</td><td>3,42</td><td>3,51</td><td>3,51</td><td>3,44</td><td>/</td><td>3,22</td></tr><tr><td>Ti</td><td>0,01</td><td>0,01</td><td>0,00</td><td>0,01</td><td>0,01</td><td>0,01</td><td>/</td><td>0,01</td></tr><tr><td>Al</td><td>2,20</td><td>2,43</td><td>2,16</td><td>2,4</td><td>1,99</td><td>2,2</td><td>/</td><td>2,57</td></tr><tr><td>Cr</td><td>0,00</td><td>0,00</td><td>0,00</td><td>0,00</td><td>0,00</td><td>0,00</td><td>/</td><td>0,00</td></tr><tr><td>Fe</td><td>0,17</td><td>0,16</td><td>0,18</td><td>0,23</td><td>0,15</td><td>0,03</td><td>/</td><td>0,07</td></tr><tr><td>Mn</td><td>0,00</td><td>0,00</td><td>0,00</td><td>0,00</td><td>0,00</td><td>0,00</td><td>/</td><td>0,00</td></tr><tr><td>Mg</td><td>0,25</td><td>0,27</td><td>0,28</td><td>0,19</td><td>0,38</td><td>0,60</td><td>/</td><td>0,19</td></tr><tr><td>Ca</td><td>0,00</td><td>0,00</td><td>0,00</td><td>0,00</td><td>0,00</td><td>0,00</td><td>/</td><td>0,01</td></tr><tr><td>Na</td><td>0,04</td><td>0,05</td><td>0,02</td><td>0,18</td><td>0,01</td><td>0,04</td><td>/</td><td>0,10</td></tr><tr><td>K</td><td>0,89</td><td>0,83</td><td>0,86</td><td>0,75</td><td>0,86</td><td>0,82</td><td>/</td><td>0,74</td></tr><tr><td>XMg</td><td>0,59</td><td>0,63</td><td>0,61</td><td>0,45</td><td>0,72</td><td>0,95</td><td>/</td><td>0,72</td></tr><tr><td>Xprl</td><td>0,07</td><td>0,12</td><td>0,12</td><td>0,07</td><td>0,13</td><td>0,14</td><td>/</td><td>0,15</td></tr><tr><td>Xmu</td><td>0,52</td><td>0,61</td><td>0,50</td><td>0,31</td><td>0,43</td><td>0,41</td><td>/</td><td>0,61</td></tr><tr><td>Xcel</td><td>0,33</td><td>0,12</td><td>0,30</td><td>0,45</td><td>0,39</td><td>0,31</td><td>/</td><td>0,07</td></tr><tr><td>Xprg</td><td>0,04</td><td>0,05</td><td>0,02</td><td>0,18</td><td>0,01</td><td>0,04</td><td>/</td><td>0,10</td></tr></tbody></table><table><thead><tr><th colspan="9">Piemont</th></tr><tr><th>Sample</th><th>/</th><th>/</th><th>/</th><th>/</th><th>/</th><th>/</th><th>/</th><th>UB</th></tr></thead><tbody><tr><td>SiO2</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>50,27</td></tr><tr><td>TiO2</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>0,09</td></tr><tr><td>Al2O3</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>27,31</td></tr><tr><td>Cr2O3</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>0,01</td></tr><tr><td>FeOtot</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>2,46</td></tr><tr><td>MnO</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>0,04</td></tr><tr><td>MgO</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>2,96</td></tr><tr><td>CaO</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>0,01</td></tr><tr><td>Na2O</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>0,22</td></tr><tr><td>K2O</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>10,29</td></tr><tr><td>total</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>93,65</td></tr><tr><td>Si</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>3,41</td></tr><tr><td>Ti</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>0,00</td></tr><tr><td>Al</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>2,18</td></tr><tr><td>Cr</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>0,00</td></tr><tr><td>Fe</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>0,14</td></tr><tr><td>Mn</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>0,00</td></tr><tr><td>Mg</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>0,30</td></tr><tr><td>Ca</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>0,00</td></tr><tr><td>Na</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>0,03</td></tr><tr><td>K</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>0,89</td></tr><tr><td>XMg</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>0,68</td></tr><tr><td>Xprl</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>0,08</td></tr><tr><td>Xmu</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>0,52</td></tr><tr><td>Xcel</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>0,33</td></tr><tr><td>Xprg</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>/</td><td>0,03</td></tr></tbody></table><table><thead><tr><th colspan="9">Llguro-Piemont</th></tr><tr><th>Sample</th><th>RU</th><th>GS</th><th>/</th><th>MC</th><th>ETA</th><th>NEV</th><th>CHA</th><th>UB</th></tr></thead><tbody><tr><td>SiO2</td><td>51,65</td><td>52,73</td><td>/</td><td>52,30</td><td>53,47</td><td>50,40</td><td>49,53</td><td>52,11</td></tr><tr><td>TiO2</td><td>0,22</td><td>0,11</td><td>/</td><td>0,16</td><td>0,16</td><td>0,11</td><td>0,12</td><td>0,07</td></tr><tr><td>Al2O3</td><td>26,68</td><td>27,64</td><td>/</td><td>27,4</td><td>24,65</td><td>26,35</td><td>28,11</td><td>29,13</td></tr><tr><td>Cr2O3</td><td>0,01</td><td>0,06</td><td>/</td><td>0,04</td><td>0,03</td><td>0,04</td><td>0,03</td><td>0,03</td></tr><tr><td>FeOtot</td><td>4,13</td><td>2,5</td><td>/</td><td>2,94</td><td>3,83</td><td>5,54</td><td>3,35</td><td>2,25</td></tr><tr><td>MnO</td><td>0,00</td><td>0,00</td><td>/</td><td>0,00</td><td>-0,03</td><td>0,01</td><td>0,00</td><td>0,00</td></tr><tr><td>MgO</td><td>2,73</td><td>3,54</td><td>/</td><td>3,22</td><td>3,65</td><td>3,2</td><td>3,00</td><td>2,76</td></tr><tr><td>CaO</td><td>0,02</td><td>0,09</td><td>/</td><td>0,03</td><td>0,12</td><td>0,07</td><td>0,02</td><td>0,04</td></tr><tr><td>Na2O</td><td>0,18</td><td>0,25</td><td>/</td><td>0,21</td><td>0,03</td><td>0,17</td><td>0,15</td><td>0,24</td></tr><tr><td>K2O</td><td>10,6</td><td>10,45</td><td>/</td><td>9,83</td><td>10,8</td><td>9,46</td><td>10,67</td><td>10,21</td></tr><tr><td>total</td><td>95,66</td><td>96,91</td><td>/</td><td>95,78</td><td>96,00</td><td>95,17</td><td>94,98</td><td>96,86</td></tr><tr><td>Si</td><td>3,45</td><td>3,44</td><td>/</td><td>3,46</td><td>3,54</td><td>3,40</td><td>3,34</td><td>3,40</td></tr><tr><td>Ti</td><td>0,01</td><td>0,01</td><td>/</td><td>0,01</td><td>0,01</td><td>0,01</td><td>0,01</td><td>0,00</td></tr><tr><td>Al</td><td>2,10</td><td>2,13</td><td>/</td><td>2,11</td><td>1,93</td><td>2,10</td><td>2,23</td><td>2,24</td></tr><tr><td>Cr</td><td>0,00</td><td>0,00</td><td>/</td><td>0,00</td><td>0,00</td><td>0,00</td><td>0,00</td><td>0,00</td></tr><tr><td>Fe</td><td>0,23</td><td>0,11</td><td>/</td><td>0,16</td><td>0,21</td><td>0,31</td><td>0,19</td><td>0,12</td></tr><tr><td>Mn</td><td>0,00</td><td>0,00</td><td>/</td><td>0,00</td><td>-0,00</td><td>0,00</td><td>0,00</td><td>0,00</td></tr><tr><td>Mg</td><td>0,27</td><td>0,35</td><td>/</td><td>0,32</td><td>0,36</td><td>0,30</td><td>0,30</td><td>0,27</td></tr><tr><td>Ca</td><td>0,00</td><td>0,01</td><td>/</td><td>0,00</td><td>0,01</td><td>0,01</td><td>0,00</td><td>0,00</td></tr><tr><td>Na</td><td>0,02</td><td>0,03</td><td>/</td><td>0,03</td><td>0,00</td><td>0,02</td><td>0,02</td><td>0,03</td></tr><tr><td>K</td><td>0,86</td><td>0,87</td><td>/</td><td>0,83</td><td>0,85</td><td>0,82</td><td>0,92</td><td>0,85</td></tr><tr><td>XMg</td><td>0,54</td><td>0,76</td><td>/</td><td>0,66</td><td>0,63</td><td>0,49</td><td>0,61</td><td>0,69</td></tr><tr><td>Xprl</td><td>0,12</td><td>0,10</td><td>/</td><td>0,14</td><td>0,14</td><td>0,16</td><td>0,06</td><td>0,12</td></tr><tr><td>Xmu</td><td>0,47</td><td>0,48</td><td>/</td><td>0,46</td><td>0,39</td><td>0,45</td><td>0,57</td><td>0,53</td></tr><tr><td>Xcel</td><td>0,33</td><td>0,35</td><td>/</td><td>0,32</td><td>0,41</td><td>0,25</td><td>0,28</td><td>0,28</td></tr><tr><td>Xprg</td><td>0,02</td><td>0,03</td><td>/</td><td>0,03</td><td>0,00</td><td>0,02</td><td>0,02</td><td>0,03</td></tr></tbody></table>