Ancient depletion and mantle heterogeneity: Revisiting the Jurassic-Permian paradox of Alpine peridotites

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1 GSA Data Repository Ancient depletion and mantle heterogeneity: Revisiting the Jurassic-Permian paradox of Alpine peridotites McCarthy Anders 1 & Müntener Othmar 1 1 Institute of Earth Sciences University of Lausanne, Géopolis, Quartier Mouline, 1015 Lausanne, Switzerland Supplementary Material Location The Civrari peridotite (~10% serpentinisation) is found 4-5 km to the North-West of the Col de Lys and the northern part of the Southern Lanzo ultramafic Massif (Northern Italy). GPS Coordinates are N , E , at about 2200m in elevation, on the Southeastern side of Monte Civrari. Analytical Methods The two mineral separates were leached with 6N HCl and cleaned several times with distilled H 2 O following the method of Rampone et al., (1998) to remove any traces of alteration. Mineral fractions were dissolved in closed Teflon vials over 7 days on a hot plat at 140 C in a mixture of 4ml HF and 15M of HNO 3. The samples were then dried on a hot plate and dissolved in 3 ml 15M HNO 3 in closed Teflon vials at 140 C and dried down again. Sr and Nd separation was carried out using cascade columns with Sr-spec, TRU-spec and Ln-spec resins following a modified method after Pin et al. (1994). Sr was loaded on single Re filaments with a Ta oxide solution and measured at a pyrometer-controlled temperature of 1480 C in static mode using the virtual amplifier design to cancel out biases in gain calibration among amplifiers. 87 Sr/ 86 Sr values were internally corrected for fractionation using a 88 Sr/ 86 Sr value of Raw values were further corrected for external fractionation by a value of +0.03, determined by repeated measurements of the SRM987 standard ( 87 Sr/ 86 Sr

2 = ). The long-term external reproducibility of the 87 Sr/ 86 Sr ratio for the SRM987 standard is 7 ppm. Nd was loaded on double Re filaments with 1M HNO 3 and measured in static mode with the virtual amplifier design. 143 Nd/ 144 Nd values were internally corrected for fractionation using a 146 Nd/ 144 Nd value of and the 144 Sm interference on 144 Nd was monitored on the mass 147 Sm and corrected by using a 144 Sm/ 147 Sm value of These values were further corrected for external fractionation by a value of +0.03, determined by repeated measurements of the JNdi-1 standard ( 143 Nd/ 144 Nd = : Tanaka et al., 2000). The long-term external reproducibility of the JNdi-1 standard is <5 ppm. Cpx separates were mounted on an epoxy mount prior to being polished. Major elements where analyzed using an EPMA JEOL JXA-8200 superprobe. Ca and Si were standardized on wollastonite, whilst Mg and Fe were standardized on forsterite and fayalite respectively. Ni, Cr, Mn and Ti were standardized on synthetic oxides or metal alloys, whilst Na and K were standardized on an albite and K-feldspar, respectively. 30s counting time was done on the peak, with 15s counting time on the background position on either side of the peak, except for Na and K which were measured for a shorter timespan (20s peak, 10s background), and measured on first positions, due to possible migration during analysis. K was used as a proxy for possible small scale alteration, and was always <0.015wt%. Trace elements were analyzed on a a sector-field spectrometer Element XR interfaced to a NewWave UP-193 ArF excimer ablation system using a 75 m beam size, with SRM-612 used as a external standard. Si previously measured on the microprobe was used as an internal standard. Data was processed using LAMTRACE (Jackson, 2008).

3 Partial Melting Modeling Ol Opx Cpx Grt Spl Source La Ce Nd Sm Eu Gd Dy Er Yb Starting Modes (Vol%) Melt Modes (Vol%) Spl Grt Spl Grt Ol Opx Cpx Spl Grt Table 1: Partition coefficients (Kelemen et al., 1993; Suhr et al., 1998), starting modes in spinel (Johnson et al., 1990) and garnet stability field (Hellebrand et al., 2002) as well as melt modes in spinel (Kinzler, 1997) and garnet stability field (Walter, 1998) used in the modeling. The cpx source is from Johnson et al., (1990). The reaction from garnet to spinel stability field is from Johnson et al., (1990). The fractional melting model equations are from Johnson et al (1990) who recast melting equations from Ghast (1986) and Shaw (1970) to derive the variation in a specific element in cpx as a function of melting. The equations for the critical melting model, which take into account the presence of a residual melt porosity (Maaloe, 1982), are from Hellebrand et al., (2002) who derived the expression for the solid residue as a function of melt porosity and degree of partial melting from the original liquid compositions of Sobolev and Shimizu (1993).

4 Clinopyroxene and Spinel compositions Cpx separate 1 Cpx separate 2 Cpx separate 1 Cpx separate 2 d.l. n=10 1 * n=9 1 * n=15 1 * n=12 1 * Sc SiO V TiO Cr Cr 2 O Ni Al 2 O Rb b.d. - b.d. - FeO Sr MnO Y NiO Zr MgO Nb CaO Ba b.d. - b.d. - Na 2 O La b.d. - b.d. - K 2 O Ce Total Pr Spinel 1 Spinel 2 Nd n=5 1 * n=5 1 * Sm SiO Eu TiO Gd Cr 2 O Tb Al 2 O Dy FeO Ho MnO Er NiO Tm MgO Yb CaO Lu Na 2 O Hf K 2 O Ta b.d. - b.d. - Total Pb Cr# Th - b.d. - b.d. - *= std deviation of the mean U - b.d. - b.d. - n=number of analysis d.l. = detection limit Table 2: Major and trace element composition of cpx and major element composition of spl, with Cr# = Cr/(Al+Cr)*100

5 Details regarding clinopyroxene compositions: The Sr negative anomaly as well as the very small Eu negative anomaly of the studied cpx are most likely related to minor melt percolation which locally affected parts of the Civrari peridotite, crystallizing plagioclase and orthopyroxene at the expense of cpx. Microscopic analysis of the studied sample did not reveal the presence of trace amounts of plagioclase nor of reacted cpx textures. However, grain-scale melt percolation resorbing cpx and forming plg+opx symplectites is locally observed within the Civrari peridotite, with zonations occurring at m-scale (McCarthy & Müntener, in prep). Nevertheless, at the large scale (Civrari serpentinite massif as a whole), whole rock compositions show depleted, nearhomogenous compositions indicating no widespread Jurassic age melt percolation (McCarthy & Müntener, in prep). References Cited Gast, P. W., 1968, Trace element fractionation and the origin of tholeiitic and alkaline magma types: Geochimica et Cosmochimica Acta, v. 32, no. 10, p Hellebrand, E., Snow, J. E., Hoppe, P., and Hofmann, A. W., 2002, Garnet field melting and late stage refertilization in 'residual' abyssal peridotites from the Central Indian Ridge: Journal of Petrology, v. 43, no. 12, p Jackson, S. E., 2008, LAMTRACE data reduction software for LA ICP MS, in Laser Ablation ICP MS in the Earth Sciences: Current Practices and Outstanding issues, S. C. S., ed., Mineralogical Association of Canada, Volume 40: Quebec, P. Sylvester, p Johnson, K. T. M., Dick, H. J. B., and Shimizu, N., 1990, Melting in the oceanic upper mantle: An ion microprobe study of diopsides in abyssal peridotites: Journal of Geophysical Research: Solid Earth, v. 95, no. B3, p Kelemen, P. B., Shimizu, N., and Dunn, T., 1993, Relative depletion of niobium in some arc magmas and the continental crust: partitioning of K, Nb, La and Ce during melt/rock reaction in the upper mantle: Earth and Planetary Science Letters, v. 120, no. 3 4, p Kinzler, R. J., 1997, Melting of mantle peridotite at pressures approaching the spinel to garnet transition: Application to mid ocean ridge basalt petrogenesis: Journal of Geophysical Research: Solid Earth, v. 102, no. B1, p Maaloe, S., 1982, Geochemical Aspects of Permeability Controlled Partial Melting and Fractional Crystallization: Geochimica Et Cosmochimica Acta, v. 46, no. 1, p Pin, C., Briot, D., Bassin, C., and Poitrasson, F., 1994, Concomitant separation of strontium and samarium neodymium for isotopic analysis in silicate samples, based on specific extraction chromatography: Analytica Chimica Acta, v. 298, no. 2, p Rampone, E., Hofmann, A. W., and Raczek, I., 1998, Isotopic contrasts within the Internal Liguride ophiolite (N. Italy): the lack of a genetic mantle crust link: Earth and Planetary Science Letters, v. 163, no. 1 4, p

6 Shaw, D. M., 1970, Trace element fractionation during anatexis: Geochimica et Cosmochimica Acta, v. 34, no. 2, p Sobolev, A. V., and Shimizu, N., 1993, Superdepleted melts and ocean mantle permeability: Trans Russ. Acad. Sci. Earth Science Sect., v. 328, no. 1, p Suhr, G., Seck, H. A., Shimizu, N., Gunther, D., and Jenner, G., 1998, Infiltration of refractory melts into the lowermost oceanic crust: evidence from dunite and gabbro hosted clinopyroxenes in the Bay of Islands ophiolite: Contributions to Mineralogy and Petrology, v. 131, no. 2 3, p Tanaka, T., Togashi, S., Kamioka, H., Amakawa, H., Kagami, H., Hamamoto, T., Yuhara, M., Orihashi, Y., Yoneda, S., Shimizu, H., Kunimaru, T., Takahashi, K., Yanagi, T., Nakano, T., Fujimaki, H., Shinjo, R., Asahara, Y., Tanimizu, M., and Dragusanu, C., 2000, JNdi 1: a neodymium isotopic reference in consistency with LaJolla neodymium: Chemical Geology, v. 168, no. 3 4, p Walter, M. J., 1998, Melting of garnet peridotite and the origin of komatiite and depleted lithosphere: Journal of Petrology, v. 39, no. 1, p

Supplementary Figure 1 Map of the study area Sample locations and main physiographic features of the study area. Contour interval is 200m (a) and 40m

Supplementary Figure 1 Map of the study area Sample locations and main physiographic features of the study area. Contour interval is 200m (a) and 40m (b). Dashed lines represent the two successive ridge