The crystallization of plagioclase-bearing equilibrium assemblages in mantle peridotites is commonly considered witness of lithospheric mantle exhumation at shallow depth (e.g. Rampone et al., 1993; Ozawa & Takahashi, 1995; Newmann et al., 1999). Experimental works have pointed out that at subsolidus conditions plagioclase lherzolite assemblages are stable up to 1 GPa. Subsolidus experimental data in the complex chemical system TiO2-Cr2O3-Na2O-FeO-CaO-MgO-Al2O3-SiO2 on depleted and fertile lherzolite compositions (Borghini et al., 2010) have documented systematic compositional variations in coexisting minerals at decreasing pressure within the plagioclase stability field, similar to what observed in natural equilibrated plagioclase peridotites. In these experiments, Ca-Na partitioning between plagioclase and clinopyroxene is strictly dependent on pressure, with plagioclase composition varying significantly (An=59-83) in a narrow range of pressure. In a recent paper, Borghini et al. (2011) have defined the anorthite isopleths in plagioclase as a function of P and T in a specific fertile lherzolite composition, and they have demonstrated that plagioclase-facies equilibrium pressures can be estimated by comparing experimental data on a fertile lherzolite and microstructural-chemical observations in natural samples with the same bulk composition. This method represents a first-order empirical tool to trace the decompressional evolution of the lithospheric mantle up to very low-pressure and it is potentially applicable to natural plagioclase peridotites of different origin. Nevertheless, the composition of plagioclase at variable bulk Na2O/CaO ratios has been not fully discerned yet, making this approach directly applicable to a limited bulk composition range. Here, we present the results of new experiments on a Na-enriched lherzolite (bulk Na2O/CaO ratio = 0.13), representative of many refertilized lithospheric peridotites at extensional settings, thus enlarging significantly our investigated compositional spectrum (Na2O/CaO = 0.08 - 0.13). The goal of this work is to provide a formulation for a geobarometer analysis based on Ca-Na plagioclase-clinopyroxene partitioning on a larger experimental data set which takes into account the effect of bulk Na2O/CaO ratio and is consequently applicable to a wider compositional range of mantle rocks. References: Borghini, G., Fumagalli, P., Rampone, E. (2010): J. Petrol., 51, 229-254; Borghini, G., Fumagalli, P., Rampone, E. (2011): Lithos, in press; Newman, J., Lamb, W.M., Drury, M.R. & Vissers, R.L.M. (1999): Tect., 303, 193-222; Ozawa, K. & Takahashi, N. (1995): Contrib, Min. Pet., 120, 223-248;  Rampone, E., Piccardo, G.B., Vannucci, R., Bottazzi, P., Ottolini, L. (1993): Contrib, Min. Pet., 115, 1-17. AGU Fall meeting, San Francisco, Calif., 5-9 Dec., 2011. Section: Volcanology, Geochemistry, Petrology. Session: Mineralogical Signals as Keys to Understanding Petrological Processes II Posters. Abstract V11A-2512
Experimentally-derived Ca-Na partitioning between plagioclase and clinopyroxene : a new geobarometer for mantle rocks / P. Fumagalli, G. Borghini, E. Rampone. ((Intervento presentato al convegno AGU Fall meeting tenutosi a San Francisco (CA) nel 2011.
|Titolo:||Experimentally-derived Ca-Na partitioning between plagioclase and clinopyroxene : a new geobarometer for mantle rocks|
|Data di pubblicazione:||dic-2011|
|Settore Scientifico Disciplinare:||Settore GEO/07 - Petrologia e Petrografia|
|Enti collegati al convegno:||American geophysical union|
|Citazione:||Experimentally-derived Ca-Na partitioning between plagioclase and clinopyroxene : a new geobarometer for mantle rocks / P. Fumagalli, G. Borghini, E. Rampone. ((Intervento presentato al convegno AGU Fall meeting tenutosi a San Francisco (CA) nel 2011.|
|Appare nelle tipologie:||14 - Intervento a convegno non pubblicato|