Calcic amphiboles in calc-alkaline and alkaline magmas: thermobarometric and chemometric empirical equations valid up to 1,130°C and 2.2 GPa

Abstract

The following article presents constraints of the stability of Mg-rich (Mg/(Mg ? Fe 2? ) [ 0.5) calcic amphibole in both calc-alkaline and alkaline magmas, testing of previous thermobarometers, and formulation of new empirical equations that take into consideration a large amount of literature data (e.g. more than one thousand amphibole compositions among experimental and natural crystals). Particular care has been taken in choosing a large number of natural amphiboles and selecting quality experimental data from literature. The final database of experimental data, composed of 61 amphiboles synthesized in the ranges of 800-1,130°C and 130-2,200 MPa, indicates that amphibole crystallization occurs in a horn-like P-T stability field limited by two increasing curves (i.e. the thermal stability and an upper limit), which should start to bend back to higher pressures. Among calcic amphiboles, magnesiohornblendes and tschermakitic pargasites are only found in equilibrium with calc-alkaline melts and crystallize at relatively shallow conditions (P up to *1 GPa). Kaersutite and pargasite are species almost exclusively found in alkaline igneous products, while magnesiohastingsite is equally distributed in calc-alkaline and alkaline rocks. The reliability of previous amphibole applications was checked using the selected experimental database. The results of this testing indicate that none of the previous thermobarometers can be successfully used to estimate the P, T and fO 2 in a wide range of amphibole crystallization conditions. Multivariate leastsquare analyses of experimental amphibole compositions and physico-chemical parameters allowed us to achieve a new thermobarometric model that gives reasonably low uncertainties (T ± 23.5°C, P ± 11.5%, H 2 O melt ± 0.78wt%) for calc-alkaline and alkaline magmas in a wide range of P-T conditions (up to 1,130°C and 2,200 MPa) and DNNO values (±0.37 log units) up to 500 MPa. The A K- [4] Al relation in amphibole can be readily used to distinguish crystals of calc-alkaline liquids from those of alkaline magmas. In addition, several chemometric equations allowing to estimate the anhydrous composition of the melts in equilibrium with amphiboles of calc-alkaline magmas were derived.

Amphibole and apatite insights into the evolution and mass balance of Cl and S in magmas associated with porphyry copper deposits

“…800-850 °C at the time of porphyry emplacement. These observations suggest that the pressure and temperature estimates using the empirical formulation of Ridolfi and Renzulli (2012) represent reasonable values for the porphyries. The increase in oxygen fugacity from the gabbrodiorite complex to the porphyries is supported by a mineralogical change of the Ti phase from ilmenite to titanite and by the increasing zircon Ce anomaly (Chelle-Michou et al 2014, 2015a.…”

“…For the gabbrodiorite complex, the estimated plagioclase composition always remarkably matches the measured composition of the plagioclase rims within each sample, which is consistent with the poikilitic texture of amphibole in these samples. In turn, estimated plagioclase composition for the porphyries was always higher than the measured one (estimated An30-60 vs a Calculated according to Ridolfi and Renzulli (2012) b Calculated according to Giesting and Filiberto (2014) measured An10-30, respectively). However, using the measured plagioclase and amphibole compositions with the thermobarometric formulation of Holland and Blundy (1994) in conjunction with the Al-in-hornblende barometer of Anderson and Smith (1995) resulted in a restricted near-solidus temperature range around 700 °C and a large pressure range of 400-100 MPa (Chelle-Michou et al 2015).…”

“…Intensive parameters (P, T, ƒO 2 , H 2 O melt ) at the time of amphibole crystallization were estimated based on amphibole composition (Chelle-Michou et al 2015a) using the empirical formulations of Ridolfi and Renzulli (2012). Despite having distinct compositions (probably reflecting different magma compositions; Fig.…”

Petrogenises of Triassic gabbroic and basaltic rocks from Chukotka, NE Russia: Eastern end of the ‘arc–type’ Siberian LIP?

“…The pressure, temperature, and oxygen fugacity conditions of amphibole crystallization can be obtained from amphibole compositions using the recent thermobarometric formulation of Ridolfi and Renzulli (2012). The obtained pressure for amphibole crystallization range from 4.1 to 8.5 kbar (average 6.8 kbar) in IAB-type gabbros and range from 0.1 to 0.3 kbar (average 0.2 kbar) in OIB-type gabbros, indicating an intrusion depth of about 22 km and 0.7 km respectively.…”

Ekecikdağ Magmatik Birliği (Orta Anadolu) Granitoyidlerinin Petrojenezi: Mineral Kimyası Perspektifi

“…)'ye karşı değişimleri, (f) K (A) 'nın Al [4] 'e karşı davranımı ve granodioritin kalk-alkalen karakteri (kalk-alkalen, alkalen alanları Ridolfi ve Renzulli (2012)'den alınmıştır) (semboller için Şekil 4'e bakınız). [4] and calc-alkaline character of granodiorite (fields of calc-alkaline and alkaline from Ridolfi and Renzulli (2012)) (see Figure 4 for symbols).…”