Ti-rich garnets are minerals related to alkali metasomatism and magmatism of carbonatic affinity, which can be found in various undersaturated alkaline igneous rocks. The chemical composition of these minerals depends on the phys- ico-chemical growth conditions under which they formed. Thin sections of these garnets often exhibit colour zonings corresponding to chemical zonings. The innovative approach of double-pulse micro-laser-induced breakdown spectroscopy (DP- μLIBS) technique coupled with optical microscopy can be fruitfully applied to the direct quantitative analysis and character- ization in atmospheric air of the petrographic thin sections [1]. This method shows significant advantages with respect to traditional techniques used to analyze geological samples such as electron-probe microanalysis (EPMA) and scanning elec- tron microscopy-energy dispersive spectrometry (SEM-EDS), including versatility, minimal destructivity, no carbon coating, no waste production, low operating costs, rapidity of analysis and sensitivity to light elements. To validate the analytical performance of this technique, several petrographic thin sections of Ti-rich andradite garnets originated from the volcanic district of Colli Albani, Italy, were investigated. Some of these petrographic thin sections have been previously investigated by EPMA [2-4], and the analyses obtained were used to set-up the one point calibration (OPC) LIBS method in order to de- termine quantitatively the chemical composition of Ti-rich garnets. This method was then applied also to thin sections of garnet not previously investigated by conventional techniques. Several analytical spots were aligned along different direc- tions on the slices. The results obtained show that the samples studied exhibit two different types of chemical zonings. A de- crease of Ti content from core to rim of slices, which reflects the physico-chemical evolution of the growth environment (concentric zoning), and an increase of Ti in the {211} growth sectors, related to growth kinetics [3] (sector zoning). The OPC-LIBS data show a good agreement with the previous EPMA data, suggesting that the DP-μLIBS can be considered a good tool to obtain quick, fast and reliable chemical analyses of petrographic thin sections. [1] Senesi GS, Tempesta G, Manzari P, Agrosì G, (2016) Geostandards and Geoanalytical Research 40(4): 533-541. [2] Agrosì G, Digennaro MA, Scandale E, (2001) Neues Jarhbuch fur Mineralogie Abh 176: 89-107. [3] Agrosì G, Schingaro E, Scordari F, Scandale E, Pedrazzi G, (2002) European Journal of Mineralogy 14: 785-794. [4] Agrosì G, Scandale E, Tempesta G, (2011) Periodico di Mineralogia 80(1): 89-104.
Micro-Laser Induced Breakdown Spectroscopy for recognition of chemical zoning of Ti-rich garnets in thin section.
Giovanna Agrosì;Paola Manzari;Gioacchino Tempesta
2017-01-01
Abstract
Ti-rich garnets are minerals related to alkali metasomatism and magmatism of carbonatic affinity, which can be found in various undersaturated alkaline igneous rocks. The chemical composition of these minerals depends on the phys- ico-chemical growth conditions under which they formed. Thin sections of these garnets often exhibit colour zonings corresponding to chemical zonings. The innovative approach of double-pulse micro-laser-induced breakdown spectroscopy (DP- μLIBS) technique coupled with optical microscopy can be fruitfully applied to the direct quantitative analysis and character- ization in atmospheric air of the petrographic thin sections [1]. This method shows significant advantages with respect to traditional techniques used to analyze geological samples such as electron-probe microanalysis (EPMA) and scanning elec- tron microscopy-energy dispersive spectrometry (SEM-EDS), including versatility, minimal destructivity, no carbon coating, no waste production, low operating costs, rapidity of analysis and sensitivity to light elements. To validate the analytical performance of this technique, several petrographic thin sections of Ti-rich andradite garnets originated from the volcanic district of Colli Albani, Italy, were investigated. Some of these petrographic thin sections have been previously investigated by EPMA [2-4], and the analyses obtained were used to set-up the one point calibration (OPC) LIBS method in order to de- termine quantitatively the chemical composition of Ti-rich garnets. This method was then applied also to thin sections of garnet not previously investigated by conventional techniques. Several analytical spots were aligned along different direc- tions on the slices. The results obtained show that the samples studied exhibit two different types of chemical zonings. A de- crease of Ti content from core to rim of slices, which reflects the physico-chemical evolution of the growth environment (concentric zoning), and an increase of Ti in the {211} growth sectors, related to growth kinetics [3] (sector zoning). The OPC-LIBS data show a good agreement with the previous EPMA data, suggesting that the DP-μLIBS can be considered a good tool to obtain quick, fast and reliable chemical analyses of petrographic thin sections. [1] Senesi GS, Tempesta G, Manzari P, Agrosì G, (2016) Geostandards and Geoanalytical Research 40(4): 533-541. [2] Agrosì G, Digennaro MA, Scandale E, (2001) Neues Jarhbuch fur Mineralogie Abh 176: 89-107. [3] Agrosì G, Schingaro E, Scordari F, Scandale E, Pedrazzi G, (2002) European Journal of Mineralogy 14: 785-794. [4] Agrosì G, Scandale E, Tempesta G, (2011) Periodico di Mineralogia 80(1): 89-104.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
