Metamorphic ultrahigh-pressure tourmaline

• Verfasst von: Ertl, Andreas [VerfasserIn]
• Verfasst von: Marschall, Horst R. [VerfasserIn]
• Verfasst von: Giester, Gerald [VerfasserIn]
• Verfasst von: Henry, Darrell J. [VerfasserIn]
• Verfasst von: Schertl, Hans-Peter [VerfasserIn]
• Verfasst von: Ntaflos, Theodoros [VerfasserIn]
• Verfasst von: Luvizotto, George Luiz [VerfasserIn]
• Verfasst von: Nasdala, Lutz [VerfasserIn]
• Verfasst von: Tillmanns, Ekkehart [VerfasserIn]
• Titel: Metamorphic ultrahigh-pressure tourmaline
• Titelzusatz: structure, chemistry, and correlations to P-T conditions
• Verf.angabe: Andreas Ertl, Horst R. Marschall, Gerald Giester, Darrell J. Henry, Hans-Peter Schertl, Theodoros Ntaflos, George L. Luvizotto, Lutz Nasdala, Ekkehart Tillmanns
• Jahr: 2010
• Umfang: 10 S.
• Fussnoten: Elektronische Reproduktion der Druck-Ausgabe ; Published online: 2015-4-2 ; Gesehen am 03.04.2023
• Titel Quelle: Enthalten in: American mineralogist
• Ort Quelle: Berlin : de Gruyter, 1916
• Jahr Quelle: 2010
• Band/Heft Quelle: 95(2010), 1, Seite 1-10
• ISSN Quelle: 1945-3027
• DOI: doi:10.2138/am.2010.3283
• Datenträger: Online-Ressource
• Sprache: eng
• Sach-SW: Dora Maira
• Sach-SW: Lago di Cignana
• Sach-SW: Saxonian Erzgebirge
• Sach-SW: Tourmaline
• Sach-SW: ultrahigh pressure
• Sach-SW: Western Alps
• K10plus-PPN: 1841041084

Abstract

Tourmaline grains extracted from rocks within three ultrahigh-pressure (UHP) metamorphic localities have been subjected to a structurally and chemically detailed analysis to test for any systematic behavior related to temperature and pressure. Dravite from Parigi, Dora Maira, Western Alps (peak P-T conditions ~3.7 GPa, 750 °C), has a structural formula of X (Na 0.90 Ca 0.05 K 0.01 ⃞ 0.04 ) Y (Mg 1.78 Al 0.99 Fe 2+ 0.12 Ti 4+ 0.03 ⃞ 0.08 ) Z (Al 5.10 Mg 0.90 )(BO 3 ) 3 T Si 6.00 O 18 V (OH) 3 W [(OH) 0.72 F 0.28 ]. Dravite from Lago di Cignana, Western Alps, Italy (~2.7-2.9 GPa, 600-630 °C), has a formula of X (Na 0.84 Ca 0.09 K 0.01 ⃞ 0.06 ) Y (Mg 1.64 Al 0.79 Fe 2+ 0.48 Mn 2+ 0.06 Ti 4+ 0.02 Ni 0.02 Zn 0.01 ) Z (Al 5.00 Mg 1.00 )(BO 3 ) 3 T (Si 5.98 Al 0.02 )O 18 V (OH) 3 W [(OH) 0.65 F 0.35 ]. “Oxy-schorl” from the Saxonian Erzgebirge, Germany (≥4.5 GPa, 1000 °C), most likely formed during exhumation at >2.9 GPa, 870 °C, has a formula of X(Na 0.86 Ca 0.02 K 0.02 ⃞ 0.10 ) Y (Al 1.63 Fe 2+ 1.23 Ti 4+ 0.11 Mg 0.03 Zn 0.01 ) Z (Al 5.05 Mg 0.95 )(BO 3 ) 3 T (Si 5.96 Al 0.04 )O 18 V (OH) 3 W [O 0.81 F 0.10 (OH) 0.09 ]. There is no structural evidence for significant substitution of [4] Si by [4] Al or [4] B in the UHP tourmaline (<T-O> distances ~1.620 Å), even in high-temperature tourmaline from the Erzgebirge. This is in contrast to high-T-low-P tourmaline, which typically has significant amounts of [4] Al. There is an excellent positive correlation (r 2 = 1.00) between total [6] Al (i.e., Y Al + Z Al) and the determined temperature conditions of tourmaline formation from the different localities. Additionally, there is a negative correlation (r 2 = 0.97) between F content and the temperature conditions of UHP tourmaline formation and between F and Y Al content (r 2 = 1.00) that is best explained by the exchange vector Y AlO(R 2+ F) -1 . This is consistent with the W site (occupied either by F, O, or OH), being part of the YO 6 -polyhedron. Hence, the observed Al-Mg disorder between the Y and Z sites is possibly indirectly dependent on the crystallization temperature.