TY - JOUR
T1 - Aluminium phosphates in muscovite-kyanite metaquartzites from Passo di Vizze (Alto Adige, NE Italy)
AU - Morteani, Giulio
AU - Ackermand, Dietrich
PY - 1996
Y1 - 1996
N2 - A metaquartzite horizon bearing aluminium phosphates occurs over several kilometres in the Penninic Lower "Schieferhülle" units of the Tauern Window at the Passo di Vizze (Alto Adige, NE Italy). It contains the following types of mineral association: A) pale-blue lazulite, colourless crandallite-goyazite, apatite, tourmaline, B) dark-blue lazulite, colourless svanbergite-goyazite, bearthite, apatite, celestite, and C) staurolite, chlorite and tourmaline. Additional minerals in all cases are quartz, muscovite, kyanite and accessory Ti-bearing hematite. Association-types A and B are the common ones, type C is found only as a thin layer on the surface of coarse quartz pebbles embedded in types A or B. Staurolite is never found in contact with the phosphates. Electron microprobe analyses show that lazulite, (Mg,Fe2+)Al2(OH)2(PO4)2, has XMg [= Mg/(Mg+Fe2+)] ranging between 0.95 and 0.75 in association-type A, and between 0.65 and 0.55 in type B. (Sr,Ca)-bearing Al phosphates are a quaternary solid-solution series between crandallite-goyazite and woodhouseite-svanber-gite (Ca,Sr)Al3H1-x[(OH)6(PO4) 2-x{(PO4)(SO4)x], and a binary one between bearthite and goedkenite, (Ca,Sr)2Al(OH)(PO4)2. The quaternary phase of type A has an Xsr [= Sr/(Sr+Ca)] in the range of 0.35 to 0.95 and an Xp [=(P-1)/(P-1)+S] in the range of 0.45 to 0.90, indicating a main solid solution series between crandallite and goyazite; in the association-type B this phase has an Xsr in the range of 0.95 to 0.99 and an Xp in the range of 0.29 to 0.90, showing a solid-solution series between svanbergite and goyazite. Bearthite is found in association-type B only and has a composition close to Ca1.1Sr0.9Al(OH)(PO4)2. Tourmaline in type A shows a variation of XMg from core to rim from 0.15 to 0.55 and in type C from 0.48 to 0.70. Staurolite has an XMg [= Mg/(Mg+Fe2++Zn)] of 0.25. Apatites are, if euhedral and set in the groundmass, in all cases Sr-rich, whereas the small and anhedral apatites found in contact or included in lazulite are Sr-poor. Lazulite blasts are often irregularly rimmed by (Sr,Ca)-bearing Al phosphates and show inclusions of anhedral apatite. Bearthite is never found in contact with celestine and kyanite. On the basis of textural evidence lazulite is older than the (Sr,Ca)-bearing Al phosphates and than bearthite. As established by previous studies the maximum P-T conditions of metamorphism in the studied area were 550°C and 10kbar. The protolith of the studied rocks was most likely a sabkha-like sediment with Na leached by flash flood waters.
AB - A metaquartzite horizon bearing aluminium phosphates occurs over several kilometres in the Penninic Lower "Schieferhülle" units of the Tauern Window at the Passo di Vizze (Alto Adige, NE Italy). It contains the following types of mineral association: A) pale-blue lazulite, colourless crandallite-goyazite, apatite, tourmaline, B) dark-blue lazulite, colourless svanbergite-goyazite, bearthite, apatite, celestite, and C) staurolite, chlorite and tourmaline. Additional minerals in all cases are quartz, muscovite, kyanite and accessory Ti-bearing hematite. Association-types A and B are the common ones, type C is found only as a thin layer on the surface of coarse quartz pebbles embedded in types A or B. Staurolite is never found in contact with the phosphates. Electron microprobe analyses show that lazulite, (Mg,Fe2+)Al2(OH)2(PO4)2, has XMg [= Mg/(Mg+Fe2+)] ranging between 0.95 and 0.75 in association-type A, and between 0.65 and 0.55 in type B. (Sr,Ca)-bearing Al phosphates are a quaternary solid-solution series between crandallite-goyazite and woodhouseite-svanber-gite (Ca,Sr)Al3H1-x[(OH)6(PO4) 2-x{(PO4)(SO4)x], and a binary one between bearthite and goedkenite, (Ca,Sr)2Al(OH)(PO4)2. The quaternary phase of type A has an Xsr [= Sr/(Sr+Ca)] in the range of 0.35 to 0.95 and an Xp [=(P-1)/(P-1)+S] in the range of 0.45 to 0.90, indicating a main solid solution series between crandallite and goyazite; in the association-type B this phase has an Xsr in the range of 0.95 to 0.99 and an Xp in the range of 0.29 to 0.90, showing a solid-solution series between svanbergite and goyazite. Bearthite is found in association-type B only and has a composition close to Ca1.1Sr0.9Al(OH)(PO4)2. Tourmaline in type A shows a variation of XMg from core to rim from 0.15 to 0.55 and in type C from 0.48 to 0.70. Staurolite has an XMg [= Mg/(Mg+Fe2++Zn)] of 0.25. Apatites are, if euhedral and set in the groundmass, in all cases Sr-rich, whereas the small and anhedral apatites found in contact or included in lazulite are Sr-poor. Lazulite blasts are often irregularly rimmed by (Sr,Ca)-bearing Al phosphates and show inclusions of anhedral apatite. Bearthite is never found in contact with celestine and kyanite. On the basis of textural evidence lazulite is older than the (Sr,Ca)-bearing Al phosphates and than bearthite. As established by previous studies the maximum P-T conditions of metamorphism in the studied area were 550°C and 10kbar. The protolith of the studied rocks was most likely a sabkha-like sediment with Na leached by flash flood waters.
KW - Bearthite
KW - Celestine
KW - Crandallite-goyazite
KW - Italy
KW - Lazulite
KW - Metaquartzite
KW - Passo di Vizze
KW - Svanbergite-goyazite
KW - Tauern Window
UR - http://www.scopus.com/inward/record.url?scp=0030452859&partnerID=8YFLogxK
U2 - 10.1127/ejm/8/4/0853
DO - 10.1127/ejm/8/4/0853
M3 - Article
AN - SCOPUS:0030452859
SN - 0935-1221
VL - 8
SP - 853
EP - 869
JO - European Journal of Mineralogy
JF - European Journal of Mineralogy
IS - 4
ER -