Melilite-group minerals at Oldoinyo Lengai, Tanzania

作者：Wiedenmann Daniel^*; Keller Joerg; Zaitsev Anatoly N

来源：Lithos, 2010, 118(1-2): 112-118.

DOI：10.1016/j.lithos.2010.04.002

• Alumoakermanite
• Akermanite
• Melilite
• Melilitites
• Nephelinites
• Volcanic rock
• Oldoinyo Lengai
• Tanzania

Oldoinyo Lengai and the volcanic centres of the Lake Natron-Engaruka province contain melilite as a widespread mineral. Extraordinarily Na-Al-rich melilites (up to 6 wt.% Na(2)O and 9 wt.% Al(2)O(3)) from recent explosive eruptions are among the most Na-rich ever reported. Their unusual mineral composition leads to optical properties with vivid birefringence colours of 2nd order. The continuous variation in mineral composition from common akermanite to Na-Al-melilite (alumoakermanite) is documented and reflects the whole peralkaline trend of Oldoinyo Lengai. The data presented allow the volcano's evolution from primitive olivine melilitites to highly evolved and peralkaline combeite-wollastonite nephelinites to be traced. Melilite compositions of Oldoinyo Lengai extend the magmatic field in the Ca(2)Fe(Si(2)O(7))-Ca(2)Mg(Si(2)O(7))-(CaNa)A1 (Si(2)O(7)) end-member ternary compositional diagram.

• 出版日期2010-7