Nyerereite from calcite carbonatite at the Kerimasi Volcano,Northern Tanzania |
| |
| Authors: | A N Zaitsev |
| |
| Institution: | 1.Department of Mineralogy, Faculty of Geology,St. Petersburg State University,St. Petersburg,Russia |
| |
| Abstract: | The extinct Quaternary Kerimasi volcano located in the southern part of the Gregory Rift, northern Tanzania, contains both
intrusive and extrusive calciocarbonatites. One carbonate mineral with a high content of Na and Ca has been found in a sample
of volcanic carbonatite, which is probably a cumulate rock. On the basis of Raman spectroscopy and SEM/EDS, this mineral was
identified as nyerereite, ideally Na2Ca(CO3)2. It occurs as solid inclusions up to 300 × 200 μm in size in magnetite and contains (wt. %) 25.4–27.4 Na2O, 26.0–26.8 CaO, 1.6–1.9 K2O, 0.6–1.8 FeO, 0.3–0.6 SrO, <0.4 BaO, 1.4–2.3 SO3, and 0.6–0.9 P2O5. The average mineral formula is (Na1.84K0.08)Σ1.92(Ca1.00Fe0.03Sr0.01)Σ1.04(CO3)1.91(SO4)0.05(PO4)0.02]Σ1.98. A few inclusions in magnetite also contain calcite, which is considered here to be a late-stage, subsolidus mineral. The
occurrence of nyerereite in carbonatite supports Hay’s (1983) idea that some of the extrusive carbonatites at the Kerimasi
volcano were originally alkaline rich and contained both calcite and nyerereite as primary minerals. |
| |
| Keywords: | |
| 本文献已被 SpringerLink 等数据库收录！ |
|
