Genesis and differentiation of nephelinitic magma
Abstract
The possibility of formation of nephelinite magma from picrite magma by separation of eclogitic fraction is discussed from experimental results on some picritic rocks. Inferred differentiation trend is obtained from the experimental data of the system Na2O-CaO-MgO-Al2O3-TiO2-SiO2: olivine nephelinite or olivine melilitite → olivine melilite nephelinite → perovskite-bearing olivine-melilite nephelinite or melilite nephelinite → corundum and perovskite-bearing melilite nephelinite (Fig. 4). The experimental data suggest that crystallization at high pressure does not lead to melilite nephelinite but produces olivine nephelinite. However, at low pressure slight difference of chemical composition of starting liquid causes the two differentiation trends: olivine nephelinite → nephelinite and olivine melilitite → melilite nephelinite. Generally crystallization of nephelinitic magma goes to the end before olivine completely disappears by reaction with the liquid. Melilite is confined to the rocks crystallized at shallower place.
- Publication:
-
Bulletin of Volcanology
- Pub Date:
- December 1978
- DOI:
- 10.1007/BF02597380
- Bibcode:
- 1978BVol...41..466Y