ISSN:
1432-0967
Source:
Springer Online Journal Archives 1860-2000
Topics:
Geosciences
Notes:
Abstract Liquidus phase relationships determined on the join anorthite-forsterite-quartz at 20 kbar show primary phase fields for quartz (q), forsterite (fo), enstatite (en), spinel (sp), anorthite (an), sapphirine (sa), and corundum (cor). Increasing pressure causes (1) thefo andan primary phase fields to contract, (2) theen, q, andcor fields to expand, (3) thefo-en boundary line to move away from the Q apex, (4) theen-q boundary line to move also away from the Q apex but by a smaller amount, and (5) a primary phase field forsa to appear at a pressure between 10 and 20 kbar. Seven liquidus piercing points at 20 kbar have been located as follows: Crystalline phases Liquid composition (wt %) Temperature (°C) sp+sa+cor An81Fo17Q2 1575 fo+en+sp An52Fo39Q9 1540 en+sp+sa An59Fo31Q10 1490 sa+an+cor An70Fo15Q15 1430 an+q+cor An66Fo7Q27 1410 sa+an+en An62Fo18Q20 1400 an+en+q An59Fo15Q26 1380 It is concluded that (1) the shift of thefo-en boundary line away from the quartz apex with pressure confirms many other studies showing that melts generated from peridotite source rocks decrease in silica content as pressure increases; (2) even though plagioclase is not a stable phase in peridotite source rocks at pressures above about 10 kbar, it can crystallize from mafic magmas at pressures at least up to 20 kbar; (3) sapphirine crystallizes from mafic magmas at high pressures and may be important in the construction of petrogenetic models based on trace element considerations.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01167290
