Документ взят из кэша поисковой машины. Адрес оригинального документа : http://geo.web.ru/users/pavel/Publications/1992_1998/art98-3.doc Дата изменения: Wed Jan 16 17:10:35 2008 Дата индексирования: Sun Apr 13 10:30:46 2008 Кодировка:

Melt inclusion synthesis in alkaline feldspars of Q-Ab-Or system.
Trusov S.V., Pletchov P.Yu. and Kotelnikov A.R.

The aim of this work was a melt inclusion synthesis during the
process of new phase growth on similar composition natural crystals.
Inclusions were trapped with subhedral growing of crystal single blocks or
within-growing crystal rims. The synthesis of melt inclusions was carried
on with the alkaline feldspar growth in the subliquidus area of the granit
system under gradually temperature decreasing. Mixture composition
corresponded to feldspar liquid-solid equilibrium under temperature 780oC
(Q - 20%, Ab - 56%, Or - 24%).
Grains of natural Or(fraction 0,5-1 mm) were used as a nuclear
centers for crystal growth. Mix with grains of natural Or were heated to
810oC (approximately by 50oC higher than the liquidus temperature) and
exposed under these conditions for 4 hours (until complete melting and
homogenization of mix). Then the temperature was reduced to subliquidus
during next 6 days with decreasing rate 10 o per day.
Fig.1
There are particularly melting and strongly rezorbed grains of Or,
which overgrown by new-formed alkaline feldspar (fig.1). New formations of
feldspar are presented by block crystal with radial direction to large Or
crystals. Via step-by-step temperature decreasing, crystals have got clear
expressed composition zones. Later (outer) zones are enriched by Na and
depleted by K to compare with earlier (inner) zones of new-formed alkaline
feldspar.
Fig. 2 shows chemical analyses of experimental products. Compositions
of artificial melt inclusions are situated on the cotectic line or above it
(in the Q field). Trapping of inclusions took place in the feldspar
crystallization field. Composition of capturing melt is situated on the
line, which connected feldspar composition to initial mixture composition.
Such effect is for feldspar crystallization to the inclusion walls. That's
why some compositions of glass inclusions, which was captured in the
feldspar
Fig.2
field, is situated on the cotectic line. The other inclusion compositions
are situated in the crystallization field of Q. Such effect can be
described by further feldspar growth, after the system comes to the
cotectic. Q can't crystallize because one hasn't nucleation centers.
Thus, we showed the principal possibility of the melt inclusions
synthesis in the process of new-formation growth on nuclear centers. This
method is easier than crack-forming synthesis methods [2]. It allows one to
observe the evolution of melt composition by study of melt inclusion
compositions in the different new-formed zones.
This work was supported by the Russian Foundation for Basic Research,
Project no. 96-05-64911
References:
Johannes W., Holtz F., (1996) Petrogenesis and experimental petrology of
granitic rocks. Springer-Verland Berlin-Heidelberg. 335p.
Pletchov P.Yu., Gramenitskii E. N., Kotelnikov A. R. (1999) Synthesis of
melt inclusions in haplogranit system. Dokladi Akademii Nauk, N1 pp. ??.