Petrogenesis of tourmaline granites and topaz granites; the contribution of experimental data

Details Petrogenesis of tourmaline granites and topaz granites; the contribution of experimental data Petrogenesis of tourmaline granites and topaz granites; the contribution of experimental data

Oct 1984

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984pepi...35...31p&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 35, Issue 1-3, p. 31-50.

Physics

24

Scientific paper

Fluorine and boron are generally only minor components of granitic rocks, but may be found highly concentrated in certain tourmaline granites and topaz granites (up to 1 wt.% B2O3 and 3.2 wt.% F, respectively). Studies of various examples of these granite types, which occur as small bodies emplaced at shallow levels (P lithostatic < 3 kbar), suggest that both represent residual melts produced in late stages of high level fractionation of crustal granitic magmas.
Textural and petrographic data indicate that the tourmaline and topaz granite magmas crystallized at low to moderate temperatures (below ~ 700°C) and that a fluid phase may have been present during the crystallization interval. Both granites varieties are peraluminous (Co up to 5%), characterized by the presence of white micas (lithium micas or muscovite), aluminium silicates and other Al-rich minerals (garnet, cordierite). Boron and fluorine are hosted by tourmaline (schörl-rich member of the schörl-dravite series), topaz and mica, respectively. These granites have low Ca, Fe, Mg and Ti contents (each < 1% oxide) and characteristically have over 95% normative Qz + Ab + Or. Trace element data and the high volatile content is also consistent with an origin by crystallization of highly differentiated residual melts. Post-magmatic hydrothermal processes may redistribute both F and B as well as other elements and often involve Sn-W mineralization.
The crystallization of tourmaline granite and topaz granite magmas is discussed using experimental data derived from studies of granitic systems with added boron and fluorine. Both elements act as a flux, enabling boron and fluorine enriched melts to persist to temperatures as low as 650°C at 1 kbar. In addition the effect of increasing fluorine content displaces the minimum in Q-Ab-Or at PH2O = 1 kbar toward the albite apex. Plots of fluorine-rich topaz granites coincide with this trend, suggesting that the role of fluorine in magmatic processes may have affected the rock composition as well as crystallization temperatures. Boron-rich granites plot near the low PH2O minima in Qz-Ab-Or, suggesting that boron has less of an influence on minimum melt compositions. The low temperatures of crystallization permits phases such as muscovite or andalusite, topaz, and two alkali feldspars to crystallize directly from F and B enriched melts at low pressures. In addition, the limited available experimental data are used to compare the effects of fluorine and boron on major and trace element distribution during melt-vapour interaction.
Present address: Department of Geology, The University, Newcastle upon Tyne, NE1 7RU, Gt. Britain.

Affiliated with

Also associated with

No associations

Rating

Petrogenesis of tourmaline granites and topaz granites; the contribution of experimental data does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with Petrogenesis of tourmaline granites and topaz granites; the contribution of experimental data, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Petrogenesis of tourmaline granites and topaz granites; the contribution of experimental data will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1229894