Open Access Repository

The missing link between granites and granitic pegmatites

Downloads

Downloads per month over past year

Thomas, R and Davidson, P (2013) The missing link between granites and granitic pegmatites. Journal of Geosciences, 58 (2). pp. 183-200. ISSN 1802-6222

[img]
Preview
PDF
Thomas-Davidson...pdf | Download (7MB)
Available under University of Tasmania Standard License.

Abstract

In this contribution we provide evidence for the extraction of volatile and incompatible element enriched melts from common granites, which provides a mechanism which show that a large proportion of granitic pegmatites are genetically directly connected to a main granite body. In granites there are often two principal types of melt inclusions: (i) melt inclusions which represent the bulk chemistry of the granite and (ii) melt inclusions with a composition strongly divergent from this composition. In the Variscan Erzgebirge granites this type is characterized by extremely high fluorine concentration. However, in other geodynamic settings inclusions in granites can contain high concentrations of other elements which may take over the function of fluorine.
From textural relationships this inclusion type represents intergranular melts enriched in all elements incompatible with the ideal haplogranite system. Due to the high volatile content of such melts the viscosity can be as much as several orders of magnitude lower than the quasi-solid bulk system and can therefore move rapidly through the partially or totally crystallized host, and flow together into a separate system forming pegmatite bodies inside or outside the granite body. Another important effect of the high volatile content is the phase separation resulting from the speciation change from OH- → H2O or CO32- → CO2 due to temperature and/or pressure changes at different locations within the granite-intergranular melt system. Since melt inclusions provide a means of conserving original undegassed compositions they are therefore important evidence for closing the gap between granites and granitic pegmatites.
The paper is dedicated to two Czech colleagues - Petr Černý and Milan Novák who have devoted their life to the study of granitic pegmatites.

Item Type: Article
Keywords: granites, pegmatites, melt inclusions, intergranular melts, F-, P-, and B-rich melts
Journal or Publication Title: Journal of Geosciences
Page Range: pp. 183-200
ISSN: 1802-6222
Identification Number - DOI: 10.3190/jgeosci.135
Additional Information:

Copyright 2013 Czech Geological Society

Date Deposited: 06 Oct 2013 22:11
Last Modified: 18 Nov 2014 04:55
Item Statistics: View statistics for this item

Actions (login required)

Item Control Page Item Control Page
TOP