Abstract
Phase relations in the NMAS system are directly applicable to the classic problem of the origin of the tholeiitic and alkali basalts. The two magma types are separated at 1 atm by a thermal divide between forsterite and albite (Schairer and Yoder 1961). Yoder and Tiley (1962) showed that this thermal divide breaks down at high pressures and is replaced by a new thermal divide between enstatite and jadeite, responsible for the change in the composition of the basaltic melts from tholeiitic at lower pressures to alkaline at higher pressures. This reflects the depth of origin, which is shallow for the tholeiitic magmas, typically generated under the mid-ocean ridges, but greater for the alkali basaltic magmas originating under the older and thicker oceanic lithosphere.
This is a preview of subscription content, log in via an institution.
Buying options
Tax calculation will be finalised at checkout
Purchases are for personal use only
Learn about institutional subscriptionsPreview
Unable to display preview. Download preview PDF.
Author information
Authors and Affiliations
Rights and permissions
Copyright information
© 2003 Springer-Verlag Berlin Heidelberg
About this chapter
Cite this chapter
Gasparik, T. (2003). System Na2O-MgO-Al2O3-SiO2 . In: Phase Diagrams for Geoscientists. Springer, Berlin, Heidelberg. https://doi.org/10.1007/978-3-540-38352-9_8
Download citation
DOI: https://doi.org/10.1007/978-3-540-38352-9_8
Publisher Name: Springer, Berlin, Heidelberg
Print ISBN: 978-3-642-05534-8
Online ISBN: 978-3-540-38352-9
eBook Packages: Springer Book Archive