VOLUME XXVI NUMBER 6 
THE 
(OMNI ME Or “GeOLOGY 
SEPTEMEER-OCT@BE ke 7075 
TWO-PHASE CONVECTION IN IGNEOUS MAGMAS! 
FRANK F. GROUT 
University of Minnesota 
A careful study of the Duluth gabbro led the writer to the idea 
of a convection circulation in the magma. A review of the litera- 
ture shows nothing conclusively opposed to the idea, though the 
structures are explained in many other ways. This paper sum- 
marizes the signs of convection and suggests its probable mechanism 
and-results. 
SIGNS OF CONVECTION IN MAGMAS 
1. The fluxion structure of many rocks is a strong indication 
that movement occurred during crystallization. When combined 
with an alternation of differentiated bands and a roughly gravitative 
arrangement of the bands, the only explanation that is at all 
satisfactory is that the movement is one of circulation rather than 
of intrusion or of deformation.’ 
2. Convection has been observed directly in lava lakes in the 
craters of volcanoes. These highly special conditions of magma, 
however, are not sufficient to convince everyone that convection 
is a common process in deeper magmas. 
t Part of a thesis presented to the faculty of Yale University for the degree of 
Doctor of Philosophy. 
’ 
2Frank F. Grout, “Internal Structures of Igneous Rocks,’ 
XXVI, No. 5 (1918). 
etc., Jour. Geol., 
481 
