Some Mesozoic and Tertiary Igneous Rocks from Portuguese East Africa

Abstract

The very interesting igneous rocks of the Mozambique Company's territory have not had much attention paid to them in the past, though some of them were noticed in the first paper dealing with the Karroo beds near Tete, that by Lapierre. That writer was in advance of some subsequent observers in his recognition of the peculiar character of the Lupata lavas: so far, indeed, have some others been from this that the various geologists working in the Tete district have actually been accustomed to call the Karroo basalts the “Lupata Volcanics”, as is done in the most recent paper referring to that area. The age of the basalts was demonstrated by the writer in some notes contributed to this Magazine in 1922, and to establish this it was necessary to discuss the position of the Lupata lavas. Messrs. Teale and Campbell Smith subsequently published the first reliable petrographical descriptions of some specimens previously collected by the former, and the present paper is intended to supplement by further field and petrographical notes the valuable work of Dr. Teale, who has long since sought pastures new. It may be mentioned that one of the chief features of the area is the way in which the various igneous rocks are sometimes intermixed. This is a leading factor in contributing to the uncertainty which surrounds the dating of some of the intrusives. Thus a large number of intrusions of various kinds traverse the Karroo basalts and these are undoubtedly of two and perhaps of three different periods. Faulting and overlaps also cause further complications, as may be seen in the small sedimentary area near Mutarara, where Tertiary, Cretaceous, and Karroo volcanics occur closely associated.