183 / 352
167
These observations lead one to conclude that the
convoluted light zonings were not formed by a
dissolution-recrystallisation process but by a
pseudomorphic alteration and most likely with
no presence of fluid phases.
7.4. Orthogneisses
In order to investigate the felsic magmatic
activity of the Neoproterozoic–Cambrian
magmatic arc system, six orthogneisses from
the Banded Gneiss formation were studied. Five
orthogneisses outcrop at the northern coast of the
Masanteo
peninsula and one from the southern
coast (see locations for each sample; Appx. 1).
The nature of these orthogneisses, on the
basis of field observations, is thought to be
intrusive instead of being the result of a huge
leucosomatic production. Studying these rocks
will provide important information about the
age of crystallisation, the nature of the sources
and the development of the felsic igneous activity
of the magmatic arc that was built at the margin
of Gondwana in the Neoproterozoic–Cambrian.
7.4. ORTHOGNEISSES