Spanish and Portuguese in Latin America

Firstly thank you for all the interesting posts regarding the
relationship between Spanish, Galician and Portuguese. Keep them coming.
If I may I would like to learn something enquire about the
pronunciation of Spanish and Portuguese in Latin America. I believe
that the dominant dialect of Spanish spoken in Latin America derives
from the dialect of Andalucia, especially Sevilla from where many of
the early European migrants came. This dialect has been modified to
some extent as it has been adopted by the indigenous population and, in
places, by African slaves.
I am aware that Brazilian Portuguese is also a distinct dialect that
differs in pronunciation, vocabulary, and occasionally grammar from the
language of Portugal. Does Brazilian Portuguese also have a base in a
regional Portuguese dialect or is it purely a product of its isolation
from the motherland?


Thanks. David James