Best case scenario:
Mansa Abubakari II of Mali relinquishes the throne in order to lead an expedition across the Atlantic. He garners a massive fleet and makes the journey, landing at Recife, Brazil. He founds a settlement there called "Boure Bambouk".
Boure Bambouk gets off to a rough start, with many settlers dying. Abubakari makes an appeal to his brother Mansa Musa in Timbuktu to aid his fledgling colony. He makes friends with the local Tupi tribes, who eventually express interest in Islam when Old World diseases hit. American crops are brought back to Africa, and vice versa.
Over time the waves of African settlers stop pouring in as Mali and Boure Bambouk drift apart. A standardized Tupi dialect becomes the linga franca as settlers and indigenous people communicate and trade. Muslim Tupi people move into Boure Bambouk, settling into permanent villages paying tribute to the capital. The agricultural society grows at a steady pace across northeastern Brazil. Even the ruling lineage of Abubakari becomes heavily mixed as he and his decendants take the daughters of native cheiftains as wives. By the end of the century, the civilization is essentially a creole Native American one rather than an African one, albeit with an Islamic West African base and a strong dose of African genetic heritage.
Sailors and merchants from Boure Bambouk come across other parts of the Americas, bringing Old World diseases, knowledge, and technology to Mesoamerica, Peru, and the Caribbean. New crops promote even further population growth in Boure Bambouk. Bamboukian cultural influence spreads further along the Brazil coast and into the Caribbean, including the very modified, creole version of Islam infused with indigenous beliefs. For the Aztecs, Mayans, and Incas, Islam does not immediately take hold but over the next few decades Muslims became a growing minority.
The Portuguese are the first to come across the New World as they stumble upon the transatlantic trade from West Africa. They find very loosely Islamic societies that are in the late stages of recovery and are too strong to be outright conquered and assimilated. The Spanish and the Portuguese make their own trading posts and eventually establish protectorates over the countries. South America is divided between two major kingdoms: Boure Bambouk and Tawantinsuyu, colonized by the Portuguese and the Spanish respectively.
