The heavy Caucasian-non-Caucasian mixing zone is from North Africa across Arabia, and then in a belt from the Urals in the north down through the Stans to Afghanistan, Pakistan and North India in the south and all the way to Siberia and even East Turkestan in China to the east.
One can say that there is a White/non-White mixing zone of recent origin in the Americas mostly from Mexico south in Mesoamerica down to Latin America all the way down to Chile, Uruguay and Argentina in the south, with more admixture to the north and much less at the south. Mesoamerica is quite thoroughly admixed or mestized as is Colombia, Venezuela, Peru and Paraguay. In Colombia, the Whites are also quite admixed with Black.
There is a White/Black mixing zone in the Caribbean and the Guyanas down to Brazil. In the Caribbean, White genes have been pretty much washed out by Black ancestry, and the Caribbean is quite a Black place. The same has occurred in Belize and to a lesser extent in Panama, both of which are seriously mulattized. Even Dominican “Whites” would probably not qualify as White to most people as they seem to have too much Black in them to be considered White. There are definitely White Puerto Ricans though and there are many White Cubans. The Guyanas are so mulattized that there are not many Whites left, similar to the Dominican Republic.
In North America, there has not been a lot of White/non-White mixing. The heavily mixed people are mostly recent immigrants from Mesoamerica, mostly from Mexico. Otherwise, Whites in the US, Canada and even Alaska have not mixed much with Indians, Inuits or Blacks.
Hawaii can be considered a White/non-White mixing zone of extremely recent origin as by this time most of the population is seriously admixed. The admixture is generally White/Asian mixes of all different sorts.
The Whites in New Zealand, Australia and even Europe are not much admixed other than recent immigrants in Europe, though there is some Asian/White admixture in the Sami. Nevertheless, I regard the Sami as Whites. Black-White mixing in Southern Europe is very negligible, despite the rantings and false science of Nordicists. Iranians are White. Turks are a bit admixed, but still they are overwhelmingly White.
There has been quite a bit of White/Black mixing in South Africa and Namibia, more than you might ever expect. The Namibian Whites in particular are quite admixed. Quite a few are so admixed that one wonders if they could be properly called White anymore as they tend to be in the “border zone” of Whiteness.