Our South American Week continues...    See this guide to our recent   South American coverage including many tasting notes Yesterday, Jancis asked Does Chilean regionality exist? , and I wondered much the same about Argentina. To investigate, I tasted a handful of Malbecs originating from specific areas of the country, from north to south.  The first impression that such a comparison gives is how reliable a varietal Malbec is. Stylistically it is a boon to MW students, being of consistently remarkable purple hue with a concentrated black fruit character and, often, a floral tone. It might perhaps be...