Detailed petrographic, electron microprobe and ion probe studies of Archaean hydromagmatic amphiboles from the Abitibi greenstone belt, Canada, yield new insights into the origin of Al-undepleted komatiitic and Al-depleted tholeiitic and ferropicritic melts. The amphiboles are present in peridotite layers and basal chill zones of thick differentiated basic and ultrabasic sills and flows, and are titanian pargasite-hastingsite in composition. They can be grouped into two petrographic types: (1) amphibole in the groundmass; and (2) amphibole-bearing melt inclusions. The groundmass amphiboles are oikocrysts, rims and interstitial grains, present in minor to major amounts. The oikocrysts host cumulus olivines (Fo(83-84)) that are rounded in shape, embayed, and smaller in size. The amphibole-bearing melt inclusions are hosted in cumulus olivines (Fo(83)-(84) in komatiitic rocks and Fo(79) in tholeiitic rocks), spherical to ovoid in shape, 50-500 mum in size, and dominated modally by amphibole. The melt inclusions also contain euhedral chromite and aluminous spinel and micrometric clinopyroxene and glass, and sub-micrometric iron-nickel sulphide, chloro-apatite and ilmenite. In-situ ion probe analyses indicate the amphibole is: (1) enriched in Nb, LREE and Zr and depleted in Sr and HREE relative to primitive mantle; (2) contains up to 1-3 wt% H2O; and (3) overall displays deltaD values from 50parts per thousand to - 140parts per thousand, including many values in the accepted magmatic range of - 60parts per thousand to - 90parts per thousand.