In this paper, we compiled previous investigations and summarize recent
results to show that the Lanzo peridotite records a sequence of deep
lithospheric igneous events that largely obliterated the previous
subcontinental history. Field, microtextural and trace element data
indicate the progressive evolution of an igneous system that forms
above an upwelling asthenosphere, most probably during the transition
from a rifted system to the establishment of an (ultra-) slow spreading
ridge of the Piedmont Ligurian ocean. Pervasive porous flow of melt
forming `reactive' spinel peridotites followed by plagioclase
peridotite is later replaced by focused porous flow, reflected by a
system of replacive harzburgite and dunites. Cooling of the Lanzo
peridotite leads to the interstitial crystallization of clinopyroxene
and plagioclase, and finally to the formation of gabbro dikes. Thus,
the Lanzo peridotites may indicate that extension-driven
`as-thenospherization' of lithospheric mantle is an important process
in the development of embryonic ocean basins.