In Patagonia, Argentina, at the northern border of the Patagonian Cenozoic mafic plateau
lava fields, newly discovered diatremes stand about 100 m above the surrounding plain.
These diatremes document phreatomagmatic episodes associated with the formation of
the volcanic fields. The identified pyroclastic and intrusive rocks are exposed lower
diatremes of former phreatomagmatic volcanoes and their feeding dyke systems. These
remotely located erosional remnants cut through Paleozoic granitoids and Jurassic/Cretaceous
alternating siliciclastic continental successions that are relatively easily eroded.
Plateau lava fields are generally located a few hundreds of metres above the highest
level of the present tops of the preserved diatremes suggesting a complex erosional
history and potential interrelationships between the newly identified diatremes and
the surrounding lava fields. Uprising magma from the underlying feeder dyke into the
diatreme root zone intruded the clastic debris in the diatremes, inflated them and
mingled with the debris to form subterranean peperite. The significance of identifying
diatremes in Patagonia are twofold: 1) in the syn-eruptive paleoenvironment, water
was available in various "soft-sediments ", commonly porous, media aquifer sources,
and 2) the identified abundant diatremes that form diatreme fields are good source
candidates for the extensive lava fields with phreatomagmatism facilitating magma
rise with effective opening of fissures before major lava effusions.