Volcan Tromen
The province of Neuquen is famed for its dinosaurs, dug out of the Mesozoic terrestrial sediments that drape the surface of the region. In the west of the province though these sediments start to be overlain by increasingly thick layers of volcanic rocks, created by the nearby subduction of the Pacific oceanic plate under the South American continental one. As the slab slides down into the mantle it both causes the compression that has uplifted the sediments into the Andes mountains, while causing melting in the mantle wedge above it due to released water resulting in a chain of volcanoes along chunks of the western part of the continent.
One of these volcanic piles is 3,964 metre Tromen, sitting on an older Caldera, where the crust has collapsed into an emptied magma chamber below. The volcano is complex, with several centres in a north-south line, and erupts a mixture of lavas ranging from basalt, through Andesite (named after the mountain chain in which it is so plentiful) to Rhyolite, with increasing enrichment in silica as the magma evolves. Its last recorded eruption was in 1822, but its record throughout the Holocene (the geological era in which we live, that started as the last ice age ended) indicates its regular bursts of activity. It has a lake beneath its slopes, where Flamingos and swans reside.
Tromen is in an tectonically interesting place, known a back arc basin, some 150km east of the main volcanic chain that marks the border between Argentina and Chile. These are caused by tensional forces (unlike the compression at the edge of the continent), caused by movements of the off coast trench and the subducting slab of oceanic crust. In the last few million years the tectonic regime has changed to compression, yet somehow, for somewhat inexplicable reasons, the magma is still reaching the surface. The name comes from the Mapuche word for soft. .
Loz
Image credit: While out Riding
http://www.volcanodiscovery.com/tromen.html http://www.summitpost.org/volcan-tromen/618963 http://www.volcanolive.com/tromen.html
