Radiometric dating volcanic rock
Since then, one very interesting albeit ancient feature has been discovered in the Coxcatlán-Tilzapotla region, about 100 km south of Mexico City, just south of the TMVB.
The elliptical NW-SE oriented dome structure, approximately 30 x 52 km, encompasses the Tilzapotla collapse caldera, rhyolitic domes, large volumes of ignimbrites, as well as the Buenavista intrusive body, and the Coxcatlán and Chautle plutons located west and east of the structural margin of the caldera, respectively.
To complicate the matter even further, both north and south of these plains run lines of ancient, heavily eroded and extinct(?
) volcanic edifices that seem to follow the subduction zone.
There is as well a dearth of large, explosive calderas in the TMVB.
The semi-official blog Geo Mexico laments: “There is still lots of work needed to fully unravel the geological secrets of Mexico’s Volcanic Axis which crosses the country between latitudes 19 and 21 degrees North.
The geological setting of the Trans Mexico Volcanic Belt.
The rocks from the older caldera are intermediate to basic in composition, while those from the more recent caldera are acidic (high silica content) rhyolites, another relatively unusual feature.(Hotu Matua) It is inevitable that the higher we get in this series, the more speculative our choices may seem.If everything was known about every volcano, identifying and motivating the choice of the ten most dangerous ones would be a relatively simple matter.The extinct volcano Sierra de Guadalupe rises 750 metres above Mexico City, it’s highest peak within 15 km of the centre of the city.In spite of conservation attempts, illegal buildings continue to sprout and at present the crater and debris avalanche have been completely covered by urban development.