GEOLOGY OF THE SOUTHWESTERN SIERRA MADRE ORIENTAL FOLD-THRUST BELT. EAST CENTRAL MEXICO: A REVIEW

It is presented a geological synopsis of the southwestern Laramide Sierra Madre Oriental fold-thrust belt in the bordering area of Hidalgo and Querétaro States. In this region are juxtaposed continuous outcrops of a classical foreland fold and thrust belt against volcano-sedimentary back arc deposits.

From west to east it is distinguished: a) A Middle?-Upper Jurassic pelagic broken formation unconformably covered by a a lower Cretaceous to upper Cretaceous marine sedimentary deposits. b) Eastward the stratigraphy is more representative of the Laramide Sierra Madre Oriental fold-thrust belt consisting of Middle Cretaceous carbonated platforms separated by the Upper Jurassic to Upper Cretaceous rocks of the Zimapan epicontinental basin. These rocks are covered with angular unconformity by Neogene felsic and basic volcanic and volcano-sedimentary continental deposits.

The broken formation suggests an active margin during Jurassic, and the style of deformation between the two carbonated platforms is very probably thin skinned being the upper plate shortened about 40 % suggesting a continental subduction toward the Tertiary and Quaternary Sierra Madre Occidental volcanic arc and the Mexican Volcanic Arc.