FLAT SUBDUCTION AND ASSOCIATED MAGMATISM. CENTRAL MÉXICO

In the bordering area of Hidalgo and Querétaro States, Central México (~ latitude 21° N) the upper Jurassic to upper Cretaceous marine sedimentary deposits of the Laramide Sierra Madre Oriental fold and thrust belt (SMOr) are juxtaposed against the seismically active Aljibes half graben (Ahg) of the active trans Mexican volcanic arc (tMva). The Ahg was installed into a Neogene volcanic and volcano-sedimentary rocks embracing late Miocene rhyolite and overlying basaltic lavas and tuffs. The Ahg faulting include partially coeval volcanism.

The southern SMOr is floored by a gneiss basement and shows apparent thin skin deformation. A balanced cross section estimate about 40 % of shortening of a 130 km length strip, and the main décollement fault dip 2.4° at 3 600 m below the sea level in the zone here discussed, therefore, subduction to depths to meet magma chambers of the rocks beneath the décollement is required to compensate the shortening in the upper plate. In this way, the sialic magma might have erupted independently from the basaltic magma. The basalts in this area as in most of the central tMva are younger than the andesitic and rhyolitic volcanism, consequently they very probably have risen to the surface during the deepening of the faulting.