Crustal structure across southern Mexico inferred from gravity data

We present a gravity model of the crustal structure in southern Mexico base d on interpretation of a detailed marine gravity profile perpendicularly ac ross the Middle America Trench offshore from Acapulco, and a regional gravi ty transect extending into continental Mexico across the Sierra Madre del S ur, the central sector of the Trans-Mexican Volcanic Belt, the Sierra Madre Oriental, the Coastal Plain, and into the Gulf of Mexico. The elastic thic kness of the Cocos lithospheric plate was found to be 30 km. In agreement w ith a previous seismic refraction study, no major differences in crustal st ructure were observed on both sides of the O'Gorman Fracture Zone. The grav ity high seaward of the trench is interpreted as due to the incipient flexu re and crustal thinning. The gravity low at the axis of the trench is expla ined by the increase in water depth and the existence of low-density accret ed or continental-derived sediments (2.25 and 2.40 g/cm(3)). A gravity high of 50 mGal extending about 100 km landward is interpreted as caused by loc al shoaling of the Moho. The crust attains a thickness of 42 km under the T rans-Mexican Volcanic Belt but thins beneath the Coastal Plain and the cont inental slope of the Gulf of Mexico. Gravity highs around the Sierra de Tam aulipas are interpreted in terms of relief of the lower-upper crustal inter face, implying a shallow basement. (C) 2000 Elsevier Science Ltd. All right s reserved.