THE GUERRERO SUSPECT TERRANE (WESTERN MEXICO) AND COEVAL ARC TERRANES(THE GREATER-ANTILLES AND THE WESTERN-CORDILLERA-OF-COLOMBIA) - A LATE MESOZOIC INTRAOCEANIC ARC ACCRETED TO CRATONAL AMERICA DURING THE CRETACEOUS

The Guerrero suspect terrane, composed of Late Jurassic-Early Cretaceo us sequences, extends from Baja California to Acapulco and is consider ed to be coeval with the late Mesozoic igneous and sedimentary arc seq uences of the Greater Antilles, the West Indies, Venezuela and the Wes tern Cordillera of Colombia. These sequences represent the remnants of an arc which accreted to the North American and northern South Americ an cratons at the end of the Cretaceous. In western Mexico, the arc se quences built on continental crust consist of high-K calc-alkaline bas alts, andesites and rhyolites enriched in LREE with abundant siliceous pyroclastic rocks interbedded either with Aptian-Albian reefal limest ones or red beds. They do not show magmatic changes during the arc dev elopment. In contrast, the arc sequences built on oceanic crust show a n evolution with time. Arc activity began with the development of depl eted low K-tholeiitic mafic suite (Guanajuato igneous sequence), follo wed first by mature tholeiitic basalts and then by calc-alkaline olivi ne basalts interbedded with micritic limestones and radiolarian oozes of Early Cretaceous age. At the end of the arc growth, during Aptian-A lbian times, calc-alkaline pillow basalts and andesites poured out in the volcanic front while shoshonitic olivine basalts extruded in the b ack arc. The tholeiitic and shoshonitic mafic rocks as well as the cal c-alkaline lavas are mildly enriched in LREE, Y and Nb and show high e psilon(Nd) ratios, typical of oceanic arcs. In contrast, the calc-alka line mafic suite enriched in LREE, Y and Nb exhibits lower epsilon(Nd) ratios suggesting that it was derived by the partial melting of a man tle source contaminated either by Paleozoic subducted sediments or old source enrichments (OIB).