The Early Cretaceous Arperos basin: an oceanic domain dividing the Guerrero arc from nuclear Mexico evidenced by the geochemistry of the lavas and sediments C. Freydier a , H. Lapierre a, * , J. Ruiz b , M. Tardy c , J. Martinez-R. d , C. Coulon e a LGCA, UMR CNRS 5025, Universite  Joseph Fourier-Grenoble 1, BP 53, 38041-Grenoble Cedex 9, France b De Âpartement of Geosciences, University of Arizona, Tucson, AZ 85721 USA c LGCA, UMR CNRS 5025, Universite  de Savoie 73376, Le Bourget du Lac cedex, France d Unidad de Investigacion en Ciencias de la Tierra, Univ Nac Autonoma Mexico-Juriquilla, AP 1-742, Santiago de Queretaro (Qro) 76001 Mexico e Lab Pet Mag, URA CNRS 1277, Universite  d'Aix-Marseille III, BP 441, 13397 Marseille Cedex 20, France Abstract During the Early Cretaceous, the Arperos basin was located between the Guerrero arc terrane and nuclear Mexico. Remnants of this basin now form an oceanic suture zone between the coeval carbonate platforms to the east and the accreted Guerrero terrane to the west. The geochemistry on the Arperos ma®c hypabyssal and volcanic rocks, based on the incompatible and trace element distribution and the eNd T 110 Ma values, shows that this basin was ¯oored by basalts that likely were generated by the mixing of OIB and N-MORB sources. The submarine lavas are overlain by and/or interbedded with siliceous sediments that have the highest eNd T 110 Ma and lowest Th levels. In contrast, the turbidites interlayered with the pelagic carbonates located at the top of the Arperos stratigraphic column show the lowest eNd T 110 Ma values and the highest Th contents. This evolution with time in the chemistry of the Arperos sediments is interpreted as marking the approach of the Guerrero juvenile arc to nuclear Mexico. q 2000 Elsevier Science Ltd. All rights reserved. Keywords: Guerrero terrane; Nuclear Mexico; Arperos basin 1. Introduction The main process in mountain building is the accretion of lithospheric fragments to the margins of cratons. In the North American Cordillera, this accretion process is often linked to the collision of islands arcs with the borderland of North America and the closure of basins ¯oored by oceanic crust. The remnants of these oceanic basins are now repre- sented by dismembered ophiolitic suites, or melanges, or even oceanic plateaus with their pelagic sedimentary cover. Most of these arc-accreted terranes show a continen- tal character. However, the isotopic signatures of the igneous and sedimentary rocks of the eastern Klamath terrane (Brouxel et al., 1987; Lapierre et al., 1987), Wran- gellia, Stikine, Alexander (Samson et al., 1990) and Guer- rero terranes (Lapierre et al., 1992a; Centeno-Garcia et al., 1993; Tardy et al., 1994) exemplify their juvenile character- istics. The Guerrero terrane, which forms almost 40% of all Mexico, is composed of Late Jurassic±Early Cretaceous igneous and sedimentary rocks which were developed in an intra-oceanic setting (Lapierre et al., 1992a,b; Centeno- Garcia et al., 1993; Tardy et al., 1994). Moreover, no volca- nic material is present in the Albian±Cenomanian platform of eastern Mexico (Fig. 1). Thus, the Guerrero arc terrane, before its accretion to North America during the Late Cretaceous, was likely offshore and separated from nuclear Mexico by a signi®cant oceanic domain. Questions remain on the nature of this oceanic domain and the present-day location of its remnants in western Mexico. Where the boundary between the volcano-plutonic and/or volcano-sedimentary rocks of the Guerrero arc-terrane and the coeval platform carbonates of the Sierra Madre terrane is exposed, the Guerrero arc-rocks are thrust upon Lower Cretaceous (Davila-Alcocer and Martinez-Reyes, 1987) micritic limestones, radiolarian oozes and pillow basalts collectively known as the Arperos basin (Lapierre et al., 1992b; Tardy et al., 1994). It has been demonstrated that the Arperos basin represents an oceanic domain that divided the Guerrero intra-oceanic arc from nuclear Mexico (Frey- dier et al., 1996b) and currently forms an important suture between the Guerrero terrane and nuclear Mexico. Here, we present a summary of the trace element and Journal of South American Earth Sciences 13 (2000) 325±336 0895-9811/00/$ - see front matter q 2000 Elsevier Science Ltd. All rights reserved. PII: S0895-9811(00)00027-4 www.elsevier.nl/locate/jsames * Corresponding author. Tel.: 133-4-7663-5906; fax: 133-4-7651-4058. E-mail address: henriette.lapierre@ujf.grenoble.fr (H. Lapierre).