Abstract

RADELLI, Luigi et al. FOSSIL CONTENT AND STRUCTURAL RELATIONSHIPS OF THE SAN LUIS ZONE and THE CABORCA ZONE OF NW SONORA, MEXICO. SUPPRESSION OF THE PRECAMBRIAN Z OF CABORCA. bol.geol. [online]. 2008, vol.30, n.2, pp.21-34. ISSN 0120-0283.

In the Caborca region of western Sonora a Precambrian Z does not cover a unique Precambrian socle as previously believed. Two tectonic zones occur there instead : the San Luis Zone and the Caborca Zone. The first is comprised of the Precambrian San Luis socle of gneiss and granite, crossed by 1.1 Ga old anorthosites, the San Luis sedimentary cover, and, above it, a Lower Jurassic volcano-sedimentary sequence. The Caborca Zone consists of the Precambrian Bamori socle of parametamorphic rocks crossed by 1.1 Ga old Aibo granite, and of the Gamuza sedimentary cover. 1.1 Ga ago the two zones were far away from each other. They have been brought together by the Nevadian orogeny. Both zones are allochthonous, and the Caborca Zone is a nappe upon the San Luis Zone. The lowermost units of the Gamuza cover furnished psammocorals and a possible Pterophyllum jageri (?). Accordingly, its geological age is either Palaeozoic or Triassic.The San Luis cover furnished Nematophites [Prototaxites (?) and Nematothallus] from its lower part; Calcispongiae, Cardaicarpus' seeds, and Artisia from its upper part. Thus, it is a Devono-Carboniferous unit. The study area belongs in the « Baja-Borderland » block, which underwent, an Eocene northwards drifting of about 900 - 1000 km, and a 30° to 40° clockwise rotation relative to the main part of Sonora.

Keywords : Sonora; Caborca; Caborca Zone; San Luis Zone; Precambrian socle; phanerozoic cover; nappe; Baja-Borderland block.

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