Journal of South American Earth Sciences 26 (2008) 343–354 Contents lists available at ScienceDirect Journal of South American Earth Sciences journal homepage: www.elsevier.com/locate/jsames U–Pb detrital zircon data of the Rio Fuerte Formation (NW Mexico): Its peri-Gondwanan provenance and exotic nature in relation to southwestern North America Ricardo Vega-Granillo a,*, Sergio Salgado-Souto b, Saúl Herrera-Urbina a, Víctor Valencia c, Joaquín Ruiz c, Diana Meza-Figueroa a, Oscar Talavera-Mendoza d a Departamento de Geología, Universidad de Sonora, Rosales y Encinas S/N, Hermosillo, Sonora 83000, Mexico b Geociencias, Centro de Estudios Superiores del Estado de Sonora, Hermosillo, Sonora 83140, Mexico c Department of Geosciences, The University of Arizona, Tucson, AZ 85721, United States d Unidad Académica de Ciencias de la Tierra, Universidad Autónoma de Guerrero, A.P. 197, Taxco, Guerrero 40200, Mexico article info abstract Article history: U–Pb detrital zircon studies in the Rio Fuerte Group, NW Mexico, establish its depositional tectonic set- Received 9 December 2006 ting and its exotic nature in relation to the North American craton. Two metasedimentary samples of the Accepted 30 August 2008 Rio Fuerte Formation yield major age clusters at 453–508 Ma, 547–579 Ma, 726–606 Ma, and sparse quantities of older zircons. The cumulative age plots are quite different from those arising from lower Paleozoic miogeoclinal rocks of southwestern North America and of Cordilleran Paleozoic exotic terranes Keywords: such as Golconda and Robert Mountains. The relative age-probability plots are similar to some reported Late Ordovician from the Mixteco terrane in southern Mexico and from some lower Paleozoic Gondwanan sequences, but Peri-Gondwanan they differ from those in the Gondwanan-affinity Oaxaca terrane. Major zircon age clusters indicate depo- Northwestern Mexico U–Pb geochronology sition in an intraoceanic basin located between a Late Ordovician magmatic arc and either a peri-Gon- Provenance dwanan terrane or northern Gondwanaland. The U–Pb magmatic ages of 151 ± 3 Ma from a granitic pluton and 155 ± 4 Ma from a granitic sill permit a revision of the stratigraphic and tectonic evolution of the Rio Fuerte Group. A regional metamorphism event predating the Late Jurassic magmatism is preliminarily ascribed to the Late Permian amalgamation of Laurentia and Gondwana. The Late Jurassic magmatism, deformation, and regional metamorphism are related to the Nevadan Orogeny. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction and Guerrero-Suástegui, 2000). The El Fuerte region is located south of the Ouachita-Marathon-Sonora orogenic belt, which is In the eastern El Fuerte region, northern Sinaloa, Mexico, regio- made of Paleozoic slope and abyssal sequences (Cortés terrane; nal metamorphosed sedimentary and volcanic sequences compose Stewart et al., 1990) thrust over mostly coeval platform sequences the Rio Fuerte Group (Mullan, 1978). To the west of the El Fuerte (Peiffer-Rangin, 1979; Poole et al., 2005) overlying an Early–Middle region, gneisses with minor schists and amphibolites compose Proterozoic crystalline basement (Caborca terrane; Campa and the Francisco Gneiss (Mullan, 1978). The El Fuerte Group and the Coney, 1983). According to Poole and Madrid (1988), the thrusting Francisco Gneiss are grouped either as Sonobari terrane (Campa of slope and abyssal sequences over platform sequences occurred and Coney, 1983) or as the El Fuerte block (Poole et al., 2005), during Carboniferous and Late Permian times. Paleozoic metamor- although these metamorphic units are separated and their geologic phic rocks of the El Fuerte region have been regarded as the inter- relationship is unknown at this time. The Sonobari terrane mostly nal zone of that late Paleozoic orogenic belt (Peiffer-Rangin, 1979) subcrops under thick Mesozoic and Cenozoic sequences; conse- and as tracts of the Gondwana continent that were attached to quently, its nature, boundaries, age, and units, remain imprecise. Laurentia (Poole et al., 2005). The El Fuerte Group underlies the northern Guerrero terrane In this work detrital zircon crystals from the older metasedi- (Fig. 1; Campa and Coney, 1983), which is a complex of Mesozoic mentary units of the Rio Fuerte Group are studied through U–Pb island arcs and interarc basins thrust over older terranes during LA-MC-ICP-MS technique in order to determine its provenance. the Late Cretaceous–Eocene Laramide Orogeny (Talavera-Mendoza In addition, U–Pb magmatic zircon analyses of deformed igneous rocks are made to improve the knowledge about the stratigraphy and the sequence of geological events. These data, together with * Corresponding author. Tel.: +52 662 2592110; fax: +52 662 2592111. available paleontological data, provide the basis for a tectonic E-mail address: [email protected] (R. Vega-Granillo). model of this region. 0895-9811/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.jsames.2008.08.011 344 R. Vega-Granillo et al. / Journal of South American Earth Sciences 26 (2008) 343–354 Fig. 1. Geological map of the El Fuerte region (modified from Mullan, 1978). Insert: Map of the main terranes of northwestern Mexico (adapted from Poole et al., 2005). BC: Baja California; CHIH: Chihuahua; SIN: Sinaloa; SON: Sonora. 2. Geological setting yrai t reT yrai t reT A NW-trending belt of metasedimentary and metavolcanic rocks, surpassing 5000-m thick, crops out (Fig. 1) in northern Sinaloa, northwestern Mexico, where it is known as the Rio PG Fuerte Group (Mullan, 1978). This group includes the Rio Fuerte, ?suoeca t e rC AF ?terC Corral Falso, and Topaco formations (Mullan, 1978). The Rio AF yl raE Fuerte Formation consists of thin-bedded chert, quartzite, argil- ZG GF lite, and a few carbonate rocks. A thin turbiditic, marbleized GF limestone bed in this formation yielded Mid–Late Ordovician conodonts (Poole et al., 2005). The undated Corral Falso Forma- TF Late Jur? tion is made of finely laminated graphitic slates, phyllites and ?suo r e f i nob r aC UTF quartzites mostly indistinguishable from the Rio Fuerte Forma- CFF CG NRM tion (Poole et al., 2005). The undated Topaco Formation consists NRM RFG of metasedimentary rocks at the base, which are overlain by a LTF thick sequence of metavolcanic rocks. Mullan (1978) regards RFF RFF Late the Topaco Formation as laterally transitional with the Corral Fal- CG Ord so Formation. Mullan (1978) separated the Rio Fuerte Formation from the overlying Corral Falso Formation based on a conspicu- A ous rhyolite flow, less than 2 m thick, named the Nodular Rhyo- B lite member. Mullan (1978) regards the Nodular Rhyolite also Fig. 2. Stratigraphic columns proposed by (A) Mullan (1978); (B) this article. AF: separating the upper and lower members of the Topaco Forma- Los Amoles Formation; CFF: Corral Falso Formation; CG: Cubampo Granite; GF: tion. The rhyolite layer borders with the metasedimentary and Guamuchil Formation; LTF: lower member Topaco Formation; NRM: Nodular metavolcanic layers are straight and sharp. A summary of the Rhyolite member; PG: Paleocene granite; RFF: Rio Fuerte Formation; RFG: Rio Fuerte Group; TF: Topaco Formation; UTF: upper member Topaco Formation; ZG: El previously described stratigraphy is in Fig. 2A. The meta-agglom- Zapote Group. erates forming the upper member of the Topaco Formation have clasts both of the metasedimentary rocks and the nodular rhyo- lite. For that reason, the contact between the Río Fuerte and the Topaco formations is considered as an angular discordance. The mation and the parallelism of the foliation in both units indicate actual position of the Rio Fuerte Formation over the Topaco For- the contact is a thrust fault. R. Vega-Granillo et al. / Journal of South American Earth Sciences 26 (2008) 343–354 345 The deformed Cubampo Granite is regarded as an intrusive equiv- tematic error, which amount to 1.7% in the studied samples. The er- alent of the Nodular Rhyolite member (Mullan, 1978), which in- ror of the age for the samples is calculated adding the quadratic of trudes into the Rio Fuerte, Corral Falso, and the lower member of both the random or measurement error and the systematic error, the Topaco formations. Regional metamorphism mainly under which is 2.0%, 3 Ma. All age uncertainties are reported at the 2- greenschist facies and pervasive deformations in the Rio Fuerte sigma level (2r). Group, Cubampo Granite and Nodular Rhyolite are assigned a Late For the detrital zircon provenance analysis we mounted 500– Jurassic orogenic event correlated with the Nevadan orogeny (Mul- 1000 zircons in epoxy regardless of size and magnetic characteris- lan, 1978). tics. The zircons are analyzed at random, with laser pits located in The El Zapote Group includes the Guamuchil Formation consist- core portions of crystals for consistency. We analyzed 100 zircon ing of volcanic rocks with a minimum thickness of 8 Km (Mullan, crystals from each sample to identify the main age groups present. 1978), and the Los Amoles Formation that is made of 100 m of Data are filtered according to precision (206Pb/238U and 206Pb/207 nonfossiliferous limestone (Mullan, 1978). This group was thrust typically 5% error cutoff) and discordance (typically 30% cutoff) over the Rio Fuerte Group during a Late Cretaceous-Paleocene oro- and then plotted on Pb–U concordia diagrams and relative-age genic event (Mullan, 1978). Granitic plutons with a K–Ar biotite probability plots (using algorithms of Ludwing, 2003) or cumula- age of 57.2 ± 1.2 Ma (Damon et al., 1983) intruded and contact tive probability plots. Our interpretations derived from the data metamorphosed the Rio Fuerte and El Zapote groups. Tertiary vol- are based on the view that only clusters of age record robust source canic and sedimentary rocks cover all previous rocks. ages. This is because a single age determination may be compro- mised by Pb loss or inheritance (even if concordant), whereas it is unlikely that three or more grains that have experienced Pb loss 3.