Structural and Tectonic Evolution of the Acatlán Complex, Southern Mexico

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TECTONICS, VOL. 28, TC4008, doi:10.1029/2007TC002159, 2009 Click Here for Full Article Structural and tectonic evolution of the Acatla´n Complex, southern Mexico: Its role in the collisional history of Laurentia and Gondwana

Ricardo Vega-Granillo,1 Thierry Calmus,2 Diana Meza-Figueroa,1 Joaquıń Ruiz,3 Oscar Talavera-Mendoza,4 and Margarita Lo´pez-Martıńez5 Received 24 May 2007; revised 22 January 2009; accepted 10 March 2009; published 25 July 2009. [1] Correlation of deformational phases and thermal opening. Citation: Vega-Granillo, R., T. Calmus, D. Meza- events in the Acatlań Complex permits definition of Figueroa, J. Ruiz, O. Talavera-Mendoza, and M. Lo´pez-Martıńez nine major tectonic events. Seven events are related to (2009), Structural and tectonic evolution of the Acatlań Complex, the evolution of the Iapetus and Rheic oceans. By the southern Mexico: Its role in the collisional history of Laurentia Early Ordovician, the Xayacatlań suite of Laurentian and Gondwana, Tectonics, 28, TC4008, doi:10.1029/ affinity was metamorphosed to eclogite facies and 2007TC002159. exhumed before colliding with the El Rodeo suite. From the Late Ordovician to Silurian, the Upper 1. Introduction Ordovician Ixcamilpa suite with peri-Gondwanan affinity was metamorphosed to blueschist facies, [2] The Acatlań Complex basement of the Mixteco exhumed, and subsequently was overthrust by the terrane contains the largest exposure of eclogites, high-P Xayacatlań–El Rodeo block. Part of the Esperanza garnet amphibolites, blueschists and eclogitized granitoids of Paleozoic age in Mexico. In a strict sense, the Mixteco suite is an Early Silurian intra-Iapetian continental arc terrane must be considered a superterrane composed of that collided with and subducted beneath continental thrust sheets containing Mesoproterozoic to Paleozoic pet- crust, generating a Silurian eclogitic event. By the Late rotectonic suites with Laurentian, Gondwanan and mixed Devonian, collision of the three high P/T suites closed affinities, which were mostly juxtaposed during the Paleo- the Iapetus Ocean. The resulting composite terrain was zoic [Talavera-Mendoza et al., 2005]. The Mixteco super- thrust over the Gondwana-bordering Cosoltepec suite terrane must have been transported to its present location to close the Rheic Ocean. During the earliest after Triassic time to avoid overlap with South American Mississippian, the collision of the Acatlań Complex crust during the assembly of the Pangean supercontinent and the Oaxaca terrane uplifted and deformed the [e.g., Pindell, 1985, 1994]. Therefore, geologic, structural composite terrane. By the Early Permian, deposition and metamorphic correlations of this exotic terrane require of the Chazumba suite occurred in a pull-apart basin. the further consideration of regions beyond presently adjacent areas. A latest Early Permian event produced thrust shear [3] The present body of work establishes the character- zones with N–S directed shortening. During the istics of each deformation phase in the main tectonostrati- Middle Jurassic, plume rise caused regional doming, graphic assemblages of the Acatlań Complex. Fabrics reveal magmatism and amphibolite facies metamorphism. complex deformation histories, and together with previous During the Late Cretaceous–Paleogene, folds and metamorphism information and P-T paths, allow the recon- thrust faults overprint the Acatlań Complex. Most struction of orogenic cycles. This survey proposes a new events in the Acatlań Complex correlate with events in model for the tectonic evolution of the Acatlań Complex the Appalachian chain, suggesting that the Acatlań and a comparison with tectonic events in the Paleozoic Complex was located near the Appalachians until the Appalachian orogen. Jurassic when it was displaced by the Gulf of Mexico 2. Geological Setting

1Departamento de Geologıá, Universidad de Sonora, Hermosillo, [4] The Acatlań Complex is a tectonic pile of seven Mexico. 2 major thrust sheets, each one with a particular lithological Estacioń Regional del Noroeste, Instituto de Geologıá, Universidad assemblage and a distinctive tectonothermal evolution. Nacional Autońoma de Me´xico, Hermosillo, Mexico. 3Department of Geosciences, University of Arizona, Tucson, Arizona, However, many issues concerning the general framework USA. and evolution of the Acatlań Complex remain controversial 4Unidad Acade´mica de Ciencias de la Tierra, Universidad Autońoma de and lack consensus [e.g., Ortega-Gutie´rrez et al., 1999; Guerrero, Taxco, Mexico. 5 Talavera-Mendoza et al., 2005, 2006; Nance et al., 2006; Departamento de Geologıá, CICESE, Ensenada, Mexico. Murphy et al., 2006]. Each thrust sheet including different Copyright 2009 by the American Geophysical Union. metamorphic rock types is defined here as a suite, and 0278-7407/09/2007TC002159$12.00 corresponds to an allochtonous nappe (Figures 1 and 2).

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Figure 1. Geologic map of the Acatla´n Complex (modified from Ramı´rez-Espinosa [2001]). Fault number indicates the chronology of thrusting.

[5] The Acatlań Complex is divided into seven major MORB [Yan˜ezetal., 1991; Meza-Figueroa et al., 2003]. The suites (Figure 2). The Tecolapa suite located in the western metasediments have a maximum age of 870 Ma (Figure 3a) area of the complex (Figure 1) consists of megacrystic and a suggested although arguable Laurentian derivation granitoids and tonalitic gneisses of Mesoproterozoic age [Talavera-Mendoza et al., 2005]. Lower-Middle Ordovician (1165 ± 30 to 1042 ± 50 Ma; U-Pb) [Campa-Uranga et al., granite and leucogranite transect and engulf xenoliths of the 2002; Talavera-Mendoza et al., 2005]. high-P rocks [Talavera-Mendoza et al., 2005; Vega-Granillo [6] The Xayacatlań suite consists of meter-thick alternat- et al., 2007] postdating the eclogitic event of the Xayacatlań ing layers of oceanic metabasites and clastic metasediments, suite. with minor felsic flows or dikes, all of which metamorphosed [7] The El Rodeo suite consists of interlayered metavol- to eclogite and epidote-amphibolite facies. Serpentinized canics, quartzites and schists, with a low P/T greenschist ultramafic bodies in or near the basal thrust are considered facies metamorphism [Vega-Granillo et al., 2007]. This unit part of this suite [Carballido-Sańchez and Delgado-Argote, was formerly included as part of the Xayacatlań or Tecomate 1989; Ortega-Gutie´rrez, 1993]. Eclogites of the Xayacatlań formations [Ortega-Gutie´rrez, 1978; Ramı´rez-Espinosa, suite have geochemical and isotopic characteristics similar to 2001]. Geochemical and isotopic data suggest an intra-arc

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Figure 2. Tectonic chart of Acatla´n Complex. rift setting for the El Rodeo suite [Ramı´rez-Espinosa, 2001]. Mendoza et al., 2005; Vega-Granillo et al., 2007]. Silurian The Lower Ordovician granites also intrude the greenschist U-Pb ages ranging from 442 ± 5 to 440 ± 14 Ma [Ortega- facies rocks of the El Rodeo suite [Talavera-Mendoza et al., Gutie´rrez et al., 1999; Talavera-Mendoza et al., 2005; 2005]. Vega-Granillo et al., 2007], are interpreted as magmatic [8] The Ixcamilpa suite, located in the central western crystallization ages of the typical Esperanza augen gneisses. part of the complex, consists of interlayered metabasites and Geochemical data from granitoids indicate a peraluminous metapelites with minor metachert beds, all of which meta- character and a calc-alkaline continental arc signature morphosed to blueschist facies [Talavera-Mendoza et al., [Ramı´rez-Espinosa, 2001]. Weber et al. [1997] include 2002; Vega-Granillo et al., 2007]. This suite had been high-grade metasediments such as garnet mica schist, mapped as part of the Xayacatla´n suite [Ortega-Gutie´rrez quartzites and paragneisses (Figure 4g) in the former et al., 1999; Ramı´rez-Espinosa, 2001]. The Ixamilpa suite Esperanza Granitoids. Field relationships reveal that Lower has a Late Ordovician (477 Ma) maximum depositional Silurian granite intrudes and engulfs xenoliths of these age based on U-Pb detrital zircon data, and the main detrital metasediments [Vega-Granillo, 2006]. The detrital zircon zircon age clusters are between 477 and 708 Ma (Figure 3b) age plot from metasedimentary rocks of the Esperanza Suite [Talavera-Mendoza et al., 2005]. The spectrum of detrital (Figure 3c) has a younger detrital zircon cluster of 719 Ma zircon ages suggests a provenance from both an Early and larger clusters of Mesoproterozoic (1244–917 Ma) age Ordovician arc and a peri-Gondwanan terrane similar to [Vega-Granillo, 2006; Murphy et al., 2006]. On the basis of the Avalon, Carolina or Suwannee terranes [e.g., Nance, the detrital age plot, Murphy et al. [2006] suggest a 1990; Wortman et al., 2000; Ingle et al., 2003]. Gondwanan affinity for the Esperanza metasediments. Basic [9] The Esperanza Granitoids term was formerly applied dikes crosscutting the metasedimentary rocks and the augen to igneous or metamorphosed granitic rocks [Ortega- gneisses, are tholeiites with continental-rift-type geochem- Gutie´rrez, 1978] regardless of their age, metamorphism or istry [Murphy et al., 2006], an interpretation supported by geochemical character. The Esperanza suite term is used for geologic relationships. The Esperanza suite was metamor- high-P metamorphic rocks whose protoliths are sedimen- phosed to medium-T eclogite facies during an Early Late tary rocks, porphyritic granites and mafic dikes [Talavera- Silurian collisional event [Ortega-Gutie´rrez et al., 1999;

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morphosed to greenschist facies. The maximum reliable depositional age for this suite is Early Middle Devonian (410–394 Ma). Detrital zircon ages suggest deposition along the northern margin of South America [Talavera- Mendoza et al., 2005], although the basement of the Cosoltepec suite is unknown. The Totoltepec Stock is an isolated trondhjemitic body of Early Permian age (287 ± 2 Ma; U-Pb zircon) [Yan˜ez et al., 1991; Keppie et al., 2004a], and crops out in the NE region where thrusting conceals its intrusive margins [Malone et al., 2002]. [11] The Chazumba suite cropping out in the eastern region of the complex includes the former Chazumba and Magdalena formations of Ortega-Gutie´rrez [1978]. The Chazumba suite is the lower structural unit of the Acatlań Complex and consists of a thick succession of pelitic- psammitic schists with metabasites interlayered near to the base. The detrital zircon age plot of the Chazumba suite indicates a maximum Leonardian depositional age (275 Ma) and suggests a provenance from Laurentian and Gondwanan sources [Talavera-Mendoza et al., 2005]. The Chazumba suite was metamorphosed to upper amphibolite facies, migmatized and intruded by leucogranites and two-mica granites [Figueroa-Salguero, 2003; Salgado-Souto, 2004] during the Middle Jurassic (175 Ma to 163 Ma; U-Pb, Rb-Sr, Ar-Ar) [Ruiz-Castellanos, 1979; Yan˜ez et al., 1991; Keppie et al., 2004a; Talavera-Mendoza et al., 2005]. [12] The Acatlań Complex is depositionally overlain by an Upper Devonian to Lower Permian sedimentary sequence, which crops out as isolated erosion remnants [Flores de Figure 3. Cumulative plots of detrital zircon U/Pb ages, Dios and Buitroń-Sańchez, 1982; Brunner, 1987; Villasenõr from (a) Xayacatlań suite; (b) Ixcamilpa suite [Talavera- et al., 1987; Enciso de la Vega, 1988; Ramı´rez-Espinosa et Mendoza et al., 2005]; and (c) Esperanza suite [Vega- al., 2000; Vachard et al., 2000; Vachard and Flores de Dios, Granillo et al., 2007]. 2002]. The Patlanoaya Formation [Villasenõr et al., 1987] remains as the most complete section of that sequence. The Tecomate Formation that is overprinted by greenschist Vega-Granillo et al., 2007]. Upper Devonian (370 Ma, facies dynamic metamorphism [Vega-Granillo, 2006] was U-Pb zircon) granites and leucogranites [Vega-Granillo et formerly considered as a separate regional metamorphosed al., 2007] intrude the augen gneisses so pervasively that unit of the Acatlań Complex. However, this unit contains they are included in the Esperanza suite, despite of not Early Permian (Kungurian) fossils [Keppie et al., 2004b; display eclogite facies assemblages [Vega-Granillo, 2006]. Vega-Granillo, 2006], and can be correlated with part of the An Upper Devonian porphyritic granite known as the La unmetamorphosed Patlanoaya Formation. Noria Granite also intrudes the El Rodeo suite [Yan˜ez et al., 1991]. [10] The Cosoltepec suite comprising up to 70% of the 3. The 40Ar/39Ar Geochronology Acatlań Complex outcrops (Figure 1) consists of interlayered quartzite and phyllite with minor volcaniclastic beds 3.1. Analytical Methods and isolated tectonic slices of pillow basalts of oceanic 40 39 [13] Three new Ar/ Ar analyses were performed at the affinity [Ramı´rez-Espinosa, 2001], all of which are meta- Geochronology Laboratory of the Departamento de Geo-

Figure 4. (a) Photography and (b) interpretative sketch of a garnet amphibolite exposure of the Xayacatla´n suite. In Figure 4b, three foliations (S2XA S4XA) and two phases of superposed isoclinal folding with axial planar foliations (S3XA and S4XA) are recognized. (c) Photography of exposure and (d) interpretative sketch of superposed folding (F2ER F4ER) in quartzite from El Rodeo suite. F2ER is an isoclinal folding of the S1ER foliation and L1ER lineation. (e) Photography of a Mid-Ordovician (461 Ma) leucogranite with xenoliths of Xayacatla´n rocks. A mylonitic foliation in the leucogranite (S/C0) is oblique respect to a S3XA foliation in xenoliths. Some xenoliths are microfaulted during the mylonitic event. (f) Subisoclinal folding of the mylonitic foliation in Mid-Ordovician leucogranite. (g) Esperanza suite garnet micaschist with a quartz-feldespathic vein emplaced along S1ES. The rock is isoclinally folded, and an axial planar coarse-grained foliation S2ES is developed. (h) Esperanza suite high-grade augen gneiss with folding of mantled K-feldspar porphyroclasts. Folds are related to a second mylonitic foliation S2ES, which commonly transpose S1ES.

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Figure 4

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Figure 5. The 40Ar/39Ar spectra for (a) mica schist and (b) metabasite from the El Rodeo suite. (c) Unmetamorphosed pegmatite intruding the Esperanza Suite.

logıá, CICESE. Two instruments were used for the argon (Figure 5a). Fine-grained white mica from mica-chlorite isotope analyses, a laser extraction system on line with a schist (sample ACA-71) of the El Rodeo suite yielded a VG5400 mass spectrometer for single grain experiments, Middle Mississippian 327 ± 2 Ma age, coeval within error while the bulk sample analyses were conducted with an to the age obtained from the amphibole (Figure 5b). The MS-10 mass spectrometer equipped with a Modifications third geochronologic study was performed on >2 cm mus- Ltd., Ta furnace. The samples were irradiated in the U- covite crystals from an undeformed granitic pegmatite enriched research reactor of the University of McMaster in (sample RAC-188) that crosscuts the high-grade gneisses Hamilton, Canada. As irradiation monitors, TCR-2 (split of the Esperanza suite. These large muscovite crystals yield G93) sanidine (27.87 ± 0.04 Ma) and internal standard an Early Mississippian 347 ± 3 Ma age (Figure 5c). CATAV 7–4 (88.54 ± 0.39 Ma) were irradiated alongside the samples. The argon isotopes were corrected for blank, mass discrimination, neutron interference reactions, radio- 4. Structural Analysis of the Acatlań Complex active decay of 37Ar and 39Ar and atmospheric contami- nation. The analytical precision is reported as two standard [15] The deformation history of the Acatlań Complex is deviations (1s). The decay constants recommended by defined through detailed field study of mesoscopic struc- Steiger and Ja¨ger [1977], were used in the argon data tures combined with microtectonic studies of about 350 thin reduction procedures. The error in the plateau, integrated sections. The StereoNett program (J. Duyster, StereoNett, and isochron ages includes the scatter in the irradiation Version 2.46, 2000, http://homepage.ruhr-uni-bochum.de/ monitors. The equations reported by York et al. [2004] were Johannes.P.Duyster/stereo/stereo1.htm) is used to analyze used in all straight line fitting routines of the argon data and display the structural data. In this section, we use letters reduction. The samples were step heated with the laser D for deformation phase, S for foliation, M for metamorphic extraction system, the Ta furnace, or both. event, and F for folding phase. Each suite underwent

3.2. Results Table 1. Location of 39Ar/40Ar Dated Samples [14] The rocks dated in this work are metabasite and muscovite-chlorite schist from the El Rodeo suite and Sample Age Coordinates UTM granitic pegmatite crosscutting the Esperanza suite. Age ACA-71 327 ± 2 E14 578254 2056208 data and sample location are displayed in the Table 1. RAC-8 320 ± 13 E14 577745 2056175 Amphibole from a metabasite of the El Rodeo suite (sample RAC-188 347 ± 2.6 E14 580071 2038791 RAC-8) yielded a Late Mississippian 320 ± 13 Ma age

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Figure 7. Megastructures in the Acatlań Complex include the Ayu´ and Ahuatempan domes, and large wavelength anticlinoriums and synclinoriums. The Papalutla fault is the western limit of the Acatlań Complex exposures. Abbreviations: TE, Tecolapa suite; XA, Xayacatlań suite; ER, El Rodeo suite; IX, Ixcamilpa suite; ES, Esperanza suite; CO, Cosoltepec suite; CH, Chazumba suite; DG, Late Devonian granite; TG, Totoltepec granite; PG, Lower Permian granite; OG, Middle Ordovician Teticic granite. separate tectonic events until they were progressively from their centers. The Chazumba suite cropping out in the juxtaposed. Therefore, a single sequential numbering cannot core of the Ayu´ dome underwent a Mid-Jurassic thermal be used for the deformation phases in all the suites. Instead, event evidenced by regional metamorphism, migmatization sequential numbering is used for deformation phases in each and leucogranite intrusion. suite. Additionally, the following subscripts are used: XA [17] Large-scale folds with 10 km wavelength are the for Xayacatlań suite; ER for El Rodeo suite; OL for Mid- most conspicuous structures of the Acatlań Complex (cross Ordovician leucogranite and granite; IX for Ixcamilpa suite; section in Figure 1). The upper structural units, including ES for Esperanza suite; CO for Cosoltepec suite; LN for La the Ixcamilpa, Xayacatlań, Tecolapa, Esperanza and El Noria Granite; CH for Chazumba suite; OT for El Otate Rodeo suites, crop out in the synclinoriums, whereas the Formation, and TE for Tecomate Formation. The sequence of Cosoltepec suite crops out in the anticlinoriums. Variation in deformational metamorphic events is displayed in Figure 6. the trend of major fold axes (Figure 7) may be due to the domes acting as buttresses during the Late Cretaceous 4.1. Structural Framework compression. The Jurassic-Cretaceous sedimentary rocks overlying the Acatlań complex display the same pattern of [16] The largest structures of the Acatlań Complex are two regional domes, the Ayu and Ahuatempan domes, and large folds [e.g., Cerca et al., 2007]. several large-scale folds (Figure 7). The domes influence the [18] Major thrust faults juxtapose the suites of the Acatlań strike of the contacts between units as far as 50 km away Complex (Figures 1 and 2). Along one of the main faults, the high-P Ixcamilpa and Xayacatlań suites are thrust over

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Xayacatla´n suite above. Either the low P/T El Rodeo or the high P/T Esperanza suites are thrust over the Xayacatla´n suite as in the Piaxtla and eastern Mimilulco regions (Figures 1 and 7). During a younger event, the Lower Permian Totoltepec pluton was thrust over the Lower Perm- ian sedimentary cover, and the Cosoltepec suite was thrust over the Chazumba suite. Ages of all these deformational events will be discussed in the tectonic evolution section.

4.2. Detailed Structures and Microtectonics of the Main Metamorphic Suites 4.2.1. Deformation of the Xayacatlań Suite [19] The Xayacatlań suite displays up to three foliations in some outcrops. Additionally, isoclinal to subisoclinal folds and overprinted folds are common in that suite (Figures 4a and 4b). The oldest deformational phase D1XA in the Xaya- catlań suite created a microscopic foliation S1XA preserved as an internal foliation within poikiloblasts (Figure 8a). Garnets commonly display helicitic folds of S1XA. A second metamorphic deformation event D2-M2XA created coarse-grained Figure 8. Sketches of the first foliations in Xayacatlań eclogite facies paragenesis, oriented along a pervasive S2XA (Figure 8a) and Ixcamilpa suites (Figure 8b). (a) Internal foliation (Figure 9d) oblique with regard to S1XA.The eclogite assemblage includes omphacite, garnet, zoisite, phen- foliation Si1XA made by epidote, phengite, chlorite, and titanite within albite poikiloblasts; the second coarse- gite, barroisite, quartz, and rutile; garnet amphibolite displays the same assemblage but with albite instead of omphacite. grained foliation S2XA is related to the eclogite facies metamorphism. (b) Albite poikiloblast with two internal [20] During a third M3XA metamorphic event, Mg- foliations Si1 and Si2 . The second foliation is parallel to hornblende, albite, clinopyroxene, pargasite, hastingsite, IX IX biotite, ilmenite and titanite crystallized as reaction rims the external coarse-grained foliation S2IX related to blueschist facies metamorphism. around the high-P phases. This mineral assemblage is related to pressure diminution and temperature increasing and indicates a transition to epidote-amphibolite facies the lower P/T Cosoltepec suite [e.g., Ortega-Gutie´rrez et al., [Vega-Granillo et al., 2007]. Isoclinal folding of S2XA 1999; Ramı´rez-Espinosa, 2001]. The structural contact and its respective axial surface foliation S3XA evidence a between these main blocks occurs throughout the Acatlań third deformation phase D3XA related to the M3XA event Complex exposures, although there is not a distinctive shear (Figures 4a, 4b, 6, and 9e). zone along that contact. The Ixcamilpa suite crops out as a [21] A fourth spaced mylonitic foliation S4XA with tectonic slice between the Cosoltepec suite below and the N10°W to N20°E strikes mostly transposes older foliations

Figure 9. Sketches of the first four foliations in a chloritoid-garnet micaschist of the Xayacatla´n suite. (a) Developing of a fine-grained foliation S1XA. (b) Growth of chloritoid and (c) garnet poikiloblasts that include the S1XA foliation. (d) Recrystallization produces a coarse-grained eclogitic foliation S2XA. (e) Isoclinal folding of S2XA and developing of a S3XA axial planar foliation transposing S2XA. (f) Folding of S3XA related to a spaced crenulation cleavage S4XA.

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Figure 10. (a) Sketch of a greenschist of the El Rodeo Suite, four foliations can be recognized each one related with isoclinal folding and greenschist to subgreenschist facies metamorphic events. (b–e) Sketches interpreting the deformational metamorphic events in the El Rodeo metabasite.

in the Xayacatlań suite, being the predominant foliation of mylonitic foliation S1OL (Figure 4e), which is isoclinally that suite (Figures 4a and 4b). Fold axes trending from folded by a later F2OL phase (Figure 4f). The mylonitic N20°WtoN20°E and ductile slickenside striations (as foliation S1OL in the leucogranite is nearly parallel to the defined by Lin et al. [2007]) trending from E–W to S4XA and S2ER foliations; hence, the three foliations are N80°W are ascribed to the same phase (Figures 6 and 9). ascribed to the same deformation phase. Although younger low-grade cleavages overprint the Xaya- 4.2.4. Deformation of the Ixcamilpa Suite catlań suite, they are not easily discernible from the fourth [25] Two fine-grained foliations Si1IX –Si2IX (Figure 8b) cleavage. trapped within poikiloblasts record the older deformation 4.2.2. Deformation of the El Rodeo Suite phases in the Ixcamilpa suite. Zoisite and opaque inclusions [22] Microtectonic studies in the El Rodeo suite reveal at within poikiloblasts of metabasites define the Si1IX internal least four foliations in some rocks (Figure 10). However, cleavage. Glaucophane, zoisite and titanite lineated inclu- generally only two foliations can be easily discriminated in sions define the Si2IX cleavage, which is parallel to a the field. Additionally, some exposures display three over- coarse-grained external foliation S2IX (Figure 8) defined printing folding phases subsequent to S1ER (Figures 4c by preferred orientation and elongation of glaucophane, and 4d). The first deformation phase D1ER imprinted on albite and clinozoisite poikiloblasts. A third deformation the El Rodeo rocks produced a fine-grained foliation S1ER phase D1IX created a spaced mylonitic foliation indicated by (Figures 10a and 10b) and thin compositional layering. A a shear band cleavage S/C0. Chlorite, pistachite, calcite and second deformation phase D2ER caused folding of the S1ER titanite, as well as reaction rims of winchite and barroisite foliation and development of an axial surface foliation S2ER around glaucophane, form a third mineral assemblage M3IX (Figure 10c) transposing the first foliation. The second related to the D3IX phase. Thermobarometry in the amphi- deformation phase also produced ductile slickenside stria- bole-plagioclase minerals of the M3IX event indicates tem- tions in some quartzites. In turn, a third deformation phase perature increasing and pressure decreasing [Vega-Granillo D3ER folded the S2ER foliation and created an axial surface et al., 2007], producing the transition from blueschist to foliation S3ER. Finally, a fourth deformation phase D4ER epidote-amphibolite facies. Microtectonic hints of younger folded the S3ER foliation and produced a millimeter-spaced deformation phases overprinting the Ixcamilpa suite occur pressure solution crenulation cleavage S4ER (Figure 10d) but are difficult to discern from the third phase. parallel to the axial surfaces of microscopic and mesoscopic 4.2.5. Deformation in the Esperanza Suite folds. [26] The sedimentary, granitic, and basic protoliths of [23] Although subsequent deformation phases overprint the Esperanza suite were metamorphosed to 800°C and and usually transpose the older structures in the Xayacatlań >16 kbar [Vega-Granillo et al., 2007], typical conditions of and El Rodeo suites, both suites share fold axes trending medium-T eclogites (as defined by Cuthbert and Carswell N40°W to N80°W (Figure 11), which are indiscernible in [1990]). Eclogitic metamorphism mostly obliterated any any other suite of the Acatlań Complex. These fold axes mineral or fabric vestige of the prograde path in the indicate shortening with a N50°–70°E azimuth. Esperanza suite. A ubiquitous coarse-grained foliation 4.2.3. Deformation of Lower-Middle Ordovician S1ES (Figures 4g and 4h) related to eclogite facies event Leucogranite M1ES is the first recognizable deformation phase D1ES in [24] Lower-Middle Ordovician granite and leucogranite rocks of the Esperanza suite. The eclogitic event trans- intrude and engulf xenoliths of the Xayacatlań (Figure 4e) formed the granite into high-grade mylonitic garnet augen and El Rodeo suites. These granites locally display a gneiss and the original K-feldspar megacrysts to mantled

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porphyroclasts (Figure 4h). In some places, intense defor- [30] Close folds F4ES with N70°–90°W trending axes mation created striped gneisses. Mafic dikes are metamor- define the fourth deformation phase D4ES in the Esperanza phosed to mildly foliated eclogite and garnet-Mg-taramite suite. An inhomogeneous mylonitic foliation related to granofels that display a mesoscopic pinch-and-swell struc- greenschist facies metamorphism, and poorly developed ture. Ductile slickenside striations and stretching lineation ductile slickenside striations L4ES trending N to N40°W, of the D1ES phase are poorly preserved in all the rocks, are also ascribed to that fourth deformation phase D4ES likely due to further static recrystallization. However, (Figure 11). An S/C0-type shear band cleavage formed by uncommon ductile slickenside striations and mantled por- D4ES indicates a top to the S shear sense. phyroclasts from augen gneisses suggest an E–W move- 4.2.6. Deformation in the Cosoltepec Suite ment direction and top to the W shear sense. U-Pb [31] The first deformation phase D1 in the Cosoltepec 40 39 CO (monazite) [Ortega-Gutie´rrez et al., 1999] and Ar/ Ar suite yielded a microscopic fine-grained continuous cleavage (amphibole) geochronology [Vega-Granillo et al., 2007] S1CO in quartzites, also defined in metavolcanics as an indicate a Early Late Silurian 430–418 Ma age for this internal foliation within albite poikiloblasts. A second defor- eclogitic event. mation phase D2CO produced a fine-grained, millimeter- 27 [ ] The Esperanza suite underwent an almost isothermal spaced schistosity S2CO, which is better developed in phyl- decompression after the eclogitic metamorphism [Vega- lites than quartzites. The S2CO foliation is the most visible Granillo et al., 2007]. That change generated partial melting and penetrative fabric in the Cosoltepec suite (Figures 12a of metasediments expressed as local migmatization and and 12b), and is indicated by preferred orientation of mus- intrusion of leucogranites (Figure 4g). Stromatic migmatites covite, albite, quartz and chlorite in metasediments, plus with ptygmatic folding are locally developed in metapelites. actinolite and titanite in the uncommon metavolcanic layers. Veinlets and pegmatitic pods of albite-quartz-phengite These assemblages formed by the M2CO event are typical of occur in the eclogite. A leucogranite yields a 372 ± 8 Ma greenschist facies. Both, the predominant N20°W–N10°E age (U-Pb, zircon), indistinguishable from a 374 ± 2 Ma age strikes of the S2 foliation planes and the uncommon 40 39 CO ( Ar/ Ar) [Vega-Granillo et al., 2007] obtained from a N80°W–N80°E trends of ductile slickenside striations mea- phengite pod in eclogite. sured over the S2CO planes indicate a WNW–ESE shorten- 28 [ ] The Upper Devonian leucogranite displays both a ing direction for D2CO phase (Figure 11). well-developed penetrative mylonitic foliation and ductile [32] The third deformation phase D3CO in the Cosoltepec slickenside striations formed in medium to high-grade suite is defined by mesoscopic to microscopic subisoclinal conditions as indicated by dynamic recrystallization of K- and isoclinal folding of the S2CO foliation and by an feldspar. The deformational phase producing the first foli- inhomogeneous axial surface cleavage S3CO (Figures 12a ation in the leucogranite created an overprinting mylonitic and 12b). The centimeter-spaced S3CO cleavage is mainly foliation S2ES in the eclogitized metasediments and augen created by pressure solution as evidenced by concentration gneisses of the Esperanza suite (Figures 4g and 4h). That of opaque and micaceous minerals along the cleavage S2ES foliation mostly transposes the first foliation S1ES in planes. Common steeply dipping brittle reverse faults are augen gneisses and mica schists of the Esperanza suite in ascribed to the D3CO deformation phase. The S3CO cleavage such a way that the first deformation phase D1ES only can usually strikes N30°E and dips more than 75° SE or NW, be discerned in uncommon areas of low strain, either as a indicating a WNW–ESE shortening direction (Figure 11). crenulated foliation, folding of mantled porphyroclasts [33] The fourth deformation phase D4CO in the Cosolte- (Figure 4h), or intrafolial folds. Well-developed ductile pec suite produced structures like those of the D3CO phase, slickenside striations in leucogranite trend mainly N80°– both in metamorphic grade and cleavage spacing; therefore, 90°W (Figure 11). Leucogranite dikes display mesoscopic it is difficult to discern D3CO from D4CO structures based on isoclinal to tight folds and the fold axes of that F2ES phase their physical appearance, except in scarce outcrops where trend N70°–90°W. The similarity of trends among the fold both structures remain visible (Figures 12a and 12b). The axes and the ductile slickenside striations suggests that the S3CO and S4CO cleavages must have originated in sub- folds are oblique folds developed in the leucogranite by the greenschist facies conditions because no new minerals 0 D2ES phase. Mantled porphyroclasts and S/C -type shear crystallized along them. Pressure solution related to D4CO band cleavage (as defined by Passchier and Trouw [1998]) locally produced centimeter-thick black layers parallel to indicate a top to the W shear sense. S4CO, which can be confused with slate beds. The S4CO [29] A third deformation phase D3ES created mesoscopic cleavage renders N to N50°E strikes and subhorizontal dips, subisoclinal folds in the Esperanza suite. Locally, a low- and it is parallel to the axial surfaces of the F4CO folds. grade cleavage parallel to the axial surfaces of the F3ES Folds formed by the F4CO phase vary from tight to isoclinal folds is developed. The D3ES phase also yielded discrete in phyllites, and from close to open in quartzites. Most of shear zones along which low-grade dynamic metamorphism these folds are recumbent or overturned with a NW ver- M3ES generated ultramylonites. The M3ES inhomogeneous gence. Refolded folds created by superposition of F4CO metamorphism produced quartz elongation, chlorite crystal- over F3CO folds are relatively common and display a type 3 lization, and pressure solution. Fold axes with trends fold interference pattern [Ramsay and Huber, 1987]. Fold between N50°–70°E and NW vergence (Figure 11) are axes forming the major cluster in the Cosoltepec suite are ascribed to the D3ES deformation phase, as are ductile ascribed to the fourth deformation phase and have trends of slickenside striations with N30°–60°W trends.

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Figure 11. Contoured (1% area) stereonets of foliation poles, fold axes, and ductile slickenside striations for the Xayacatla´n, El Rodeo, Esperanza, and Cosoltepec suites. An interpretation of the deformation phases causing these structures is included on the right.

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Figure 12. (a) Photography of phyllites from the Cosoltepec suite, three cleavages may be recognized, the latter two related with folding events. (b) Sketch from Figure 12a. (c) Photography of the Upper Devonian La Noria Granite, a protomylonitic granite with elongated K-feldspar porphyroclasts. (d) Thin section photography of a metalimestone of the Lower Permian Tecomate Formation. A microfaulted calcite intraclast can be seen in the center. (e) Photography of subisoclinal folds in the El Otate Formation rocks. (f) Sketch of a slate thin section from the El Otate Formation. A very fine grained foliation S1EO and a second spaced foliation S2EO are displayed, both developed under very low grade conditions.

N10°–50°E and plunges lesser than 20° to NE or SW Devonian age (371 ± 34 Ma, U-Pb zircon) [Yan˜ez et al., (Figure 11). Common subhorizontal curved thrust faults and 1991]. This granite was formerly included in the Esperanza scarce striations with N50°–80°W trends are attributed to Granitoids [Yan˜ez et al., 1991] but separated by its younger the D4CO phase. age [Ortega-Gutie´rrez et al., 1999]. Additionally, La Noria 4.2.7. Deformation in the La Noria Granite Granite lacks the eclogitic metamorphism of the Esperanza [34] The La Noria Granite is a coarse-grained two-mica gneisses. Near the town of La Noria, the granite retains a granite with K-feldspar phenocrysts, that yields a Late granular texture that grades into a mylonitic fabric to the

13 of 25 TC4008 VEGA-GRANILLO ET AL.: TECTONIC EVOLUTION ACATLA´ N COMPLEX TC4008 east (Figure 12c). The mylonitic deformation is related to a the Tecomate Formation is thrust over the El Rodeo suite, low-T greenschist facies hydrothermal metamorphism, which in turn, is thrust over the Xayacatlań suite. The main which produced sericite and chlorite from feldspars and structure of the Tecomate Formation is a fine-grained biotite, respectively. The mylonitic foliation displays N10°– mylonitic foliation (Figure 12d) striking N0°–20°W, which 40°W strikes and NE dips, while ductile slickenside stria- is related to horizontal ductile slickenside striations. Gra- tions are mainly horizontal. S/C0-type cleavage in the granite nitic conglomerate clasts are stretched parallel to the stria- mylonite indicates a top to S shear sense. Thus, the single tions. Minerals of the phyllonites, slight recrystallization of foliation recognized in the La Noria Granite was originated calcite and widespread pressure solution cleavages indicate along a shear zone with a NNW–SSE movement direction greenschist facies metamorphism related to the mylonitic and top to the S shear sense. deformation. Thus, dynamic metamorphism occurred in the 4.2.8. Deformation of the Chazumba Suite Tecomate Formation after Early Permian time, along a shear 0 [35] In the eastern region of the Acatlań Complex, the zone with a NNW–SSE movement direction. S/C -type Cosoltepec suite is thrust over the Chazumba suite. Both cleavage indicates a top to the S shear sense. Afterward, suites display a regional foliation with general E–W strike large-scale folds with axes trending N0°–20°W bent the and N dip. Two deformation phases D1CH –D2CH, each one mylonitic foliation. related to greenschist to upper amphibolite metamorphic events [Figueroa-Salguero, 2003; Salgado-Souto,2004], imprint the Chazumba rocks. Metamorphic minerals, leucosomes of migmatites and granitic dikes, yield Mid-Jurassic 5. Discussion: Tectonic Evolution of the ages (175–162 Ma) [Ruiz-Castellanos, 1979; Yan˜ez et al., Acatlań Complex 1991; Keppie et al., 2004a; Talavera-Mendoza et al., 2005]. 5.1. Early Ordovician Event (Pre-478 Ma): Subduction In the higher-T zone, recrystallization and deformation of the Xayacatlań Suite and Collision With the related to the second tectonic event obliterated the first Tecolapa–El Rodeo Arc foliation S1CH. 4.2.9. Deformation of the Acatlań Complex [38] The first two deformational phases in the Xayacatlań Sedimentary Cover suite D1XA and D2XA are ascribed to the earlier and later [36] The Patlanoaya Formation is the most complete stages of the subduction of oceanic lithosphere until low-T Paleozoic sedimentary sequence deposited in nonconformity eclogite facies conditions (609–491°C and 13–12 kbar) over the Acatlań Complex (Figure 1) [Brunner, 1987; were reached [Meza-Figueroa et al., 2003; Vega-Granillo et Villasenõr et al., 1987]. The lower beds, which contain al., 2007] (Figure 6). This tectonic event, one of the oldest latest Devonian (Famennian) fossils [Vachard and Flores de recorded in the Acatlań Complex [Vega-Granillo et al., Dios, 2002], are overlain by conglomerate beds with clasts 2007], probably occurred under a continental fragment of porphyritic granite and metamorphic rocks. A platform separated from the Laurentian margin (Figure 13a) sequence of sandstones and limestones overlying the con- corresponding to the Tecolapa suite [Talavera-Mendoza et glomerate contain fossils dated from the Early Mississippian al., 2005]. Later, the Xayacatlań suite was exhumed and (Kinderhookian) to the Early Permian (Leonardian) subsequently overthrust by the El Rodeo and Tecolapa [Brunner, 1987; Villasenõr et al., 1987; Vachard et al., suites (Figure 13b). This tectonic juxtaposition (block 1 in 2000; Vachard and Flores de Dios, 2002]. Originally, the Figure 6) yielded the third deformational metamorphic Upper Devonian beds were included in the Patlanoaya D3XA –M3XA event in the Xayacatlań suite and the first Formation [Vachard and Flores de Dios, 2002]; however, D1ER –M1ER event in the El Rodeo suite. Afterward, these beds display isoclinal folding (Figure 12e) and two Lower-Middle Ordovician 478–461 Ma (U-Pb zircon) slaty cleavages (Figure 12f) formed by pressure solution, as two mica granite and leucogranite intruded the Xayacatlań evidenced by truncated layering and concentration of and El Rodeo suites and the thrust fault between them, opaque minerals in dark seams. Since the Carboniferous- engulfing xenoliths of the high-P rocks (Figures 4e and 13c) Permian beds do not display isoclinal folding or cleavage, [Talavera-Mendoza et al., 2005; Vega-Granillo, 2006]. and the conglomerate overlies the Famennian beds on an Thus, these granites constrain the time of metamorphism angular unconformity, the Devonian beds must be separated and tectonic amalgamation of the Xayacatlań, El Rodeo and from the Patlanoaya Formation. The name El Otate Forma- Tecolapa suites. tion, proposed by Hernańdez-Suárez and Morales-Martıńez [39] The Taconic phase in New England, the Humberian [2002] for slightly metamorphosed beds of El Otate Creek, phase in western Newfoundland and the Grampian phase in can be used to name this unit. Scarce fold axial surfaces the Scottish Highlands are nearly coeval with the Early measured indicate N–S shortening deformation D1EO in Ordovician collision of the Xayacatlań and the El Rodeo the El Otate Formation, but a more systematic study is suites. All these events are attributed to the collision required to precisely define the orientation of that deforma- between Laurentia and a peripheral magmatic arc tion phase. [McKerrow et al., 2000]. The Penobscotian phase is a [37] The Tecomate Formation was formerly considered coeval event but caused by collision between an intra- part of the Acatlań Complex, but its lithology and Early Iapetian magmatic arc and the Ganderia terrane [McKerrow Permian fossils indicate that the unit is part of the Patla- et al., 2000]. The detrital zircon ages from the Xayacatlań noaya Formation. South of the town of Acatlań (Figure 1), suite suggest a Laurentian provenance [Talavera-Mendoza

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Figure 13. Interpretative sketches for the tectonic evolution of the Acatla´n Complex.

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Figure 13. (continued)

16 of 25 TC4008 VEGA-GRANILLO ET AL.: TECTONIC EVOLUTION ACATLA´ N COMPLEX TC4008 et al., 2005]; consequently, the correlation with the Taconic suite were buried (Figure 13f) and metamorphosed to phase seems more feasible. medium-T eclogite facies [Vega-Granillo et al., 2007]. The first deformation phase D1ES recognized in the Esper- 5.2. Late Ordovician-Silurian Event: Subduction of the anza rocks is related to prograde eclogite facies metamor- Ixcamilpa Suite phism M1ES. Uncommon ductile slickenside striations from augen gneisses suggest E–W movement direction, and [40] The Ixcamilpa suite protolith was formed during the Late Ordovician within an intra-Iapetian basin (Figures 13c mantled porphyroclasts indicate top to the W shear sense. Amphibole crystals from eclogite yield an Early Silurian and 13d) receiving sediments from an Early Ordovician arc 40 39 and a peri-Gondwanan terrane as suggested by its detrital age (430 ± 5 Ma, Ar/ Ar) [Vega-Granillo et al., 2007], zircon age plot [Talavera-Mendoza et al., 2005, 2006]. The coeval within errors with a 418 ± 18 Ma U-Pb monazite age first two tectonic phases in the Ixcamilpa suite are related from augen gneiss [Ortega-Gutie´rrez et al., 1999], indicat- to the initial and final stages of a subduction process ing an Early Late Silurian age for eclogitic metamorphism. (Figure 13e), during which the Ixcamilpa protolith was However, latest Devonian–Early Mississippian ages buried to 25 km depth and metamorphosed to blueschist (360–345 Ma, U-Pb zircon) (M. Elıás-Herrera et al., facies (200–390°C and 6–9 kbar) [Vega-Granillo et al., New geochronological and stratigraphic data related to the Paleozoic evolution of the high-P Piaxtla Group, Acatlań 2007]. The third tectonic event S3IX –M3IX caused the exhumation of the Ixcamilpa suite and subsequent over- Complex, southern Mexico, paper presented at IV Reunion thrusting by the Xayacatlań–El Rodeo–Tecolapa block Nacional de Ciencias de la Tierra, Sociedad Geolo´gica (block 2 in Figure 6 and Figure 13e). Ixcamilpa lithology Mexicana, Quere´taro, Mexico, 2004) derived from zircon and overprinting fabrics are similar to those of the Xaya- overgrowths in augen gneisses also are interpreted as the catlań suite excepting the metamorphic grade. However, age range of the eclogitic event [Murphy et al., 2006]. the Ixcamilpa rocks contain a larger detrital zircon cluster [43] Some authors have correlated the metamorphic rocks of Early Ordovician age (477 Ma, U-Pb) (Figure 3b) of the Xayacatlań suite with some parts of the Esperanza [Talavera-Mendoza et al., 2005], precluding correlation suite [e.g., Murphy et al., 2006]. However, the composite either with the Xayacatlań suite or with its Early Ordovician block of the Xayacatlań, El Rodeo and Ixcamilpa suites fail eclogitic metamorphism. Moreover, detrital zircon popula- to display fabric, mineralogical or geochronological evi- tions of the Xayacatlań and Ixcamilpa suites are different dence of the Silurian event imprinted in the Esperanza suite, (Figures 3a and 3b), indicating derivation from dissimilar implying these two blocks remained separated during Silu- sources. The time of deformation and metamorphism in the rian time (Figure 13f). In addition, Silurian granites have Ixcamilpa suite is poorly constrained. Fine-grained phen- not been observed intruding the Xayacatlań–El Rodeo gites from blueschists yield a Late Mississippian 40Ar/39Ar composite block. Furthermore, field relationships demon- age (323 ± 6 Ma) [Vega-Granillo et al., 2007], but this age strate the Xayacatlań suite is composed of interlayered does not conclusively define the age of the high-P event as it volcanic flows and sediments; whereas in the Esperanza may represent a younger thermal event. Thrusting of the suite, mafic dikes crosscut sedimentary rocks and the Lower Esperanza suite over the Ixcamilpa suite during the Late Silurian granites. Also, the Early Ordovician age for the Devonian may constrain the blueschist metamorphism of high-P event in the Xayacatlań suite and the Early Late the Ixcamilpa suite to sometime during the Lower Ordovi- Silurian age for the high-P event in the Esperanza suite cian to Silurian. preclude correlation of these events as has been proposed [Ortega-Gutie´rrez, 1978; Ortega-Gutie´rrez et al.,1999; [41] As mentioned above, detrital zircon ages suggest an intra-Iapetian origin for the Ixcamilpa suite. The New Murphy et al., 2006]. Additionally, medium-T eclogites like Brunswick Complex in the Northern Appalachians has a those of the Esperanza suite have been interpreted as similar depositional tectonic setting, metamorphic facies resulting from continental subduction [e.g., Ernst, 1977; and age of tectonic events [van Staal et al., 1990; van Cuthbert and Carswell, 1990; Putis et al., 2002; Puelles et Staal, 1994] to those proposed for the Ixcamilpa suite. The al., 2005; Shervais et al., 2003], whereas low-T eclogites tectonic event including the subduction of the Ixcamilpa like those in the Xayacatlań suite are typically attributed to suite and the collision with the Xayacatlań–El Rodeo– oceanic subduction [e.g., Schliestedt, 1990]. On that basis, Tecolapa block (Figure 6) may be correlated with the an Early-Late Silurian continental subduction (Figure 13f) Salinic event in the Northern Appalachians, which is created the eclogitic assemblages and the first foliation of attributed to the collision of the Ganderia terrane against the Esperanza suite. That event is clearly distinct from the the Notre Dame Arc during the Silurian, which closed the Early Ordovician eclogitic metamorphism in the Xayacatlań main Iapetus Ocean [van Staal et al., 1990]. suite. [44] Magmatic rocks with the same age, lithology, and 5.3. Early to Late Silurian Event (430–418 Ma): geochemical affinities, like those in the Esperanza suite Subduction of the Esperanza Suite exist in the northern Appalachian in two different tectonic settings. One is the Notre Dame Subzone [Whalen et al., [42] During the Early Silurian, a calc-alkaline granite 2006], which corresponds to a Laurentian peripheral arc; the batholith intruded clastic sedimentary rocks (Figure 13e). other is the Kingston terrane, which is a magmatic arc Basaltic rocks with continental rift geochemical affinity located between Ganderia and Avalonia [Barr et al., 2002]. [Murphy et al., 2006] intruded the granite and its host rocks The Kingston terrane in southern New Brunswick com- [Vega-Granillo, 2006]. These rocks forming the Esperanza

17 of 25 TC4008 VEGA-GRANILLO ET AL.: TECTONIC EVOLUTION ACATLA´ N COMPLEX TC4008 prises Early Silurian arc volcanic and intrusive rocks, Ortega-Gutie´rrez, 2002]) may be related with the migma- (442–435 Ma) [Doig et al., 1990; Barr et al., 2002]. tization event following the eclogitic metamorphism, instead Numerous sheeted mafic dikes intrude the arc rocks of the of the peak eclogitic metamorphism as previously consid- Kingston belt, suggesting an extensional arc [e.g., Nance ered [e.g., Murphy et al., 2006]. However, that age range and Dallmeyer, 1993; McLeod et al., 2001]. Thus, the coincides with the age of fossils in the Patlanoaya Forma- petrology, geochronology and tectonic settings of the King- tion, which it can be contradictory and further analysis and ston terrane and the Esperanza suite are startling similar. discussion is required. Deposition of the Famennian El The detrital zircon plot from the Esperanza metasediments Otate beds and the Kinderhookian to Leonardian Patlanoaya (Figure 3c) remains inconclusive in discriminating a Gond- beds over the metamorphosed suites of the Acatlań Com- wanan or Laurentian provenance, although Murphy et al. plex indicates that by the Late Devonian and afterward the [2006] suggest a Gondwanan affinity. The clastic character complex was exposed, which prevents that the high-P of the host rock of the Esperanza granite and the continental metamorphism of the Esperanza suite could be occurring rift affinity of mafic dikes traversing these rocks, point to an at the same time as suggested by Murphy et al. [2006]. origin within a continental block. Such a block may be [48] A granite pegmatite crosscutting the Esperanza suite similar to Ganderia, although the ages of the detrital zircons high-grade gneisses yields an Early Mississippian age of in the Esperanza metasediments (Figure 3c) fail to match 347 ± 3 Ma (40Ar/39Ar white mica, this work). That those observed in Ganderia [e.g., van Staal et al., 2004]. pegmatite lacks of the HP metamorphism and deformation [45] Metamorphic conditions like those of the Esperanza of the host gneisses; therefore, it postdates the eclogitic suite are reported from the Carolina terrane in the Southern event in that suite, supporting an older age for that event. Appalachian by Shervais et al. [2003]. Shervais et al. The Esperanza suite uplift may be related to erosion and/or [2003] regard the eclogitic metamorphism in the Carolina tectonic thinning of an overthickened crust and the con- terrane as formed by continental collision of two separate comitant isostatic compensation (Figure 13g). peri-Gondwanan terranes. That metamorphism is ascribed [49] Field relationships in the Piaxtla and eastern Patla- either to a Neoproterozoic–Early Cambrian (575–535 Ma) noaya regions indicate the Esperanza suite is thrust over the event or to a Late Ordovician–Early Silurian event [Shervais Xayacatlań–El Rodeo–Tecolapa and Ixcamilpa block et al., 2003]. The latter time span is similar to that defined (block 3 in Figure 6 and Figure 13h) along an E–W directed by the eclogitic event in the Esperanza suite. The Silurian thrust with top to the W shear sense. Mylonitic deformation eclogitic event in the Esperanza suite is coeval with the of both Mid-Ordovician and Upper Devonian leucogranites Salinic event in the northern Appalachian. The Salinic event intruding the Xayacatlań and Esperanza suites, respectively is related to the Ganderia-Avalonia collision zone, although (Figure 4e), are ascribed to that compressive event (Figure 6). not restricted to that zone [van Staal, 2007]. Other structures related to the same event are (1) the fourth [46] A Late Silurian tectonic event also occurred in the foliation S4XA in the Xayacatlań suite; (2) the second Colombian and Venezuelan Andes. There, the detrital foliation S2ER in the El Rodeo suite; and (3) folds with sequence of the Silgara´ Formation with Silurian fossils N–S axes and ductile slickenside striations with E–W [Rıós et al., 2003] was deformed, metamorphosed to trends in both the El Rodeo and Xayacatlań suites (Figures 6 amphibolite facies, and thrust over the metamorphosed and 11). The Esperanza over Xayacatlań–El Rodeo thrust- Mesoproterozoic crust before deposition of Lower Devonian ing must be coeval or subsequent to the Late Devonian beds [Forero Suarez, 1990]. Thus, the subduction of the emplacement of leucogranites in the Esperanza suite and Esperanza block may have been caused either by a trans- predates deposition of the Famennian El Otate beds. Early pressional collision between Laurentia and Gondwana as Middle Devonian ages (416 ± 12 Ma and 386 ± 22 Ma; proposed by Dalziel et al. [1994], or between two peri- Sm-Nd Grt-WR) reported from eclogites of the Xayacatlań Gondwanan terranes located in the boundary of the Iapetus suite [Yan˜ez et al., 1991] probably date a thermal event and Rheic oceans as suggested by Shervais et al. [2003]. produced by the thrusting of the Esperanza suite, instead of The second option is depicted in Figure 13f. the subduction-related eclogitic event as interpreted by Yan˜ez et al. [1991]. 5.4. Late Devonian Event (374 Ma): Uplift of the [50] The thrusting event described above is nearly coeval Esperanza Suite with a mid-Devonian tectonic-metamorphic event known as the Acadian phase, which occurred throughout the northern [47] Thermobarometry indicates that an almost isother- Appalachians and Europe [McKerrow, 1988]. Although the mal pressure decline from 16 to 9 kbar follows the eclogitic Northern Appalachian Acadian orogeny is difficult to trace metamorphism in the Esperanza suite [Vega-Granillo et al., through the central and southern Appalachian, Rast and 2007], causing the transition from eclogite to amphibolite Skehan [1993] discuss some evidence of its imprint in these facies. That transition generated partial melting evidenced regions. by sparse migmatitic metasediments and intrusion of leu- [51] In Figures 13f and 13g we suggest that a collision cogranites (Figures 4g and 13h). A Late Devonian age of with a peri-Gondwanan terrane caused the Esperanza block 372 ± 8 Ma (U-Pb zircon) from leucogranite is coeval with a first to descend along a subduction zone and subsequently 40 39 374 ± 2 Ma ( Ar/ Ar, phengite) age from a pod in eclogite uplift to collide with the Early Ordovician block composed [Vega-Granillo et al., 2007]. Zircon overgrowths in augen of the Xayacatlań, El Rodeo, and Ixcamilpa suites. Although gneisses yielding latest Devonian–Middle Mississippian rocks of Neoproterozoic age have not been found in the ages 360–345 Ma (U-Pb zircon [Elıás-Herrera and

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Acatla´n Complex they are present in the Chiapas Massif of including La Noria Granite and leucogranites of the Esper- the SW Maya terrane [Schaaf et al., 2002]. Therefore, we anza suite (371–372 Ma) [Yan˜ez et al., 1991; Vega-Granillo propose that either oblique subduction or strike-slip faulting et al., 2007]. In the northern Appalachians, the term Neo- parallel to the topographic belt laterally displaced the acadian orogeny was introduced by Robinson et al. [1998] proposed peri-Gondwanan terrane (Figure 13i). In the to encompass Middle Devonian to Early Carboniferous northern Appalachians, evidence exists for dextral strike- deformation and metamorphism in southern New England. slip movement following the Avalon terrane collision with The Neoacadian orogeny is coeval with the docking and Laurentia [Dalziel et al., 1994; Keppie, 1993; van Staal and orogenesis of the Meguma terrane in Canada [Hicks et al., de Roo, 1995]. 1999; Keppie et al., 2002].

5.5. Late Devonian Event (Post-374–Pre-359 Ma): 5.6. Devonian-Mississippian Boundary Event: Collision Collision With the Gondwanan Cosoltepec Suite of a Gondwanan Block

[52] After the Middle Devonian, the composite block [54] A compressive tectonic event created the last two formed by the Xayacatlań, Ixcamilpa, Esperanza, El Rodeo very low grade deformation phases D3CO –D4CO in the and Tecolapa suites, was thrust over the Gondwana affinity Cosoltepec suite. Structural analysis in the Cosoltepec suite Cosoltepec suite (block 4 in Figure 6 and Figure 13k) as indicates a N50°–80°W shortening direction for the D3CO – indicated by geological mapping (Figures 1 and 7). The D4CO phases (Figure 11), and the common mesoscopic predominant N20°W to N10°E strikes of the S2CO foliation folds have a NW vergence. Structures related to the same planes and scarce N80°E–°N80°W trends of ductile slick- event include (1) two phases of isoclinal to tight folding enside striations in the Cosoltepec suite (Figure 11) indi- F3ER–F4ER in the El Rodeo suite (Figures 4c and 4d) with cates an E–W shortening direction for the compressive fold axes trending N50°–80°E, and their respective axial event causing the thrust. The sense of motion remains planar cleavages; (2) a minor group of fold axes trending undefined, although some mantled porphyroclasts in thin N30°–50°E in the Xayacatlań suite; (3) isoclinal folding of ultramylonites crosscutting the Esperanza suite rocks sug- Mid-Ordovician leucogranite dikes (Figure 4f); and (4) tight gest a top to E shear sense. The timing for the juxtaposition folds and two very low grade cleavages in slates of the El of the high P/T suites over the Cosoltepec suite is subject of Otate Formation (Figures 12e and 12f). The Devonian- debate. The thrusting may create a piggyback basin where Mississippian boundary event is also evidenced by the thick the relatively deep-water sedimentary sequence of El Otate conglomerate separating the Kinderhookian-Leonardian Formation with Famennian fossils was deposited. Thus, the beds of the Patlanoaya Formation from the underlying thrusting event must postdate the Late Devonian leucogranite Famennian beds of the El Otate Formation. That conglom- emplacement and predate deposition of the El Otate For- erate contains clasts of metamorphic rocks and granites mation. The paleontological content of sedimentary units derived from the Acatlań Complex, and it overlies in overlying the Grenvillian granulitic basement in Oaxaca and angular unconformity the folded beds of the El Otate Ciudad Victoria areas provides additional evidence of the Formation. proximity of the Laurentia and Gondwana continents by the [55] Phengites from the high P/T suites were dated with Mississippian. Whereas the Lower Ordovician and Silurian the 40Ar/39Ar method by Vega-Granillo et al. [2007]. sedimentary sequences only contain fossils of Gondwanan Eclogite and mica schist from the Xayacatlań suite in the affinity [Pantoja-Alor,1993; Stewart et al.,1999],the Piaxtla and Mimilulco regions yield Middle Mississippian Mississippian to Lower Permian beds contain fossils of ages of 336 ± 6 Ma and 336 ± 4 Ma respectively. A mixed Laurentian and Gondwanan affinities [Stewart et blueschist from the Ixcamilpa region yields a Late Missis- al., 1999]. sippian age of 323 ± 12 Ma. A mica schist from the [53] In a regional context, the closing of the Rheic Ocean metasedimentary sequence of the Esperanza suite yields a culminated with the thrusting of the high P/T block formed Middle Mississippian age of 345 ± 2 Ma. Furthermore, by the Xayacatlań, Ixcamilpa, and Esperanza suites, over phengite from a Mid-Ordovician 461 Ma (U-Pb zircon) the Cosoltepec suite. The subduction related to the closure leucogranite dike [Talavera-Mendoza et al., 2005] intruding of the Rheic Ocean is inferred to have been west dipping the Xayacatlań suite yields a 335 ± 2 Ma (40Ar/39Ar) age (Figure 13j), because no magmatic arc was emplaced on the [Vega-Granillo et al., 2007]. The Mid-Late Mississippian Cosoltepec suite, whereas Upper Devonian granites cut the 327 ± 2 Ma and 320 ± 13 Ma ages obtained from El Rodeo high P/T block. A west dipping subduction is compatible suite (40Ar/39Ar, phengite and amphibole, this work), as with some interpretations in the Southern and Northern well as the 347 Ma age (40Ar/39Ar, white mica, this work) Appalachian [e.g., Hatcher, 1987; Ziegler, 1988; Scotese, from an undeformed granite pegmatite crosscutting the 2001], but some paleogeographic reconstructions propose Esperanza gneisses also indicates a Mississippian event. southeastern subduction direction in the Ouachita region These 40Ar/39Ar ages ranging from 347 to 318 Ma may [e.g., Loomis et al., 1994; R. Blakey, Sedimentation, tec- represent the interval during which the Acatlań Complex tonics, and paleogeography of the North Atlantic region, was progressively raised and cooled below phengite closure 2007, http://jan.ucc.nau.edu/rcb7/340Nat.jpg]. In the temperature of 350 ± 50°C[Geyh and Schleicher, 1990]. Appalachians, Acadian postmetamorphic plutons range in Yan˜ez et al. [1991] report similar Mid-Late Mississippian age from 388 to 371 Ma [Loiselle et al., 1983]; therefore, 332–318 Ma (Rb-Sr muscovite) ages for the Xayacatlań they are coeval with granites from the Acatlań Complex, suite rocks. Therefore, a tectonic compressive event occurred

19 of 25 TC4008 VEGA-GRANILLO ET AL.: TECTONIC EVOLUTION ACATLA´ N COMPLEX TC4008 at the Devonian-Mississippian boundary, producing defor- [1997] suggest that they indicate an N–S extension mation and gradual exhumation of the Acatlań Complex, as tentatively assigned to the Early Carboniferous. The defor- well as the angular unconformity between the El Otate mation must occur by the latest Early Permian (from 275 Formation and the Patlanoaya Formation. The Devonian- to 270 Ma) because it overprints the Early Permian Totol- Mississippian boundary event may result from the collision tepec Stock (278 Ma) and Tecomate Formation and of the Gondwana-related Oaxaca terrane with the Acatlań predates deposition of the Leonardian Matzitzi Formation. Complex (block 5 in Figure 6 and Figure 13l). That event Furthermore, the thrusting of the Cosoltepec and previously reversed the sense of movement of the Late Devonian event amalgamated suites over the Chazumba suite requires a that caused the thrusting of the high-P suites over the compressive deformation. If the Leonardian age of the Cosoltepec suite. In a wider context, a Late Mississippian Matzitzi Formation is correct, the time required to deposit (325–320 Ma) compression-related uplift, similar to that the very thick Chazumba suite and for the subsequent occurred in the Acatlań Complex, also occurred in the thrusting event must have been brief. In that case, the first southern Appalachians [Hatcher, 2004]. deformation phase D1CH and regional metamorphism event M1CH in the Chazumba suite may be ascribed to the latest 5.7. Lower Permian Event (275–270): Dextral Early Permian N–S compressive event (Figure 6). Alterna- Strike-Slip Movement and Compression tive explanations for the brief time span between the Chazumba suite deposition and the Permian compressive [56] The eastern boundary of the Acatlań Complex with event are (1) The Matzitzi Formation is not precisely the Mesoproterozoic granulitic Oaxaca terrane is regarded Leonardian but rather younger in age or (2) the lower as an Early Permian N–S dextral strike-slip fault [Elıás- contact of the Matzitzi Formation over the Oaxaca ter- Herrera and Ortega-Gutie´rrez, 2002]. Red beds of the rane–Acatlań Complex boundary is structural rather than Matzitzi Formation with fossils attributed to the Leonardian depositional. In the latter case, the Matzitzi Formation [Weber and Cevallos-Fernańdez, 1994] overlap the tectonic would not constrain the movement between the Acatlań boundary between the Acatlań Complex and the Oaxaca Complex and the Oaxaca terrane and the N–S compressive terrane [Elıás-Herrera and Ortega-Gutie´rrez, 2002]. The event could have occurred between the Late Permian and time of strike-slip faulting is constrained by the 275 ± 1 Ma Middle Jurassic. The final amalgamation of Pangea in the (U-Pb, zircon) age of leucosomes in syntectonic migmatites Southern Appalachian concluded about the Wordian stage [Elıás-Herrera and Ortega-Gutie´rrez, 2002] and the Leo- 265 Ma [Hatcher, 2004] during the late stage of the nardian deposition of the Matzitzi Formation. On the basis Alleghanian orogeny. Accordingly, the Permian event in of the detrital zircon ages, the Chazumba suite deposition the Acatlań Complex may be related to that process. began about the same time (275 Ma) [Talavera-Mendoza et al., 2005]. These observations suggest that the Chazumba suite may have been deposited in a pull-apart-type basin 5.8. Mid-Jurassic Event: Plume Rise and Dome-Shaped (Figure 13n) created by dextral lateral movement between Structures the Acatlań Complex and the Oaxaca terrane. The detrital [59] The second deformation and lower P/T metamor- zircon ages in the Chazumba suite indicate zircon sources phism event D2CH and M2CH in the Chazumba suite, and are both the Acatlań Complex and the Oaxaca terrane related migmatization, granite intrusion, and regional dom- [Talavera-Mendoza et al., 2005], supporting the pull-apart ing, evidence a mid-Jurassic thermal event. Apparently, the basin hypothesis. upper structural levels of the Acatlań Complex and its late [57] Hatcher [2002] mentions an Early Permian dextral Paleozoic sedimentary cover are not affected by that event, shear with NE40°SW strike in the southern Appalachians. excepting by the doming deformation. The thermal event In a wider context, Muttoni et al. [2003] propose that has been linked to mantle plumes (Figure 13q) [Keppie et ENE–WSW dextral strike-slip displacement between al., 2004a]. In this context, the domes may represent the Laurentia and Gondwana occurred in the Early Permian. middle crust response of deep-seated magmas. The dextral displacement in the Appalachian chain and the [60] By Jurassic time, Gulf of Mexico opening displaced Acatlań Complex may be related to the same regional the Maya terrane to the south [Pindell and Dewey, 1982; tectonic event. To make this correlation plausible, an Pindell, 1985, 1994; Pindell and Kennan, 2001], probably anticlockwise rotation about 40° for the Acatlań Complex with the Oaxaca terrane and the Acatlań Complex attached is required to have occurred since the Early Permian. (Figure 14b). Paleomagnetic data indicate 50–60° of [58] Mylonitic deformation with N–S ductile slicken- anticlockwise rotation of the Maya block [Molina-Garza side striations related to greenschist facies metamorphism et al., 1992], with a rotation axis near to the south end of the locally overprints the Tecomate Formation; the La Noria Florida Peninsula [Handschy et al., 1987; D. E. Bird and Granite [Vega-Granillo, 2006], the Totoltepec pluton K. Burke, Pangea breakup: Mexico, Gulf of Mexico, and [Malone et al., 2002], the Esperanza suite [Weber et al., Central Atlantic Ocean, paper presented at 76th Annual 1997; Vega-Granillo, 2006], and the Xayacatlań, El Rodeo International Meeting and Exposition, Society of Exploration and Cosoltepec suites [Vega-Granillo, 2006]. Kinematic Geophysicists New Orleans, Louisiana, 1 October 2006]. indicators as S-C0-type cleavages display a top to the S That plate reorganization also implies about 1200 km shear sense in all localities (references cited). Malone et al. displacement to the south of the SW limit of the Maya [2002] infer that mylonitic structures represent an Early block. By the Late Jurassic, the Acatlań Complex and the Permian compressive event; alternatively, Weber et al. Oaxaca terrane must have been laterally displaced with

20 of 25 TC4008 VEGA-GRANILLO ET AL.: TECTONIC EVOLUTION ACATLA´ N COMPLEX TC4008

Figure 14

21 of 25 TC4008 VEGA-GRANILLO ET AL.: TECTONIC EVOLUTION ACATLA´ N COMPLEX TC4008 respect to the Maya terrane to reach their present position mostly a subsurface terrane of pre-Triassic, strongly (Figure 14d). deformed, low-grade metamorphic rocks [Handschy et al., 1987; Sedlock et al., 1993, and references therein; Lopez et 5.9. Late Cretaceous–Paleogene Orogeny: Collision al., 2001]; and probably the interior metamorphic belt of the With the Guerrero Terrane Ouachita orogenic belt [Flawn et al., 1961; Viele and Thomas, 1989]. The Gondwanan and peri-Gondwanan crust [61] The conspicuous large-wavelength folds (Figure 7) is represented by the Carolina terrane [O’Brien et al., 1996], deforming both the Acatlań Complex and its overlying the Suwannee terrane [Rankin et al., 1989], the south and Jurassic-Cretaceous platform strata originated during a Late eastern part of the Maya terrane [Sedlock et al., 1993; Cretaceous-Paleogene orogenic event. That event created Stewart et al., 1999; Schaaf et al., 2002], the Oaxaca terrane thrust faults like the Papalutla fault (Figure 7) in the western [Campa-Uranga and Coney, 1983] and part of the Sierra limit of the Acatlań Complex exposures, which place rocks Madre terrane [Stewart et al., 1999]. In this model, the of the Cosoltepec suite over Cretaceous sedimentary rocks 0 proposed Oaxaquia block would have a NE–SW orien- (section A-A in Figure 1). That orogenic event is attributed tation instead of the N–S orientation suggested by Ortega- to the collision of the Acatlań Complex against the Guer- Gutie´rrez et al. [1995]. Upper Pennsylvanian, Permian and rero terrane [Cerca-Martıńez, 2004]. The large Ayu´ and Triassic granites that may be considered pre-, syn-, and Ahuatempan domes served as buttresses during Late Creta- post-Pangea final amalgamation respectively, intrude the ceous-Paleogene compression and the axes of major folds Oaxaca terrane [Torres et al., 1993; Sedlock et al., 1993; are bent around the domes (Figure 7). Stewart et al., 1999; and references therein], the Acatlań Complex [Yan˜ez et al., 1991] and the SW Maya terrane 5.10. Tectonic Remarks [Damon et al., 1981; Schaaf et al., 2002]. The Permian [62] Deformational, metamorphic and magmatic histories granites would make an NE–SW oriented magmatic belt suggest a strong correlation between the events in the emplaced along the Paleozoic orogen and they are probably Acatlań Complex and the Central Mobile Belt of the related to the late Alleghanian collisional event instead of Appalachian-Caledonian orogen. Tectonically mingled frag- the Farallon plate subduction as proposed by Torres et al. ments with Laurentian and Gondwanan affinity compose [1993]. Hatcher [2004] reports a suite of Lower-Middle these two regions. Pangean reconstructions require post- Permian (300 to 265 Ma) plutons that is largely confined to Jurassic translation of the southern part of Mexico including the Carolina terrane, which he relates to the Gondwana- the Acatlań Complex and the Oaxaca and Maya terranes to Laurentia collision. Similar granites extend to the Hercynian avoid overlapping by the South America crust (Figure 14) orogen of Europe and Africa [e.g., Giuliani et al., 1989; [Handschy et al., 1987]. Thereby, the Acatlań Complex may Faure et al., 2005] where they are interpreted as intruded in have been located between the Oaxaca-Maya block and the a late collisional setting. Ouachita orogenic belt by Late Permian time, forming a southern extension of the Appalachian Orogen (Figure 14a). 6. Conclusions The large-scale tectonic configuration for the Permian consist of (1) The Laurentian craton; (2) an external zone [63] Seven major thrust sheets compose the Acatlań corresponding to the Marathon-Ouachita-Appalachian fold Complex, each one with its own distinctive stratigraphy and thrust belt; (3) an internal zone composed of the and tectonothermal evolution. The Xayacatlań suite is an tectonically mingled metamorphic rocks of Laurentian and oceanic volcanosedimentary sequence that was subducted Gondwanan affinities; and (4) Gondwanan-related terranes. and metamorphosed to eclogite facies. The first two defor- Mississippian metamorphic ages are common in the internal mational metamorphic events in the Xayacatlań suite are zone [Stewart et al., 1999, and references therein]. The attributed to that subduction process. Then, the Xayacatlań internal zone may have included the Acatlań Complex rocks were exhumed and subsequently overthrust by the El [Talavera-Mendoza et al., 2005], the Piedmont zone [Miller Rodeo and Tecolapa suites. Lower-Middle Ordovician et al., 2000], the Dunnage zone [van Staal, 1994], the granites and leucogranites intrude the thrust faults. After Wiggins terrane [Thomas et al., 1989], the northern part Middle Ordovician time, the Ixcamilpa suite was deposited of the Maya terrane (north of the Yucatań Peninsula), where in an intra-Iapetian basin near a peri-Gondwanan terrane as there is subsurface information about metamorphic and suggested by its detrital zircon ages. This suite was sub- igneous rocks with Silurian to Pennsylvanian ages [Sedlock ducted under the Xayacatlań–El Rodeo block and meta- et al., 1993; Stewart et al., 1999]; the Coahuila terrane, morphosed to blueschist facies during an event ascribed to

Figure 14. Hypothetical plate tectonic evolution from the Late Permian to Late Cretaceous. (a) Sketch of the Pangea reconstruction with location of main belts of the Appalachian-Caledonian orogen (Appalachian region modified from Neugeabauer [1989]). (b) Late Permian reconstruction with proposed location of the Acatlań Complex and the Oaxaca terrane in the northern Gulf of Mexico (adapted from Pindell [1985]). (c) During initial Gulf of Mexico opening, the Acatlań Complex moved adjacent to the Yucatań Peninsula. (d) By Middle-Late Jurassic the Acatlań Complex moved to the west against the southern part of the Sierra Madre terrane. (e) Late Cretaceous collision of the Acatlań Complex and the Guerrero terrane. CM, Chiapas Massif. Terranes are Coa, Coahuila; J, Jua´rez; M, Mixteco; Ma, Maya; O, Oaxaca; SiMa, Sierra Madre; C, Carolina; Ch, Chortis.

22 of 25 TC4008 VEGA-GRANILLO ET AL.: TECTONIC EVOLUTION ACATLA´ N COMPLEX TC4008 the latest Ordovician-Silurian. The Lower Silurian conti- major thrusting with N–S movement direction and top to nental magmatic arc of the Esperanza suite was also sub- the S shear sense occurred about the same time involving all ducted and metamorphosed to medium-T eclogite facies by the suites of the Acatlań Complex, as well as the Upper the latest Early Late Silurian [Vega-Granillo et al., 2007]. Devonian and Lower Permian granites and parts of the This event is provisionally attributed to the collision be- platform sequence (Tecomate Formation). During the Mid- tween two continental peri-Gondwanan blocks. Isostatic and dle Jurassic, a plume rise produced regional doming and an compressive forces could have triggered the uplift of the overprinting metamorphism-deformational event in the Esperanza suite during the Early Late Devonian, causing the Chazumba and Cosoltepec suites, which do not reach the transition from eclogite to amphibolite facies, local migma- late Paleozoic platform sequence. Finally, by Late Creta- tization and emplacement of Upper Devonian leucogranites. ceous, collision of the Acatlań Complex and the Guerrero During the early Late Devonian, the Esperanza suite was terrane caused regional folding and local thrust faults in thrust over the block formed by the El Rodeo, Xayacatlań both terranes [Salinas-Prieto et al., 2000; Cerca-Martıńez, and Ixcamilpa suites, resulting in a generalized deforma- 2004]. tional metamorphic event. The resulting composite block [64] Lithological suites, metamorphic-magmatic events, was subsequently thrust over the Cosoltepec suite deposited deformational phases and geochemical signatures of the along the northwestern Gondwanan margin [Talavera- Acatlań Complex have correlatives in the Appalachian Mendoza et al., 2005]. That thrust is the final stage in the chain of eastern North America. Considering that palins- closing of the Rheic Ocean. The early Late Devonian pastic reconstructions of the Pangea indicate an overlap of thrusting may create a piggyback basin where the relatively southern Mexico and northern South America, we propose deep-water sedimentary sequence of El Otate Formation that the Acatlań Complex may have been located in the with Famennian fossils was deposited. At the Devonian- north part of the Gulf of Mexico as a southern extension of Mississippian boundary, the impingement of the Acatlań the Appalachian chain. The Acatlań Complex may have terrane against the Gondwanan Oaxaca terrane produced been displaced to its present location through an anticlock- another deformational metamorphic event that overprinted wise movement of the Yucatań Peninsula. That displace- the whole Acatlań Complex and the Famennian El Otate ment occurred during the Jurassic and accompanied the Formation. Subsequently, the Acatlań Complex was Gulf of Mexico opening. On that basis, the tectonometa- uplifted, cooled and partially eroded prior to deposition of morphic events in the Acatlań Complex may be useful for a the Lower Mississippian (Kinderhookian) to Leonardian more comprehensive understanding of the geological evo- platform sequence of the Patlanoaya Formation. During lution of the Appalachian-Caledonian orogen. the Leonardian, the Acatlań Complex was displaced with respect to the Oaxaca terrane along a dextral strike-slip [65] Acknowledgments. This work was supported by a CONACYT- fault. The motion along that fault created a pull-apart basin Me´xico grant (J32549-T) to Diana Meza-Figueroa. We gratefully acknowl- edge Timothy Lawton and Tim Wawrzyniec, whose valuable suggestions where the Chazumba suite was deposited 275 Ma ago. A improve the manuscript.

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