Journal of South American Earth Sciences 15 (2002) 511–524 www.elsevier.com/locate/jsames Deformational history of part of the Acatlán Complex: Late Ordovician – Early Silurian and Early Permian orogenesis in southern Mexico J.R. Malonea, R.D. Nancea,*, J.D. Keppieb, J. Dostalc b a Department of Geological Sciences, Ohio University, Athens, OH 45701-2979, USA Instituto de Geologı́a, Universidad Nacional Autónoma de México, Mexico DF 04510, Mexico c Department of Geology, St Mary’s University, Halifax, Nova Scotia, Canada B3H 3C3 Received 1 July 2001; accepted 1 December 2001 Abstract The Paleozoic Acatlán Complex of southern Mexico comprises polydeformed metasedimentary, granitoid, and mafic– ultramafic rocks variously interpreted as recording the closure of the Iapetus, Rheic, and Ouachitan Oceans. The complex is tectonically juxtaposed on its eastern margin against Grenville-age gneisses (Oaxacan Complex) that are unconformably overlain by Lower Paleozoic strata containing fossils of Gondwanan affinity. A thick siliciclastic unit (Chazumba and Cosoltepec Formations) at the base of the complex is considered part of a Lower Paleozoic accretionary prism with a provenance that isotopically resembles the Oaxacan Complex. This unit is tectonically overridden by a locally eclogitic mafic – ultramafic unit interpreted as a westward-obducted ophiolite, the emplacement of which was synchronous with mylonitic granitoid intrusion at ca. 440 Ma. Both units are unconformably overlain by a deformed volcano-sedimentary sequence (Tecomate Formation) attributed to a volcanic arc of presumed Devonian age. Deformed granitoids in contact with this sequence have been dated at ca. 371 (La Noria granite) and 287 Ma (Totoltepec pluton). Three phases of penetrative deformation (D1 – 3) affect the Cosoltepec Formation; the last two correlate with two penetrative deformational phases that affect the Tecomate Formation. D1 is of unknown kinematics but predates deposition of the Tecomate Formation and likely records obduction at ca. 440 Ma (Acatecan orogeny). A folded foliation in the Totoltepec pluton appears to record both deformational phases in the Tecomate Formation, bracketing D2 and D3 between 287 Ma and the deposition of the nonconformably overlying Leonardian Matzitzi Formation. D2 records north– south dextral transpression and south-vergent thrusting and is attributed to the collision of Gondwana and southern Laurentia (Ouachitan orogeny) at ca. 290 Ma, the kinematics being consistent with the northward motion of Mexico that is required by most continental reconstructions for the final assembly of Pangea. D3, which produced broadly north– south, upright folds, is also attributed to this collision and likely followed D2 closely in the latest Paleozoic. q 2002 Elsevier Science Ltd. All rights reserved. Keywords: Acatlán Complex; Paleozoic orogenesis; Totoltepec pluton 1. Introduction The Acatlán Complex of southern Mexico has been interpreted as the vestige of a Lower Paleozoic ocean that closed during the Late Ordovician– Early Silurian (Ortega-Gutiérrez, 1993; Ortega-Gutiérrez et al., 1999). Comprising a repeatedly deformed assemblage of Paleozoic metasedimentary rocks, granitoid bodies, and metamorphosed mafic –ultramafic units that form the basement of the Mixteco terrane, the complex is tectonically juxtaposed against Grenville-age (ca. 1 Ga) gneisses of the granulite * Corresponding author. Tel.: þ 1-740-593-1107; fax: þ1-740-593-0486. E-mail address: [email protected] (R.D. Nance). facies Oaxacan Complex at its eastern margin along the north– south Caltepec fault zone (Fig. 1). Lower Paleozoic rocks that nonconformably overlie the Oaxacan Complex are unmetamorphosed and contain fossil taxa of Gondwanan affinity (Robison and Pantoja-Alor, 1968). On the basis of its tectonostratigraphic similarity to parts of the Appalachian orogen and its close proximity to the Grenville-age gneisses of the Oaxacan Complex, the Acatlán Complex has been interpreted in terms of Laurentia – Gondwana collision (Yañez et al., 1991; Ortega-Gutiérrez et al., 1999; Keppie and Ramos, 1999). However, the paleogeographic position of the Acatlán Complex during the Paleozoic is uncertain, and several models have been proposed to account for its tectonic 0895-9811/02/$ - see front matter q 2002 Elsevier Science Ltd. All rights reserved. PII: S 0 8 9 5 - 9 8 1 1 ( 0 2 ) 0 0 0 8 0 - 9 512 J.R. Malone et al. / Journal of South American Earth Sciences 15 (2002) 511–524 Fig. 1. Location and tectonostratigraphic setting of the Acatlán Complex in southern Mexico (from Ortega-Gutiérrez et al., 1999). Index map shows Cenozoic volcanic rocks of the Sierra Madre Occidental (SMOCC) and Trans-Mexican volcanic belt (TMVB). evolution. For example, Yañez et al. (1991) related the complex to the Acadian belt of the Appalachians, suggesting that both were deformed in a latest Silurian – Middle Devonian collision (Mixtecan orogeny) between eastern Laurentia and northwestern South America. According to Yañez et al. (1991), the Acatlán Complex was then transported southward with Gondwana to a position near present-day Colombia and recollided with southern Laurentia during the late Carboniferous before moving to its present position following the breakup of Pangea. On the basis of new age data interpreted to indicate an earliest Silurian date for its deformation, Ortega-Gutiérrez et al. (1999) proposed that the Acatlán Complex represents a vestige of the Iapetus suture formed during a Late Ordovician – Early Silurian collision (Acatecan orogeny) between eastern Laurentia and Oaxaquia, a crustal fragment of Grenville-age in present-day Mexico (Ortega-Gutiérrez et al., 1995). In this context, Oaxaquia represents either a microcontinent or part of the Columbian margin of Gondwana. In contrast, Keppie and Ramos (1999) proposed that the Acatlán Complex lay adjacent to northwestern South America throughout the Paleozoic on the southern margin of the Rheic Ocean and was not involved in continent – continent collision until the Permo-Carboniferous assembly of Pangea. These contrasting tectonic models are based largely on the pioneering regional mapping of the Acatlán Complex by Ortega-Gutiérrez (1975) and are currently being tested as aspects of the complex are reexamined in more detail. Recent geochronological studies have focused on the ages of the main tectonothermal events. For example, Ortega-Gutiérrez et al. (1999) obtained an age of ca. 440 Ma for the Acatecan collision (originally thought to be Early Devonian) by dating a granitoid body that they interpret as syntectonic. Similarly, by interpreting the emplacement of a younger granitoid body as synchronous with the Mixtecan orogeny, Sánchez Zavala et al. (2000) date this event at ca. 370 Ma (Yañez et al., 1991). This paper examines the deformational and kinematic history of the Acatlán Complex by focusing on the structural J.R. Malone et al. / Journal of South American Earth Sciences 15 (2002) 511–524 513 Fig. 2. Simplified geological map and cross-section of the northern part of the Acatlán Complex. Outlined region shows study area and its division into structural subareas (modified from Ortega-Gutiérrez et al., 1999). history of two of its principal metasedimentary units, the Cosoltepec Formation (deposited prior to the proposed Late Ordovician –Early Silurian collision) and the Tecomate Formation (deposited following this event). Our results show that the complex has experienced three periods of penetrative deformation, one of which is assigned to the Late Ordovician –Early Silurian Acatecan event, whereas the other two are of Early Permian age and synchronous with the Ouachitan orogeny of the southern United States and an unnamed orogenic belt in northwestern South America. 2. Acatlán complex Understanding of the geology of the Acatlán Complex (Fig. 2) is based largely on the doctoral work of Ortega-Gutiérrez (1975), who identified its principal lithologic units and recognized within it two major thrust slices unconformably overlain by a sequence of deformed metasedimentary rocks. Ortega-Gutiérrez (1993) later assigned the rocks of the lower and upper plates to the Petlalcingo and Acateco subgroups, respectively, and interpreted the lower as an obducted accretionary prism and the upper plate as an ophiolitic sequence. 2.1. Petlalcingo subgroup The lower plate of the thrust nappe, or the Petlalcingo subgroup (Fig. 3), comprises a thick sequence of siliciclastic rocks derived from a Grenville-age provenance that isotopically resembles the Oaxacan Complex (Yañez et al., 1991). The subgroup is divided into two formations: a lower Chazumba Formation of alternating psammitic and pelitic rocks and an upper Cosoltepec Formation dominated by quartzose phyllites. Metamorphosed to the amphibolite facies, the Chazumba Formation is dominated by quartzrich biotite schists that contain occasional garnet, staurolite, 514 J.R. Malone et al. / Journal of South American Earth Sciences 15 (2002) 511–524 Fig. 3. Simplified tectonostratigraphic column for the Acatlán Complex (modified from Ortega-Gutiérrez et al., 1999). and sillimanite and, at the highest grade, are transitional with the underlying Magdalena migmatite. The Chazumba Formation is overlain by the Cosoltepec Formation, which makes up more than 90% of the exposed Acatlán Complex. The Cosoltepec Formation is not thought to have experienced more than greenschist facies metamorphism and is dominated by phyllitic quartz –chlorite – phengite schists with occasional retrogressed biotite and abundant quartz veins. Other components locally include pillowed greenstones, metachert, massive quartzite, serpentinite, and manganiferous rocks (Ortega-Gutiérrez, 1993). The nature of the contact between the Cosoltepec and Chazumba Formations is uncertain, though its association with amphibolite bodies suggests it may be tectonic. On the basis of its siliciclastic composition, extreme thickness, and the presence of inferred ocean floor fragments, Ortega-Gutiérrez et al. (1999) interpreted the Petlalcingo subgroup as the parautochthonous trench and forearc deposits of a convergent continental margin. The Magdalena migmatite, formerly thought to form the base of the lower plate (Fig. 3), has recently yielded a concordant U – Pb crystallization age of 170 ^ 2 Ma and is now attributed to Jurassic extension (Powell et al., 1999) coeval with the posttectonic emplacement of the granitic San Miguel dikes at 173 ^ 0.3 Ma (Rb/Sr whole-rock isochron; Ruiz-Castellanos, 1979). 2.2. Acateco subgroup The upper plate of the thrust nappe, or the Acateco subgroup (Fig. 3), consists of high-grade, mafic – ultramafic and interlayered pelitic and siliceous metasedimentary rocks (Xayacatlán Formation) that are structurally overlain by high-pressure metagranitoids and migmatites (Esperanza granitoids). The Xayacatlán Formation includes micaceous schists, gneisses, porphyroblastic amphibolites, sepentinites, and related ultramafics that are commonly mylonitic and locally preserve relict eclogite facies mineral assemblages (Ortega-Gutiérrez, 1975, 1993. The sheet-like mylonitic Esperanza granitoids comprise megacrystic Kfeldspar augen gneiss, migmatite, schist, and minor amphibolite. On the basis of a mineralogy that includes high-silica phengite, grossular-rich garnet, pseudomorphs of zoisite or epidote þ phengite þ albite ^ garnet after plagioclase, and relict rutile, the granitoids are considered to have experienced eclogite facies metamorphism and are interpreted to be syntectonic with respect to the emplacement of the thrust nappe at 440 ^ 14 Ma (U –Pb zircon lower J.R. Malone et al. / Journal of South American Earth Sciences 15 (2002) 511–524 515 Fig. 4. Geochemistry of the Totoltepec pluton. (a) Jensen cation plot (Jensen, 1976) for rock classification. Fields: PK ¼ peridotitic komatiite; BK ¼ komatiitic basalt; HFT ¼ high Fe tholeiitic basalt; HMT ¼ high Mg tholeiite basalt; TA ¼ tholeiitic andesite; TD ¼ tholeiitic dacite; TR ¼ tholeiitic rhyolite; CB ¼ calc-alkaline basalt; CA ¼ calc-alkaline andesite; CD ¼ calc-alkaline dacite; CR ¼ calc-alkaline rhyolite. (b) Chondrite-normalized REE abundances for felsic and mafic components of the Totoltepec pluton. Normalizing values after Sun (1982). (c) Mantle-normalized trace element abundances for felsic and mafic components of the Totoltepec pluton. Normalizing values after Sun and McDonough (1989). (d) Variations of Nb (ppm) versus Y (ppm) in the felsic rocks of the Totoltepec pluton (Pearce et al., 1984). VAG ¼ volcanic arc granites; syn-COLG ¼ syn-collision granites; WPG ¼ within-plate granites; ORG ¼ ocean ridge granites. intercept age; Ortega-Gutiérrez et al., 1999). The relative displacement of the upper plate, according to its outcrop pattern, exceeds 200 km and is attributed to westwardvergent thrusting during the Late Ordovician – Early Silurian Acatecan orogeny. The upper intercept age of the metagranitoids (1161 ^ 30 Ma), as well as their peraluminous composition, depleted mantle model age ðTDM ¼ 1:50 GaÞ; high initial strontium ratio ð87 Sr=86 Sr ¼ 0:7189Þ; and negative epsilon neodymium value (e Ndð0Þ ¼ 210:0; Yañez et al., 1991), suggest a Precambrian source (Ortega-Gutiérrez et al., 1999). The Acatecan subgroup is inferred by these authors to represent an obducted slice of oceanic and continental lithosphere. 2.3. Tecomate Formation Both the Petlacingo and Acateco subgroups were exhumed before the deposition of the uppermost unit of the Acatlán Complex, the volcano-sedimentary Tecomate Formation. On the basis of poorly preserved fossils, this unit is thought to be of Devonian age (Ortega-Gutiérrez, 1993) and represents the earliest overstep across the upper and lower plates of the thrust nappe (Fig. 3). The formation is mildly metamorphosed but strongly deformed and consists of thinly bedded pelitic and psammitic sedimentary rocks, occasional marbles and pebble conglomerates, and volcaniclastic units of basaltic – andesite and less common felsic composition (Sánchez Zavala et al., 2000). Metagranitic clasts, common in the conglomerates and thought to be derived from the ca. 440 Ma Esperanza granitoids (Yañez et al., 1991), provide a maximum depositional age for the Formation. A minimum depositional age of ca. 370 Ma is provided by the deformed La Noria granite, which is reported to intrude the formation (Ortega-Gutiérrez et al., 1999). Zircons from this granite have yielded upper and lower intercept ages of 1116 ^ 44 and 371 ^ 34 Ma 516 J.R. Malone et al. / Journal of South American Earth Sciences 15 (2002) 511–524 Table 1 Representative analyses of rocks of the Totoltepec pluton Sample SiO2 (wt%) TiO2 Al2O3 Fe2O3 MnO MgO CaO Na2O K2 O P2O5 LOI Total Cr (ppm) Ni Co V Cu Pb Zn Rb Cs Ba Sr Ga Nb Hf Zr Y Th U La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu F-1 F-2 F-3 M-1 M-2 M-3 74.40 0.12 14.89 0.92 0.04 0.37 1.26 5.73 2.25 0.06 0.48 66.97 0.31 16.43 3.36 0.06 1.46 2.74 4.97 1.32 0.11 2.19 73.79 0.10 16.32 0.87 0.02 0.45 2.77 5.41 0.74 0.04 0.20 56.76 0.75 17.06 8.75 0.12 4.87 6.43 2.73 1.06 0.09 1.34 48.72 0.78 17.74 10.86 0.18 7.79 8.39 1.60 2.30 0.05 1.41 56.15 0.66 14.28 8.09 0.13 4.29 5.48 4.42 0.94 0.08 5.28 100.51 99.93 100.71 99.96 99.82 99.80 9 26 20 4 9 58 12 26 77 3.14 1907 316 17 2.41 1.52 61 22.79 2.31 0.68 6.09 14.11 2.04 9.55 2.71 0.72 3.06 0.55 3.68 0.84 2.44 0.38 2.38 0.38 12 69 52 3.49 1461 554 19 1.22 0.91 32 14.99 0.70 0.22 3.11 7.50 1.10 5.34 1.69 0.55 2.07 0.36 2.46 0.55 1.60 0.24 1.60 0.24 20 8 34 51 2.04 550 752 17 2.46 1.69 6.9 22.25 2.59 0.81 6.90 16.43 2.36 9.68 2.62 0.73 3.03 0.53 3.50 0.86 2.28 0.35 2.40 0.38 55 13 32 180 72 11 92 29 1.37 1669 248 18 1.98 0.84 29 6.80 1.00 0.22 2.52 5.89 0.80 3.32 0.86 0.18 0.90 0.15 1.05 0.24 0.64 0.10 0.69 0.12 140 35 43 212 99 10 55 37 1274 281 15 2.27 1.16 44 7.87 0.45 0.22 4.57 9.95 1.38 6.12 1.44 0.43 1.32 0.22 1.39 0.31 0.84 0.13 0.90 0.13 33 10 32 129 56 9 136 3.9 1.11 703 530 13 0.38 0.74 22.5 1.20 0.02 0.10 1.32 2.47 0.27 1.09 0.20 0.18 0.19 0.03 0.16 0.04 0.11 0.02 0.12 0.02 F ¼ felsic samples; M ¼ mafic samples. (Yañez et al., 1991), the latter of which is interpreted as the date of its crystallization (Ortega-Gutiérrez et al., 1999). Originally thought to represent a postorogenic, molasselike unit deposited in the wake of thrust nappe emplacement (Ortega-Gutiérrez, 1993), the Tecomate Formation has recently been interpreted as a turbiditic volcanic arc sequence deposited in advance of an arc-continent collision (Mixtecan Orogeny) in the Late Devonian that was responsible for its deformation (Sánchez Zavala et al., 2000). Early Mississippian sedimentary rocks (e.g. San Salvador Patlanoaya Formation) that are reported to overlie the Tecomate Formation unconformably (Esquivel-Macı́as et al., 2000; Vechard et al., 2000) are folded but unmetamorphosed. 2.4. Totoltepec pluton The Tecomate Formation is tectonically overridden by the foliated Totoltepec pluton along the pluson’s mylonitic southern margin. Zircons from the more felsic component of this body have yielded a concordant U – Pb zircon age of 287 ^ 2 Ma (Yañez et al., 1991). The pluton grades upward (to the north) from a basal gabbro/diorite through trondhjemite/tonalite to a mafic marginal phase at the top. Foliation and compositional banding generally dip steeply north. The pluton is nonconformably overlain by deformed, but unmetamorphosed, clastic rocks of the Early Permian (Leonardian, 280 ^ 4– 269 ^ 7 Ma; Okulitch, 1999) Matzitzi Formation (Silva-Romo and Mendoza-Rosales, 2000). This formation also dips steeply north and is unconformably overlain by gently dipping Jurassic clastic rocks that contain leaves of Bennettita leau. Samples collected from the Totoltepec pluton as part of this study exhibit typical calc-alkaline geochemical signatures (Fig. 4a) accompanied by relatively flat rare earth element (REE) patterns with only minor enrichments of light REE and (La/Yb)n , 2– 3 (Fig. 4b). Representative samples of both mafic and felsic rocks were analyzed by Xray fluorescence for major and some trace elements (Rb, Sr, Ba, Zr, Nb, Y, Cr, Ni) and by inductively coupled plasmamass spectrometry (ICP-MS) for the REE, Nb and Th, at the Ontario Geological Survey in Sudbury (Table 1). The ICPMS method, described by Ayer and Davis (1997), indicates a precision and accuracy of 2– 10% for trace elements. All rocks were affected by secondary processes including amphibolite grade metamorphism and hydrothermal activity, which may have modified their composition. Hence, the samples were petrographically and chemically screened. Strongly altered samples, including those with high LOI values, were discarded. The remaining samples are compositionally similar to modern rock suites, and thus, the concentrations of most major elements, as well as the high field strength elements (HFSE), REE, and transition elements are believed to reflect the primary magmatic distribution. These samples are employed for petrogenetic considerations and to discriminate the tectonic setting. Mantle-normalized trace element patterns (Fig. 4c) display small negative Nb anomalies and distinct enrichment of Ba. Felsic rocks have SiO2 in the range of 66– 75 wt% and low K2O but high Na2O. Their REE patterns are rather flat with low (La/Yb)n , 1– 2 and (La)n , 10– 22. Mantle-normalized trace element patterns are also relatively flat with Nb depletion and distinct enrichment of Ba and Rb. On the Nb – Y discrimination diagram (Fig. 4d), the felsic rocks plot in the arc field. Thus, the pluton appears to be one of a series of Permo-Triassic granitoid bodies that extend the length of Mexico and have been interpreted as a J.R. Malone et al. / Journal of South American Earth Sciences 15 (2002) 511–524 517 (Weber et al., 1997). But whereas the structural geometry of the Cosoltopec Formation reveals three main phases of penetrative deformation, that of the Tecomate Formation reveals only two. According to their structural style and overprinting relations, these phases are designated DC1 – DC3 and DT1 –DT2, respectively. To clarify the relationship between these phases and highlight the east – west variations displayed in their structural orientation, the field area has been divided into three structural subareas (Fig. 2). Fig. 5. Equal-area stereographic projection of structures within the Cosoltepec Formation. (a) DC2 structures; (b) DC3 structures. primitive arc developed above an east-dipping subduction zone along the western margin of Pangea (Torres et al., 1999). 3. Deformational history To clarify the deformational history of the Acatlán Complex, the structural geometry of the Cosoltepec and Tecomate Formations have been examined in detail east of Acatlán de Osorio (Malone, 2000), where east –west road and river sections provide excellent access to the complex along the cross-section AB (Fig. 2). Because deposition of the Cosoltepec Formation predates the emplacement the Acatecan thrust nappe, whereas that of the Tecomate Formation does not, a comparison of their individual structural records provides a unique opportunity to unravel some of the details of the region’s deformational history. To assist in constraining the timing of the deformation, a brief examination also was made of the structure of the Totoltepec pluton, which is in tectonic contact with both formations. 3.1. Structural geometry The metasedimentary rocks of both the Cosoltepec and Tecomate Formations are known to be strongly deformed 3.1.1. Cosoltepec Formation East of Acatlán, the Cosoltepec Formation comprises a monotonous sequence of strongly veined and polydeformed phyllites with thin psammitic interlayers that are thought to record original bedding (SC0). A prominent, and possibly composite, bedding-parallel foliation forms the principal fabric in outcrop and is defined by the orientation of greenschist facies phyllosilicates. Matrix quartz and coarser quartz grains in veins that subparallel the foliation are strongly annealed with granoblastic textures. Minor plagioclase grains in psammitic layers show similar textures. Mesoscopic fold structures, most clearly outlined by the veins, are of several generations and accompanied by locally strong crenulation cleavages, a prominent mineral lineation, and a variety of intersection lineations. Where observed, contacts between the quartz– phyllitic rocks of the Cosoltepec Formation and those of other units are sharp and tectonic in origin. The first phase of penetrative deformation in the Cosoltepec Formation (DC1) produced a prominent bedding-parallel schistosity (SC1) that is the earliest recognizable fabric in outcrop. Defined by phengite – chlorite ^ biotite, the schistosity is axial planar to rare, small-scale, tight to isoclinal folds (FC1) and possible largescale structures of the same style. Foliation-subparallel quartz veins that were formed either before or during the early stages of this deformational event provide the best means of defining the SC1 fabric in later structures because the SC1 schistosity is often difficult to distinguish from later foliations in outcrop. However, its presence can be clearly demonstrated at the closures of the FC2 folds. Any lineation that may have been associated with this deformation has been entirely overprinted by LC2, so the kinematic significance of the event is unknown. In all subareas, SC1 is essentially parallel to SC2, and variations in its orientation are largely a function of younger (FC3) folding. The mineralogy of the phyllosilicates that define SC1 suggests that the metamorphism associated with DC1 did not exceed the greenschist facies. The second phase of penetrative deformation (DC2) produced tight to isoclinal curvilinear (sheath) folds (FC2) that possess an axial planar schistosity (SC2) defined by the alignment of the phyllosilicates. The folds are typically several centimeters in wavelength and deform both the SC1subparallel quartz veins and SC1, which wraps around FC2 hinges in thin sections. FC2 axes lie within the combined 518 J.R. Malone et al. / Journal of South American Earth Sciences 15 (2002) 511–524 Fig. 6. Equal-area stereographic projection of structures within the Tecomate Formation. (a) DT1 structures; (b) DT2 structures. SC1/SC2 foliation and generally plunge NNW to NNE at gentle to moderate angles (Fig. 5a). Associated with DC2 is a strong mineral lineation (LC2) that is defined by the alignment of elongate quartz grains on SC2 foliation surfaces. LC2 plunges NE to NW at gentle to moderate angles subparallel to the axes of FC2 folds and slightly oblique to those of FC3, which are largely responsible for the scatter in its orientation (Fig. 9a). The presence of a mineral lineation and FC2 closures of demonstrable sheath fold geometry (Fig. 10a) are consistent with the subparallel alignment of LC2 with the near-isoclinal FC2 axes and suggests that DC2 was associated with an important component of simple shear. On a regional scale, steeply dipping FC2 shear zones appear to separate the north – south lithologic units in the vicinity of Acatlán, whereas a north-dipping DC2 thrust forms the base of the Totoltepec pluton along its southern margin (Fig. 2). The phyllosilicates that define the SC2 fabric (muscovite – biotite –chlorite – phengite) suggest that the metamorphism associated with DC2 was of a greenschist facies grade similar to that which accompanied DC1. The third phase of penetrative deformation (DC3) produced upright to inclined, open to close folds (FC3) that plunge NNW to NE at gentle to moderate angles (Fig. 5b). With outcrop wavelengths ranging from several centimeters to several meters, these structures refold FC2 to form Type III refolded isoclines (Fig. 10a) and possess an Fig. 7. DT1 structures in the Tecomate Formation. (a) Folded layering in calc mylonite within DT1 dextral shear zone (coin diameter ¼ 2.1 cm); (b) deformed conglomerate showing top-to-the-right (south) pebble asymmetry and asymmetric folds (coin diameter ¼ 2.7 cm). axial planar crenulation cleavage (SC3) that is often broadly coplanar with that of the combined SC1/SC2 foliation. FC3 axes vary only slightly in orientation across the field area, but though they are subparallel to FC2 axes and LC2 in subarea 1, they are slightly oblique to these structures in subarea 3 and are aligned at a high angle to them in subarea 2 (Fig. 9a). Megascopic FC3 folds with wavelengths of several kilometers are responsible for the regional structure (Fig. 2) and suggest that DC3 was associated with a significant component of east – west shortening (Ortega-Gutiérrez, 1978). The generally steeply dipping SC3 crenulation cleavage associated with DC3 is a NW- to NE-striking fabric that is often the most prominent structural feature in outcrop. The lineation (LC3) produced by its intersection with the combined SC1/SC2 foliation parallels the axes of FC3 folds and is best developed at their hinges. On the basis of textural relations, DC3 is thought to have accompanied retrograde greenschist facies metamorphism that is evident in the alteration of biotite to chlorite. 3.1.2. Tecomate Formation The Tecomate Formation in the area east of Acatlán is dominated by laminated metapelites and feldspar-bearing J.R. Malone et al. / Journal of South American Earth Sciences 15 (2002) 511–524 Fig. 8. Equal-area stereographic projection of structures within the Totoltepec pluton. metapsammites with local interbeds of pebble conglomerate and marble. Bedding is clearly discernable in places, and the primary bedding-subparallel schistosity, which is the most prominent structure in outcrop, is demonstrably noncomposite and defined by phyllosilicates (phengite, chlorite, and retrograded biotite) that are less common than they are in the Cosoltepec Formation. In comparison with the Cosoltepec Formation, widespread quartz veins are also less common, quartz grains are only locally annealed, and the matrix is more feldspathic, with K-feldspar and plagioclase (An28 to An52) locally composing 5 and 20% of the mode, respectively. Although repeatedly folded and possessing a strong mineral lineation, the Tecomate Formation is less deformed than the Cosoltepec Formation and has only a single prominent crenulation cleavage and intersection lineation. The marble horizons, which are typically 1 – 10 m in width, form distinctive marker horizons and are in 519 tectonic contact with rocks of both the Cosoltepec and Xayacatlán Formations. In the conglomerates, white to light pink granitic clasts, commonly 10 cm in diameter, define a strong LS tectonite fabric. Two phases of folding (FT1 – FT2) are recognized in the Tecomate Formation. The earliest phase of penetrative deformation (DT1) to affect the Tecomate Formation produced tight to isoclinal folds (FT1) that deform the bedding and are associated with the formation of a bedding-subparallel greenschist facies (phengite – biotite –chlorite) schistosity (ST1). FT1 closures are only rarely seen in outcrop, and where observed, their axes plunge NNW to NE at gentle to moderate angles, parallel to those of FC2 (Fig. 6a). Where associated with steeply dipping DT1 shear zones, however, FT1 are steeply plunging and show a clockwise asymmetry consistent with north– south dextral shear (Fig. 7a). A strong mineral lineation (LT1), defined by the alignment of elongate quartz crystals on ST1 foliation surfaces, also plunges NNW to NE subparallel to the axes of FT1 folds (Fig. 6a). As with LC2, the scatter in the orientation of LT1 reflects its slight obliquity to later (FT2) folding (Fig. 9b). In the conglomerates, where it is defined by elongate pebbles, LT1 is clearly a stretching lineation and associated with kinematic indicators (pebble s-structures and asymmetric folds) that document thrusting from north to south along east – west striking zones (Fig. 7b). The second penetrative phase of deformation to affect the Tecomate Formation (DT2) produced open to close, upright to inclined folds (FT2) that plunge gently to moderately NW to NE (Fig. 6b). The axes of these folds show little variation in their orientation across the field area. Similar to those of FC3, the axes are most oblique to LT1 in subarea 2 (Fig. 9b) and, at a megascopic scale, play an important role in the regional structure. The FT2 folds locally refold FT1 to form Fig. 9. Comparative equal-area stereographic projections of (a) LC2 and FC3 and (b) LT1 and FT2 in each of the three structural subareas. 520 J.R. Malone et al. / Journal of South American Earth Sciences 15 (2002) 511–524 Type III interference patterns (Fig. 10b) and contain an axial planar crenulation cleavage (ST2) that is generally coplanar with ST1. The ST2 cleavage is often the most prominent structural feature in outcrop and, similar to SC3, is associated with the retrogression of biotite to chlorite. ST2 dips steeply NW, north, or NE and intersects ST1 at FT2 hinges to form an intersection or crenulation lineation (LT2) that plunges broadly north, parallel to the axes of FT2 folds. 3.1.3. Totoltepec pluton To the east of Acatlán, the trondhjemitic to hornblende dioritic Totoltepec pluton is tectonically juxtaposed against the Cosoltepec and Tecomate Formations along its southern margin (Fig. 2). Two phases of penetrative deformation (DP1 –DP2) are recognized (Fig. 8). The first deformational phase (DP1) produced a steeply north-dipping (608– 808N) foliation (SP1) defined by flattened quartz and feldspar grains and the alignment of altered magmatic hornblende. Enclaves of strongly banded gneissic hornblende gabbro in the southern part of the pluton are concordant with this fabric and cut by granitic dikes that are themselves foliated parallel to their margins. These features suggest that emplacement of the pluton may have been, at least in part, syntectonic with respect to DP1. The foliation is locally associated with sinistral shear zones with subhorizontal mineral alignments; however, it is also accompanied by a north-plunging mineral lineation (Lp1) associated with asymmetric hornblende fish showing top-to-the-south shear sense. The north-dipping deformational fabric intensifies toward the southern margin of the pluton, becoming locally mylonitic near the basal contact with S – C fabrics that indicate that the plutonic rocks have been thrust south over the Tecomate and Cosoltepec Formations in a direction similar to the vector of DT1 vergence in the underlying Tecomate Formation. The second phase of penetrative deformation (DP2) takes the form of north-plunging structures (FP2), about which SP1 is locally folded. The planar SP1 fabric also shows regional variations in trend consistent with the presence of megascopic, north – south FP2 folds (Fig. 8). 3.2. Structural correlation The geometries of the fold phases produced by DT1 and DT2 in the Tecomate Formation correspond closely to those produced by DC2 and DC3 in the Cosoltepec Formation, and the planar fabrics that these phases generated were produced under very similar metamorphic conditions. That these two fabric-forming events are correlative is evident from not only the orientational data, but also their structural styles in outcrop. This can be demonstrated, on the one hand, by the nearly identical orientations of LC2 and FC3 in each of the three subareas (Fig. 9a) to those of LT1 and FT2 in the same subareas (Fig. 9b) and, on the other hand, by the similarity of the two fold structures illustrated in Fig. 10. Thus, Fig. 10a shows a refolded FC2 sheath fold in the Cosoltepec Fig. 10. Comparative structural styles of DC2 and DT1, and DC3 and DT2. (a) Type III FC3 refolded FC2 isoclinal sheath fold in Cosoltopec Formation (coin diameter ¼ 2.5 cm). (b) Type III FT2 refolded FT1 isocline in Tecomate Formation (coin diameter ¼ 2.7 cm). Formation that deforms a schistosity-parallel quartz vein, whereas Fig. 10b shows a refolded FT1 isocline in the Tecomate Formation that is of very similar appearance but that deforms only the bedding. Similarities also exist between the structures associated with DT1 and DT2 in the Tecomate Formation and those that affect the Totoltepec pluton, in that the earlier deformation of both units produced LS tectonite fabrics of similar attitude and kinematics, whereas the later deformation produced folds of similar geometry and orientation. However, SP1 in the Totoltepec pluton dips more steeply than ST1 in the Tecomate Formation, and the kinematics associated with it include steep, east –west sinistral shear zones not observed in the Tecomate Formation. The dip of SP1 is also slightly steeper than that of the bedding in the nonconformably overlying Matzitzi Formation and Jurassic rocks, which implies both significant rotation of the pluton and a rotation that took place in at least two stages: Late Permian –Triassic and syn- to post-Jurassic. This rotation is inferred to have occurred on a south-dipping listric normal fault that should crop out somewhere to the north and resurfaces along the southern margin of the pluton as a south-vergent thrust. Restoration of this post-Leonardian rotation produces a gently north-dipping SP1 foliation in the pluton approximately parallel to that in the underlying J.R. Malone et al. / Journal of South American Earth Sciences 15 (2002) 511–524 521 3.3. Timing of deformation Fig. 11. Schematic structural evolution of the Acatlán Complex recorded in the Cosoltepec and Tecomate Formations and the Totoltepec pluton. Tecomate Formation. At the same time, the steeply dipping sinistral shear zones are restored to zones with west-vergent thrusting. The existence of such thrusts can be interpreted in terms of dextral transpression with strain partitioning between dextral, north– south shear zones and west-vergent thrusts in the form of a positive flower structure, and southvergent thrusting at constraining bends. This is consistent with observations in a nearby area, where Elı́as-Herrera and Ortega-Gutiérrez (2000) have shown that Early Permian dextral shear was accompanied by west-vergent thrusting. Further work, currently in progress, is required to resolve the kinematic inhomogeneities. However, the sequence of structures is similar in both the Totoltepec pluton and the Tecomate Formation, and both phases (DT1/P1 and DT2/P2) are synchronous with or postdate intrusion of the pluton at 287 ^ 2 Ma (concordant U –Pb zircon age; Yañez et al., 1991). We therefore conclude that the two principle phases of deformation recorded in the Tecomate Formation (DT1 and DT2) correlate with the second two deformational phases (DC2 and DC3) recorded in the Cosoltepec Formation (Fig. 11), thereby lending support to the conclusion of Ortega-Gutiérrez (1975) that the original relationship between the two Formations was an unconformity. DC1 and DC2 may also correlate with two low-grade deformational events described elsewhere in the Acatlán Complex by Weber et al. (1997), which are likewise separated by an episode of deposition. We further conclude that the Totoltepec pluton contains both the DT1 and DT2 fabrics of the Tecomate Formation (Fig. 11), DT1 having occurred perhaps during and shortly after crystallization in a dextrally transpressive shear regime. Hence, the Acatlán Complex witnessed three main phases of deformation (D1 – D3), the first of which predates the Tecomate Formation whereas the remaining two postdate the intrusion of the Totoltepec pluton. Of the three penetrative phases of deformation recognized in the Acatlán Complex, the first (D1) is associated with the development of pervasive quartz veins and an early greenschist facies schistosity (SC1), neither of which are present in the Tecomate Formation. D1 is therefore considered to predate the deposition of the Tecomate Formation, a conclusion supported by the reported occurrence of deformed Esperanza granitoids in the conglomerates of this formation (Yañez et al., 1991) and the abundance of feldspar in its psammitic lithologies. D1 is consequently interpreted to record the tectonic emplacement of the high-grade upper plate (Acateco subgroup) onto the Cosoltepec Formation, which is inferred to have occurred during the syntectonic emplacement of the Esperanza granitoids at ca. 440 Ma (Ortega-Gutiérrez et al., 1999). Evidence of the proposed westward vergence of this event, however, is not discernable within the Cosoltepec Formation, though a possible resolution of its kinematics may lie in the structural fabrics of the metagranitoids and the Xayacatlán Formation of the upper plate. Constraints on the timing of D2 and D3 rest with their relationship to the Totoltepec pluton, which, on the basis of its structural sequence and geometry, is considered to record both deformational events. If so, the age of D2 is tightly constrained because it can be no older than the pluton and no younger than the unmetamorphosed Early Permian (Leonardian) Matzitzi Formation, which overlies the pluton nonconformably (Silva-Romo and Mendoza-Rosales, 2000). D2 is consequently considered Early Permian in age, constrained to the narrow time interval between the pluton’s crystallization at 287 ^ 2 Ma (Yañez et al., 1991) and the Leonardian at 280 ^ 4– 269 ^ 7 Ma (Okulitch, 1999). Sedimentary rocks of the Matzitzi Formation also rest nonconformably on syntectonic granitoids dated at 274 ^ 11 Ma (U – Pb zircon; Elı́as-Herrera and Ortega-Gutiérrez, 2000) that stitch the contact between the Acatlán and Oaxacan Complexes, thereby indicating an Early Permian age for their final tectonic juxtaposition. The age of D3 cannot be defined with the same degree of certainty because it is not known if the Matzitzi Formation redbeds overlying the Totoltepec pluton are affected by these folds. A younger limit on the D3 structures in the Chazumba Formation is provided by the San Miguel felsic dikes, dated at 173 ^ 0.3 Ma (Ruiz-Castellanos, 1979), which cut across the D3 folds (unpublished data by the authors). However, the absence of any metamorphism in the Matzitzi Formation strongly suggests that its deposition postdates D3, the strong crenulation cleavage of which would appear to have developed under lower greenschist facies conditions. It is therefore considered likely that both D2 and D3 are of Early Permian (pre-Leonardian) age, as is suggested by a K/Ar age of 288 ^ 14 Ma reported from D3 sericite by Weber et al. (1997). If so, D2 and D3 may be the 522 J.R. Malone et al. / Journal of South American Earth Sciences 15 (2002) 511–524 Fig. 12. Permian Pangea reconstruction for North, Central, and South America (modified from Ross and Scotese (1988) and Pindell and Barrett (1990)) showing the transpressional deformation in the Acatlán Complex of southern Mexico in relation to the Late Paleozoic Ouachita orogen and an unnamed orogenic belt in northwestern South America. MSN ¼ MojaveSonora megashear; TMVB ¼ Trans-Mexican volcanic belt; present-day coastal areas dotted. product of a single period of deformation bracketed between 290 and 270 Ma and may reflect a gradual anticlockwise swing in the associated stresses. The extensive annealing of quartz fabrics in the Cosoltepec Formation suggests that much of the Acatlán Complex underwent a period of static metamorphism following the development of D3. Ortega-Gutiérrez (1993) attributed this static event to the development of a large thermal dome cored by the Magdalena migmatite. If this is correct, it is likely the product of a Jurassic (ca. 170 Ma) thermal pulse (Powell et al., 1999) that is known in this part of Mexico to be associated with the opening of the Gulf of Mexico (Salvador, 1991). 4. Discussion Of the three phases of penetrative deformation recorded in the Acatlán Complex, D2 is the most tightly constrained with respect to its timing and kinematics. The north –south dextral transpression and south-vergent thrusting recorded by this Early Permian event is approximately synchronous with the dextral transpression recorded along the north– south boundary between the Acatlán and Oaxacan Complexes at ca. 274 Ma (Elı́as-Herrera and Ortega-Gutiérrez, 2000). Permian deformation of unknown kinematics has also been recorded in northern Mexico (López et al., 2001), central Mexico (Ochoa-Camarillo, 1996), and Chiapas in southernmost Mexico (Sedlock et al., 1993). In most Permian reconstructions (Pindell, 1985; Ross and Scotese, 1988; Pindell and Barrett, 1990; Dickinson and Lawton, 2001), Mexico and Central America are bounded by Late Paleozoic orogens: the Ouachita orogenic belt bordering the southern Laurentian craton and an unnamed belt in the northern Andes bordering the Amazon craton (Fig. 12). These two belts show a transition from externides adjacent to the neighboring craton to internides that face each other. Yet they are unlikely to represent the sides of a single Ouachita-protoAndean collisional orogen because Late Paleozoic metamorphism in Mexico and Central America (areas that lie between the two belts) is of generally low-grade, in contrast to that of an orogenic root zone. The development of separate collisional belts may reflect the fact that much of Mexico and northern Central America is underlain by Precambrian basement, which likely represents a microcontinental block trapped between Laurentia and Amazonia during the final amalgamation of Pangea. The style of Permian deformation observed in Mexico may be classified as externide, which is consistent with two orogenic belts passing to the north and south of the microcontinent. In this scenario, the dextral transpressive deformation observed in the area east of Acatlán suggests that the final amalgamation of Pangea involved some northward movement of Mexican blocks relative to Pangea. Such a motion is consistent with the requirement in current Pangea reconstructions that Mexico and northern Central America were displaced to the northwest. This appears synchronous with subduction along the western margin of Pangea, which was responsible for the Permo-Triassic arc magmatism (exemplified by the Totoltepec pluton) that extended from the southwestern United States through Mexico and into northwestern South America (Torres et al., 1999). 5. Conclusions Three main phases of deformation (D1 – D3) are recognized in metasedimentary units of the Acatlán Complex east of Acatlán. D1 affects only the Cosoltepec Formation and is attributed to the Late Ordovician– Early Silurian Acatecan orogeny, during which the eclogitic mafic – ultramafic and metagranitoid rocks of the Xayacatlán/Esperanza plate are thought to have overthrust the lower-grade siliciclastic lithologies of the Cosoltepec and Chazumba Formations. D2 and D3 are considered to be of Early Permian age and affect the Cosoltepec Formation, the unconformably overlying Tecomate Formation, and the granitoid Totoltepec pluton dated at ca. 287 Ma. D2 involved south-vergent thrusting and north – south dextral shear and was likely responsible for the tectonic juxtapositioning of the Acatlán and Oaxacan Complexes. D3 involved significant east –west shortening and produced the megascopic folding that is responsible for the regional structure. No evidence is found in this part of the Acatlán Complex of a proposed Mixtecan orogeny during the Middle – Upper Devonian. Instead, the J.R. Malone et al. / Journal of South American Earth Sciences 15 (2002) 511–524 kinematics of its Early Permian deformation are consistent with the northward movement of Mexican crustal blocks required in current continental reconstructions of the final amalgamation of Pangea. Acknowledgements For his support and encouragement at all stages of this study, we are deeply indebted to Dr Fernando OrtegaGutiérrez. Funding for this project was provided by grants from the FIPSE North American Mobility in Higher Education Program (P116N9600018-99) and the Ohio University Baker Awards Committee (39-10-9668) to RDN, and from CONACyT (25795-T) and PAPIIT (IN136999) grants to JDK. Logistical support provided by the Instituto de Geologı́a at the Universidad Nacional Autónoma de México in Mexico City is gratefully acknowledged. David Fraser kindly provided unpublished structural data on the Totoltepec pluton. Constructive reviews by G. Draper and W. Frisch greatly improved the final manuscript. References Ayer, J.A., Davis, D.W., 1997. Neoarchean evolution of differing convergent margin assemblages in the Wabigoon Subprovince: geochemical and geochronological evidence from the Lake of the Wood greenstone belt, Superior Province, Northwestern Ontario. Precambrian Research 81, 155 –178. Dickinson, W.R., Lawton, T.F., 2001. Carboniferous to Cretaceous assembly and fragmentation of Mexico. Geological Society of America Bulletin 113, 1142–1160. Elı́as-Herrera, M., Ortega-Gutiérrez, F., 2000. Roots of the Caltepec Fault Zone, southern Mexico: Early Permian epidote-bearing anatexic granitoids. GEOS, Union Geophysica Mexicanan, 2nd Reunion Nacional de Ciencias de la Tierra, Resumenes y Programa 20 (3), 323. Esquivel-Macı́as, C., Ausich, W.I., Buitrón-Sanchez, B.E., Flores de Dios, A., 2000. Pennsylvanian and Mississippian pluricolumnal assemblages (Class Crinoidea) from southern Mexico and a new occurrence of a column with tetralobate lumen. Journal of Paleontology 74, 1187–1190. Jensen, L.S., 1976. A new cation plot for classifying subalkalic volcanic rocks. Ontario Division of Mines, Miscellaneous Paper 66. Keppie, J.D., Ramos, V.A., 1999. Odyssey of terranes in the Iapetus and Rheic Oceans during the Paleozoic. In: Keppie, J.D., Ramos, V.A. (Eds.), Laurentia–Gondwana Connections Before Pangea, Geological Society of America, Special Paper 336, pp. 267–276. López, R., Cameron, K.L., Norris, W.J., 2001. Evidence for Paleoproterozoic, Grenvillian, and Pan-African age Gondwanan crust beneath northwestern Mexico. Precambrian Research 107, 195–214. Malone, J.A., 2000. Kinematic and structural analysis of the Cosoltepec and Tecomate Formations, Acatlán Complex, southern Mexico. Unpublished MS Thesis, Ohio University, Athens, OH, USA, 103 pp. Ochoa-Camarillo, H., 1996. Geologı́a del anticlinoria de Huayacocotla en la región de Molango, Estado de Hidalgo. Unpublished MSc Thesis, Universidad Nacional Autónoma de México, Mexico City, Mexico, 91 pp. Okulitch, A.V., 1999. Geological time scale 1999. Geological Survey of 523 Canada, Open File 3040 National Earth Science Series, Geological Atlas—Revision. Ortega-Gutiérrez, F., 1975. The pre-Mesozoic geology of the Acatlán area, south Mexico. Unpublished PhD Thesis, University of Leeds, Leeds, UK, 166 pp. Ortega-Gutiérrez, F., 1978. Estratigrafia del Complejo Acatlan en la Mixteca Baja. Estados de Puebla y Oaxaca. Universidad Nacional Autónoma de México, Instituto de Geologı́a, Revista 2, 112–131. Ortega-Gutiérrez, F., 1993. Tectonostratigraphic analysis and significance of the Paleozoic Acatlán Complex of southern Mexico. In: OrtegaGutiérrez, F., Centeno-Garcı́a, E., Morán-Zereno, D., Gómez-Caballero, A. (Eds.), Terrane Geology of Southern Mexico, Universidad Nacional Autónoma de México, Instituto de Geologı́a, First CircumAtlantic Terrane Conference, Guanajuato, Mexico, Guidebook of Field Trip B, pp. 54–60. Ortega-Gutiérrez, F., Ruiz, J., Centeno-Garcı́a, E., 1995. Oaxaquia, a Proterozoic microcontinent accreted to North America during the Late Paleozoic. Geology 23, 1127–1130. Ortega-Gutiérrez, F., Elı́as-Herrera, M., Reyes-Salas, M., Macı́as-Romo, C., López, R., 1999. Late Ordovician–Early Silurian continental collisional orogeny in southern Mexico and its bearing on Gondwana– Laurentia connections. Geology 27, 719 –722. Pearce, J.A., Harris, N.B., Tindle, A.G., 1984. Trace element discrimination diagrams for the tectonic interpretation of granitic rocks. Journal of Petrology 25, 956–983. Pindell, J.L., 1985. Alleghenian reconstruction and subsequent evolution of the Gulf of Mexico, Bahamas, and Proto-Caribbean. Tectonics 4, 1– 39. Pindell, J.L., Barrett, S.F., 1990. Geological evolution of the Caribbean region. In: Dengo, G., Case, J.E. (Eds.), The Caribbean Region: Boulder, Colorado, Geological Society of America, Geology of North America H, pp. 405 –432. Powell, J.T., Nance, R.D., Keppie, J.D., Ortega-Gutiérrez, F., 1999. Tectonic significance of the Magdalena Migmatite, Acatlán Complex, Mexico. Geological Society of America, Abstracts with Programs 31 (7), 294. Robison, R., Pantoja-Alor, J., 1968. Tremadocian trilobites from Nochixtlan region, Oaxaca, Mexico. Journal of Paleontology 42, 767–800. Ross, M.I., Scotese, C.R., 1988. A hierarchical tectonic model of the Gulf of Mexico and Caribbean region. Tectonophysics 155, 139 –168. Ruiz-Castellanos, M., 1979. Rubidium–strontium geochronology of the Oaxaca and Acatlán metamorphic areas of southern Mexico. Unpublished PhD Thesis, University of Texas, Dallas, TX, USA, 178 pp. Salvador, A., 1991. Triassic– Jurassic. In: Salvador, A., (Ed.), The Gulf of Mexico Basin: Boulder, Colorado, Geological Society of America, Geology of North America J, pp. 131–180. Sánchez Zavala, J.L., Ortega-Gutiérrez, F., Elı́as Herrera, M., 2000. La orogenia Mixteca del Devonico del Complejo Acatlán, sur de Mexico. GEOS, Union Geophysica Mexicanan, 2nd Reunion Nacional de Ciencias de la Tierra, Resumenes y Programa 20 (3), 321–322. Sedlock, R.L., Ortega-Gutiérrez, F., Speed, R.C., 1993. Tectonostratigraphic terranes and tectonic evolution of Mexico. Geological Society of America, Special Paper 278, 143. Silva-Romo, G., Mendoza-Rosales, C., 2000. La unidad piedra hueca secuencia clastica Paleozoica (sur de puebla). GEOS, Union Geophysica Mexicanan, A.C., 2nd Reunion Nacional de Ciencias de la Tierra, Resumenes y Programa 20 (3), 325. Sun, S.S., 1982. Chemical composition and origin of the Earth’s primitive mantle. Geochimica et Cosmochimica Acta 46, 179–192. Sun, S.S., McDonough, W.F., 1989. Chemical and isotopic systematics of oceanic basalts: implications for mantle composition and processes. In: Saunders, A.D., Norry, M.J. (Eds.), Magmatism in the Ocean Basins, Geological Society London, Special Publication 42, pp. 313 – 345. Torres, R., Ruı́z, J., Patchett, P.J., Grajales-Nishimura, J.M., 1999. PermoTriassic continental arc in eastern Mexico; tectonic implications for reconstructions of southern North America. In: Bartolini, C., Wilson, J.L., Lawton, T.F. (Eds.), Mesozoic Sedimentary and Tectonic History 524 J.R. Malone et al. / Journal of South American Earth Sciences 15 (2002) 511–524 of North-central Mexico, Geological Society of America, Special Paper 340, pp. 191–196. Vechard, D., Flores de Dios, A., Buitrón, B.E., Grajales, M., 2000. Biostratigraphie par fusulines des calcaires Carbonifères et Permiens de San Salvador Patlanoaya (Peubla, Mexique). Geobios 33, 5 – 33. Weber, B., Meschede, M., Ratschbacher, L., Frisch, W., 1997. Structure and kinematic history of the Acatlán Complex in the Nuevos Horizontes-San Bernardo region, Puebla. Geofı́sica International 36, 63 –76. Yañez, P., Ruiz, J., Patchett, P.J., Ortega-Gutiérrez, F., Gehrels, G.E., 1991. Isotopic studies of the Acatlán Complex, southern Mexico: implications for Paleozoic North American tectonics. Geological Society of America Bulletin 103, 817– 828.