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Schematic geologic map of northern Guerrero, showing the location of the study area, sections sampled for paleomagnetism and magnetostratigraphy (closed stars), and localities (open stars) where Tertiary volcanic rocks have been dated, from Cerca-Martínez (2004). The inset shows the location of the map area and some of the principal structures in southern Mexico. TCsz marks the Tierra Colorada shear zone.
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El relleno Cenozoico de la cuenca the Tuzantlán-Copalillo, en el noreste de Guerrero, México, se asigna a dos unidades estratigráfi cas distintas. La primera unidad consiste de conglomerado de guijas y guijarros que gradúan hacia el este a areniscas gruesas conglomeráticas interestratifi cadas con areniscas y lodolitas. La secuencia de areniscas y...
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... original defi nition of this unit (Fries, 1956(Fries, , 1960) applies to unfossil- liferous limestone cobble and boulder conglomerates, sand- stones, mudstones and volcanic rocks, that Fries called the Balsas Group. No type locality has been formally defi ned, but the description of Fries (1960) suggests that is located in the outcrops along the Mezcala River east of Mezcala, Guerrero (Figure 1). Similarly, no formal formations were defi ned to compose the Balsas Group. ...
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... age of the Balsas Groups has thus been assumed to be Paleocene to upper Eocene. Linares and Urrutia-Fucugauchi (1981) reported a K-Ar age of 49 ± 3 Ma for the Tilzapotla rhyolite, and as- sumed Balsas strata in the area north of Taxco (Figure 1) to be lower Eocene, but those ages are no longer considered reliable due to the more coherent group of dates (38 to 32 Ma) reported later (Alaniz-Álvarez et al., 2002). Additional radiometric data are available for the Balsas Group in the Copalillo basin (Cerca-Martínez, 2004). ...
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... no suffi cient data are provided by Campa-Uranga et al.(2002), these data should be viewed with caution. Near Atenango del Río (Figure 1), Cerca-Martínez (2004) reports a date of 37.6 ± 0.3 Ma for andesites that appear to be intercalated with rocks considered by him correlative with the Balsas Group. Thus, available radiometric data restrict the Balsas Group to the Late Eocene and Early Oligocene. ...
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... and Lang (1997) suggested that Balsas strata accumulated in depres- sions formed by "basin and range" style extension. These authors typify this style of deformation and deposition in the Arcelia graben, in north central Guerrero, northeast of Altamirano City (Figure 1). In this area, deposition of Paleogene clastic strata (assigned to the lower Balsas Group) appears to be controlled by north to north-northwest trend- ing normal faults of pre-Oligocene age (Jansma and Lang, 1997). ...
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... Guerrero, an area that includes the Tuzantlán- Copalillo basin. Centeno-García et al.(2004) have shown that the use of Balsas Group for continental strata in the Arcelia region, south of Morelia (Figure 1), is inadequate; deposits characterized by limestone conglomerate and coarse sandstone facies can be shown biostratigraphically to be of Cretaceous to Paleocene(?) age. Centeno-García et al.(2004) proposed instead the use of the name Cutzamala Formation for these upper Cretaceous and Paleocene strata. ...
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... Cutzamala Formation contains abundant volcanic clasts; it may thus be partially coeval with the Tetelcingo Formation of northern Guerrero. Dávila-Alcocer (1974), Fitz-Díaz (2001), and Cerca- Martínez (2004) have identifi ed and mapped basins where Cenozoic strata accumulated in the region between Paso Morelos and Copalillo, in northeastern Guerrero ( Figure 1). The Copalillo basin ), the most eastward of the basins, is bordered to the east by the Papalutla fault and by uplifted metamorphic rocks of the Acatlán complex (Figure 1). ...
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... (1974), Fitz-Díaz (2001), and Cerca- Martínez (2004) have identifi ed and mapped basins where Cenozoic strata accumulated in the region between Paso Morelos and Copalillo, in northeastern Guerrero ( Figure 1). The Copalillo basin ), the most eastward of the basins, is bordered to the east by the Papalutla fault and by uplifted metamorphic rocks of the Acatlán complex (Figure 1). The Tuzantlán basin is bordered to the west by a domal structure characterized by thick exposures of carbonate rocks of the Morelos Formation (Figure 1). ...
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... Copalillo basin ), the most eastward of the basins, is bordered to the east by the Papalutla fault and by uplifted metamorphic rocks of the Acatlán complex (Figure 1). The Tuzantlán basin is bordered to the west by a domal structure characterized by thick exposures of carbonate rocks of the Morelos Formation (Figure 1). Outcrops of Oligocene volcanic rocks poorly defi ne the northern margins of the basins, and the basins are connected to the south with the upper Balsas-Mezcala river basin. ...
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... fi ll of the Tuzantlán-Copalillo basin along the western margin is characterized by polymictic, limestone boulder, matrix-supported conglomerate, well exposed near Paso Morelos (Figure 1), which overlies folded strata of the Mezcala Formation. Conglomerates are massive or poorly bedded, and the matrix is coarse to medium sandstone of red color. ...
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... workers (Dávila-Alcocer, 1974;Fitz-Díaz, 2001;Cerca-Martínez, 2004) mapped the fi ne-grained se- quence that overlies the Balsas conglomerate beds between Paso Morelos and Atenango del Río (Figure 3c) as the Oapan Formation, although lithologic similarities between rocks originally defi ned as the Oapan Formation and the rocks ex- posed near Tuzantlán are weak. The original defi nition of the Oapan Formation at San Agustín Oapan (Figure 1) applies to predominantly lacustrine claystone, gypsum, limestone, and green tuffaceous sandstone (Nájera-Garza, 1965). More typical throughout the Tuzantlán basin, there are exposures of greenish-gray sandstone interbedded with mudstone, also mapped as Oapan Formation (e.g., Fitz-Díaz, 2001). ...
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... Ma. The sequence is well exposed along the Amacuzac river valley dipping gently (~27°) to the north (Figures 1 and 3f). The correlation of the Zacango beds in the Tuzantlán-Copalillo with either the Oapan Formation or the Balsas Group is partly the motivation of this article. ...
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... facies as those typical of the Oapan Formation at its type locality are not abundant in the sec- tions that we studied, but Fitz-Díaz (2001) recognized a ho- rizon of lacustrine limestone in the Zacango beds along the Amacuzac valley (Figure 1). In an abstract, Campa-Uranga et al.(2002) reported palynomorphs of Eocene age from these deposits north of the village of Zacango, but assigned the rocks containing these fossils to the Oapan Formation, despite the fact that they underlie an (undated) ignimbrite. ...
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... section exposed along the highway north of the Mezcala river (Figure 3h), and overlying Cretaceous strata, is domi- nated by thick red sandstone facies and red mudstones with secondary gypsum. The highway section includes a 3 m thick pumice rich ignimbrite that we sampled for 40 Ar/ 39 Ar geochronology (Highway locality, Figure 1). The sequence that overlies the ignimbrite at this locality is lithologically similar to the sequence beneath it. ...
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... (=one bed) consist of 5 to 7 oriented samples drilled preferentially in medium to fi ne-grained sandstone beds, and spaced through the section at irregu- lar intervals averaging about 5 meter. Sampling locations are shown in Figure 1 and sampled sections are sketched in Figures 5a and 5b. As mentioned above, a 3 m thick, deposits, mapped as the Oapan Formation by previous workers, overlie this ignimbrite deposit. ...
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... general, rotations are linked to en-echelon geometries that involve strike-slip faults, distributed shear in a region bounded by strike-slip faults, fault drag, and to transpression or transtension. Some observations in the Guerrero-Morelos platform suggest that crustal block rota- tion has occurred at variable scales, such as the defl ection of Laramide structures apparent in Figure 1, north and south of Chilpancingo ( Cerca-Martínez et al., 2004), which is also supported by paleomagnetic data for Mesozoic strata (Molina-Garza et al., 2004). ...
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... lateral strike-slip motion has been proposed for several northwest to west-northwest trending structures in southern Mexico (e.g., Meschede et al., 1997;Martiny et al., 2000;Alaniz-Álvarez et al., 2002;Nieto-Samaniego et al., 2005), thus the geometries required to explain counterclock- wise rotation can be tested against available paleomagnetic data. A possible mechanism linked to transpression is illus- trated in Figure 10; here, sampling sites in southern Mexico are framed within a broad left lateral shear system ( Figure 10a), and Laramide structures that trend north-south are required to accommodate a small right lateral component in order to explain counterclockwise rotation (Figure 10b). Right-lateral faults have been reported by Nieto-Samaniego et al.(2005) in the northeast portion of the Guerrero-Morelos platform, and we observed similar structures, yet small, affecting the Amacuzac section. ...
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... lateral strike-slip motion has been proposed for several northwest to west-northwest trending structures in southern Mexico (e.g., Meschede et al., 1997;Martiny et al., 2000;Alaniz-Álvarez et al., 2002;Nieto-Samaniego et al., 2005), thus the geometries required to explain counterclock- wise rotation can be tested against available paleomagnetic data. A possible mechanism linked to transpression is illus- trated in Figure 10; here, sampling sites in southern Mexico are framed within a broad left lateral shear system ( Figure 10a), and Laramide structures that trend north-south are required to accommodate a small right lateral component in order to explain counterclockwise rotation (Figure 10b). Right-lateral faults have been reported by Nieto-Samaniego et al.(2005) in the northeast portion of the Guerrero-Morelos platform, and we observed similar structures, yet small, affecting the Amacuzac section. ...
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... lateral strike-slip motion has been proposed for several northwest to west-northwest trending structures in southern Mexico (e.g., Meschede et al., 1997;Martiny et al., 2000;Alaniz-Álvarez et al., 2002;Nieto-Samaniego et al., 2005), thus the geometries required to explain counterclock- wise rotation can be tested against available paleomagnetic data. A possible mechanism linked to transpression is illus- trated in Figure 10; here, sampling sites in southern Mexico are framed within a broad left lateral shear system ( Figure 10a), and Laramide structures that trend north-south are required to accommodate a small right lateral component in order to explain counterclockwise rotation (Figure 10b). Right-lateral faults have been reported by Nieto-Samaniego et al.(2005) in the northeast portion of the Guerrero-Morelos platform, and we observed similar structures, yet small, affecting the Amacuzac section. ...
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... faults have been reported by Nieto-Samaniego et al.(2005) in the northeast portion of the Guerrero-Morelos platform, and we observed similar structures, yet small, affecting the Amacuzac section. Alternatively, a greater amount of shortening must be accommodated by the thrust faults in the southern part of the rotated domain ( Figure 10c). Greater amount of shortening in the southern part of the platform is rather evident (Cerca-Martínez, personal communication 2005). ...
Citations
... En la región comprendida entre Taxco y Chilpancingo, Guerrero, que incluye la localidad tipo del GB, se encuentra una gran diversidad de sucesiones referidas en la literatura como formaciones Tetelcingo, Agua de Obispo, Papagayo, Alquitrán, Oapan, Tepetlapa, Huajintlán y Capas Zacango (Fríes, 1960;De Cserna, 1965;Nájera-Garza, 1965;Morán-Zenteno et al., 2007). En esta región, las edades documentadas para estas unidades varían desde el Cretácico Tardío (De Cserna, 1983;Benammi et al., 2005;Cerca et al., 2007) hasta el Eoceno Tardío (Molina-Garza y Ortega-Rivera, 2006;Morán-Zenteno et al., 2007;Meza-García et al., 2010). ...
Los depósitos continentales del Paleógeno (Grupo Balsas) del sur de México han sido poco estudiados y se desconoce en gran medida su origen, edad, naturaleza y ambiente tectónico de formación; elementos cruciales para comprender la relación del sur de México con Centroamérica y América del Sur. En este sentido, se realizó un estudio en el que se reportan por primera vez datos de estratigrafía, geoquímica y geocronología U-Pb de las rocas volcánicas de la Formación Tetelcingo del área de Chilpancingo-Tixtla, Guerrero. La Formación Tetelcingo es una secuencia volcano-sedimentaria cuyas rocas están depositadas discordantemente sobre rocas cretácicas (formaciones Morelos y Mezcala). La geoquímica de las rocas volcánicas indica una variación composicional de andesita a dacita. Todas las muestras presentan enriquecimiento en elementos litófilos de radio iónico grande (LILE) y en tierras raras ligeras (LREE), con respecto a los elementos de alto potencial iónico (HFSE) y tierras raras pesadas (HREE). Además, exhiben anomalías negativas en Nb, Ta, P y Ti; positivas en Ba, Sr y K; y escasas a inexistentes anomalías en Eu (0.69-1.04), así como concentraciones altas de Sr y bajas en Yb, Y, Ni y Cr. El emplazamiento de las rocas volcánicas estudiadas ocurrió durante dos ciclos de vulcanismo sucesivos; el primer ciclo inició entre 65.21 ± 0.97 Ma (zircón) y 66.7 ± 2.9 Ma (esfena), mientras que el segundo entre 65.27 ± 1.9 Ma (zircón) y 64.9 ± 4.4 Ma (esfena) U-Pb. Las rocas volcánicas de la Formación Tetelcingo muestran características geoquímicas similares a las adakitas formadas en un ambiente de arco continental. El emplazamiento de las rocas volcánicas ocurrió en el límite Cretácico-Paleógeno, en un contexto geodinámico con subdución activa y subsecuente transtensión y exhumación relacionada al desprendimiento y migración del bloque Chortís hacia el sureste.
... • , Inc = 34.3 • ; Molina- Garza & Ortega-Rivera 2006) in the Guerrero-Morelos platform in nearby sites. This suggests that a regional remagnetization has not affected Zicapa strata, as it appears to have affected shallow marine limestones of the Morelos Formation (Molina- Garza et al. 2003). ...
Poles from continental redbeds are a large fraction of the world's palaeomagnetic database. Nonetheless, the time of acquisition and origin of the remanent magnetization of redbeds has been long debated. We report palaeomagnetic data, rock magnetic data, and microscope observations for Lower Cretaceous redbeds in southern Mexico. These data allow us to discriminate between the hysteresis properties of remanent magnetizations of detrital and chemical origin, and to establish the early origin of a chemical remanence. Red sandstones of the Zicapa Formation contain a multi-component remanence revealed by thermal demagnetization, and consisting of three stable components with partially overlapping laboratory unblocking-temperatures of < 250°C, ∼300°C to ∼500°C, and > 600°C, (low, intermediate, and high temperature, respectively). They are interpreted as a viscous remanence residing in detrital magnetite, a chemical remanence residing in authigenic hematite, and a depositional remanence residing in detrital hematite, respectively. The low-temperature component is nearly parallel to the recent dipole field. The tilt-corrected overall site means of the intermediate (chemical) and high temperature (depositional) components are indistinguishable (Dec = 282.0°, Inc = 12.4°, k = 13.33, α95 = 10.1°, N = 17, for the intermediate temperature; and Dec = 272.5°, Inc = 16.5°, k = 14.04, α95 = 11, N = 14, for the high temperature). Elongation/inclination analysis suggests that depositional and chemical components require applying a f = factor of approximately 0.4. Both of these components define a magnetic polarity zonation, but the polarity of the chemical and detrital components may or may not be the same. The chemical remanence coincides, more often than not, with the polarity of the depositional remanence of the overlying (younger) strata, suggesting a delay in remanence acquisition of tens to a few hundred ka for the chemical component. Pigmentary and detrital haematite were recognized with microscopic observations. The particle size of haematite ranges from approximately 10 to 300 μm for detrital haematite (martite, specularite, and laterite), and from ca. 0.2 to 1 μm for pigmentary haematite flakes. The IRM of these rocks can be modeled with components of low coercivity (H1/2 between 5–10 mT interpreted as detrital magnetite), and components of a wide coercivity range (prevailing H1/2 from ∼400 to 600 mT interpreted as haematite). Hysteresis ratios show a systematic correlation with demagnetization behavior, with lower Hcr/Hc values and higher Mrs/Ms values for samples with a dominant chemical component, than form samples with a significant ( > 40%) depositional component.
... The top of the Paleocene-Eocene hiatus is constrained by cobble and boulder conglomerates, sandstones, mudstones and volcanic rocks included in the Balsas Group (Fries, 1960) (BG; Fig. 8), deposited by alluvial fans and fluvial systems over several basins in the area of the Guerrero-Morelos platform (e.g., Molina- Garza and Ortega-Rivera, 2006;Cerca et al., 2007;Centeno-García et al., 2008). In the Oaxaca terrane similar strata are represented by the Tamazulapam and Yanhuitlán Formations (Ferrusquía-Villafranca, 1976) (10-12; Figs. ...
... Es probable que para ese tiempo, la futura cuenca de México fuera una cuenca baja, localizándose a una menor altura, a diferencia de la cuenca moderna que esta a > de 2000 msnm resultado del levantamiento asociado al vulcanismo. Además, la composición litológica de la muestra más profunda (2063 m) del pozo TX-I se caracteriza por un conglomerado calcáreo que puede ser contemporáneo al Grupo Balsas de edad Eoceno (Molina-Garza y Ortega-Rivera, 2006). Ambos hechos sugieren que la microflora de esta sección del pozo TX-I pudiera tener una edad del Eoceno tardío. ...
We present the palynological record of Texcoco-I (2065 m) and San Lorenzo Tezonco (2008 m) deep wells from the Basin of Mexico. The Pliocene-Pleistocene assemblages of both sequences are characterized by temperate taxa Pinus, Quercus, Liquidambar and Picea. Microfossils of Pediastrum and Botryococcus provide evidence that the basin hosted a lake. Although temperate taxa is present in the Oligocene Texcoco-I sediments the general pollen assemblage is distinct, with Bursera, Carya, Liquidambar and Myrtaceae. The absence of temperate elements along with the presence of anhydrite the late Eocene environment.
... Es probable que para ese tiempo, la futura cuenca de México fuera una cuenca baja, localizándose a una menor altura, a diferencia de la cuenca moderna que esta a > de 2000 msnm resultado del levantamiento asociado al vulcanismo. Además, la composición litológica de la muestra más profunda (2063 m) del pozo TX-I se caracteriza por un conglomerado calcáreo que puede ser contemporáneo al Grupo Balsas de edad Eoceno (Molina-Garza y Rivera, 2006). del pozo TX-I pudiera tener una edad del Eoceno tardío. ...
We present the palynological record of Texcoco-I (2065 m) and San Lorenzo Tezonco (2008 m) deep wells from the Basin of Mexico. The Pliocene-Pleistocene assemblages of both sequences are characterized by temperate taxa Pinus, Quercus, Liquidambar and Picea. Microfossils of Pediastrum and Botryococcus provide evidence that the basin hosted a lake. Although temperate taxa is present in the Oligocene Texcoco-I sediments the general pollen assemblage is distinct, with Bursera, Carya, Liquidambar and Myrtaceae. The absence of temperate elements along with the presence of anhydrite the late Eocene environment.
... The volcanic succession overlies folded limestone beds of the Cretaceous Morelos Formation, evaporites of the Huitzuco Formation, fluvial deposits of the Palaeocene-Eocene Balsas Group, and distal pyroclastic flows of the neighbouring Tilzapotla caldera (Figures 3 and 4;Fries 1960;Morán-Zenteno et al. 2004, 2007b. The fact that the upper Balsas beds are intercalated with volcanic tuffs and that the lower part of the Maravillas ignimbrite of the HVF (which will be described later) contains intercalations of fluvial deposits similar to those of the Balsas Group are suggestive of the transitional relationship between the pre-volcanic terrestrial deposits and the volcanic succession of the HVF; an analogous transitional relationship has been also documented in adjacent areas (Molina-Garza and Ortega-Rivera 2006;Morán-Zenteno et al. 2007b). ...
... The episode of voluminous siliceous magmatism in the study area occurred between ∼33.4 and 31.5 Ma and produced the Maravillas ignimbrite and the Agua Fría dacite, which are distributed in the eastern and central sectors of the HVF with a minimum exposed volume of ∼260 km 3 . The presence of coeval plutonic bodies such as the Chiautla granodiorite (Cerca et al. 2007; this study) and ignimbrite successions (33.01 ± 0.4 Ma; Molina-Garza and Ortega-Rivera 2006) in the area surrounding the study region indicate that the siliceous episode extended beyond the limits of the HVF. ...
The Huautla volcanic field (HVF), in the Sierra Madre del Sur (SMS), is part of an extensive record of Palaeogene magmatism reflecting subduction of the Farallon plate along the western edge of North America. Igneous activity resulting from Farallon subduction is also exposed to the north, in the Sierra Madre Occidental (SMO) and Mesa Central (MC) provinces. We present the results of a stratigraphic and K–Ar, Ar–Ar, and U–Pb geochronological study of the Huautla volcanic successions, in order to refine our knowledge on the petrologic and temporal evolution of the northern SMS and gain insights on magmatic–tectonic contrasts between the SMS and the SMO–MC provinces. The HVF is made up of lava flows and pyroclastic successions that overlie marine Cretaceous sequences and post-orogenic continental deposits of Palaeogene age. In the study area, the main Oligocene succession is pre-dated by the 36.7 million years its caldera west of the Sierra de Huautla. The HVF succession ranges in age from ∼33.6 to 28.1 Ma and comprises a lower group of andesitic–dacitic lava flows, an intermediate sequence of ignimbrites and dacitic lavas, and an upper group of andesitic units. The silicic succession comprises a crystal-poor ignimbrite unit (i.e. the Maravillas ignimbrite; 31.4 ± 0.6, 32.0 ± 0.4 Ma; ∼260 km3), overlain by a thick succession of dacitic lavas (i.e. the Agua Fría dacite; 30.5 ± 1.9, 31.0 ± 1.1 Ma). Integration of the new stratigraphic and geochronological data with prior information from other explosive centres of the north-central SMS allows us to constrain the temporal evolution of a silicic flare-up episode, indicating that it occurred between 37–32 Ma; it consisted of three major ignimbrite pulses at ∼36.5, ∼34.5, and ∼33–32 Ma and probably resulted from a progressive, mantle flux-driven thermomechanical maturation of the continental crust, as suggested in the HVF by the transition from andesitic to voluminous siliceous volcanism. The information now available for the north-central sector of the SMS also allows recognition of differences between the temporal and spatial evolution of magmatism in this region, and of that documented in the southern SMO and MC provinces, suggesting that such contrasts are probably related to local differences in configuration of the subduction system. At ∼28 Ma, the MC and southern SMO provinces experienced a trenchward migration of volcanism, associated with slab rollback; on the other hand, the broad, more stable distribution of Oligocene magmatism in the central and north oceanic plate was subducting at a low angle.
... Para el Cenozoico, las diferencias en la sedimentación en el área de estudio no son tan obvias. Los depósitos más viejos corresponden a conglomerados calcáreos depositados en cuencas sedimentarias sobre el Mesozoico (Formación Yanhuitlán, conglomerado Tecomatlán, Formación Tamazulapam) y son correlacionables con los conglomerados de la base del Grupo Balsas del sur de México (Molina-Garza et al., 2006;Morán-Zenteno et al., 2007). El volcanismo es diferente a ambos lados de la zona de falla de Caltepec. ...
Acatlán and Oaxaca complexes in contact. In the Tamazulapam region, both complexes crop out but the contact is covered by Mesozoic and Cenozoic rocks. This paper presents the detailed stratigraphy of the area and a structural analysis in order to establish if the Caltepec fault has exerted a structural control on the Cenozoic deformation. The structural analysis is diffi cult because the faults show a multiple fault pattern with complex kinematics. In order to resolve the kinematics of this region, we propose the use of Cinematic Compatibility Diagrams (CCD), which illustrate the whole possible movement of faults under a unique stress tensor. The CCD show that in the western side of the fault, where the Acatlan Complex constitutes the basement, the Cenozoic deformation occurred in two tectonic events, the fi rst one under a tectonic transcurrent regime with a maximum shortening towards NE-SW during the late Eocene-Early Oligocene, followed by the second event, extensional, with maximum extension in the same direction, which occurred during late Oligocene (between 26 and 29 Ma). The direction and regime type of these events correspond with previous deformational events recorded in other areas in southern Mexico. In contrast, in the eastern side, where the Oaxaca Complex constitutes the basement, the deformation is heterogeneous, probably generated by the synchronous movement of the Oaxaca and the Tamazulapam faults above a detachment formed partially by anhydrites. The differences in the deformation styles on both sides of the southern extension of the Caltepec fault shows that, in this case, the basement fault infl uenced the deformation style of the Cenozoic units La región de Tamazulapam se encuentra localizada en la continuación al sur de la falla de Caltepec, que pone en contacto a los complejos Oaxaqueño y Acatlán. En Tamazulapam afl oran ambos complejos pero su contacto está cubierto por rocas mesozoicas y cenozoicas. En este trabajo se estudia la estratigrafía y las estructuras de esta región para conocer si la presencia de la falla de basamento infl uyó en la deformación cenozoica. El análisis estructural mostró que las fallas de la región estudiada tienen orientaciones en al menos cuatro direcciones preferenciales y que su cinemática, en conjunto, es compleja. Para entender la deformación cenozoica se propone en este trabajo el uso de los Diagramas de Compatibilidad Cinemática, los cuales defi nen el rango de direcciones de deslizamiento que puede ocurrir sobre los planos de fallas bajo un sistema de esfuerzos determinado. El análisis de los Diagramas de Compatibilidad Cinemática indica que del lado poniente de la falla, donde subyace el Complejo Acatlán, la deformación se liberó en dos eventos tectónicos fácilmente diferenciables: un evento transcurrente con compresión máxima al NE-SW activado entre el Eoceno tardío y el Oligoceno temprano (entre 35.9 y 29 Ma) y un segundo evento, de extensión principalmente, en el Oligoceno tardío (entre 26 y 29 Ma) con dirección máxima de extensión al NE-SW, lo cual es consistente con las fases propuestas a nivel regional. Del lado oriente, donde subyace el Complejo Oaxaqueño, la deformación no tiene la simetría ortorrómbica homogénea típica de la deformación generada por un tensor de esfuerzos, y nuestras observaciones sugieren que la deformación es heterogénea, quizá generada por el movimiento sincrónico de las fallas de Oaxaca y de Tamazulapam en un bloque parcialmente infrayacido por una capa de anhidritas. La diferencia en el estilo de deformación de la cobertura a ambos lados de la falla de Caltepec demuestra que, en este caso, la falla de basamento infl uye en la deformación de la cobertura.
... Para el Cenozoico, las diferencias en la sedimentación en el área de estudio no son tan obvias. Los depósitos más viejos corresponden a conglomerados calcáreos depositados en cuencas sedimentarias sobre el Mesozoico (Formación Yanhuitlán, conglomerado Tecomatlán, Formación Tamazulapam) y son correlacionables con los conglomerados de la base del Grupo Balsas del sur de México (Molina-Garza et al., 2006;Morán-Zenteno et al., 2007). El volcanismo es diferente a ambos lados de la zona de falla de Caltepec. ...
The Tamazulapam region is located in the southern extension of the Caltepec fault, which places the Acatlán and Oaxaca complexes in contact. In the Tamazulapam region, both complexes crop out but the contact is covered by Mesozoic and Cenozoic rocks. This paper presents the detailed stratigraphy of the area and a structural analysis in order to establish if the Caltepec fault has exerted a structural control on the Cenozoic deformation. The structural analysis is difficult because the faults show a multiple fault pattern with complex kinematics. In order to resolve the kinematics of this region, we propose the use of Cinematic Compatibility Diagrams (CCD), which illustrate the whole possible movement of faults under a unique stress tensor. The CCD show that in the western side of the fault, where the Acatlan Complex constitutes the basement, the Cenozoic deformation occurred in two tectonic events, the first one under a tectonic transcurrent regime with a maximum shortening towards NE-SW during the late Eocene-Early Oligocene, followed by the second event, extensional, with maximum extension in the same direction, which occurred during late Oligocene (between 26 and 29 Ma). The direction and regime type of these events correspond with previous deformational events recorded in other areas in southern Mexico. In contrast, in the eastern side, where the Oaxaca Complex constitutes the basement, the deformation is heterogeneous, probably generated by the synchronous movement of the Oaxaca and the Tamazulapam faults above a detachment formed partially by anhydrites. The differences in the deformation styles on both sides of the southern extension of the Caltepec fault shows that, in this case, the basement fault influenced the deformation style of the Cenozoic units.
... The Morelos Platform, although is not considered a terrane by itself, the lack of exposed basement rocks in the region, and the major faults that delimit the province, make the boundary between the Mixteco and Guerrero terranes ambiguous (e.g., Campa and Coney, 1983;Sedlock et al., 1993). Nevertheless, the region intersects a large part of the central TMVB, and although its surface geology is well known (Fries, 1960;Hernández-Romano et al., 1997;Molina-Garza and Ortega-Rivera, 2006) the nature of the buried crust under the platform supracrustal strata is only poorly characterized as probably Precambrian by the presence of high-grade metapelitic xenoliths in Neogene volcanic rocks at Chalcatzingo, Morelos (Gómez-Tuena et al., 2008) and by isotopic geochemical inference (e.g., Levresse et al., 2007). ...
With the main objective of further constraining models that debate how and where magmas are generated in the Mexican subduction factory, how they ascend through the overlying viscous layers, and how and where they interact with the traversed crust to produce the diversity of the magmas that compose the system, the nature of the lower crust and its immediate surroundings under the volcanic front of the Trans-Mexican Volcanic Belt (TMVB), as well as its fore-arc in southern Mexico, are analyzed and integrally characterized in this work. The study is mainly based on the analysis of geophysical and geological existing and new data, as well as on our new data obtained from deep-seated xenoliths. Taken as that part of the crust located from the Moho to a depth of 20-25 km below the surface, it is concluded from our analysis that all of the lower crust in the study area should be in the granulite facies, if geophysical modeling correctly predicted temperatures of 700-800ºC for its base, and a crustal thickness varying between 40 and 45 km. Xenoliths and surface geology information, when integrated to tectonic modeling, support the notion that most of the lower crust under the eastern and central sectors of the TMVB should be of Mesoproterozoic age, and tectonically overlapped by Paleozoic and Mesozoic juvenile crust in the central sector and its corresponding fore-arc region. It is also concluded in this work, in agreement with recent seismological high resolution studies, that the apparent differences existing between geophysical modeling and the P-T conditions required to generate the primary andesitic, dacitic and adakitic magmas that characterize the TMVB in the study area, may be resolved if the angle of the slab that extends northward and beyond the fl at segment is increased substantially, thus creating optimal thermal and rheological conditions in a mantle wedge under the volcanic front much thicker than currently accepted. These conditions would increase the temperature of the entire subduction system to values that would permit the generation of such primary magmas by partial melting of the basaltic part of the subducting slab, the mantle wedge, and the mafi c lower crust.
... The Morelos Platform, although is not considered a terrane by itself, the lack of exposed basement rocks in the region, and the major faults that delimit the province, make the boundary between the Mixteco and Guerrero terranes ambiguous (e.g., Campa and Coney, 1983;Sedlock et al., 1993). Nevertheless, the region intersects a large part of the central TMVB, and although its surface geology is well known (Fries, 1960;Hernández-Romano et al., 1997;Molina-Garza and Ortega-Rivera, 2006) the nature of the buried crust under the platform supracrustal strata is only poorly characterized as probably Precambrian by the presence of high-grade metapelitic xenoliths in Neogene volcanic rocks at Chalcatzingo, Morelos (Gómez-Tuena et al., 2008) and by isotopic geochemical inference (e.g., Levresse et al., 2007). ...
With the main objective of further constraining models that debate how and where magmas are generated in the Mexican subduction factory, how they ascend through the overlying viscous layers, and how and where they interact with the traversed crust to produce the diversity of the magmas that compose the system, the nature of the lower crust and its immediate surroundings under the volcanic front of the TransMexican Volcanic Belt (TMVB), as well as its forearc in southern Mexico, are analyzed and integrally characterized in this work. The study is mainly based on the analysis of geophysical and geological existing and new data, as well as on our new data obtained from deepseated xenoliths. Taken as that part of the crust located from the Moho to a depth of 2025 km below the surface, it is concluded from our analysis that all of the lower crust in the study area should be in the granulite fades, if geophysical modeling correctly predicted temperatures of 700800°C for its base, and a crustal thickness varying between 40 and 45 km. Xenoliths and surface geology information, when integrated to tectonic modeling, support the notion that most of the lower crust under the eastern and central sectors of the TMVB should be of Mesoproterozoic age, and tectonically overlapped by Paleozoic andMesozoic juvenile crust in the central sector and its corresponding forearc region. It is also concluded in this work, in agreement with recent seismological high resolution studies, that the apparent differences existing between geophysical modeling and the PT conditions required to generate the primary andesitic, dacitic and adakitic magmas that characterize the TMVB in the study area, may be resolved if the angle of the slab that extends northward and beyond the flat segment is increased substantially, thus creating optimal thermal and rheological conditions in a mantle wedge under the volcanic front much thicker than currently accepted. These conditions would increase the temperature of the entire subduction system to values that would permit the generation of such primary magmas by partial melting of the basaltic part of the subducting slab, the mantle wedge, and the mafic lower crust.
