Post-Laramide and Pre-Basin and Range

Tectonophysics 471 (2009) 136–152

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Post-Laramide and pre-Basin and Range deformation and implications for Paleogene (55–25 Ma) volcanism in central Mexico: A geological basis for a volcano-tectonic stress model

Margarito Tristán-González a,b,1, Gerardo J. Aguirre-Díaz b,⁎, Guillermo Labarthe-Hernández a, José Ramón Torres-Hernández a, Hervé Bellon c a Instituto de Geología/DES Ingeniería, Universidad Autónoma de San Luis Potosí, Av. Dr. Manuel Nava 5, Zona Universitaria, 78240, San Luis Potosí, Mexico b Centro de Geociencias, Universidad Nacional Autónoma de México, Campus UNAM-Juriquilla, Querétaro, Querétaro, 76230, Mexico c UMR 6538, Domaines Océaniques, IUEM, Université de Bretagne Occidentale, 6, Av. Le Gorgeu, C.S. 93837, F-29238 Brest Cedex 3, France article info abstract

Article history: At central-eastern Mexico, in the Mesa Central province, there are several ranges that were formed after the Received 3 May 2008 K/T Laramide compression but before the Basin and Range peak extensional episodes at middle–late Accepted 23 December 2008 Oligocene. Two important volcano-tectonic events happened during this time interval, 1) uplift of crustal Available online 13 January 2009 blocks exhuming the Triassic–Jurassic metamorphic sequence and formation of basins that were filled with red beds and volcanic sequences, and 2) normal faulting and tilting to the NE of these blocks and Keywords: fanglomerate filling of graben and half-graben structures. The first event, from late Paleocene to early Eocene, Volcano-tectonics – Paleocene–Oligocene was related to NNE and NNW oriented dextral strike-slip faults. These faults were combined with NW SE en Basin and Range extension echelon faulting in these blocks through which plutonism and volcanism occurred. The second event lasted Sierra Madre Occidental volcanism from early Oligocene to early Miocene and coincided with Basin and Range extension. Intense volcanic Mexico activity occurred synchronously with the newly-formed or reactivated old fault systems, producing thick sequences of silicic pyroclastic rocks and large domes. Volcano-tectonic peaks occurred in three main episodes during the middle–late Oligocene in this part of Mexico, at about 32–30 Ma, 30–28 Ma, and 26– 25 Ma. The objectives of this work is to summarize the volcano-tectonic events that occurred after the end of the Laramide orogeny and before the peak episodes of Basin and Range faulting and Sierra Madre Occidental Oligocene volcanism, and to discuss the influence of these events on the following Oligocene–Miocene volcano-tectonic peak episodes that formed the voluminous silicic volcanism in the Mesa Central, and hence, in the Sierra Madre Occidental. A model based upon geological observations summarizes the volcanic- tectonic evolution of this part of Mexico from the late Paleocene to the Early Miocene. © 2009 Elsevier B.V. All rights reserved.

1. Introduction McDowell, 1991; Ferarri et al., 2005). According to Aguirre-Díaz and Labarthe-Hernández (2003) these two geologic provinces overlap in An elevated plateau in central Mexico, with an average elevation of space and time throughout their extent across Mexico, including Mesa about 2000 m above sea level (Fig. 1), includes some of the best Central. The eastern border of Mesa Central is marked by the Sierra mapped Tertiary volcanic areas of Mexico. It is known as Mesa Central, Madre Oriental folded belt (Fig. 2), which is composed of Mesozoic which is described as part of the southern Basin and Range marine sediments deformed during the Laramide orogeny at late extensional province (Henry and Aranda-Gómez, 1992; Stewart, Cretaceous–early Paleocene (De Cserna, 1956; Tardy et al., 1975; 1998; Nieto-Samaniego et al., 1999; Aranda-Gómez et al., 2000; Padilla, 1985; Chávez-Cabello et al., 2004 –Fig. 2). Other ranges, fault- Nieto-Samaniego et al., 2005) and the Sierra Madre Occidental bounded and with Triassic metamorphosed basement cores, can be volcanic province (McDowell and Clabaugh, 1979; Aguirre-Díaz and observed near this eastern margin and towards the interior of the Mesa Central (Fig. 2). These ranges have been interpreted also as caused by the Laramide orogeny (Martínez-Pérez, 1972; Aguillón- Robles- Tristán-González, 1981; Labarthe-Hernández et al., 1982a,b; ⁎ Corresponding author. Gallo-Padilla et al., 1993; Gómez-Luna et al., 1998), but our data E-mail addresses: [email protected] (M. Tristán-González), [email protected] (G.J. Aguirre-Díaz). presented here indicates that they were apparently formed after 1 Tel.: +52 444 8171039. Laramide orogeny.

Fig. 1. Index map of the Sierra Madre Occidental and Mesa Central provinces indicating the location of the study area.

Most of the studies in this area have focused either on the Laramide observations, which can be used as a case study to test experimental or compression-related structures and Mesozoic stratigraphy or on the mathematical volcano-tectonic stress models of continental crust that Basin and Range extension-related structures and Oligocene Sierra was first submitted to an intense compressive stress regime (Laramide Madre Occidental volcanism. In contrast, little is known on the fault- orogeny), then to a crustal relaxation and trans-tension stress period, bounded structures with Triassic and Jurassic cores mentioned above and finally to an intense extensional regime (Basin and Range ex- because the available works have been published in local internal tension); all of these occurring at the final stages of a long-lasting geological reports (e.g., Labarthe-Hernández et al., 1982a,b, 1995; continental-margin subduction regime (Aguirre-Díaz and McDowell, Tristán-González and Torres-Hernández, 1992; Tristán-González et al., 1991). Similar situations have been reported in other places and dif- 1995). From these reports, it can be inferred that important volcano- ferent geologic times with the result of an intense period of rhyolitic– tectonic events occurred between the late Paleocene and the late andesitic volcanism in the form of domes and/or stratovolcanoes and Oligocene that developed these fault-bounded ranges and some fault- ignimbrites; for instance, at the Catalan Pyrenees, where Permian– bounded basins as well, synchronously with plutonism and volcanism. Carboniferous ignimbrites are apparently related to calderas influ- The main purpose of this study is to summarize the volcano- enced by the strike-slip tectonics (Martí, 1991), or at the Taupo tectonic events that occurred between the end of the Laramide Volcanic Zone, where silicic caldera volcanism and andesitic strato- orogeny and the initiation of Basin and Range faulting and Sierra volcanoes can be associated with rift-extension and trans-tension Madre Occidental Oligocene volcanism. We discuss the influence of respectively (Spinks et al., 2004). Using the particular case of the Sierra these events on the following Oligocene–Miocene volcano-tectonic Madre Occidental, Aguirre-Díaz et al. (2007, 2008) have coined the peak episodes that formed the voluminous silicic volcanism in the term of graben calderas for these types of volcano-tectonic caldera Mesa Central, and hence, in the Sierra Madre Occidental. In order to structures. achieve these goals, the stratigraphy, geochronology and structure of three representative areas of the Mesa Central are briefly described, 1) 2. Tectonic framework La Ballena-Peñón Blanco range, 2) Las Minas range and 3), Ahualulco basin (Fig. 2). The first and second cases represent fault-bounded The northern, northeastern and eastern limits of the Mesa Central ranges with Triassic and Lower Cretaceous basement cores, respec- are formed by the ranges of the Sierra Madre Oriental folded belt tively, and the third one, a listric-fault basin that initiated as a pull- (Fig. 3). Several studies have been undertaken in this belt to apart basin filled with a volcano-clastic sequence. understand the tectonic shortening at this area during the Upper This work provides a volcano-tectonic evolution model of a large Cretaceous–Early Tertiary, and in particular, on the portion where the area in central Mexico (Figs. 1, 2), based upon rigorous geological belt makes a turn to the west at the Monterrey salient or “Curvatura de 138 M. Tristán-González et al. / Tectonophysics 471 (2009) 136–152

Fig. 2. Digital elevation model showing the main tectonic structures in the eastern and southeastern part of Mesa Central. 1—Sierra de Catorce, 2—Sierra de Coronado, 3—Sierra de Charcas, 4—Sierra Santa Catarina, 5—Sierra de Guanamé, 6—Sierra Las Minas, 7—Sierra La Ballena-Peñón Blanco, 8—Sierra de Zacatecas; A—Ahualulco Basin, B—Coronado Basin; C— Matehuala-El Huizache Basin; D—Villa de Arista Basin; E—Peotillos Basin; F—Aguascalientes Graben; G—Villa de Reyes Graben; SLPVF—San Luis Potosí Volcanic Field; MC—Monterrey Curvature.

Monterrey” (Fig. 3, De Cserna, 1956; Tardy et al., 1975; Padilla, 1985; southward from the Monterrey salient and forms the eastern limit of Chávez-Cabello et al., 2004). This deformation is characterized by the Mesa Central. From this eastern boundary and towards the inner folding and thrusting of the upper crust with an ENE transport parts of the Mesa Central the folded belt changes to fault-bounded direction, as well as by transcurrent faulting associated to these ranges with NNE-trending and NW-trending patterns, some of which displacements. The Monterrey salient has been interpreted as the (mostly the NNE-trending) expose Triassic metamorphosed basement result of an orthogonal ﬂexural folding that occurred in the late stage of and that are separated by ﬂat valleys (Fig. 4). The faults that bound the the Laramide orogeny, and this regional deformation has been related ranges are either strike-slip or normal faults, and apparently both to a “décollement” that produced the detachment of the upper lateral and lateral displacements occurred in the same faults carbonated and clastic sequence over the Minas Viejas evaporites juxtaposing different faulting episodes. In some cases, such as La (Padilla, 1985; Fischer and Jackson, 1999; Marrett and Aranda; 1999; Ballena-Peñón Blanco, Sierra Real de Catorce, Coronado, and Zacatecas, Chávez-Cabello et al., 2004). The fold and thrust belt continues the ranges are bounded along one side by NNE normal faults causing M. Tristán-González et al. / Tectonophysics 471 (2009) 136–152 139

Fig. 3. Main regional tectonic structures for northeastern and central Mexico, based on satellite image interpretation and field geological studies (modified after Vélez-Scholvink, 1990). tilting to the east and exposing basement cores with Triassic rocks and Ahualulco lineaments have been interpreted as caused by a dextral (Fig. 4). In other cases, such as Charcas, Santa Catarina, Las Minas and simple shear under transpression as described by Wilcox et al. (1973), Guanamé ranges (Fig. 4), the ranges are outstanding blocks limited by or an oblique simple shear following Jones and Holdsworth (1998). NW and SE normal faults on both sides, which indicate relative vertical In general, all the elevated ranges of the eastern Mesa Central are uplift with little or no tilting (Fig. 4). The ranges of Santa Catarina, cut internally, i.e., within the range, by NW–SE normal faults that were Sierra Las Minas, La Parada as well as the Ahualulco basin form part of a formed at late Paleocene–early Eocene, an age constrained from large crustal block named here as the Pinos-Moctezuma block, with plutonic and volcanic rocks that were emplaced through these faults dimensions of at least 100 by 40 km, and that is limited by two large (more details are described below). Parallel to these elongated ranges parallel NE trending lineaments that could be interpreted as fault and at the eastern part of the area there are a series of basins that have systems. Strike-slip dextral displacements are inferred along these been filled up with continental clastic sediments (red beds), such as lineaments from en-echelon patterns, lateral displacement of units the basins of Matehuala-Huizache, Coronado, Villa Arista, Ahualulco, and from direct observation of a few cinematic indicators that were not and Peotillos (Fig. 2). All these basins include early to middle Tertiary erased by posterior vertical displacement on the same faults. These volcanic rocks, too. At some of them, intrusive and volcanic rocks were lineaments are named by us as La Pendencia (the western lineament) emplaced through their fault-bounded margins, suggesting that these which extends for at least 100 km, from Villa García to Charcas, and igneous rocks were tectonically controlled. Ahualulco (eastern lineament), extending ~85 km from Pino Suárez to Following is a brief geologic and structural description of the three Villa Arista (Fig. 4). Adjacent to this large block and to the west there is representative ranges of La Ballena-Peñón Blanco, Las Minas and the another NE-oriented series of aligned ranges that form another large Ahualulco basin, with their respective simplified geologic maps. Due crustal block, named here the Salinas-Charcas block, which is parallel to the size reduction of these maps because of publication purposes, to the Pinos-Moctezuma block and separated by the La Pendencia many details from the original maps (scales 1:25,000 and 1:50, 000) lineament (Fig. 4). The right-lateral movements along the La Pendencia have been omitted, but we do show the most relevant information.

Fig. 4. Geologic map of the southeastern portion of the Mesa Central showing late Paleocene–early Eocene structures. 1—Sierra de Charcas, 2—Sierra de Coronado, 3—Sierra de Guanamé, 4—Sierra La Ballena-Peñón Blanco, 5—Sierra Santa Catarina, 6—Sierra Las Minas, 7—Sierra La Parada, 8—Sierra La Tapona, 9—Ahualulco Basin. Interpreted geologic cross- sections for three different types of uplifts in the region are shown at bottom of Fig. 1)A–A′ vertical with exhumed core (Sierra de Charcas). 2) listric B–B′ at eastern sector (Sierra de Coronado). 3) c–c′ vertical without exhumed core (Sierra de Guanamé). 4) D–D′ listhric at eastern sector. Base map based on LANDSAT Thematic mapper image bands 1, 4, 7. Original scale 1:250, 000. 140 M. Tristán-González et al. / Tectonophysics 471 (2009) 136–152 M. Tristán-González et al. / Tectonophysics 471 (2009) 136–152 141

Fig. 5. Geological map of the La Ballena-Peñón Blanco range (modiﬁed after Labarthe-Hernández et al., 1982a,b).

2.1. La Ballena-Peñón Blanco range bounded to the west by a listhric normal fault with a NNE strike (Fig. 5). The range is internally segmented in ﬁve parts separated by The Sierra La Ballena-Peñón Blanco forms the southeasternmost four normal faults with an average strike of N60°–70°W. A series of end of the Salinas-Charcas block (Fig. 4). This range includes the granitic intrusions are exposed along the faults within the central oldest rocks of the area (Late Triassic) and Eocene Peñón Blanco parts, the main of which is Peñón Blanco granite of middle Eocene age granite, with 2700 m above sea level, is one the highest peaks in the (45.5±1.1 Ma, Table 1). Several granitic dikes and small apophyses region. The Ballena-Peñón Blanco range is 30 km long and 5 km wide were also emplaced along these faults. In some of the faults it was 142 M. Tristán-González et al. / Tectonophysics 471 (2009) 136–152

Table 1 New K–Ar ages from the Mesa Central.

40 b 40 c d Volcanic unit Sample Coordinates Age Ar ArR K2O Fraction Latitud N Longitud W ±1σa (%) (wt.%) Las Joyas basalt (Tbj) 01–25 2499 631 283 207 01.5±0.8 18.1 0.99 2.06 WR Upper Panalillo ignimbrite (Trp) 01–24 2487 607 287 070 25.4±0.6 81.7 49.26 6.04 WR Riolitic domes (Tdr) 01–32 2476 050 269 295 31.0±0.7 82.7 54.59 5.41 WR Riolitic domes (Tdr) 01–28 2480 728 270 404 31.6±0.8 49.1 49.30 4.78 m Portezuelo latite (Tlp) 01–22 2492 003 281 659 31.0±0.7 68.7 47.68 5.22 m Portezuelo latite (Tlp) 01–26 2504 063 280 774 31.0±0.7 91.6 47.60 4.71 WR Portezuelo latite (botton of ignimbrite) 01–30 2494 836 280 240 32.2±0.8 79.6 63.35 6.09 WR Jacavaquero dacite (Tdj) 01–21 2490 725 276 673 31.6±0.8 75.4 47.50 4.70 WR Zapatero riodacite (Trz) 01–29 2479 946 274 610 31.2±0.7 86.6 59.49 5.86 WR Casita Blanca andesite (Tcb) 01–33 2493 349 271 210 44.4±1.0 82.4 28.50 1.79 WR Casita Blanca andesite (Tcb) 01–31 2499 923 276 778 45.5±1.1 72.5 26.60 1.79 WR Peñon Blanco granite (Tgr) 01–14 2493 748 224 449 45.3±1.1 77.90 145.90 9.86 mu

Ages performed in the laboratory of geochronology at Université de Bretagne Occidentale at Brest France. Coordinates in UTM system, 14Q Zone, using NAD27 projection. a Error at one σ was calculated with the equation given by Cox and Dalrymple (1967). b40Ar; radiogenic argon content of sample, in percent of total. c40 −7 3 ArR; radiogenic argon in sample is expressed in 10 cm /g. d Dated material; WR-whole rock, m-matrix, mu-muscovite.

possible to observe fault surfaces with striae indicating right-lateral from a trans-pressional deformation that pushed-up the block along its displacement (Fig. 5). The Peñón Blanco granite did not form a marginal faults, following the oblique simple shear model of Jones prominent contact metamorphism aureole, but makes a sharp contact and Holdsworth (1998). Besides, a few kilometers to the south of Las with the country rock, Jurassic on one side, and Cretaceous on the Minas range there are faults with left-lateral displacement affecting other due to the fault displacement before the granite emplacement Upper Cretaceous rocks (Fig. 4). These are small faults (not shown in (Fig. 4). The La Ballena-Peñón Blanco range is bounded to the west by Fig. 6 because of the scale) within the Pinos-Moctezuma block that a listhric normal fault inferred from stratigraphic and geologic are here interpreted as antithetic strike-slip faults, which resulted relations and is named here as La Ballena fault (Figs. 4, 5). This fault from a clockwise rotation of the Pinos-Moctezuma block (Fig. 4). has an average N 05°E strike and tilted the Mesozoic sedimentary Therefore, these observations favor the trans-pression interpretation sequence 15° to 18° to the SE. The tilting caused further exposure of for Las Minas range. Andesitic dikes of late Eocene associated to this Late Triassic basement (Zacatecas Formation). The Peñón Blanco trans-pressional episode are found in the NE part of the range; thus, granite as well as smaller contemporaneous granitic plutons (dikes suggesting that these conditions were also favorable for magma as- and apophyses) were emplaced parallel to the trace of this fault. cension and/or near-surface emplacement as was in the case of La Plateaus formed by the Panalillo ignimbrite in the southern portion of Ballena-Peñón Blanco range. this range are completely horizontal and thus they were not affected by the La Ballena fault, indicating that principal fault movement 2.3. Ahualulco Basin predated the 25.4±0.6 Ma Panalillo ignimbrite (Table 1). However, at other sites at the eastern part of the study area, Panalillo ignimbrite This basin is located at the northeastern part of the Pinos- is affected by normal faulting of the late Basin and Range extension. Moctezuma block (Fig. 4). It also includes the northern part of the San Luis Potosí Volcanic Field (Fig. 7). The Ahualulco basin has been 2.2. Las Minas range defined as a tectonic depression related to Oligocene Basin and Range normal faulting (Labarthe-Hernández and Tristán-González, 1981; The Las Minas range is located at the northernmost part of the San Labarthe-Hernández et al., 1982b, 1995; Martínez-Ruíz, 1994). The Luis Potosí Volcanic Field (Figs. 2, 4). It is a small range with a basin has a rough rhombohedral shape with dimensions of 45 by rhombohedral shape that covers an area of about 50 km2.Itis 15 km (Fig. 8). The floor of the basin consists of Upper Cretaceous considered as a plunging anticline developed during the Laramide sedimentary rocks. The basin fill includes Eocene andesitic lavas, orogeny at the end of Cretaceous (Aguillón-Robles and Tristán- Oligocene red beds, volcano-clastic sediments, Oligocene rhyodacitic González, 1981). This range outstands from an alluvial plain with domes and Oligocene rhyolitic ignimbrites, for a total thickness of structural windows showing Maastrichtian marine sedimentary rocks about 800 m (Fig. 9). Capping the basin fill as well as the rocks outside and remnants of Oligocene volcanic rocks (Fig. 6). It shows the typical the basin, is a younger sequence made by the late Oligocene Panalillo folding of the Laramide orogeny, with folds axes trending N–S(Fig. 5—1), ignimbrite, Miocene–Pliocene? continental conglomerates and Qua- fold vergence to the east and an average tectonic transport azimuth of ternary basalts. Small graben-forming faults that affect the intra-basin 95°, with slicken-sides on So fault planes (equal area net 2 of Fig. 6). rocks can be constrained at 31–28 Ma from cross-cutting relation- This deformation style is similar to that observed in other ranges in ships. Thus, this second faulting event is interpreted here as an the region with Lower Cretaceous rocks (Fig. 4). However, field episode different from the original one that formed the Ahualulco evidence indicates that Las Minas range is a horst and not an basin, which occurred at the early Eocene, based upon the first lavas anticline. It was up-lifted in the early Tertiary (after the Laramide that filled the basin (50–42 Ma). However, conglomerate deposits orogeny) and is limited by two main faults striking N40°W, dipping to covering the Panalillo ignimbrite over the Ahualulco basin are tilted the NE and SW. At its southern end the eastern fault changes strike but the Quaternary basalt is not, indicating that faulting continued to a more N–S direction (Fig. 6). Dextral strike-slip faults within after Panalillo ignimbrite for an unknown time but ended before the the horst have a strike of N60°–80°W. Therefore, this range was eruption of the Quaternary basalt, possibly during late Miocene. apparently formed after Laramide deformation by a trans-pressional We interpret the Ahualulco basin as a pull-apart graben instead of tectonics. This hypothesis is based upon the bounding and the a simple Basin and Range graben as previously believed. This internal faults observed in the range; that is, the uplifting occurred interpretation is based upon several observations, 1) the intra-basin M. Tristán-González et al. / Tectonophysics 471 (2009) 136–152 143

Fig. 6. Geological map of the Sierra Las Minas range. This range is 300 m higher with respect the adjacent plain (mostly of Upper Cretaceous rocks). Note that the core is formed by Lower Cretaceous rocks. Lower hemisphere equal area projections are shown in the bottom of Fig. 1) Laramide fold axis poles and slicken-sides lineation on So beds. 2) Laramide tectonic transport direction (modified after Aguillón-Robles and Tristán-González., 1981). faults have a braided arrangement with a general strike of NW–SE and (Portezuelo dacite) to 40° in middle Eocene andesites (Cenicera an average dip of 82° SW, (equal area net 1, 2 of Fig. 10), 2) the slicken- Formation). This gradual tilting change with time indicates that tilting sides on the intra-basin fault planes are oblique and horizontal accumulated during episodic faulting events from the late Eocene to indicating lateral displacements, 3) the rhombohedral shape of the the Miocene (Fig. 10). basin and 4), the dextral strike-slip inferred movement along the La The volcanic rocks that filled the basin were apparently synchro- Pendencia and Ahualulco regional faults (Fig. 4). Some of these early nous with basin development, as they accumulated within the basin Eocene strike-slip faults were overprinted with vertical-slip displace- as subsidence was occurring. These rocks are more voluminous within ments that occurred at the late Oligocene during the Basin and Range the basin, and are rather sparse outside the basin. Emplacement of tectonics, causing the misinterpretation of Ahualulco basin as just some andesitic dikes contemporaneous with the volcanic rocks of the another typical graben of the Basin and Range that does not takes into filling sequence confirms this hypothesis. account its initial strike-slip stage. This early stage was coeval with the regional strike-slip displacements that occurred in all the area during 3. Summary of volcano-tectonic-sedimentary events from the late Paleocene–early Eocene. All the sequence that filled the Laramide orogeny to Basin and Range extension in the eastern Ahualulco basin is tilted to the NE due to a large listric fault (Section Mesa Central D–D′ of Fig. 4) that reactivated the fault that originally bounded the basin at the west (Fig. 8). Tilting increases from the youngest to the The final stage of the Laramide orogeny in central-eastern Mexico oldest rocks of the sequence, from 26° in 31.5 Ma volcanic rocks occurred by the end of the late Paleocene–early Eocene. The latter 144 M. Tristán-González et al. / Tectonophysics 471 (2009) 136–152

Fig. 7. Geologic map of the northern sector of the San Luis Potosi Volcanic Field, included Ahualulco Basin and the Sierra Las Minas sectors (modified after Labarthe-Hernández et al., 1982a,b). according to the ages of several intrusive bodies that do not show volcanic rocks were accumulated (Fig. 11). Several andesitic NNW dikes compressive deformation, the latest of which is dated at 55 Ma (Table 2). and small cones aligned NNW were emplaced within these basins. This Following Aguirre-Díaz and McDowell (1991), it is summarized fissural volcanism still show a subalkaline composition that can be graphically the different volcanic, tectonic and sedimentary events associated to the subduction regime of the Farallon–North American that occurred in the Mesa Central after the end of the Laramide orogeny plates, which should have continued active by this time along western (Fig. 11). These events are correlated with the main tectonic and Mexico (Fig. 11; Atwater, 1989; Aguirre-Díaz and McDowell, 1991; magmatic regimes affecting Mexico between 60 and 20 Ma, from Ferrari et al., 1999). The fact that the middle Eocene andesitic volcanism subduction-related (subduction of the Farallon plate beneath North was fed from dikes, suggests that an incipient extensional regime was America) to extensional-related (Basin and Range extension). starting (transitional volcanism, Fig. 11). Extensional activity increased After the Laramide orogeny, and along the limit between the crustal with time, and by 32 Ma it was already relatively intense (Fig.11). At 32– blocks of the Valles-San Luis Potosí Platform and the Mesozoic Basin of 30 Ma there was a peak in the extension in northern Mexico including Central Mexico, a shear zone oriented NNE was developed. Dextral the study area, which can be related with the regional tectonics change strike-slip movement between these crustal blocks produced a series of caused by the collision of the East Pacific Rise with North America en echelon folds and uplift of smaller blocks with basement nuclei as old (Fig. 11; Atwater, 1989, Aguirre-Díaz and McDowell, 1991). This peak as Triassic that formed high ranges within the shear zone. These ranges extensional episode was accompanied by a syn-extensional volcanic were then displaced by high-angle NW–SE normal faults at about episode that produced voluminous felsic ignimbrites and lava domes middle Eocene, which served as conduits for intrusive and volcanic rocks dated at 32–29 Ma (Fig. 11). After this peak event, the magmatic of this age. At the same time, subsidence occurred in the corresponding conditions changed from predominantly felsic and subalkaline to a NW–SE grabens in which continental clastic deposits (red beds) and bimodal style of high-silica rhyolites and alkalic basalts. These bi-modal M. Tristán-González et al. / Tectonophysics 471 (2009) 136–152 145

Fig. 8. Structural map of Ahualulco Basin at the northern portion of the San Luis Potosi Volcanic Field showing the curvilinear pattern of faults. 1—Equal-area net showing attitude of normal, high-angle NW–SE faults in the western sector of the basin. 2—Equal-area net sowing attitude of normal faults in the northeastern sector of the basin. B, C, D and E represent the equal area net from tilting of the Tertiary sequence shown in Fig. 10. 146 M. Tristán-González et al. / Tectonophysics 471 (2009) 136–152

Fig. 9. Composite stratigraphic column for the northern sector of the San Luis Potosi Volcanic Field and the Ahualulco Basin (K–Ar ages data are shown in Table 1). volcanic events occurred mainly at 28–26 Ma (Fig. 11), and were fed 30–50 km wide (Fig.12C). Due to these characteristics, it is named here from fissures related to the high-angle faults that formed the NNE and as the Matehuala-San Luis Maximum Extension Zone. At 28–25 Ma, NNW grabens and half-grabens of the study area (Torres-Aguilera y syn-extensional pyroclastic volcanism occurred along some of the Rodríguez-Ríos, 2005; Aguirre-Díaz et al., 2008). The same faults were faults of the Matehuala-San Luis Maximum Extension Zone. reactivated later as several discrete episodes until Quaternary (1 Ma). Some times these reactivations were accompanied with basaltic 4. Tectono-magmatic evolution model for the eastern Mesa volcanism with alkaline composition that shows a clear intra-plate Central for the 55–25 Ma period signature (basanites, alkalic basalts, hawaiites; Luhr et al., 1995). The shear zone that was formed along the limits of the crustal It is presented here a geologic model that summarizes the blocks of the Valles-San Luis Potosí Platform and the Mesozoic Basin of tectono-volcanic evolution of the central-eastern Mesa Central Central Mexico, represent a crustal weakness zone (Fig. 12). This zone from late Paleocene to late Oligocene (Fig. 13). The timing for the was developed following the Matehuala-San Luis lineament (Fig. 4). At final events related to the Laramide compression in the area can be 32–31 Ma, dacitic and trachytic lava domes were emplaced following deduced from the ages of the non-compressionally-deformed the high-angle normal faults formed during the Eocene and Oligocene plutons, which indicates that this compressive regime finished at (Fig. 12A). At 31–28 Ma, high-angle extension and Oligocene syn- the early Paleocene (Fig. 13A). This compression shortened the extensional volcanism episodes of rhyolitic lava emissions and Mesozoic sedimentary sequence eastward, and formed numerous pyroclastic rocks occurred along the SW margin of the Matehuala- recumbent folds, thrusts and inverse faults (napes and decollements) San Luis lineament (Fig. 12B). At 28–26 Ma, there was another intense that culminated with the Monterrey salient to the northeast and extensional episode that affected only the narrow zone along the outside the Mesa Central. After the compressive phase of the Matehuala-San Luis lineament, producing low angle listric faulting Laramide orogeny, a major tectonic change took place during the that tilted the affected blocks up to 50° to the NE. The zone that Paleocene at the central-eastern Mesa Central that could be concentrates the maximum extension follows a NNE trend and is about visualized as a crustal relaxation period that followed after a long- M. Tristán-González et al. / Tectonophysics 471 (2009) 136–152 147

Fig. 10. Lower hemisphere equal-area projection showing attitude of tilt direction of the Tertiary sequence in Ahualulco Basin. A) Attitude of tilt direction of Cenicera Formation in the northwestern part of the basin. B) Data from the ignimbrite underlying Portezuelo latite in the northwestern portion of the basin. C) Attitude of tilt direction in the San Nicolás epiclastics. D) Attitude of tilt direction of Upper Panalillo ignimbrite at the western part of the basin. E) Tilt direction of upper conglomerate at the eastern part of the basin.

lasting intense compression, similarly as has been proposed farther andesitic lavas were emplaced in or next to the uplifted blocks, north in the central-eastern Sierra Madre Occidental (Aguirre-Díaz using the marginal and internal faults of the blocks as conduits during and McDowell, 1991). During this period large listric faults were ascension (Fig. 13C). In this time, basins developed next to the developed together with several basins and strike-slip accommoda- uplifted blocks were ﬁlled by continental clastic sediments (Fig.13C). tion faults at the eastern Mesa Central (Fig. 13B), whereas at the At Oligocene (32–30 Ma) took place the most voluminous volcanic central portion of the Mesa Central large blocks were vertically event in the area, consisting of both explosive and effusive eruptions uplifted as crustal wedges due to space accommodation (Fig. 13B). At that formed sequences of silicic pyroclastic rocks and lava domes. the beginning of the Eocene (58–45 Ma), several plutons and This volcanism occurred simultaneously with reactivation of old 148 M. Tristán-González et al. / Tectonophysics 471 (2009) 136–152

Table 2 Table 2 (continued) Structural data of the faults of the central and the north portion of Ahualulco Basin. No Dip Pitch Coordinates direction No Dip Pitch Coordinates North East direction North East 75 220°/65° 0° 2490839 281280 76 255°/55° 90° 2491460 280417 1 055°/88° 40° SE 2494669 276964 2 055°/88° 40° SE 2494669 276964 77 260°/68° 0° 2489081 280158 3 195°/75° 00° 2494581 277059 78 040°/70° 0° 2489599 281832 4 210°/85° 90° 2494581 277059 79 050°65° 90° 2489545 281657 5 240°/45° 90° 2494552 277216 80 215°/65° 90° 2489770 281678 6 205°/60° 60° SE 2494552 277225 81 220°/65° 90° 2489897 281380 7 090°/75° 80° N 2494441 277303 82 215°/65° 90° 2489964 281387 83 225°/60° 90° 2490023 281263 8 270°/50° 90° 2494406 277353 84 240°/65° 90° 2489739 280931 9 065°/60° 10° SE 2494406 277353 10 220°/85° 90° 2494542 277408 85 270°/57° 90° 2489799 280340 11 220°/80° 90° 2495442 277765 86 280°/60° 90° 2493010 271565 12 060°/55° 65° SE 2495815 276949 87 263°/74° 90° 2492469 271356 13 060°/55° 80° SE 2495815 276949 88 110°/35° 90° 2496551 280481 14 200°/75° 60° NW 2491928 275579 89 170°/70° 90° 2495213 282265 90 050°/80 90° 2494911 281964 15 155°/85° 45° SW 2491804 276395 91 297°/53° 90° 2494941 281716 16 250°/70° 90° 2491328 276395 17 220°/88° 90° 2490596 276381 92 075°/87° 90° 2491583 282308 18 220°/60° 90° 2490596 276381 93 040°/89° 0° 2491675 282308 19 250°/70° 70° NW 2490488 276217 94 310°/50° 90° 2492699 283097 20 250°/65° 90° 2490517 276075 95 070°/70° 90° 2494573 285889 21 245°/75° 90° 2490730 275927 96 216°/80° 90° 2494163 284421 22 250°/85° 20° NW 2491540 274213 97 215°/78° 90° 2495352 282541 98 195°/43° 44° NW 2495 352 282541 23 295°/50° 90° 2491661 274159 99 090°/75° 90° 2492705 286434 24 090°/65° 90° 2492211 276652 25 245°/55° 70° SE 2491819 277014 100 090°/70° 0° 2492456 286170 26 200°/75° 25° NW 2491516 277345 101 360°/70° 90° 2496144 283747 27 200°/75° 80° NW 2491516 277345 102 245°/87° 90° 2496016 283924 28 200°/70° 90° 2491535 277480 103 190°/75° 50° SE 2496016 283924 29 220°/65° 35° NW 2491278 278493 104 245°/62° 90° 2496307 283125 30 205°/70° 80° SE 2491306 278053 105 270°/755° 90° 2496922 283007 106 210°/70° 90° 2496765 283088 31 220°/80° 10° NW 2491458 277804 107 060°/65° 90° 2492135 282547 32 050°/80° 90° 2495186 280997 33 220°/80° 00° R 2495151 280914 108 114°/47° 90° 2492724 286422 34 250°/65° 00° R 2495203 280850 109 160°/88° 45° SW 2492818 283533 35 305°/80° 90° 2494938 280908 110 230°/43° 90° 2492785 283475 36 270°/80° 90° 2495654 281679 111 240°/65° 90° 2489601 287268 37 090°/75a 90° 249598 281763 112 270°/55° 90° 2490133 287174 38 190°70° 90° 2495213 282265 113 210°/60° 90° 2487362 287780 39 040°/88° 60° SE 2495440 281881 114 055°/81° 90° 2487680 286984 40 210°/50° 90° 2495323 281285 115 250°/60° 90° 2486797 286566 41 202°/70° 60° SE 2494887 280702 Notes: Coordinates in UTM system, 14Q Zone, using NAD27 projection. 42 280°/60° 90° 2494617 279682 43 075°/60° 70° SE 2494427 279937 44 270°/53° 0° 2494825 280696 fi 45 170°/85° 0° 2494825 280696 faults related to the rst-developed basins. Both the pyroclastic 46 075°/42° 90° 2496668 278298 deposits and the lava domes were emplaced within these basins 47 200°/63° 73° NW 2496704 278501 (Fig. 13D). Volcanism of this period was rhyodacitic and the vents 48 225°/53° 90° 2496704 278501 related to the effusive products (domes) formed NNW chains parallel to 49 085°/68° 90° 2496534 278611 the basins' main orientations. At 30–28 Ma, syn-extensional volcanism 50 240°/65° 90° 2496534 278641 51 245°/60° 90° 2496411 278721 developed chains of elongated lava domes with a high-silica rhyolitic 52 240°/50° 53° NW 2496496 279038 composition. Extension at this time marks the beginning of the Basin 53 220°/55° 90° 2496131 279134 and Range event in this area. These domes were controlled by NW- 54 252°765° 90° 2495750 279233 oriented normal faults, which were used as conduits of these magmas 55 080°/50° 90° 2496637 278122 56 065°/35° 90° 2496468 278153 (Fig. 13E). Then, between 28 and 26 Ma Basin and Range extension 57 250°/75° 90° 2496023 278338 reaches its peak in intensity in this area, and formed NW-oriented fault 58 106°/65° 66° NE 2495823 278196 systems and grabens, reactivating older faults and creating new fault 59 270°/60° 90° 2495459 278402 systems. At 26–25 Ma, widespread ignimbrite-forming pyroclastic flows 60 280°/46° 90° 2495737 278402 were erupted through these faults that filled the graben and half-graben 61 090°/56° 0° 2493283 275602 62 205°/55° 90° 2494023 277933 structures produced in this extensional event (Fig. 13F). Finally, these 63 300°/75° 0° 2494006 277970 depressions were further filled with conglomerates and epiclastic rocks 64 O95°/80° 90° 2494082 278137 that were tilted during Basin and Range faulting activity that continued 65 273°/70° 90° 2493955 278233 at least until Miocene. 66 250°/65° 90° 2493374 280062 67 270°/50° 90° 2494087 278009 68 240°/63° 90° 2492044 281698 5. Conclusions 69 240°/70° 90° 2492020 281609 70 210°/70° 90° 2492124 281484 Uplifting of blocks associated with basin development related to 71 195°/74° 90° 2492315 281065 right-lateral strike-slip tectonics characterized the late Paleocene–early 72 245°/76° 38° NW 2491993 280416 73 340°/88° 0° 2491164 281614 Eocene interval of central-eastern Mexico. Early Eocene large plutons 74 335°/87° 0° 2491071 281527 and volcanic rocks were emplaced within these blocks by means of an en-echelon fault system affecting these blocks. The uplifted blocks and M. Tristán-González et al. / Tectonophysics 471 (2009) 136–152 149

Fig. 11. Summary of tectonic, volcanic, and sedimentary events in the Mesa Central for the time range between 60 and 20 Ma (after Aguirre-Díaz and McDowell, 1991). See text for explanation.

associated plutons formed some of the highest ranges observed in the continental crust affected by intense compression, then by a relaxation eastern Mesa Central province, such as Peñón Blanco and Sierra del and trans-tension stage, and finally by an intense extensional regime, Catorce. At the same time, thick sequences of continental clastic deposits combined with a long-term subduction. as well as silicic-andesitic lavas accumulated in pull-apart basins, as occurred in Ahualulco. Acknowledgements During the early to middle Oligocene, intense volcanic activity occurred synchronously with the activity of newly-formed faults, We thank to Adelina Geyer and Hiroaki Komuro for reviewing this reactivated old fault systems and produced thick sequences of silicic work and for their comments, which substantially improved the lava domes and pyroclastic rocks. Lava domes composition changed manuscript. The authors also thank the comments of Elena Centeno with time, from rhyodacitic to rhyolitic, and were formed contempor- and Scott Bryan on an earlier version. We also thank to Alfredo Aguillón aneously with faulting episodes. The pyroclastic rocks are directly Robles and Rodolfo Rodríguez for their suggestions and support during related with the faulting events, using these faults as their principal the development of this work. We appreciate the Principal Office of the vents. NE oriented Basin and Range extension initiated at about the Instituto de Geología of the Universidad Autónoma de San Luis Potosí, same time of rhyodacitic dome emplacement (32–30 Ma), and through Director Dr. Rafael Barboza, for financial and logistic support to continued during emplacement of rhyolitic lava domes and pyroclastic this study. We recognize the help of Gildardo González and Ana Lizbeth rocks (30–28 Ma). Rhyolitic explosive volcanism continued in the area Quevedo in the digitization of maps and figures. We are grateful to about ~26–25 Ma, which filled the contemporaneously formed graben. “Programa de Formación de Profesores” (PROMEP) for a 3-year This study provides a volcano-tectonic evolution model based upon scholarship to the first author. This study was financially supported in geological observations, which can be used as a case study to test part by grants to GJAD from CONACYT No. 46005-P and from UNAM- experimental or mathematical volcano-tectonic stress models on PAPIIT No. IN-115302. 150 M. Tristán-González et al. / Tectonophysics 471 (2009) 136–152

Fig. 12. Schematic diagram showing the different stages (A to D, see text for explanation) for the formation and development of the shear zone (SZ) between the crustal blocks of Valles-San Luis Potosí Platform and the Mesozoic Basin of Central Mexico at the end of the Laramide orogeny, which was later affected by high-normal faulting and syn-extensional volcanism during the Oligocene, and then affected by listric extension and syn-extensional volcanism after 28 Ma to develop the Matehuala-San Luis Maximum Extension Zone. Explanation of symbols, 1—pre-Tertiary crust, 2—magma of intermediate composition, 3—magma of rhyolitic composition, 4: Valles-San Luis Potosí Platform, 5—Mesozoic Basin of Central Mexico, 6—dacitic–trachytic lava domes, 7—silicic lava domes, 8—silicic pyroclastic rocks, 9—granitic batholiths. M. Tristán-González et al. / Tectonophysics 471 (2009) 136–152 151

Fig. 13. Tectono-volcanic schematic model of the southern and southeastern Mesa Central for the period between the end of the Laramide orogeny (late-Cretaceous–late Paleocene) and the onset of Basin and Range faulting (late Oligocene). See text for explanation of phases A to F. 152 M. Tristán-González et al. / Tectonophysics 471 (2009) 136–152

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