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The Temascalcingo volcano is located 70 km to the NW of Toluca city, and next to the town of the same name, in the State of México. It is one of several volcanoes within the Acambay graben. The Temascalcingo is an andesitic-dacitic stratovolcano, apparently of Pliocene age, with a summit caldera and affected by several normal faults of the Acambay Graben system. At the end of its volcanic evolution there was a destructive phase in the form of a lateral collapse, which formed a debris avalanche deposit and a lithics-rich pyroclastic flow deposit. This collapse occurred on the western flank of the volcano, leaving a horseshoe shaped amphitheater opened to the west and with a size of 6.5 by 3.5 km. The debris avalanche deposit is distributed on the same W direction, reaching at least 6 km from the source; includes hummocks up to 100 m high, and covers an area of 23 km2, representing a rock volume of 0.8 km3, including the exposed rocks in the hummocks. The lateral collapse of the Temascalcingo volcano is of Bezymianny type. The event was probably similar to that of the December 1997 eruption of Soufrière Hills volcano at Montserrat, and was caused by a combination of factors, including: 1) magma injection and emplacement of a lava dome that caused overpressure in the magmatic system and instability of the volcano, 2) an earthquake associated to the Acambay fault system that triggered the sector collapse of the volcano; and 3) fast depressurization related to the quick opening of the system by the landslide and the dome collapse that resulted in an explosive eruption that formed a block and ash pyroclastic flow and an eruptive column that formed a lapilli fallout.

We present the results of a gravimetric study carried out in the region of the General Levalle sedimentary basin, Cordoba Province, Argentina. We obtained the geometry of the basement roof and the surface of the crust-mantle interface for the region where the basin is located. The latter resulted in a surface with a gentle slope deepening to the west. The fact that the crust-mantle interface is rather plane indicates that the sedimentary column has not an anti-root to isostatically compensate it. Also, the gravimetric effect of the sediments was evaluated and substracted from the Bouguer anomalies. In the basin area, a positive gravimetric effect was identified, which may be linked to inhomogeneities located in the intermediate crust.On the basis of the gravimetric results, and their comparison with stratigraphic analysis and basin studies of the region, we propose possible alternatives that consider the presence of thick masses in the intermediate crust: 1)Emplacement of alkaline magmas during the Cretaceous extension; 2) an anomaly in the crust geometry, whether by the effect of a thinned crust associated to Cretaceous rifting or to Cenozoic extension, or 3) due to the flexion of the crust upper during the Andean compression.

The comments by Stinnesbeck et al. (2007) to our manuscript (Blanco-Piñón et al., 2007) refer to four main points:Stinnebeck et al. (2007) question the validity of the FCT acronym that we used for our description of the specimen of Ptychodus mortoni Agassiz, 1843. The acronym used for this specimen is FCT-341, and we believe it is valid as far as a formal acronym for the paleontological collection of Facultad de Ciencias de la Tierra, Universidad Autónoma de Nuevo León has not yet been assigned.The first works suggesting anoxic conditions in the Vallecillo Member were published by Blanco et al. (2001), Blanco (2003), Blanco-Piñón (2003), and Blanco-Piñón et al. (2002, 2005). Later, Blanco et al. (2006) suggested that anoxic conditions observed in Vallecillo and in other three Mexican assemblages could be related to the Oceanic Anoxic Event 2. The last reference was not included because the work was under revision at the time we submitted Blanco-Piñón et al. (2007). Concerning the works of Ifrim et al. (2005) and Ifrim (2006), we did not omit intentionally those works as suggested by Stinnesbeck et al. (this issue). Ifrim (2006) is the PhD thesis of Christina Ifrim at Karlsruhe University. By the time we submitted our manuscript (February 7, 2006), we did not have access to that thesis because it was defended on a later date (April 26, 2006). Ifrim et al. (2005) was published in the first issue of a novelty journal of restricted circulation that was not accesible to us before submitting Blanco-Piñón et al. (2007) for revision.Stinnesbeck et al. disagreed with the observation we cited after Cappetta (1987) that Ptychodus was a durophagous shark in the phrase “Ptychodus is a highly specialized durophagous shark that lived during the Late Cretaceous” and instead they note that “studies on the gastric contents of extant pycnodont fishes (e.g., Sparassius) demonstrated that these fishes are omnivorous and well able to prey on fishes and other food items (Ifrim et al., 2005)”. We disagree on this observation because:a)  Pycnodonts (formally into the order Pycnodontiformes) are all extinct fishes.b)  We could not find references to a fish genus named Sparassius (=Sparassis), because this name correspond to a fungus and not to a fish (Dai et al., 2006).c) Ptychodontids are sharks having a characteristic crushing dentition that allowed the shark to feed on hard bodied preys, such as mollusks. This is clearly attributed to Cappetta (1987), actually a world specialist on sharks.d)  Nowhere in Blanco-Piñón et al. (2007) we wrote “pycnodonts”, and the triangulation Ptychodus-Pycnodontids- Sparassius expressed by Stinnesbeck et al. is out of order. After the carefully review of Ifrim et al. (2005), we consider that this mainly arises from their report of some similarities in the body form of Nursallia and Sparus (not Sparassius). However, we did not find any analysis to support the comparison of the diet, food habits or mouth mechanisms between Sparus, pycnodonts, and sharks. Actually, the comparison between the dentition and diet of these osteichthyans (Nursallia and Sparus), and that of chondrichthyes (Ptychodus) is not easily supported nor formally published. Finally, Blanco and Frey (2001) provided a discussion about the diet of Nursallia sp., which was not cited in Ifrim et al. (2005).Concerning the stratigraphic control of Ptychodus mortoni within the Vallecillo Member, we would like to replya)   Ptychodus mortoni was reported in Blanco et al. (2001), and Blanco-Piñón et al. (2002) as a part of the Vallecillo Member assemblage and W. Stinnesbeck, L.G. Lopez Oliva and D. Frey were co-authors in those publications. In Blanco-Piñón et al. (2007) we reported that FCT-341 was collected from the uppermost part of the Vallecillo Member (and not discovered in a small museum situated at Vallecillo, as mentioned by Stinnesbeck et al.), almost in contact with the dark-gray, non-platy unit of the Agua Nueva Formation. That could explain the grayish micrite matrix of the rock that contains the teeth of FCT-341 (see Blanco-Piñón, 1998).b)  Stinnesbeck et al. argued that we omitted to refer “the record of P. mortoni from the El Rosario quarry, Coahuila, described by Stinnesbeck et al. (2005)”. However, the latter authors just provided imprecise and/or tentative identification of the fish fauna in this locality when wrote “These fishes have apparently been collected randomly at El Rosario and other quarries in the area from coeval sediments of the same depositional area. The following taxa have been tentatively identified by one of us (L. Cavin) on the basis of photographs: Ptychodus cf. P. mortoni Agassiz, 1843 (Figure 4a)” (Stinnesbeck et al. 2005, p. 407). In addition, the tooth in their fig. 4a does not show the characters of P. mortoni.c)   The assignation of FCT 341 as the oldest record ofP. mortoni in the world was based on the presence of Watinoceras coloradoense. This ammonite was collected from the same level where FCT 341 was collected and was housed in the Colección Paleontológica de la FCT as unidentified specimen under the catalogue number FCT-257. Later, the specimen was identified by Wolfgang Stinnesbeck as Watinoceras coloradoense, and this is the data we used in Blanco-Piñón et al. (2007). Besides, such species of ammonites has been considered as a Lower Turonian ammonite (see e.g., Aguilera-Franco, 2003).d)  The paper by Ifrim and Stinnesbeck (2007), with information about a detailed taxonomic and biostratigraphic distribution of the ammonites of the Vallecillo Formation at Nuevo León, was published in June, 2007, and was thus not available at the time our manuscript was accepted for publication (November, 2006).Finally, we deeply thank Stinnesbeck et al. (2007) for his comments on the article and for providing new information concerning the Vallecillo assemblage.

We believe the article by Blanco-Piñón et al.(2007) contains severe formal and scientific errors which, to our view, should be revised according to international scientific rules.The specimen presented by Blanco-Piñón et al.(2007) belongs to the type collection of the FCT at Linares. Its correct acronym is UANL-FCT-VC 341 (VC for Vallecillo) or UANL-FCT-R (R for reptiles). FCT alone is incorrect and does not allow the identification of the specimen.Specimen UANL-FCT-VC341 originates from the Vallecillo area and was discovered in 1995 by one of us (WS) in the collection of the small museum at Vallecillo. The specimen lacks any finding data. Based on the black colour, the high carbonate content as well as the imperfect cleavage of the host rock, it appears to us that the specimen does not originate from the platy limestone member but from the monotonous sediment sequence of black marlsto ne and limestone overlying the Vallecillo Member. These sediments are widely known from northeastern Mexico as the Agua Nueva Formation. In the Vallecillo area, the unit clearly overlies the platy limestone and is stratigraphically younger. In consequence, the Ptychodus specimen discussed here must also result from stratigraphic levels younger than the Vallecillo limestone (Ifrim, 2006).Blanco-Piñón et al.(2007) refer to the presence of Watinoceras coloradoense (see also Blanco-Piñón et al., 2005, where the authors refer to Arkell et al., 1978 for the biostratigraphic assignation of UANL-FCT-VC341). In fact, the Treatise of Invertebrate Paleontology on Mesozoic ammonoidea was published by Arkell et al. in 1957, and is an overview on generic level only. A more recent volume of the “Treatise” exclusively on Cretaceous ammonites was published by Wright et al.(1996). However, these monographs are entirely taxonomic and do not refer to the stratigraphic signi fi cance of W. coloradoense and the dating by Blanco-Piñón et al. is thus invalid. W. coloradoense was unknown from the Vallecillo deposits, between 1998 and 2003, when Blanco-Piñón studied the site (Blanco-Piñón, 2003). Later publications, by Buchy et al.(2005) and Ifrim et al.(2005) refer to W. coloradoensis, but they are ignored by Blanco-Piñón et al. (2007).W. coloradoensis does not occur in the black limestone beds of the Agua Nueva Formation. At Vallecillo, this species is restricted to lower part of the platy limestone member, with its last occurrence at least 3m below the transition into the Agua Nueva Formation s.s. (Ifrim, 2006, Ifrim and Stinnesbeck, 2007). A co-occurrence of Watinoceras and UANL-FCT-VC341 is thus highly unlikely.Blanco-Piñón et al.(2007, p.28) also mention Spathites and Collignoniceras as representatives of the Vallecillo Member of platy limestones. These genera, however, are representatives of the middle Turonian and not the early Turonian assemblage. In case of cooccurrence with UANL-FCT-VC341, this specimen would thus be of middle Turonian and not early Turonian age. The stratigraphic occurrence of Ptychodus mortoni at Vallecillo would then be in line with other localities in NE Mexico (e.g., Peyotes, Coahuila and Xilitla, San Luis Potosí), arguing against the title of their contribution (“The oldest record of…”). In consequence, the argumentation of Blanco-Piñón et al.(2007) regarding the age of UANL-FCT-VC341 is incorrect in all aspects. A detailed taxonomic description and biostratigraphic distribution of the ammonites of the Vallecillo Member was recently published by Ifrim (2006) and Ifrim and Stinnesbeck (2007) and is now available.Other references to the work of our research group are also omitted by Blanco-Piñón et al.(2007). For instance, the relationship between the formation of the platy limestone and the latest Cenomanian global oceanic anoxic event (OAE 2) was established by Ifrim et al.(2005), and it was speci fi ed by Ifrim (2006). It was not Jacobs et al.(2005) who established the presence of a plesiopedal mosasaur as part of the Vallecillo fossil assemblage, even though these authors brie fl y mention the existence of this fossil. The detailed taxonomic description of the specimen by Buchy et al.(2005), published in the same volume of the Nederlands Journal of Geosciences, however, was not cited. Blanco- Piñón et al.(2007) also omit the record of P. mortoni from the El Rosario quarry, Coahuila, described by Stinnesbeck et al.(2005). This specimen is there precisely dated to early Coniacian age but is not included in the stratigraphic range chart given by Blanco-Piñón et al.(2007).Blanco-Piñón et al.(2007) conclude that Ptychodus and other vertebrates with button-shaped teeth are necessarily durophagous. We believe that this conclusion is erroneous. Studies on the gastric contents of extant pycnodont fishes (e.g., Sparassius) demonstrated that these fi shes are omnivorous and well able to prey on fi shes and other food items (Ifrim et al., 2005).

The Etla, Mitla-Tlacolula and Nejapa volcanic regions in central and southeastern Oaxaca comprise the southeastern part of a wide Cenozoic magmatic arc in the Sierra Madre del Sur. Most volcanic events in these regions ocurred between 22 to 15 Ma, almost contemporaneously with the initial volcanic events of the Trans-Mexican Volcanic Belt. Petrographic, geochemical, and isotopic characteristics were determined for representative volcanic samples from the three regions, where ignimbrites, volcaniclastic and epiclastic deposits, lava flows and minor lacustrine deposits are found. In a SiO2 vs. alkalis diagram, chemical classification of volcanic products for the study area indicate variations from basaltic andesites to rhyolites, following a subalkaline trend, but with a bimodal pattern. Components with SiO2 concentrations between 58 to 67 wt. % are absent. The trace-element patterns for andesites and rhyolites are similar, with enrichment in the large-ion lithophile elements relative to the high- field-strength elements. Chondrite-normalized REE patterns display light rare earth element enrichment (La-Sm) with respect to the heavy rare earth elements (Eu-Lu), which show flat patterns. These chemical characteristics are typical of volcanic arc rocks. Initial Sr and Nd isotopic data show certain differences between samples from the Etla and Mitla-Tlacolula regions (87Sr/86Sr: 0.7047 to 0.7066 and εNd: -1.15 to 1.75) and the Nejapa region (87Sr/86Sr: 0.7035 to 0.7048 and εNd: +0.52 to +1.42). These data and those reported for the basement rocks suggest greater involvement of continental crust for the magmas of the two first regions in comparison to magmas of the Nejapa region. The isotopic compositions are similar to those observed in other volcanic regions of the Sierra Madre del Sur. Early to middle Miocene volcanic events in central and southeastern Oaxaca, together with the contemporaneous initial magmatic events in the Trans-Mexican Volcanic Belt, could conform a magmatic arc with an anomalous orientation before attaining its present position.

In the Valle de Bravo area, central Mexico, two assemblages of cretaceous rocks are exposed. Both units present very low grade metamorphism: (1) a meta-sedimentary rock assemblage (EMS), and (2) a meta-volcanic rock assemblage (EMV). These rocks are part of the Ixtapan de la Sal–Teloloapan volcano-sedimentary metamorphosed Mesozoic sequence. The history of deformation of the two assemblages is represented by three sub-horizontal shortening events (D1, D2 y D3), that display similar NE-SW orientation, but alternating tectonic transport direction. D1 has a general vergence toward 043°, whereas D2 toward 218°, and D3 toward 045°. The three events have been recognized in different localities in Guerrero and Michoacan states, and they represent important shortening episodes at regional scale.Event D1 exhibits ductile deformation at grain scale, while D2 is brittle-ductile, and D3 presents strictly brittle characteristics. We propose that D1 is the peak metamorphic/deformational event and that D2 and D3 occurred during exhumation of the rocks. During D1 and D2, two generations of veins (V1 and V2, respectively) were developed. Abundance of the veins has been related directly to the penetrativity of deformation; which suggests that the mobilization of soluble material (mainly by pressure-solution/reprecipitation) was the effective mechanism of deformation at the microscopic scale. This soluble material was deposited in veins in later stages of the deformation event and was more intense during D1. This is demonstrated by the analysis of microstructures in thin section, by outcrop observations and by the comparative-quantitative determination of density of veins through image analysis.In addition to the earlier V1 and V2 veins, late veins (V3) were also identified, and are associated dominantly to normal faults that cut D3 structures. Petrography and microthermometric analyses on fluid inclusions were done on quartz and calcite crystals of the three generations of veins in a 15 km2 area in the EMS. The average homogenization temperatures were: 250 °C for V1, between 167 and 202 °C for V2 and 220 °C for V3. Corresponding salinities obtained were: between 6.1 y 7.4 (V1), 5.2 (V2), and between 2.6 and 4.6 (V3) (weight % of NaCl equivalent). The data obtained in V1 and V2 are in agreement with a progressive exhumation of the rocks in the studied area, while the temperatures measured in V3 indicate that hotter fluids circulated along normal faults and associated vertical fractures after D3.

The granodiorite intrusions with associated Cu-Au skarn mineralization of La Paz district are located in the east part of the Mesa Central of Mexico. The skarn developed at the contact between a middle Cretaceous calc-argillaceous sedimentary sequence and the magmatic intrusions. A Ag-Pb-Zn vein system postdates the intrusive-skarn assemblage. Two well defined fault systems (N-S and E-W) divide the La Paz district. The N-S Dolores fault, with a normal vertical displacement estimated between 500 to 1000 m, separates the western Au-Cu skarn zone from the eastern hydrothermal Ag-Pb-Zn vein system. This fault is considered to be part of the Taxco-San Miguel de Allende fault system. The U-Pb dating of the intrusives at the La Paz district clearly indicates a single emplacement event dated at ca. 37 Ma (monocrystal zircon age). This age probably represents the last post-Laramide orogenic mineralizing event known to occur in the Sierra de Catorce district. Also, four calculated discordant ages suggest the presence of greenvilian basement underneath a a thick crust (35-45 km).The chemistry of the intrusive show a certain variability in composition, but they mostly belong to the high-K calc-alkaline magmatic series. Major and trace elements relationships for the intrusives show a chemical evolution from the adakite to the island arc fields, and from mineralized to barren intrusives, repectively. They also suggest the importance of crustal delamination processes, and the necessity of deep cortical drains to transfer oxidized magmas and metals to surface.

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 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.

 Combined magnetic mineral, organic and inorganic carbon content and geochemical analysis were conducted on laminated sediments from Santa Maria del Oro, a crater lake in Nayarit (western Mexico), to build up a model of the paleoenvironmental conditions for the last 2,600 years. This sequence is of particular importance as it constitutes a high resolution record of late Holocene climatic and environmental change in west-central Mexico. The analyses attained in this study allowed to recognize abrupt changes, to identify dry periods, and to compare these variations with available records in central Mexico. Laminations are caused in general by alternations of their main components: lithogenic detritus, biogenic and authigenic carbonates, and amorphous material from biological and volcanic remains. The volcaniclastic accumulations include two tephras, one of them, the Toba Jala, produced by the Ceboruco volcano. Six facies of silt, sand and peat were recognized. Horizons characterized by high inorganic carbon content, authigenic siderite, and the dissolution of the finest ferrimagnetic mineralogy (magnetite) in reductive conditions, are upward followed by an increase in the concentrations of fine grained ferrimagnetic minerals. This sequence represents dissolution-precipitation cycles of magnetic minerals by anoxic/oxic variations in the water-sediment interface during warmer and dryer periods. These environmental conditions are especially present around 600 – 1140 A.D., and 1410 – 1830 A.D., which coincide with the archeological Classic period (300 - 900 A.D.) drought, the Little Ice Age (1350 –1800 A.D.) and the droughts of the last 700 years. The effects of climatic variations such as the drought occurred in the archeological Classic period, the Medieval Warm Period, the Little Ice Age, and the droughts over the last 700 years, have been documented in sites along central Mexico.

The coastal Sonora batholith comprises a series of Cretaceous granitoids that intruded a metasedimentary basement of possible Mesozoic age. They are partially covered by Tertiary volcanic flows and pyroclastic rocks. In order to elucidate the crystallization and cooling history of the granitoids, nine rock samples were collected from Bahía Kino to Punta Tepopa. Eight samples dated by U-Pb zircon geochronology show that the Coastal Sonora batholith was emplaced during the Late Cretaceous, between90.1 ± 1.1 and 69.4 ± 1.2 Ma. The interval of ~20 Ma between the different stages of crystallization indicate that magmatism was relatively static within coastal Sonora, although the magmatic arc recorded an eastward migration as a whole during Cretaceous and Paleogene. In addition, three of these samples were also dated by 40Ar/39Ar in biotite and K-feldspar separates. Ages vary from ~74 to 67 Ma in biotite and from ~68 to 42 Ma in K-feldspar. We interpret these ages as the cooling progression of the batholith, associated with exhumation of the region before the Basin and Range extension. Furthermore, these results show a local trend towards younger ages to the north of the batholith, and they are in good agreement with the model of a general eastward migration of the Cretaceous-Tertiary magmatic arc  in northwestern Mexico. In general, the available ages suggest that the arc moved slowly across Baja California between 140 and 105 Ma, and continued its eastward migration across the eastern portion of Baja California and Sonora between 105 and ~60 Ma. According to the isotopic ages, the Coastal Sonora batholith would be the westernmost part of the Laramide magmatic event (~90 – 40 Ma). Thus, on the basis of new and available geochronologic, petrographic, and geochemical data, we propose that the Coastal Sonora batholith and the eastern portion of the Peninsular Ranges batholith belong to a single magmatic arc, which was separated during the continental breakup and rifting of the Gulf of California in the Tertiary.