Igneous rocks

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TítuloFirst data on testate amoebae in speleothems of caves in igneous rocks

TítuloFirst data on testate amoebae in speleothems of caves in igneous rocks

Massifs formed by igneous rocks are characterized by their low porosity and scarce solubility, so in these cases runoff normally moves on the surface. However, runoff may drain exceptionally under- ground through the systems of cavities re- lated to fractures, faults or diaclases when they are open totally or partially. When these types of caves are very large they are considered pseudokarstic systems as they are developed in non soluble rocks and are also differentiated from the karst sensu sc- tricto, characteristic of calcareous massifs (VIDAL ROMANí & VAQUEIRO 2007; Vidal Romaní et al., 2110 a y b). Pseudo- karst is also distinguished because water circulation is normally produced at low velocity as trickles which disperse slowly onto the floor, walls or ceiling of the caves. In physical continuity with these trickles, it is normal to find specific deposits (speleo- thems) of small dimensions and character- ized by a varied mineralogical spectrum, the most frequent mineral species being: amor- phous opal, evansite, pigotite, alophane, or even carbonates (FORTI, 2005; VIDAL ROMANí et al., 2110 a y b). These types of speleothems were first described by Cald- leugh in 1829, and during a long time it was considered that they were due to the rock weathering produced by the water (VIDAL ROMANí et al., 1979; VIDAL ROMANí, 1983; VIDAL ROMANí & VILAPLANA, 1984; WEBB & FINLAYSSON, 1984). For this reason, these deposits were first char- acterized almost exclusively by their min- eralogy ignoring their relationship with the activity of microorganisms which lived in these caves. Later, the introduction of the scanning electronic microscopy in the

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Geochemistry of Carboniferous low metamorphic grade sedimentary and tholeiitic igneous rocks in the western Acatlán complex, southern Mexico: deposition along the active western margin of Pangea

Geochemistry of Carboniferous low metamorphic grade sedimentary and tholeiitic igneous rocks in the western Acatlán complex, southern Mexico: deposition along the active western margin of Pangea

Deposition of the Progreso and Zumpango units is regarded by Keppie et al. (2008a, 2008b) as coeval with deformation associated with extrusion of high-pressure rocks into the Acatlán complex in an active tectonic margin (Ramos-Arias et al., 2009). Extrusion of high pressure rocks is a process that occurs only in an active margin setting. Thus the rift setting suggested by the geochemistry probably in- dicates extension during extrusion. Furthermore, Keppie et al. (2008b) have proposed that the Devonian-Carboniferous arc was removed by subduction erosion: remnants occur as Devonian-Carboniferous igneous detrital zircons, and in high-pressure extruded rocks (e.g., Meza-Figueroa et al., 2005; Galaz et al., 2009). Paleogeographic reconstructions consistent with paleomagnetic data (Figure 13; Keppie et al., 2008a, 2008b and references therein; Morales-Gámez et al., 2009) indicate that this active margin is probably the western margin of Pangea, as suggested by the Mid-conti- nent (USA) affinities of Mississippian fauna found above the Oaxacan complex (Navarro-Santillán et al., 2002), which presumably underlies the Acatlán complex (Keppie et al., 2008b, Ortega-Obregón et al., 2009, 2010).

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Timing of the magmatism of the paleo Pacific border of Gondwana: U Pb geochronology of Late Paleozoic to Early Mesozoic igneous rocks of the north Chilean Andes between 20° and 31°S

Timing of the magmatism of the paleo Pacific border of Gondwana: U Pb geochronology of Late Paleozoic to Early Mesozoic igneous rocks of the north Chilean Andes between 20° and 31°S

Middle Triassic to Early Jurassic volcanic rocks yiel- ded zircon U-Pb ages from 249.7±3.8 to 194.0±9.2 Ma, their outcrops are more discontinuous (patchy) and dispersed compared to the older volcanic rocks, and are separated from them by erosional surfaces. During this period andesitic to basaltic volcanism coexisted with felsic volcanism (bimodal volcanism), and was synchronous with rift-related, continental and/or marine sedimentary deposits in northern Chile (e.g., Suárez and Bell, 1992; Bell and Suarez, 1994). Middle to Upper Triassic strata show strong facies changes along the longitudinal axis of the High Andes, for example according to the U-Pb data the mostly basaltic-andesitic La Totora Formation (250-210 Ma) overlaps in age with the upper part of the mainly clastic, sedimentary San Félix Formation (223-212 Ma), but also with rhyolites of Los Tilos Sequence (232-221 Ma), within less than 100 km in the Atacama Region. These striking north-south facies changes probably reflect the main northwest orientation of extensional basins that developed in the Mid-Late Triassic in Chile and Argentina (Charrier, 1979; Chong and Von Hillebrandt, 1985; Uliana et al., 1989; Ramos and Kay, 1991; Jenchen and Rosenfeld, 2002; Charrier et al., 2007; Barredo et al., 2012).

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Early Jurassic arc related magmatism associated with porphyry copper mineralization at Zafranal, Southern Peru unraveled by zircon U-Pb ages

Early Jurassic arc related magmatism associated with porphyry copper mineralization at Zafranal, Southern Peru unraveled by zircon U-Pb ages

ABSTRACT. Early Jurassic arc-related igneous rocks host porphyry copper prospects and gold-bearing quartz vein deposits in southern Peru. Ten new zircon U-Pb ages for wall rocks of gold-bearing quartz veins, Jurassic rocks and copper-mineralized porphyry bodies in Zafranal porphyry copper, together with published ages for Jurassic rocks, reveal a continuous magmatic evolution of the early Jurassic arc. The Jurassic rocks and gold-bearing quartz vein systems in the western flank of the Western Cordillera are hosted by Paleo- and Meso-proterozoic orthogneisses of the Arequipa Massif (1.75-1.44 Ga) that underwent Grenville-age metamorphism ~1 Ga. The early mafic magmatism is recorded between 199.6-193.2 Ma, and was followed by dominantly felsic magmatism from 184.1-174.9 Ma. Both magmatic events have formed the thinnest intrusive belt (<15 km wide) of the Coastal Batholith in southern Peru. The last magmatic event of the early Jurassic (181.0-174.9 Ma) is represented by several phases of porphyries associated with copper mineralization in the Zafranal porphyry copper deposit. The published ages indicate that the magmatic arc migrated along eastern limit of the Arequipa Massif during Middle Jurassic. In the late Jurassic (~146 Ma) the magmatic locus returned near early Jurassic intrusion. Overall, the plutonic intrusive rocks and porphyry bodies with copper mineralization represent the oldest magmatic events of the Coastal Batholith of Peru formed during the early Jurassic.

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Provenance of sands from Cazones, Acapulco, and  Bahía Kino beaches, México

Provenance of sands from Cazones, Acapulco, and Bahía Kino beaches, México

The study area Acapulco (Figure 2b) is located in southern part of Mexico (Lat 16º50’N and Long 99º56’W). Rocks are dominated by: (1) granites and granitoids of Early Paleocene age; (2) volcanic rocks of intermediate to acid composition, mostly of early Tertiary age (andesite to rhyolite); (3) sedimentary rocks of Mesozoic to Tertiary ages; and (4) Quaternary alluvium. The beach sands of Acapulco receive sediments derived from central part of the MVB (Velasco-Tapia and Verma, 2001a, 2001b; Verma, 2002, 2009a) as well as largely from Guerrero state (Meza- Figueroa et al., 2003; Freydier et al., 2000). In the MVB, igneous rocks from basaltic to rhyolitic compositions have erupted, which may also contribute to the beach sands of Acapulco. The Gerrero terrane (Campa, 1985; Coney, 1989) is composed of Late Jurassic to Early Cretaceous igneous and sedimentary rocks considered to be developed in an intra-oceanic setting (Centeno-Garcia et al., 1993; Tardy et al., 1994). The major river that discharges relatively near to Acapulco beach is Papagayo (Figure 2b).

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Maturing Arc signatures monired by trace element and Hf isotope systematics in the early cretaceous Zacatecas volcanic field, Mexico

Maturing Arc signatures monired by trace element and Hf isotope systematics in the early cretaceous Zacatecas volcanic field, Mexico

Available geochemical data for the Zacatecas Group are limited. Because these rocks underwent hydrothermal/deuteric alteration and greenschist facies metamorphism, fluid-mobile elements such as K, Na, Rb, or Sr need to be treated with caution in petrogenetic and tectonic interpretation. In the Zacatecas Formation, limited Sm-Nd isotopic stud- ies on three samples indicate a primitive igneous suite, interpreted to be akin to ocean-floor assem- blages (Centeno-Garcı´a and Silva-Romo 1997). For the Las Pilas Complex, Ranson et al. (1982) pre- sented major elements and two trace elements (Rb and Sr) for five igneous rocks. However, due to hy- drothermal/deuteric alteration, these results may be compromised by secondary processes rather than reflect primary igneous signatures. Verma (1984) analyzed Rb-Sr and Sm-Nd isotopes in one basaltic sample from the LPC and inferred that oce- anic crust was involved in its magma generation. Subsequently, Tardy et al. (1992, 1994) and Cen- teno-Garcı´a and Silva-Romo (1997), based on two igneous rock samples, defined an island arc tectonic setting. It is noteworthy that only Verma (1984) mentioned the sample location; all the other sam- ples are from unknown localities. In summary, all previous analyses suggest a primitive, mantle- derived origin for the volcanic rocks but with op- posing tectonic interpretations (IAB vs. MORB) and based on rather limited data. Hence, our systematic approach of sampling volcanic, plutonic, and sed- imentary rocks in conjunction with the robust- ness—i.e., dominantly fluid immobile nature—of the Lu-Hf isotope system during alteration offers a promising way to reevaluate the tectonic frame- work of this terrane.

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Tectonothermal history of the Mesoproterozoic Novillo Gneiss of  eastern Mexico: support for a coherent Oaxaquia microcontinent

Tectonothermal history of the Mesoproterozoic Novillo Gneiss of eastern Mexico: support for a coherent Oaxaquia microcontinent

The Novillo Gneiss is one of several exposures of Mesoproterozoic (ca. 1.0–1.2 Ga) basement in eastern Mexico interpreted to be outcrops of a single crustal block (Oaxaquia) that has figured prominently in continental reconstructions for the late Precambrian-Paleozoic. Exposed within the Sierra Madre Oriental near Ciudad Victoria, the Novillo Gneiss comprises two major Mesoproterozoic igneous suites that intrude rare metasedimentary rocks. The older suite, previously dated at 1235–1115 Ma, principally comprises garnet K-feldspar augen gneiss and granite gneiss with arc/back-arc geochemical affinities. The younger suite (charnokitic gneiss, anorthositic metagabbro) has been dated at 1035–1010 Ma and is interpreted to be part of an anorthosite-mangerite-charnockite-granite assemblage. Both suites are intruded by two sets of amphibolite dikes, the earlier of which predates metamorphism under granulite facies conditions at ca. 990±5 Ma, whereas the later set is of low grade and was emplaced at ca. 546 Ma.

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C1ENS509

C1ENS509

Sedimentary rocks are formed by deposition of other rocks or the remain of living creatures, followed by compaction of the particulate matter and cementation. The latter can occur at or near the earth's surface, especially in the case of carbonate- rich sediments.

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Late Triassic and Early Cretaceous sedimentary
				sequences of the northern Isfahan Province (Central Iran):
				stratigraphy and paleoenvironments

Late Triassic and Early Cretaceous sedimentary sequences of the northern Isfahan Province (Central Iran): stratigraphy and paleoenvironments

Upper Triassic and Lower Cretaceous rocks are spread widely in central and northern Iran. The major objective of the present study is the Upper Triassic (Norian to Rhaetian) sediments of the Nayband Formation exposed in three sections located in Dombi and Bagher Abad, north of Isfahan Province. In these localities, the Triassic deposits are overlain with a distinct angular unconformity by the Lower Cretaceous deposits, whereas Jurassic sediments are missing almost completely. The unit of conglomerate at the base of the Lower Cretaceous contains pebbles of carbonate and siliciclastic rocks without any sign of the Jurassic fossils.

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TítuloCaves in granitic rocks: types, terminology and origins

TítuloCaves in granitic rocks: types, terminology and origins

dence. Both forms are commonly developed in arid and coastal environments in which salt occurs at the land surface in crystal form, sug- gesting that the same process may have a role in the formation of the larger as well as the smaller hollows (e.g. WINKLER, 1975; BRADLEY et al., 1978). Efflorescences of halite have been observed on the walls and ceilings of some relatively open tafoni on northwestern Eyre Peninsula. Halite is hygro- scopic and water accelerates the rates of vari- ous forms of chemical weathering (e.g. McINNIS and WHITING, 1979; WINKLER, 1981). That salt crystallisation and hydration exert a force sufficient to overcome the tensile strength and rupture fresh rocks including granite has been demonstrated experimentally (WINKLER and SINGER, 1972; WINKLER, 1975; KNACKE and ERDBERG, 1975). In addition, however, the effects of hydration, and especially the production of hydrophilic clays from the reaction of feldspars and micas with water (see e.g. BLACKWELDER, 1929; LARSEN, 1946; HUTTON et al., 1977), can- not be overlooked.

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Mapeo Geocientífico de las Sierras Pampeanas, 3166-18, Provincia de Córdoba

Mapeo Geocientífico de las Sierras Pampeanas, 3166-18, Provincia de Córdoba

Interlayered boudinaged amphibolite bodies, up to tens of metres thick and a kilometre in length, generally form strike ridges. Although very difficult to distinguish on aerial photographs, they have low gamma-ray spectrometric responses and magnetic signatures characterised by a moderate to strong narrow, elongate anomalies (average magnetic susceptibilities of 40010-5 SI), which allow concentrations of the unit to be identified on regional magnetic images. They are fine- to medium-grained rocks, commonly banded, and principally composed of prismatic to sub-prismatic hornblende or actinolite (50-70%) and plagioclase (25-30%). Common minor and accessory minerals and alteration products include quartz, epidote, carbonate, diopside, magnetite, and titanite. Geochemical analyses suggest some amphibolite bodies may be after high Mg protoliths. Throughout the Sierras de Córdoba the common association of amphibolite with marble suggests the possibility that they are para-amphibolites.

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Implementación de un sistema de clúster con rocks en una red tradicional. Caso Plan Automotor Ecuatoriano S.A

Implementación de un sistema de clúster con rocks en una red tradicional. Caso Plan Automotor Ecuatoriano S.A

La implementación del clúster se realiza haciendo uso del software VMware que permite crear máquinas virtuales, así como también de varias herramientas para el diseño y configuración de clúster de las cuales se ha seleccionado las más adecuadas mediante la comparación de las mismas a través de normas de calidad de software, definiendo Rocks como Sistema Operativo del clúster, Piranha para configurar alta disponibilidad y balanceo de carga de servicios web y Ganglia para el monitoreo de recursos de cada nodo del clúster.

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Colaboración entre artesanos y diseñadores mexicanos: en busca de nuevos signos

Colaboración entre artesanos y diseñadores mexicanos: en busca de nuevos signos

En este documento se busca entender cómo se construyen las relaciones y el aprendizaje que ocurre entre diseñadores y artesanos a través de los proyectos que desarrollan en co- mún; para comprender estos temas desde un punto de vista actual y activo, se realizó un cuestionario a cuatro proyectos con diversos propósitos pero que comparten una relación cercana con artesanos, el primero fue el extinto Centro de diseño de Oaxaca elegido por desarrollar una metodología para poder implementar proyectos de trabajo entre diseña- dores y artesanos del estado de Oaxaca, el segundo es The chair that rocks, el cual fue elegido por facilitar experiencias de aprendizaje entre alumnos de diseño y artesanos, el tercero Rituales contemporáneos por trabajar con pequeños talleres de manera local, es decir, situados en la Ciudad de México y el cuarto Víctor Alemán por fusionar procesos de desarrollo digital con el trabajo artesanal.

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Active microbial biofilms in deep poor porous continental subsurface rocks

Active microbial biofilms in deep poor porous continental subsurface rocks

Deep continental subsurface is defined as oligotrophic environments where microorganisms present a very low metabolic rate. To date, due to the energetic cost of production and maintenance of biofilms, their existence has not been considered in poor porous subsurface rocks. We applied fluorescence in situ hybridization techniques and confocal laser scanning microscopy in samples from a continental deep drilling project to analyze the prokaryotic diversity and distribution and the possible existence of biofilms. Our results show the existence of natural microbial biofilms at all checked depths of the Iberian Pyrite Belt (IPB) subsurface and the co-occurrence of bacteria and archaea in this environment. This observation suggests that multi-species biofilms may be a common and widespread lifestyle in subsurface environments.

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TítuloDevonian and Carboniferous pre Stephanian rocks from the Pyrenees

TítuloDevonian and Carboniferous pre Stephanian rocks from the Pyrenees

The Aspet-Brousset Fm can have an unconformable contact below the overlying siliciclastics rocks on Culm Facies, termed the Bellver Formation in the el Comte domain (Brower in Hartevelt, 1970). Culm rocks include a large diversity of lithologies; Delvolvé et al. (1983) and Delvolvé et al. (1996) interpreted siliciclastic rocks as flysch sediments, corresponding to deep fan systems. The systems have poor lateral continuity, with patchy outcrops, but these authors recognised the presence of slope, canyon and fan facies. However, Sanz López (1992) has locally interpreted some lower bodies in the Bellver Fm as fan delta deposits, below turbiditic facies. These shallow-water facies fossilize olistoliths, exo-karstic sheets, palaeokarst fillings and faults with a normal component. Bichot (1986) previously described tensional faulting of the underlying formations during the Bellver sedimentation, and normal faults were actives in places during the early development of the foreland basin. On the other hand, palaeokarst development with iron and manganese ore bodies was located below the Bellver Fm and related in origin with pre-concentration in the La Mena Fm in several localities of the north and eastern Pyrenees (Jaeger et al., 1956, 1958; Fournié, 1956; Sanz López, 1992).

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Mapeo Geocientífico de las Sierras Pampeanas, 3166-21 Desiderio Tello, Provincia de La Rioja

Mapeo Geocientífico de las Sierras Pampeanas, 3166-21 Desiderio Tello, Provincia de La Rioja

The neosome comprises two types of leucosome: fine to medium-grained muscovite- biotite monzo- or syenogranite and muscovite-bearing pegmatite, and granodiorite. The plagioclase is an- to subhedral, equidimensional and shows very little compositional zoning. The K-feldspar (microcline) is anhedral, relatively coarse and occasionally poikilitic. The quartz commonly occurs in irregular aggregates. The leucosomes are commonly separated from the paleosome by a melanosome forming a thin selvedge of dark grey to black biotite-feldspar-quartz rock which in places also contains hornblende or cordierite. The biotite forms parallel streaky aggregates aligned about the same trend as the layering. The contact with the paleosome is gradational and with leucosome abrupt. The neosome rocks form discontinuous, lenticular bodies up to 50 cm thick. With advanced migmatism the paleosome and neosome become progressively more disrupted, intermingled and intermixed, and eventually it is impossible to differentiate the two phases.

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Mapeo Geocientífico de las Sierras Pampeanas, 3166-33 Corral de Isaac, Provincia de La Rioja

Mapeo Geocientífico de las Sierras Pampeanas, 3166-33 Corral de Isaac, Provincia de La Rioja

faulting the rocks are relatively little deformed. The rocks may have been emplaced during the waning stages of the late Ordovician phase of east-west compressive deformation; however, no other felsic magmatism has been recorded from that time in the region. In other parts of the southern Sierras Pampeanas pegmatites are genetically related to the Devonian Achala Granite Complex (Morteani and others, 1995), but in the Sierra de Las Minas there is no field and aeromagnetic evidence that the Devonian granite plutons, concealed beneath the alluvial plains adjacent to the sierras, are accompanied by pegmatites and other highly differentiated rocks. On the other hand, these dykes and veins may also have been derived from the felsic magma which produced the granites of the Chepes Igneous Complex, but they were only slightly affected by deformation as they are located in zones of low strain.

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K/Ar ages of 54 igneous and metamorphic rocks from western, central and southern Mexico

K/Ar ages of 54 igneous and metamorphic rocks from western, central and southern Mexico

Fifty-four samples of igneous and metamorphic rocks from south, central and northern Mexico have been analyzed by the K/Ar method. Samples were provided to Instituto de Geología of Universidad Nacional Autónoma de México by the Consejo de Recursos Minerales (now Servicio Geológico Mexicano) from selected regions of the following states: Baja California Sur, Colima, Durango, Estado de México, Guerrero, Jalisco, Oaxaca, San Luis Potosí, Sinaloa y Zacatecas. All relevant information for each sample, including location, geological unit, petrographical description, mineral analyzed and age is described in the text; analytical data for each sample are given as a table. Ages range from 2 Ma to 249 Ma, with about 30% being Oligocene ages related to volcanism and plutonism in the Sierra Madre Occidental and Sierra Madre del Sur.

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Mapeo Geocientífico de las Sierras Pampeanas, 3163-13 Jesús María, Provincia de Córdoba

Mapeo Geocientífico de las Sierras Pampeanas, 3163-13 Jesús María, Provincia de Córdoba

Relationships between the Ascochinga Igneous Complex and other Paleozoic units are poorly known. Granitoid units within the complex intrude minor bodies of para- and ortho- gneiss with contacts mostly concordant to the differentiated metamorphic fabrics. Howev- er, they display only variably developed foliations indicating late syntectonic emplacement with respect to the S1 fabrics in paragneiss. Minor dykes of undeformed pegmatite, aplite and lamprophyre intrude the complex. Within gneissic enclaves, boudinaged bodies of am- phibolite, less than 2 m long, may represent deformed early mafic dykes. Contacts with other basement units are fault-bounded. The western extent of the complex is limited by the east-dipping Carape Fault where it is thrust over the El Manzano Formation to the west. In the north, Cretaceous sediments of the Los Terrones Conglomerate unconformably over- ly the unit, and in the east, unconsolidated Mesozoic and Cainozoic sediments onlap base- ment rocks.

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Mapeo Geocientífico de las Sierras Pampeanas, 3166-14 Malazán, Provincia de La Rioja

Mapeo Geocientífico de las Sierras Pampeanas, 3166-14 Malazán, Provincia de La Rioja

During the Cainozoic the peneplained Paleozoic basement was uplifted in north-south oriented, elongate fault blocks forming the present-day characteristic topography of rugged sierras separated by flat intermontane basins. It is generally thought that the sierras were uplifted and tilted by late Cainozoic listric reverse faults (Jordan and Allmendinger, 1986). However, during this survey no unequivocal field evidence was found to ascertain the nature of faulting. Along many escarpments bounding the sierras occur regular, moderately to steeply-dipping triangular facets which appear to have formed on east-dipping planar fault scarps dissected by erosion. If so, the escarpments would represent normal faults. Another argument for young extensional faulting in the Sierra de Las Minas is the presence of westerly and/or northerly trending graben structures, which are bounded by escarpments with similar geomorphic expression as the border escarpment. The graben structures are up to a few kilometers wide, and also cut the basement beneath the Cainozoic sediments of the plain, as indicated by the aeromagnetics. On the other hand, in a compressional tectonic regime the east-west oriented grabens may have formed at a high angle to the north-south oriented minimum principal stress, and the narrow, north-south oriented graben structures (for example in northeast Sierra de Las Minas) may have developed on tension fractures associated with arching of the basement rocks during east-west compression. Jordan and Allmendinger (1986) discussed the occurrence of two broad and northerly plunging arched structures developed in crystalline basement underlying the two northern conical projections of the Sierra de Los Llanos (north of the map area).

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