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Search Results: 1 - 10 of 349493 matches for " Roberto S.;Chávez-Cabello "
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Paleomagnetism, structure and 40Ar/39Ar geochronology of the Cerro Mercado pluton, Coahuila: Implications for the timing of the Laramide orogeny in northern Mexico
Molina-Garza, Roberto S.;Chávez-Cabello, Gabriel;Iriondo, Alexander;Porras-Vázquez, Mario Alberto;Terrazas-Calderón, Guillermo Daniel;
Revista mexicana de ciencias geológicas , 2008,
Abstract: the cerro mercado pluton, emplaced in the coahuila fold belt, contains magmatic, ductile, and brittle fabrics that suggest local and regional deformation during igneous emplacement, later affected by regional deformation in the area. the cerro mercado pluton intruded, deformed and uplifted upper cretaceous strata in the southern edge of the central depression of the sabinas basin. a hornblende mineral separate from the pluton yielded a 40ar/39ar plateau age of 44.29 ± 0.19ma (1σ), interpreted as an approximation to the crystallization age of the monzonite. a younger biotite total fusion age of 41.23 ± 0.21 ma (1σ) from a different rock sample is interpreted to represent slow cooling (80°c/ma) of the cerro mercado pluton. paleomagnetic analyses of the pluton yieldwell defined remanent magnetizations of nearly uniform reverse polarity, with a grand mean of d=178.2° and i=-61.7° (n=9 acceptable sites; k=57.5, α.95 = 6.8°). these data are discordant with respect to the eocene reference direction, indicating apparent clockwise rotation (8°) and inclination steepening (21°). the simplest interpretation of the discordance is that northwestward tilting of the pluton occurred during basin inversion within a weakly right lateral transpressive regime with nnw directed contraction. the strain field is consistent with contraction during the laramide orogeny. also, remanence acquisition is contemporaneous with both tectonic and magmatic fabrics in the pluton indicating that it is syntectonic. this suggests - in agreement with stratigraphic data - that the laramide orogeny in central coahuila ended some time after about 44 ma. we propose that reactivation of the san marcos fault and other basement faults in the sabinas basin represents the last manifestation of shortening produced by the laramide orogeny. this was a short episode of deformation that ended by the time of emplacement of younger plutons of the candela-monclova magmatic belt ca. 41 ma. this indicates that culmination
Paleomagnetic study of Jurassic and Cretaceous rocks north of San Marcos fault, central Coahuila, México
González-Naranjo, G. A.;Molina-Garza, R. S.;Chávez-Cabello, G;
Geofísica internacional , 2008,
Abstract: upper jurassic and lower cretaceous continental strata at potrero colorado, in the core of sierra la fragua anticline in central coahuila, carry dual-polarity characteristic magnetizations that we interpret as near primary chemical remanent magnetizations. upper jurassic fluvial and eolian sandstones of the colorado beds yield a tilt-corrected mean of d=10.2° i=28.2° (n=18 sites, k=22.1, α95=7.5°). a steeper inclination magnetization observed in five sites of the colorado beds is interpreted as a secondary, post-laramide folding, magnetization. lower cretaceous fluvial sandstones of the san marcos formation yield a combined mean of d=358.1°, i=46.4° (n=13 sites, k=22.7, α95=8.9°), but the stratigraphically lower sites on the eastern side of the anticline have south-southwest directed and moderately steep negative magnetizations (mean of d=191.7° i=-54.9°; k=38.7, α95=9.8°, n=7 sites) which are statistically distinct from northwest directed magnetizations (mean of d=333.6° i=58.0°; k=28.3, α95=12.8°, n=6 sites) observed in stratigraphically higher sites in the west-central part of the anticline. we interpret the difference in declinations in the san marcos formation as the result of rotation during deposition of this unit. the characteristic shallow-inclination magnetization in jurassic strata is also discordant with respect to the late jurassic reference direction. both, the lower san marcos formation and the colorado beds indicate clockwise rotations of 38.5°±8.3° and 30.0°±2.3°, respectively. the sampling sites are located within a clastic wedge that records activity of the san marcos fault during late jurassic and early cretaceous time. these data indicate that during deposition of the colorado beds and san marcos formation, the fault behaved as a normal fault with a small right-lateral component. the area of potrero colorado is interpreted as a zone of relay in the normal san marcos fault, which accommodated clockwise rotation recorded by upper jurassic and lowe
Paleomagnetic study of Jurassic and Cretaceous rocks north of San Marcos fault, central Coahuila, México.
G. A. González-Naranjo,R. S. Molina-Garza,G. Chávez-Cabello
Geofísica internacional , 2008,
Abstract: Upper Jurassic and Lower Cretaceous continental strata at Potrero Colorado, in the core of Sierra La Fragua anticline in central Coahuila, carry dual-polarity characteristic magnetizations that we interpret as near primary chemical remanent magnetizations. Upper Jurassic fluvial and eolian sandstones of the Colorado beds yield a tilt-corrected mean of D=10.2° I=28.2° (n=18 sites, k=22.1, α95=7.5°). A steeper inclination magnetization observed in five sites of the Colorado beds is interpreted as a secondary, post-Laramide folding, magnetization. Lower Cretaceous fluvial sandstones of the San Marcos Formation yield a combined mean of D=358.1°, I=46.4° (n=13 sites, k=22.7, α95=8.9°), but the stratigraphically lower sites on the eastern side of the anticline have south-southwest directed and moderately steep negative magnetizations (mean of D=191.7° I=-54.9°; k=38.7, α95=9.8°, n=7 sites) which are statistically distinct from northwest directed magnetizations (mean of D=333.6° I=58.0°; k=28.3, α95=12.8°, n=7 sites) observed in stratigraphically higher sites in the west-central part of the anticline. We interpret the difference in declinations in the San Marcos Formation as the result of rotation during deposition of this unit. The characteristic shallow-inclination magnetization in Jurassic strata is also discordant with respect to the Late Jurassic reference direction. Both, the lower San Marcos Formation and the Colorado beds indicate clockwise rotations of 38.5°±8.3° and 30.0°±2.3°, respectively. The sampling sites are located within a clastic wedge that records activity of the San Marcos fault during Late Jurassic and Early Cretaceous time. These data indicate that during deposition of the Colorado beds and San Marcos Formation, the fault behaved as a normal fault with a small right-lateral component. The area of Potrero Colorado is interpreted as a zone of relay in the normal San Marcos fault, which accommodated clockwise rotation recorded by Upper Jurassic and Lower Cretaceous strata.
Magnetoestratigrafía de la Formación San Marcos del Cretácico Inferior, Coahuila, México: Implicaciones tectónicas y paleogeográficas
Arvizu-Gutiérrez, Irving Rafael;González-Naranjo, Gildardo Alonso;Stanley Molina-Garza, Roberto;Chávez-Cabello, Gabriel;
Boletín de la Sociedad Geológica Mexicana , 2011,
Abstract: we report the results of a magnetostratigraphic study of the san marcos formation in central coahuila, at two localities along the san marcos fault. these localities are characterized by outcrops of a sequence of conglomerates, immature sandstone and red mudstone, cemented by hematite; the sequence was deposited in a continental environment, and has been assigned to the early cretaceous. all specimens, from a total of 35 paleomagnetic sites, were subjected to alternating field and thermal demagnetization, the latter being the most effective in isolating the (high temperature) characteristic magnetization. the characteristic component is unblocked between 625° and 660 °c. both normal and reverse polarity magnetizations are represented, and the overall mean is of dec = 352.7 °, inc = 55.5 °, n = 3 localities (18 sites), k = 27.07, α95 = 6.8 °. this result suggests a small clockwise rotation with respect to the expected reference direction for the cretaceous, estimated from the apparent polar wandering curve for cratonic north america. however, the data suggest that there was relative rotation between localities, and the observed rotations are more likely explained as local vertical-axis rotations. the magnetic polarity zonation in the san marcos formation suggests that this unit represents the early barremian through early aptian. the correlation to global magnetic polarity timescale suggests that this unit is correlative with cupido formation, and that the transgressive littoral facies of the las uvas formation, as well as flooding of coahuila paleo-island at potrero colorado, occurred in the early aptian. the best correlation with the global magnetic polarity time scale corresponds to the interval from m5n (normal) to m0r (inverse) approximately between 131-125 ma. the sedimentation rate indicated by this correlation, assuming a constant rate, is relatively low (~30-50 m/ma) for an active tectonic environment and is more consistent with a region where accommodation
Gneises bandeados paleoproterozoicos (1.76-1.73 Ga) de la Zona Canteras- Puerto Pe?asco: Una nueva ocurrencia de rocas de basamento tipo Yavapai en el NW de Sonora, México
Arvizu, Harim E.;Iriondo, Alexander;Izaguirre, Aldo;Chávez-Cabello, Gabriel;Kamenov, George D.;Foster, David A.;Lozano-Santa Cruz, Rufino;Solís-Pichardo, Gabriela;
Boletín de la Sociedad Geológica Mexicana , 2009,
Abstract: the zona canteras-puerto pe?asco area, previously known as seven hills, is located ~20 km ene of the town of puerto pe?asco in nw sonora, mexico. crystalline basement in this area is key to defining proterozoic provinces of sw laurentia and has important implications for phanerozoic tectonics and formation of the active continental margin of north america. new u-pb zircon ages (la-mc-icpms) of two banded gneisses in this area yield 207pb/206pb ages at 1764 ± 3 ma and 1725 ± 3 ma. zircons from both samples are well-behaved in the u-pb systematics and present age and compositional homogeneity, suggesting that these rocks are paleoproterozoic orthogneisses. these crystallization ages combined with whole rock major- and trace-element geochemistry and sm-nd in whole rock and lu-hf isotopic determinations on zircons by laser ablation suggest that the banded gneisses have affnities with rocks of the yavapai province as defned in the quitovac area ~45 km to the east and in the region of gunnison-salida, colorado, usa. both samples plot in the volcanic arc environment of granite formation (y vs nb discrimination diagram) and have epsilon hf (initial) values between +1.85 and +5.05 with corresponding single-stage hf model ages (tdm) at 1.98-2.07 ga and two-stage hf model ages (tdmc) at 2.07-2.50 ga. sm-nd whole rock isotopic analyses from three paleoproterozoic gneisses have epsilon nd (initial) values between +1.86 and -0.57 with corresponding nd model ages (tdm) at 1.91-2.02 ga. the magmatic protoliths of these gneisses could have been formed mostly from mantle sources with some degree of crustal contribution, which is similar to rocks from the yavapai province in sw north america. this petrogenesis contrasts with typical mojave-province rocks that are characterized by significantly greater crustal contamination (as much as 30-40% in death valley). if these mojave province rocks exist in nw sonora they must be located to the west of the zona canteras-puerto pe?asco area.
Rocas graníticas pérmicas en la Sierra Pinta, NW de Sonora, México: Magmatismo de subducción asociado al inicio del margen continental activo del SW de Norteamérica
Arvizu, Harim E.;Iriondo, Alexander;Izaguirre, Aldo;Chávez-Cabello, Gabriel;Kamenov, George D.;Solís-Pichardo, Gabriela;Foster, David A.;Lozano-Santa Cruz, Rufino;
Revista mexicana de ciencias geológicas , 2009,
Abstract: multidisciplinary studies in the sierra pinta area in nw sonora, including u-pb zircon geochronology, mayor and trace element geochemistry as well as sm-nd isotopic studies have allowed a precise characterization of permian granitic rocks. the results suggest the existence of a suite of permian granitoids with u-pb zircon ages between ~275 y ~258 ma. initial epsilon nd values between -19.2 and -10.4 and corresponding nd model ages (tdm) between 2.5 and 1.6 ga, as well as some geochemical characteristics, indicate melting of proterozoic crustal basement associated to the early stages of subduction forming the continental magmatic arc of sw north america. it is likely that this permian magmatic pulse in nw sonora was part of a larger event in the american cordillera extending from western-southwestern usa, passing through northern mexico and up to central and southern mexico and, perhaps, to northern south america (i.e., colombia). we suggest that the occurrence of the permian granitoids in sierra pinta is associated with a paleoproterozoic crustal weakness zone formed by a narrow stretch of the yavapai crustal province. this weakness zone could have acted as a channel-way that facilitated the ascent towards higher crustal levels of the first magmas generated by subduction.
Gravity Field Variations Associated with the Buried Geological Structures: San Marcos Fault (NE Mexico) Case Study  [PDF]
Vsevolod Yutsis, Yaneth Quintanilla-López, Konstantin Krivosheya, Juan Carlos Montalvo-Arrieta, Gabriel Chávez-Cabello
Journal of Modern Physics (JMP) , 2012, DOI: 10.4236/jmp.2012.329160
Abstract: Gravity data are sensitive to local vertical offsets across high-angle faults, where rocks with different densities are juxtaposed. Yet high densities in some Mesozoic sedimentary rocks just above the basement may smear out the subtle gravity signatures of basement faults. At this study the gravity data processing tends to avoid ill-described “black-box” techniques. The study area is situated in the Palomas site, Cuatrociénegas region, Coahuila, NE Mexico. The San Marcos Fault is at least 300 km long and has WNW-ESE trend from the central part of Nuevo León State through Coahuila, and finally to the eastern part of Chihuahua State. Gravimetric data shows that the lowest values of free air and Bouguer anomalies are in the southern part of the area, and the highest values are in the western and central part of the area. Between these parts exists a zone of high horizontal gravity gradient. Configuration of linear elements of gravity field (gradient zones) delimited the San Marcos Fault in the San Marcos valley below thickness of recent sedimentary cover. Two density models were carried out, which showed that the Cretaceous rocks are in discordant contact with the Paleo- zoic rocks that can be related to the San Marcos Fault. The density was determinate using to Nettleton’s method, which results highlight the presence of the San Marcos Fault. Density models showed that the Quaternary sediments are in direct contact with the San Marcos Fault.
Tectónica de la sierra Cuesta El Infierno y su posible relación con fallas reactivadas cerca del levantamiento de Plomosas, Chihuahua, México
Oviedo-Padrón, Edgar Gerardo;Aranda-Gómez, José Jorge;Chávez-Cabello, Gabriel;Molina-Garza, Roberto Stanley;Iriondo, Alexander;González-Becerra, Paula Cecilia;Cervantes-Corona, Jorge Alfredo;Solorio-Munguía, José Gregorio;
Revista mexicana de ciencias geológicas , 2010,
Abstract: geologic and structural mapping of volcanic rocks in sierra cuesta el infierno, located on the western flank of the plomosas uplift, allowed us to divide the paleogene volcanic section into two succesions. the volcanic rocks unconformably overlie sedimentary rocks of the chihuahua fold belt. the lower volcanic succession felsic ash flow tuffs and epiclastic continental deposits) is separatedfrom the upper volcanic succession (andesitic lavaflows with interlayered rhyolitic ash flow tuff) by a small angular unconformity. the volcanic successions are exposed in northern and southern structural domains of the sci, which are separated by an inferred basement fault (n70°w) with a complex history. the basement fault acted since middle to late paleogene as a transfer zone that accommodated the deformation of fault systems with different trends in the areas located north and south of its trace. the basement fault also controlled the distribution ofsome of the ash flow tuffs, the eruption of the lava flows, and the local basin and range strain pattern during the cenozoic. a sse-plunging syncline with a n20°w trend associated with a system of listric normal faults parallel to the fold axis and a small roll-over anticline occur in rocks of the lower volcanic succession in the northern structural domain. the syncline is interpreted as a fault bendfold. in the southern domain of the study area, we recognize an accommodation zone between two antithetic listric faults that consists of a n45°w-trending antiform.
Interacción termal entre magmas graníticos laramídicos y rocas encajonantes mesoproterozoicas: Historia de enfriamiento de intrusivos de la Sierrita Blanca, NW Sonora
Enríquez-Castillo, Mónica A.;Iriondo, Alexander;Chávez-Cabello, Gabriel;Kunk, Michael J.;
Boletín de la Sociedad Geológica Mexicana , 2009,
Abstract: a semi-quantitative thermochronological study, combining u-pb and 40ar/39ar geochronology, has allowed assessment of the crystallization and cooling history of the laramide sierrita blanca granite as well as the thermal effects resulting from the intrusion into the mesoproterozoic host rocks (~1.1 ga murrieta granite). the u-pb zircon age discrepancy between two samples of the sierrita blanca granite (72.6 ± 1.2 ma and 69.7 ± 1.0 ma) could be explained by a process of faster magma cooling in the contact zone with the host murrieta granite. however, that the sierrita blanca granitic unit was made up of multiple intrusions of similar compositions emplaced relatively close in time cannot be discarded. the 40ar/39ar ages of both biotite and k-feldspar for the granite collected close to the contact are also signifcantly older than the ages for the sample collected in a more internal zone of the intrusion. the initial cooling of the sierrita blanca granite was fairly fast and monotonous from the closure temperature of zircon to that of biotite (~36-32°c/ma). subsequently, the cooling of these laramide rocks became relatively slow (~10-9°c/ma) between the closure temperature of biotite and k-feldspar. these estimated cooling rates are similar, perhaps slightly slower, to the ones estimated for other laramide granitoids in nw mexico. three samples of the host murrieta granite, collected at different distances from the laramide intrusion, were dated by u-pb zircon geochronology at ~1.1 ga, reiterating that the u-pb zircon systematics are quite resistant to thermal effects inficted by intrusions like the one in the sierrita blanca. however, close inspection of the u-pb zircon data suggests the presence of pb loss for some of the zircons. this pb-loss phenomenon is most pronounced in the zircons from the sample collected at the contact with the sierrita blanca intrusive where heat and/or hydrothermal fuids are released by the laramide intrusion. it is important to note that aw
Estudio petrográfico y geoquímico del Complejo Plutónico El Pe?uelo (Cinturón de Intrusivos de Concepción del Oro), noreste de México
Velasco-Tapia, Fernando;González-Guzmán, Reneé;Chávez-Cabello, Gabriel;Lozano-Serna, Javier;Valencia-Moreno, Martín;
Boletín de la Sociedad Geológica Mexicana , 2011,
Abstract: this work presents the petrographic and geochemical data for the el pe?uelo plutonic complex (eppc), which is an intrusive that belongs to concepción del oro intrusive belt (coib; northeastern mexico). the eppc is a semi-circular structure, constituted by three emplacement centers, situated in the eastern part of the coib and the northern extension of the taxco-san miguel de allende fault system. however, the complex was not affected by the activity of this fault system. the eppc is constituted by intrusive rocks varying from quartz monzodiorite to quartz syenite, the latter covering most of the complex surface. the eppc was emplaced in upper cretaceous marine sedimentary rocks. the quartz syenite is cut by quartz monzodioritic and porphyritic meso-syenitic dykes. also, this unit contains irregularly distributed monzodioritic microgranular enclaves. additionally, pegmatitic dykes cut the rest of the lithologic units. the eppc mineralogical assemblage shows variable quantities of plagioclase + alkaline feldspar + quartz ± amphibole + biotite ± orthopyroxene + clinopyroxene + fe-ti oxides. intrusive rocks have a chemical composition of sio2 = 45.7-72.0 %, mg# = 39.2-60.2, and n-fe = 0.54-0.73. they show chondrite-normalized ree patterns enriched in light elements [(la/yb)n = 6-11] with no eu anomalies. primitive mantle-normalized multi-element diagrams show lile enriched patterns relative to the hfse. their trace-element geochemistry is comparable to high-ba-sr granitoids: (a) high ba concentration (= 594-2302 ppm) and sr (= 444-2192 ppm); (b) low concentrations of y (= 10-46 ppm) and nb (= 6-17 ppm); and (c) high values for sr/y (= 25-85) and (la/yb = 8.9-16.5) ratios. the origin of eppc has been related to partial melting of an enriched lithospheric mantle, in a post-orogenic setting, followed by fractional crystallization coupled to crustal assimilation.
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