Sistema Regional de Información
en línea para Revistas Científicas de América Latina,
el Caribe, España y Portugal

The analysis of the different features that characterize a landscape is an essential requirement to know the geomorphological evolution, having a great impact on the productive development of a region, knowing the positive and negative aspects that can affect or enhance them. For this, it is necessary to recognize, characterize and classify the morphologies present, which account for the factors and processes that acted in their formation, and contribute to the interpretation and reconstruction of the evolution of the relief at various scales. The Amarillo river basin is located in the Sierra de Famatina, which is located in the center-north of the province of La Rioja, in northwestern Argentina. Office and field tasks were carried out in order to analyze, recognize and identify the main geomorphological features present, and establish their spatial arrangement. In the highest sectors of the basin, geoforms associated with glacial, periglacial and gravitational processes stand out, caused by low temperatures, steep slopes and lack of vegetation. Fluvial forms, both accumulation and erosion, were identified throughout the analysed area, while lacustrine deposits are described where it is interpreted that their formation was associated with the global arid event defined as the Meghalayan Stage. This distribution and typology of geoforms, conditioned by tectonics and exogenous processes, led to a complex geomorphological evolution in the Quaternary of the Amarillo river basin.

Weathering is one of the most important phenomena that affect the balance dynamics of the Earth's crust. The chemical composition of soil samples and hardened horizons from seven profiles (P1 to P7) of the State of Mexico was compared to detect the degree of alteration by means of weathering indices. In hardened horizons, the dominant elements are SiO2, Al2O3, Na2O, K2O and TiO2, corresponding to 86.8 % of the total oxides. The weathering indices based on the mobility and immobilization of alkaline and alkaline earth elements reveal that the B horizons and the hardened horizons of profiles P4, P5, P6 and P7 are generally more altered than the surface horizons, therefore they have a greater pedogenic development. Profiles P1, P2 and P3 show incipient weathering. The geochemical indices and chemical relationships used in this study to evaluate weathering and associated basic alteration processes showed consistent results. These coincide in indicating incipient to moderate weathering acting in the seven profiles, with variable intensity in all the hardened horizons. The intensity variation defines a sequence of chemical weathering for the hardened horizons: P6> P4> P5> P7> P2> P3> P1, where P6 has the highest degree of weathering in the indices: CIA, CPA, CIA-K, CIW, PIA,IPark, V.

Paleozoic outcrops in Mexico containing echinoderms are located to the north, center and south of the country, mainly in the states of Baja California, Sonora, Chihuahua, Tamaulipas, Coahuila, Hidalgo, Puebla, Guerrero, Oaxaca, and Chiapas. These rocks correspond to marine carbonates deposited in warm shallow environments, with an approximate age of 541 to 251 Ma. Also containing a varied and diverse biota made up of phylloid algae, foraminifera (fusulinids), coralline sponges, corals, bryozoans, brachiopods, mollusks, trilobites and echinoderms. In order to know the diversity of Crinozoa from the Paleozoic of Mexico, an analysis of the species documented for the country was carried out, with the objective of contributing to the knowledge of the biostratigraphy and paleogeography of Mexico. The methodology consisted of a detailed analysis of bibliographic sources with information on echinoderms from the Paleozoic of Mexico. Cambrian eocrinoids (Gogia, and Ubaghsicystis) are distributed mainly in Sonora. Crinoid plates from the Carboniferous and Permian, particularly morphospecies of the genera Cyclocaudex, Cyclocrista, Heterostelechus, Lamprosterigma, Mooreanteris, Pentagonopternix, Preptopremnum, and Pentaridica, are widely distributed throughout the country. Analysis of the Mississippian-Permian biota indicates that the cosmopolitan distribution of the fauna studied in this work is due to the connections between the seas of western North America and eastern Asia. The Late Permian benthic fauna of Sonora was widely dispersed in the Tethyan realm, which stretched from western North America to North Africa and Asia. The comprehensive study of Paleozoic marine stratigraphic successions and their biotic content provided information on faunal migrations regarding the Paleozoic carbonate facies. It also contributed to reconstructing the geographical, climatological, and ecological characteristics of the Paleozoic of Mexico.

Orthogneisses outcropping in the central and eastern regions in the Santander Massif consist in interlayered of hornblende gneiss, biotite gneiss and quartzo–feldspathic gneiss. Biotite and hornblende gneisses are the predominant lithologies. In these orthogneisses, sporadic amphibolite lenses appear. The orthogneisses are the result of the synthectonic emplacement of granitoids in the rocks of the Silgará Schist Unit during the metamorphic peak of this meta–sedimentary unit. Some structural and compositional differences are observed in the orthogneisses of the central and eastern sectors; the most developed foliation is observed in the central sector and the presence of muscovite, apparently it is restricted only to the eastern sector. The geochemical characteristics show that the orthogneisses of the central sector are granitic in composition, while, for those located in the eastern sector, their composition varies between granite and granodiorite. These orthogneisses were formed on an active continental margin. According to rare earth elements – REE behavior the rocks displayed three geochemical trends: 1) The felsic orthogneisses are moderating depleted in Light Rare elements–LREE (La–Sm) and depleted in Heavy Rare Earth elements–HREE (Eu–Lu); 2) negative europium anomaly is typical for orthogneisses; 3) Amphibolite is depleted in LREE and slow increment of HREE without europium anomaly. P–T metamorphic conditions were estimated for the central region as T = 690–770 °C and P = 0.53–0.85 GPa whereas amphibolite from eastern region reached metamorphic thermal peak conditions at T = 680–693 °C. Occurrence, field relationship of studied orthogneisses respect to metasedimentary country rocks are very similar that those orthogneisses outcropping along the Andes and southeastern terranes of Mexico as result of magmatic arc developed along the Western Gondwana protomargin.  

The Late Miocene volcanism related to the Trans-Mexican Volcanic Belt modified the paths of sediment transport from the Late Oligocene-Early Miocene landscape on west-central Mexico. We hypothesize that the ignimbrites from the Sierra Madre Occidental have had reached the floodplain of the Puerto Vallarta Graben. The volcanic activity of the Trans-Mexican Volcanic Belt at the south of the Sierra Madre Occidental, probably changed the sediment discharge from the Sierra Madre Occidental towards the floodplain of Nayarit trough the Santiago River. Such event restrained the sediment transport from the Sierra Madre Occidental towards the Puerto Vallarta Graben and Bahía de Banderas isolating a part of the landscape of the Ameca river basin which, nowadays, feeds the sediments that forms the floodplain of the Puerto Vallarta Graben. The Late Oligocene to Early Miocene age distribution of detrital zircons close to the mouths of Santiago and Ameca rivers support the idea that both rivers share sediments originated from the Sierra Madre Occidental.

Pleistocene subaerial volcanism along the margins of the Ballenas Channel, northern Gulf of California, is represented by two morphologically young dacite dome complexes exposed at the opposite edges of sheared continental crust: Isla Coronado in coastal Baja California, and the Lobera volcanic complex in west-central Isla Ángel de la Guarda. Single crystal zircon U-Pb crystallization ages of Coronado and Lobera volcanoes range between ca. 250 and 1000 ka, indicating maximum ages for the eruptions. Eruption ages are directly constrained by an 40Ar/39Ar whole-rock age of 692 ± 164 ka for one of the lava units in the Lobera volcanic complex. Trace elements in Pleistocene zircon indicate continental affinity, which supports radiogenic (Nd, Sr) isotopic data that were modeled using different mixing and AFC scenarios indicating a MORB-type primary magma with significant (~10–20 %) crustal assimilation involving tonalitic basement of the eastern Peninsular Ranges Batholith.

We present a summary of the tectonic elements of the North America-Caribbean-Cocos triple junction area. In the vicinity of the triple junction, displacement related to the North America-Caribbean plate boundary takes place along the left-lateral Motagua-Polochic fault system, and convergence between the Cocos and the other two plates occurs along the Middle America trench. The trace of the Motagua-Polochic system is lost at its westernmost end and does not reach the convergent boundary. Deformation of the plate boundary in this location is then distributed along a system of reverse faults (the Reverse-faults tectonic province), a system of left-lateral faults (Strike-slip faults province), two or more large NW-SE oriented left-lateral faults (Angostura and Concordia faults), and a left-lateral fault (Tonalá) that might be construed as the continuation of the Polochic fault along the southern border of the Chiapas Massif. Somewhere within this deformation zone, transition in overriding plate between North America and Caribbean takes place, but it is not clear exactly where. It is probably at about longitude 96° W because both the dip and the shape of the subducted Cocos slab change significantly at this longitude.

The La Paz Plutonic Complex is located in southern Baja California Peninsula. In this complex calc-silicate rocks are associated with other metamorphic and intrusive rocks. The focus of this research is on the calc-silicate rocks in the eastern part of the Los Cabos Block with marble, calc-silicates and amphibolitic gneiss which extend for more than two kilometers and grouped as an informal unit called El Mezquite calc-silicates. Field relationships, megascopic, and microscopic characteristics indicate that the protoliths of the metasedimentary rocks were siliciclastic rocks alternated with calcareous sediments and volcaniclastic rocks deposited in a marine environment and subsequently metamorphosed. In the Arroyo El Mezquite, outcrops of undeformed igneous rocks of tonalitic composition and amphibolitic gneisses and orthogneiss are observed, theses last. The metamorphic unit is in contact with the undeformed intrusives and the calc-silicate rocks. This lithology indicates two metamorphic events, the first of regional character, represented by orthogneiss and amphibolitic gneiss and the second as contact metamorphism, represented by migmatites. Geochronology of the tonalite and the amphibolite gneiss with the U-Pb method on zircons yielded ages of 85.44 ± 0.66 Ma and 116 ± 1.5 Ma, respectively, indicating to magmatic events. The first age indicates indirectly the maximum age for contact metamorphism, while the second allows us to infer the possible minimum age of deposition and potentially the maximum age of regional metamorphism. The data obtained from the zircons of tonalite and amphibolitic gneiss were used to estimate their emplacement temperature of 650 ± 33 °C and 701 ± 42 °C, respectively. The presence of minerals such as diopside, wollastonite and rutile traces indicate temperatures of at least >700 °C of the metamorphism. The regional metamorphism reached the amphibolite facies. The El Mezquite calc-silicate rocks were deposited in the zone between a continental platform and an oceanic basin, subsequently affected by regional metamorphism (<116 Ma) and a contact metamorphic overprint (>85 Ma).

Cretaceous carbonate deposits are widely distributed along the Sierra Madre Oriental thrust belt from northern Veracruz to southern Nuevo León. At Cerro Boludo (Hidalgo), dark marly limestone samples were collected from the “Otates Horizon”. The samples include a well-preserved planktic foraminiferal assemblage composed of Globigerinelloides algerianus Cushman and ten Dam, 1948, Globigerinelloides ferreolensis (Moullade, 1961), Globigerinelloides barri (Bolli, Loeblich and Tappan, 1957), Globigerinelloides aptiensis Longoria, 1974, Globigerinelloides blowi (Bolli, 1959), Hedbergella roblesae (Obregón de la Parra, 1959), H. occulta Longoria, 1974, H. luterbacheri Longoria, 1974, H. similis Longoria, H. trochoidea Longoria, 1974, H. semielongata Longoria, 1974, Pseudoplanomalina cheniourensis (Sigal, 1952) and Schackoina cenomana Schacko, 1897. Radiolarians are also present. Based on the planktic foraminiferal assemblage we recognized the Globigerinelloides algerianus Total Range Zone of early late to middle late Aptian age. The paleonvironmental reconstruction inferred from the lithology and the foraminiferal association suggests an open pelagic deposit, besides the occurrence of pyrite framboids and the organic matter indicate oxygen-depleted conditions in a meso to eutrophic setting probably linked to the “late Aptian anoxic event”.

La Unión pluton (LUP) belongs to the metamorphic and igneous Sula Terrane (ST) of Central Guatemala, limited to the north by the Motagua fault (MF) and to the south by the Jocotán-Chamelecón fault system (J-CH-FS). The basement of the ST is characterized by the high-grade metamorphic rocks belonging to the Las Ovejas Complex and the extensive low-grade San Diego phyllite, the latter in tectonic contact with LUP. A combination of field data, petrographic and geochemical analyses as well as geochronologic dating by U-Pb method, allow to classify LUP as a monzogranite with an age of 170 Ma (average of two dated samples), characterized by high-K calcalkaline and peraluminous affinity and with a REE pattern typical of a continental magmatic arc. Some trace-elements behavior and a comparison of similar-age units found elsewhere in eastern, central and southern Mexico, allow to associate its formation to the lithospheric thinning and extension that occurred during the breakup of Pangea and the opening of the Gulf of Mexico.