ABSTRACTIn this work we present a 1:50,000 geological map of the basement rocks of Andorra that is the harmonization of the results of two decades of field work and data analyses in the frame of the ...1:25,000 Geological Map of Andorra Project by CENMA–IEA (at present AR + I, Andorra Research + Innovation). The study area lies entirely in the Axial Zone of the Pyrenees, where only late Neoproterozoic and Paleozoic rocks and Quaternary deposits crop out. The map is produced at 1:25,000 scale and Quaternary deposits have been removed, in order to obtain a continuous basement map that can be used as the basis for stratigraphical and structural works. The main results of this work are the publication of new cartographic and structural data, as well as a better understanding of the stratigraphy in this sector.
The tectonic style of the eastern morphostructural units of the Central Andes between 32degrees20' and 33degrees20'S is strongly influenced by pre-Andean structures, especially those developed during ...the late Carboniferous-Early Permian San Rafael orogeny of the Gondwanan orogenic cycle. Moreover, in the study area pre-Carboniferous rocks were deformed in Late Devonian-early Carboniferous times by the Chanic orogeny. In this paper we argue that the Cordon del Plata and the Southern Precordillera ranges, first order features of the eastern ranges of the Andes, have been shaped in large part by the Permian event. Our data suggest that the double verging character of the Andean Precordillera fold- thrust belt is mainly the result of the reactivation of Gondwanan structures which conform a fold-thrust belt with distinct characteristics north and south of 33degreesS. The northern sector of this belt corresponds to a bivergent system, while the southern sector had a widespread east vergence. The vergence of the Chanic structures is more difficult to determine, but we infer a westward vergence in the Frontal Cordillera and western sector of Precordillera, and an eastern vergence in the eastern sector of the Precordillera. The sharp disappearance of the Precordillera morphostructural unit south of 33degreesS is inferred here to be related to the distribution of inherited Permian structures. Keywords: Southern Central Andes, Permian fold-and-thrust belt, Andean thrust front, Chanic orogeny, Frontal Cordillera El estilo tectonico del sector oriental de las unidades morfoestructurales de los Andes Centrales entre los 32degrees20'y 33degrees20'S se encuentra fuertemente influenciado por estructuras pre-andinas, especialmente aquellas desarrolladas durante el Carbonifero superior-Permico Inferior y asociadas al orogeno San Rafael del ciclo orogenico Gondwanico. Ademas, en el area de estudio, las rocas pre-carboniferas se deformaron durante el Devonico Superior y Carbonifero inferior, en relacion con la orogenia Chanica. En este trabajo discutimos los rasgos de primer orden del sector oriental de los Andes, que comprende al Cordon del Plata y a la Precordillera Austral, fueron en gran parte modelados a partir del evento permico. Nuestros datos sugieren que la doble vergencia de una faja plegada y corrida en la Precordillera Andina es el resultado principalmente de la reactivacion de estructuras gondwanicas que conformaron una faja plegada y corrida con caracteristicas distintivas al norte y sur de los 33degreesS. El sector norte de la faja corresponde a un sistema bivergente, mientras que el sector sur posee una vergencia predominantemente oriental. La vergencia de las estructuras chanicas es mas dificil de predecir, pero se sugiere aqui una vergencia hacia el oeste para las estructuras de la Cordillera Frontal y el sector occidental de la Precordillera y otra hacia el este para las estructuras del sector oriental de la Precordillera. Se infiere que la marcada desaparicion de la Precordillera como unidad morfoestructural andina al sur de los 33degrees esta relacionada a la distribucion de estructuras chanicas y gondwanicas. Palabras clave: Andes Centrales del Sur, faja plegada y corrida permica, frente de deformacion andino, orogeno Chanico, Cordillera Frontal
The Palaeozoic basement outcropping to the north of Los Vilos is formed by (i) the Choapa Metamorphic Complex (ChMC) made of metabasites (amphibolites and retrogressed eclogites), fine-grained ...gneisses, schists and quartz-schists, and (ii) the meta-sedimentary and sedimentary rocks of the Arrayan and Huentelauquen formations respectively. Near Huentelauquen (31degrees 30' S), the ChMC has been affected by three deformation episodes related with the Gondwanan orogenic episode. The first episode (D1) is represented by a foliation (S1) formed under HP-LT metamorphic conditions and preserved in syn-D2 garnet and albite porphyroblasts. A generalised crenulation cleavage (S2) was developed under pressure decreasing conditions during the second deformation episode (D2). This episode is responsible for the exhumation of the ChMC, which took place through an east-directed reverse fault system that thrusts the ChMC over the Arrayan Formation, producing more than 20 km shortening. The third deformation episode (D3) is represented by a west-verging kilometre-scale anticline, with a thrust in its reverse limb (Las Caldas thrust). Minor folds and crenulations are also associated with D3. D3 structures affect the ChMC and the Arrayan Formation and are responsible for the overturning of the D2 thrusts. The Huentelauquen Formation, late Carboniferous--Permian in age, is the latest unit deformed by Gondwanan structures. The characterisation of the structure and its relation to metamorphism in the study area, lead to propose a geodynamic model related with an Andean type non-collisional orogenic process, for the Gondwanan orogenic episode of the Andes at this latitude. Keywords: Gondwanan structure, tectono-metamorphic evolution, Choapa Metamorphic Complex, Chile, system thrust El basamento Paleozoico que aflora al norte de Los Vilos esta constituido por (i) el Complejo Metamorfico de Choapa (CMCh), formado por esquistos, cuarzo esquistos, gneises de grano fino y metabasitas (anfibolitas y retroeclogitas) y (ii) rocas metasedimentarias y sedimentarias de las formaciones Arrayan y Huentelauquen respectivamente. En los alrededores de Huentelauquen (31degrees 30' S), las rocas del CMCh han sido afectadas por tres fases de deformacion (D1, D2, D3), relacionadas con el episodio orogenico Gondwanico. Las estructuras D1 estan representadas por una foliacion tectonica (S1), que se desarrollo bajo condiciones metamorficas de AP-BT y que esta preservada en porfiroblastos de granate y albita, crecidos durante el segundo episodio de deformacion. Durante la fase de deformacion D2 se produce una bajada de la presion y se desarrolla la foliacion regional S2. La foliacion S2 es contemporanea con el emplazamiento de un duplex de cabalgamientos dirigidos hacia el este que exhuman el CMCh y lo situan sobre las series epimetamorficas de la Formacion Arrayan. El acortamiento que producen las estructuras D2 es superior a 20 km. La tercera fase de deformacion esta representada por pliegues y crenulaciones asociados a un antiforme de escala kilometrica, vergente al oeste, al que se asocia un cabalgamiento dirigido en esa misma direccion (cabalgamiento de Las Caldas). Estas estructuras D3 son las responsables de la inversion de los cabalgamiento D2 de la zona estudiada. La Formacion Huentelauquen, del Carbonifero superior--Permico, es la unidad mas moderna afectada por estructuras Gondwanicas. El analisis de la estructura y su relacion con el metamorfismo en la zona estudiada permiten proponer un modelo geodinamico ligado a un proceso orogenico no-colisional, de tipo Andino, para el episodio orogenico Gondwanico de los Andes a esta latitud. Palabras clave: Estructura gondwanica, evolucion tectono-metamorfica, Complejo Metamorfico de Choapa, Chile, sistema de cabalgamientos
The Punta Negra Anticline is a thrust-related fold, several kilometres wide, located at the front of the Argentine Central Precordillera. A stratigraphic succession including Ordovician, Silurian and ...Devonian rocks is exposed in its core, instead of a Devonian and Carboniferous succession as previously had been considered. The Punta Negra Anticline also involves a Tertiary sequence displaying syntectonic unconformities in the transition between the Albarracin and Mogna formations, recording the timing of thrusting and folding at the front of the Central Precordillera. This anticline folds thrust systems detached at the Silurian and Devonian shales, which we interpret as pre-Andean (Gondwanan) thrusts in this part of the Precordillera. The pre-Andean age of these thrusts is also consistent with their truncation by Tertiary subvolcanic intrusive bodies that predate the onset of the Andean deformation in the Punta Negra area. Moreover, the size and structural style of the Punta Negra Anticline, Andean in age, is in contrast with the other folds of the Central Precordillera, whose sizes do not exceed the hectometric scale and can be related to Gondwanan thrusting. This implies an Andean deeper thrust, probably detached at the bottom of the Cambrian succession.
The Cordon del Carrizalito is located in the southern sector of the Andean Frontal Cordillera. In this area, the Andean basement is composed of meta-sedimentary rocks (Las Lagunitas Formation) of ...Ordovician age. In addition, no- or very low grade metamorphism and less deformed rocks also occur in the study area. We call these rocks Selerpe series, whose characteristics are comparable to other series, late Carboniferous in age, described in nearby areas. The Las Lagunitas Formation is affected by west-verging folds, developed under low-grade metamorphic conditions. These structures can be attributed to the Chanic orogeny (Late Devonian--early Carboniferous). The Selerpe series and Las Lagunitas Formation are deformed by east-verging thrusts and folds developed in narrow bands and generated in the absence or under very low metamorphic conditions. These structures always deform the Chanic structures, and are attributed to the Gondwanan deformation (San Rafael orogeny, late Carboniferous--Permian in age). The Chanic structures of the study area can be placed in the western branch and in the hinterland of the Chanic orogen, which was developed as a result of the accretion of the Chilenia terrane at the west Gondwana margin during Late Devonian and early Carboniferous. The eastern branch of this orogen is located in the Andean Precordillera. The Permo-Triassic cover, deformed by the Andean orogenic cycle (Mesozoic--Cenozoic), rests unconformably on the Palaeozoic basement rocks. Keywords: Palaeozoic basement, Chanic orogeny, Gondwanan deformation, Andes, Argentina En el Cordon del Carrizalito, situado en el sector meridional de la Cordillera Frontal de los Andes, afloran metasedimentos ordovicicos pertenecientes a la Formacion Las Lagunitas y otro conjunto de rocas menos deformadas, en ausencia de metamorfismo o con metamorfismo de muy bajo grado, que hemos denominado serie de Selerpe. Esta ultima es litoestratigraficamente comparable a series del Carbonifero superior descritas en areas proximas. La Formacion Las Lagunitas esta afectada por pliegues apretados, vergentes al oeste y desarrollados bajo condiciones de metamorfismo de bajo grado. Estas estructuras pueden ser atribuidas a la orogenia Chanica (Devonico Superior--Carbonifero inferior). La deformacion Gondwanica, atribuida a la orogenia San Rafael, (Carbonifero superior--Permico), afecta tanto a la serie de Selerpe como a la Formacion Las Lagunitas y se caracteriza por cabalgamientos y pliegues vergentes al este y generados en ausencia de metamorfismo o bajo condiciones metamorficas de muy grado bajo. Las estructuras chanicas de la zona estudiada se encuentran en las zonas internas de la rama occidental del orogeno del mismo nombre. Estas estructuras se desarrollaron como resultado de la acrecion del terreno de Chilenia al margen occidental del antiguo continente de Gondwana durante el Devonico Superior--Carbonifero inferior. La rama oriental del orogeno Chanico se situa en la Precordillera andina. La cobertera permo-triasica, deformada durante el Mesozoico y Cenozoico por el ciclo orogenico Andino, se apoya discordantemente sobre las rocas del basamento paleozoico. Palabras clave: Basamento Paleozoico, orogeno Chanico, deformacion Gondwanica, Andes, Argentina
The paper describes ubiquitous extensional structures developed in a passive margin of Ordovician age in the Argentine Precordillera. These extensional structures include normal faults and boudinaged ...sequences. In some places the boudinage reaches very high extension values, giving rise to block-in-matrix formations. Most of these extensional structures developed when sediments were not well lithified, as recorded by hydroplastic fractures, slump folds and pinch-and-swell structures. The presence of slump folds coeval with the extensional deformation, the variable extension directions obtained from the kinematic analysis and a weak cleavage recording layer-perpendicular shortening support the interpretation that gravitational collapse related to submarine sliding was the cause for extensional deformation. Well-consolidated rocks, located at the lower part of the stratigraphic sequence, also display scarce extensional faults. These extensional faults predate folding because they were breached by flexural-slip faults and, as a result of their passive rotation in fold limbs, these initial normal faults may now appear as reverse faults, particularly in steep and overturned limbs. The truncation of extensional faults by flexural-slip faults produces typical bed thickness changes across the extensional faults, giving rise to apparent synsedimentary faults. These normal faults can be attributed to the crustal extension that generated the passive continental margin or may represent deep parts of faults related to gravitational collapse.
Research in caves is rare and restricted to speleological explorations. Picos de Europa Massif shows a spectacular development of vertical caves deeper than 500 m. Torca Teyera is a 738 m-deep and 4 ...km-long vertical cave. The aim of this work is to establish a methodology to characterize the geological and geomorphological aspects of this special group of caves, as well as to identify the factors conditioning karst development. The research involves (1) the cave survey at a 1:500 scale and the construction of a 3D model, (2) the geomorphological mapping on the topographical survey, (3) the geological mapping of the cave environment at 1:5000 and (4) the comparison in stereographic projection of the obtained survey data and joint measures.
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