Pedraza Gilsanz, Javier deCarrasco González, Rosa MaríaMartín Duque, José FranciscoSanz Santos, Miguel Ángel2023-06-202023-06-2020040583-7510https://hdl.handle.net/20.500.14352/51481El Macizo de Peñalara se localiza en el sector central de la Sierra de Guadarrama (Sistema Central Español) y sus cimas sobrepasan en unos 200 m el nivel general de cumbres que presenta aquí 2100 m de cota media absoluta (Fig. 1). En la estructura de bloques (Block mountain) que caracteriza el relieve de esta montaña intraplaca de reactivación Alpina, el Macizo de Peñalara corresponde a una dovela flanqueada por bloques más deprimidos (Fig. 2). Los límites del Macizo están asociados a fallas y, dentro de ellas, destacan las pertenecientes a los sistemas NNE-SSW y NNW-SSE (Fig. 3). La litología dominante del zócalo son ortogneises glandulares (también hay algunos leucocráticos) de edad preordovícica. Localmente aparecen rocas plutónicas (leucogranitos aplíticos) y filonianas (Aplitas) del ciclo hercínico. Los sedimentos de las coberteras mesozoicas (del Cretácico) y cenozoicas (del Paleógeno y Mioceno) y los recubrimientos de mayor entidad (de origen fluvial) se localizan en la fosa o depresión intramontana aledaña de El Paular o Alto Lozoya (Fig. 4). En el Macizo, sin embargo, afloran los materiales del zócalo o aparece recubiertos por Formaciones Superficiales o depósitos reciente (cuaternarios) discontinuos y de poca entidad: es le caso de los depósitos fluvioglaciares y torrenciales de los fondos de las gargantas, los tills de los complejos morrénicos pleistocenos (Fig. 5), y los depósitos de vertiente (aglomerados de bloques o canchales y lenguas de solifluxión) debidos a la actividad periglaciar. En hombreras, rellanos, y planicies de las cimas o de los piedemontes, abundan las depresiones semi-endorreicas (navas, algunas de origen cárstico) donde se producen fenómenos de decantación de finos (limos, arcillas) y reducción (depósitos turbosos). En las cimas y tramos superiores de las laderas, en cotas que superan los 2000 m., hay formaciones de ambiente frío (nivación y ciclos de helada), con signos de actividad. Son surcos o canales de arroyada por fusión nival, flujo de derrubios (debris flow), pedreras de bloques con crestas de imbricación, y suelos estructurados (rosetas, guirnaldas, enlosados) con signos de flujo (Figs. 6 y 7). La magnitud e intensidad de dichos fenómenos, es un tema que se debe investigarse en profundidad y servirá para concretar la idoneidad o no de definir estas áreas como un verdadero ambiente o piso periglaciar.The Peñalara Massif is located in the central area of the Guadarrama Mountains (Spanish Central System), and it constitutes the highest terrains within this mountain range (Peñalara Peak, 2428 m). The mountain tops exceed here about 200 m the generalized level of summits, which in this area of the Central System reach 2100 metres above sea level on average (Fig. 1). These topographic characteristics, along with its northern and continental imprint, make possible to argue about the presence of a current periglacial environment in the Peñalara Massif. This environment would be equivalent to the cryo-Mediterranean vegetation layer (summit grasslands). For the morpho-structure of serialized blocks (block mountain) which characterizes this intra-plate –Alpine reactivated-type— mountain, the Peñalara massif represents the ‘keystone’, to which other down-thrown blocks are laterally attached (Fig. 2). The appearance or physiognomy formed by this structural arrangement is the so-called ‘stairway piedmont’ (piedmonttreppen). The massif boundaries are related to faults, within which two systems are predominant: NNE-SSW and NNWSSE (Fig. 3). The faults which define the boundaries of the front Massif with respect to its interior valleys (El Paular and Alto Eresma) belong to the first system. The faults which define the link between the summit plains and the slope shelves belong to the second system. Orthoderived metamorphic rocks (from pre-Hercynian/pre-Ordovician rocks) constitute the predominant lithology of the basement. They are mostly glandular gneisses, but also leuco-gneisses. Locally, they appear Hercynian and post-Ordovician plutonic (aplitic leuco-granite) and dyke (aplite) rocks. As far as the sedimentary cover is concerned, including recent deposits, they are preferably concentrated at the basis of the Massif, and also in its slopes (Fig. 4). Sedimentary cover is mainly represented by Mesozoic and Cenozoic formations, located at the bottom of the El Paular (or Alto Lozoya) Valley graben. They consist in Cretaceous carbonate (dolomites and marl) and detritic (sands and sandstone) rocks, and also Palaeogene (conglomerate and sands) and Neogene (conglomerate and arkoses of the Miocene) rocks. Piedmont and valley-filling surficial deposits have a major fluvio-torrential origin (alluvial fans and fluvial terraces), of a Pleistocene age. To a lesser extent, there are also channel deposits (alluvial sand, silt, gravel and pebbles) and almost-endorreic lowland sediments (some of them of karstic origin, filling sinkhole-type pits), where decanting of silt and clay –and reduction processes, with peat formation— occurs. Recent slope deposits, despite not being of a great entity in this massif, they have an interest for the interpretation of cold climate geomorphic processes—they are fluvio-glacial and torrential deposits in gorge bottoms, glacial tills and moraine deposits (Fig. 5) and hillslope sediments (scree, talus slope and solifluction lobes), originated by periglacial (cryogenic) activity. Within the summits and the highest zones of the slopes, almost always above 2000 m.a.s.l, there are surficial deposits with signs of current activity, which will be determining factors in order to establish the current magnitude of the cold climate geomorphic activity (snow and freeze-and-thaw processes). Examples of these surficial deposits and landforms are avalanche gullies and debris flow channels, imbricate stones and small ridges within talus slope deposits, and patterned grounds (stripes, garlands and stone pavements) with signs of current flow (Figs. 6 and 7). The magnitude and intensity of these cold climate processes is an issue that should be investigated deeply (a first step is the periglacial processes gauge at Dos Hermanas). This research will serve for defining or not these areas as a truly periglacial environment.spajournal articlehttp://historia.bio.ucm.es/rsehn/index.php?d=publicacionesopen access551.324(234.1)(234.1)551.324Sierra de GuadarramaMontaña intraplacaGeomorfología Glaciar y PeriglaciarSistema Central EspañolGuadarrama mountain rangeIntraplate mountainGlacial and Periglacial GeomorphologySpanish Central SystemGeodinámica2507 Geofísica