El Magmatismo del sector de Atienza (Guadalajara): Cartografía geológica, estudio estructural, petrología y geoquímica y modelo de emplazamiento

Majarena Serrano, Urbez
Lago San José, Marceliano (dir.)

Universidad de Zaragoza, CIEN, 2015
Ciencias de la Tierra department, Petrología y Geoquímica area

Graduado en Geología

Abstract: The Atienza magmatism is formed by hypovolcanic and volcanic intermediate rocks of Lower Permian age. Previous studies were focused in a preliminary description of the magmatic rocks as a whole and the dating of the magmatism, proposing a radiometric age of 287±12 Ma (Lower Permian). The aim of this study is to characterize the petrology and geochemistry of the igneous rocks of this sector and to establish the geological relationships between the different igneous outcrops. The final objective of this study is to identify the origin, evolution and emplacement of the magmas during the Lower Permian. There are two hypovolcanic sills in the studied area. The main sill is emplaced between the Silurian and Permian sequences and includes most of the identified subvolcanic outcrops. The second sill is smaller, located to the NW part of the studied area and emplaced into the Permian sedimentary sequence. In addition to these sills, some N-S trending dikes have been identified intruding the main sill in its northeastern part. On the other hand, the volcanic unit is composed by several levels of pyroclastic coarse-grained rocks with intercalations of fine-grained cinerites. The identified layers of these rocks indicate different volcanic pulses. The studied rocks range from amphibole andesites to dacites with minor pyroxene andesites. The differences between hypovolcanic and volcanic rocks are related to the presence or absence of pyroclasts and fossil flora and to the nature of the matrix of the rocks, fine-grained or glassy and vacuole-rich. Metapelite xenoliths and xenocrysts of garnet are common in all the studied rocks. According to the mineralogical and geochemical data, this magmatism is calc-alkaline and belongs to the SiO2-saturated series. Although all samples are similar, two compositional groups can be identified. The main group includes dikes and the bigger sill. The second group is formed by the sample of the small sill and the studied volcanic rock. The evolution of the composition of the main mineral phases allow to recognized different magmatic processes: magmatic chamber recharge, fractional crystallization and assimilation of crustal xenoliths. Trace element composition of the rocks indicates the crustal influence in the origin of the magma. Finally, the common presence of crustal xenoliths and xenocrystic garnets and overgrowth rims in amphibole indicate a rapid ascend of magma favored by deeper faults. The Bornova fault, located to the E of the main sill, could act as a feeder conduct of the magma to the emplacement level. The discontinuity between the Silurian and Permian was a favorable surface of emplacement of the magma.

Tipo de Trabajo Académico: Trabajo Fin de Grado

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