{"title":"Superposed Variscan and Alpine deformation in the basement rocks of southern Andorra, Central Pyrenees","authors":"A. Margalef, P. Granado, J.M. Casas","doi":"10.1144/jgs2023-099","DOIUrl":null,"url":null,"abstract":"Detailed mapping, structural analysis and cross-section constructions yield new data on the geometry and chronology of Variscan and Alpine deformations in the central Pyrenees of southern Andorra. The studied area is characterized by polyphase deformation and strain partitioning due to the presence of an efficient décollement level within Silurian black shales. Variscan macrostructures gave rise to a minimum shortening of ca. 22% for Cambrian-Ordovician and Upper Ordovician units below the décollement level and of ca. 35% for Silurian and Devonian units above it. Variscan structures are cut by out-of-sequence thrusts, presumably developed after late Variscan igneous intrusions, and extensional faulting. Those thrusts cut previous Variscan D 2 (main-phase) folds and originate additive and subtractive contacts. We propose an Alpine age for most of these thrusts which, together with the Variscan structures, are affected by subsequent Alpine deformation, which causes changes in their orientation around the intrusions, and a progressive steepening of the cleavage from south to north. We discuss the usefulness and limitations of balanced cross-sections in polydeformed areas and propose that the technique is valid to construct regional sections and to obtain geologically reasonable pre-deformational configurations.","PeriodicalId":17320,"journal":{"name":"Journal of the Geological Society","volume":"21 1","pages":"0"},"PeriodicalIF":2.6000,"publicationDate":"2023-09-27","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Journal of the Geological Society","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/10.1144/jgs2023-099","RegionNum":3,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q2","JCRName":"GEOSCIENCES, MULTIDISCIPLINARY","Score":null,"Total":0}
引用次数: 0
Abstract
Detailed mapping, structural analysis and cross-section constructions yield new data on the geometry and chronology of Variscan and Alpine deformations in the central Pyrenees of southern Andorra. The studied area is characterized by polyphase deformation and strain partitioning due to the presence of an efficient décollement level within Silurian black shales. Variscan macrostructures gave rise to a minimum shortening of ca. 22% for Cambrian-Ordovician and Upper Ordovician units below the décollement level and of ca. 35% for Silurian and Devonian units above it. Variscan structures are cut by out-of-sequence thrusts, presumably developed after late Variscan igneous intrusions, and extensional faulting. Those thrusts cut previous Variscan D 2 (main-phase) folds and originate additive and subtractive contacts. We propose an Alpine age for most of these thrusts which, together with the Variscan structures, are affected by subsequent Alpine deformation, which causes changes in their orientation around the intrusions, and a progressive steepening of the cleavage from south to north. We discuss the usefulness and limitations of balanced cross-sections in polydeformed areas and propose that the technique is valid to construct regional sections and to obtain geologically reasonable pre-deformational configurations.
期刊介绍:
Journal of the Geological Society (JGS) is owned and published by the Geological Society of London.
JGS publishes topical, high-quality recent research across the full range of Earth Sciences. Papers are interdisciplinary in nature and emphasize the development of an understanding of fundamental geological processes. Broad interest articles that refer to regional studies, but which extend beyond their geographical context are also welcomed.
Each year JGS presents the ‘JGS Early Career Award'' for papers published in the journal, which rewards the writing of well-written, exciting papers from early career geologists.
The journal publishes research and invited review articles, discussion papers and thematic sets.