Abstract
A new gravity survey (1164 gravity stations and 180 samples for density analysis) combined with two new geological cross sections has been carried out in a sector of the Central Pyrenees in order to improve the characterization of basement and cover architecture. From North to South, the study area comprises the southern half of the Axial Zone and the northernmost part of the South-Pyrenean Zone. New gravity data were combined with previous existing databases to obtain the Bouguer and residual anomaly maps of the study area. The two cross sections, oriented NNE–SSW, were built from field data and previous surficial and subsurface data and cross the La Maladeta plutonic complex. The residual anomaly map shows values ranging from −18 to 16 mGal and anomalies mainly oriented N120E. The two 2.5D modelled cross sections show similar observed gravity curves coinciding with similar interpreted structural architecture. Data show a gravity high oriented N120E coinciding with the Orri basement thrust sheet and an important gravity depression, with the same orientation, coinciding with the leading edge at depth of the Rialp basement thrust sheet and interpreted as linked to a large subsurface accumulation of Triassic evaporites. The volume at depth of the La Maladeta and Arties granites has been constrained through gravity modelling. This work highlights that the combination of structural geology and gravity modelling can help to determine the structural architecture of an orogen and localize accumulations of evaporites at depth.
Highlights
The Pyrenees (Northeast of Spain and South of France) have attracted multitude of research during the past decades due to their excellent outcrops generating an extensive knowledge of its surface geology and map-based reconstructions
In large areas to the south of the Axial Zone, the Mesozoic and Cenozoic cover was decoupled from the basement along the Triassic evaporites, which act as the regional décollement
Some points have been refined through the gravity modelling, i.e. the distribution and thickness of the Triassic evaporites
Summary
The Pyrenees (Northeast of Spain and South of France) have attracted multitude of research during the past decades due to their excellent outcrops generating an extensive knowledge of its surface geology and map-based reconstructions. The ECORS-Pyrenees deep seismic reflection profile acquired during the 80s provided the first image of the structure and reflectivity of the crust across the Central Pyrenees. In the central part of the chain, the internal architecture of the orogen consists of an antiformal stack of basementinvolved units dominated by Paleozoic rocks (Axial Zone) and two fold-and-thrust belts involving Mesozoic and Cenozoic units flanking the Axial Zone to the north and south (e.g., Muñoz 1992; Fig. 1). The subsurface structure of the Mesozoic and Cenozoic cover has been mainly constrained from the interpretation of seismic data and wells acquired during the 60s, 70s and 80s (e.g., Muñoz 1992; Vergés 1993; Teixell and Muñoz 2000; Muñoz et al 2018). In the Axial Zone and leading edges, subsurface data are very scarce and the geometry of structures at depth is more speculative
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