601.
AbstractLocated in the central part of the Betic Cordilleras, the large carbonate Sierra Gorda Massif provides an example of a west-Mediterranean karstic aquifer. In spite of a complex polyphased tectonic history, the fracturing presents, from aerial views and at outcrop scale a quite organised geometry. Four fracture directions are found over the massif. N000—010, NOS0-070, N090–100 and N140–170. The statistical and geostatistical approach allows the characteristics (lengths, orientations) and the spatial structure for each fracture set to be determined. The N000–010 and N140–170 sets are grouped in packets whereas the two other sets are grouped in bands. The microtectonic study describes the evolution of the massif in the geodynamic context of this part of Mediterranea, distin guishing three recent stages of brittle tectonic activity in t e massif: a WNW-ESE Middle Miocene compression, then a NNW-SSE to NW-SE compression with a poorly wrenching regime, and finally a probably pre-Quaternary N-S radial distension. This last stage is essential for the karstification of the massif and groundwater circulation. From the combined analysis of fracture network geometry and palaeostresses a multiple porosity model in agreement with hydrological observations made inside the massif can be proposed: in particular, the hectometric N090–100 (and N050–070) fractures which are essential for the network connectivity, and have a major drainage role at aquifer scale, while the N000–010 and N140- 170 ones have a more local drainage role. This extensive tardy regime, which is for the first time described separately from the internal zones of the Cordilleras, must be considered as a significant phenomenon on a regional scale, and henceforth integrated in future geodynamic schemes of this part of Mediterranea. © Elsevier, Paris
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