Towards a Geological Information System: the CARGeo System and the Regione Lombardia Geological Database.

In the framework of the national mapping program «CARGNew Italian Geological Map at 1:50.000 scale», Regione Lombardia is generating a detailed map (1:10.000 scale) of its territory. Surveying criteria have been carefully defined in order to produce homogeneous geological maps: geological survey has been performed at the 1:10.000 scale, and data have been stored in a GIS-oriented database. The detailed survey scale improved the geological knowledge: the new maps represent an important tool for territorial planning requirements of public administrations and engineering geologists (e.g. in hydrogeological and seismic risk evaluation). Field geologists performed data input in the geological data base by alternating field campaigns and data input throughout the year, taking advantage of periods when field activities are slackened (i.e. according to climate conditions). In this way, data entry is nearly synchronous with data collection, and field data become quickly accessible. Data entry by the field geologists on one side slows down the field activity, however, it guarantees a precise digitalization of geometric data and a correct attribute assignment, allowing to optimize working time. To allow the data entry to non-GIS-specialized users, we developed an ArcView®-VisualBasic®-MSAccess® application, enabling the simultaneous acquisition of geometric and alphanumeric data. Data base management and cartographic production are performed with ArcInfo®, through specific procedures which, after data reorganization and control (both alphanumeric and geometric), lead to the final cartographic output at different scales. The 1:10.000 geological database is migrated in the ArcSDE structure and prepared for data view, query and download (www.cartografia.regione.lombardia.it/cargweb) using ESRI (ArcIMS) tools. From the 1:10.000 geological database we derived the database for the 1:50.000 CARG maps by both automatic and manual generalization according to the CARG-APAT standards. During the different phases of the project, several problems arose, due to both project organization and data storage system (from data collection in the field to elaboration and digitalization, and, in case, to final publication). – Data collection: the survey activity was divided between «bedrock » and «quaternary» specialists. The double survey provided a high-quality geological description of the territory, but slowed the generation of the data-flow. Based on this experience, the last assigned areas are surveyed by a single geologist, under the supervision of quaternary and bedrock experts. – Users feedback: geologists are normally used to draw their maps on paper; learning how to produce electronic maps can be difficult, and the software tools have to be studied very carefully and present user friendly interfaces. Nevertheless, in our experience, a training period has to be planned, and geologists have to be supported by a GIS expert, who can understand their needs and modify the software accordingly. – System architecture: the ArcView®-VisualBasic®-MSAccess® (Windows platform) – ArcInfo® (UNIX platform) environment, revealed problems in the client-server stability of an earlier version; some unsolved troubles remain, mainly related to the network architecture. The presence in the CARG-Regione Lombardia crew of consultant geologists, experienced and trained in collection, analysis and data entry in the final database, accelerated the critical phases of: – Data base derivation from Regione Lombardia dataset to CARG-APAT standard

Deformation and metamorphism associated with crustal rifting : Permian to Liassic evolution of the Lake Lugano-Lake Como area (Southern Alps)

In connection with movements between Europe and Adria, the Southern Alps underwent extension leading to the formation of the Middle Jurassic South-Alpine passive continental margin. As a result of mainly S-vergent Alpine thrusting and folding, a substantially preserved Mesozoic crustal section, ranging from the surface to a paleo-depth of ca. 15 km is exposed in the Lugano-Lake Como area. Tectonic processes associated with Permo-Mesozoic extension can thus be investigated at different crustal levels. Rifting began with a thermal anomaly during which rocks at middle-crustal levels were sheared at ca. 650-750\ub0C. Deformation was distributed on a several km wide zone and late-kinematic pegmatites were emplaced at this stage. Temperatures then decreased and beginning in the Norian, extension was accommodated by a major, E-dipping normal fault, the Lugano-Val Grande normal fault. The fault which can be followed down to a paleo-depth of ca. 12 km, was listric and flattened (to 20\ub0) at ca. 7-9 km depth. In the upper 8-10 km, deformation was only brittle, whereas at deeper crustal levels greenschist mylonites were formed. With continued normal faulting the colder hanging wall cooled the fault zone and greenschist mylonites were progressively replaced by lower-temperature ultramylonites and cataclasites. The thickness of the fault zone varies from some tens of meters in the upper 5-6 km to several hundred meters at deeper levels: deformation was thus discrete at a crustal scale

The Central Southern Alps (N. Italy) paleoseismic zone: a comparison between field observations and predictions of fault mechanics

The internal sectors of the Orobic Alps (Northern Italy) are characterised by Alpine age regional shortening showing a transition, through time, from plastic to brittle deformation. Thrust faults cut Alpine ductile folds and are marked by cataclasites and, locally, by pseudotachylytes, suggesting that motion was accommodated by seismic frictional slip. In the Eastern Orobic Alps the thrusting initiated at depths deeper than 10 km (the emplacement depth of the Adamello pluton) and possibly continued at shallower depths. This demonstrates that thrust motion occurred between 10 km depth and the brittle-ductile transition, i.e., at mid-crustal depths. The Orobic Alps exhumed paleoseismic zone shows different geometries along strike. In the central sectors of the Orobic Alps, thrust faults, associated with pseudotachylytes, have average dips around 40 degrees and show no pervasive veining. Much steeper thrusts (dips up to about 85 degrees) occur in the eastern Orobic Alps. In this area, faults are not associated with pervasive veining, i.e., fluid circulation was relatively scarce. This suggests that faulting did not occur with supralithostatic fluid pressure conditions. These reverse faults are severely misoriented (far too steep) for fault reactivation in a sublithostatic fluid pressure regime, We suggest that thrust motion likely started when the fault, were less steep and that the faults were progressively rotated up to the present day dips. Domino tilting is probably responsible for this subsequent fault steepening, as suggested by a decrease of the steepness of thrust faults from north to south and by systematic rotations of previous structures consistently with tilting of thrust blocks. When the faults became inclined beyond the fault lock-up angle, no further thrusting was accommodated along them. At later stages regional shortening was accommodated by newly formed lower angle shear planes (dipping around 30-40 degrees), consistently with predictions from fault mechanics. (c) 2005 Elsevier B.V. All rights reserved

Superposed syn-metamorphic structures of the Alpine and pre-Alpine convergent cycles in the Southalpine basement of the Orobic Alps (Northern Italy)

New detailed maps of two key areas of the Southalpine basement unravel the superposition of pre-Alpine deformation stages associated with different metamorphic imprints, and distinguish Alpine thrust and fold structures involving basement and Permian-Mesozoic sedimentary cover. Basement rocks consist of metasediments (micaschists, quartzites and paragneisses) and metagranitoids and cover rocks comprise Permian volcanics and sediments. The boundaries between two tectono-metamorphic units have been distinguished at the map scale, thanks to the integrated use of structural and petrological analyses, on the basis of foliation trajectories supported by metamorphic assemblages. Two different pre-Alpine metamorphic evolutions characterise a basement portion that seemingly appears as a monotonous sequence dominantly affected by a greenschist-facies imprint. The volcano-sedimentary sequence of Permian age has been used as the time marker that separates Alpine from pre-Alpine superposed structures; Alpine deformation consists of two superposed groups of structures, the first of which is locally associated with a very low-grade metamorphic imprint and related at the regional scale to a south-verging thrust system