New gravity interpretations in the northern and eastern side of the Colli Albani Volcanic District: first results

Vienna, Austria, 02-07 April 2006

The Colli Albani is a quiescent Volcanic District, located almost 20 Km southeast of
Rome. It has been active since at least 600 ka and it belongs to the potassic and ultrapotassic
Roman Magmatic Province, a northwest-trending chain of volcanoes that
developed along the Tyrrhenian Sea Margin of Italy during middle and late Pleistocene
time. The Albano maar (< 70 ka) represents the most recent activity of the
hydromagmatic phase and cannot be considered extinguished yet. First Gravimetric
map of Colli Albani Volcanic District was made by the Italian Geological Service
from the 1:100,000 Gravimetric Map of Italy (Maino et al., 1969) and later some new
gravity interpretations were performed by Di Filippo & Toro (1980, 1995). This paper
gives preliminary gravity results in the northen and eastern side of the Volcanic
District in order to obtain a detailed gravity map of Colli Albani Volcanic District. A
broad area N of lake Albano (Rome, Ciampino-Marino) is the most one strongly characterized
by the occurence of geochimical manifestation of a still-active subvolcanic
system which are hazardous factors for the resident population. In eastern side of the
volcano the previous studies showed that some areas are completely missing gravity
stations. In this study the mesh interval between each gravity station are 500 m2 on
average; in the previous was 2 km2 on average. A new Residual anomaly map has
been prepared by substracting the first order Regional Field from Bouguer anomalies.
The Residual anomaly map is very detailed and represents the most suitable picture
for understanding the structure of the prevolcanic substratum. Residual anomaly map
shows a maximium gravity value of Ciampino High, spatially continuous along the
major NW-SE axis, corresponds to where the high distribution of radon and CO2 was
observed. Another maximum value is located in the southern part of the Ciampino
High relative to Rocca di Papa, where the second activity of the volcano took place.A minimum region gravity is located in the eastern part of the Ciampino High. The
map shows faults obtained by gravity interpretations. The superficial geological data,
the drill log data, and metamorphic xenoliths from the eruption of Colli Albani (Funiciello
& Parotto, 1978) and gravity data have been analyzed all together in order to
know sub-surface structure of this area and make a bi-dimensional gravity model. In
order to define the heterogeneity of the lithotypes some sections have been prepared
by gravity model.