ABSTRACTS / RESUMES - Comitato Glaciologico Italiano

sponse times are examined for a thufa and depression. Results
show that the mean depression temperatures are considerably
warmer than the mean thufa temperatures at 12
ern depth. Pronounced temperature differentials occurred
during the winter months when thufur were frozen for several
weeks and depressions remained predominantly unfrozen.
The findings indicate current thufur activity at favourable
sites in the Lesotho Mountains under present climatic
conditions.
VINCENT GRANDGIRARD
Geomorphologie et protection de la nature en Suisse.
L'inventaire des geotopes d'importance nationale
Institut de Geographie, Universite de Fribourg, Perolles,
1700 Fribourg, Suisse
La nature, comprise dans Ie sens de «milieu physique», ne
se limite pas au monde vivant. Les composants de la lithosphere,
de l'hydrosphere et de l' atmosphere participent
egalement a la dynamique du milieu nature!' En vertu de
cette conception, la protection de la nature ne saurait se
restreindre a la protection de la flore et de la faune.
Dans Ie domaine des sciences de la Terre, une discipline
nouvelle est en train de naitre: la «geoconservation». D'une
maniere generale, celle-ci se preoccupe de la protection
des geotopes, c'est-a-dire des portions de la geosphere presentant
une importance particuliere pour la comprehension
de l'histoire de la Terre. La geoconservation represente
un important champ d'activite pour les geomorphologues.
Nombre de formes du relief et de processus
morphogeniques possedent en effet unevaleur scientifique
et didactique qui en fait des geotopes dignes de protection.
L'etude de ces phenomenes, leur evaluation et leur gestion
sont autant de defis lances aux geomorphologues.
En Suisse, les bases legales et les instruments de planificationpermettant
la protection des geotopes sont insuffisants.
Le Groupe de travail pour la protection des geotopes
en Suisse, qui rassemble des specialistes des differentes
disciplines des sciences de la Terre, consacre beaucoup
d'energie a promouvoir la cause desgeotopes, Ce groupe
prepare actuellement un inventaire de geotopes d'importance
nationale. La realisation de cet instrument de gestion
repose sur une large consultation, effectuee par Ie biais
d'un questionnaire, aupres de tous les milieux interesses
(autorites, responsables de la protection de la nature, societes
scientifiques, enseignants et chercheurs oeuvrant
dans Ie domaine des sciences de la Terre, geologues praticiens,
musees d'histoire naturelle, etc.). Outre une description
detaillee des geotopes proposes, les informations
concernant ces derniers, recueillies par Ie biais d'un questionnaire,
permettent d'apprecier leur valeur, les menaces
qui les affectent et les mesures de gestion existantes ou
proposees,
Au terme d'une selection, une centaine de geotopes d'importance
nationale seront proposes. Complete par un guide
sur la protection des geotopes, cet inventaire pourrait
constituer un premier pas en direction de la realisation
d'une «Ordonnance sur la protection des geotopes d'importance
nationale».
DARRYL E. GRANGER 1, LEONARDO PICCINI 2 ,
JAMES W. KIRCHNER\ LUIGI CARMIGNANI\
PIERO FANTOZZI 4, MARCO MECCHERI 4
& ENRICO TAVARNELLI 5
Dating exhumation of orogenic belts using cosmogenic
isotopes in cave deposits and alluvial terraces
1Department of Earth and Atmospheric Sciences, Purdue University,
West Lafayette, Indiana, 47907-1397, U.S.A.
2 Dipartimento di Scienze della Terra,
via G. La Pira 4, 50121 Firenze, Italy
3 Department of Geology and Geophysics, University of California,
Berkeley, California, 94720-4767, U.S.A.
4 Dipartimento di Scienze della Terra,
via delle Cerchia 3, 53100 Siena, Italy
5 Centro di Geodinamica, Universita della Basilicata,
85100 Potenza, Italy
The exhumation rate of orogenic belts determines both the
isostatic component of rock uplift and the timing of mountain
landform development. Many orogenic belts are formed
by folding and thrusting during a compressional phase,
followed by normal faulting during extensional collapse.
The compressional phase usually produces metamorphic
minerals that can be radiometrically dated. By
contrast, the timing and rate of extension and exhumation
are often poorly constrained. Cosmogenic isotope methods
can be used to date exposure ages and measure erosion rates
over 10 3-105 years (Bierman, 1994; Cerling &, Craig,
1994), and to date sediment burial over 0.3-5 million years
(Granger & alii, in press). Here we propose that these techniques
can be used to clarify the tectonic evolution of
mountain belts, as we demonstrate for the Alpi Apuane
mountains of Italy.
The Alpi Apuane are a rugged mountain range, developed
on a metamorphic core complex exhumed from beneath
unmetamorphosed sediments during post-Oligocene extension
(Carmignani & Kligfield, 1990). Although these
unmetamorphosed sediments currently flank the Alpi
Apuane at low elevations, erosional remnants of these sediments
can still be found as alluvial deposits in caves and river.
terraces at high elevations in the core of the range. Because
these alluvial deposits lie up to 1000 m above modern
outcrops of their parent lithologies, they must have
been deposited during the unroofing of the core complex.
We are using the cosmogenic radionuclides 26Al and lOBe to
date the emplacement of these erosional remnants, in order
to constrain the Alpi Apuane exhumation rate. 26Al
and lOBe are produced in quartz by cosmic rays near the
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