The Abruzzo-Molise-Sannio region is part of the Central Apennines
foreland fold and thrust belt, a structure that formed during the
Neogene as a result of the continental collision between the European
and Adria plates. Certain areas of this crust experienced anomalously
high temperatures due to deep burial, while others did not. This burial
has been investigated using optical indicators of organic matter (OM)
maturity and clay mineralogy. The maximum depths of burial of Tertiary
surface sequences have been established based on the vitrinite
reflectance (R(0)) and thermal alteration index (TAI) of OM dispersed in
synorogenic sediments and from clay mineralogy of pre-thrusting clayey
deposits. The synorogenic deposits show low levels of organic maturity
having R(0) values less than 0.6% indicating early mature to mid-mature
hydrocarbon generation. The pre-thrusting deposits are shales
characterised by a very high percentage of clay minerals with lesser
amounts of quartz, K-feldspar, plagioclase and calcite. The dominant
minerals are highly smectitic interstratified illite/smectite (RIS).
Both R(0) and I/S ratios were used to calibrate burial and thermal
evolution of this chain sector by numerical modelling. The results
indicate that the structural units which outcrop in the study area
(particularly the Molise Unit) were never overthrust by significant
thicknesses of rocks during mountain building, at least before Pliocene
times; the hypothesis that more internal units overthrust the presently
exposed units also seems to be unlikely. (C) 1998 Elsevier Science B.V.
All rights reserved.