Page 9 - Ragg_et_al-1999-Tectonics

RAGG ET AL.: TECTONIC STRESS IN SICILY 677

Table 2. BoreholesGroupedin SevenDifferentGeologicContexts

Name SHmax +/- Total Lengthof Numberof Breakout

Hyblean Plateau StandaDrdeviation Breakoumts, Intervals
Foredeep
Catania Plain 148ø+/- 30ø 3912 61
Gela 131ø+/- 63ø 3536 41
WesternSicily 47 ø +/- 18ø 872 4
Ramacca 20 ø +/- 16ø 1158 15
Angelo 131ø+/- 34ø 2416 33
66 ø +/- 13ø 280 2
36ø+/- 12ø 298 4

The directionof the maximum horizontalstressSHmax, the standarddeviation,the total (added)
length of the individualbreakoutsa, ndthe totalnumberof breakoutsin eachareaare listed.

Monaco et al., 1996]. The N to NNW SHmax orientation is southeasteSrnicilyvia Maltato Tunisiatheconvergenbtelt
interpretedto be associatedwith the active developmentof the Africa-Europeis characterizedby NNW to NW-SE SHmax
thrustbelts owing to the oblique convergenceand intraplate orientations,which are largely coherentover distancesof
deformationobservedalong this sectorof the northernmargin
of the African plate. hundredsof kilometersb, eingroughlyorthogonatlo the
collisionapllateboundaryT.he sameis observeadlongthe
Figure 10 showsthat the SHmax direction obtainedby the NW-SE orientedcollisionfront between.Apuliaand the
analysis of borehole breakouts from the Hyblean Plateau of
southeasternSicily has marked analogies with the whole set southernApennines, where the data show NE-SW oriented
of data from the African plate margin. In fact, from
SHmaxdirectionsL.ocally,ason theorogenifcoredeepof
southeasteSrincily(Gelaforedeepandin westernSicily),the

Mozia(21) Triglia(20) Corvi(22) Menfi(19)

II Chalks(LowerPliocene)

0 180 Marls (Pliocene)

0 180 Sands(UpperMiocene)

0 180 Clays(UpperMiocene)

Evaporites(UpperMiocene)

Clayswith sandyintercalations
(Mid-UpperMiocene)
Limestones(Middle-Lower Miocene)

Marls (Paleocene)Allochthonous

Chertylimestones
(AmedlloFm., UpperCretaceous)
Marly limestones
(Hybla Fm., LowerCretaceous)

Limestones

(ChiaramontFern.,LowerCretaceous)
Dolomitegsndlimestones
(Equiv.SiracusaFm., LowerJurassic)

Breakout

0 180

Figure8. ThewellsCorvi(well22),Mozia(well21) andTriglia(well20) aredrillednearthewesterncoast
of Sicilyanddisplaya softswingin SHmaxorientationfrom N (well 20) to NW. All of themreachthe
carbonaticbasementthroughthe allochthonouusnit while Menfi (19) is locatedin the southerncoastand

drilled only the clays of the allochthonous.