Page 8 - Ragg_et_al-1999-Tectonics

676 RAGGETAL.'TECTONICSTRESSIN SICILY

Chiesa(18) Simeto(16) Dittaino(17) The N to NNW compressionshould account for the

0 180 I'''1 = mechanismosbservedalongthe Adventurethrustbelt wherea

- N-Sstrikingtranscurreznotnec, haracterizbeydtranspressive

- sinistral mechanism, is associated with the thrust front

- [Argnaneital., 1989'Ben-AvrahaamndGrasso1, 990].TheN
- to NNW compressiaolnsofits wellwiththeN-S shortening

-• inferrebdythefocaml echanisomf theJanuar1y968Belice
-a0 180 earthquaksewarm(5 < M < 5.4)whichaffectedtheimmediate

- hinterlandof the fouranalyzedwells [Caccamoet al., 1996'

Fluviatilegravels Breakout

Ramac(c1a5) Angel(o14)

-•:.•_• Sands

Clayasndmarls

t'.';;.'.;". Volcanics Plio. o 180
Mio.
Figure6. ThewellsoftheCataniPalainS, imet(owell16), Creta.
Dittaino(well17),andChiesa(well18),displaay N-W
breakouotrientatio(n90ø to SHmaxorientationN)o. neof Trias

themdoreachtheHybleancarbonasteuccessioInnst.hewell
Dittainono breakoutcan be identified.The breakout

orientatiofonundin theupperPlio-Pleistoccelnaeysis
paralletol theNE trendinggrabesntructurfelasnkintghe

northernmarginof theHybleanPlateau.

axisS2 strikingparallelto the fault planesof the rotating 0 18o
stresstensor due to increasing gravitational stresseswith
I Breakout
depth.
Allochthonous
3.WellsonthewesterHnybleanmarginandin theforedeep
displayscattereSdHmaxorientationTsh. isis possiblycaused (clayss, andstonaensdevaporites)

by low-stress anisotropy. Therefore the zone can be Volcanicaslternatinwgithchalks(Pliocene)
interpreted as a transition zone between the NE SHmax
orientations of the Gela frontal thrust and the NW SHmax

orientationfoundin the SE HybleanPlateau.

4.2. Western Sicily .ß[ -.-] Evaporite(sUpperMiocene)

The fourwellsin westernSicily arelocatedon thenorthern Marls(Mid-Miocene)
boundaryof theAdventurePlateau(Figure1). Threeof them
(Mozia (well 21), Corvi (well 22) andTriglia (well 20)) are Marls,claysandsandstones
(WellAngeloE; ocene-MiMdiocene)

drilled near the western coast of Sicily and reach the Packstones-grains(tOolnigeos-Miocene)

carbonaticbasementhroughthe allochthonousunit. The data Marlylimestone(AsmerilloFro.)
areof moderate(C) quality.The well Menfi (well 19) is located (WellRamaccUa;ppeCr retaceous-Eocene)
alongthe southerncoastanddrilledonly withinthe claysof
the allochthonous(Figure 8). The well Menfi shows no Shallow water limestones

(SiracusFam.;LowerJurassic)

preferentiabl reakoutorientationand the resultingstressdata Dolomiteswithintercalationosf volcanics
is of D quality(Figure8 andTable 1). (UpperTriassic)

The measuredSHmax orientationrangesfrom N to NW Figur7e. ThewellAsnge(lowel1l 4)andRamac(cwael1l 5)
(Figure9). All wellsbelongto anorogenicbeltconsistinogf arelocatoednandaheaodftheMounJtudicaareare, spectively
twosegmentsth, eEgadiandtheAdventurethrustbelts(Figure
1). Triglia,Mozia, andCorvi are locatedaheadof the Egadi (Figure1), andbothdisplaya consistenotrientatioonf

Thrust Belt while Menfi is located ahead of the Adventure breakoauztimuwthithdepthI.nparticultahre,welRl amacca,
locateodnthefrontaGl elaNapped,isplayasNWbreakout
thrust belt which formed from the earliest Pliocene onwards.
orientatiosnubparaltloelthatfoundin theCataniPalainT. he
Both thrust belts are the result of the continental collision
wellAngel(owell14),drilledwithintheMounJtudicsatack,
betweenAfrican forelandedgeswith carbonateunitslocated showastrendwhichisconsistewniththatofManfri(awell
13)andSettefari(nweell12)wellsin theGelaarea.Thewell
northof it in westernmoSsict ily[Catalaneot al., 1985,
Ramacc(awell15)givesnobreakouint formatiofnromthe
1995;Argnaniet al., 1989]. Hybleacnarbonatuensderlyinthgenappe.