Page 5 - Tavarnelli_et_al2003

COMPOSITE STRUCTURES RESULTING FROM NEGATIVE INVERSION 32 3

graphic sequence has recorded the structural signature of cm
an episode of negative tectonic inversion. This switch in
tectonic regime produced composite structures, where Fig. 5 - Schemat.ic cliagram sh owing the se lf-s im ilat· geomet.ry o f t.he
early folds and thrusts are offset by late extensional def- compos ite st.tuctur es clescribecl in t his stucly. a) The Favignana
ormation. The overprint of late extension on early con- cr os s-sect.ion. b) The foot w-all stt·ucture of t.he Fa,·ignana Tlu'USt at
traction is seen on two different scales of observation (fig. Pw1t.a Faraglie ne. Circlecl numerals indica t e fault.s t.hat occupy t.he
5). In particular, the mesoscopic structure of fig. 5b is s an1e pos it.ion w it.hin t.he composite stl'Uctures.
located within the macroscopic structure of fig. 5a. - Diagramma schematico che mostra la somiglan=a delle strutture com -
p osite macroscopica e 1nesoscopica anali::::ate in questo studio. a) Se=io-
A comparison of the geometrica! features of the two ne attraverso 11sola di Favignana (traccia X -X' di fig. 2a). b) Strutture
composite stn1ctur es investigated reveals remarkable sim- mesoscopiche compressive e distensive nel letto del Sovrascorrintento di
ilarities, regardless of the different scales of observation Favignana. l nwneri p rogressivi cerchiati indicano faglie che occup ano
(fig. 5). In particular·, ali contractional structures share a la stessa posi=ione all'interno delle strutture composite.
front.al imbricate fan ( 1-3 of fig. 5 a-b) and a basai
décollement ( 1 offig. 5a-b), from where reverse faults and similar positions within the composite structures of fig. 5
related folds emanate. Ali bas ai décollement.s are system- produce contractional and extensional displacements that
atically truncated and offset by nonna! fault.s with oppo- ar·e comparable when nonnalised (fig. 7) . For example,
site dip (4-6 of fig. 5a-b), that bound graben located on the contractional disp lacement taken up by the basai
top of the thrust sheets. décollements (labelled l in fig . 5a-b) is maximum, and
decreases in the frontal imbricates (labelled 2 and 3 in fig .
The occurrence of d istinct stratigraphic horizons
makes it possible to quantify the amount of contr actional
and extensional displacement accornmodated by the
investigated structures (fig. 6) . This is achieved tluough
sequential restoration of early thrusts and late norma!
faults affecting the hanging-wall of the main dècolle-
ments (labelled l in fig. 5a-b) within the Favignana mac-
roscopic (fig. 6a) and Punta Faraglione mesoscopic (fig.
6b) sections. The sequential r estoration (fig. 6) shows a
similar sequence of events, and collectively illustrates that
the invest igated structures are not only geometrically sim-
ilar, but, more important, also shar·e a cormnon kinematic
history (TAVARNELLI et a/;;, 2003).

The quantitative consistency of the displacements
accormnodated by ear·Jy contractional and late exten-
sional structures is graphically expressed through a nor-
malised disp lacement plot (fig. 7). The faults occupying

a - Favignana b - Punta Faraglione

...f·.. ..: ....__ ......-..'..:: f

'''' ··-
'''''
'\ '\~ C =30 cm
.....i~ ',d'''
C = 350m ~Jc-~~q~+-
......t:::~'''''''''''' ' ''''''''''''
E= 100m : ' .. \

~ '''''''''' '''''''''' E= 20 cm

o 500 1000 N ......

Sm s 50 N

cm

Fig. 6 - S equent.ia l rest orat.ion of tlu·ust anclnonnal faults affect.ing t.he hanging-w all o f t he main clécollement.s . a) Kinemat.ic his t01y o f t.he

Favignana macros cop ic st.ruct.ures. b) Kinemat.ic his toty o f the Punta Faraglione mesoscopic st.ntctures.
- R icostn c ioni p alinsp astiche sequen=iali delle strutture comp ressive e distensive nel tetto dei p rincipali s co/lamenti studiati. a) E volu::ione
cinematica delle strutture macros copiche d i Favignana. b ) E voltc ione cinematica delle strutture mesoscopiche di Punta Faraglione.