Chapter 5 109
72°C. Dolostone samples were corrected according to Rosenbaum and Sheppard, 1986).
Resulting gases were analyzed automatically using a Thermo Finnigan Delta V+ mass spectrometer. A total of 40 peaks, in 10 steps, were measured for each sample. Each sample was analyzed twice. Data uncertainty is ±0.10‰ and ±0.15‰ for 13C and 18O, respectively.
4.4 Strontium isotopes
Strontium isotope ratios were measured with a ThermoElectron Triton plus TIMS at Vrije Universiteit, Amsterdam. 87Sr/86Sr ratios were measured in 20 blocks of 10 cycles with an 8 s per cycle integration time. 87Sr/86Sr ratios were corrected for mass fractionation using Russell’s exponential law with an 86Sr/88Sr ratio of 0.1194 (Steiger and Jager, 1977).
NBS987 is the international standard used for 87Sr/86Sr ratio calibration. Analytical reproducibility was checked with load sizes of 10 ng and 100 ng of the international Sr standard NBS987 (N=58). Mean 87Sr/86Sr ratio for the 10 ng NBS987 loads measurements was 0.710245 ± 0.000022 while it was 0.710242 ± 0.000008 for the 100 ng loads (Font et al., 2012).
4.5 Noble gases isotopes
The abundances and isotopic composition of the noble gases were measured by in vacuo crushing release using a VG5400 noble gas mass spectrometer that has upgraded electronics and software (Isotopx NGX) to improve instrument stability during the measurements. Around 200 mg of 0.5-1 mm-sized sample fragments were washed in acetone followed by de-ionised water in an ultrasonic bath. The washed samples were dried under a heat lamp. The cleaned samples were placed in a stainless-steel screw-type crusher (Stuart et al., 1994) and baked under vacuum at ~150 °C for 12 hours to reduce adsorbed atmospheric gases. The crushing step involved screwing down the piston to crush the samples and release gases from fluid inclusions. After the crushing step, the released noble gases underwent purification using a hot SAES GP50 getter for 10 minutes to remove active gases. The heavy noble gases, Ar, Kr and Xe were trapped on a cold finger of activated charcoal, cooled by liquid nitrogen to 77K, whilst the light noble gases, He and Ne, were expanded into the mass spectrometer. Following He and Ne isotope determinations, Ar, Kr and Xe were released from the cold finger by heating to 250 K and admitted to the mass spectrometer. 3He/4He and 40Ar/36Ar ratios were determined together with abundances of 21Ne, 84Kr and 132Xe. Blanks were obtained by using an identical procedure to sample analysis, but without operating the crushers and were carried-out after each sample loading. The noble gas blank level is <1% of a sample release of He, Ar and Kr and no higher than 3% for Ne and Xe. Data were acquired using either Faraday
4He (Ar isotopes) or electron multiplier detectors measured over 20 cycles and regressed to inlet time. Calibration for instrument mass discrimination and sensitivity was determined using the HESJ standard for He (3He/4He = R = 20.63 ± 0.01, R/Ra; Ra = atmospheric
3He/4He = 1.39 x 10-6; Matsuda et al., 2002) and air for Ar, Kr and Xe. Calibrations were analyzed at the start of each day.
with abundances of 21Ne, 84Kr and 132Xe. Blanks were obtained by using an identical procedure to sample analysis, but without operating the crushers and were carried-out after each sample loading. The noble gas blank level is <1% of a sample release of He, Ar and Kr and no higher than 3% for Ne and Xe. Data were acquired using either Faraday
4He (Ar isotopes) or electron multiplier detectors measured over 20 cycles and regressed to inlet time. Calibration for instrument mass discrimination and sensitivity was determined using the HESJ standard for He (3He/4He = R = 20.63 ± 0.01, R/Ra; Ra = atmospheric
3He/4He = 1.39 x 10-6; Matsuda et al., 2002) and air for Ar, Kr and Xe. Calibrations were analyzed at the start of each day.
5. Contractional Structural Architecture
The mapped fault pattern and contractional structural data are illustrated in Fig. 4.
The map indicates that the Monte Camicia Thrust is a complex fault system consisting of a basal master slip surface (1 to 4 in Ghisetti and Vezzani, 1986) mostly placing northward-dipping Jurassic to Cretaceous limestones onto northeastward-northward-dipping Upper Triassic bituminous dolostones and Early Jurassic massive dolostones at the footwall. Two main splay thrusts (3 and 2 in Ghisetti and Vezzani, 1986) emanate from the basal one, respectively near Mt. Camicia and to the south-west (Figs. 5A, B). Overall, this thrust array can be described as an out-of-sequence structure characterized by a strong lateral variability.
The Monte Camicia Thrust basal master slip surface strikes WSW-ENE in the Le Veticole area to the west (sites CF26 and CF27), E-W near the summit of Mt. Camicia (sites CF16 and CF17) and in the klippe to the east (sites CF22 and CF23), and again WSW-ENE at the east of Colle dell’Omo Morto (site CF18; Fig. 4). Tectonic transport directions are typically to the north, provided by S-C like arrays of compactional and shear surfaces (Fig. 6). Only in Le Veticole area the tectonic transport direction is towards the north-west (Fig. 5C). In the Miniera di Lignite tectonic window, fault geometry shows a higher variability, from WNW-ESE strike (sites CF3, CF7, CF8 and CF9) to E-W (sites CF5 and CF11), up to WSW-ENE (site CF10), SW-NE (site CF12) and almost N-S (site CF13).
Despite such a variability, tectonic transport directions are constantly to the north, apart from sites CF7, CF8 and CF9, where shear sense is towards NNE (Fig. 5C). This implies that NNE-SSW to N-S faults attain a left-lateral transpressional (site CF12) to almost strike-slip (site CF13) kinematics (Fig. 5D). As a consequence, the basal thrust sheet in this area pinches out towards the east and attains a lensoidal shape (Fig. 5E). Structural
15
40
40 60 75 85 85 80 30
50 50 60 55 30
30
60 40
85 60
70 40
50
55 55 30 70
40 70
60 25
25 40
65 50 70
50 35
30
10
20 85
15 25 25 20
30 20
55 50
35 65
20 30
VF1 VF2
VF3
VF4 VF5
VF6 VF7
VF8 VF9VF10 CF26
CF15
CF16CF17
CF20
CF25 CF24
CF21 CF23
CF22 CF3 CF18
CF6
CF7 CF13
CF11 CF10CF12 CF8CF9 CF5
M. CAMICIA
Quaternary
N
500 m
LE VETICOLE L’AL
TARE
VALLONE DI VRADDA
MINIERA LIGNITEDI
COLLE DELL’OMO
MORTO FORNACA
CF3 n=61
CF5CF6 n=39
CF7
CF8CF9 n=67
CF10 n=30
CF11 n=42
CF12
n=30 CF13
n=19 CF15
n=8
CF16CF17 n=33
CF18 n=22 CF26
n=32
CF22CF23 n=47 CF20
n=66
CF21 n=9 CF24CF25
n=95 VF8
n=45 VF9
VF4 n=25
VF1 n=72 VF2
n=53 VF3
VF5
VF6
n=44
VF7
n=30 VF10
n=42 n=75
n=31
n=40
n=45
Thrust faults
Extensional faults Bituminous dolostones (Upper Triassic) Massive dolostones-limestones (Early Jurassic) Corniola limestones (Early Jurassic)
Ammonitic green (Middle Jurassic)
Entrochi calcarenites (Upper Jurassic-Early Cretaceous) Rudist calcirudites (Upper Cretaceous-Eocene) Structural sites
Figure 4. Aerial orthophoto showing lithostratigraphic units, thrusts, extensional faults and structural si-tes in the study area. Red for the Camicia Thrust, bordeaux for the Vado di Ferruccio Thrust and orange for the Prena splay Thrust. In the stereographic projections, great circles and slickenlines in red represent thrust surfaces and relative lineations, grey for tectonic stylolites, blue for bedding parallel stylolites, gre-en for C’ shear surfaces, pink for subsidiary thrust surfaces and blue dots correspond to poles to bedding.
Stereonets with white background for the Camicia Thrust and grey background for the Vado di Ferruccio Thrust.
with abundances of 21Ne, 84Kr and 132Xe. Blanks were obtained by using an identical procedure to sample analysis, but without operating the crushers and were carried-out after each sample loading. The noble gas blank level is <1% of a sample release of He, Ar and Kr and no higher than 3% for Ne and Xe. Data were acquired using either Faraday
4He (Ar isotopes) or electron multiplier detectors measured over 20 cycles and regressed to inlet time. Calibration for instrument mass discrimination and sensitivity was determined using the HESJ standard for He (3He/4He = R = 20.63 ± 0.01, R/Ra; Ra = atmospheric
3He/4He = 1.39 x 10-6; Matsuda et al., 2002) and air for Ar, Kr and Xe. Calibrations were analyzed at the start of each day.
5. Contractional Structural Architecture
The mapped fault pattern and contractional structural data are illustrated in Fig. 4.
The map indicates that the Monte Camicia Thrust is a complex fault system consisting of a basal master slip surface (1 to 4 in Ghisetti and Vezzani, 1986) mostly placing northward-dipping Jurassic to Cretaceous limestones onto northeastward-northward-dipping Upper Triassic bituminous dolostones and Early Jurassic massive dolostones at the footwall. Two main splay thrusts (3 and 2 in Ghisetti and Vezzani, 1986) emanate from the basal one, respectively near Mt. Camicia and to the south-west (Figs. 5A, B). Overall, this thrust array can be described as an out-of-sequence structure characterized by a strong lateral variability.
The Monte Camicia Thrust basal master slip surface strikes WSW-ENE in the Le Veticole area to the west (sites CF26 and CF27), E-W near the summit of Mt. Camicia (sites CF16 and CF17) and in the klippe to the east (sites CF22 and CF23), and again WSW-ENE at the east of Colle dell’Omo Morto (site CF18; Fig. 4). Tectonic transport directions are typically to the north, provided by S-C like arrays of compactional and shear surfaces (Fig. 6). Only in Le Veticole area the tectonic transport direction is towards the north-west (Fig. 5C). In the Miniera di Lignite tectonic window, fault geometry shows a higher variability, from WNW-ESE strike (sites CF3, CF7, CF8 and CF9) to E-W (sites CF5 and CF11), up to WSW-ENE (site CF10), SW-NE (site CF12) and almost N-S (site CF13).
Despite such a variability, tectonic transport directions are constantly to the north, apart from sites CF7, CF8 and CF9, where shear sense is towards NNE (Fig. 5C). This implies that NNE-SSW to N-S faults attain a left-lateral transpressional (site CF12) to almost strike-slip (site CF13) kinematics (Fig. 5D). As a consequence, the basal thrust sheet in this area pinches out towards the east and attains a lensoidal shape (Fig. 5E). Structural
M. CAMICIA
COLLE DELL’OMO
MORTO
LE VETICOLE L’AL
TARE MINIERA
LIGNITEDI FORNACA
n=45
n=25
C
B A
D
N S S N
NE SW
E W
A
B D
E
Site CF12
CF12
CF10 Site UT11
CF7 CF7
D
100 m
E
CF12
Figure 5. Pictures and line-drawings of the Camicia Thrust seen from the west (A) and from east (B).
The master basal slip surface is in red, minor splays are in orange, green and purple while high-angle extensional faults are in black. Arrows indicate kinematics. (C) Architecture of the Camicia Thrust and mean directions of the kinematics measured in the structural sites. Red arrows represent slickenlines on thrusts, grey arrows are orthogonal to the intersection line between S and C planes of thrusts and black arrows for slickenlines on extensional faults. “Eye” symbols indicate where pictures were acquired.
(D) Picture and drawing of Site CF12, where the Camicia Thrust shows transpressional kinematics. (E) Picture and linedrawing of the top of the Miniera di Lignite area, where the hanging wall acquires a lensoi-dal geometry. The splay thrust on the west, in Site CF7, shows southwest dipping planes while they are southeast dipping in the eastern part (Site CF12; D). Stereographic projections show average planes and slickenlines in the respective site. Grey for tectonic stylolites and red for thrust surfaces and slickenlines.
N S
C
FC
DZ B
A
n=42
n=68
Site CF3
Site CF3 Site CF11
Tectonic Stylolites
Thrust Plane
N S
N S
Thrust Plane
Tectonic Stylolites
Figure 6. Pictures showing contractional structures of the Camicia Thrust. (A) Fon-te GrotFon-te cave, SiFon-te CF11, showing sharp south dip-ping thrust surface with top-to-the north kinematics and high-angle south-southwest dipping tectonic stylolites in the hanging wall damage zone. (B) Western side of the Miniera di Lignite area, Site CF3, showing karstified fault core and tectonic pres-sure solution planes in the footwall damage zone that dip south-southwest and have a top-to-the north-nor-theast transport direction.
(C) Picture acquired in the same site of B showing a subsidiary thrust which causes duplexing of the Thrust zone. Stereographic projections show average planes and slickenlines in the respective site. Grey for tectonic stylolites and red for thrust surfaces and sli-ckenlines.
Chapter 5 113
with abundances of 21Ne, 84Kr and 132Xe. Blanks were obtained by using an identical procedure to sample analysis, but without operating the crushers and were carried-out after each sample loading. The noble gas blank level is <1% of a sample release of He, Ar and Kr and no higher than 3% for Ne and Xe. Data were acquired using either Faraday
4He (Ar isotopes) or electron multiplier detectors measured over 20 cycles and regressed to inlet time. Calibration for instrument mass discrimination and sensitivity was determined using the HESJ standard for He (3He/4He = R = 20.63 ± 0.01, R/Ra; Ra = atmospheric
3He/4He = 1.39 x 10-6; Matsuda et al., 2002) and air for Ar, Kr and Xe. Calibrations were analyzed at the start of each day.
5. Contractional Structural Architecture
The mapped fault pattern and contractional structural data are illustrated in Fig. 4.
The map indicates that the Monte Camicia Thrust is a complex fault system consisting of a basal master slip surface (1 to 4 in Ghisetti and Vezzani, 1986) mostly placing northward-dipping Jurassic to Cretaceous limestones onto northeastward-northward-dipping Upper Triassic bituminous dolostones and Early Jurassic massive dolostones at the footwall. Two main splay thrusts (3 and 2 in Ghisetti and Vezzani, 1986) emanate from the basal one, respectively near Mt. Camicia and to the south-west (Figs. 5A, B). Overall, this thrust array can be described as an out-of-sequence structure characterized by a strong lateral variability.
The Monte Camicia Thrust basal master slip surface strikes WSW-ENE in the Le Veticole area to the west (sites CF26 and CF27), E-W near the summit of Mt. Camicia (sites CF16 and CF17) and in the klippe to the east (sites CF22 and CF23), and again WSW-ENE at the east of Colle dell’Omo Morto (site CF18; Fig. 4). Tectonic transport directions are typically to the north, provided by S-C like arrays of compactional and shear surfaces (Fig. 6). Only in Le Veticole area the tectonic transport direction is towards the north-west (Fig. 5C). In the Miniera di Lignite tectonic window, fault geometry shows a higher variability, from WNW-ESE strike (sites CF3, CF7, CF8 and CF9) to E-W (sites CF5 and CF11), up to WSW-ENE (site CF10), SW-NE (site CF12) and almost N-S (site CF13).
Despite such a variability, tectonic transport directions are constantly to the north, apart from sites CF7, CF8 and CF9, where shear sense is towards NNE (Fig. 5C). This implies that NNE-SSW to N-S faults attain a left-lateral transpressional (site CF12) to almost strike-slip (site CF13) kinematics (Fig. 5D). As a consequence, the basal thrust sheet in this area pinches out towards the east and attains a lensoidal shape (Fig. 5E). Structural data on the splay thrust near the summit of Mt. Camicia (site CF20) indicate a northward transport direction (Fig. 5C).
Structural data of the Vado di Ferruccio Thrust are synthetically illustrated in Fig. 4 and show that the master slip surface strikes almost E-W and dips southward, apart from sites VF8 and VF10 where it attains a NW-SE strike and a south-westward dip. The fault zone is characterized by well-developed S-C-C’ structural fabrics (Figs. 7A-D) indicating significant variability in the tectonic transport, ranging from top to the NW in the southwestern sector of the Fornaca tectonic window, up to top to the NE in the southeastern one. Folding in the footwall damage zone is common and poles to fold limbs describe N-S girdles (Leah et al., 2018).
To sum up, cumulative analysis of structural data collected along the Monte Camicia Thrust indicates that the mean strike of the master slip surface is 092° and the mean dip is 33° to the S. Slickenlines mean rake is 008° 35°, with a northward tectonic transport direction, as indicated by pressure solution surfaces in the thrust damage zones, which strike 109° and dip 68° southward (Fig. 8). Cumulative analysis of structural data collected along the Vado di Ferruccio Thrust show two main clusters oriented 083° 24° and 088° 48°, respectively. Slickenlines have a mean rake of 037° 39° and dip to the south.
Pressure solution surfaces in the thrust damage zone have quite variable orientations, with three main maxima, at 138° 40°, 130° 80° and 090° 70°, respectively.