Palaeostress review of the Zagros fold-and-thrust belt … review of the Zagros fold-and-thrust belt...
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Palaeostress review of the Zagros fold-and-thrust belt and tectonic implications Payman Navabpour 1 and Eric Barrier 2 1 Universität Jena, Institut für Geowissenschaften, Burgweg 11, 07749 Jena, Germany 2 iSTeP, Université Paris 6, CNRS, Case 129, 4 place Jussieu, 75252 Paris, France Introduction The present-day Zagros fold-and-thrust belt of SW-Iran corresponds to the former Arabian passive continental margin of the southern Neo-Tethyan basin since the Permian–Triassic rifting, undergoing later collisional deformation in mid-late Cenozoic times. Here, an overview of brittle tectonics and palaeostress reconstructions of the Zagros fold-and-thrust belt is presented through the Figs 1–6 (after Navabpour et al., 2007, 2008, 2010, 2011 and the references cited therein). Conclusion Results indicate that after the Permian–Triassic rifting and during the Neo-Tethyan oceanic opening, an extensional tectonic regime affected the sedimentary cover in Triassic–Jurassic times with an approximately N–S trend of 3 stress axis oblique to the present-day trend of the mountain belt. Some local changes in the stress field indicate a NE–SW trend of the 3 axis during Jurassic–Cretaceous times. The stress state then significantly changed to thrust setting, with a NE–SW trend of 1 stress axis, and a compressional tectonic regime prevailed during the continental collision and folding of the sedimentary cover in Oligocene–Miocene times. The compression was followed by a strike-slip stress regime with an approximately N–S trend of the 1 axis oblique to the mountain belt during inversion of the inherited extensional basement structures in Pliocene–Recent times. The brittle tectonic reconstructions, therefore, highlighted major changes of stress state in conjunction with transitions between thin- and thick-skinned structures. An oblique divergence is thus suggested for the rifting and oceanic opening, and an increase in plate coupling is evidenced under an oblique covergence after the collision. Fig. 1. Index map of the studied areas (white boxes) within the Zagros fold-and-thrust belt. MZT, Main Zagros Thrust; MRF, Main Recent Fault; HZF, High Zagros Fault; MFF, Mountain Front Fault. Large black arrows indicate GPS plate convergence directions in the Iranian reference frame. Inset: location map in the Middle East. Fig. 2. Main tectonic events of the Zagros fold-and-thrust belt, since the Permian–Triassic rifting and oceanic opening until the mid-late Cenozoic continental collision and shortening. Fig. 3. Typical geometries of brittle structures, indicating relative chronologies. (a) Successive normal and reverse striae on a fault plane (S1 then S2). (b) Successive reverse and right-lateral strike-slip striae on a fault plane (S1 then S2). (c) Sedimentary wedge (light grey in inset) on the hanging wall (dark grey in inset) of a palaeo-submarine normal fault, indicating an approximately N–S extension during Jurassic period. (d) Conjugate reverse faults in the present-day folded strata, interpreted as pre-folding conjugate normal faults by back-tilting the strata to initial horizontal attitude (in inset). (e) Syn-fold bedding-parallel reverse slips. (f) Post-fold vertical right-lateral strike-slip faults (F) cut through earlier folded strata. Fig. 6. Schematic presentation of structural evolution of the Zagros fold-and-thrust belt, based on brittle tectonics and palaeostress reconstructions, since the Mesozoic extension (a and b) until the mid-late Cenozoic compression (c and d). 1, oceanic crust; 2,continental crust; 3, thick basal detachment; 4, inherited structure; 5, thick- and thin-skinned structures; 6, inferred plate divergence; 7, plate convergence; 8, directions of extension and compression within the sedimentary cover; 9, direction of seismic compression within the basement. MOR, mid-ocean ridge; PN, palaeo-north. Other abbreviations as in Fig. 1. References - Navabpour, P., Angelier, J. & Barrier, E., 2007. Cenozoic post-collisional brittle tectonic history and stress reorientation in the High Zagros Belt (Iran, Fars Province). Tectonophysics, 432, 101-131. - Navabpour, P., Angelier, J. & Barrier, E., 2008. Stress state reconstruction of oblique collision and evolution of deformation partitioning in W-Zagros (Iran, Kermanshah). Geophysical Journal International, 175, 755-782. - Navabpour, P., Angelier, J. & Barrier, E., 2010. Mesozoic extensional brittle tectonics of the Arabian passive margin, inverted in the Zagros collision (Iran, interior Fars). Geological Society, London, Special Publications, 330, 65-96. - Navabpour, P., Angelier, J. & Barrier, E., 2011 (in press). Brittle tectonic reconstruction of palaeo-extension inherited from Mesozoic rifting in W-Zagros (Iran, Kermanshah). Journal of the Geological Society, London. Fig. 5. Stress tensors, calculated based on fault slip data, indicating major changes in stress regimes through time from normal (a, b, c and d) to thrust (e and f) and strike-slip (g and h). In diagrams, the principal stress axes are shown with their 60, 75 and 90% confidence ellipses. Pairs of convergent and divergent arrows show directions of compression and extension, respectively, with azimuthal confidence in grey curves. Fig. 4. Stereoplot presentation of fault slip data, indicating kinematic changes. (a) North-dipping normal faults reactivated as reverse faults. (b) South-dipping normal faults reactivated as left-lateral strike-slip faults. (c) Northeast-dipping bedding-parallel reverse slips reactivated as right-lateral strike-slip faults. (d) Back-tilting presentation for the corresponding fault slip data of Fig. 3d. Faults are shown by great circles and slip arrows. Dashed great circles are bedding planes. XL298 EGU2011-2535 1000 2000 3000 Elevation 0 m 46 48 50 52 54 56 34 32 30 28 50 52 54 56 34 32 30 28 26 0 100 200 km ST R A I T OF H O R M OZ P E R S I A N G U L F MRF MZT HZF MFF CENTRAL IRAN F W-Zagros E-Zagros 2 2 28 28 2 50 50 0 50 0 P Eurasian Plate Arabian Plate Indian Ocean 1000 km Permian Triassic Jurassic Cretaceous Palaeocene Eocene Oligocene Miocene Pliocene Recent 251 -- 199 -- 145 -- 65 -- 55 -- 33 -- 23 -- 5.3 -- 1.8 -- Neo-Tethyan rifting Passive margin normal faulting Oceanic obduction Continental collision Sedimentary cover folding Basement fault reactivation Age (Ma) Tectonic event ? SE NW S2 S1 S2 S1 SE NW NE SW F F SW NE b NNW SSE a NE SW Back tilting c d e f Reverse Normal Strike-slip Normal Strike-slip Reverse Normal Reverse a d b c W-Zagros E-Zagros Triassic-Jurassic Jurassic-Cretaceous Oligocene-Miocene Pliocene-Recent a b cd e f gh Stress axes: σ 1 σ 2 σ 3 HZF MZT MRF P e r s i a n G u l f N ~200 km HZF MFF MFF Arabian Plate Iranian Plate ZF F ZF ZF HZF MRF Pliocene-Recent d N ~200 km E-Zagros W-Zagros MZT Arabian Plate Iranian Plate W W Oligocene-Miocene c PN ~200 km Jurassic-Cretaceous Neo-Tethys Arabian Margin b E-Zagros W-Zagros PN ~200 km Neo-Tethys Arabian Margin Triassic-Jurassic MOR a 1 2 3 4 5 6 7 8 9
Transcript of Palaeostress review of the Zagros fold-and-thrust belt … review of the Zagros fold-and-thrust belt...
Palaeostress review of the Zagros fold-and-thrust belt and tectonic implicationsPayman Navabpour 1 and Eric Barrier 2
1 Universität Jena, Institut für Geowissenschaften, Burgweg 11, 07749 Jena, Germany2 iSTeP, Université Paris 6, CNRS, Case 129, 4 place Jussieu, 75252 Paris, France
IntroductionThe present-day Zagros fold-and-thrust belt of SW-Iran corresponds to the former Arabian passive continental margin of the southern Neo-Tethyan basin since the Permian–Triassic rifting, undergoing later collisional deformation in mid-late Cenozoic times. Here, an overview of brittle tectonics and palaeostress reconstructions of the Zagros fold-and-thrust belt is presented through the Figs 1–6 (after Navabpour et al., 2007, 2008, 2010, 2011 and the references cited therein).
ConclusionResults indicate that after the Permian–Triassic rifting and during the Neo-Tethyan oceanic opening, an extensional tectonic regime affected the sedimentary cover in Triassic–Jurassic times with an approximately N–S trend of �3 stress axis oblique to the present-day trend of the mountain belt. Some local changes in the stress field indicate a NE–SW trend of the �3 axis during Jurassic–Cretaceous times. The stress state then significantly changed to thrust setting, with a NE–SW trend of �1 stress axis, and a compressional tectonic regime prevailed during the continental collision and folding of the sedimentary cover in Oligocene–Miocene times. The compression was followed by a strike-slip stress regime with an approximately N–S trend of the �1 axis oblique to the mountain belt during inversion of the inherited extensional basement structures in Pliocene–Recent times. The brittle tectonic reconstructions, therefore, highlighted major changes of stress state in conjunction with transitions between thin- and thick-skinned structures. An oblique divergence is thus suggested for the rifting and oceanic opening, and an increase in plate coupling is evidenced under an oblique covergence after the collision.
Fig. 1. Index map of the studied areas (white boxes) within the Zagros fold-and-thrust belt. MZT, Main Zagros Thrust; MRF, Main Recent Fault; HZF, High Zagros Fault; MFF, Mountain Front Fault. Large black arrows indicate GPS plate convergence directions in the Iranian reference frame. Inset: location map in the Middle East.
Fig. 2. Main tectonic events of the Zagros fold-and-thrust belt, since the Permian–Triassic rifting and oceanic opening until the mid-late Cenozoic continental collision and shortening.
Fig. 3. Typical geometries of brittle structures, indicating relative chronologies. (a) Successive normal and reverse striae on a fault plane (S1 then S2). (b) Successive reverse and right-lateral strike-slip striae on a fault plane (S1 then S2). (c) Sedimentary wedge (light grey in inset) on the hanging wall (dark grey in inset) of a palaeo-submarine normal fault, indicating an approximately N–S extension during Jurassic period. (d) Conjugate reverse faults in the present-day folded strata, interpreted as pre-folding conjugate normal faults by back-tilting the strata to initial horizontal attitude (in inset). (e) Syn-fold bedding-parallel reverse slips. (f) Post-fold vertical right-lateral strike-slip faults (F) cut through earlier folded strata. Fig. 6. Schematic presentation of structural evolution of the Zagros
fold-and-thrust belt, based on brittle tectonics and palaeostress reconstructions, since the Mesozoic extension (a and b) until the mid-late Cenozoic compression (c and d). 1, oceanic crust; 2,continental crust; 3, thick basal detachment; 4, inherited structure; 5, thick- and thin-skinned structures; 6, inferred plate divergence; 7, plate convergence; 8, directions of extension and compression within the sedimentary cover; 9, direction of seismic compression within the basement. MOR, mid-ocean ridge; PN, palaeo-north. Other abbreviations as in Fig. 1.
References
- Navabpour, P., Angelier, J. & Barrier, E., 2007. Cenozoic post-collisional brittle tectonic history and stress reorientation in the High Zagros Belt (Iran, Fars Province). Tectonophysics, 432, 101-131.
- Navabpour, P., Angelier, J. & Barrier, E., 2008. Stress state reconstruction of oblique collision and evolution of deformation partitioning in W-Zagros (Iran, Kermanshah). Geophysical Journal International, 175, 755-782.
- Navabpour, P., Angelier, J. & Barrier, E., 2010. Mesozoic extensional brittle tectonics of the Arabian passive margin, inverted in the Zagros collision (Iran, interior Fars). Geological Society, London, Special Publications, 330, 65-96.
- Navabpour, P., Angelier, J. & Barrier, E., 2011 (in press). Brittle tectonic reconstruction of palaeo-extension inherited from Mesozoic rifting in W-Zagros (Iran, Kermanshah). Journal of the Geological Society, London.
Fig. 5. Stress tensors, calculated based on fault slip data, indicating major changes in stress regimes through time from normal (a, b, c and d) to thrust (e and f) and strike-slip (g and h). In diagrams, the principal stress axes are shown with their 60, 75 and 90% confidence ellipses. Pairs of convergent and divergent arrows show directions of compression and extension, respectively, with azimuthal confidence in grey curves.
Fig. 4. Stereoplot presentation of fault slip data, indicating kinematic changes. (a) North-dipping normal faults reactivated as reverse faults. (b) South-dipping normal faults reactivated as left-lateral strike-slip faults. (c) Northeast-dipping bedding-parallel reverse slips reactivated as right-lateral strike-slip faults. (d) Back-tilting presentation for the corresponding fault slip data of Fig. 3d. Faults are shown by great circles and slip arrows. Dashed great circles are bedding planes.
XL298 EGU2011-2535
1000
2000
3000
Elevation
0 m
46 48 50 52 54 56
34
32
30
28
50 52 54 56
34
32
30
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0 100 200km
STRAIT O
F HORMO
Z
PER
SIAN GULF
MRF
MZT
HZF
MFF
CENTRAL IRANF
W-Zagros
E-Zagros2228282
5050050 0
PEurasian Plate
Arabian Plate IndianOcean1000
km
PermianTriassicJurassicCretaceousPalaeoceneEoceneOligoceneMiocenePlioceneRecent
251 --199 --145 --
65 --55 --33 --23 --5.3 --1.8 --
Neo-Tethyan riftingPassive margin normal faulting
Oceanic obduction
Continental collisionSedimentary cover foldingBasement fault reactivation
Age (Ma) Tectonic event
?
SE NW
S2
S1S2S1
SENW
NE SW
F
F
SW NE
bNNW SSE
aNESW
Backtilting
c d
e f
ReverseNormal Strike-slipNormal
Strike-slipReverse NormalReverse
adb
c
W-Zagros E-Zagros
Tria
ssic
-Jur
assi
cJu
rass
ic-C
reta
ceou
sO
ligoc
ene-
Mio
cene
Plio
cene
-Rec
ent
a bc d
e fg h
Stress axes: σ1 σ2 σ3
HZF
MZTMRF
Persian GulfN
~200 km
HZF
MFF
MFF
Arabian Plate
Iranian Plate
ZFFZFZFHZF
MRF
Pliocene-Recent
d
N~200 km
E-ZagrosW-Z
agros
MZT
Arabian Plate
Iranian Plate
WW
Oligocene-Miocene
c
PN
~200 km
Jurassic-CretaceousNeo-Tethys
Arabian Marginb
E-ZagrosW-Z
agros
PN ~200 km
Neo-Tethys
Arabian Margin
Triassic-JurassicMOR
a
1 2 3 4 5 6 7 8 9
