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Continental collision mountain belts: the Arabia-Eurasia system Paolo Ballato, 11-02-2009.

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Presentation on theme: "Continental collision mountain belts: the Arabia-Eurasia system Paolo Ballato, 11-02-2009."— Presentation transcript:

1 Continental collision mountain belts: the Arabia-Eurasia system Paolo Ballato,

2 Today's class contents 1) Continental collision: a brief outlook (definition, causes, implications…..) 2) How is tectonics deformation accommodated within the Arabia-Eurasia collision zone? 3) A case study from the Alborz mountains, an intracontinental mountain belt linked to Arabia-Eurasia collision (the record from foreland basin deposits) a) When did the deformation related to continental collision start in the Alborz mountains? b) How did deformation evolve? c) What can we learn from foreland basin deposits (i.e. climate vs tectonic) ?

3 1) Continental collision: a brief outlook (definition, causes, implications…..) PART 1

4 www2.bc.edu/~kafka/ge180.f03/PT_4.ppt Prior to a continental collision, the landmasses are separated by oceanic crust, formed during an earlier episode of sea-floor spreading As the continental blocks converge, the intervening sea floor (lower plate) is subducted beneath the upper plate The descending oceanic slab generates a volcanic arc Upper plate deformation is limited (tectonics stress is not transferred far away from trench) and shortening is mainly accommodated along plates interface (accretionary wedge) Pre-collisional setting India-Asia convergence rate decreased from 160 to 50 mm/yr in the last 70Ma Lower plate Upper plate

5 www2.bc.edu/~kafka/ge180.f03/PT_4.ppt As the continental lithosphere of the lower plate approaches the upper plate subduction terminates, suturing occurs, and continents are amalgamated Tectonics stress is progressively transferred to the upper plate, where deformation is accommodated across a broad region (thousands of km from the suture zone). Possibly reactivation of structures forming old orogenic belts A fold and thrust belt develops in the lower plate Mountain range/ranges are formed and several km of crust can be exhumed Collisional setting

6 Why does continental collision occur? Oceanic lithosphere ( g/cm 3 ) crust (density ca. 2.9 g/cm 3 ) mantle (density ca. 3.3 g/cm 3 ) Continental lithosphere ( g/cm 3 ) crust (density ca. 2.7 g/cm 3 ) mantle (density ca. 3.3 g/cm 3 ) Oceanic lithosphere is denser than continental lithosphere, so it tends to sink (subduction) into the asthenosphere when convergence takes place When the continental crust reach the subduction zone the buoyancy forces oppose resistance to the slab pull forces; subduction ends and the pulling slab will break off sinking into the asthenosphere Cloos, 1993

7 How is it tectonics deformation absorbed in the upper plate? 1) Crustal thickening (exhumation) 2) Extrusion tectonics (lateral transport of crustal blocks) Tapponnier et al., 1982, 1986

8 3) Large scale folding (lithospheric buckling) Burg et al, 1999 Difficult to demonstrate….is it an efficient mountain building process? 4) “Intra-collision zone subduction” (subduction of denser microplates located in the collision zone) Matte et al, 1997

9 PART 1…..Summarizing 1) Continental collision occurs when plate convergence cannot absorbed anymore via subduction process 2) Continental collision takes place because buoyancy forces do not allow large amount of continental subduction 3) During continental collision tectonics deformation is not anymore localized along the plate margin (accretionary wedge), but affects a large area in the upper plate and propagate cratonward in the lower plate (fold and thrust belt) 4) Deformation in the upper plate is absorbed via : Crustal thickening Lateral extrusion of rigid blocks Possibly via lithospheric buckling “Intra-collision zone subduction” 5) Intracontinental deformation is generally localized along crustal weakness (i.e. old orogenic belts)

10 PART 2 2) How is tectonics deformation accommodated within the Arabia-Eurasia collision zone?

11 The Arabia-Eurasia collision zone Nubia Somalia Arabia Eurasia India Zagros Alborz Kopeh Dagh Caucasus Gulf of Aden Red Sea Makran Black Sea Casp Central Iran Hellenic Cyprus Anatolia T-I plateau Owen FZ Helmand Lut Aegean Eastern African Riften Aspheron

12 McQuarrie et al., 2006 Arabia-Eurasia system: from oceanic subduction to continental collision Opening of the Gulf of Aden

13 Reilinger et al., 2006 Active tectonics of the Arabia-Eurasia collision zone: seismicity

14 Active tectonics of the Arabia-Eurasia collision zone: quantifying present- day deformation with GPS data Reilinger et al., 2006 Westward extrusion of Anatolia (escape tectonics) Crustal thickening Subduction of a denser microplate (Southern Caspian Basin)

15 Guest et al., 2007 Active deformation in North Iran Alborz Brunet et al., 2003 Intra-collision zone subduction South Caspian Basin crust is thinner and denser than adjacent regions

16 Reilinger et al., 2006 The Arabia-Eurasia collision zone: kinematics model GPS based Black numbers: 3 strike (3) dip slip White numbers: plate velocities

17 Active deformation takes place along crustal heterogeneity (i.e. old suture zone and orogenic belts) Horton et al., 2008

18 PART 2……..Summarizing 1) Deformation is accommodated along seismic belts (mountain chains and large intracontinental strike-slip faults) bounding aseismic blocks 2) Deformation in the upper plate is absorbed via : Crustal thickening (Zagros, Alborz, Caucasus, etc.) Lateral extrusion of rigid blocks (Anatolia and smaller crust blocks) Possibly via lithospheric buckling (Alborz-South Caspian basin system?) “Intra-collision zone subduction” (South Caspian basin) 3) Intracontinental deformation is localized along crustal weakness like inherited structures (paleosutures and old orogenic belts)

19 PART 3 a) When did the deformation related to continental collision start in the Alborz mountains? b) How did deformation evolve? c) What can we learn from foreland basin deposits (i.e. climate vs tectonic) ? 3) A case study from the Alborz mountains, an intracontinental mountain belt linked to Arabia-Eurasia collision (the record from foreland basin deposits)

20 Foreland basin anatomy and sedimentary facies distribution Tectonic load (crustal shortening and thickening; exhumation of crustal section) Plate deflection (flexural subsidence) Grain-size decrease DeCelles and Giles, 1996 Coarse-grained facies are generally confined in proximity of the fold and thrust belt front. However in some cases they can prograde into the foreland for tens of km……Why?

21 Burbank et al., 1988 Lateral and vertical sedimentary facies evolution in a foreland basin system: syn-thrusting progradation of coarse-grained facies Stable thrust front Distance from the thrust front (km) Progradation of gravel facies during a major thrusting phase

22 Flemings and Jordan 1990 Time (Ma) Lateral and vertical sedimentary facies evolution in a foreland basin system: post-thrusting progradation of coarse-grained facies

23 Lateral and vertical sedimentary facies evolution in a foreland basin system: climatic forcing Zhang et al., 2001

24 Simplified tectonostratigraphy of the Alborz Mountains Guest et al., 2006 The Alborz range is characterized by a complex crustal fabric, with inherited structures related to both compression and extension since Paleozoic time 36 Ma (end of magmatism)

25 Modified after Geological maps of Tehran, Semnan, Saveh, Sari, Qazvin and Amol 1: , Geological Society of Iran, and Guest et al., 2006 Central Alborz Mountains ca. 6 mm/yr of shorteningca. 4 mm/yr of left-lateral shearing

26 ASTER satellite image, bands 731-RGB Eyvanekey stratigraphic section 5 km

27 5m NS Unit 1C: braided river dep. system Unit 1 SN 70m Unit 1A: playa lake dep. system Unit 1B: distal river dep. system N 4m S N

28 Unit 2 SN Unit 2B: braided river dep. system Unit 2A: playa lake dep. system N S

29 Unit 3C: alluvial fan dep. system NS Unit 3 3B 3C Unit 3A: playa lake dep. system NS Unit 3B: braided river dep. system NS 5m

30 Stratal geometric relationship ASTER satellite image, bands 321-RGB

31 Magnetostratigraphy Normal Polarity Reverse Polarity Reference MPTS Main prerequisites: Fine-grained lithologies Continuous sedimentation Independent age constrains

32 Magnetostratigraphy In 75% of samples a Characteristic Remanent Magnetization (ChRM) was isolated Ballato et al., 2008

33 Magnetostratigraphic Correlation Ballato et al., 2008

34 Sediment accumulation rates Fine-grained sed. Coarse-grained sed.

35 PART 3…..Concluding a) When did deformation related to the Arabia-Eurasia continental collision start in the Alborz mountains? 36 Ma 17.5 Ma 7.5 Ma 6.2 Ma Sed.acc.rate = 0.04 mm/yr Sed.acc.rate = 0.58 mm/yr Sed.acc.rate = 0.65 mm/yr At ca Ma the basin records a sharp increase in sedimentation rate (0.04 to 0.58 mm/yr). This increase reflect onset of flexural subsidence related to crustal shortening and thickening

36 Densmore et al., 2007 Tectonic vs climate: retrogradation of coarse-grained facies Sediment flux Time (Myr) Distance from fault (Km) Time (Myr) Sediment flux Increase in slip rate +100% = increase in subsidence and sed. flux Decrease in precipitation -50% = decrease in sed. flux Pre-perturbation Post-perturbation In both cases retrogradation of sedimentary facies is recorded in the basin. However, when precipitation decrease the sedimentation rate does not change since there is no perturbation in subsidence Post-perturbation Pre-perturbation Facies retrogradation Pre-perturbationPost-perturbation Pre-perturbation Facies retrogradation

37 Densmore et al., 2007 Tectonic vs climate: progradation of coarse-grained facies Sediment flux Time (Myr) Distance from fault (Km) In both cases progradation of sedimentary facies is recorded in the basin. However, when precipitation increase the sedimentation rate does not change since there is no perturbation in subsidence Pre-perturbation Post-perturbation Pre-perturbationPost-perturbation Pre-perturbationPost-perturbation Facies progradation Decrease in slip rate -50% = decrease in subsidence and sed. flux Increase in precipitation +50% = increase in sed. flux

38 Unit 1

39 Stratal geometric relationship ASTER satellite image, bands 321-RGB

40 Unit 2 ca. 5 km ca. 25 km

41 Unit 3 ca. 5 km ca. 25 km

42 a) How did deformation evolve? b) What can we learn from foreland basin deposits (i.e. climate vs tectonic) ? PART 3…..Concluding The locus of deformation moved forth and back, without a predictable pattern on a time scale ranging from 2 to 0.6 Ma In a medial-distal part of a foreland basin high sediment accumulation rates coincide with fine-grained sediments and reflect an increase in subsidence due to tectonic loading Low sediment accumulation rates coincide with coarse-grained sediments and reflect decrease in subsidence related to intraforeland uplift Progradation of coarse grained sediments during a moderate to high subsidence rate seems be related to an increase in sediment flux possibly triggered by enhanced precipitation

43 Thank you With the contribution of Angela Landgraf, Manfred Strecker, Cornelius Uba, Norbert Nowaczyzk, Anke Friedrich, and many others…


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