Presentation on theme: "Continental collision mountain belts: the Arabia-Eurasia system"— Presentation transcript:
1 Continental collision mountain belts: the Arabia-Eurasia system Paolo Ballato,
2 Today's class contents1) 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 PART 11) Continental collision: a brief outlook (definition, causes, implications…..)
4 Pre-collisional setting LowerplateUpper platePrior to a continental collision, the landmasses are separated by oceanic crust, formed during an earlier episode of sea-floor spreadingAs the continental blocks converge, the intervening sea floor (lower plate) is subducted beneath the upper plateThe descending oceanic slab generates a volcanic arcUpper plate deformation is limited (tectonics stress is not transferred far away from trench) and shortening is mainly accommodated along plates interface (accretionary wedge)India-Asia convergence rate decreased from 160 to 50 mm/yr in the last 70Mawww2.bc.edu/~kafka/ge180.f03/PT_4.ppt
5 Collisional settingAs the continental lithosphere of the lower plate approaches the upper plate subduction terminates, suturing occurs, and continents are amalgamatedTectonics 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 beltsA fold and thrust belt develops in the lower plateMountain range/ranges are formed and several km of crust can be exhumedwww2.bc.edu/~kafka/ge180.f03/PT_4.ppt
6 Why does continental collision occur? Continental lithosphere ( g/cm3 )crust (density ca. 2.7 g/cm3)mantle (density ca. 3.3 g/cm3)Oceanic lithosphere ( g/cm3)crust (density ca. 2.9 g/cm3)mantle (density ca. 3.3 g/cm3)Cloos, 1993Oceanic lithosphere is denser than continental lithosphere, so it tends to sink (subduction) into the asthenosphere when convergence takes placeWhen 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
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, 1999Difficult 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…..Summarizing1) Continental collision occurs when plate convergence cannot absorbed anymore via subduction process2) Continental collision takes place because buoyancy forces do not allow large amount of continental subduction3) 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 thickeningLateral extrusion of rigid blocksPossibly 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 CaucasusBlack SeaEurasiaAspheronAnatoliaCaspT-I plateauKopeh DaghAlborzAegeanCentral IranHellenicCyprusZagrosLutHelmandNubiaMakranRed SeaArabiaOwen FZGulf of AdenIndiaEastern African RiftenSomalia
12 Arabia-Eurasia system: from oceanic subduction to continental collision Opening of the Gulf of AdenMcQuarrie et al., 2006
13 Active tectonics of the Arabia-Eurasia collision zone: seismicity Reilinger et al., 2006
14 Active tectonics of the Arabia-Eurasia collision zone: quantifying present-day deformation with GPS dataSubduction of a denser microplate (Southern Caspian Basin)Westward extrusion of Anatolia(escape tectonics)Crustal thickeningReilinger et al., 2006
15 Intra-collision zone subduction Active deformation in North IranAlborzIntra-collision zone subductionSouth Caspian Basin crust is thinner and denser than adjacent regionsBrunet et al., 2003Guest et al., 2007
16 The Arabia-Eurasia collision zone: kinematics model GPS based Black numbers:3 strike(3) dip slipWhite numbers:plate velocitiesReilinger et al., 2006
17 Active deformation takes place along crustal heterogeneity (i. e Active deformation takes place along crustal heterogeneity (i.e. old suture zone and orogenic belts)Horton et al., 2008
18 PART 2……..Summarizing1) Deformation is accommodated along seismic belts (mountain chains and large intracontinental strike-slip faults) bounding aseismic blocks2) 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 33) 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) ?
20 Plate deflection (flexural subsidence) Foreland basin anatomy and sedimentary facies distributionTectonic load (crustal shortening and thickening; exhumation of crustal section)Grain-size decreasePlate deflection (flexural subsidence)DeCelles and Giles, 1996Coarse-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 Progradation of gravel facies during a major thrusting phase Lateral and vertical sedimentary facies evolution in a foreland basin system: syn-thrusting progradation of coarse-grained faciesStable thrust frontProgradation of gravel facies during a major thrusting phaseDistance from the thrust front (km)Burbank et al., 1988
22 Lateral and vertical sedimentary facies evolution in a foreland basin system: post-thrusting progradation of coarse-grained faciesTime (Ma)Flemings and Jordan 1990
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 36 Ma (end of magmatism)The Alborz range is characterized by a complex crustal fabric, with inherited structures related to both compression and extension since Paleozoic timeGuest et al., 2006
25 ca. 4 mm/yr of left-lateral shearing Central Alborz Mountainsca. 4 mm/yr of left-lateral shearingca. 6 mm/yr of shorteningModified after Geological maps of Tehran, Semnan, Saveh, Sari, Qazvin and Amol 1: , Geological Society of Iran, and Guest et al., 2006
35 6.2 MaPART 3…..ConcludingSed.acc.rate = 0.65 mm/yr7.5 Maa) When did deformation related to the Arabia-Eurasia continental collision start in the Alborz mountains?Sed.acc.rate = 0.58 mm/yrAt 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 thickening17.5 MaSed.acc.rate = 0.04 mm/yr36 Ma
36 Tectonic vs climate: retrogradation of coarse-grained facies Increase in slip rate +100% = increase in subsidence and sed. fluxDecrease in precipitation -50% = decrease in sed. fluxPost-perturbationPost-perturbationPre-perturbationPre-perturbationPre-perturbationPost-perturbationPre-perturbationPre-perturbationFacies retrogradationFacies retrogradationSediment fluxSediment fluxTime (Myr)Time (Myr)Time (Myr)Distance from fault (Km)Time (Myr)Distance from fault (Km)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 subsidenceDensmore et al., 2007
37 Tectonic vs climate: progradation of coarse-grained facies Decrease in slip rate -50% = decrease in subsidence and sed. fluxIncrease in precipitation +50% = increase in sed. fluxPost-perturbationPost-perturbationPre-perturbationPre-perturbationPre-perturbationPost-perturbationPre-perturbationPost-perturbationFacies progradationFacies progradationTime (Myr)Sediment fluxSediment fluxTime (Myr)Time (Myr)Distance from fault (Km)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 subsidenceDensmore et al., 2007
42 PART 3…..Concluding a) How did deformation evolve? The locus of deformation moved forth and back, without a predictable pattern on a time scale ranging from 2 to 0.6 Mab) What can we learn from foreland basin deposits (i.e. climate vs tectonic) ?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 loadingLow sediment accumulation rates coincide with coarse-grained sediments and reflect decrease in subsidence related to intraforeland upliftProgradation 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 youWith the contribution of Angela Landgraf, Manfred Strecker, Cornelius Uba, Norbert Nowaczyzk, Anke Friedrich, and many others…