Efficient exhumation of (ultra) high-pressure rocks by slab extraction

Efficient exhumation of (ultra) high-pressure rocks by slab extraction Zhao, Z., P.D. Bons, Eberhard Karls University Tbingen, Germany E. Gomez-Rivas, University of Aberdeen, Scotland, UK A. Soesoo, Tallinn University of Technology, Tallinn, Estonia E. Burov, Universit P. & M. Curie (Paris VI), Paris, France

1OutlineIntroduction to slab extractionDefinitionDivergent double subduction zone setting

Numerical simulations with FLAMAR

Cases in geological recordsPaleotethys in Qiangtang Suture, TibetD'Entrecasteaux eclogites, Papua New Guinea

Conclusion"Normally" suture between plates has reverse movement

When plates divergerollback, orslab extraction

Slab extractionOpposing slab pulls: F2 > F1Fresistance shear force at base and overlying oceanic lithosphereWhen F2 > F1+ Fresistance Short slab may be pulled up by long slabRelated to L1-L2, temperature-density relationships, x, a1,2, rheology of slab and mantle, etc.Slab extraction is likely to happen when x becomes smallxL1a1L2a2F1F2Divergent double subduction zone (DDSZ)It solves simultaneously Newtonian dynamic equations of motion,

in a Lagrangian formulation, coupled with visco-elasto-plastic constitutive equations,

heat transport equations

and state equation(Burov et al., 2001; 2003; Burov and Yamato, 2008)

Cp (T/t + uT) (k) - Hr - Ha- fracIIII/t = 0 r = f(P,T)The parameters A, n, Q are experimentally determined material propertiesNumerical simulations: FLAMAR

40km110kmLength differences170km (variable)10km80kmGeometry: divergent double subduction zoneMaterial properties from Angiboust et al. (2012)Parameters varied: Vx, L and rheology of slabLVxStarting model and settings

SimulationsVx=0

Simulations

The-Depth of passive markersExhumation rate of passive markers

SimulationsVx=-2cm/y

SimulationsThe-Depth of passive markersExhumation rate of passive markers

Slab gets extracted whenx is shortL largesubducted lithosphere strongLubricate layer is necessary (serpentinite)High-pressure rocks exhumed rapidlybrought in contact with sediments/LP rocksin locally strong extensional settingin case of plate divergencerapid exhumation of HP rocks on both sidesopening of pull-apart basinResults

HP rocks in direct contact with non-metamorphic sedimentary mlangeConsistent top-to-south shearSedimentation and volcanismno extensive erosion to exhume HP rocksCase 1: Qiangtang suture, Central Tibet (Zhao et al., 2015). Young eclogites 4.6-5.6 Ma

Exhumation rate ~2 cm/yr

NW movement of Solomon sea plate

New pull-apart basin

(Baldwin et al., 2004; DesOrmeau et al., 2014; Korchinski et al., 2014). Case 2: D'Entrecasteaux eclogitesExtraction is an efficient mechanism for rapid exhumation of (U)HP rocksBrings (U)HP rocks in contact with LP rocksNo need for erosionClose to eduction1 and extension model2Extracted slab can be negatively buoyant (ocean)Requires divergence of subducted slab and overriding plateSingle suture (Western Gneiss, Norway)DDSZ (Qiangtang, d'Entrecasteaux Islands)ConclusionRefs.: (1) Duretz et al., 2012; (2) Brueckner et al., 2013Thank you

Zhao, Z., Bons, P., Wang, G., Soesoo, A., and Liu, Y.: Tectonic evolution and high-pressure rock exhumation in the Qiangtang Terrane, Central Tibet, Solid Earth, 2015.