Plasticity and diffusion creep of dolomite

Davis, N. E.; Kronenberg, A. K.; Newman, Joseph W.

doi:10.1016/j.tecto.2008.02.002

Cited by 43 publications

(106 citation statements)

References 66 publications

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“…Hence, the time necessary to separate a layer by necking is t N = 1/ nBτ n xx0 . For example, if a necking experiment for τ xx = 250 MPa was performed at a temperature T = 800 • C with Madoc dolomite following the flow law of Davis et al (2008), given by D xx = εµ −n e −Q RT τ n xx = Bτ n xx with ε = 10 29 s −1 , µ = 45.6 GPa, Q = 420 kJ mol −1 , R = 8.31 kJ mol −1 K −1 and n = 7, then B = 8.1422 × 10 −67 Pa −n s −1 and it would take nearly a year to separate the dolomite by necking because t N = ∼ 328 days.…”

Section: Single Layer Neckingmentioning

confidence: 99%

Folding and necking across the scales: a review of theoretical and experimental results and their applications

Schmalholz

Mancktelow

2016

Solid Earth

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Abstract. The shortening and extension of mechanically layered ductile rock generates folds and pinch-and-swell structures (also referred to as necks or continuous boudins), which result from mechanical instabilities termed folding and necking, respectively. Folding and necking are the preferred deformation modes in layered rock because the corresponding mechanical work involved is less than that associated with a homogeneous deformation. The effective viscosity of a layered rock decreases during folding and necking, even when all material parameters remain constant. This mechanical softening due to viscosity decrease is solely the result of fold and pinch-and-swell structure development and is hence termed structural softening (or geometric weakening). Folding and necking occur over the whole range of geological scales, from microscopic up to the size of lithospheric plates. Lithospheric folding and necking are evidence for significant deformation of continental plates, which contradicts the rigid-plate paradigm of plate tectonics. We review here some theoretical and experimental results on folding and necking, including the lithospheric scale, together with a short historical overview of research on folding and necking. We focus on theoretical studies and analytical solutions that provide the best insight into the fundamental parameters controlling folding and necking, although they invariably involve simplifications. To first order, the two essential parameters to quantify folding and necking are the dominant wavelength and the corresponding maximal amplification rate. This review also includes a short overview of experimental studies, a discussion of recent developments involving mainly numerical models, a presentation of some practical applications of theoretical results, and a summary of similarities and differences between folding and necking.

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Section: Single Layer Neckingmentioning

confidence: 99%

Folding and necking across the scales: a review of theoretical and experimental results and their applications

Schmalholz

Mancktelow

2016

Solid Earth

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“…Therefore, one of the reasons why twinning in naturally deformed dolomite rocks is less common and less abundant than e-twinning in calcite marbles is because dolomite does not twin at low temperatures. Moreover, at the range of temperatures we inferred for deformation of the Pohorje marbles, dolomite grains in calcite-dolomite composites remain completely rigid whereas calcite is considerably weaker and will display various crystaloplastic deformation mechanisms (Davis et al, 2008;Kushnir et al, 2015).…”

Section: Deformation Twinsmentioning

confidence: 79%

Calcite deformation twins in Pohorje marbles

Nastja¹,

Vrabec²

2018

Geologija

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Marbles in Pohorje occur in lenses and smaller bodies in the southern and southeastern part of the massif. Marbles are very pure, predominantly calcitic and rarely calcitic-dolomitic, containing a maximum of 5 % of non-carbonate mineral phases. The latter comprise pyroxenes (diopside), amphiboles (tremolite), olivines (forsterite) in places replaced by serpentine, quartz, feldspars (potassium feldspars and plagioclases), epidote, zoisite, vesuvianite, scapolite, muscovite, biotite partly replaced by chlorite, phlogopite, rare grains of titanite, rutile, zircone, apatite, and small grains of ferric oxides and sulfides. Calcite exhibits intensive deformational e-twinning whereas dolomite is undeformed and untwined. All four known types of mechanical twins in calcite were recognized: thin Type I twins, straight thick Type II twins, curved, lensoid and tapered thick Type III twins, and thick patchy Type IV twins. Type III twins are the dominant mechanical twins in the Pohorje marbles indicating the temperature of deformation somewhat above 200 °C. Since they lack signs of grain boundary recrystallization, we assume that the twinning was followed by a decrease temperature during exhumation. With increasing temperature the process of recrystallization along calcite grain becomes pronounced. Small individual untwined calcite crystals are progressively replacing bigger calcite grains. In few examples second generation of Type I deformational twins develop in recrystallized calcite grains, which also implies lowering of temperature due to exhumation. IzvlečekPohorski marmor se pojavlja v lečah in manjših telesih v južnem in jugovzhodnem delu pogorja. Marmorji so po sestavi zelo čisti, skoraj izključno kalcitni, izjemoma kalcitno-dolomitni in vključujejo največ do 5 % nekarbonatnih mineralnih faz. Te vključujejo piroksene (diopsid), amfibole (tremolit), olivine (forsterit) mestoma nadomeščen s serpentinom, kremen, glinence (kalijeve glinence in plagioklaze), epidot, zoisit, vezuvianit, skapolit, muskovit, biotit deloma nadomeščen s kloritom, flogopit, redka zrna titanita, rutila, cirkona in apatita ter majhna zrna železovih oksidov in sulfidov. Kalcitni kristali so močno deformirani z mehanskim dvojčenjem, dolomitni kristali pa so nedeformirani in brez dvojčkov. Našli smo vse štiri znane tipe mehanskih dvojčkov v kalcitu: tanke dvojčke tipa I, ravne in debele dvojčke tipa II, zakrivljene, lečaste in zašiljene dvojčke tipa III, ter debele krpaste dvojčke tipa IV. Prevlada dvojčkov tipa III v pohorskem marmorju nakazuje temperaturo deformacije nekoliko nad 200 °C. Ker ti dvojčki ne kažejo znakov rekristalizacije na robovih zrn, sklepamo, da je dvojčenju sledilo znižanje temperature zaradi ekshumacije kamnin. Z višanjem temperature postane bolj izrazit proces rekristalizacije vzdolž robov kalcitnih zrn. Velika kalcitna zrna so pri tem vedno bolj nadomeščena z majhnimi kristali brez mehanskih dvojčkov. V nekaj primerih so v rekristaliziranih kalcitnih zrnih nastali mehanski dvojčki tipa I druge generacije, kar tudi na...

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“…For example, sample CaMg-21 (σ ax = 7 MPa, 29 h) contains densities of about 2.1 ± 0.7 × 10 13 m −2 (Fig. 7c), determined by the point intersect method (Butler 1969). Dislocations are usually curved and tangled near .…”

Section: Reaction Rim Microstructuresmentioning

confidence: 99%