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Dislocations and Dislocation Creep Dislocations and dislocation creep... 1. Introduction: a) Observations of textures associated with dislocation creep b) MOVIES of dislocations in metals. 2. How do dislocations move?: single dislocations: stress, energy and motion. Orowan’s equation. Frank-Read sources, Work Hardening (Fatigue, paper clips) 3. Recovery: dislocation climb, subgrain formation 4. Recrystallization: Fabric development and grain size evolution Grain rotation (LPO development) Reduction: Mechanisms of recrystallization Growth: forces driving grain growth... ----> Localization REVISIT THE QUARTZ regimes 5. Grain Growth: static and dynamic ? Thursday: 6. Piezometers and Wattmeters Empirical Piezometers (dislocations, subgrain and grain size). Stress in the lithosphere from xenoliths (Mercier) Stress across shear zones (Kohlstedt and Weathers) The WATTMETER 1. Intro: Observations First, ALL the complexity that we want to understand ! THEN, deconstruction: simple - - - - > complex small scale (single dislocation) ----- > larger scale (behavior of ensembles) Journal of Structural Geology, Vol. 14, No. 2, pp. 145 to 159, 1992 0191-8141/92 $05.00+0.00 Printed in Great Britain (~ 1992 Pergamon Press plc Dislocation creep regimes in quartz aggregates Journal of Structural Geology, Vol. 14, No. 2, pp. 145 to 159, 1992 Dislocation creep regimes in quartz aggregate0s 191-8141/92 $05.00+0.00 147 Printed in Great GBritainREG HIRrH and JAN TULLIS (~ 1992 Pergamon Press plc 1400 Departmreengimest of Geolo gdetericalS cieminednces, Brow bn Uyn relativiversity,P reo vidence, RI 02912, U.S.A. rates of (Received 11 September 1990; accepted in revised form 30 June 1991) 1. dislocation productionDislocation creep regimes in quartz aggregates Abstract--Using opti2.ca l dislocationand TEM microsc oclimbpy we have determined that threei regimes of dislocation creep ocRcur. ,ml j : in experimentally deformed quartz aggregates, depending on the relative rIa- tes of grain boundary migration, / J Regime 1 dislocation climb and3. d igsloraincation boundarproduction. Wyit hmigin eacrationh regime a(GBM) distinctivGe mRiEcGro sHtrIuRctruHre aisn pdr oJdAuNce Td UduLeL IS primarily to the operation of different mechanisms of dynamic recrystallization. At lower temperatures and faster strain rates the rate of dislocation production iDs teopoa grrtemate nfotr of di Gffuesoiloong-iccoanltS rocliel1en0d c -de8i ss,l Bocrao1t;wi o"n7n Uclnimiv1b;e tr-o6s ibtey ,aP n1r ;o- sv idenc1 e,. R4 I 0291.28 , U.S1.A; - 7. 1; .8 1 ; - s 1, -4 effective recovery mtheseechanism rates. In this are regim ae functionrecovery is ac ofcom mstressodated b, y strain-induced Sgtrrain Rbaotue n(dl/as)r y Strain rate (l/s) migration recrystallization. With an increase in temperature(Received or decrea s1e1F iSeptembergn. s2t. rPailont sr ao tf1e temperature9, 9th0e; accepted rate vosf straind inis lrevisedo ratecati oshowingn f orm the 30 location June 1 o9f9 the1) dislocation creep regimes for quartz aggregates climb becomes suffictemperatureiently rapid to accom andmodat ew reatercovery content. In this regimdeformede dynam (a)ic 'as-is'recry andsta (b)lliz withatio 0.17n oc wctu%r swater by added. The boundaries between the regimes are gradational. Open circles progressive subgrain rotation. With a further increase in temperature or derepresentcrease iregimen stra i1n, plus rate symbols dislocrepresent ation cl iregimemb 2, open squares represent regime 3, and a plus inside a square represents remains sufficiently rapid to accommodate recovery. However, in this regime grain boundary migration is rapgradationalid, between regimes 2 and 3. thus recrystallization occurs by both grAaibns btroaucntd--aUrys imngig orapttiiocnal aanndd p TroEgMre smsivcero ssucbogprya iwne r ohtaavteio dne. tTerhme iindeedn ttihfia-t three regimes of dislocation creep occur cation of the three regimes of dislocatiionn ecxrepeepri maeyn thaallvye dimefpoormrtdaeendpt e qinmudapsr ltiozcn aa tigtohgners e dfgoearvt eetshl,oe p ddmeepetenrntm doinf gaat iosontne atohdfey f lrosetwlaa ttei vme ircarote-s of grain boundary migration, 1000 law parameters and the calibration of rdeicsrloysctaatliloizne cdl igmrabi na nsdiz ed ipsisleotzrcuoacmttiueortne .rp sr.So iIdnnuc caet ditdohinet.i oaWnx,i iathl eisn hi doeeartncethni firinecgga tiimgoeneo omaf e dati rsyti nocft itvhee microstructure is produced due particular dislocation creep regime coulpdr ibme aursielyfu tl oi nt hel poipnegr taot icooenxn psotefrr aidimnif etfnheterse c noltin mmdiitetsic ohtnhasen aitsa mmwhso iuocnhft ad oygfni vasemtnrai ncina r teuacrnardyl stthaullsi ztahtieo n. At lower tempa eratu0r0e0s a0n d faster strain rates the rate of dislocation production is too great for diffusion-controlled dislocaotioo. n clim¢bP to be an o W-377 (quartzite) deformation has occurred. amount of recrystallization possible, we also describe effective recovery mechanism. In this regime recovery is accommodated by strain-induced grain boundary microstructures from samples of the fine-grained nova- 600- migration recrystallization. With an increase in temperature or decrease in strain rate, the rate .oOof di s location o 0 climb becomes sufficientlcyu lriatep itdo tioll uasctcraotme mthoed partoec erescseosv ewrhyi.c hIn w teh ibse rleiegviem we oduylnda mic recrystallization occurs by occur in quartzite at higher strains. 400- INTRODUCTION progressive subgramine rtortyat ioofn .c-axis With ap fruerftheerrr iendc roearsie nint atetmiopnesra (tuSrceh omr didec &re aCsea isne sytr ain rate di•s location climCbQ -83 (novaculite) remains sufficientl1986)y rapid aton adc pcolamnmaord faateb reicosv deeryf.i nHeodw bevye r,e icnr tyhsista rellgiizmeed g qrauianr btozu ndary2 m00i.g Or ation is rapid, gime 1 thus recrystallization occuMicrostructuralrs by both gra ionb bseoruvnadtiaornys manigdr ainterpretationstion and prog ressive subgrain rotation. The identifi- EXPERIMENTAL studies on the de eformation of geologic grains in S - C mylonites (Lister & Snoke 1984) can be i . cation of the three regimes of dislocation creep may have important implications for the0 deter0m4 ination of flow R l I I I I law parameters anuds tehde tcoa ldibertaetiromn ionf ere tchryes tkaillnizeemd agtriacins osifz ed puicetziolme estheresa. rI nz oanddeist.i on, the identification of a materials have generally concentrated on either the Regime 1. At lower temperatures and faster strain 0 10 20 30 40 50 60 particular dislocation creep regime could be useful in helping to constrain the conditions at which a given natural determination of flow laws or the characterization of In addraitteiso nm,i cdriossltoruccatutriaoln ocbrseeervpa timonisc rsousgtgreustc ttuhraet sd i(sslou-c h as deformation has occurred. 1000. microstructures produced by different deformation recrysctaatliolinz ecldim gbr aisi nd isize)fficult haandv eth bate erenc ocvaelriyb irsa atcecdo mfomro u- se as b mechanisms. Rheological data in the form of a flow law paleopdaietezdo mbye tgerarisn b(oeu.ngd. aryTwiss migra tio1n9 7re7cr,y sKtalolihzaltsitoend. t & 800. relating strain rate, temperature and stress (and possibly WeathQeurasrt z1i9te8 0sa, mOprldes &de Cfohrmriesdt iein 1984).this re gime show the highest strengths, and they are the only ones to undergo | . INTRODUDCeTsIpOitNe the large amount ofm pertervyi ouf sc-axis rese aprrcehf eornre d orientations (Schmid & Casey other thermodynamic variables) can be used to predict appreciable strain weakening (Fig. 3a). However, nova- CQ- 94 (novaculite) ,o0 the mechanical behavior of rocks at gR1eol o(highgic co nstressditions, loqwua T):rtzc,u l tiproductionthee sraem hplaess bdefeonrm nfast,eod cino rm erecogpimr1986)eeh e1v nserhs aoivwnye d l bi etptxyllepa enclimbstrariarmi nf eanbtr aiandcl s de fGBMined b yslo recwrystallized quartz grains in S - C mylonites (Lister & Snoke 1984) can be provided that extrapolation inE XtePmERpIeMraEtNuTreA La nstdu dsiterasi no n tshtued dye wtfeooa rkimelnluianstgit or(aFnti ego. tf3h ag)e.e porlogceics ses associated with dislo- e + materials have generally concenMtriactreosdtr uocntu reesi thfreomr tqhuea rtzitues esdam tpol eds estheorrmteinnede the kinematics of ductile sheawr- 3z3o9 (nqueasrtz.i te) rate can be proven valid. Flow laws have been used to cation creep over the entire range of conditions where it D determination of flow laws or t2h0e% cshhoawr athcatte driiszloactaitoionn colifm b iIs nno ta adbdlei ttioo anc,c odmimsloo-c ation creep0 microstructures (such as provide constraints for the modelling of a wide range of is thed adteo mrecinovaenryt idne rfeogirmmea 1.ti oTnE Mm oebcsheravnaitsiomns. fDroims ltohce ation o . geologic processes including fomldicinrgo s(ter.ugc. tuPraersri sphr eotd aulc. ed crbeyep cdoiirnfefsc elourfed onertsi g idnaa el fsgotrrraaminisna tsihpoorwno dhiugrchei cndregny ssimtiaeelslc iohzfae tndani gsgmrlead i n(dis- size) have been calibrated for use as 1976), continental rifting (e.g.m Zecuhbaenr isemt asl.. R1h9e8o6l)o agnicda l dlaotcaa tiindo itnshl ogecl aiftdiooern mso r (o,u pfi nat o sf lo-o1m0w1e 6l acmwa -s2 e)s ,wp hcaillciehm ocbpo)im eamznodnm lyae threeavrcseo ve(rey.g .| Twissc 1977, Kohlstedt & mantle convection (e.g. Christreenlsaetnin &g sYtruaeinn r1a9te8,9 t)e. mByp eramtuerceh astnnraidisg mshttr se(edsgsims (elaontncsad at npidoo nssh sociwbli lnmyo b e voiWdre negcaert ahfioenr r tshbe o1 du9env8ed0lo,a pOr-y r dm &i- Christie 1984). ment of subgrain boundaries (Fig. D4ae).s pAitt eth et hoept iclalr ge amou:n1t o f previous research on comparing microstructures preostehrevre
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