Grain growth kinetics inolivine aggregates
Transkript
Grain growth kinetics inolivine aggregates
168 (1989) 255-2'73 Scrence PublisheÍs B.v.' Amsterdam _ Printed in The Netherlands Ta,w4htsics, Eta..er Graingrowthkineticsin olivineaggregates S. KARATO Ocean Research Institute, Uniuersity of Tokyo, Nakano, Tokyo 164 (Japan) * (Received June 1ó, 1988; revised version accepted January 12' 1989) Abstract Karato, S., 1989. Grain growth kinetics in olivine aggÍegates' Tectonophysics, |68:255-2.73' Grain growth kinetics were studied in hot-pressed fine-grained olivine aggregates Experimental conditions include pressuÍesof 0.1 MP4 300 MPa and 1 GPa, and temperatures of 1473, 1573 and 16.73K, with or without the presence of water. At the initial stage of grďn growth, growth of larger grains occurs rapidly, consuming smaller grains, which results in significant poÍe entÍapment. Almost homogeneous grain-size distribution ís established in this process. After this stage, grain-size distribution remains almost homogeneous in most cases. It was found that the presence of water enhances the grain growth kinetics when the amount of water is limited. However, when the amount of water is large, the water-containing pores significantly inhibit the grain boundary migration. Therefore the enhancement of grain growth due to the pÍesence of water is due to the role of dissolved water in olivine rather than the mass transport through wateÍ. AbnoÍmal grain growth was found in some samples. In these cases, normal grain growth was inhibited by the presence of a significant amount of water-filled pores, or grains with significantly larger size than the rest occurred in the staÍting materials. In 0.1 MPa runs, significant porosity developed and the grain growth Íates were significantly lower than in those at high confining pressures. These results show that both water and pores have important effects on grain growth kinetics in olivine. When the effects of pores (or secondary phases) in inlubiting grain gÍowth are unimportant, the grain growth rate in olivine is very fast: gÍowth to 100 pm size wil| occur in 102 to 103 hours at 1500 K. Thus fine grain size in olivine will be maintained only for a short geological time, unless the grain boundaries are effectively pinned by secondary particles. Introduction Microstructures of rocks at the grain scale have an important bearing on a variety of geological and geophysical problems. These problems include the estimation of paleostresses from recrysta|Iized grain size (Avé Lallemant et al., 1980), the mechanisms of preferred orientation and the reSultant seismic anísotropy (Karato, 1987; Nicolas and Christensen, 1987), and grain-size sensitive creep (Karato et al., 1986). Several processes may influence the grain size of rocks (Karato, 1984). They include dynamic * Present address: Department of Geology and Geophysics, University of Minnesota, Minneapolis, MN 55455, U.S.A. 0040-195r,/89,/$03.50 o 1989 Elseúer Science Publishers B V. recrystallization, grain growth and primary recrystallization. Dynamic recrystallization is a process during deformation in which the total grain boundary energy increases (i.e. grain size decreases) at the expense of strain energy within grains. The driving force for this process is the strain energy stored in dislocations, and grain size is mainly determined by the applied shear stress (Twiss, 1977). During grain growth, the grain boundary energy is reduced (i.e. grain size increases), the driving force being grain boundary energy. Grain boundary migration may also occur after deformation, being driven by dislocation energy (primary recrystallization). The importance of these processes depends primarily on the ratio of strain energy stored in dislocations to grain boundary energy. Dynamic S- K-{RATO 2)t) recrystalfization and primary recrystallization are important at relatively high (initial) stress and/or coarse grain size. Extensive studies have been carried out on dynamic recrystallization (for a review, see Urai et a1., 1986; Karato, 1987). Toriumi (1982) studied the primary recrystallization in olivine (see also Morcier, 1979). However, relatively little attention re grain growth in minerals. t82) studied the grain growth aggregates, and Olgaard and the effect of secondary phases :alcite. No experimental studken on grain growth in olivine inary results by Karato (1984). The purpose of this study was to obtain the first data set on grain growth in olivine and thereby to better understand the physical processes that may govern the grain size of olivine in the upper mantle. The driving force for grain growth is the grain boundary energy and the grain growth rate decreases significantly with increase of grain size (e.g. Kingery et a1.,7916). Therefore fine-grained starting materials are necessary in order to observe significant grain growth within an experimental time scale. Hot-pressed fine-grained olivine aggregates were used in this study. The starting material was the San Carlos olivine. Its chemical comoosition is shown in Table 1. TABLE 1 Chemical composition of the starting materiď wt.Vo FeO Nio Mgo CaO Total Sample Method of grair Average grain size size separation " (p m) Powder suspended in 1.3 (cs)"o (cs)," alcohol after 20 hours Powders suspended in 1.0 alcohol after 2 hours but deposited after 20 hours Powders suspended in 2.3 ).1 ,a 8.3 alcohol after 10 min. Powder suspended in alcohol after 20 min. but deposited after t hour u The powder samples and alcohol were kept in a 50 cm height cylinder for graín síze separation' o (GS)" refers to the mean grain size defined by number " (G,S), refers to the mean grain size defined by volume fraction, i.e. (GS), : Iť,so) dr, where g(r) dr is the volume fraction of grains the grain size of which is r - r { dr. Specimen Jabrication sio2 Methods of grain size separation and average grain sizes of olivine powders de nsity, i'e . (Gs)" : I ť, ÍQ) d r, whe re f (r)d r is the nu m ber fraction of grains the grain size of which ís r - r ldr. Experimental procedure Al 2 o 3 TABLE 2 41.23 0.00 7.83 0.26 50.72 0.00 100.04 About 3-5 mm size optically clear olivine grains were hand-picked, crushed in a tungsten carbide rock crusher and then ground in an alumina or an agate mortar for 30 to 200 min. The optical microscope observation on decorated powders showed that these processes introduced few dislocations. Powders of particular grain sizes were separated by sieves for grain sizes larger than 38 pm, and by the sedimentation method (in alcohol) for the smaller grains (see Table 2). After separation of grain size, the samples were dried ín a Co/Co, K for gas mixture (Ío,:10-5 Pa) at 73.73_14,73 10-20 hours. In order to avoid the precipitation of carbon, argon was flushed after the temperature dropped below ca. 1000 K. The grain-size distribution of the starting powders was measuÍed by the Elzon Particle Counter and the results are shown in Table 2 and in Fig. 1. Hot-pressing was carried out with or without the addition of water using a gas medium apparatus described by Paterson (1970). The thermodynamic conditions and the details of the hot- S KAR.\TO rain ,M"{tr\ GROWTH IN OLIVINE AGGREGATES sizes oÍ lm srze c a o tr _--:- c o o o (( '5 ), .' E o 5. 1 8.3 c 1 a o 6 6 c o r:O cm height d by number b is the numsr - r l dr. (! c o o o E a E l by volume d ( r rdr 35 t5 I is t he 4 45 5 gra insize, P m h is r -r*dr . É c lirine grains ilen carbide nmlna or an ltical microlers showed ilislocations. nE separated pm, and by pl) for the cparation of a co/co2 -1473 K for cipitation of temperature size distribusued by the ts are shown 6 (í c o o o c o E o ! ) o 1o 5 ) ó c c ó 0 6 tr o o C o G o o E o o = l 5 r or without lium appararc thermodyof the hot- grainsize , Fm gra inslze, pm gr ain size, P m 5 lo t5 20 g r ai n si z e , P m F i g ' 1 .G ra in - sizedist ribu t ron ofst a rt in goliúne p owd e rs'Me thod sofpowd e rpre parationare d e scribe dinT able 2. 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Ú@ -) condilng prsfor hor14. 49L progresthe same faur srze4le v'as E mtcropossible iles rl'ere fuom the Eesslve d out in Ences ln :. Grain m *-here n as the time is n- n-hich pint" of r growth rl stress r-added fosmpy arato et e under essures. (at 300 lffa as gas ap- us@ [n& filol s101 .{-tr . Temper- Pressure atule (K) (MPa) r573 r4'73 r4'73 Water o Duration Average Density c (hours) grďn size (E/"^. ) (pm) 0.5 45 187 46 90 r32 200 10 18 to /J 300 0.1 0.1 0.1 0.1 0.1 0.1 0.1 0 .1 0.1 dry dry dry dry dry dry dry dry dry dry 300 300 300 300 wet wet I 1 2 wet 4 l) /J l5'r3 7573 1573 7673 7673 ÚHil m;il Í1)1 rÍ]'01 {nn A flg 4914 {Dtr 1924 14'73 I4'.73 7473 1473 {NM m ffi {I8!r A 4918 4923 4925 rs'73 15'73 15',t3 7573 300 300 300 300 wet 1 wet 1 s.mr c D t5'73 14'73 300 300 wet #.,8F {5ó 160 {m4 {EI {SE3 s3D 4891 {lm B B C B A c 75'73 1573 1573 75'13 14'73 1413 1513 1.573 15'73 300 300 300 300 300 300 300 300 300 B A 7s73 75'73 300 1000 sz1 1929 lokb A A Comments wet wet wet wet dry wet 5ó 2.6 3.6 5.3 '7.9 10.8 11.8 15.5 r23 18.3 z 5 .2 '7.8 2 Á 4.5 3 40;r 25.5 3.2'l 8 1 5 22.0 3.33 3.30 3.27 2r.8 wet wet J dry dry 3 20 11.1 37.2 wet 3.29 3.24 2.5 2.5 1 2 wet 3.17'r 3 . 1 1d 3.21d 3 . 1 3d 3.04d 7'7.3 24.5 35.0 44.1 dry wet 3 . 3 1d 3.30d 3.30d 3.22d 10.7 14.8 21,.0 45.2 13.1 18.3 20.5 3.6 t7.7 29.8 wet J.JI ).21 Deformation (abnormal grain growth) J.JJ Deformation Deformation 2.6-2;7 3.2'7 3.26 Deformation 3.30 3.33 (abnormalgrain growth) Deformation ' For explanation of A, B, C and D, see Table 2. o *DrY'' indicates water-free conďtions; ..wet'' indicates water-added conditions' ' Density of olivine grain is 3.33 g/cm3. d Estimated from point counting on thin sections. paratus as for hot-pressing was used, but in a 1 GPa run, a piston cylinder type solid-medium apparatus was used. In two runS (NoS. 4821. and 4929), grain gÍowth occurTed during deformation. The ďfferential stress ransed from 25 to 72 MPa. 0.1 MPa pressure "dry" runs. The starting material was hot-pressed (at 300 MPa) without water. Thin slices with ca. 0.5 mm thickness were cut from the hot-pressed sample and annealed at 0.1 MPa in a CO/CO' gas mixture (/o,: 10-s Pa) at 1473-1673 K. lonur8rur Árepunoq urer8 o1 enp ssecord luaurderlue erod r 3uuvroqs 'tavr patre1ue q7 .3 .Árepunoq urer8 Bul^otu eql -i{ pouuoJep serod pelq-rele.r tur,roqs ,revr pa8rulue uy 'g urcr8 q8noJql ssecord luaruder1ua arod Jo pJocal aql ano:€ rroqs surer8 eql eplsur arod ;o uollnqulslp áqJ .s3ll"punoq fuiaour Áq padder1ua aq Áeu sau?punoq urzrB 1u sero6 TuTJ snonuÍluoc sB ueql Jeql€ J seJod pál?Iosl uI sJncco Jel?^\ s'uepunoq urÚJ3 lv 'souepunoq upr8 1u puu surerB eql eplsul q|oq sJncco Jal?^\ .,t\er^IT€ J e^o .V .suolllpuoJ PaPp?.Jel?^l lÚ pepe(ru? pw passard-1oq aldurus eqt Jo sornlcrulsolclll1 'g 'tld pelpy (selqqnq Jo) sarod Jo acueserd er{l sr sernlEaJ alq€lou eql Jo euo .snoeue8ouroq eJolu aurc'eq uorlnqrJlsrp ezrs-rruJB oql pu" paJJncJo q1lrroJ8 ur?Jt lupcrJru8rs 'tuqueuue puB Bursserd-1oq ralJv '()I 'Erg) uoqnqulsrp ezrs-uTpr8apr.r, qlr^\ " Jep^\oduror; pesserd-loq se^\aIduIBssTtIJ .€ .tl'q uI u^\oqs eJ€ suolllpuoc papp?-Jel",/l\ Jepun peleeuu€ pue passerd-1oq eldures e ;o sqdertoJcrruoloqd sunJ .(lad1,,anssail qfup .,^Í\oloq pessncslp eq ilI/l\ s? 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Fig 3). Most of the pores inside Úll[/M. tu 5:":: fl03lij!-r-:-::a:llialh in zones surrounding the angulúi.ur-.'T-!:c. -...res. in which no pores are found. 'Det*'een -:; ll'lc , :-s the zone and the grain .]1Í|lllirillLi]ú].i.:.r e a relatively small number of pores. .tl!5 ' -.::epores on grain boundaries are de]|lÍÍ]TTu:': i"3. .l3. C). Deformed pores are associL..-ú..ť' ::ned grain boundaries, and the shape l, |1ť::: : :Ínedpores Suggeststhat grain boundary E:E;- --.in these cases is driven by the grain !í r|]'::.. Čnergy(Karato' 1988). In Some cases, [!É:.:. bl moving boundaries is so marked that l r:: torn and trapped into the grains (Fig. -. '{-- ]-:-: srze of pores inside the grains appears to Ír-::s- irom the center to the outer part (see also ;r i -,'r. This suggests an increase in pore size -: ;-:.rain growth. Fig. 4 are shown the dislocation structures of -.siine sample as shown in Fig. 3. Three regions ^rr. :.early recognized. The central portion, often ":. r---.:lar shaped, has relatively low dislocation den- very high dislocňion deisities which coincides with the pore-rich zone. The dislocations in the outer rim between the dislocation and pore-ricl zone and grain boundaries are mostly straight and perpendicular to the grain boundaries. These dis. locations tend to be parallel to the [100] or [001 orrentatron. Initial rapid grain growth consuming fine grainr was also observed with the other starting materi. als. However, the kinetics of this initial stage ol grain growth was found to depend on the initial grain-size distribution. The wider the starting grair distribution, the faster the initial stage grair growth. The pore-rich zone was not clearly seer when the starting powder had a relatively uniforn and fine grain size. Entrapped porosity was gener ally larger in samples hot-pressed from powders with wider grain-size distribution (see Table 3). The SEM micrographs of sample No. 4891, the densification of which was imperfect due to the effective sealing of water, are shown in Fig. 5. Thr rounded shape of grains clearly indicates signifi. cant mass transport driven by surface energy. Thr 30 pm Fig 4. Díslocations in a hot-pressed and annealed sample revealed by oxidation j : . 1^^^+: ^. decoration. Note the dislocation-rich zone .ŮeJpeq Jel"^\peppu lnoqllt\ (eac t ro e66 gg5) ernsserd turur;uoc q8q t" suorllpuoc ee{-Jolu,t\ E pelueuup pue pesserd-1oq saldurzs eqJ suru ,,rup,, anssatd q3111 'lseJ aql u?ql azrs raBrul qcnur qtr,t sumr8 peul€luoc plJel€ur 8utuels aqt rc/ptn atru1 senr Á1tsorod eJeq.tr punoJ s"1t\I{lť\oJEurer8 IEurJouqV 'surur8 Jalleurs Jo slslsuoc qcrq^\'xuleur eql uI punoJ surn oceds erod luecr;ru8rs pue 'serod .seszc esoql .iueur paure1uoc sÁerrrp surer8 otre1 eqt .(0I .3rg) sroqro eql u"ql ra8re1 Á1uturouqu uI e u\ ,(L suprE Jo JeqÍIlnu IIeuIs 3 ses€c 'narE ^\eJ .trg) 1eurrou-Bo1 Á1a1eurxordde sen se1drues eql Jo lsoru ur uollnqulsrp ezrs-urert aqt qtnoqtly 'e1er qpror8 rrrert 1ca;;u Á1luucgr.uB1s1ou seop deerc uotsn;pp tuulo'rur uorl"IuroJep luql uees st 11 '(9961 "p 1a o1erey) daerc uorsn;Jlp sI ses€c esaql uI peAIo^uI .uoll€turo;ap 8urrnp rusru€qceru uoll€IuJoJáp eq1 saler qilrorB urert aql are 6 '8rg ur pettold oqy .|ouJ/Í\' 09I: * g pve G,/,ut; aql x 9'T:0r1 surulqo euo (ernleredulsl alnlosqe'-o' .Átreua uoll€^Ilce sI J puu lu€lsuoc set aql sr y aql sr * !r 'urre1 lurluauodxa-erd aql sr 0r1 ueq,t.) k) 'l '8ta q ud\oqs sI llns lururou-8o1 tsorup uV eql Bursn -er eql :poqleu (qsor) usurllnJ-uqu3 sa1duresoql Jo aluos ur peleullse s€',r\ uorlnqulslp azrs-ur?Jo 'eur1 ttrrpeuuu qtrl\ soseeJcurezrs urert leql uaas $ tI '9 'tI.{ ul u,{oqs sr seldurus pepeu -uB uI seJnlcrulsoJcTtu Jo uoll"u€^ alull eqJ 'seldurus (firsuep pcrleroeqt oÁL6<) esuep Á1anr1BIeJJoJ Á1uo apeur eq II1rn .8urzno11o;áql uI .sa1dures srsÁ1eue a,r1lztlluznb Jesuep Jaqlo eql uuql Je^\oIÁ1tuecr1ru8rssem (o691 .ec Álrsorod) s1dulzs snorod slql sI a1ur qyrrorB urzr8 eql 'Jene,uro11'(Vf 'tta eas) rep,v'od Surlrels eql JoJ ueql reBruy sPA\ ezls ururB atereiru eql uollnqlJlsrp ezrs-urerE pue snoauatouotl eJoru su,^.t, '(6 'Btg aes) seldtues Jesuep uI 13q1 uzql ra1prus Á1luecr;ruBrs sr e1dures snorod s1ql .:eaa,to11 .Átreue ace;rns Áq ua,,rup ut a1er q1,raorBurer8 1zra,ro surerB ;o adeqs pepunor eq1 sel€ J IPuI ssBlu e^rlc? uodsuer1 '(Vf 'ttS) rap,trod EurlrBls eql ol paredruoc ezts urer8 .ra8rel .(rogt .oN) Álrsorod q3Tq qt1m lnq uIJoJÍun Á1e,rqz1ereql eloN .E .Btg e1dures passerd-loq 3 Jo sqde:8orcrur uol1calá Buruuec5 (tu/"í-)dxe o , t : , t :IIIJoJsnÍquaJJv eq1 ur pesserdxe .(Á1rsorod sr ecuepuadap ern1eredruel eql uaq16 eql 01 .Á1qerunsard .enp) a3re1 fuaa ut uoll€u€^ sB^\sunJ lueJeJJIp 8uoure uoI13IJ3^eql ecurs Ápn1s sTtll IuoJJ paulluJolep Á1rood Á1uo selr ecuepuedep ernleredurol '6 '8Id ur ps11o1d sr elBJ qunorE .lu€lsuoc ururt ;o ecuepuadep ernleredurel eqJ pue 1 : I eulll eleJ ? sI 4 pue.Á1e,rr1cedser0:l 0Sg pug eraqzn eql eJ" urer8 '7 : u ql!\l ezTs ls S.) (r) DI::59 -,S9 :uorl?IeJ 3uus,o11o;oql llJ 'suru oqt lnoq8norql purrou-8o1 lsourle Et"p aqJ peurerueJ uorlnqulslp ezrs-urztB aq1 'poued iloqs Á1qr8ffieu ? sB1ť\qlndoJ8 urer8 ;o etu1s pl}ruI eql pu€ (VI .Erg) azs urur8 eur; uJoJIun lSoIuIE {I3 peq reprrrod SulrBls eql 'sesec eseql uI '8 'tlJ uI u^\oqssr azrs rrrer8 etere,\e Jo uoIl€IJeA aIuI1eqJ .(1161 .uoproc pue lu€qcJuI^tr .3.e) qrtror8 urer8 lerurou 8unse88ns 'punoJ sed\ uorlnqulsrp orvuvx s z9z s I.d,.:" tr [ ,,ill| \L*- -' - '-\E {C'GREGATES 263 tormal gÍ-.rr 9i7). size is shor: powder hac :ig. 1,A.)an; a neglig:bn'" L1nrema1nď n-s.The dau (1 r grarn SŽe aI l Á. is a rate lce of grain Temperature ad from this ent mns was vJnatlon ln pendence is \2 ) t_ tBt E* is the and ?" is ; :1 .6 x gro\\'thrates t rnechanism reep (Karato (.}ninvolúng aťfectgrain n in most of o".rmal (Fig. gÍerns grew Fig. 10). In rrarnedmany frrund in the s. -{bnormal Ltl \\aS large J sÍains with annealed in rng pressure ater had few 2 hours; (B) at 1573 K, 300 MPa at wateÍ-added conditions' (A) After Fig. ó. Time variation of microstructures in samples annealed after 4 hours; (C) after 8 hours' uo Á1ululrrpeJJncco seJod eql .(srnoq 00I < ) tuol ro; puz $ EISI <) sernleradurat FI lB pel"euu" saldures ur pe^Jesqo seantuqlems .I"Fel€ur 8ur}rels eql q uelil snoou r c9ru3t5 douoq eJorusB^\saldues paleaurrueqt rn uorlnq {Bsrp ezls-ururt eqa .(g etqzr) Buríuauuetu]rnp firporod uI es?eJcul u3 atull aru"s aql l€ pue *.rs urur8 rn es?eJcrn Im pe^\oqsseldures eseql -II .tIď uI uÁ\oqs sI BdI^i I.0 1" pepeuue se1d {res eqt Jo eJnlcrulsoJcrruagl ;o eldurexe uy 'lu€ l suoc alPJ 3 sI 11pue Á1a'rncadsero l pu€ .t7: elml lB ezrs urert eql aru o59 pIIB ,s9 eJeqÁ .a.I .irre1qprorB ure:8 arunbs aql lIJ ?l€ P aql .T€ e uu" ': ' - zs9 's9 á^Issaccns re1;u e1dures eIIIBs eq1 uo ep"Iu arax ern1eradtuo1 qfie lB sluerueJnseeru eql 'ezrs urer8 Jo uolpu"^ eula'g '319 (,1)lo'bot to suru .<^Jp,'DďW I'0 o o .Jele^\papp€ lnoqllt peleeuue se1duruseql ;o .ursorod roiaol eql epdsep '(O '8tg) suollrpuoc pep -pe.Jel€^l Japun a1BJq}rrort ururt eq1 uuql JolIBIIIs .sorod i1luecqru8ts s€^\ el€J qyrrorE ururE aq1 o í!, N o (h oJ9 cE 5 .! yt19 I 'deerc uors -ng;rp Suunp seler ql,tor8 urerB eql el"crpur salBueul 'suotltp .uoJ eeJJ-Jál"/t\ JoJ aJ? seuo uedo puz suolllpuoc pepp?-JelP1Y\ .ube Áq peur;ap lu"lsuo' ro3 ere s1oqwÁs pqos .lxel eqt ut (l) urur8 5o acuspuedep a:n1e:adurea '6 '3r4 elpJ ? sr 1ql,trort (v)1/r0l ot 89 9.9 ý.9 z'9 0.9 .peJnýaruare,rrr P uo srrrer8oý8 .uoDceslBuolsueulp-o1ý\l eql uIoJJ uollnqulslp eql luelueJns"áIu lEuolsuarulp.eergl á,l?ul .Ilsa o1 pesn sEÁ\poqleu (9s6I) uetullnd-utT€ J eqJ .uollcas .ox) e1durespa1ueu ur.ql? uo ep?ru s"^\lueuelnsuáI^I.(ooot eq"L 'l 'BId eas-utert pessard-1oq ur uorlnqrllsrp pue -Tr" " (uJd ) YI 0ý0e oz ol azls ure J o 9 ( r68t * O ) I V o I arnsseloqolq O ,tup. vL o ! 3 3 o o o o o D D tr a oJvllvx s
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