deformation partitioning and porphyroblast rotation in meta

7/27/2019 Deformation Partitioning and Porphyroblast Rotation in Meta

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J . me tamo r ph i c Geo l . 1985, 3, 109-1 18

Deformation parti t ioning and porphyroblast rotation in meta-morphic rocks: a radical reinterpretationT. H. B E L L , Department of Geology, James Cook University, Townsvil le,Queensland 481 I , Australia

Abstract. Most porph yroblasts never rotate duringductile deform ation, provided they d o not intern-ally deform during subsequent events, with theexception of relatively unco mm on but spectacularexamples of spiralling garnets. In stead, the sur-rounding foliation rotates and reactivates dueto partitioning of the deformation around theporphyroblas t . Consequent ly , porphyroblas t scommonly preserve the orientation of earlyfoliations and stretching lineations within strainshadows or inclusion trails, even where thesestructures have been rotated or obliterated'in thematrix due to subsequent deformation. Theserelationships can be readily used to help developan understanding of the processes of foliationdevelopment and they demonstrate the prominentrole of reactivation of old foliations during subse-quent deformation. They can also be used todetermine the deforma tion history, as porphyro -blasts only rotate when the deformation cannotpartition and involves progressive shearing withno combined bulk shortening component.K e y - w o r h :deform ation history; deformation par-titioning; inclusion trails; porphy roblast r otatio n;reactivation of old foliations

I N T R O D U C T I O NPorphyroblasts with inclusion trails that can beconvincingly demo nstrated to result from rotationof the porphyroblast are uncommon a nd app earto be confined to spectacular examples of garnetporphyroblasts with spiralling inclusion trails(Rosen feld, 196 8,1970; Schon eveld, 1977; Powell& Vernon, 1979). However, porphyro blasts havegenerally been regarded as objects that rotateduring deformation, mainly due to the prominencein the literature of the above-mentioned garnetsand the use of the theory of flow in fluids to tryand understand deforma tion in rocks (e.g., Lister&Williams, 1983).As a consequence, rotation ofinternal inclusion trails in porphyroblasts (Si) v .

external foliation (S,) has been variously attri bu -ted to ( I ) rotation of the porphyroblasts (Spry,1963; Cox, 1969; Powell & Tre agu s, 1970; Dixon,1976; Schoneveld, 1977; Williams &Schoneveld,1981; Lister & Williams, 1983); (2) rotation ofthe matrix (R am say, 1962; Wilson, 1971; Bell &Ruben ach, 1983); and (3 ) differential ro tation ofthe porphyroblast and matrix (Ramsay, 1962;Wilson, 1971; Bell & Rubenach, 1983; Olesen,1978).Realization of the role of deforma tion partition-ing during deform ation, with particular referenceto foliation development (Bell, 1981; Williams& Schoneveld, 198 ), has considerably advancedour understanding of microstructural processesin rocks. Porphyroblasts, in particular, are im-portant in this regard, as they commonly growsyntectonically in specific locations controlled bydefo rma tion partitioning-that is, zon es of sho rt-ening (Bell, Fleming & Rubenach, 1985)-andthen, in turn, control the partitioning of defor-mation around them (Bell, 1985).DEFORM ATI ON PARTI TIONI NGDeformation partitioning occurs on a largevariety of scales as a result of primary orsecondary heterogeneity in rocks, such that atvarious stages during the deformation differentminerals, beds, rock types and portions of therock (cf. Fig. la) take up (1) no strain; (2)dominantly progressive shortening strain (i:e.,progressive coa xial deform ation ); (3) progressiveshortening plus shearing strain (i .e., progress-ive non-coaxial defo rmation); or (4) progressiveshearing. strain (i.e., progressive non-co axialdeformation) .However, both 3 and 4 can be coaxial at a largerscale of consideration of the strain. Co nseque ntly,the terms 'coaxial' an d 'non-coaxial' ar e no t usedwith a deformation partitioning connotation inthis paper, and instead are reserved for thedescription of bulk strain histories or strains (cf.Bell, 1981). This range of four possibilities can

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aFig. la . Diagram showing a dis t r ibut ion of deformation part i t ioningon a s t rain-field diagram c onstructed for the XZ plane, representinga block of rock which has undergone non-coaxial progressive bulkinhom ogeneou s shortening. T he fol lowing numbere d sect ions areexplained in , an d correspon d with, the text . I , N o st rain occurredwithin the dashed ellipses; 2, progressive shortening s t rain dom inatedthe zones between the dashed an d dot ted l ines; 3, progressiveshortening plus shearing strain occurred between the dotted lines.Progressive shearing strain alone (i ,e,, 4 in the text) is not shown onth i s d iagram. l b . Sketch of a strain field resulting from non-coaxialprogressive bulk inho moge neous shortening where the de format ion hasrepart i t ioned about a porphyroblast . This diagram shows why aporphyro blast (out lined by the dashed l ine) does not generally rotateif i t does not deform. Zones of deform ation pa rt i t ioning are del ineatedas in Fig . l a . The shear ing component of t he deformat ion ispart i t ioned ab out the porphyrob last which thus protects a n el lipsoidalisland of matrix from th e effects of progressive shearing.


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Deformation part i t ion ing and por ph yro blast rotat ion 1 1 1

Fig. Za. Sketch showing porphyroblasts that have overgrown four stages of development of a crenulation cleavageduring D, (for example). A fifth stage of development is shown in the matrix. The S, orientation revealed ineach (oriented N-S) is parallel to the S , foliation in the matrix. 2b. S, anastomosing around a plagioclaseporphyroblast and preserved within the rim. The crenulations in the rim have a millipede geometry (Bell &Rubenach, 1983). Crossed polars. Width of field is 13.5mm. Zc. Staurolite porphyroblasts with S , inclusiontrails. These have the same orientation in both porphyroblasts, and both have a millipede geometry. Crossedpolars. Width is 1 I mm. d. Photograph showing garnet porphyroblasts that have overgrown crenulations ofS , and have the same axial plane orientation in each porphyroblast; this orientation is parallel to the S, foliationin the matrix, within which there are no remains of S, . Crossed polars. Width is 8 m m .


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112 T. H .generally be discussed in terms of progressiveshortening (1 and 2 above) and progressiveshearing (3 and 4 above) components . This ispossible because it is apparent from micro-structural examination of foliations that thepresence of a significant component of pro-gressive shearing con trol s dissolution dur ingdeformation (Bell, 1981 ; Bell ef a/. , 1985).EVIDENCE FOR LACK OFPORPHYROBLAST ROTATIONTh e most readily available an d easily interpretedevidence for lack of porphyroblast rotation ispreserved within syntectonic porphyroblasts whichhave overgrown various stages of developmentof a crenulation cleavage generated during onedeformation event. Bell & Ruben ach (1983) dis-tinguished six stages of D, crenulation cleavagedevelopment , where S , preserved in syn-D,porphyroblasts remained constant in orientationthro ug hou t a thin-section and parallel to S , in thematrix (shown schematically in Fig. 2a); this ofcourse takes into account the effect of foliation orcrenulat ions anastomosing around a porphyro-blast, the foliation being subsequently over-grown and preserved in the porphyroblasts rim(Fig. 2b).Indeed, if porphyroblasts grow early durin g adeformation (e.g., D,) , such that they preservestraight or weakly crenulated inclusion trails ofthe foliation developed by the previous defor-mation event, the trails or the axial planes ofthe crenulations within them will co mm onl y havesimilar or ientat ions from porph yrobla st to por-phyroblast (Fig. 2c), even if no remains of thatfoliation occur outside (Fig. 2d). Of course, S ,may have been rotated to varying degrees earlyduring D, folding, pr ior to i ts incorporat ionas trails within porphyroblasts. Porphyroblastsnucleating in such zones will tend to have lengthto width ratios controlled by the orientation ofS , relative to S , a t the t ime of nucleation (fig. 17in Bell el a/ . , 1985). This will create the effectobserved by Ferguson & Harte (1975) and Ward( I 984), namely that porphyroblasts with higherlength to width ratios appear to be closer inorientation (more rotated) to a foliation th atpostdates or is synchronous with their growththan to those with lower length t o width ratios.Nevertheless, in a single thin section i t is verycom mo n to f ind that ear ly syn-D, porphyroblasts(for example) have overgrown and preserved S ,inclusion trails, all having approximately thesame orientation in the porphyroblast cores (Figs2c, 2d and 3).

BellMany metamorphic te r rains conta in numerou sporphyroblasts with superb inclusion trails, bu tno evidence for spiral l ing in any of th em ; e .g. , theM t Isa and Georgetown Provinces, northe asternAustralia (Bell &Rub enach , 1983), the M t Loftyand Ka nm anto o Provinces, So uth Australia (Bell

et a/. , 1985), the Picuris-Truchas-Mora Re gio n,New Mexico, USA (e .g. , Holcom be, 1985), andsouthwest Fiordland, New Zealand (W ard , 1984).Other terrains are domin ated by porphyroblas t sthat show no spiralling, but very locally containnarrow zones with spiral l ing garnet porphyro-blasts, e.g., New Caledonia (Bell & Brothers ,1985).

DEFORMATION PARTITIONING ANDPORPHYROBLAST ROTATIONWhether or not porphyroblas t s ro ta te is a func-t ion of part i t ioning of the deformation. I f thedeformation partitions into progressive strain-types I , 2, 3 an d 4 listed ab ove, thro ugh out thebody of rock, porphyroblasts wil l not rotate ,provided they do no t deform (Fig . Ib) . Porphyro-blasts generally con trol the partitioning of defor-mation around them because of their coarsegrain-size and/or strength relative to matrixminerals (Etheridge & Vernon , 1981; Bell et al . ,1985). Consequently, each porphyrob last protectsan ellipsoidal island of matrix as wide as theporphyroblast (Fig. Ib) from the effects ofprogressive shearing. This com pon ent of th edeformation is accommodated external ly, asshown in Fig. 1b, and therefore does not causerotation of material within the ellipsoidal island.Even if the shearing on porp hyrob last marginspar t i t ions to the ex ten t tha t no concur ren tshortening takes place (i.e., progressive strain-type 4 above) , the porphyroblas t s d o n ot ro ta te .For example, this degree of deformat ion par -titioning may o ccur wherever q uar tz an d feldsparhave been totally removed by dissolution andsolut ion t ransfer in a zone that has undergoneshearing(Bel1et af., 985) and only phyllosilicatesremain. W here these latter minerals have the geo-metrical relationships shown in Fig. 3a, they ca nonly readi ly a ccom mod ate progressive shearingstrain (Bell et a / . , 1985). Examples of porphyro-blasts that lie either side of a micro shear zone,such as a crenulat ion cleavage containing onlyphyllosilicates, are com mo n, a nd yet the porphy ro-blasts have generally n ot ro tate d (F ig. 3b). Th isconflicts directly with interpretations that por-phyroblasts rotate due t o a shear couple developedon thos e rims which lie tangential to the external


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Deform ation partit ioning and porphyroblast rotation 113

Fig. 3a . Sketch showing two garnet porphyroblastswhich have preserved crenulated S , inclusion trails atstage 2 of crenulation cleavage development (Bell &Rubenach, 1983) during a second deformation. Thecrenulations have continued to develop outside, anda differentiated crenulation cleavage has formedbetween the two porphyroblasts, from which all thequartz and feldspar has been removed. When onlyphyllosilicates remain, the porphyroblasts shear pastone another, essentially by progressive shearing withno shortening component, because phyllosilicatescan readily accommodate shear with this geometry,but no t shortening. However, the porphyro-blasts have not rotated, as revealed by the parallelismof the axial planes of D, crenulations withinthem and the zone of crenulation cleavage (S,) in thematrix. 3b . Garnet porphyroblasts that have overgrownand preserved millipede-shaped S, inclusion trailsof early syn-D, age. They have the same orientationin each porphyroblast, even though S , has beendestroyed in the matrix ande,a-zone of fullydifferentiated crenulation cleavage exists betweenthe top two porphyroblasts. The millipede-shapedtrails are not readily visible at this magnification,especially since they occur on the edges of the garnet,which lie parallel to S,. However, their presence isworth noting as their geometry indicates that theporphyroblasts have not rotated relative to the externalfoliation. Crossed polars. Width is 12.5mm.

foliation. Examples of such interpretations includeSchmidts (1918) and Mugges (1930) model of asphere rolling between two boards, Rosenfelds(1970) an d Ghoshs (1975) model of ro tatio n of arigid sphere in a h omog eneous isotropic matrix,or Lister &Williams (1983) mode l of rotatio n ofa porphyroblast due to vorticity during fluidflow.Th e reason for this lack of r otat ion can be mostreadi ly understood by examining the micro-structural /deformation part i t ioning processeswhich can cause the rotation recorded in those

garnet porphyroblasts that contain genuinelyspiralling inclusion trails. If the deformation onthe bulk scale is progressive inhomogeneoussimple shear and locally cannot partition ashortening comp onent, then foliation planes con -taining a porphyroblast must undergo shearingstrain (Fig. 4a). However, those foliation planesthat truncate against the porphyroblast (Fig.4 a s ) a re commonly keyed in to i t v ia overgrowtheffects and small irregularities in its boundary.Consequently, as each folia shears past its neigh-bour (Fig. 4b), the porphyroblast is forced to


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1I4 T . H . Bell

0 b C

d eFig. 4a-. Sketches showing stages of a process by which aporphyroblast can rotate during progressive simple shear in a situationwhere the deformation cannot partition, and the effect of thisphenomenon on the surrounding foliation geometry. Note that whenthe deformation cannot partition the shear must operate equally oneach of the foliation planes including those truncated by theporphyroblast. 46e. ketches from Schoneveld (1977) showing hisring model for development of the inclusion trails in spiral garnets atrotations of 180" and 400" . Note how the inclusion trails aremicrofolded at increasingly wider gaps from the core to the rim. Thiswould result in a lack of microfolded folia preserved within the rims ofporphyroblasts which had spiralled to such an extent. rhis was notobserved by Rosenfeld (1968) and Powell & Vernon (1979).

rotate. However, as a consequence of this non-coaxial shearing strain, the foliation abu tting theporphyroblast will tend to develop two smallasymmetrically distributed microfolds (Fig. 4c).These may be obscured by subsequent rim growthof the porphyroblast, recrystallization of micawithin the microfolds, or reactivation of th eexternal foliation due to a subsequent defor-mation. However, the presence of these micro-folds may be identified with close mic rostru ctura lexamination because (1) the microfold forms

outside the porphyro blast (which distinguishes itfrom Schoneveld's (1977) model shown in Figs4d and 4e); 2) qua rtz fibres (m icro-saddlereefs?)as well a s foliation are comm only also microfolded(e.g., Powell & Vernon , 19 79; Rosenfeld , 1968)an d are no t explicable by Schoneveld's modelwithout modification; and (3) the microfold willcommonly have an axial plane a t a high angle tothe fol iat ion away from the porphy roblast . Ho w-ever, in a zone of rock undergoing progress-ive simple shear, the deformation must locally


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Deformation partitioning und porphyroblast rotation 115partition (Bell et al . , 1985) and, consequently,some porphyroblasts in this zone may neverrotate throughout its development.This interpretation requires a modification toSchonveld's (1 977) model for developing spirallinginclusion trails. In tha t mod el, after a rotation of7 5 " , the foliation becomes so separated and thepressure-shadow region so large that the spiralsare dominated by blocky, pressure-shadow q uartz ,with foliation lam inae crossing qu artz spirals atwell-spaced intervals (Figs 4d an d 4).owever,Rosenfeld (1968) and Powell & Vernon (1979)showed apparently foliated quartz as microfoldhinges, continuously along the spiral, for rotationsgreater than 5 0 0 " . If these microfolds in apparentlyfoliated q ua rtz represent relics of folia separa tedby q ua rtz pressure shadows, then the spacing ofthe folds is far to o close fo r Schoneveld's m odel.An alternative explanation is that the folia arequa rtz fibres that have grown within the pressureshadow as beard-l ike s tructures rather than asblocky qua rtz. Their geometry could then mimicthat of folia overgrown in Schoneveld's model.Howev er, both Rosenfeld's a nd Powell &Vernon'sphotographs appear to indicate the presence oflarge numbers of folia ot her than simply micro-folded relicts of qu art z fibres. This prob lem m aybe resolved by modification of Schoneveld'smodel such that microfolding of the foliationoccurs outside the growing garnet, possibly withgaping and quartz infi ll . This may tak e the formof 'saddle reefs' between folded mica folia, or offibres (Fig. 4c) that are subse quently included inthe growing garnet.FOLIATION REACTIVATIONThe m ost frequent argument for porphyroblastrotation is that the inclusion trails are common lyoblique, but partially or completely continuouswith the external foliation, an d therefore appe arto have been generated in a single deformationevent (e.g., Fig. 2d). However, many foliationsdevelop by reactivation of earlier ones (Bell,1985). Even after the development of a differen-tiated crenulation cleavage (e.g., stages 3 or 4 ofBell & Rub enac h, 1983), the earlier foliation canstill be reactivated as the strain becomes morehighly non-coaxial and the earlier crenulationsunfold (Bell, 1985). Consequently, in theseexamples the external schistosity is a prod uct ofdeformation subsequent to that which generatedthe foliation preserved as inclusion trails insidethe porphyroblasts. Depending on the timing ofporphyroblast growth, the foliation may haveundergone some rotat ion due to subsequent

deformat ion , a l though porphyroblas t s com-monly overgrow and preserve unrotated relicsof the earlier foliation because of the controlof deformation partitioning on porphyroblastnucleation and growth sites (Bell et nl . , 1985).Examples of supposed porphyro blast rotationin the literature illustrate the role of foliationreactivation, whereby inc lusion trails preserved ina porphyroblast actually are relics of an earlierfoliation. F or ex amp le, fig. 7 in Dix on (1976) ca nbe interpreted as a product of three stages ofalbite growth over developing crenulations, withno evidence for rotation (Fig. 5a). Figure 8 inPowell &Treagus (1970), reproduced here as Fig.5b, can also be interpreted a s two stages of garnetgrowth in two separate deformations, withoutrotation of the porphyroblasts: in fact, S, in eachha s the sa me orientation, in spite of its externalobliteration by D, plus a subsequent crenulationevent. The same arguments apply to twistedgarnet porphyroblasts (Fig. 5c) described byKrig e (1916), featu red by Rea d (1957, fig. 10)andrecollected and used by Williams & Schoneveld(1981, fig. 12b). Figure 12a in Williams &Schoneveld (1981), reproduced here as Fig. 5d,can be interpreted in a similar fashion or i t couldbe a product of reactivation c ausin g refraction ofthe extern al foliatio n (Bell, 1985).SIGNIFICANCEIf porphyroblasts typically d o not rotate du ringsubsequent deformations, then structural geol-ogists and metamorphic petrologists have anextremely powerful tool a t their disposal. In fa ct,this may be an interpretative tool unrivalled byany other geometric or microstructural phenom-enon, for the following reasons.

1. Porphyroblasts can preserve, in inclusiontrails or adjacent strain-shadow regions, theorien tation s of earlier foliations an d lineations atthe time of porphyroblast growth, even thoughthe rock m ay subsequently have been substantiallydeform ed an d the remains of that foliation largelyor totally obliterated in the matrix. Thu s they ma yenable determina tion of original tectonic transpo rtdirections in rocks (e.g., porphyroblasts over-growing originally mylonitic foliations), andcorrelation of deformations from one area whereS, (for example) has been overprinted by variousdeformations to another one that has not beenaffected by these later events.2. Porphyroblasts that overgrow an earlyfoliation enable us to more readily understandfold development. For example, the trails pre-served in porphyroblasts that predate or grow


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early enough in a specific folding event indicatewhether the folding mechanism involved initialbuckling or not. If no buckling occurred, por-phyroblasts would preserve the original orienta-tion of the inclusion trails aroun d the entire fold,as shown for garnet in Fig. 6a. Natu ral exampleso f this have been given by Wa rd (1984, fig. 5.37)an d Holcom be (1985, figs 2 and 3) . Alternatively,if they grew after folding began, they wouldpreserve the orientation of the foliation at thetime they grew (e.g., K en na n, 1971), as show n forstaurolite in Fig. 6b.3. Porphyroblasts giveclear information on thedeform ation history. They do not rotate (providedthey do not deform) during coaxial or non-coaxial progressive bulk inhom ogeneou s short-

ening, but can rota te durin g progressive s impleshear. Criteria distinguishing deformation his-tories are uncommon (cf. Bell, 1981).4. Porphyroblasts tha t d o not rotate al lowready interpretation of their timing relativeto deformation events , via the relat ionshipsbetween inclusion trails and external foliation.The assumption tha t they have not rotated ca n ingeneral be readily tested by d em ons trati ng (1)parallelism of inclusion trails indicating theorientation of axial planes, or axial-plane foli-ations formed at the time of their growth (Figs 2aand 2b); and (2) parallelism of earlier inclusiontrails from porph yroblast to porphyroblast througha thin section (Figs 2 and 3).

5 . Reactivation of earlier foliations is clearly

Deform ation parti t ioning and porphyrob last rotat ion 117

demonstrated by the relationship between inclusiontrails in many porphyroblasts and the matrixfol iat ion, and app ears to be ad om ina nt process infoliation development (Bell, 1985).6. Thin sections crowded w ith porphy roblastsd o not show evidence of rotation du e to oneporphyroblast being forced against another , asshown schematically in Fig . 6b, even thou gh thisis potentially possible during progressive bulkinhomogeneous shortening. I t app ears that suchporphyroblasts 'lock' ogether an d act as a single

H

BFig. 6a . Sketch showing inclusion trail geometry ingarnet (clear) and staurolite (shaded) porphyroblasts,which grew at different stages durin g the developmentof a fold. The garnet porph yroblasts grew early andpreserve the original orientatio n of S , (e.g., fig. 5.37in Ward, 1984, and figs 2 and 3 in Holcombe, 1985),whereas the staurolite p orph yrob lasts grew later andpreserve S , inclusion trail orientations from a laterstage in the fold's development (e.g., Kennan, 1971).6b . Sketches showing a possible way in whichporphyrob lasts might be forced t o rotate during adefo rma tion that involved progressive bulkinhomogeneous shortening.

ellipsoidal core, about which the shearing com-ponent of the deformation repartitions.ACKNOWLEDGEMENTSI thank Roger Bateman, Jeff Grambling, RonVernon an d Chris Ward for reading a nd discussingthe manuscript. I thank the reviewers for indicatingsections that needed clarification. The supportof the Australian Research Grants Scheme andN.S.F . Grant EAR 8406572 is also gratefullyacknowledged.REFERENCESBell, T.H ., 1981. Foliation d evelo pm ent: the contri -butio n, geometry and significance of progressive bulkinhomogeneous shortening. Tecronophysics, 75,273-296.Bell, T. T ., 1985. Folia t ion development an d refract ionin metamorphic rocks: reactivation of earlier foli-ations and decrenulat ion du e to shifting patterns ofdeformation part i t ioning. J . metamorph ic Geol .(submitted).Bell, T.H . &Brothers, R.N., 1985. Development of P-Tprograde and P-retrograde/T-prograde isogradic sur-faces during blueschist to eclogite regional metam or-phism in New C aledo nia as indicated by progressively

developed porphyroblast microstructures. J . mefa-r i iorphic Geol. , 3, 59-18.Bell, T. H . , F leming, P .D. & Rubenach, M . J . , 1985.Porphyroblast nucleation, grow th and dissolution in


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118 T. H . Bellregional metamorphic rocks as a function of defor-mation partitioning du ring foliation development. J .metamorphic Geol . (submitted).Bell, T . H . & Rubenach, M.J. , 1983. Sequential por-phyroblast grow th an d crenulation cleavage develop-ment during progressive deformation. Tecrono-

C ox , F.C., 1969. Inclusions in g arnets : discussion andsuggested mechanism of growth for syntectonic gar-nets. Ge ol . M ag . , 106, 5 7 4 2 .Dixon, J .M., 1976. Apparent double rotat ion ofporphyroblasts during a single progressive defor-mation. Tecfonophysics, 34, 101-1 16.Etheridge, M.A. & Vernon, R. H. , 1981. A deformedpolymictic conglomerate-the influence of grain sizeand composition o n the mechanism and r ate ofdefor-mation. Tcctonophysics, 79, 237-254.Ferguson. C.C. & Har te, B., 1975. Tex tural patternsat porphyroblast m argins and their use in determiningthe time relations of defor matio n and crystallization.Ge ol . M ag . , 112, 4 6 7 4 8 0 .Ghosh , S.K., 1975. Distortion of planar structuresaround rigid spherical bodies. Tectonophysics, 28 ,

Holcombe, R.J. , 1985. Foliation piracy durin g multipledeformation. J . struclural Geol. (submitted).Kennan, P. , 1971. Porphyroblast rotat ion and thekinematic analysis of a small fold. Ge ol . M ag . , 108,Krige, L.J. , 1916. Petrografisce Untersuchungen iiberdas Verhaltnis der Schieferung ziir Faltung unterBerucksichtigung des Stockwerkproblems. Eclog.geol . Helv . , 14, 519-654.Lister, G.S. & Williams, P. F. , 1983. Th e part it ioningof defo rmati on in flowing rock masses. Tecrono-

Miigge, 0 . . 930. Bewegungen von Porp hyro blasten inPhylliten und ihre Messung. Neues Jb. Miner. Geo l.Palaonr Mh., 61A , 469-510.

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Olesen, N . O . , 1978. Distinguishing between inter-kinematic and syn-kinematic porphyroblastesis. Ge ol .Powell , C.McA . & Vernon, R.H. , 1979. Gro wth an drotation history of garnet porphyroblasts with in-clusion spirals in a Karakoram schist. Tectono-physics, 54, 25-43.Powell, D . & Treagus , J . E . , 1970. Rotat ional fabricsin metamorphic minerals. M in . M ag . Lon d . , 37 ,Ramsay, J.G. , 1962. Th e geometry a nd mechanics offormation of similar type folds. J . Ge ol . , 70,Read, H .H . , 1957. The Granite Controversy. T h o m a sMurby & Co. , London.Rosenfeld, J.L., 1968. Garne t ro ta tions d ue t o themajor Paleozoic deformations in southeas t Vermo nt.In Studies of Appalachian Geology (ed. Zen, E-an ela l . ) , pp. 185-202. Wiley Interscience, New York .Rosenfeld, J .L. , 1970. Rotated garnets in meta morp hic

rocks. Spec . Pap. geol . Soc. A m . , 129.Schoneveld, C . , 1977.A study of som e typical inclusionpattern s in strongly paracrystalline-rotated garn ets.Tcctonophysics, 39, 4 5 3 4 7 1 .Schmidt, W., 1918. Bewegungsspuren in Porphyro-blasten K ristalliner Schiefer. S b . A kad . W iss . W ie n .,Spry , A ,, 1963. Th e origin a nd significance of snow ballstructure in garnet . J . geol . SOC.Aust . , 10, 193-208.Ward, C .M . , 1984. Geology of the Dusky Sound a rea ,Fiordland, with emphasis on the structural-metamor-phic development of som e porphyroblast ic stauroli tepelites. Unpubl. PhD thesis, Univ. Otago, Dunedin,New Zealand.Williams, P.F. &Schoneveld.C., 1981. Ga rne t rotat ionand the development of axial plane crenulat ioncleavage. Tectonophysics, 78, 307-334.Wilson, M.R., 1971. O n syntectonic porphyroblastgrowth. Tecronophysics, 11, 239-260.

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Reccitled 27 Nocember 1984: revision accepted 21 January 1985

deformation partitioning and porphyroblast rotation in meta

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