C O N F E R E N C E R E P O R T S D efo rm atio n o f C ru stal R o ck s M t. Buffalo, Victoria, A ustralia, 2 一6 February 1987 In the H a rt s Range area P.R . Jam es and P. Ding have re- interpreted infrastructural basem ent and supracrustal cover O ne hundred and thirty structural geologists m et recently at to represent tw o related orogenic belts separated by a thick, M t. Buffalo in the high country of Victoria to discuss com plex, m id-crustal detachm ent zone characterized by aspects of crustal rock deform ation. The international early N -S crustal extension. In the southern A runta, C . conference w as hosted by the Specialist G roup in T ectonics A m ri and others have recognized a sub-horizontal shear and Structural G eology (SG T SG ) of the G eological Society of zone in Proterozoic gneisses w ith a N E directed shear and A ustralia. The conferences are held approxim ately every have suggested opposed thrusting during the Proterozoic and three years and provide a forum for the discussion o f re- Palaeozoic orogenies. Thrusting associated w ith the Late search results w ithin A ustralia. U nfortunately there w ere D evonian-Early Carboniferous event has determ ined the only eleven foreign participants (from Sw itzerland, Italy, present outcrop relations of the A runta com plex (A .J. A ustria, Canada, U .S.A . and M alaysia). H ow ever, a pleasing Stew art, R .Q . Oaks, W .J. Collins and C . Tessyier). aspect w as the sixty students w ho attended, highlighting a keen interest in the subject and ensuring a bright future for Several papers dealt w ith m ore them atic topics related to structural geology and tectonics in A ustralasia. crustal extension and shortening. G .S. Lister and others presented detachm ent m odels for the form ation of passive Topics covered at the conference under the them e of continental m argins, w hereas M .A . E theridge discussed the deform ation of rocks included the nature and sequence of role of transfer faults (analogous to oceanic transform events in areas of crustal shortening and extension, rock faults) in areas of continental extension. N .B . W oodw ard strength and factors affecting it, and the interrelations and E. R utherford (U .S.A .) introduced the concept of betw een deform ation and m etam orphism . The first three stru ctural lith ic u n its an d d em o nstra ted h ow th ese co n trol days dealt w ith the geological evolution of three crustal ram ps in thrust-belts, w hile R .H . Groshong and D .J. provinces w ithin the A ustralian continent: the Proterozoic Patterson (U .S.A .) used fault-bend folding geom etries to belts of M ount Isa (north Queensland), the A runta block m odel the Birm ingham anticlinorium . (central A ustralia), and the Palaeozoic Lachlan fold-belt of s o u t h e a s t e r n A u st ra lia . A nother m ajor them e at the conference w as the strength of crustal rocks. Talks w ere related to m ineral deform ation, V .J. M orand and D .R . G ray (all speakers from A ustralia fluid-rock interaction effects and crustal m odelling. unless otherw ise noted in this report) a rg ued that the Aspects of m ineral behaviour included experim ental defor- W agga-O m eo m etam orphic belt constitutes a region of m ation results on quartz (A . O rd and B .E. H obbs, J. localized high heat flow sim iliar to that described for the Gerretsen, J.D. Fitzgerald et al.), quartz aggregates (F .C . Pyrenees. This belt show s no evidence of fl at-lying, high- L uan and M .S. Patterson). uuartz m vlonites (S. Raiser et strain zones typical of m etam orphic core com plexes, and it aw , g a le na tz:i.r . U ox ) a na z in c sulph id e (J.L . D a vidso n e t is bounded by a system of steep w rench faults. O ther talks al.). M icrostructural relations for naturallv deform ed by C .L. F ergusson, D .R . G ray, M .P. Stubley , C .M eA . Pow ell, plagioclase (J.H . Krulil, A ustria) and am phibole (Y. Lui and T .J. Fo w ler a nd o the rs d escrib ed th e structures w ith in the P.R . Jam es) w ere also presented. The m ajor questions O rdovician, quartz-rich turbidites (continental m a馆in, raised w ere the nature of w ater w eakening in quartz and the back-are and fore-arc sedim ents), w hich characterize the role of m icrocracking in quartz deform ation. Lachlan Fold belt, and the recognition o f the toe of an accretionary prism on the south coast of N ew South W ales The role of fl uids in controlling rock-strength in the crust w ith prism build-up as early as the Late C am brian Period has been long recognized. Experim ental studies on dilatancy (E.I. Prendergast). above the brittle-ductile transition (G .J. Fischer) show ed tha t com paction and dilatation increase w ith increasing pore The other regional sessions dealt w ith evolution through tim e o f the be lts o f P roteroz o ic ro cks a t M o un t Isa an d central A ustralia. Evidence w as presented for north and 瓣嚣 northw est-directed, thin-skinned thrusting at M ount Isa (D .E . Bettess and R .J.H . Looseveld) in contrast to previously 燕一哪一赞一臀耀黔 published interpretations (Bell, T.H ., 1983; N ature, 304, p. 493-497), and for extension involving m id-crustal 一溉 detachm ents during upper am phibolite facies m etam orphism in the eastern half of the inlier (R .J. H olcom be et al., P.J. Pearson et al.). G .S. Lister and his colleagues discussed the effects of transpressional strike-slip faulting (D 3) upon the early structures; D 2 structures w ere ro ta te d fro m N -S in to E-W orientations w ith the production of pop-out structures associated w ith D 3 thrusts. Talks on the A runta com p lex of central A ustralia high- lighted the intraplate extensional-collisional nature of the orogen. This w as based on structural relations in the eastern Arunta (P.R . Jam es and P. D ing) and on analysis of the sedim enta即 succession in the A m adeus B asin (R .J. K orsch and J.F . Lindsay, R .D . Shaw ). Basin analysis indi- cated an initial period of extension in the Late P roterozoic, another period o f extension at about the Proterozoic/ Figure 1 : Conference participants distracted by Ca m brian boundary, and finally shortening in Late h an g -卯 id er s f r om e xa min in g a g ran it e on M oun t D evonian-Early Carboniferous tim e. Buffalo . Victorian high country in the background . E PISO D ES, Vol. 10, N o. 2, June 1987 121 C on ference R ep orts fluid pressure and that dilatation decreases w ith increasing ta lk on rea c tiva tion o f e a rlier fo lia tio ns a n d d e-cre nula tio n tem perature. Fischer also described a new m ethod for due to shifting patterns of deform ation partitioning. H is m easuring perm eability in tight rocks at elevated tem pera- w ork w as also based on studies of porphryoblast-m atrix turos (up to 1200 0 . Field studies on this aspect led to a re la t io n s . description of structurally c ontrolled infiltr ation -m e ta- so:natism involving saline fluids and high fluid-to-rock ratios O ne of the interesting outcom es o f the conference w as an in north Q ueensland (N.H .S. O liver et al.), structurally con- in c r e a se d a w a re n e s s a b o u t th e ro le o f e x t e n s io n a l te c to n ic s trolled Ag-Pb-Z n m ineralization at Elura, N.S.W . (J.A . de during orogenesis, and about the oscillations betw een com - Roo), and the effects o f fluid-to-rock ratios in the evolution pressional and extensional events during crustal deform a- of shear zones a t H ilton, north Q ueensland (R .K. Valenta tion. This was exem plified in talks by G .S. Lister on M io- an d B .E . H o bbs). cene ductile stretching of over-thickened continental crust in the A egean Sea, and by N . M ancktelow (Sw itzerland) on Com puter m odelling of the crust W .E. H obbs and A . O rd) the Sim plon fault zone in the Pennine A lps of Sw itzerland provided a m odel to explain the driving forces in plate and northern Italy. tectonics that does not invoke "ridge pushing" and/or "trench pulling." Variations in rock rheology w ith depth, C onference abstracts have been published by the G eological coupled with therm al variations due to hot spots, generates Society of A ustralia (10 M artin Place, Sydney, N .S.W .