C O N F E R E N C E R E P O R T S

T race Fossils, Sm all Shelly Fossils an d th e Precam brian-Cam brian Boundary

St. John's, New foundland, C anada, 8 一18 A ugust 1987

The Precam brian-Cam brian boundary m arks a fundam ental stratigraphic ranges of ichnotaxa are needed for m ore change in Ea rth history, the first developm ent of abundant sections, particularly in A ustralia and the R ussian Platform , skeletal and bioturbating orga nism s. A lthough there is to fu rthe r te st the co rrelation s. A c rita rch s ha ve no t be e n general agreem ent w ith the principle of placing the bound- as w idely studied, but presentations by G . Vidal (Sw eden), M . ary "as close as practical to the first appearance of abun- M oczydow ski (Poland) and X ing Y usheng em phasized their dant shelly fossils," m arked provincialism o f the earliest potential biostratigraphic utility in the boundary interval. sk eletal fossils an d the ir virtua l restric tio n to ca rbo na te facies have ham pered g lobal correlation in the boundary In the past, paleontologic studies in the Precam brian- C am brian boundary interval have focused upon the evolution interval (Cowie, 1985, Episo旦es v. 8, p. 93-98). of the biota. A m ajor them e of the conference was the need In A ugust of 1987, fifty geologists from ten countries m et to to reconsider the effects of environm ental and p reserva- consider a possible stratotype site in eastern N ew foundland. tional factors on the stratigraphic distribution of these The overall them e of the conference w as correlation, and predom inantly benthic fossils. E . Landing and J. M ount dialogue betw een specialists in different disciplines w as (U .S.A .) show ed how first appearances of sm all shelly fossils encouraged by poster sessions and them atic discussions. taxa in any section a re very strongly influenced by these Sm all shelly fossils are critical in zoning the Precam brian- factors, and J.P.A . M agw ood (C anada) and T.P. Crim es C am brian bounda ry interval, particularly in the carbonate m ade sim ilar observations concerning trace fossils. A ll facies of central A sia. In his keynote address, J. Cow ie organism s are environm entally controlled to som e degree, (U .K .) pointed out the need for greater know ledge o f the and only by carrying out detailed sedim entologic analyses in taxonom y and correlation of these fossils. S. B engtson conjunction w ith the paleontologic studies can w e assess the (Sw eden) and S. Conw ay M orris (U .K .) discussed the taxo- relative im portance of evolution, ecology and preservation nom ic problem s presented by the m orphologic variability in controlling the stratigraphic distribution of the fossils. and m ulti-elem ent nature of m any sm all shelly fossils and show ed how careful analysis of large num bers of specim ens can significantly reduce the num ber of synonym ous form s. M .D. Brasier (U .K .) discussed the correlation of the Tethyan carbonates of A sia (including M eischucun), show ing several potential horizons for correlation based on first appearance of various sm all shelly fossil taxa. Inter-continental cor- relation of sm all shelly fossils w as m ore controversial, w ith presentations of several distinct correlations of the three candidate stratotypes. D etailed descriptions of these key sections in Siberia (N . Esako va, U .S.S.R .), M eischucun, C hina (Xing Yusheng, C hina), and Fortune H ead, New found- land (G .M . N arbonne, Canada a nd E . Landing, U.S.A .) also provided lively discussions and a great deal of new infor- m a tio n . O ne m ajor new them e of the m eeting w as the prospect for global correlation using trace fossils, w hich are especially com m on in siliciclastic facies w here shelly fossils typically are rare and poo rly preserved . Correlation in siliciclastic facies is critical, as these deposits com prise nearly 70% of exposed rocks in the boundary interval. In his keynote address, T.P . C rim es (U .K .) outlined three globally corre- la ta ble tra ce fossil zo ne s tha t oc c ur b e lo w the lo w e st trilo bites. In ta lks o n th e W e rn e ck e M o unta in s o f no rth - w estern C anada and the C hapel Island Form ation of eastern N ew foundland, N arbonne and his co-w orkers em phasized the fact that trace fossils are cosm opolitan, and the sam e genera and species can be used to zone silicielastic strata w o r ld w id e .

J. Paczesna (Poland), G . K um ar (India) and Jiang Z hiw en F i gur e 1 : S om e m em b e rs o f th e P r ec am br ian -C am br ian (C hina) also pointed out the biostratigraphic potential of B o und a ry W ork in g G ro up ex am in in g th e ba s al p ar t o f trace fossils. H ow ever, careful m orp hologic a nalysis, 亡力 e s e c t i o n a t F o r t u n e H e a d 7h e a rro w p o in ts to rigorous taxonom y and detailed docum entation of the t 力e can d id a te bo un d ar y s tr a to typ e p o in t .

E PISO D ES, Vol. 10, N o. 4, D ecem ber 1987 339 门 ｜ ｜ C on ference R ep orts ｜ ｜ I l we R ecently, there has been so m e concern about the possible Phanerozoic- type trace fossils (Phycodes pedum Z one), presence of disconform ities in candidate stratotype see- w hich approxim ately corresponds w ith the first appearance tions. P.H. Signor (U .S.A .) applied J.M . Sadler's statistical of sim ple sm all shelly fossils (Sa b ellid ite s c a m b rien sis analyses of stratigraphic co m pleteness to the three candi- in te rva l) in the sec tio n . date stratotypes and concluded that the N ew foundland see- tion had a m uch higher statistical likelihood of stratigraphic Som e concerns w ere expressed about the relative scarcity of com pleteness in the boundary interval than the other tw o sm all shelly fossils in the im m ediate vicinity of the bound- candidate stratotypes, but even it is not unduly thick for the ary, and the distinct possibility that the A cadian orogeny length of tim e available for deposition. m ay ha ve reset the paleom agnetic and geochronom etric signatures of the section. These considerations w ere o ffset In another keynote add ress, S. Bengtson pointed out that his by the extrem e accessibility of the section, the apparent collections of the three sm all shelly fossils assem blages at absence of disconform ities or m arked facies changes in the M eischucun have few if any species in com m on, and he boundary interval, the presence of the distinctly Preca m - hypothesized that m arked facies shifts or stratigrapbic brian fossil assem blage in the underlying strata (H arla niella breaks m ay account for this. Several participants suggested podolica Zone), and the excellent prospects 而下 global that detailed sedim entologic analyses be carried out on all co rre la tion . candidate stratotypes to help ascertain the degree of environm ental fluctuation and stratigraphic com pleteness in A t the end of the field trip, seven of the ten voting m em - the boundary interval. bers of the Precam brian-C am brian Boundary W orking G roup (o f the IU GS International C om m ission on Stratigraphy) A nother new developm ent on the Precam brian-Cam brian present voted that the section and horizon w ere suitable for boundary concerns the absolute age of this boundary, a boundary stratotype. F urther deliberations w ill be held in traditionally regarded as approxim ately 570-600 M a. In a Bristol in M ay of 1988 before a postal ballot o f the full contribution to the guidebook, S. Conw ay M orris arg ued that thirty-one voting m em bers is held. lithostratigraphic relationships and available dates from the A valon zone strongly suggest a younger age, perhaps around The conference and field trip w ere sponsored by the W orking 530 M a. His argum ents received strong support from A . G roup, and partly suppo rted by the Natural Sciences and Benus (U.S.A .) w ho reported a date of 565 1 3 Nla (based on Engineering R esearch C ouncil of C anada and the C anadian U -P b in z irc on s) fo r an a sh be d he re a t M istak e n Po in t N ational C om m ittee for IG C P (Project 29). Special thanks containing Preca m brian m e tazoans. The stratigraphic are due to D r. C hris Barnes for m aking the spacious cam pus position of this bed is m ore than 7 km belo w the Precam - and resources of M em orial University of N ew foundland brian-C am brian boundary horizon. available for the conference. A bstracts of the m eeting and the field trip guidebook w ill be published in 1988 as Ne w T he conference was follow ed by a seven-day field trip led by Y ork S ta te M u se u m B ulletin 46 3． 口 E. Landing, P . M yrow , G .M . Narbonne, A . B enus and M .M . A nderson to exam ine the U pper Proterozoic-Low er C am - G . M . N a r b o n n e brian strata of eastern N ew foundland (Fig. 1). Interest w as D epartm ent of Geological Sciences focused on the new ly proposed Precam brian-C am brian Queen's U niversity boundary stratotype candidate (Narbonne et al., 1987, C an- K ingsto n, O ntario K 7L 3N 6 adian Journal of Earth Sciences v. 24: p. 1277-1293).，而论 C a n a d a boundary is placed at the abrupt appearance of com plex

H utton Bicentenary: The O rigin of G ranites

Edinburgh, U .K ., 14 一16 Septem ber 1987

T w o hundred years ago 血m es H utttOon had just spent tw o A m ong theof m ain them es discussed w ere m aterial and s o u r c e s a n d heat y e a rs searching for field evidence by support his view pub- granite m agm as t h e i r transport a n u lis b e d in 1785 that granite form ed the crystallization of em placem ent m echanism s. A lso d e a lt w it h w e re th e c a u s e s hot m agm a injected into cold host rocks. W hile travelling ot com positional diversity on all scales, including the S c o t la n d seeking the essential evidence, he correctly relationships betw een granitoids and their volcanic products, d e d u c e d the significance of unconform ities a n d c o lle c t e d and the role of w ater in m agm atism and m etallogrenesis. the basic data w hich satisfied him that his Theory c二the Earth w as correct. The R oyal Society of Edinburg h and the The sources of granite m ag m a have been vigorously debated R oyal Society of London jointly celebrated this bicentenary recently w ith an international m eeting in H utton's city o f in recent years. It w as clear from the m eeting that crustal Edinburgh on the topical problem of the origin of granites. m elting is now w idely accepted and that m any subduction- related m agm as involve the com plex interplay of several M o re tha n 30 0 sc ie n tists fro m 21 c ou n tries a tte nd ed the processes. R ecent work on the Peninsular R anges Batholith, m eeting and enjoyed G .Y . C raig (U .K .) dra m atic recon- described by L.T. Silver (U .S.A .), reveals rem arkably regular struction of H utton's presentation of his novel idea for the geographic varia tions in m ost isotopic and geochernical origin of granite in 1785. The historical context w as set by param eters, yet in detail the structure is co m plex and not W .S. Pitcher (U .K .) w ho rem inded us o f the chequered his- am enable to sim ple m ixing m odels. R .J. Pankhurst (U.K .) tory of granite research; he gave pro m inence to little-know n considered A ndean m agm atism to be closely controlled by scientists w hose principal failing was to be decades a head of subd uction processes w ith occasional contributio ns from the their tim e . Ind eed he sh o w ed tha t m o st c urren t id ea s ha ve deep crust. A .N . H alliday (U .S.A .) em phasised the diffi- long histories, though only now are they capable o f being culties in distinguishing the various sources involved and tested rigorously. sta ted tha t th e c oe xisten ce o f m an tle an d c rust-d e rive d

3 4 0 E PISO D ES, Vol. 10, N o. 4, D ecem ber 1987 C onferen ce R epo rts m agm as m ay be com m on. B .W . C happell (A ustralia) pro- used num erical m odels to lim it to considerable depths the posed "rem agm atization" for the rem obilization in the crust level above w hich diapirs can barely deform their enclosing of earlier m antle-derived m agm as. H is evidence for this rocks and continue rising. D .H .W . Hutton (U .K .) described process com es from ion m icroprobe studies of U-Pb in zir- various plutons he has analysed structurally and convincingly cons from the B ega Batholith that w ere presented by I.S. dem onstrated the im portance o f local structures on W illiam s (A ustralia). em placem ent. R elationships betw een volcanism and cogenetic plutonics in The role o f w ater in granitoids from hyd rotherm al system s N ew M exico w ere discussed by P.W . Lipm an (U .S.A .) who to batholiths based on stable isotopes w as presented in a dem onstrated that the volcanic rocks w ere interm ittently tour de force bv H .P. Tavlor (U .S.A .) w ho hizhlizhted the quenched sam ples from the upper part of the m agm a cham - p ro Die m s o t io w -- L) m a g m a so urc es. -i-ne im p ortan t roie o t ber, w hereas the plutonics preserved the integrated record water in peg m atites w as dem onstrated at Tanco, w here A .V . of protracted crystallization. R . M acDonald (U .K .) des- Thom as (C anada) used fluid inclusion determ inations to cribed ex tre m e tra ce e lem en t en ric hm e n ts in silicic v ol- speculate that m agm as existed as low as 2650C . canics also in New M exico, and he suggested that liquid- The Edinburgh m eeting provided not only a review of cut- state processes w ere probably responsible. In contrast, T.H . D ruitt (U .K .) described m ore m odest variations in a calc- rent thinking, but also a forum for the discussion of som e novel ideas. It is to be hoped that the spirit of Jam es Hut- alkaline sequence from O regon that are explicable in term s ton w ill inspire these granite researchers now to visit the of crystal一iquid processes. field in search of the evidence! The papers presented at the H utton m eeting w ill be published in 1988 in the Transactions 口 W .E. Stephens 军 D epartm ent of G eology U niversity of St. A ndrew s St. A ndrew s, Fife K Y 16 9ST U .K .

．I I V ： ． I ．

Easyto use, fast, accuratea nd designed to m eet the dem ands A natectic processes w ere exa m ined in m ig m atitic terrains of th e-m od ern qeo lo q ica l la borato ry, the N E W S G 106 by C . W eber (France) w ho show ed disequilibrium processes Petrographic Thin Section G utter-G rinder一 A revolutionary to be com m on, and by S.L . Harley (U .K .) w ho argued for the new concept in geological specim en saw ing and grinding generation of tonalitic m agm as in the crust by infiltration of w ater into m a fic granulites to generate tonalitic m ag- * U n ive rs al V ac uu m C hu ckfa ce - a cco m m od ates 6 o ff 2 8 x 4 8m m o r m as. The various form s of S-type granite in the classical 4 off7 6 x 2 6m m o r2 o ff 76 x 5 0 m m Lachlan fold belt w ere described by A .J.R . W hite (A ustra- O r 1 o ff 1 10 x 7 6m m slid es lia), and spectacular exam ples of this type in the H im alayas ．A utom atic Feed in S aw ing M ode - w ere clearly dem onstrated by P . Le Fort (France) to ha ve full autom ation at this part of the 《 their sources in gneisses of the T ibetan slab in a collision operation gives m axim um -'-4 environm ent. Eruptive equivalents of S-type granites are productivity *S ec tio ns G ro u nd to 10 0 M ic ro ns o r know n, though they are relatively rare, but a m ost im por- J J 若 tant exam ple of extrem e S-type com positions w as described Less一depending upon the n ature c the m aterial, sections m ay b e 尹 扩 in ash flow tuffs and volcanic glasses from M acusani in Peru ground to l esst han 100 m icrons 曦 护 by M . Pichavant (France). Taking a statistical overview , ready forf inal lapping bym achine or 咦、 J.A . Pearce (U .K .) described m eans of discrim inating dif- h a nd ferent plate environm ents using trace elem ents. eD igital Readout - this option gives 、、俨 direct indication of specim en A nagging problem throug hout the m eeting w as the supply of th ic kne s s heat for the crustal m elting required by so m any speakers. *Integral V acuum and C oolant *Fully com patible w ith all other S e rv ic es - h ou se d in the m ac hine f o r LO G IT EC H geological specim en W hereas isotopic and geochernical param eters of granitoids c o n v e n ie n c e p re pa ration syste m s are inherited directly from their parents, the heat source leaves no such convenient signature. Som e answ ers w ere T o ta l w o rld le a d e rs provided by tw o distinct m odelling approaches. H .E. H up- In Ing pert (U.K .) used fl uid dynam ic m odels to show that the F O 叫 F LIA } E R I N F } M A T IO N P L E A S E C } T A C T advection of heat into the crust through the em placem ent of basaltic sills w ould prom ote the generation of larg e volum es of crustal m elt. E . Zen (U .S.A .) described num erical m odels 拐 of sta ck ed thrust she ets to c rea te th erm al co nd itio ns su it- able for m elting in a greatly thickened crust.

The inverted tear-drop diapiric m ag m a body and plIuU to n s o fa m ilia r in c a r to o n s a n d c ro s s s e c t io n s w a s su bject t o s o m e critical exam ination at this m eeting. T .M . H a rris o n (U .S .A

E PISO D ES, Vol. 10, N o. 4, Decem ber 1987 341 C on ference R ep orts O bserving the Continental Crust T hrou沙 D rilling

M n r .q - S w p d p.n . 7 一 1 0 S p n te m b e r I q 8 7

T he third international sym posium on this topic was held sub-surface geology w ith exposed terranes and geophysical recently at the sm all tow n of M ora w ithin the Siljan im pact data and to interp ret the results in term s of m odels of the stru ctu re in S w ed en a nd clo se to th e site o f the c on tro ve r- lithospheric evolution of No rth A m erica. sial deep gas drilling project in crystalline rock. This pro- ject and deep drilling of the continental crust for scientific A s expected, there w as considerable interest in the results of the hole at Siljan, w hich has been drilled to explore the purposes w ere the m ain them es of the sym posium , w hich potential of crystalline rock for m ethane gas. The occur- w as attended by som e 300 participants from 20 nations. re nce o f suc h gas is predicted by the controversial hypoth- D eep drilling refers to the penetration to depths greater esis o f T ho m a s G o ld (U .S .A .) tha t th e m a n tle c o n ta in s than 4.5 km . Such depths can be reached by slim line, w ire prim odial abiogenic m ethane, w hich can leak upw ards into coring techniquest but at greater depths, in so-called the crust. The drill hole at Siljan is sited at G ravbe啥， ultra-deep holes greater than 7 km , there are difficulties 14 km from the center of this 52 krn diam eter im pact w ith conventional d rilling and coring techniques. It w as structure. Earlier w ork had indicated a num ber of geo- m ade clear that, although technically feasible, such deep c h e m ic a l a n o m a lie s in t h e a r e a a n d t h e h o le w a s lo c a t e d drilling projects require the close and early cooperation of over a 一20 m gal gravity anom aly, w ith indications of seis- scientists and drilling engineers. T he costs and technical m ic reflectors at depth. The hole is in Precam brian granite problem s, such as penetration rate, bit life and the effects and has reached a depth of 6.3 km . D rilling is currently of tem perature, are considerable and increase as the fourth suspended. pow er o f the depth. A m ong the national program s review ed w as that of the U.S.S.R ., the only nation so far to have drilled an ultra-deep hole. A t K ola, a 12 km vertical section of Proterozoic and A rchean continental crust has been sam pled. There are plans to deepen K ola to 15 km and to drill 12 m ore deep holes in the U .S.S.R ., seven in crystalline rocks. A t the tim e of the sym posium , a fully cored, 3-5 km pilot hole w as set to begin at the W est G erm an site for deep drilling in Bavaria. The m ain hole is planned for 12-14 km a nd is s ch ed uled to be d rille d in 1 98 9-90 . C o nside ra b le pre一rilling geological and geophysical investigations over a period of three years w ere necessary before selecting the drilling site, for the choice is not sim ply a scientific one but m u st also in clu de te ch nica l c o nsid era tio ns. In th e ca se o f W est G erm any, the other potential site at Schw arzw ald w as considered technically m ore difficult, because the pre- investigations indicated a geotherm al gradient w hich sug- gested tem peratures of 3000C at 7-8 km . O ther national program s review ed included the program 11G6ologie Profonde de la France," which has drilled three holes, the deepest to 3.5 km , in crystalline basem ent. A lso discussed w as the U .S. drilling of the 2 km hole at C ajon Pass to study the San A ndreas fault and plans for a 10 km hole in the A ppalachians. Less advanced plans in the U .K . and C anada w ere also review ed. It is evident that, although m uch can be learn t about the crust at depth, these deep 嘿F ig ur e 1 ： Ex am in in g d r il l b it s a t G ra vb e rg ． holes are m assive m ulti-disciplinary projects involving con- siderable m onetary, technical and tim e investm ent. A num ber of scientific projects that have utilized d rilling , The hole has been extensively studied by dow n一ole w ire but not necessarily to great depths, w ere also review ed. logging instrum ents, including a geochem ical logging tool A m ong them w ere the highly successful O cean D rilling and fracturing im aging w ith a m icroelectric scanner. There Prog ram and various projects in geotherm al a reas such as have been problem s due to breakouts from differential the V alles C ald e ra a nd S alto n S e a in the U .S .A . A lso note d stress in the fractured granite, and unlike logs in sedim en- w as the scientific gains that m ay be m ade through using tary rocks, there is no co m plem entary data bank for "holes of opportunity" d rilled for com m ercial purposes. O ne correlating and evaluating the logs w ith changes in the such project called Upper C rust uses holes d rilled to the properties o f crystalline rocks. U nfortunately, core bu ried P reca m b ria n ba se m e nt in th e c en tra l U .S .A . T his recovery a t G ravberg has been very poor. O nly 7 out of 14 allow s geologists to obtain sam ples for geochronologic, coring runs contained core and they had recoveries o f only 1 petrologic and geochem ical studies in order to correlate to 4 0 % ．

3 4 2 E PISO D ES, Vol. 10, No. 4, D ecem ber 1987 一 一Conference Reports

T h e r e a re five sub-horizontal, high-am plitude seism ic W hile m ost participants felt there w as little or no case to be re fle ctors i n the area of G ravbe馆． D rilling results indicate m ade for m antle-derived m ethane in the granite, they w ere th a t t h e pper three are dolerites w ith an associated in general agree m ent that the hole should continue to in c r e a s e i n fracturing o f the surrounding granite. In these 7.5 km , w here it w ill penetrate the third m ajor seism ic a r e a s t h e ．highest concentra生ions． (approximatel 护“pr . ) o f reflector, cited as having the best potential for gas. The m e t h a n e n a v e D e e n to u n Q . In Is 1s e n r lc fl e o In - 。七 a n d g iv e s feeling w as that unless this target w as reached, there w ould isotopic values sim ilar to abiogenic m ethane (16-260 /oo alw ays be som e lingering doubt as to the potential of SiIjan ‘13C). In the granites m uch lower concentrations of m ethane occur and are isotopically lighter than those in the T he sym posium em phasized w hat can be learnt from drilling dolerites. The granite m ethane appears to be associated w ith the m agnetic fraction, w here it m ay have been into crystalline basem ent. It also stressed the large invest- produced by the reaction of carbon m onoxide and hydrogen m ent required for deep drilling. This m eans that the w ith m agnetite acting as a catalyst 一 the so-called potential num ber of deep drill holes w ill be lim ited and Fischer-Tropsch reaction. requires that site selection m ust lead to solving geological problem s beyond those at the particular site and m ust pro- Hydrogen and helium , are also present. The latter appears m ote understanding of the continental crust elsew here. A t to be crustal in origin, but that of the hydrogen is not kno w n the sam e tim e, w ork m ust be undertaken to select areas at present. It could be indigenous or produced from w ater w here the deep targets o f interest are at abnorm ally shallow by the therm al action of drilling. T nis so-called bit m eta- depths. G iven the high costs of such projects and the m orp hism and conta m ination from m ud and other m aterials lim ited num ber of potential deep holes it would seem used in drilling is clearly a problem in identifying the appropriate that the com m unity give consideration to som e sources of the various gases. form of international cooperation, perhaps sim ilar to that Although open to som e interpretation, it appears that w hich has been so successful in the drilling prog ram to abiogenic m ethane gas is restricted to the dolerites. This is explore the oceanic crust。口 consistent w ith the isotopic data from calcite vein fillings in R i c h a r d A . F . G r i e v e the granite. These w ere originally used as an argum ent for G eological Survey of C anada abiogenic m ethane in the granite, but it now appears that I O bservatory Crescent, O ttaw a their isotopic trend is consistent w ith the sim ple precip i- C a n a d a K I A O Y 3 t a tio n o f c a lc ite f ro m m e te o r ic w a te r .

A frican G eology R eview ed

Berlin, G erm any 18 一22 A ugust 1987

in a w eek w hen tropical thunderstorm s gave way to glorious of intracratonic basins as a function of therm al age ancl sunshine, 300 people from 41 countries converged on B erlin structure of the underlying basem ent, ancient glaciations, for the fourteenth C olloquium of A frican G eology. T he and intraplate deform ations. Evidence from A frica is also C olloquia date back 23 years to the first m eeting in Leeds, im portant in the study of rifting and continental frag m en- w hich w as convened by W .Q . K ennedy in 1964, the year in tation, anorogenic m agm atism (alkaline ring com plexes, w hich he defined the W est A frican, Congo and Kalahari carbonatites and kim berlites), and of course in the inves- c r a t o n s a n d th e P a n - A fr ic a n th e rm o t e c to n ic e v e n t. A lte r- tigation of evolution of life form s, including m an, and of nating at regular intervals since then betw een the U nited Q uaternary clim atic evolution. K ingdom and continental Europe, the colloquia have grow n Each of the previous colloquia w ere cha racterized by a from sm all gatherings, into large international m eetings particular them e often reflecting the expertise of the w ith parallel sessions and an international audience. hosting institution. A ccording to R ussell Black (France), the The m eetings provide a forum for scientists studying all 1966 and 1983 m eetings in B russels w ere m uch concerned aspects of A frican geology, and they offer the opportunity w ith the interpretation of geochronological data, Sheffield both for E uropean geologists w orking in isolation in dif- (1967) and Leicester (1971) by geochem istry and the rela- ferent regions of A frica and for A fricans, restricted by tionship betw een vulcanism and tectonic setting, C lerm ont national boundaries, to m eet and discuss their results before Ferrand (1969) by the M auritanides, Pan-A frican orogeny an international audience including em inent scientists not and geophysics. T he 1973 colloquium in Florence focussed directly involved in A frica. The colloquia have also pro- on the A far triangle, G ottingen (1977) and M ontpellier vided a break-through in co m m unications betw een English (1 97 9) o n the P an -A frica n o f W e st A fric a a nd the D a m a ra , and French-speaking geologists and betw een researchers M ilton K eynes (1991) on the Pan-A frican of northeast A frica w orking in w est A frica and those operating in north, central, and the M ozam bique Belt and St. A ndrew s (1985) on alkaline e a st a n d s o u t h e rn A f ric a . anorogenic ring com plexes. A lthough m any continents w ere m obile throughout the T he Berlin m eeting w as hosted by the "Special R esearch Phanerozoic, the m ain part of A frica w as then cratonic, Project in A rid A reas," a group concentrating on projects in w ith fold belts only along the north-w est and southern m ar- north-eastern A frica, in co-operation w ith counterpart gins. In the study of ancient cratons that have been institutions in Egypt, Sudan and So m alia. T he m ajor them e, involved in m ore than one period of continental accretion new to the colloquia, w as "G eology for D evelopm ent." A t and fragm entation, m ajor scientific contributions have com e the outset, delegates w ere told that only I％ of the w orld's from A frica in a w ide variety of fields. These include geologists are A frican and that m ore encouragem ent should A rchaean greenstone belts and granulite terranes, Pan- be given to co-operation both betw een A fricans and Euro- A frican continental accretion and plate tectonics, evolution p ea ns a nd b etw e en A frica n s o f d iffere nt cou n trie s.

E P IS O D E S , Vo l. 1 0, N o . 4, D ec e m be r 19 8 7 3 4 3 C on ference R ep orts

R esults from geotraverses by international team s in central, different areas. U nder the topic of basin analysis there w est and southern A frica w ere presented, and suggestions w ere num erous reviews of lithologies ranging from Upper w ere m ade for sim ple w ays of replenishing soil nutrients by Proterozoic to Tertiary w ith several papers considering the applications of pow dered rocks. "G eology for Survival" resource potential of hydrocarbons, phosphates and bauxite. covered vital aspects of palaeoclim ate and water resources Papers on m etallogeny covered not only specific m etals such in the Sahel and considered not only the characteristics of as C u, Sn, N b, Ta, W , R EE, A u and Fe m inerals but also aquifers, but also the quality of different w ater, aspects of considered exploration techniques and ore-form ing pro- w ater storage, the effects of the Saharan clim atic response cesses. To balance these and other specific topics, five to glaciation and geological support for agricultural pro- lectures w ere presented on continental sedim ents in A frica, duction. Special sessions w ere devoted to the IU G S － Precam brian of northeast A frica and A rabia, the A rchaean U nesco program s on the G eological A pplication of R em ote of W est A frica, palaeobotany for stratigraphy, and A frica in Sensing and on M ineral D eposit M odelling. G o n d w a n a la n d . M any papers w ere presented on aspects of A rchaean and R epresentatives of international organizations and projects Proterozoic rocks, w ith e m phasis on crustal evolution and stressed the increasing need for co-operation betw een geocbronology in specific regions and correlation betw een European and A frican scientists. In this respect it was encouraging that there w ere 112 participants from 28 A frican countries at the colloquium , including 31 from Egypt, 16 from Nigeria and 12 from Sudan. In addition, IG C P P roject 255 w as initiated for central A frica. T his concerns the developm ent and co-ordination of research program m es on the m ineral deposits associated w ith the K ibaran orogeny. C opies of the 215-page A bstract volum e are available for 80FF from C IF EG , 103 R ue de Lille, 75007 Paris, France. (Editor's N ote: A lso available already is a 486一age volum e "Current R esearch in A frican Earth Sciences," published by A .A . Balkem a for $48.50US (Postbus 1675, N L-3000 B R R otterdam , The N etherlands). Edited by G . M atheis and H . Schandelm eier, this is a com pilation of "extended abstracts from the Berlin m eeting, each about 4 pages long w ith key illustrations and references, in the increasingly popular "short reports" form at being encouraged by IC SU P ress.) The 15th C olloquium on A frican G eology is to be held in Figure 1 ： Listening to a keynote paper at th e N ancy, France, in 1990. 0 Berlin colloquium . Dr . G . Matheis, a key organizer J u d i t h K i n n a i r d of the meeting , is front right , next to Dr. C . D epartm ent of G eology K og be , I UG S Vi ce -P r es id en t a n d P re si d en t o f th e U niversity of St. A ndrew s Geological Society of A frica, a co-sponsor of th e St. A ndrew s, Fife m e e t i n g . U K K Y 1 6 9 S T

Structure of M elts at Ifi gh Pressures： PLe.trogenesis in the M antle

Vancouver, Canada, 12 A ugust 1987

D uring the last decade significant progress has been m ade in The proportion of these units does not change significantly studies of the structure and physical properties of silicate at pressures to 2.5 G Pa, though T -O -T angles (w here T m elts over w ide pressure and tem perature ranges. M ajor represents tetrahedral cations) decrease by 2-4 % ． progress has also been m ade in the determ ination of m elting relations of m antle m inerals and rocks to pressures of 25 Structural changes in silicate m elts w ith pressure were discussed by A .L . Boettcher and others (U .S.A .) on the basis G Pa and their applica tion to the m elting of the Earth's m antle and the genesis of m agm as. Papers on these tw o of solubility of C0 2, and by P.F. M cM illan (U.S.A.) based on im portant topics w ere presented at a sym posium held during R am an spectroscopy. A lthough m ost A l is in tetrahedral the recent IU G G G eneral Assem bly and sponsored jointly by coordination in alum i no-si licate m elts, the average coordi- the IU G S C om m ission on Igneous and M etam orp hic nation of A l m ost likely increases gradually w ith increasing Petrogenesis and IA V C EI. pressure. E . O htani (Japan) proposed that at pressures greater than 6 G Pa, a significant am ount of A l m ay be in M elt structures based on R am an spectroscopic studies w ere six-coo rdination, as observed by N M R spectroscopy and in sum m arized by B .O . M ysen (U .S.A .), w ho show ed that m elting relations of A l-bearing silicates. The im portance of silica te m elts co nsist o f sev e ra l d iffere nt stru ctu ra l u nits : understanding the influence of quenching from above the m onom er, dim er, chain, sheet and 3-dim ensional netw orks. liquidus on structural studies Of AT was e m phasized during

3 4 4 E PISO D ES, Vol. 10, N o. 4, D ecem ber 1987 C on ference R ep orts

the discussion. It w as questioned w hether sam ples quenched The genesis of m agm as in subduction zones was discussed by from tem peratures considerably above the liquidus are Y . Tatsum i (Japan) in relation to d ehyd ration in the representative of m elt structure at the liquidus. hydrated m antle just above a subducted slab. Based on phase equilibrium experim ents a t high pressure, D . C . The viscosity o f silicate m elts as a function of com position Presnall (U.S.A .) proposed that w hereas prim ary M O R B and volatile (C02) content was discussed by D.B. Dingwell m agm as are olivine tholefites that equilibrated at 0.5-1.1 (F.R .G .) and D . Virg o (U .S.A .) w ho dem onstrated system atic G Pa, the prim ary m agm as for H aw aiian tholejites are viscosity changes due to the addition of alkalis and alkali picritic and equilibrated at pressures grea ter than 1.8 G Pa. ea rth e lem e nts. T he inte rac tio n be tw ee n C -0 -11 fluids a nd silicate m elts and the effects of such fluids on phase The m elting relations of peridotites and chondritic m ate rials relations w ere discussed by R .H . Luth (U .S.A .). to pressures of 25 G Pa w ere determ ined by E . O htani, by E. Takahashi (Japan), E. Ito (Japan) and C .M . Scarfe (C anada) The density of silicate m elts at high pressures is a central and by C .T . H erzberg (U .S.A .). T he co m positions of liquids factor in m agm a transport in the m antle. To calculate this form ed by partial m elting of these m aterials becom e very density, partial m olar volum es of oxide com ponents OliViDe-rich and even peridotitic at pressures above 10 G Pa, applicable to high pressures w ere obtained by R .A . Lange suggesting that upper m antle peridotites them selves are (U .S.A .) and I.S.E. C arm ichael (U .S.A .), based on accurate frozen partial m elts. O htani dem onstrated that m ajorite m ea sure m e nts o f th e I-a tm volu m e s o f m elts a s w ell as on garnet is the liquidus phase over a w ide pressure range ultrasonic velocity and calorim etric data. Using these (14-25 G Pa). There w as considerable discussion concerning partial m olar volum es of oxide com ponents, it is possible to the fractionation of m ajorite garnet versus M g一erovskite in calculate the density of m ag m as at high pressures. T . Fujii the early history of the Earth's m antle. (Japan) tested his calculations of densities by flotation and T he first m easurem ents of the attenuation of com pressional sinking of olivine crystals in basaltic m elts at pressures to w aves in peridotite w as reported by H . Sato (U .S.A .), I.S. 8 .5 G Pa . H e d e m o nstrated tha t olivin e do e s n o t floa t in Sacks and others (U .S.A .) at both subsolidus a nd supersolidus m elts equilibrated w ith peridotite to pressures of at least tem peratures at pressures to 0.73 G Pa. It w as show n that Q 8 . 5 G P a . decreases significantly even below the solidus. T he results w ere used to estim ate the tem perature of the asthenosphere The diffusivities of Si, 0 , M g and Ca in m elts in the system near m id-ocean ridges． 口 jadei te-diopside w ere m easured by N . Shim izu (U .S.A .) a nd 1. K ushiro (Japan) to 2 G Pa using diffusion couples w ith dif- Ik u o , K u s h i r o C hristopher M . Scarfe ferent isotopic ratios. D iffusion profiles w ere m easured G eological Institute Departm ent of G eology w ith an ion-probe. T hey show ed that the diffusivities of Si U niversity of Tokyo U niversity of A lberta and 0 increase w ith increasing p ressure in jadeite-rich 7-3-1 Hongo, T okyo 113 Edm onton, Alberta T 6G 2E3 m elts; w hereas they decrease in diopside-rich m elts. T he Ja pa n C a n a d a results are consistent w ith viscosity changes as a function of pressure. T he presence of tetrahedrally coordinated M g in the m elts w as also suggested. ｝｝回% European Sedimentologists Meet

K rakov, Poland, 23 一26 M ay 1987

T w o hundred and fifty sedim entologists from 26 countries carbonate-evaporite form ations of Southeastern A sia, Late m et earlier this year in the ancient city of Krakov to discuss C arboniferous deposits of the southw estern U .S.A ., C reta- sedim entation and the o rigin of sedim e ntary form ations. ceous basins of D akhla (Egypt), and the C- am brian-O rdovic- T his 7th European conference sponsored by the International ian shelf sedim ents of the Turingia basin. A ssociation of Sedim entology had two m ajor them es: car- In the study of recent sedim entary processes w ithin the bonate and evaporite sedim entation, and terrigenous rock coastal-shelf zone, specialists from Poland, East G erm any form ation as com pared to m odern sedim entary environm ents and U .S.S.R . place particular em phasis on dynam ic and other in o c e a n s a n d in la n d s e a s . factors of sedim entation that control sedim entary differ- Special interest was show n by speakers from The Nether- entiation both on the surface and w ithin sedim entary lands, Poland, East G erm any and Sw eden in the detailed sequences. Statistical treatm ent by co m puter is now com - m on, as is detailed analysis and com parison of distribution interpretation of shallow sedim entary environm ents. R econstructions w ere given of palaeo-current regim es, and curves for granulom etric com position of sedim ents from there w ere discussions of structural features of deposits different zones. Studies of m arine sedim entation lay that traced regular changes in lithological com position due em phasis on ancient sedim entary sequences, and special to variations in character and intensity of dyna m ic factors consideration w as given to the conditions of form ation of such as the roughness of the sea and tidal currents. T hese present glacial-m arine sedim ents (Polish specialists, for environm ental param eters w ere also inter-related w ith exa m ple, use detailed analysis of clay m inerals), as w ell as to the distribution of suspended alluvial m aterial in m arine tectonic m ovem ents, transg ressions and regressions. basins (w ith application of heavy-m etal tracing techniques). R epo rts on the geology of specific sedim entary basins, I.I. B e b eshe v w hich de m o nstra te d b o th the a c tua l e vid en ce a nd w ell- Geological Institute grounded genetic conclusions, included the follow ing regions U .S.S.R . A cadem y of Sciences and deposits: Late C retaceous 一Early Paleogene-N eogene Pyzhevsky 7, M oscow 109017 form ations of the Sudan Basin, Jurassic terrigenous-

E PISO D ES, Vol. 10, N o. 4, D ecem ber 1987 3 4 5 N ew and recent GE OSCIEN CE 加 M 助finger

V o lu m e 9 M in erals an d R ock s J. H oefs Stable Isotope G eochem istry E ditor in C hief. P. J. W yllie 3rd com pletely revised and enlarged edition . 1987. 62 figures. X , 241 pages. H ard cover D M 96，一ISB N 3-540-17341-2 E ditors: A . El G oresy, W . von Engelhardt, T . H ahn C ontents: T heoretical and Experim ental Principles. - Isotopic Properties ofS elected E lem ents 一V ariations ofS table Isotope V o lum e 20 R ations in N ature. - R eferences. - Subject Index. D . J .D e P a olo V olum e 18 N eodym ium Isotope G eochem istry G . G ottardi, E .G alli A n In tro du ction N atural Z eolites A pprox. 200 pages. H ard cover, in preparation. 1985. 218 figures. X II, 409 pages. H ard cover D M 168- IS B N 3-540 -1864 8-4 IS B N 3-54 0-139 39-7

V o lu m e 17 V olum e 19 F . J . S aw kin s J. G anguly, S . Saxena M etal D eposits in R elation to M ixtu res an d M in eral R eactions P late T ecton ics 1987. 108 figures. A pprox. 290 pages. H ard cover D M 108，一 IS B N 3-54 0-1766 7-5 1984. 173 figures. X IV , 325 pages. H ard cover D N I 128，一 IS B N 3 -5 40-12 752-6 C ontents: T herm odynam ic Functions of Solutions 一A ctivity- C om position R elations and M ixing M odels. - Phase Separa- V o lu m e 16 tion in Solution. - C h em ical R eaction and Equilibrium . - J .B . G ill T herm odynam ic P roperties of Selected M ineral Solid Solu- tions，一Exchange Equilibriu m and Inter-C rystalline F ractiona- O rogenic A ndesites and P late T ectonics tion. - A tom ic O rdering in M inerals. - Estim ation and 1981. 109 figures. X IV , 390 pages. H ard cover D M 118，一 E xtrapolation of- 1 herm odynarnic Properties. - A ppendices. ISB N 3-540-10 666-9

V . A . D rits J.V . S m ith, W . L .B row n E lectron D if raction and H igh-R esolution Feldspar M inerals I E lectron M icroscopy of M ineral S tructures Introduction, C rystal S tructures and Physical P roperties T ranslated from the R ussian by B . B . Sm oliar 2nd com pletely revised and enlarged edition. 1988. 352 figu res. 1987. 126 figures. X II, 304 pages. H ard cover D M 248，一 A pprox. 760 pages. H ard cover D M 360，一ISB N 3-540-17692-6 ISB N 3 -5 40-173 23-4

T his book deals w ith th e advantages and lim itations ofe lec- M . L . B udyko, G . S. G olitsyn, Y u A . lzrael tron dif raction and high-resolution transm ission electron m icroscopy for the structural study ofm inerals. It draw s atten- G lobal C lim atic C atastrophes tion to the new possibilities that these m ethods ofer for the 1988. A pprox. 110 pages. Soft cover. study of finely dispersed and poo rly crystallized m inerals. IS B N 3-540-18647 -6

V . A . M ilash ev Explosion Pipes 1988. A pprox. 260 pages. H ard cover, in preparation. IS B N 3-540 -18649 -2

346 E PISO D ES, V ol. 10, N o. 4, D ecem ber 1987 N ew an d recent G E O S C IE . rom 助finger

F.J . P ettijo hn, P. E . P otter, R . S iever 0 . B onacci S an d an d S an dston e 而丽editiorl K arst H ydrology 2nd edition. 1987. 355 figures. X LX , 553 pages. W ith Special R eferen ce to D in aric K arst H ard cover D M 168，一ISBN 3-540-96355-3. 1987. 114 figures, 19 tables. A pprox. 210 pages. (Springer Series Soft cover D M 118，一ISB N 3-540-96350-2 in Physical E nviro nm ent, V olum e 2). H ard cover D M 138，一 ISB N 3 -540-18 105-9 K . K leinspehn, C h. P aola A .A . P etrov N ew Perspectives in Basin Analysis 1988. A pprox. 500 pages. (Frontiers in Sedim entary G eology) P etroleum H ydrocarbons H ard cover, in preparation. ISBN 3-540-96611-0 T ranslated from the R ussian by A . Y . Shoum ikhin 1987. 90 figures. M 255 pages. H ard cover D M 168，一 IS B N 3-540-17329 -3 W . L . G raf

Fluvial P rocesses in D ryland R ivers G .F riedrich, P . H erzig (E ds.) 1988. A pprox. 143 figures. A pprox. 350 pages. (Springer Series in Physical E nvironm ent, V olum e 3). H ard cover D M 148，一 B ase M etal S ulfide D eposits in S edim entary ISB N 3 -5 40-17 59 1一I an d V olcan ic E nviron m ent 1988. A pprox. 269 pages. (Special P ublications of the Society W . Salom ons, U . F6rstner (E ds） for G eology A pplied to M ineral D eposits, V olum e 5). H ard cover, in preparation. ISB N 3-540-18202-0 Chem istry and Biology of Solid W aste D redged M aterial and M ine T ailings E . G ocht 1988. A pprox. 300 pages. H ard cover, in preparation. ISB N 3 -540-18 23 1-4 In tern ation al M in eral E con om ics 一 M ineral E xploration, M ine V oluation, M ineral M arkets, In tern ation al M in era l P o licies W . Salonions, U . F6rstner (E ds.) 1988. ISB N 3-540-18749-9. In preparation Environm ent M anagem ent of Solid W aste C ontents: Part 1: E conom ic G eology, M in eral Exploration, and D redged M aterial and M ine T ailings M ineral D evelopm ent. - P art 11: M ineral E conom ics. - 1988. A pprox. 450 pages. H ard cover, in preparation . P art III: In te rn ation al M in e ral P olicie s，一R e fe ren ces. - ISB N 3-540-18 232-2 A ppendices A -D . - Index .

L . D rude de Lacerda, U . Seeliger (E ds.) A . N . Khram ov M etals in C oastal E nvironm en ts of P aleom agnetology L atin A m erica T echnical E ditor: D . H . T arling 1988. ISB N 3-540-16945-8. In preparation 1987. 117 figures. 17 tables. A pprox. 330 pages. H ard cover D M 178，一ISBN 3-540-17360-9

N . P. Jam es, Ph . W . C hoquette (E ds.) P aleokarst 1988. 277 figu res in 409 parts. A pprox. 510 pages. H ard cover D M 148，一ISB N 3-540-96563-7

G .-R . H ofm ann, D . F. Snelling (E ds ） Springer-V erlag Berlin H eidelberg N ew Y ork London Paris To材。 M ultiprocessing in M eteorological M odels H eidelbe rger P latz 3, D -1000 B erlin 33 175 F ift h A v e ．N e,,Y o rk, N Y 100 10, U S A 28, L u rke S treet, B edfo rd M K 40 3H U , E nglan d - 26, ru e des C artn es, F -75005 P aris 1988. X-V II, 446 pages. (T opics in A tm ospheric and O ceano- 37-3, H o ngo 3-cho rn e, B u nkyo -ku , T o kyo 113, Japan graphic Sciences). Soft cover, in preparation.

EPISO D ES, Vol. 10, N o. 4, D ecem ber 1987 347