P A N A F R IC A N C R U S T A L E V O LU T IO N

by

A lfre d K r U n e r

Th e Pan African (Late Precam brian to early Palaeozoic) w as one of the m ajor crust-form ing periods in earth history. This paper outlines the structural differences betw een individual A frican foldbelts, suggesting a com plex evolution involving varying degrees o厂h orizontal plate m otion, in places resem bling m odern plate tectonic m ovem &nts. Ophiolites and sheeted dykes show that sea-floor spreading w as established in the la te Precam brian and that the W ilson-cycle had becom e an im portant elem ent of orogenic evolution. Pan A frican belts m ay contain im portant ore deposits and som e are recom m ended as targets for future m ineral exploratzon.*

Late tectonic alaskitic granite cutting m etasedimen杏s of the Khan 和rmation near RUssing：一amara belt. N am ibia. The alaskites show strong_ 7u r-a_n i u, m--A enr --ic hIm en t in certa.i n T'a4r -eIr-a- fs an d ar:e_ pr-o -D-aZ}-wZ] y re tat ed to anatectic m elting of pre-D am ara basem ent at about 500 M a ag o.

In tro du c tio n The term "Pan African" (loosely m eaning "all Africa") w as originally proposed by K ennedy becam e w idely established coined by W .Q . Kennedy (1964) who recognized "an im portant w hen Vachette com piled a m ineral age m ap of A frica and w idesp read tectonic and therm al event" w hich led to (reproduced in Bessoles, 1977) w hich confirm ed the general 11structural differentiation of an original shield into cratons range from ca. 450 M a to about 650 M a ago. A lso, in view of and circum -structural (orogenic) areas" about 500 M a ago. the presence of several d istinct episodes during this period, K ennedy observed that in som e areas of the continent this the term "Pan A frican event" becam e popular in the process involved geosynclinal sedim en tation and subsequent lite ra tu re . d e fo rm a tion an d D ro 2rad e re 2 io n a l m e ta m o rD h ism . w h ile in o tne rs, n o taD ly in t ast 八Irica , o m y o ase m e n t ’roc iorogeny" and pro户osed "P an- igneous activity and m etam orphism date 'back to m ore than A frican therm o-tectonic episode". It is interesting to note 750 M a in som e regions of the continent (K rUner, 1980a) and that the pheno m enon of w idespread structural reactivation of to about 1000 M a in the A rabian Shield (F leck et al., 1979). older crystalline basem ent during this episode w as seen by A lso, there were suggestions (G ass, 1977) to expand the Pan K ennedy (1964) as evidence against t he concept of A fric an a n d in c lu d e th e Dre -te c ton ic c v cle o f se d im en ta tion c on tine n ta l a cc re tion . a n a v o ic a n is m . w n ic n W O U ICI D e in iin e w i tn r\ e n n e a v 's k 1 ';1b 4 ) o e iin iiio n D U I w o u ic e x T e n a Tn e e v e n t D a C K T o a D O U 1 I U L)U - K ennedy's defin ition w as largely based on the then available K -A r and R b-Sr m ineral ages w hich, as w e know now , only 1100 M a, the beginning of deposition in m ost Pan A frican belts. The problem , how ever, is that such extension w ould reflect blocking tem peratures reached late in the therm al m ean an overlap in tim e w ith the K ibaran event w hich, in evolution of a belt, and so the tim e designation of ca. 500 M a m ust be seen as relating to the final therm al rather than the som e areas of A frica, lasted until ca. 950 M a ago. T he entire tectonic episode. problem of no m enclature is not resolved at present, though som e suggestions are given at the end of this review . C lifford (1967) recognized this problem , and in a detailed evaluation of radiom etric data, he dem onstrated that the P an It has fu rtherm ore em erged that the P an A frica n in its A frica n o f so u th e rn a n d c e n tra l A fric a c on siste d o f a t le a st e x ten d ed d e fin ition w as n o t res tric te d to th e A frica n two episodes 一the D am aran (in the general range 450-570 c o n tin en t bu t w as a lso fou n d in a ll o th e r G o n dw an a c ru sta l M a), and the K atangan (in the range 580-680 M a). Vail (1964) segm ents (Fig. 1), thereby m aking it one of the m ost had also concluded that the M ozam bique O rogeny of E ast im portant and extensive tectono-m etam orphic events of A frica took place betw een 400 M a and 650 M a ago. T he earth history. Significantly, it seem s largely confined to the extension of the Pan A frican to a longer period than Southern H em isphere.

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，2 靡忿草黑熟嚣）：：暇嗯｛钞理纪理旋枷e二 ～ ～～一福福三‘二一一一 F igure 1. Possible con厂iguration o厂proto-C-ondw ana supercontinent at the end 0厂the Precam brian, show ing distribution o厂P an A厂rican terrains (m odi厂ied a厂ter B lack, 1978, and M orel and Irving, 1978). N ote that new palaeom a一gnetic data （M Cw illiam s. 1980; M cW illiam s et al., 里卫ress) suggest that this supercontinent only cam e into existence at about 550-600 M a ago through collision o了 East G ondw ana (A ntarctica, India. A ustralia) w ith W est G ondw ana (A frica, South A m erica and , perhaps, N orth A m erica) east of the present M ozam bique belt (see also Fig. 4, B). The possible su ture is indicated and m ay extend into the A rabian Shield. Pan A frican Structural T ypes F our m ain types of Pan A frican developm ent have been recognized; these are sum m arized by K rU ner (1979) and a re also illustrated in F ig ure 2. G) The 'orogenic" belts consist of deform ed thick ''geo- synclinal" sequences and show a depositional and tecton ic developm ent w hich m ay be broad ly sim ilar to that of m any Phanerozoic orogens (for exam ple, N os. 4一12 in Fig. 2). (ii) The "m obile'' belts (for exam ple, N os. 2 and 3 in Fig. 2) consist of m edium 一to hig卜grade m etam orphic rocks of w hich the m ajority represent structurally reconstituted older I H l' - M.gm .fi, A,} sia lic b a se m e n t, in so m e c ase s d a tin 2 b a c k to the A rc h ae a n 2 M . .. r b ,q- B e lt kN roner, i，／／）． ine cover seolm ents, w riere recognized, are 3 Z Q m b e zl B e l t 4 Mat- 仑‘b以rY B elt thin and of shallow -w ater type, and it is the refore suspected 5 G ar．eP B e lt 6 0 am a r0 B elt that these belts never w ent through a "geosynclinal" stage. L.t} P ,．C om br．. 1 A s w e shall see, this irterpretation has considerable con- 7 Kat- go BeM 一 1}1.r d Qrc p r o 丫I- 8 W e，t C o n go Belt L口t． 尸re co m br「。n sequences for crustal evolution m odels. 9 0 . 八o rie Y . , 公 geo5丫肖创In ．5 10 P ha r ' s a , , I P on A f r (iii) Large parts of north-central and northern A frica are 11 M . - t- d e , 一‘一t.} ton 0 一 t卜．- .1 12 尺ok e lide s b as em e n 七 re - characterized by P an A frican m ineral ages and igneous J} . . . . 1 3 T ,r,,,n . B e lt activity, but corresponding penetrative tectonic effects are - } P on A f rl- A 二W e st A fric a C ra to n 一召 傀h.1 住1 overprtnt largely absent or not know n. I t w ould appear that in this 8 -Congo Craton In g C - K . i. h - C ,. to, region the Pan A frican event is solely m anifested by strong D = 住a st S a h a ro C rato n therm al activity and represents a period of elevated heat f lo w . Figure 2. A reas affected by the late Precam brian to early P alaeozoic (ca. 1100-450 M a) P an A 厂rican even t. A rabia is GO A m agm atic arc of considerable dim ension is situated in rotated to close the R ed Sea. M adagascar is in its tw o N E A frica and A rabia and, together w ith the adjoining older possible pre-M esozoic positions (m odified a厂ter K rUner, basem ent to the W est, constitutes the A rab ian-N ubian Shield. 19 79). T he extensive developm ent of thick caic-alkaline volcanic success}ons, togethe r w ith genetically related gral il im portant regions of the Pan A frican (such as in M ozam bique, sives and rrafic to ultral com plexes, at least in part of Zam bia, Tanzania, K enya, Ethiopia, Sudan, C entraJ-A frican ophiolitic affinity, m akes this Hijaz Arc (Fig. 2) the largest Republic, Tchad and C am eroun) is lacking and reliable age m agm atic province of the continentl. i ts rock types and data are not available . M ost w ork in recent years has tectonic relationships are unlike those of the other Pan concentrated on several "orogenic" belts such as the D am ara A frican terrains and m ost closely reflect conditions as seen and G ariep of N am ibia, the w est C ongo and K atanga belts o f in m odern island arcs (G reenw ood et al., 1976). C entral A frica and the D ahom ey-Pharusian belt of W est A frica (see K rU ner, 1979, for refe rences), and considerable The significance of these different types w ith a pparently international interest in the developm ent of the A rabian- contrasting tectonic evolution cannot be explained satis- N ubian Shield (A l-Shanti. 1979-80) has Jed to the e stablish - factorily at present, m ainly beca use detailed know ledge of m e n i in l 岁／岁 o T a n e w I七七 尸 v r o je c t ‘．

I A rabia is considered [Dart of the A frican continent in Pre-Tertiarv tim es. ‘ in e F roje c t, kn o w n a s "F a n 八tric a n c rusTa i e vo iu iio n in in e 八ra Dia n-N UD ia n })n ie ld " kN o . 16 4 ) is un d e r the direction of Project Leader P rof. A . A l-Shanti, Institute of A pplied G eology, P .O . B ox 1744, Jeddah, Saudi A ra b ia . E PISO D E S, Vol. 1980, N o. 2 4 (iii) there are no blueschist assem blages as in Phanerozoic b elts; Ov) there are no true ophiolites in m ost belts and there is also a conspicuous lack of calc-alkaline m agm atism except for the Pharusian belt of W est A frica and the H ijaz M agm atic A rc; M continuity of sialic basem ent can be dem onstrated or inferred in several belts; (vi) m ost collisional boundaries postulated by the m obilists are cryptic or are hallucino-sutures; (vii) Precam brian oceanic crust w as not subducted due to therm al constraints and W ilson-cycle evolution w as therefore im possible. T r·ansitional T ectonic Interpretation N ew field observations and laboratory results suggest tha t Spectacular slump breccia in carbonate unit o厂the m ioge- none of these contrasting view s are entirely correct, and that oclinal part o厂the C arAiep belt, sou-t4hern N am ib D eser4t, the Pan A frican event represents a transitional tectonic N a m ib ia . regim e between ca. 1100 M a and ca. 500 M a ago during w hich T e c to n i c M o d els both intraplate (ensialic) and plate m argin (W ilson-cycle) orogeny m ay have taken place m ore or less sim ultaneously in M obilistic Interpretations differen t regions of the continent as w ell as in G ondw ana as a E ver sin ce plate tectonics becam e fashionable , attem pts have w hole (K rU ner, 1979, 1980b). R ecent results seem to sub- stan tiate th is vie w . been m ade to interpret the evolution of the Pan A frican belts in term s of the W ilson cycle of ocean opening and closing. 1. A synchronous Even ts: The tectono-therm al evolution T he "orogenic" belts, in view of their pre-orogenic geosyn- during the P an A frican event w as m ore com plex than hitherto clinal developm ent, w ere seen in term s of collision 一f two assum ed and geochronology show s that it w as not synchronous continental m argins, w hile the high-grade m obile zones (such throughout the continent. F igure 3 gives a sim plified and as the M ozam bique belt) w ere regarded as the uplifted and com parative view o f individual regions on the basis of avail- subsequently eroded portions of basem ent reactivation result- able published and unpublished age data and it is evident that ing from c rustal thickening during H im alaya-type plate con- som e belts (such as the Katangan and M ozam bique) have a vergence (Burke and D ew ey, 1972, and further references in long and polyphase history, w hile others seem to display a K rU ner, 1977 and 1979). T he H ijaz A rc of A rabia w as seen as relatively sim ple and short tectono-m etam orphic develop- a prim e exam ple of pre-M esozoic ensim atic island arc grow th m ent (for exam ple, the Dahom ey belt). These apparently and lateral continental accretion (G reenw ood et al., 1976). "sim ple" belts w ill probably reveal a m ore com plex history These m obilistic interpretations received considerable w hen additional detailed isotopic dating becom es available. c ritic ism fro m tho se w h o sa w no o c ea n c lo su re a n d su bd uc - 2. O phiolites: A t Bou A zzer in M orocco and at several tio n in th e P a n A fric a n b e lts b u t fa vo u red a n "e n sia lic " localities in the A rabian-N ubian Shield in E gypt and Saudi evolution w ith crustal shortening in sialic-floored basins (see A rabia, ophiolites that probably represent obducted frag- K rUner, 1977, and M artin and Porada, 1977 for discussion and m e n ts o f la te P re ca m b ria n o ce a n o r ba c k-a rc b asin flo o r h a ve references). Their argum ents were that been identified. T he B ou A zzer com plex appears to be the m ost com plete and best preserved piece of ca. 790 M a old G) the A frican continent behaved as an essentially coherent oceanic crust (L eblanc, 1976), w hile other occurrences are unit during and before P an A frican tim es, as indicated by tectonically dism em bered but show m any of the typical palaeornagnetic data (see M cElhinny and M cW illiam s, 1977, elem ents of ophiolites such as chert, pillow lava, sheeted for discussion), thus ruling out la rge-scale m otion of indepen- dykes, layered gabbro, harzburgite and dunite w ith chrom ite dent cratonic plates; pods. M afic and ultrarnafic rocks associa ted w ith glauco- 60 if orogeny took place virtually sim ultaneously in all Pan phane-bearing schists and a possible trench m 6lange from the A frican belts as indicated by the then available geochrono- G ariep belt of coastal N am ibia have also been d escribed logical data, it is geom etrically and dynam ically im possible (KrUner, 1979; No.，in Fig. 2) and these m ay constitute a that all belts resulted from collision ; dism em bered ophiolite.

F i g u r e 3. T he tem poral distribution of ign eous, m etam orphic and tectonic activity in the dif eren t P an A 厂rican terrains. B lack bars',denote approxim ate tim es of individual episodes or phases. Last colum n show s 1M4956780120Da0O -} X -GEAdEFoRIDMLa1CYA7NtM} RA2 &1Ia R_oF 7NICAMT7k.SAI Gf SL}NB-EIRGE 1,Vr4.P GL2_}FRP-oTA 1OU 'ESmPEs - aINlENlCL%AEU RKOArMDSLNAElY-RpCeTE, lUAR }EgN.IL.FG-ICTiA EISoEMN BO- nEI }N9-yLEsT 1}SME c 1o C1Xm1 -&m1EaW A1F}bRE}_O. ILS.Hc_YiT -IMn_.C -R -N_TCOLKIe7-OIcN I7.OmdG}AIRNFSj7CEO-GT.E} 7PO B-}.ET7 LB CETMCa . s eMIdGDW E}UDOLP} SLoAPYHE }nCR O M_IO}EITF L}MpYI NSTGAu BENI E-P AbLIN-TSW lE iE sI h - }e -SdG-}EFA}TO -RISaLR-NIYNH gRI-O TICM' GEN-e 'GCES-sTAs I-BRENdA -ISUP -P}aI N S- tEa - ([M X}aI MOv}M aLWAN FiN}M1lTCP }.EOaI -S-AI bSTT.S I1MLTEOl1 AINe CS EfV E Nr To xX m O POHSP IAHt OUL[OhDILTjIEeTi SAECF SNRA aA B u IA t h or D1ToM1U "R0nZ7mS.AI_[ MT,rBc'OI l-eI TDNQIlL,qUI' OENw FuOD CB M,eEN TLEs TR Ct , )r .E NTIRE} P A1N A F-R ,I C A N E PISO D E S, Vol. 1980, N o. 2 5 M odels w ere therefore proposed w hich entailed the genera- tion of an ensialic geosynclinal basin through crusta l attenu- a tion w hich w as subsequently closed follow ing subcrustal delam ination and continental subduction (M artin and Porada, 1977; K rUner, 1979 and Fig. 4). Such a process, long repulsive to theoretical plate tectonicians w ho rejected the "subductibility" of continental crust, is now also considered a likely m echanism for crustal shortening in the A lps, the A pennines a nd the C olorado P lateau (see discussion in K rU ner, 1980b) and is nam ed A -subduction in honour of 0 . A m pferer w ho first suggested "V er schl ucku ng" of continental crust as a likely cause of orogenic deform ation.

鬓Layered 薰gabbro from m afic-to-ultram /a19 厂7iAc' com plex at R abigh, north o厂 Jeddah, Saudi A rabia. This un it is overlain by sheeted dykes and pillow lavas and probably constitutes part 0厂an ophiolite com plex. T he identification of dism em bered ophiolites in A rabia and E gypt occurring in association w ith calc-alkaline volcanics w hose chem istry and Sr-isotope system atics are indicative of island arc environm ents leaves little doubt that plate tectonic processes, probably sim ilar to those of the present- day Pacific O cean, m ay have operated in the late Precarn- brian. D etailed m odels of the crustal accretion process vary betw een A ndean-type, m arginal basin and ensim atic evolution and are the subject of international m ultid isciplinary research w ithin IG C P Project N o. 164. Lim ited palaeo- m agnetic data for A rabia and Egypt indicate that these regions w ere part of the A frican plate by about 600 M a ago (M cW illiam s, 1980) at w hich tim e the accretion process m ust have been virtually com pleted. 3. P assive and A ctive M argins: T he P an A frican assem blage in M ali and A lgeria (No. 10 in Fig. 2) appears to have all the attributes of a passive continental m argin (along the W est A frican C raton) and an active m argin (along the Tuareg Shield) w hich collided about 600-650 M a ago (Caby et al., 1980). W hether a w ide P an A frican ocean w as destroyed during this process is uncertain, but considerable volum es of calc-alkaline volcanic greyw acke and related intrusives argue for som e subduction and generation of arc assem blages. 4. E nsialic Fold B elts: !n contrast to the collisional orogeny w hich produced the Pharusian belt of the W estern H oggar, the apparently entirely ensialic T iririne fold belt (N o. 13 in Fig. 2) with up to 8000m of clastic sedim ents w as form ed so m e w h a t la te r 一 a t a b o ut 6 00 M a in the e a ste rn H o eR a r kn e rira n a e T a i., 1，／己）· in e ito o r o i TniS De iT is m a ae up 0 1 pre-Pan A frican basem ent, and basin form a tion w as probably related to crustal stretching during uplift after collision in Figure 4. Sim plified and schem atic sections showing sug- the Pharusian belt, w hile deform ation can be related to gested evolution o厂 the apparently ensialic Pan A 厂rican intraplate crustal shortening as a result of further collision D am ara belt o厂N am ibia through crustal thinning, delam ina- and continental subduction farther w est, sim ilar in principle tion and intracrustal A -subduction . For detailed explanation to th e R e c en t d efo rm a tio n in T ibe t an d in th e T ie n -Sh an 三of m odel see K rUner (1980b). following continental collision of India with A sia (Caby et al., 1980). The results of detailed palae o m agnetic w ork in the D am ara belt and on the tw o adjoining cratons are incom patible w ith 5. O cean O pening and C losure: E vidence for lim ited ocean any postulated large-scale relative m otion of independent opening and closure w ithout svbduction of oceanic crust is plates betw een ca. 1000 M a and 600 M a ago (Fig. 5a) and thus accum ulating for several Pan A frican belts of southern and support the above m odel (M cW illiam s, 1980). central A frica. The D am ara belt of N am ibia is particularly interesting in this respect since it has m any sim ilarities w ith Sim ilar conclusions can be reached for the W est C ongo belt such Phanerozoic orogens as the A lps in containing w ell (No. 8 in Fig. 2) whose northern part consists of a broad defined m iogeoclinal and eugeoclinal rock assem blages w hich ensialic basin w here field relationships clearly reveal conti- w ere intensely deform ed during several pha ses of orogenic nuity of older basem ent under the Pan A frican geosynclinal activity. These produced polyphase m etam orphic rocks, large sedim ents and no suture seem s to be present (C ahen, 1978). am ounts of syntectonic and post-tectonic granitoids and Perhaps this be滚t evolved through a w edge-shaped opening spectacular nappe em placem ent in the southern foreland of and closing of a rift-related basin w ith the rotation axis close th e b e lt. to its northern m argin. F or the K atanga belt of southeastern In v iew o f the a b se n ce o f c alc -a lka line v o lca n ics o r v o lc a n ic - Z aire and Z am bia, the available data also poin t to an ensialic derived sedim ents and ophiolites (only a discontinuous belt of evolution, particularly since the geosynclinal strata consist am phibolite is know n from a flysch trough in the south), and exclusively of sedim ents and syn-to post-tectonic granitoids the proven continuity of pre-D am ara basem ent from the are alm ost com pletely lacking. north into the Centre of the belt, the destruction of a large 6. M etam orphic M obile B elts: T he high-grade m obile belts ocean is considered unlikely during the D am ara orogeny. such as the Zam bezi and M ozam bique have received little

E PISO D ES, Vol. 1980, N o. 2 厂朴 ＼ ／ GO N DW AN A LA ND 挤薰滩 W E S下 G O N肠叭 朋 (AFRICA AND I 口日月 韶 1-5 90A 咤 S. AMERICA) ． 0 1 口 一0 口 ＼ ～一 ～一 ．1 ． B钾S ， 、 炸一一4* W}. NZ 'F . 产、、、、、

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舀 口I ‘ 宁 5 E AS T G ON D WA NA ， A 日下门么日月 ． C O N G O (AUSTRAL IA A . IC A ． LvB ． INDIA K A L A H A R I IN D A O A ND A N TA R C下ICA 5,A . E阅沁西 口 八N T A R C n C 月△ a ） b ） F igure 5．(a) A pparent polar w ander path (A P W P) for the K alahari and C ongo C ratons for the period ca. 1100- 700 M a ago, suggesting that no large-scale m otion of these crustal blocks relativ e to each other has taken place during that tim e (from M cElhinny and M cW illia m s, 1977). (b) Pan A frican A PW P for E ast and W est G ondw ana suggesting a collisional event in latest Precam brian to early Palaeozoic tim e (see also Fig. 1) from M cW illiam s et al., in press. attention in recent years, and K rU ner (1977, 1979) proposed endow ed and so far produce la rgely pegm atite m inerals. T he an evolution follow ing intraplate distortion w ithin the la rge "geosynclinal" sequences contain either syngenetic stratiform proto-G ondw ana supercontinent. H ow ever, at le a st t h e m assive sulfide deposits, probably related to subm arine fum a- M ozam bique belt contains several m afic to u lt ra m a f ic rolic exhalations, or stratiform K upferschie fer-type m inerali- com plexes that som e researchers liken to tectonized ophio- zation found in specific pelitic horizons of the stratigraphic lites, and new palaeom agnetic data suggest that A frica and sequences. It m ay w ell be advisable to launch m ajor m ineral at least A ustralia w ere not part of the sam e continent in P an exploration surveys in the P an A frican belts of W est A frica A frica n tim e s b u t see m to h av e b ee n in vo lve d in a co llision to search for sim ilar deposits. about 550-600 M a ago (M cW illiam s, 1980, see also Fig. 5b). it is possible that the M ozam bique belt reflects this event and T he K atanga and D am ara belts are also m ajor producers of constitutes the leading eastern edge of the P an A frican uranium and, in the latter, m ineralization occurs in co n tin en t w ith th e su tu re no w co n c ea led so m e w he re e a st of pegm atites and alaskitic granites w hich have now been found M adagascar. to represent rem obilized (ca. 2 G a old) basem ent. , T his W hatever the de tailed m echanism , current inform ation on justifies a new look at the large areas of reconstituted these belts is inadequate for a reliable geodynam ic inter- basem ent and Pan A frican granitoids in the M ozam bique belt and in north-central A frica w here sim ilar ore deposits m ay be pretation and it is hoped that IG C P P roject N o. 164 w ill provide new insights from w ork in N E A frica. expected. T he H ijaz A rc contains sm all deposi ts of gold in the ophiolitic 摹一摹赘鑫臀蒸滩蒸辨翼馨馨馨 翼翼攀攀馨摹缨翼 zones and sm all m assive sulfide occurrences of K uroko-type have also been discovered. Exploration here and in neigh- bouring E gypt, Sudan and Y em en m ay locate further deposits, but the m ain target should perhaps be the search for porphyry copper deposits of the type know n from post-M esozoic sub- duction-related m agm atic a rcs. C o n clu sio n s T he Pan A frican belt system displays evidence of a com plex crustal evolution w hich took place in several phases during the period ca. 1100 M a to about 450 M a ago. Som e belts clearly indicate that m odern-type plate tectonic processes w ere already at w ork in the late P recam brian, w hile other regions suggest a developm ent not involving plate separation and subduction of oceanic crust. If this is correct, the P an A frican m ay represent a tectonic regim e transitional betw een predom inantly intraplate deform ation of the older Precam brian and predom inan tly plate m arg in deform ation of the P hanerozoic. The first occurrence of true ophiolites w ith A . K rU ner takes core sam ples for palaeom agnetic w ork along evidence for sea-floor spreading (sheeted dykes) m ay signify the edge of the F ish R iver C anyon in southern N am ibia. The this change in global tectonics and one m ay speculate that flat-lying sedim en ts belong to the late P recam brian low er P4n A frican crustal evolution also reflects a change in the N om a G roup and contain an Ediacara-type faun a. m antle convection system as a result of the continuous d e clin e in he a t flow fro m th e in te rio r o f the ea rth . P an A frican Belts and o re D eposits T h e d iscu ssio n o n P a n A frica n tec ton ism w ill n o d o ub t There is little doubt that the "orogenic" belts and the H ijaz M agm atic A rc constitute, econom ically, the m ost im portant continue, though tw o general conclusions should be borne in regions of the Pan African. Clifford (1966) observed that a m in d : large proportion of A frica's base m ineral w ealth occurs in 0 ) T he duration of the Pan A frican event (550 M a) exceeds belts of southern and central A frica, w hereas the high-g rade that of Phanerozoic orogenies by 100 per cent or m ore. T his structurally reconstituted zones of E ast A frica are less w ell and the considerable duration of individual tectonic episodes

EP ISO D E S, V ol. 1980, N o. 2 7 (Fig. 3) suggests that tectonic processes were slower than in L astly, in com ing back to the problem of definition of the m odern collision system s and m ay therefore not have P an A frican, som e w ant the term restricted to the continent- produced m ountain belts (G audette and H urley, 1979). w ide peak of m etam orphism at 500+50 M a; others wish to include the entire tectogenetic cycle from deposition to final (ii) The generalized application of W ilson-cycle m odels as consolidation. K ennedy (1964) clearly m eant to specify the proposed for P hanerozoic collision belts m ay perhaps not be entire structural differentiation o f an original shield into justified in view of the increasing evidence favouring non- orogenic a reas and, according to present data, this started uniform itarian crustal evolution through tim e (KrUner, betw een 1100 M a and 1000 M a ago. In this sense, the Pan 1980b). This is not to say that plate tectonics did not operate A frican constitutes one of the m ajor crust-form ing events of during the P recam brian , but it is likely that som ew hat dif- earth history, and the term should therefore be applied ferent plate interaction at that tim e produced different accordingly. Individual episodes of the P an A frican should be effects in the rocks that w e now see, and the excellent nam ed after the areas in w hich they are observed, as, for exposures in som e P an A frican terrains should enable us to exam ple, the D am ara, K atanga, and P haruslan episodes. It decipher this process. m ay eventually also becom e advisable to extend the term to 酥了咬 二认分 一 分 臼卜 oth er G o n dw an a c on tin e n ts o r to d e vise a ne w n a m e tha t could be applied to all these regions.

R ecent and forth com ing m eetings w ith em phasis on Pan A frican geology: February 6-16, 1978: Sym posium on Evolution and M ineraliza- tion of the A ra bian-N ubian Shield. Institute of A pplied G eology, K ing A bdulaziz U niversity, Jeddah, Saudi A rabia, convened by A .M .S. Al-Shanti (Proceedings published in 4 volum es 1979-1980 for Institute of A pplied G eology by Pergam on Press, O xford). O ctober 6-15, 1979: 5th C onfe rence on A frican G eology. G eologica l Society of A frica, G eological Survey of E gypt, C airo. Papers w ill be published in a special issue of the A nnals of the G eological Survey of E gypt. Tectonic m 6lange associated w ith m a厂ic volcanic rocks 。厂the G ariep belt near A lexander B ay, South Africa. The dark A pril 198 1: Ilth C olloquium on A frican G eology. D ept. of rocks are sheared basaltic andesites and tuffs, the light rocks Ea rth Sciences, The O pen U niversity, M ilton K eynes, U .K . a r e m a s s iv e d o lo m it e b e d s a n d le n se s . F o r furthe r in fo rm ation c on tac t D r. A . R ie s a t th is a d d re ss.

R efe ren ce s A l-Sh anti, A .M .S. (C onvene r), 1979-90, E volu tion a nd m ine r- P rotero zoic 一 Lo w er P aleozo ic stru ctural history of K rU ner, A ., 1980a , C hro nologic evo lu tion of the P an-A frican alizatio n of the A ra bian-N ubian Shie ld . Procee dings o f a sou the rn A fric a: G eol. Soc . A m erica , Spec . P aper 9 2, D am ara be lt in N am ibia, southw e stern A fric a, in sy m posiu m : P e rgam on P ress, O x ford, 4 vols. 100 P. N eum ann , J. (ed .), M obile ea rth. Fina l re port of the G eod yn am ics P ro je ct, F ede ral R epublic of G erm any: B ertrand, J.M .L ., L anc elot, J.R ., M ou ssin e-P ouc hkine , A . and F leck , R .J., G reen w ood , W .R ., H ad ley, D .G ., A nde rson, R .E . B o ld t V erlag , Bo ppard, in pre ss. Sada llah , A ., 197 8, T he late P an-A frican intra continental and Sch m id t, D .L., 19 79, R u bidium -stron tium g eochro- linear fold b eit of th e e astern H o ggar (cen tral S ahara, n ology and p late tectonic evo lution o f the so uthe rn pa rt K rUne r, A ., 1980 b, P re cam bria n plate tec tonics, in K rU ne r, Algeria): geology, structural developm ent, U-Pb geo- o f the A rabian shield: U .S . G eol. Su rv . Sa udi A rabian A . le d.), P re cam brian p late tec tonics: E lsev ie r, chronology , tec ton ic im plicatio ns for th e H og gar sh ie ld: Project, R ep. 24 5, 105 p. A m sterdam ,里J竺旦丝· P rec am brian R es ，v. 7, p. 3 49-376. G a ss, I.G ., 19 77, T he e vo lution of th e P an A frican c rystalline Le blanc, M ., 197 6, P rote rozo ic ocean ic c rust at Bo u A zze r: B esso les. B ., 19 77. G 6o lo eie de I'A friaue : Le c raton ouest- b ase m e nt in N E A frica and A rabia: I G eol. S oc. L ond ., v . N atu re , v . 2 61, p. 34-35. africain : B ur. R ech . geo l. m in . F rance, M em . 8 8, 402 p. 134, p. 129-138 . M artin, H . a nd P o rad a, H ., 1977, T he in tracra ton ic branch o f Black, R., 1978, Propos sur le Pan-Africaln: Sec. g6ol. G au dette, H .E . a nd H urle y, P .M ., 197 9, W here w e re the Pa n- the D am ara oro gen in So uth W est A frica : P re cam bria n F rance , Bu ll, v . 20 , p . 8 43-8 50. A frican m oun tains? N o evide nce of 500 M .Y . d etrital R es., v. 5, p . 3 11-3 57. z ircon s: Te cton ophysics, v . 5 4, p. 21 1-230. B urke, K .C . a nd D e w e y, J.F ., 1972, O rog eny in A frica, in M cE lhinny, M .W . a nd M c W illia m s, M .O ., 1977, P re cam brian Dessauvagie, T.F.J. and W hitem an, A.J. (eds.), African G r eenw ood, W .R ., A n derson , R .E., F leck , R .J. a nd Sc hm idt, ge odynam ic s 一a paleom a gnetic view : T ectonop hysics, v. geolog y: lb adan U niversity P ress, lbada n, p. 583-608. D .L ., 1976, L ate Prote rozo ic c ra toniz ation in so uth - 4 0, p . 137-160. C aby, R ., B ertrand , J.M . and B lack , R ., 198 0, P an-A frican M cW illiam s, M .O ., 19 80, P alaeom ag netism and th e Preca m - ocean c losure and con tinen tal collision in the H ogga r- w51e5s-te5r:军．Saudi Arabia: Phil·丁rans.“·SCc.'‘·280A, p. b rian tectonic evo lu tion of G on dw ana , in K rU ner, A . (ed .), Iforas segm e nt, cen tral Sahara, in K rUne r, A . (ed.), Pre- K en nedy, W .Q ., 1964 , T he stru ctu ral d iffe ren tiation of A frica Precam brian plate tectonics- Elsevier, A m sterdam , 些 cam brian pla te te cton ic s: E lse vie r, A m sterda m 过几卫哩竺· in the Pan-African G 500 m .y.) tectonic episode: Res. E上e兰互． C ahen, L ., 1978 , La Stratig raph ie e t la tectonique du Supe r- Inst. A 犷r. G eol., U niv . o f L eeds, 8th A nn. R e p., p. 48-49. M cW illiam s, M .O ., M c Elh in ny, M .W . and K rUn er, A ., Pan groupe O ue st-C ongo lien da ns les zo nes m ed iane et K rU ne r, A ., 1977, Preca m b rian m ob ile b elts o f southern and A frican tec ton ic s: e vidence fro m paleo m agnetism : E arth externe de 110 rogen ese O ue st-C o ngolien (P an -A fricain) au eastern A frica 一 a ncien t suture s or sites of ensialic P la net. Sc i. L ett., 些J芝兰 s B as-Za ire et dans le s re Rions voisine s: M u s. rov. A fr. m ob ility? A case for cru stal evolu tion tow ards pla te centre ., Te rvu ren , A nn ., Serie in -8 *, Sci. G e ol., no. 8 3, tecto nics: T ectonop hysic s, v. 40, p. 10 1-135. M ore), P. and Irving , E ., 1978 , Te ntative paleoc on tine nta l 150 p. m a ps fo r the ea rly P hanerozoic an d Prote rozo ic: J our. K rU ne r, A ., 1979 , Pan -A frican m o bile be lts as eviden ce for a G eol.. v. 86. D. 53 5-56 1. C liffo rd , T .N ., 196 6, T ec tono-m e tallogen ic u nits and m e tal- transition al tecto nic regim e from intrapla te o roge ny to logenic p rovinc es o f A frica: E arth P lan et. Sci. L ett., v. 1, plate m argin orogeny, in Tahoun, S.A . (ed.), Evolution and V ail, 3 .11 ，1964, Th e M oza m bique be lt of e astern A frica : R e s. p. 42 1-434. m ineralizatio n of the A rabian-N ubian shield: Pe rga m on Inm M r. G eo l., U n iv. Le eds, 8 th A nn. R e p., p . 3 2-34 . C liffo rd , T .N ., 1967, T he D am aran e pisode in the U pper P ress, O xfo rd , v . 1, p. 2 1-37.

A B O U T T H E A U T H O R : P rofessor of G eology and currently C hairm an of the D epartm ent o f G eosciences at the U niversity of M ainz, F ederal R epublic of G erm any, D r. A lfred K r8ner started w ork on the P recam brian geology of southern A frica as Senior R esearch F ellow of the P recam brian R esearch U nit, U niversity of C ape T ow n, South A frica, afte r receiving his P h.D . there in 1968. H e has travelled w idely in A frica and his research interests include A rchaean and P an A frican crustal evolution. A fter returning to G erm any in 1977, he continued his w ork in A frica and also becam e involved in research in Saudi A rabia. H e is one of the coordinators for the C G M W Tectonic M ap of A frica, a m em ber of the 1U G S 蘸 Subcom m ission on Precam brian Structural Type R egions, as w ell as a participan t in several IG C P P rojects.

E PISO D ES, V ol. 1980, N o. 2 8