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Pan African Crustal Evolution 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 uran ium enrich m en t in certain areas and are proDaw y retated to _7 -_ , --A -- I . T'4 -Ir-- f :_ - --Z}-Z] 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 i<s w e re In recent y ears, considerable research has taken place in apparently affected by an intense therm al event that caused th ese P a n A frica n te rra in s an d it h as b e c om e c lea r fro m granitization and reset radiom etric clocks. H ．e therefore w hole-rock and zircon isotopic data that deform ation, hesitated to apply the term "orogeny" 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. * This is an updated and m odified version of a paper presented at the 5th C onference on A frican G eology, C airo, E gypt, O ctober, 1979. E P ISO D E S, V ol. 1980, N o. 2 3 厂一了、竺川洲 州· 尸牡 二曰 Mal,点：：欢 -a 、『 〔二 召黯一默赶念t丫｝盆粼：、 尸 P},I L ! N一r 1l C ｝ “e ，t Al , - 曰} t- ｝｝ ( ,g,,沙1, 11 ｝11 肠｝d队〕叫 八 。 rl ｛V 加声 。一加 ， 舀 。 ｝，〕．1d V Sa} F,,,. ..1 1 C, 1-- V ｝ 11}- 1,111- 11 311, d V ｝ A自t},ct" S- ij V 川 A ustral- S- 1d Ix Chir- W eld x S,}, 「：S- 1d ，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.
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