La t e Ter t i ar y t o Quat er nar y Tec t oni cs o f I r i an J ay a by D. B. Dow and R. Sukar nt o Bet ween 1 978 and 1 982 a t eam o占Au6 tal f i an and Du t ch t e am ( Do zy , 1 93 8) dur i n r an a t t empt t o cl i mb t he I n d o n e s t a n g e o l o g i s t s c at t i e d o ut。ma 了 o - t ma p pt n g hi ghest mountai n i n I ri an Jaya, now named Puneak Jaya. The J a y a t n wnt e t nmo6 t I n d o n e s i a. Th i s a t t i c l e de 6 c t - i f i n t h e人 i e扭t echni ques us e d an d s ummat i zo t he 6 成ent i - maj or l odes i n the wor l d, though becaus e of i ts ext raor - di nari l - y remote l ocal i t y at an el evati on of over 3, 000 m, 6 t c i e s u l N i n c l u d i n g t h e t e c o g n i t t o n I , I o 6 t h e Me l a n e s i a n i s al so one of t he hi ghes t i n t he wor l d. p i o j e c t i n h i t h e i t o g e o l o g t c a l l y u n k n o wn p a i t 6 o 6 ti f a n 0t oqe ny,田h之 ch be gan t n工 he机不 es Mt o cene ana mi ne devel oped her e has si nce Dr oved t o be one of the ri ches t di r e ct l y bel ow t he i c ec ap of Pu ne ak J a ya, i t s c os t s t r u ct ur e Introduction Unf ort unatel y our wor k had to he suspended f or securi t y reas ons i n 1982, by whi ch ti me onl y the west er n hal f of the pr ovi nce had been mapped at 1 : 250, 000, However, we have been abl e t o compi l e a reas onabl y rel i abl e veol oVi cal map at 1: 1, 000, 000 s cal e of the whol e r egi on i ncl udi ng the east er n hal f of t he Drovi nce. Thi s was pos si bl e because t he 1 : 100, 000 ai r photos, i n combi nati on wi t h t he LANDSAT i mager y, s how Unti l recentl y I r i an Jaya, t he I ndonesi an pr ovi nce coveri ng r esul t s of wi del y spaced tr aver se done duri ng oi l expl orati on co nt i nues to day. Thi s t nvo l ve6 cont empot aE y undet - t h , 二, t i n g o } t he Au 6 t i a i i an c o n t i ne n t b y t h e l p a c i } i c Pl at e一a p- z ocea t h at i s expz n6 ed on t he 6 uz 石 ace by 6 hal e di api - t i 6m, mud vo l c anoes and act t ve占 aul t i ng. t h e we s t er n h al f o f t he I s l a nd o f New Gui ne a ( P i . g . 1 ) , was one of t he l eas t expl ored revi ons i n t he worl d. The mai n r eason f o r t hi s i s t h e v er v di f f i c u l t ac ce s s po s e d b y t he wi de f r i nge of j un g l e - c ov er e d s wamp s a n d D l ai n s , an d f a r t h er i nl an d by the rugged mount ai ns of t he Centr al Range, where the bul k of t he popul ati on l i ves. t he ma j o r f e at ur es o f t he g eo l og y re mar ka bl y we l l . Th e ( Vi s s e r a nd Her me s , 1 96 2) wer e al s o h e l pf ul . Wo r ki ng i n I r i an J ay a Except for smal l networks ar ound the few coast al towns, t he r e a r e no r o ad s i n I r i a n J ay a, s o gr ou nd t r a ve l i s i n v ar i ab l y di f fi cul t . Access to t he j ungl e-covered swamps and pl ai ns i s By the ear l y 1960s, most of the countr y wi t h hydr ocar bon pot enti al had been geol oFi cal ly mapped by oi l compani es ge ner al l v l i mi t ed t o me an de r i n g r i v er s , an d t h es e a r e ( Vi s s e r a nd He r me s, 1 96 2 ) , bu t t he mo unt ai no us hi nt e r l an d Th us t he on l y pr ac t i cab l e way t o ga i n a cce s s t o t he mo un t ai ns i s t o f l y by l i gh t ai r c r af t t o t he man y s ma l l was sti l l most l y unknown. A contr i buti ng factor has been a l ack of rel i abl e maps : over l ar ge areas the avai l abl e t opographi c sheet s ar e wi l dl y i naccurate. A great advance was made when ai r phot os at 1 : 100, 000 scal e were acqui r ed by a defence cooper ati on pr oj ect between t he I ndones i an and Aus tr al i an gover nments , and, al t hough l arge areas i n the east are us ual l y cover ed i n cl oud and were theref or e not p ho t o gr ap hed , c l o ud- f r e e LANDSAT i mag er y i s a va i l a bl e f or many of thes e gaDs. By 1978 arrangements wer e f i nal i zed between t he I ndonesi an and Austr al i an government s to undert ake a geol ogi cal survey o f I r i a n J a ya as D ar t o f Aus t i t a l i a' s bi l a t er al ai d pr og r am under the auspi ces of the Aust ral i an Devel opment Assi stance Bu r e au . Thi s pr oj e ct wa s a gr e at ch al l e n ge t o o ur t e am of ge ol ogi s t s f r om t he I nd on es i an Ge ol ogi ca l Re s e ar c h a nd De ve l o pmen t Ce nt r e ( GRDC) an d t he Au s t r al i an Bu r e au of i mpassabl e as soon as the hi nter l and mountai ns are reached. ai r str i ps servi ng l ocal admi ni s tr ati ve cent res and chur ch mi ssi ons. Fr om here one mus t wal k, and i n the popul at ed hi ghl ands ther e i s a networ k of tr acks whi ch al l ow r eason- abl e, i f arduous , tr avel . However , where t he mount ai nous Figure 1: Locality map. The island of New Guinea is traditionally likened to a bird with a head, body and tail 。 1 1 达 嚎 ‘ 二) r egi on. body 犷 乡 N EW 七 JAYA e l GUI NEA | | V 1 over l yi ng the Aust rali an conti nental cr us t i n I ri an Jaya was by t hen wel l known, especi al l y i n t he west where commerci al oi l deposi ts had been found. The natur e of the deformed nort hern margi n of t he cr ust was, however, an al most BANDA SEA 4} PA PUA 、1 Th e g eo l og y of t h e Mes oz oi c a nd Te r t i a r y s e di me nt a r y b as i ns 叱立 IR I AN Mi neral Res ources ( BMR) when i n 1978 we commenced work i n t h e we s t er n e xt r emi t y of t h e i s l a nd, t h e Bi r d' s Hea d ; 5 。 。 I SLAND O F NEW GUINEA 弓;之 二卜 400 km . I . 1 1 1 C c ompl et e my s t e r y. Th e g r ea t po t e nt i a l of t hi s r eg i o n f or mi ner al deposi t s was demons trated as ear l y as 1936 by the chance di s cover y of t he Er ts ber g copper-gol d deposi ts by a Epi s odes , VoL 7, No. 4, December 1984 16/09门 62 3 extrapol ati ng the per year ( AAPG 1981 ) back i n ti me t o the Mi ddl e Pl ei s tocene. of 125 ki n c o nv erae nc e obt ai ned by oostulated pr esent -day rate of 12. 6 cm M ai n Crustal El ement s The s ou t he r n p l ai n s an d s wamps o f I r i an Ja va a nd mo s t of t he Bi r d' s Head are underl ai n by stable Aus tral i an conti nental cr us t ( Fi g. 4) , whe r ea s t he no r t h co as t mar ks t he s o ut he r r l i mi t of s i mi l ar l y l i t t l e - d ef o r me d o ce an i c cr us t o f t he Paci f i c Pl at e. Th e i n t e r v eni n g be l t o f def or ma t i on, whi ch mak es u p mo s t of t h e bo dy of t he bi r d, i s t he wes t e r I V extensi on of t he New Gui nea Mobi l e Bel t of Dow (1977) . 攫 嘿 5o} Figure 2: A difficult landing site. The helicopter made a one-skid landing using t he large boulder on Though i t i s mos tl y covered by sea, the composi ti on of the Paci fi c Pl at e here i s known f rom outcrops on the nort h coast a nd o n t he out l yi ng i s l an ds . The s e r oc ks a r e al l r e mar ka b l y si mi l ar i n mi ner al ogy and repres ent t he wester n conti nuat i on of the Oceani c Cr ust and I sl and Arcs pr ovi nce of Papua New Gui n e a ( Dow, 1 9 77 ) . The y c on si s t o f pe r v as i ve l y al t er e d, basi c to i ntermedi ate i s l and-ar c vol cani cs and subor di nate t力 户 left. o cea ni c ba s a l t s of Up pe r Cr et ac eo us an d Pal ae og ene a ge . c ou nt r y i s un po pul at ed o r ha s on l y a f e w s e mi - n omad i c t r i b es , l a i n b y Mi ddl e Mi oc en e r ee f l i me s t one ( i n pl a ce s wi t h l at e Lower Mi o ce ne at t h e b as e ) an d mar l a nd y ou nge r e l as t i c wal ki nL y tr acks ar e al most non-exi stent, and t ravel by f oot i s Throughout t he pr ovi nce, t he i sl and-ar e vol cani cs ar e over - sedi ment s. Ul t ramafi c rocks are exposed al ong maj or zones e xt r eme l y di f f i cul t a nd t i me co ns umi n g. of di sl ocati on but are not extensi ve. To overcome t hes e obst acl es the proj ect adopted traverse The Austr al i an conti nent al rocks consi st of a bas ement of t ec hni ou es us e d s uc ce s s f ul l y by BMR dur i n g t he ma ppi ng of a dj oi ni ng Pa pu a New Gu i ne a i n t he pr ec edi ng d ec ad e, us i n g mai nl y fi ne-gr ai ned, hi ghl y i ndurated, and i n pl aces hi ghl y sheared, Pal aeozoi c sedi ment ar y rocks. Thes e are overl ai n l i ghtl y l aden, mobi l e, par ti es posi t i oned by hel i copters b y s he l f s e di men t s f r om 6 t o 8 ki n t hi ck , r an gi n g i n a ge f r om ( Fi g. 2 ) . Th e gr ou ps , ea ch co ns i s t i ng of on e or t wo ge o l og i s t s l ate Pal aeozoi c t o mi d-Ter ti ar y. The Mes ozoi c r ocks are and three t o fi ve por ters, then f ol l owed predetermi ned mai n l y el a s t i c s edi me n t s , wh er ea s t h os e of Ter t i ar y a ge ar e r ou t es , ge ne r a l l y f o l l o wi n g r i v er s or s t r eams , on t r a ve r s e s al mos t excl usi vel y shel f l i mest one. t hat occupi ed t hree to seven days . However , i n ar eas devoi d of hel i copter l andi ng si t es, treks up to 10 days dur ati on wer e oft en needed. I n thes e l atter areas i t was usual l y neces sary The boundar y between t he New Gui nea Mobi l e Bel t and the a t t h e en d o f a t r av e r s e t o c u t he l i c op t e r l a nd i n g p ad s ou t of t he j u ng l e, a t a s k t ha t ca n t ak e u p t o a da y an d a h al f of v e r y h ar d wor k. At t he e n d o f one t r ave r s e t he pa r t y r et ur ne d t o camp to record the obser vati ons and pr epare for the next one. The work was cert ai nl y no pi cni c and t he fi el d work woul d not have been pos si bl e wi thout the cooper ati on of the l ocal i nh abi t a nt s ( Fi g . 3) who act ed as gu i de s an d p or t er s an d s ha r e d al l t he d i f f i c u l t i e s a nd har ds hi ps wi t h f or t i t ude an d Paci f i c P l at e i s a comp l e x f a ul t z one o f gr ea t ma g ni t ude ( Fi g. 4 ) . I n t he we s t t hi s i s ca l l e d t h e Sor on g Fau l t Zo ne , wi t h pr oven l ef t l at er al di s pl acement of over 350 ki n. To the east t hi s f aul t i s of fset to t he sout h and s ucceeded by the Yapen Faul t Zone, whi ch because i t i - s covered by the sea or recent al l uvi um i s not wel l known. Farther eas t agai n the faul t zone i s al s o off set t o the s out h and conti nues i nt o Papua New Gui ne a a s t he Bewan i - To r r i c e l l i Fau l t S ys t em of Hut ch i s o n an d Nor v i ck ( 1 98 2, unp ub l i s he d) . Fo ca l pl ane s ol u t i o ns ( Ri pp er , 1 9 75 ) i nd i c at e t h at t h i s s ys t em i s a l s o good humour . I t i s al so a tri bute to the st ami na and competence of the t eam member s一and the hel i copt er pi l ots predomi nantl y l eft l ateral . i l l n es s or ac ci d en t . Al t ho ug h ou r mai n ai m of ma ppi ng t h e Ce nt r al Ra nge a nd f i ndi n g ne w mi ner a l de po s i t s was no t a ch i ev e d, t h e geo l o gi ca l r e s ul t s of t he ma ppi ng ha ve t h r own mu ch new l i g ht on one o f t he f ew co nve r gen t p l at e Figure 3: Indonesian geologist questioning villa- gers high on the northern slopes of t he Central Range. 一 that f our fi el d seasons were car ri ed out wi t hout s eri ous boundari es exposed on land. The Maj or Pl at e Movements Th e pr es en t f o r m of I r i a n J a ya h as be e n s ha pe d ve r y r e ce nt l y by profound ear th movements t hat star ted i n t he l at est Mi ocene and conti nue t o the present day. Thi s Mel anesi an Or og en y ( Dow a nd Su ka mt o, 1 98 4 ) i s t he r e s u l t of co nve r gen ce be t we en t h e Paci f i c and Aus t r a l i a n p l at es . The crus tal adj us tment i nvol ved has been extr aor di nari l y compl ex and i nvol ved the i nt er acti on of many smal l cr us tal f r ag me nt s . Howev er , t h e geome t r y o f t h e maj or s t r uct ur es , al l of whi ch are compressi onal , i ndi cat es t hat the conver - g enc e i s r o ug hl y t o t he s o ut h we s t ( Do w an d Suk amt o, i b i d ) . Thi s di r e ct i on c or r e s p on ds c l o s el y wi t h t h at po s t ul at e d b y Mi ns t e r an d J or da n ( 19 78 ; s e e a l s o AAPG, 1 981 ) . The r e i s no e vi d enc e t ha t t h e d i r e c t i o n h as c ha nge d ma r k ed l y s i nc e t he b egi nni n g of t he Mel ane s i an Or og en y. On t he c on t r a r y, t he major s truct ures are bes t expl ai ned by a mor e or l ess con- si stent conver gence i n a S550W di recti on. The ma gn i t ude of t he co nv er gen ce , howe ve r , i s n ot kn own, but t he crust al s hor teni ng si nce the Earl y Pl ei st ocene has pr obabl y exceeded 100 km. Thi s accords wel l wi t h t he f i gure 4 Epi s odes, Vol . 7, No. 4, December 1984 The mos t s tri ki nL y feat ur e of the ge3 l ogy of 1 ri an Jaya i s the Bi r d' s Head, a great sal i ent of undeformed conti nent al crust t hat pr otr udes nor thwards i nt o the Paci f i c 5 0 I } , N 率T N E 娜井称介一件瓜井挤争 厂- anomal ous sali ent were pr oduced duri ng the Mel anesi an Or openy, but t he me- chani sm by whi ch they f ormed i s not 朽 known. Mos t author s have as cri bed t he f ormati on to cl ockwi se rotati on or nor th- 峨 Aus t r al i an con t i nen t al c r u s t ( Hami l t on, I Latl e-def - ed ocean, c crust Lotl e-def - ed co,t inental crust ^ I I STRALIA PLATE ZDD i n l i ght of t he resul t s of the recent map- pi nv -, we have pr opos ed t hat t he Bi rd' s Head owes i t s protr usi on t o a gr eater crust al s hort eni ng i n the body r egi OD ( Dow 矛 困口 - ki l ometr es to i t s pr esent DOSi ti on. C E N T R A = M E R V A L N G K E T r H 苛I R I S TS F A Y U 7 L E & I S N - T D , I war ds transl at i on, by as much as several hundr ed ki l omet res , of a f r agment of lq79; Hermes , 1968; Norvi ck, 1979; Robi nson and Ratman, 1978; Vi s ser and Her mes, 1962) . Recentl y, however, Pi gr am et al . (1982) and Pi gr am and Panvi a yabean (1 983) pr oDosed that t he Bi r d' s "ead r e- gi on cons ti t ut es a separat e mi crocont i nent that has been raft ed many . hundreds of 尸八 少 尸 襄 F A U L TP N A E I C 遥 pl at e. Th e ma j or s t r u ct ur es ou t l i ni ng t h i s 一象 The Bi rd' s Head ‘m M ajor faul t ar i r l S uk amt o , 1 98 4) . Her e t h e s h or t en i n g, whi ch pr ob ab l y exceeded 200 km si nce t he s tar t of t he Mel anesi an Or ogeny, has been accommodated enti rel y wi thi n the New Gui nea Mob i l e Bel t by compr e s s i o na l d ef or ma t i on of t he co nt i ne nt al cr ustal rocks and by compl ex over and under -t hrusti ng of oceani c cr ust and mantl e of t he Paci fi c Pl ate. 几 gure 4: Main structural elements of Irian Jaya。 New Guinea Mobile B elt unstippled. b y s ou t hwa r ds ove r t hr us t i n r of t he r o ck s of t h e n or t h er n mar gi n of t he Austr al i an conti nent al bl ock. The Meer vl akte on the other hand i s one of the sDectacul ar mani festati ons of Accordi ng t o our hypothes i s, the Bi rd' s Head has react ed as a s tabl e but tress , and as the Paci fi c Pl at e has encr oached s outhwards i n the body r egi on the cont i nent al crust of the Bi r d' s Head has prot ruded nor thwards i nto the westerl y movi ng Paci f i c Pl ate. The di ff erent i al di s pl acement has been t aken up al ong t he Wandamen Faul t Zone by a combi nat i on of overt hr us ti nR and ri ght l at er al str i ke- sl i p di s pl acement. u n der t hr us t i n g of Pa ci f i c P l at e c r u s t t hat s t ar t ed i n t h e e ar l y There are, however , pr obl ems wi t h both hypothes es . The r ot ati on hypothesi s does not expl ai n why t he conti nental f rap , ement has moved agai nst t he r el ati ve southwest er l y dr i ft of the Paci fi c Pl ate. On t he other hand, our hypothesi s r ecui res the crus t underl yi ng the Banda Sea to have provi ded a butt ress t hat has pr evented t he appar ent l y vul nerabl e Bi rd' s n or t h er n t wo - t hi r ds a pp ea r t o be al mo s t e nt i r e l y of o ce an i c He a d r egi on f r om be i n g car r i e d s out hwe s t war ds . Mos t author s consi der t he Banda Sea cr ust to be oceani c and, therefore, not abl e to wi thst and the southward moti on, but r ecent reDort s that rocks of conti nental or i gi n have been dr edged from wi des pread l ocal i ti es i n the nort h Banda Sea ( Pr a s et yo , 1 98 3 , u np ub l i s he d ) s u gg es t t h at t h e s e a ma y b e l argel y under l ai n by conti nental crust whi ch coul d possi bl y have acted as a buttress. Wha t ev e r i t s o r i gi n , t h e pr ot r us i on of t he Bi r d' s Hea d i nt o t h e wes tw ar ds - movi ng Paci fi c Pl at e has exposed the nor ther n extr emi t y t o huge stess , and the conti nental cr ust has r e a ct ed b y t he t e ar i ng - o f f of l ar ge cr us t a l f r a gmen t s , whi ch have been carr i ed westwar ds by t he Paci f i c Pl ate. Mi ddl e Mi ocene aci d vol cani c r ocks on the nor thwestern extr emi ty of t he Bi r d' s Head have been of set by thi s means at l eas t 370 ki n al on g t he So r o n g Faul t Zo ne ( Dow a n d S ukamt o, 1 98 4 ) . N ew Guinea M obi le Bel t Th e ea s t e r n h al f o f I r i a n J ay a i s domi n at ed b y t wo co nt r a s t i ng maj or ph ys i o gr a phi c f e at ur e s : Th e Cen t r a l Ran ge Pl ei st ocene and cont i nues t o t he present day. These, and al l t he other st ructures resul ti ng from the pl ate conver gence duri ng the Mel anesi an Or og r eny, are t he wes tern conti nuati on of t he New Gui nea Mobi l e Bel t i n Papua New Gui nea. Not sur pri si ngl y, the r ocks exposed al ong t he s outher n thi r d of t he Bel t are of conti nent al ori gi n, whi l e t he or i sl and-are affi ni ti es . De f or me d Nor t he r n Mar gi n o f t h e Au s t r al i a n P l at e Th e s t r o ngl y def or me d, c on t i n en t a l cr us t al l i t h o l og i e s of t h e Cen t r a l Ra ng e Thr us t Be l t f or m a zo ne 1 0 0 km wi d e ( Fi g. 5) . Thes e r ocks, whi ch i nvol ved t he Pal aeozoi c bas ement and the over l yi ng l ate Pal aeozoi c to mi d-Terti arv shel f sedi ment s, ar e overt hr us t to the south and i n many pl aces are ti ght l y f ol ded. The uppermost uni t of the s hel f s ucces si on over much of t he Centr al Range i s the New Gui nea Li mest one, whi ch aver aves about 2, 000 m i n thi cknes s and provi des an i nv a l ua bl e s t r a t i gr a ph i c h or i zo n f o r u nr a ve l l i ng t h e s t r u ct ur e. The nor thernmost f ri nge of the def ormed conti nental cr ust i s mad e up of Me s ozo i c a nd ea r l y Ter t i ar y f i ne- g r ai ne d cl as t i e s an d i n t e r c al at e d mar i n e v ol c ani c s , wi t h a t ot a l t hi ck ne s s o f over 10, 000 m. These were l ai d down on t he nor ther n c ont i ne nt al s l op e a n d r i s e, an d h ave b een t i ght l y f ol de d b y s e ve r a l de f o r mat i on s an d r e gi o na l l y me t amor ph os ed t o t h e gr ee ns chi s t f aci es . Si mi l ar r oc ks i n t he e as t er l y ex t e ns i on o f thi s met amor phi c zone i n Papua New Gui nea were me t amor ph os ed d ur i ng an i s l an d a r c/ con t i nen t c ol l i s i on i n t h e Ol i g oc en e ( Dow, 1 97 7 ; J ac qu es an d Robi ns on , 1 97 7 ) , s o i t i s pr obabl e that the I r i an Jaya r ocks were metamor phosed at the same t i me. Never thel es s, on the evi dence avai l abl e to da t e , t he met amo r ph i c s co ul d con c ei v ab l y h av e b ee n f or me d t hat f orms the mount ai n backbone, and the remarkabl e l ake pl ai n ( Meervl akte) t o t he nor th that channel s most of the duri ng the Mel anes i an Or ogeny. dr ai na ge f r om t he n or t he r n ha l f of t he b o dy. The Ce nt r a l Ol i gocene i n age, the col l i si on di d not af fect the s hel f Range, whi ch exceeds 4, 000 i n el evat i on over most of i t s l ength and whi ch cul mi nat es i n the i ce-capped Puncak Jaya at over 5, 000 m, was formed earl y i n t he Mel anesi an Or ogeny corr el ati ves i n Papua New Gui nea, wer e l ai d down, essent i al l y wi thout i nterr upti on, unti l the Mi ddl e Mi ocene. Epi sodes , Vol . 7, No. 4, December 1984 I t i s i mp or t an t t o n ot e t ha t i f t he me t amo r phi sm was s edi me nt s mak i n g up t he Cen t r al Ra nge , f o r t he s e, l i ke t he i r 5 t he ba s e o f t he l i t ho s ph er e of hot l ow- d ens i t y mant l e mat e- r i al , by i s os t a t i c compe ns at i on a nd by ot h er f ac t or s. Thes e ver t i cal move ment s ar e r e s p ons i bl e f o r t h e bl o ck s t r u ct u r al pa t t e r n of t h e c ont i n en t al a nd o c eani c c r us t s ( Ar t yu s hk ov旦 丝・ ,1 97 9 ) . Man y da t a on t hes e and ho r i z ont al mov eme nt s co me f r om g eo det i c an al y s es on t he g r ou nd and f r om s a t el - l i t e s ( Bu l an z he, 1 981 ) . Ad va nce s i n s e i s mol ogy h av e h ad a ma r k ed bea r i ng on t h e f i e l d of t e ct on i cs ( Fi g. 4 ) . Ex t ens i ve da t a on s e i s mi c ev ent s wi t hi n the U. S. S. R. and el sewhere have demonst rat ed a li nk be t we en ea r t h qu ake s ou r c es and z ones of act i ve de ep f a ul t s . The ex p ans i on of s ei s mi c net wo r k s an d geo ph ys i cal pol y gons s et up i n a ct i ve s ei s mi c ar e as o f t h e c oun t r y h as p er mi t t e d s ei s mol ogi s t s t o wor k out a r at her s uc ces s f u l t e chn i qu e f o r l on g- t er m ea r t h qu ake pr edi ct i on, wh i ch has a l r e ady b ee n ver i f i ed i n a nu mber of cas es ( Anon. 1 9 82 ) . A med i um t o s h or t - t er m ear t hq ua ke p r ed i ct i on t ec hni q ue i s n ow b ei n g de ve l op ed, ba s e d on t yp es of mo vemen t s al on g t he dee p faul ts . Met a l l o ge ny One of t h e i mp or t an t ac hi ev ement s of So vi et ge os c i en ce i s t he r ec ogn i t i on of cer t ai n r egul ar p at t er ns i n t he f or mat i o n and di s t r i b ut i on of mi ner al s ( Sh ch egl o v, 1 9 80; s ee al s o S mi r nov, a nd Ru ndq ui s t , t h i s i s s ue o f Epi s o des一Ed. ) . For ma- t i on al ana l y s i s app l i e d t o met a l l o geny ma kes i t po s s i bl e t o i de nt i f y met a l l i f er ous as s oc i at i o ns ( f or mat i ons ) , and t odet er - mi n e t h e l oc at i on of mi ne r al dep os i t s wi t h i n t he s e as s o ci a- t i o ns . Thi s po pul ar new appr o ach t o g eol ogi cal ex pl o r at i o n per mi t s us t o s i ngl e ou t an d ra nk pr o mi s i n g ar eas , and t o pr o vi de a pr e l i mi n ar y q ua nt i t at i ve es t i mat e of mi n er al r e- s er ves o f b ot h l ar g e and s mal l ar eas . Hy dr og e , ol o gy a nd Eng i nee r i ng Geo l ogy Fund a ment al r es e ar ch i n hy dr o geo l o gy i s ai me d at r ev eal i ng t he l a ws gov er ni n g t h e mi gr at i on of gr o un d wat er i n t he f r e e- wat er exc ha nge zo ne of t h e hyd r os ph er e. Thi s wo r k c ont r i b- ut e s l ar g el y t o t h e expl or at i on f o r and e s t i mat i o n of t he gr ou ndwat er r e s er ves , t he p r ed i ct i on of wat er i nf l ows i n t o un der gr ou nd wor ki ngs du r i ng mi ni ng, and t h e con t r o l of wa t er - s al t r eg i mes on r e cl a i med l a nds Mat s an d S he s t ak ov, 1 981 ) . Wor k on t he s pat i a l va r i at i o n i n engi ne er i ng pr o pe r t i es of r ock s a s s i s t s h yd r o geol og i s t s t o def i n e r egi on al ch ar ac t er - i s t i c s, t o d ev el op t h e t h eor et i cal ba s i s f or pr edi ct i ng ex oge n- et i c p r oce s s e s , an d t o con s t r uct maps s howi n g t h e pr edi ct ed de vel op men t of ge ody na mi c p r oc es s es t o t he ye ar 200 0 Fi gur e 5 : Dr i l l i ng加r gr ou ndwat er i n Cent r al As i a. U. S. S. R. Si z eab l e co al de pos i t s ha ve al s o bee n ex pl or e d i n t h e P ech or a, Kar a ga nda, Eki b a s t uz and S ou t h Yak ut i a b as i n s , amon g ot h er s , and t her e ar e i mme ns e r e s ou r ce s i n t h e as y et poorl y studi ed Tungus ka and Lena basi ns of Si beri a. 黑s u r u c p e p s l y ( S o m f 1 i r f - n e ` o r v r _ o , _ u _ s I 9 _ m 7 _ 4 e T . t _ a l s I r o i s n 裂d p e r 纂 寰o f f r o t m h e m K i n r e i v r a o l i Rog b as i n i n t he Ukr ai ne and of t h e Kur s k Mag net i c An omal y ar ea o ccu py l e adi n g p os i t i ons b ot h i n i d ent i f i e d r es er v es and pr odu ct i on. La r ge i r on de pos i t s ar e al s o mi ne d i n t h e Ur a l s and t he Kol a Peni ns ul a, i n Karel i a, Kazakhstan, and West and Eas t Si ber i a, an d new di s t r i ct s ar e bei n g exp l or e d i n So ut h Yak ut i a. Th e S ov i et Uni on p os s es s es c ons i d er ab l e r es our ces of mang ane s e or es i n t h e Uk r ai ne, Geo r gi a and ce nt r al ( Ar t y s hk ov, 1 982; S er ge ye v, 1 9 76 -1 978 ) . Kazakhst an, and chromi um or es i n nort hwest Kazakhstan. Mi ner al Resour ces L l i a s h r e g e d . r e s C e o r v p e p e s r o f d e n 5 o o n s - - j f t e s r r a o r u e s m b e e i n t a g l s w h o a r v k e d a l s i o n b K e a e z n a k e h s s t a t a b n - T h e U. S . S . R. p o s s e s s e s l a r g e r e s e r v e s o f o i l an d g a 兰 ( s e e Mey er hof f, 1 981 , 1 9 83一 Ed. ) , i n cl udi ng one of t he wor l d' s l ar g es t oi l an d gas pr o vi n ces , t h at of Wes t Si b er i a. Thi s l at t er r eg i on has b een r ap i dl y d evel op ed, f r om an out put of 200 t ons of oi l i n 1 96 4 t o t h e p r es ent f i gu r es , whi ch r ep r es e nt ove r 60% of t he t ot al vol ume of o i l a nd 5 0% of t he gas p r od uc ed i n t h e U. S. S. R. The l ar ge s t oi l and g as p r ov i . n c es wi t h i n t h e Ru s s i an p l at f or m ar e r e pr e s e nt ed by t h e Vol g a- Ur al , Ti man- Pe cho r a and Cas pi an pr ovi nce s . Lar g e g as f i e l ds have b een ex pl or ed i n t h e Amu- Dar y a r eg i on of Cen t r al Asi a, a nd con s i d er a bl e oi l and ga s p ot e nt i al i s as s o ci at e d wi t h t h e Lena - Tun gus ka, Ye ni s ei - Lap t e v and Lena- Vi l yul pr o vi nces of East Si ber i a. The Sovi et Uni on i s ri ch i n res erves of bi t umi nous and brown c o a l ( An o n, 1 9 6 2 - 1 9 7 8 ) . T h e ma j o r Do n b as b a s i n p r o v i d e s o ne- t hi r d of t he S ov i et pr o du ct i on of co al , al mos t ha l f of whi ch i s of cok i ng q ual i t y. The Ku zn et s k b as i n of Wes t S i ber i a ha s bec ome t h e l ar g es t s ou r ce of hi gh- q ual i t y p owe r - g en er a t i n g a nd co ki ng c oal s ; c oal s f r om t hi s bas i n ar e d i s t i n- g ui s hed by t he i r hi g h q ua l i t y and gr e at v ar i e t y i n r an k. The Kans k- Ac hi n s k ba s i n i s un i qu e i n i t s l ar ge b r o wn c oal r es er v es a nd f av ou r a bl e mi ni ng cond i t i on s; t h e de ve l op ment of t h i s 踩i k f i e s r t o a u n s ( C s a u n d p o s t r o p n h e y s r , y 足 h s e u l U p r h a i d l s e ( a C n u d 5 s C u l u p h p i o d e r p s h ) , y r t y h e o a r e r s e ) a , o f t he Bai k al - Amur Rai l wa y ( cu pr i f er ou s s a nds t on es ) and t o get her wi t h Ni i n t he Nor i l s k di s t r i ct and t he Kol a Peri n- s ul a. Pb and Zn ar e mi ne d i n Ru dny i Al t a i an d cent r a l Kazakhst an, Uzbeki stan, Tadzhi ki stan, Transbai kal i a, Azer - b al i an and i n t he Kr as n oy ar s k r e gi o n. Al comes f r om b aux i t es of t he Ur a l s, Ti ma n, Kaz ak hs t an, t he Kur s k Mag - ne t i c Anomal y ar ea an d t he Ar k hang el s k r eg i on as wel l a s f r om ne phe l i n e- b ea r i ng r o cks o f t he Ko l a Peni ns ul a and Wes t Si ber i a. There ar e al so the al uni te or es of Trans caucas i a,W i n the North Caucasus, Kazakhst an, Tr ansbai kal i a and Far Eas t , Sn i n t he Fa r Ea st an d Ki r gi zi a, an d Mo i n Eas t S i ber i a, Kaz ak hs t an and Ar meni a. The dev el op ment of t h e di amon d de p os i t s of Yaku t i a re p r es e nt a re mar k abl e ach i eve ment ( An on,1 96 7) . Lar ge r es er ves of r aw f er t i l i z er mat e r i a l s hav e be en di s - c ov er ed i n t he wcr l d- f amo us ap at i t e de po s i t s of t he Khi bi n g r oup on t he Kol a Peni ns u l a, i n p hos ph or i t e dep os i t s o f Kaz ak hs t an, cen t r al ar eas of t he Eur o pe an p ar t of t h e U. S. S . R. and Es t o ni a, and i n p ot a s h s al t s o f t he Per m ar ea Bye l or u s s i a, We s t e r n Ukr a i ne, Tur kme ni s t an, and Ea s t basi n i s one of t he most i mport ant energy goal s of t he Epi sodes, Vol . 7, No. 1. sediments wer e l ai d down under shal l ow-water to l acustr i ne condi ti ons. Thi s change i n sedi ment ati on probabl y refl ects t he s t ar t o f t he un de r t hr us t i n g des cr i be d l at e r . The Nor th Coast Basi n i s f l oored mai nl y by Paci f i c Pl ate c r u s t a s s ho wn b y upf au l t ed s l i ve r s of Ea r l y Ter t i a r y i s l a nd arc and oceani c vol cani cs, whi ch are found s poradi cal l y t hr oughout. The for edeep t hus appear s to have resul ted from d own buc k l i ng , of t h e oc ea ni c cr us t dur i n g t he c ompr es s i o n t ha t f or me d t h e Cen t r a l Ran ge . The Mel anes i an Orogeny: Pl ei st ocene t o Recent At s ome t i me af t e r t he e l ev at i on of t he Ce nt r al Ra ng e, t he mechani sm of cr us tal adj ustment under went a maj or change a s t h e s ou t hwa r ds o v er t hr us t i n g o f t he c on t i n en t a l r oc k s c e a s ed an d t h e Pa ci f i c Pl at e be gan t o un de r t h r u s t t h e No r t h Coa s t Ba s i n . Evi de n ce f o r t he t i mi n g o f t h e ch an ge i s s c a nt y, but i t probabl y r oughl y coi nci des wi t h the change of sedi mentati on i n Ear l y Pl ei s tocene ti mes menti oned above. The maj o r ma ni f e s t a t i on o f t h i s und er t h r us t i n g i s t h e Mamber amo Thr us t Bel t, a bewi l deri ngl y compl ex s ys tem n ea r l y 40 0 kn i l on g by 1 00 km wi d e, o f cu r ve d, an as t amo s i n g f au l t s t h a t c ut s obl i q uel y s o ut he as t war d s f r om t he co as t i n t he nor thwest nearl y t o the Papua New Gui nea border at the e as t e r n end of t he I r i an J a ya Ophi ol i t e Bel t. The Mamb e r amo Th r us t Be l t i s n ow t h e si t e o f ve r y i nt e n s e s e i s mi c act i vi t y ( Fi g. 7 ) , an d f o ca l p l an e s o l ut i o ns on s ome of t he earthquakes i ndi cate thr ust i ng. The Paci fi c Pl ate i s a pp a r ent l y a ct i ve l y un der t hr us t i n g t he r e gi o n t o da y. Figure 7: Seismicity of Irian Jaya. Epicenters for earthquakes to 34 km depth and with magnitude >4.99. Data to Dece mber 8, 1983, from the BMR earthquake file. upwar d s . Man y o f t h e di a pi r s a r e s t i l l a ct i ve an d s c a l y cl a y ca n be s e en d omi n g r ec en t r i v er t er r a ce s an d s qu eez i n g i nt o st ream beds l i ke toot hpast e. Away fr om the str eams the di api r s a re cha r a ct e r i ze d b y ubi qui t ous mu ddy l a nd s l i de s i n vo l vi ng t he j u ngl e co ve r , ev en i n a r e as o f l ow r e l i ef . Th e who l e ef f ec t i s one o f di s c on ce r t i n g i n s t abi l i t y. The ot he r ma j or ma ni f es t i o n i s mud v ol can oe s of whi ch t h er e a r e man y hun dr ed s i n t he di ap i r b el t , r an gi ng f r om s ma l l mounds a f ew met res wi de to subst anti al domes a ki l ometr e A s pect acul ar feat ur e of t he Thr ust Bel t i s the per vasi ve i nt rusi on of shal e di api r s whi ch make up most of the s ur face outcr oD of the 50 km-wi de medi al zone ( Wi l l i ams et al . , or more acros s and up to 100 m hi gh. The l at ter can be s een even on the LANDSAT i mager y. The most i mpr es si ve 1 98 4) . The s ur f ace man i f e s t at i o ns of t hes e di ap i r s ca n be p uz z l i n g f or t he f i e l d L y e ol o gi s t , f or t he onl y co he r e nt s t r at i g r ap hy i s f ou nd i n t he l a r ge r r af t e d f r agme nt s , whi ch coal es ci ng mud vol canoes f orm a mass over 50 km acr os s. Many of t he mud vol canoes are l ocat ed near maj or fault s may be di spl aced many hundreds of met res verti cal l y r el ati ve t o nei gh bo ur i ng f r agme nt s . I mpo s e t h e ef f e ct s of r egi on a l u n de r t h r u s t i ng , a nd t he e l u ci d at i on of t he ge ol og y be c omes i mpossi bl e. As an i l l us tr ati on, one l ar ge, al most hor i zontal s l ab of sedi ments over 800m t hi ck and fr om 4 to 5km across, was mapped duri ng earl i er petrol eum expl or ati on as a n o r ma l s uc ce s s i on, b ut a bu nd an t s e di men t a r y f ea t u r e s s h ow concl usi vel y that the whol e sl ab i s COMDl etel v overt ur ned k see ai so, 1 ! 1 g. 8) . AS i t aDuts a gent l e syncl i ne ot normal ap pe ar an ce one ca n un de r s t an d t he d i f f i cu l t i es po s e d i n wor ki ng out t he str at i gr aphy and st ruct ure. occur rence i s near t he cent re of the Thrust Bel t wher e whi ch ha ve D r o ba bl v pr ov i de d c h ann el wa ys f or t he dewa t e r i w o f pr e s s u r e d s ha l e s a t dep t h . Mechani sm of Undert hr ust i ng As s ee n i n F坡u r e 4 , t he Ma mbe r amo Thr u s t Be l t f or ms t he l i nk between the Yapen Faul t Zone t o t he west and the Be wani - Tor r i c el l i Fau l t S y s t em t o t he e as t , bo t h of whi c h ar e pr edomi nantl y l eft - l at er al str i ke- sl i p. I t i s appar ent , ther efore, that t he Mamber amo str uct ur e must have a pr edomi nant thr us t component, and that i t must be al most e nt i r e l y c on ve r ge nt i n na t u r e. Thi s a cc or ds we拜 wi t h t h e f i e l d obs er va t i o ns , t ho ug h t he r e i s s ome r oo m f or di v er ge n ce The mos t common s ur face expressi on of the di api r s i s a mass , ge ne r al l y k i l ome t r es a cr o s s , of s ca l y cl a y ( Fi g . 9 ) co nt ai n i n g c ha ot i c a nd u n s or t e d f r agme nt s of a l l s i z es , f r om s an d gr ai n s Figure 8: Competent greywacke beds right "flapped" u p wa rd s ( ce ntr e) by s hal e di a pir (s lu m pi ng , m ate ri al) Figure 9: Diapiric shale showing randomly contorted slickensides forming a Iscaley clay。. Small polymict rafted rock fragments are shown. Some (bottom left少 have been highly polished duri ng transport. making up the lef t third of the photo.’ Textural details of this diapir are seen in Figure 9. 纂 } 夔摹羹 鬓摹 摹摹 Epi s o des , Vol . 7 , No. 4 , Decembe r 1 98 4 黔) 攀彝耀纂巍下 7 A 勺 6闷U TII t, , Ogene ophool ite Sh. l e dap- 三 二了- / 旧 胭, 6 . I l i - 毛 PACI F I C 只打班 口亡EAN S.d, . .nta 203口诊 J.Y.P.. . } ' St nk. r i dge <」N工二巴 | |十 J卜一 ~于 一 、、 、、、 Al luvi um of the M e- lal ,te 20 k. 一 16- 门 Figure 10: The Gauttier Offset showing progressive left-lateral displace ment of Pleistocene sediments. 、 For location see Figure 5. f r om t hi s s i mpl e pi ct u r e b e ca us e t he s e i s mi c i t y of t h e r e gi o n s h ows t h at a s ma l l p r o po r t i on of t he c onv er ge nce i s be i n g t aken up by ot her parts of t he New Gui nea Mobi l e Bel t. Gautti er Of fs et . 】叨 }0口 The Ga ut t i e r Of f s et ( Fi g. 1 0 ) t r en ds abo ut 3 50 s ou t hwe s t , a nd di s p l a ce s t he Mamb er amo Th r u s t Be l t l e f t l a t er al l y b y ab o ut 40 km. The di s pl acement has been pur el y s tr i ke sl i p, s o t he s tr uct ur e i s anal ogous to a tr ans - f o rm f au l t an d p r o bab l y pr ovi de s a n A accur ate measure of the di r ecti on of ma xi mum c onv er ge nc e. 。卜 \ 、 \、 . , 、 / { 豪 ‘ } 4 " 3 ' 0 1 4V 30 一 Major fauf t 一 ‘占,~ Nor- 1 fault T, ,k ri d- te, d o- t h- }ide Fig' ure 11: Tensional faults exhibited by two la sheets of Middle rge Miocene Hollandia limestone. location see Figure The Gautti er Of fset 七、 、 50 七, Nev er t he l e s s t he r e i s o ne mo r e pi e ce of e vi de nce i n di ca t i n g that the conver gence acr oss the Mamberamo Thr us t bel t i s cl os e t o t he post ul ated di r ecti on of S551W. Thi s i s the Dr esence of another f undament al s truct ure, cal l ed her e the / 、- 慧 67 5. r o r Figure 12: Diagrammatic c ro ss section shown on Figure 5 to section along line of 劝 ow 亡为e Post一 付iocene evolution of the New Guinea Mobile Belt。 PL旧 CENE CEN TRAL RANGE Ophi ol i l e be件 t S Fo N de The di spl acement i s al so s hown by Pl ei st ocene sedi ment s t hat wer e l ai d down over the Of fset whi l e i t 20 was movi ng. Thus the ol der sedi - ment s have been di spl aced by pro- gr es si vel y gr eater amount s up to a maxi mum of 20 km, whi ch i s t he di spl acement of the ol dest beds 40 60 k. p r es er ve d ( Fi g. 1 0 ) . si mi l ar amount but not t he cont i - PRESENT DAY CEN TRAL RANGE Ophi ol i t e bel t I m br i cate zone l at er al di spl acement on the Off set 加 ha s b een a cco mmod at ed b y t h r u s t - i n g of t h e Pa ci f i c P l at e r o ck s ov er ,0 the conti nent al mar gi n by about ma s s o f coa l e s ci ng mu d v ol c an oe s described earlier i s centred on the nor theastern extens i on of the Gaut ti er Of fs et, whi ch must have pr ovi ded a maj or condui t for t he dewa t e r i n g of t h e s ha l e s . 8 尸l i o-Pl ei st ocene cl ast i cs 60 I t i s wor th noti ng t hat the great 皿团四 40 km . Tensi onal f r actur es D nental r ocks of the Centr al Range. I t appears , ther efore, that the l eft - 卜Sn匡工1 0之哎〕山0∥0」 The Gaut ti er Of fs et al so di spl aces the I ri an Jaya Ophi ol i te Bel t by a 80 k. - Major f aul t 16/09门 69 Cont i nent al crust Oceani c cr ust and m antl e B Epi s odes , Vol . 7, No. 4, December 1984 The amount of cr us tal shor teni ng that has taken pl ace i n e as t er n I r i an Ja ya s i n ce un de r t hr u s t i n g s t ar t e d i n t he Mi d d l e Pl ei st ocene i s not known, but we have made rough esti mates of the conver gence accommodat ed by t he maj or struct ur es of the New Gui nea Mobi le Bel t. These are as fol l ows: ov er t h r u s t i ng of t h e Op hi o l i t e Be l t ( 40km) , i mbr i ca t i o n ac r os s t h e Mambe r amo Th r us t Be l t ( 30 km) , a n d t hr u s t i n g e o n t h e Fo r el an d Thr us t ( 1 0 k m) . The co mbi ned f i g ur e o f 8 0 km shorteni ng pr obabl y does not r epr esent t he total i nvol ved because the ear thquake hypocentres ass oci at ed wi t h t he Mamber amo Thr ust Bel t occupy a zone that pl unges s teepl y s ou t h wa r d s t o a d ep t h of ab ou t 10 0 km. Thi s h as l e a d H. Le t z ( p e r s o na l commun i c at i on ) t o s p e cul at e t hat t h e Pa ci f i c Pl a t e ma y be s u b duc t i n g a l o ng t he n or t h er n mar gi n of t h e Thr u s t Belt. i f thi s i s i ndeed the case i t woul d expl ai n very neat l y t he l a r ge a r ea s of t e n s i on a l f au l t i n g o n t h e s ou t h er n mar gi n of t he Paci f i c P l at e wh er e t he r oc ks a r e e xpo s e d n or t he a s t of t he Mamb er amo Th r u s t Be l t a r o un d Ja y apu r a a n d a cr o s s t he b o r de r i n P apu a New Gui n ea ( Fi g. 1 1 ) . Thes e a r e t he on l y t en s i on al s t r uc t u r e s ma p ped i n t h e bo dy o f I r i a n Ja ya , a nd t hey coul d have res ul ted f rom t ensi onal s tress wher e t he Paci f i c l i t hosphere bends downwar ds i nto the s ubducti on zone. Si mi l ar tensi onal feat ures are known from the Paci f i c Oc ea n ma r gi n ( Hi l d e 1 98 3 ) , bu t t o ou r kn owl ed ge i n n o ot h er r eg i on hav e t he y be en r e c ogn i ze d on l an d. As sumi ng that the Paci f i c Pl ate i s subducti ng al ong t he norther n coas t of the body of I ri an Jaya, then t he Mamberamo Thrust Bel t can be seen to be a zone of under thr us ti ng have been over pr es sur ed and ar e bei ng buoyed t o t he s ur face as shal e di api rs and mud vol cani cs. Some of t he compr es si ve st ress i s bei ng tr ans mi tt ed across the n or t he r n mar gi n of t he c on t i nen t al b l oc k an d i s bei ng r e l i e ve d b y s out hwar d s ov er t hr us t i n g a l o n g t wo f r ac t u r e z on es , one a l on g t he Oph i o l i t e Be l t a n d t h e o t he r a t t he s o ut he r n mar gi n of the Mobi l e Bel t . Acknowl edgement s Thi s p ape r i s ba s e d on da t a c ol l e ct e d b y me mbe r s o f t he I r i a n J ay a Geo l o gi cal Map pi n g Pr o j e ct wh o con t r i bu t ed a l s o i n d eve l o pi ng t he i d ea s pr es en t e d. The i r h e l p i s gr a t ef ul l y a c- k no wl ed ge d. Pu bl i s h ed wi t h t he pe r mi s s i on o f t he Di r e ct or , Geol ogi cal Resear ch and Devel opment Cent r e, Bandung, I nd one s i a, a nd Di r e c t or , Bur ea u o f Mi ne r a l Re s o ur c es , Geo l - ovy and Geop饰 si cs , Canberra, Austr al i a. D. B. Dow has worked si nce 1955 wi th the Aust ral i an Bur eau of Mi neral Resour ces and has mapned wi de l y i n Aus t r a l i a a nd Pa pu a New Gui nea. He was Di r ect or of t he Ge ol ogi ca l S ur vey of Et hi o pi a between 1968 and 1971, and Chi ef Ge ol ogi s t of t he Geo l ogi ca l S ur v e y of Ken ya bet we e n 1 9 74 a nd 1 97 7. Si nce 1978 he has been the Au s t r a l i an Ma na ge r of t he I r i an Ja ya Pr oj e ct ( I AGMP , JI . Ci l a ki 49, Bandung, I ndonesi a) . i mbr i ca t i on a l o ng t he c on ve x f r on t of t h e s ub du ct i n g p l a t e . R. Sukamto i s chi ef of the Geo- Though the end product i s si mi l ar to an accreti onary wedge l og i cal Mapp i n g Di v i s i on o f t he a n d i n c l ud es a maj o r s c a l y cl a y c ompo ne nt ( Wi l l i ams e t al . , 1 98 4 ) , i t s o r i gi n i s compl e t e l y di f f er e nt f r om t h at u s u al l y as cr i bed to accret i onary wedges. Here the s edi ments ar e au t o ch t h ono us , b ei n g der i v ed ma i n l y f r om er os i o n o f t he o r og eni c be l t t o t he s o ut h, a nd t he s c al y cl a ys ar e f o r me d, no t b y t ec t on i c down - pu s h i n g, b ut r a t h er b y t he upwa r ds , buoyant, di api ri c res ponse. I f P aci f i c Pl at e cr us t i s i n dee d down - g oi n g, i t i s a pp ar en t that the subducti on i s i n i t s ear l y st ages , becaus e nowhere i n I ri an Jaya i s ther e r ecent i gneous acti vi t y. The si nki ng s l ab, t h er ef or e , h as n o t ye t r ea ch ed de p t h s n ec es s ar y f o r ma gma ge ne r at i on . The de pt h o f t h e z one of e ar t h qua ke f o ci i ndi cates t hat up to 100km of crust coul d have been s ub du ct e d, gi v i ng a t ot al c r u s t a l s h or t e ni n g s i nc e t h e be gi nn i n g of t he Mi d dl e Pl e i s t oc e ne of up t o 1 80 km. Summar y Geol ogi cal Research and Devel op- m ent Cent re e ( JI . Di pon e go r o 57, I n don es i a ) , a nd the I n do ne s i a n Pr oj e ct Man a ger o f t h e Bandung, I r i an Jaya Pr oj ect. He has been a f i el d geo l o gi s t of t h e Ge ol ogi ca l Res earch and Devel opment Centr e si nce 1958, and has been i nvol ved wi t h f i e l d mapp i n g i n Ja va , S ul a we s i , Ba ng gai , Su l a, Ta l au d an d Halm ahera. References Amer i ca n Ass oci at i on of Pe tr o l eum Ge ol o gi s t s , 19 81. Pl a te Tect oni c Map of t he户i rc um-Paci fi c Regi on. Bl ow, W. H. , 19 69. Lat e mi ddl e Eoce ne t o Rec ent pl a nkt on i c f or ami ni fe ra l bi os tr at i gr aph y. Pro cee di n gs o f t he Is t I nt er nat i onal Conf e re nce on Pl ank to ni c Mi cr of os s i l s . , 1 967, Ge neva , Swi t zer l and, v. 1, p. 19 9- 422. \ Dow, D. B. , 1977 . A geol ogi cal s ynt h esi s of Pa pua New Gu i ne a. Aus t ra l i a n Bur e au of Mi ner a l Re so ur ces , Geo l og y Geo phy si cs , n o. 201. 41 p. I n t he Lat e Mi ocene and Pl i ocene, compres si on i n eas tern I r i a n J a ya r es u l t i n g f r o m con v er ge nce be t wee n t h e Aus t r al i an a nd Pac i f i c pl at e s ca us ed s ou t hwa r ds ove r t hr us t i n g of t h e c on t i n en t a l cr us t al r oc ks o f t he no r t he r n mar gi n o f th e Aus t r al i an c ont i n en t a l b l o ck ( Fi g. 1 2 A) . Thi s l ed t o t h e f or ma t i on o f a t hi c ke ne d an d up l i f t e d we dg e o f co nt i ne nt al cr u s t t h a t no w f o rms t he Ce nt r a l Ran ge . Th ou gh t h er e i s n o di rect evi dence, i t seems l i kel y that the I r i an Jaya Ophi ol i te Be l t was up l i f t ed t o i t s pr e s en t e l e vat i on b y ov er t h r u s t i n g ( obducti on) of the Paci fi c Pl ate crust and mant le r ocks. Down bu ck l i n g of t he l i t h o s pb er e on bo t h s i des of t he o ve r t hr us t we l t f or med d ee p ba s i n s , e s pe ci a l l y i n t he n or t h ( Fi g. 12 B) . I n t he s e a c cumu l at e d gr e at t hi ck ne s s es of s ed i men t s der i ve d f r om t he er odi ng mo u nt ai ns . S ub s e que nt l y, t he ov er t hr us t wel t r es i s t ed f ur t he r de f o r mat i on a nd d ur i ng t he Pl ei s t oce ne t h e no r t he r n f or e de ep b e came t h e s i t e of s ou t hwa r ds un de r t h r u s t i ng o f Pa ci f i c Pl a t e l i t h os ph er e. I t i s bel i eved that t he l i t hosphere has detached al ong the nor thern ma r gi n of t he Mo bi l e Be l t a nd i s n ow s u bd uc t i ng at a s t ee p angl e. Immedi at el y south of t he subducti ng l i thospher e,stranded zone of oc ea ni c cr u s t i s b ei n gst rongl y i mbri cated al ong a undert hrusti ng. The Pliocene sedim ents involved in this Epi sodes, VoL 7, No. 4, December 1984 Dow, D. B. a nd Har t ono , U. , 1982 . The nat ur e of t h e cr us t und er l yi ng Cend er awas i h ( Gee l vi n k) Bay I r i an Ja ya. 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The con ti nen t /i s l an d ar e col l i s i on m nor the rn Pap ua New Gui n ea. BMR Jo ur nal of Au s tr al i an Geo l og y an d Ge oph ysi c s, v . 2 , no. 4, p. 289 -30 3. Mi ns t er , J. B. and J ord an , T. H. , 19 78. Pr es ent - da y p l at e moti ons . Jo urn al of Geoph ys i ca l Res ear c h, v. 83 , no . Bit , n. 533 1- 535 4. No rv i ck , M. S. , 1 979 . Th e t ec t oni c h i s t or y o f t he Banda ar cs , e as ter n I ndon es i a: a re vi ew. J our na l of t he Ge ol o gi ca l S oci et y ofL o ndon, 13 6 ( par t 5 ) , p. 51 9- 527 . Pi gr am, C. J. , Ro bi ns o n, G. P. and Tobi ng, S. L. , 1 982 . Lat e Cai n ozoi c or i gi n f or t he Bi n tu ni Bas i n and ad j ac ent Len ggur u Fol d Bel t , I r i an J aya. I n done si a Pet r ol eum As s oci at i on Pr oce edi ngs lI th Ann ual Conventi on. Pi gr am, C. J. and Pan gga bean , H. , 1 983 . 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