Geochemical Journal, Vol.18, pp.217 to 232, 1984
P etr o gr a p h y a n d m aj o r ele m e nt c h e m istry o f th e v olc a n ic ro c k s of t h e A n d es, s o u th e rn P e r u
SHIGEO A RAMAKI,1 N AOKI O NUMA2 and FELIX PORTILL03 Earthquake Research Institute,University ofTokyo,Bunkyo-ku,Tokyo 113,1 Departm entofEarth Sciences,Ibaraki U niversity,Mito 3102 and Instituto GeologicaMinero y M etalurgico,Lim a,Peru
(R eceived Decem ber12,1983, Accepted M ay 29,1984)
M ore than 200 sam ples oflate Tertiary to Quaternary volcanic rocks have been collected from the northern sector ofthe central volcanic zone oftheA ndean belt occupyingsouthern Peru . The m ostabun- dantrock typeisthepyroxene andesite. M any oftherock sam plescarry hornblende and/orbiotite pheno- crysts. Sm allam ounts ofshoshonites occur on the back arc side nearPuna and Siquaniand olivine-augite basanites occur on the western shore of Lake Titicaca. The Si02 frequency has a m odein the 60-65% range which is about 5% high er th an the Quaternary volcanic rocks ofJapan. The K20 contentshows a distincttendency to increase away from the front,while the Na20 content tends to decrease in thesam e
direction. The K,Sr and Bacontentsofthelate Tertiary to Quaternary volcanicrocksofthe northern partofthe central zone ofthe Andean volcanic belt (southern Peru) show regularincrease aw ay from the volcanic front. Atthesam etim e,aslight northwestwardincrease alongthearcisdetected. TheNacontentregularly decreases away tr om the front m aki ng a strong contrastto the Japanese Quaternary volcanic arcs, which does not show any regular change. The Na contentisconspicuously higherin the northw estern frontal zonethantherest.
INTRODUCTION Prediction, Tohoku U niversity, seism ology) and N. FUJII (D epartm ent of Earth Sciences, K obe A cooperative project on the geochem ical U niversity, volcano physics). The Peruvian study of central A ndean volcanic zone w as research group consisted of the staff of carried out during the period from M ay, 1980 IN G EM M E T, C. G UEVARA (Chief, G eology through M arch, 1982, inclu ding the field w ork section), F. PORTILLO (geology), M . M ONTOYA and laboratory analyses. The project w as co- (geology) and J. A. L AJO (geology). sponsored by the O verseas Scientific R esearch, O ur objective w as to elucidate the processes Ministry of Education (M om busho) ofJapan and of generation and evolution of the m agm a Instituto Geologico M inero y M etalurgico form ed through the chem ical interactions (IN G EM M ET) of Peru. The Japanese research betw een the subducting N azca plate and the group consisted of N. O NUMA (Project leader, m antle at depths on the basis ofthe geochem ical D epartm ent of Earth Sciences, Ibaraki U ni- studies of A ndean andestiesin the centralA ndes versity, trace elem ent geochem istry), S. volcanic belt (southern Peru) w here volcanism is A RAM AKI (Earthquake R esearch Institute, U ni- taking place over the crust w hich is the thickest versity of Tokyo, geology and m ajor elem ent (about 70km )in the w orld. geochemistry), K. N OTSU (Institute of Chem - The m ain field w ork took place in the sum - istry, U niversity of Tsukuba, Sr isotope geo- m er of 1980 for about 70 days and the area chemistry), I. K ANEOKA (G eophysical Institute, covered ranged from 14'S to 18'S crossing the U niversity of To kyo, K-A r dating), A. w hole width of the A ndean volcanic belt (Fig. H ASEGAW A (Observ ation Center for Earthquake 1). The area is located at the northernm ost
217
2 18 S.A RAM AKIetal.
sector of the central zone of the A ndean vol- straintsstated above. canic belt w hich overlies the N azca plat e sub- ducting eastw ard, and corresponds to a transi- SAM PLE C OLLECTION tion zone betw een the norm al- and abnorm al subduction segm ents of the N azca plate (H ASE- Selection of the sam pling locality depended GAWA and SACKS, 1981). The northern lim it of totally on the extensive inform ation already the central zone roughly corresponds to the collected by IN G E M M E T, Peru. Based on the northern lirn it of the part of the N azca plate published and unpublished geologic quadrangle subducting at an angle of about 30 degrees m aps and reports, sites w ere selected for the (norm al subduction). T o the north of this, the representative Q uaternary volcanic suites in N azca plate dips at about 30 degrees for the southern Peru. In principle, rocks designated first 100km of the descent from the tren ch, as Barroso group (see K ANEOKA and G UEVARA, but rem ains nearly horizontal for the next 1984, Fig. 2) w ere our m ain target w hile those
300 km and then dips agai n at about 30 degrees of the Senca and Tacaza w ere excluded. It
(abnorm al subduction). The horizontal portion w as h oped that by restricting the geologi c age roughly corresponds to the northern extension 80" e O' W ofthe centralvolcanic zone. T he virtualabsence of the young volcanic activity in this area m ay ~ ~~ be due to the shallow depth of the subducting ¥ N azca plate and the very thick (about 70km , ¥ C OC OS¥ - C UM MlNGS and SCHILLER, 1971) crust acting P LAT E I $' together to restrict the am ount of the astheno- l~ sphere edge below this area (H ASEGAW A and Oq ':= / /:/ SO U TH Oo Galapagos AM ERICA N SACKS,in preparation). This reportis one ofa series ofpapers result- Is. l P LAT E ing from the current project and deals with the ¥ sum m ary of petrography, m ajor elem ent geo- ¥ chem istry and chem ical m apping ofthe volcanic N A ZC A ~o~<(~¥A'L - rocks. PL ATE "t;~;¥ A bundant volcanic cente rs and volcanic ¥ .'5 20q e o l '.e 20'S m aterials occur in the studied area spanning in '~~; :c t ' age from early T ertiary to historic tim e. Strati- ~~a~L:Oc~ ~):~¥ rfT:l,l .. graphy has been extensively studied by the ~ l . IN G EM M ET scientists but radiom etric dating 2~l ~ has been so far very lim ited (K ANEOKA and o l '1F I l JL /. G UEVARA, 1984). Therefore one of the m ain Chlye ~)fse t difficulties in characterizing the A ndean vol- l 40" canism in com parison with m ore w ell-defined 4 0q 18 t. volcanic arcs such as those in the Japanese I " A N TA R C TIC Lt ~ islands is to distinguish the spatial variation of s the volcanic m aterials from the tem poral one. P L ATE ¥' ' ¥~~~ ~ ~ M ajor and m inor elem ent data published by - ~ _ LEF~VRE (1973, 1979) cover the southern half of the area of the present study. H e dem on- iO O' 80' strated a clear tendency ofincreasing K content Fig. 1. Index m ap of the A ndean volcanic belt. D ots aw ay from the volcanic front but his results indicate the distribution of the Quaternary volcanoes. also cannot escape from the tem poral con- O bliquely ru led area correspondsto Fig.2.
Volcanicrocks oftheA ndes 219
cz-03 PERU Illczc-z0-2ol SICUANI ~) N ,~- PPD- 30' l/ 'PPD-so "', PP0-56t op-ﾏ op-02 op-ol tl PPD0_-4781'~' rd~ PPo-'08' op-045¥~¥~;¥~:~;¥.;¥･･/c~~cM~__05045 e AYAV'Ri ,1 PA *04 tPPD-~ol oPp~oe7 ¥¥l /ctt-02 t CORACORA l COTAHUAS'op-08~~'¥~;~¥: CAILLOAdA PU-04 ¥ , ll~t [PA{012 .~csoja_ _/ opice _ 'c'l-ol PUP-Uos- .¥ PA-06 pA03 ¥c~sol' optlto cv-02 'I~l'PU-ot t/ ¥ ¥ PA-05~ic~si06/~/1' i¥04 ¥~~~_opt2t JULIACA Pu-06 f" cso ¥ opt3 /cv-041~cv-08 l/~l~Ac~-A0c3-04~/ op~5 op14 l"l"¥ '+¥~*~cv-0076 _~Il!l1~( Ac-02 L~ CHALA 'cs15 cv-c0v3-05AP-08 Ac-of t csll cv-ot }AR-09 cH-ol PU-05 LTITICACA ¥ cs12 I PVPv--fo09/~//~"' ~~ cs-13 AR0oa20ol2~t~'I pv-oe/=/;~~/~ 'Ac-c5¥)9¥1 t~~]1 cs-t4 i;AP~;I0~7/~;~' /A:~I"//./"c;_H-'0T~;U3~8ol_cH-07 pv-07 jtgl21/'¥_LIiLo~¥._~~~ AR06 /1~ ~///~ cH-05 J]uuJL03¥_)~~~~~l AR04 l'j'e If cH-06 oM-t4 'JL-'O / AR03 '~1R~QUIPA ¥ oM-on o'a-~6 IMc-02 'JYL-1tl/~-_ CAMANA /AR~{17 ¥¥AARARjC~H:0~t4'~~3~¥4t¥~~¥~~oN¥Ill~0'M1-c:ol'MCos AR*t65 - . et l MAZOCRUZ .¥ l - f~. AR-oi o'Ma-0o2e e~p "*~~:o"M-1*213IFr-¥-_MNc-0os4'/' PACIFIC OCEAN oM-ot:/1 ~ FTA~t2 ~'~~!~baMcc-0067 oTtA'-057j~/~//~;7)/~"/'~'r¥TA_~oT-AB.-1: '-'¥~/P'tc/-08 MOQUEGUA TA'02 '¥TATIAo09 ¥¥~M;c"-dLco-09 BOLIVIA TTAA--o0~4 Mc-ll TA*05 ¥¥d'¥¥Mct'-c13-i2lt TA-0076 'dc-14//t M~/c~/ ¥¥ 20 40 50 80 ~eokfn l 1f ¥ ¥ ;TACNA j d-¥" // t/ -'--'~. CHIL E ~' L
Fig.2. M ap showingthelocality ofthesam ple. Num bersreferto Appendices I and 2.
of the sam ples as close as possible, the spatial sam ples w as over 200. T he m ost recent m ate- characterization ofthe m agm a chem istry m ay be rials apparently form snow-clad high peaks and best achieved. it w as im possible to cover them in the lim ited D uring the field w ork,the im pression ofone tim e of our expedition. O ne of the youngest of the authors (S.A .) w ho has an intim ate sam ples w e were able to collect w as from a acquaintance with w et and tem perate environ- block lava flow issuing from N evado C oropuna southw estw ards (CS-12). Th is lava m ay very m ents of Japanese islands butis quite unfam iliar with the arid environm ent of Altiplano, w asthe w ell be a historic flow. Block lava flows in the difficulty of assessing the age of the volcanic Siquani region (CZ-OI through CZ-03) dated edifices from their state of erosion. For ex- by K ANEOKA and G UEVARA (1984) as < 0.027 am ple,inspections of aeri al photographsgave us M a show a very fresh topography and un- a very young age estim ate (say less than several doubtedly are am ong the youngest of all the tens of thousand years) of the pyroclastic volcanic productsin southern Peru. cones and lava fiow s of the Orcopam pa region because of their apparent freshness and lack of gullys etc. w hich are indicative of stream ero- M ICROSCOPIC PETROGRAPHY sion. In the field it w as apparent thattherocks U nder the m icroscope, about 82% of the are m uch w eathered, m icrotopography showing total sam ples m ay be nam ed andesite and about significant m ass w asting and indicating ap- 1O% dacite orrhyolite. Ten sam ples w ere nam ed pre ciably older age than our first estim ates. shoshonite (PU-OI through PU-06, and C Z-OI, Localities of sam pling are show n in Fig. 2 -02, -03), following the nom enclature of and li sted in A ppendix I. Total num ber of LEF~V RE (1973, 1979), and three (A C-O1,-02,
220 S.ARAM AKIetal.
-03) basanite. A good proportion of such andesites m ay be classified as dacites from high M AJOR ELEMENT C HEMISTRY Si02 contents as revealed from chem ical ana- lyses although it w as difficult to distinguish X R F analysis w as m ade on 10 m ajor oxides dacites from andesites under the m icroscope. using G eigerflex IK F-3064 at the G eofo gical If chem ical schem e of nom enclature is strictly Institute, U niversity of T okyo. Pow dered sam - applied, so m e other "andesitic" rocks like M C- ples w ere fused with LiB 04 fl ux into glass O1, M C-03, M C-06 etc. should be called sho- tablets (1 to 5 dilution) and the m easured shonite or banakite. A Iist of detailed m icro- intensities w ere corrected according to the scopic petrography of all the thin sections m ay procedure described by M ATSUMOTO and U RABE be available from the authors upon request. (1980). Results are given in A ppendix 2. The Basanites occurring in a sm all peninsula on sum ofthe IO oxidesis m ade IOO% . the southern shore of Titicaca Lake (A C-OI,A C- A11 of the 87 sam ples analyzed except one 02) contains abundant fresh olivine phenocrysts, carry norm ative quartz. The only exception is no plagioclase, and K-feldspar and nepheline the basanite m entioned earlier (A C-O1) with (or zeolite?) in the groundm ass. T hey contain 6.9% nepheline m aking a strong contrast with m ore than 6% of norm ative nepheline and K 201 other rocks in the region. In Table 2,frequency N a20 = 1.4. Sam ple A C-03 is probably sim ilar in Si02 wt% is com pared with LEFtv RE･S data in petrography. (LEF~vRE, 1973). Th e tw o m atch closely and Assem blage of phenocrysts is show n in show a m ode in 60 - 65% Si02 range (Fig. 3). T able I. Totally aphyric lavas com prise about W hen com pared with the w hole Japanese 7% of our collection and 17% Iack plagioclase Q uaternary volcanic rocks (A RAMAKI and Ul, phen'ocrysts. The assem blage clinopyroxene- 1978), southern Peruvian suite gives a sharper orthopyroxene-hornblende (and m agnetite) peak than the Japanese ones with an average phenocryst is the m ost abundant (15070) and the shifting by about 5% tow ard the high Si02 side. rocks with clinopyroxene + orthopyroxene Som e of the H arker variation diagram s are phenocrysts m ake up 36 % of the total. H orn- show n in Figs.4 through 7. The sam ples are blende without biotite occurs in 33 % and horn- geographically subdivided into tw o parallel blende with biotite occurs in 22% of the rocks. zones running along the arc: (1) the zone along In other w ords, horn blende occurs in 55% of the volcanic front and (2) the northeastern zone the rocks and biotite in 35% . adjacent to (1). The m ost striking contrast is
Table 1. Phenocrystassem blageofthevolcanicrocksofsouthern Peru. N um bersin parentheses,ind icate those rocks withoutplagioclase phenocry sts Hornblende Biout e NONE Hornblend e +biotite 3(1) 2(1) Olivine Olivine+ 11(3) 1(1) clinopyroxene Olivine+ clinopyroxene+ 1(O) 3(1) 1(O) 3(o) onhopyroxene Clinopyroxene+ orthopyroxene 14 (1) 25(O) 12(O) 10(O) Orthopyroxene 1(O) 10(O) 5(O) l(O) 17(2) 7(3) 13(O) 7(2) NONE Clinopyroxene 2(O) 8(3) 5( O) 1(O) Olivine+ orthopyroxene 2(1)
Volcanicrocksofthe Andes 221
in the K20 content w hich increases aw ay from Table 2. Fr eq u en cy d is tr i bu ti o n ofS i 02 conten ts the front (Fig. 4). W hen com pared with the Numberof Q uaternary Japanese islands, the least potassic analyses Thisreport LEFEVRE(1973) trend in sothern Peru is m ore potassic than the % Si02 >75 1 2 m ost potassic trend in the Japanese islands. T o 75-70 2 l the contrary, w hile the Japanese rocks do not 70-65 8 4 show appreciable difference in the N a20 Ievels 65*60 39 38 60-55 31 31 (Fig. 5), the rocks ofthe frontal zone (sym bol 55-50 5 7 50> 1 O + in Fig. 5) of so uthern Peru is definitely richer in N a20 than the inland zone (sym bol o). The general constancy of the N a20 contents with varying Si02 contents holds both for Japan and A1 and Ca are the only rem aining m ajor southern Peru. elem ents w hich show som e detectable zonation in com position across the arc (Figs. 6 and 7).
oo T he ge neral level of A1203 and CaO is higherin the frontal zone (1) as com pared with the inland zone (2). In the frontal zone, the A l20 3
conte nt m onotonously decreases with increasing Si0 2 content in the range of 50 to 70c70 w hile so 8~ 7(3 80 in th e inland zone,it increasesin the Si0 2 com - positional range of 45 to 60% (Fig. 6). CaO JAPAN 200 conte nt decreases m onotonously with Si02 lOO content in both zones (Fig. 7). T his indicates
5~ s2, 7~ B~ that the com positional variations of Al20 3 and
C aO are governed m ainly by fractionating IOO KURILE(HOKKAiDO) ARC plagioclase in the m agm as of the frontal zone cr) w hile they are controlled m ainly by clino- LLJ (f) 5~ s~ 7~ 8~ pyroxene and probably hornblede and biotite >- J in the inland zone. T he phenocryst assem blage 5e) 80 70 80 O ~ 4 / o ~ + + + o + 80 o o :~h++ + SW JAPAN oe) o _+_+:1F_ｭ'E;_+_+~~~ 1 SOUTHWEST JAPAN 2 ---+--~'+t#~t+:~;~ : ~,/ oo ARC f- ++.__ -~.~/IMZUAR-IANA ¥f_/~~- o40 50 60 70 80 s~ 80 ~~ 8B SiOz Si02 w t V. Fig. 4. Si02-K20 variation diagram of the volcanic Fig. 3. Frequency distribution of Si02 contents of the rocksin southern Peru . +.' rocksinthefrontalzone,o.' volca nic rocks in southern Peru (top), com pared with rocksin the inland zone. Arrow indicatesolivine-augite those of the Japanese Q uaternary volcanic rocks basa nite(A C-O1). The generalrange oftherocksofthe (A RAM AKIand UI,1978). southwest Japan are and lzu-M ariana arcisalso shown. 222 S.A RAMAKIetal. lO 5 ~'-t+++1~+~-1 8 O e (¥l SWJAPAN¥ _ ___+c+IT:;~TIJ~ o Z 4 ~---~-:tiF~:'h-~~;:~4~j~:r~+*+ + + l~:) r~ o't~ｽ;'~~~'_~aLlFPl~:~~_(L_~;i~:ie-+ +++-+--~ﾖ'~~~ O of¥<~__+_ ';=' 2 ¥* ',~' ~~¥ tZU-~lIARI ANA + + o +*;0~ :d:+ 40 50 60 7a 80 oi~+ + S'02 8 ~*+ ++ Fig.5. Si02-N a20 variation diagram of the volcanic + + rocksin southern Peru, Sym bols arethesam easin Fig. o40 50 ﾖi-~6~a+=h~-h-~ 70 + 80 4. Si02 Fig. 7. Si02-CaO variation diagram of the volcanic rocksin southern Peru. Symbolsare thesam easin Fig. G EOGRAPHIC M APPING OF C ONTENTS OF 4. CERTAIN E LEMENTS Coherent geographic changes in contents of certain elem ents in volcanic rocks as the prod- variation across the m ost part of the volcanic ucts of arc volcanism across the arc are w ell front with certain undulatory changes along the established. F or exam ple A RAMAKI and Ul arc. Especially it w as noted that behind the (1982, 1983) dem onstrated that the Si0 2- junction of tw o arcs, the regularity appears to norm alized K 20 contents of the Japanese be broken by unusually low K 20 contents of Q uaternary volcanic rocks show a very regular thelavas(A RAMAKI and Ul, 1983). Figure 8 show s the geographical variation of the K20 contents. The K 20 values are nor- m alized against Si02 = 60% on the assum ption that the Si02-K20 variation follows a standard 25 trend w hich is a set of straight lines obtained from m ore thah IOO variation diagram s of the Japanese Q uaternary volcanoes. A 11 these 20 standard trend lines are subparallelto each other ~+d+l'l~ﾖ~~ + + but their slope increases with the K20 content. +;*hF~~+4~0~+~+~0+H+++ They are expressed asfollow s(A RAM AKI and Ul, ~ ^~ G> + oo " o 6) + + 1983): ~~ 15 o~) + o Z X (0.365 X Si02 (wt% ) - 1.0) o - 3.65 X K 20 (wt% ) = 2.46 f w here Z is a constant for any particular "stan- dard trend line". U sing this equation, para- 540~+~~ 50 60 70 80 m eters indicating the level of K20 content such Si02 as the k-values of D ICKINSoN (1975) can be com puted from any single chem ical analysis. In Fig. 6. Si02-Al203 variation diagram of the volcanic rocks in,southern Peru. Sym bols are the sam e as in the following, the K20 content standardized to Fig. 4. Si02 = 60% is designated as K20(Si0 2 = 60). Volcanicrocksofthe Andes 223 7Z'w 70'w 14'S 1lb S!CUANl K 2 O (SiO 2:: e O ) // rJ r~ ' >5'o P E R U ' ' 5'o-4O o '4~)-3'o COTAHuAS' CAILLO~4A ¥ '30-2~ (/ ' 20> ArYDAHUA '･CHiVAY ( C' L TITICACA puNQ 'v¥:) ¥ ~ 16'S ~ , JULt~lt ~- ~~ ) AF?EQU;PA ' l~ , CANIANA > f , / / P~ ClflC O CE A ~ _lr , lj~ b~ O LIVIA ¥~ l* ~ J' ~ lOOKm L CH IL E TACNA / I8~S Fig. 8. M ap showing the geographicvariation ofK20 (Si02 = 60)(K20 contentnorm alized to Si02 = 60%) ofthevolcanicrocksinsouthern Peru. 3.0% Per 100km ). Since our sam ples covered SpATIAL T RENDS OF K ,N a, Sr AND Ba quite a large range of geologic age (6M a to C ONTENTS IN SOUTHERN PERU present, K ANEOKA and G UEVARA, 1984) as In Fig.8, it is clearly show n that K20 LEF~vRE'S sam ples did, direct com parison with (Si02 = 60) values system atically increase aw ay the Japanese case (< IM a to present) m ay not from the volcanic front (or trench axis). This be w elljustified. regularity is pointed out by previous w orkers Figure 9 show s distribution of N a20 con- like L EFivRE (1973, 1979). The generaltrend is tents of sam ples. As the N a20 content does not the m ost regular of all the elem ents exam ined increase appreciably w ith the Si0 2 content and the only exception is the unusually K-rich (Fig.5), N a20 contents are directly plotted. A s augite andesite (PPD-101) to the northw est of show n in Fig. 9,N a20 contentis ge.nerally low er Cotahuasi. W hen com pared with the depth of in the inland zone than in the frontal zone. the Benioff zone beneath this region (H ASEGAW A In m ay other arcs,including arcs ofthe Japanese and SACKS, 1981), K 20(Si02 = 60) increases islands (A RAM AKI and Ul, 1983), N a20 content about I.5% in average with 100km increase in does not show any regular zonalvariation across the depth of the Benioff zone aw ay from the the arc. In our present study, the apparent fro nt. A s discussed by A RAM AKI and Ul (1983), "reverse" zonation of N a20 is quite striking and this rate is m uch low er than in the transect can not be explained by such fractional crystal- across the northern H onshu arc of Japan (2.5 to lization processes as those discussed by O NUM A 224 S.A RAM AKIetal. 72'w 70'w 14'S 'It S,CUANl N a 2 0 ~ / !J ,t. , r 16'S ･ >5,1~ , P E R U ' ･51-4S , e.. ･45-40 COTAHUAS, C CAILLOMA .4O-3.5 db. " i ' /~ .35> e'r te f ,, t ,J ArvOAHuA ･~･ e, CHIVAY {/ , '~ .~! L TITICACA PUNo ¥ , ~ '~b':･...- JULit' ~/- ~ /~ AR~QUIPA ' 1) ･ l/ CAMArvA , > ,: ･ r~ ~~~' , , , ,P l,,A9~ e.･t t J Fl~.9. M ap showingthegPeo~grCalpfhlicCvariOatiCoEnAofNNa20 contentsinthevolcanicrocksin s,out,hern Peru. ~ ,.,,., /~ ,I l_ BOLIVIA ~ ll1 and M ONTOYA (1984). Also interesting isthe dif- changes both in Sr a 50 looKm clearly show s geographical r-// ~¥ ference of N a20 Ievels in southeastern (A R-, and B a contents. Both increase ajwCaHyILfrEom the C H-, O M-, and M A- groups; see A ppendix I) volcanic front in the saTmACeNA m an~ner as the K and northw estern (CH-, C V-, C M-, O P-, PA-and content. In the northw estern sector of the PPD- groups) sectors. T he N a20 contentis th e frontal zone, the level of Sr is interm ediate highestin the northw estern sector ofthe fro ntal and very sim ilarto the relativelevel of K, but B a zone, interm ediate in southeastern sector ofthe appearsto show higherlevelthere. frontal zone and the low est in the inland zone. In sum m ary, K , Sr and Ba contents allshow Therefore, the N a20 cpntent apparently show s regular increase aw ay from the front as w ell as a variations across and along the arc. In this case slight northw estw ard increase along the arc again it is difficult to assign any particular m in- w hile the N a content decreases aw ay from the eral phase(s) responsible for this difference front and is conspicuously higher in the north- through fractionalcrystallization. w estern frontal zone. R egional variations of the Sr and Ba con- tents are show n in Figs. IO and 11,respectively. Acknowledgem ents-This w ork was done under a pro- The data are from O NUMA and M ONTOYA (1984). ject entitled "Geochem ical investigation of the Central A ndesvolcanic zone,southern Peru" un:dertheauspices Th e Sr contentregularly decreases with the Si02 of the Overseas Scientific Research,M inistry of Educa- content but the Ba content stays m ore or less tion, Science and Culture (Grant N os. 504112 and constant. H ow ever, direct plot on the m ap 56043O12). Volcanicrocksofthe Andes 225 72'W 70'w 14'S ppll t SICUANl S r r J , ,i' ,,, 16'S{ ･ >12SO pp PER U ) e1250-1000 , ,.. ･1000*750- COTAHUASI l CAJLLOMA ･750-500 ,.t ' t d' J ･SOO> "fl'. .~ ANDAHVA ･-･ e,CHIVAY ( ',$ CJP LTITJCACA PU~,o tJ~S ~ ~C･:t JUU,~h~ . .. ) AREQU,P,A, CAMANA , ~ , ': ,.l' /j Fig.10. M ap showingthegeographic variation ofSrcontentsofthevolcanicr:o.cksinsouthern Pefru. PAC!FIC OCEA~l , . 'l( ... ' 'r BOLIVlA , 72*W 70'w ,f l/14~t's O 50 100Xfl~ r~J ¥¥ L¥ CHILE TACNA le･S ,8's Fig.11. M ap showing thegeog,1aphic variation ofBa contentsofthe volcanicrocksinsouthernPeru. ,, SICUANl B a ) /r lJ rJ e >1800ppm PE~U ' ･1800-1500 . ¥ .1500-1200 COTAHUAS! l CA~LL0'4A ¥¥ .1200-900 //b .900> ,..!,.. .~ ANDAHUA , l ･CH,V;4Y ~ PUN,O 1･~J, L T!T,CACA , ¥¥¥ 1(..t JULI1,¥.. *^ ~ AREroulp:4 ' l CAMANA ~ t /r~ I tt 1･' f/' P~ ClflC O CEAAl ' l( *t/ B OLIVIA //t¥ O 50 IOOXm t ¥ ¥l CHILE¥ TACNA 226 S.A RAM AKIetal. huata,on Arequipa-Juliaca high way. 3 CH-03 R EFERENCES Hb-aug-hyp andesite, W of Laguna Sali- nas,at4,300m. ARAM AKI, S. and Ul, T. (1978) Major element 4 CH-04 Biot-aug-hb andesite, NW ofCerro Baldio, frequency distribut io n of the J apanese Quat erna ry SE ofLaguna Salinas. v olcanicr ocks. Bull. Volcanol. 41, 390-407. 5 CH-05 Hb-aug-hyp andesite, S foot of Volcan A RA MAK I, S. and UI,T. (1982) J apan . In An desites: Ubinas. Orogenic andesites and related rocks (ed. R. S. CH-06 Hyp-aug-hb andesite, SE foot of Volcan THORP E),2 59 -292 . W iley,Chic heste r. Ubinas. 1.8kn ESE ofroadjunction. 6 CH-07 Hb-hyp andesite, W foot of V olcan Ubi- ARAMAKI, S. and Ul, T.(1983) Alkali m apping of th e Japa nese Q uaternary volcanicrocks. J. Volcanol. nas,at4,570m. Ge otherm . Re s.18, 549-560 . CH-08 Hyp andesite, probably of Llallahui CUMMl NGS, D. and S CHILLER , G.I.(1971) Isopach Group. Road cut 0.7km SSW ofH uito, m ap ofthe earth' scrust. Earth Sci.Rev. 7,97- 125. on LagunaSalinas. DICKlNS ON, W. R. (1975) Potash -dept h (K-h) r ela- 7 AR-O1-01 A ug-biot-hb andesite, upperlayer, Cerro tions in c ontinent alm argin and intraoceanic m agm a- Atalaya,E ofArequipa.. ti c arcs. Geol ogy 3,53 -5 6. AR-O1-02 Aug-hyp andesite. Sam e locality as HAS EGAW A, A. an d SA CKS,I. S.(1981) Subduction above. o f the Nazca plate bene ath Peru as d eterm ined from 8 OP-13 Aphyric andesite, I.3kn ENE of Anda- seismic observations. J. Geophys. R es., Sect. 86, hua. A R-02-01 Aug-hb-biot andesite, Lava from Volcan 4971~ 980. K ANEOKA, I. and GUEVARA, C. (1984) K-Ar age Chachani. Cerro Cortaderas, NE of determination of upper Tertiary and Quat ernar y Arequipa. Andean volcanic rocks,southern Peru. G eochem.J. 9 A R-02-02 Aug-hyp-hb-biot andesite, Lava from 18, 233-23 9. Volcan Chachani. Sam elocality as above. LEFtv RE, C. (1973) Les caracteres magmatiques du 10 A R-03 Plag andesite, QuebradalosAndes,16km EN E ofArequipa. volcanism e plio- quaternaire des Andes dansle Sud de P6ro u. C ontrib.M i ne ral.Petrol. 41,259 - 272. AR-04 Aug-hyp-hb andesite, Iava flow from LEFtv RE, C. (19 79) Un ex em ple de volcan isme de Chachani. "Quebrada los Andes", ca. m arge active dans le s Ande s du P6rou (sud) du 16km from Arequipa. m io c~ ne a1'acruel. Thesis,D. Sc., 55 5p .(M S) . 11 A R-05 Aug-hyp andesite, El Barretado, 20km E ofArequipa. M ATSUMOTO, R. and U RABE, T. (1980) A n auto- m atic anal ysis of m ajor ele m ents in silicate r ocks AR-06 Aug.hb-hyp andesite,Iava from Chachani. with X-ray fluorescen ce spectr om eter using fused "Quebrada el Cuico" on high way Arequi- pa-Yura,23.kn from Arequipa. disc sam ples. Ganse.kiK obutsu K osho Gakkaishi 75 , 272-278 (in Japanes e). AR-07-01 A ug-hyp-hb andesite, Iava flow from ONU M A, N. an d M ONT OY A, M. (1984) Sr/Ca-Ba/Ca Chachani. "Uyupam pa" near railroad Arequipa-Puno,5km N ofYura. system atics ofvolcanicrocksfrom the Central Andes, So ut hern P eru anditsi m plicatio nfo rAndean m agm a- 12 AR-07-02 O1-hb(? opacite)andesite,Lava flow from tism . Geochem. J.,18,251- 262. Chachani. Entrance of "Uyupam pa", 5 km N of Yura. A ppENDIX l AR-08 H b-hyp andesite,Iava flow from Chacha- ni. "Quebrada Cabreira" 16km N of LIST OF SAM PLES Arequipa. Abbreviations 13 AR-09 Hyp-hb andesite, Near Tam po de Pisag, 22 kn N of Arequipa. ol olivine aug autite hyp hypersthene 14 AR-lO Hyp-hb andesite, Pam pa Kutypam apa,34 hb hornblende biot biotite plag plagioclase km NN E ofArequipa. < Numbersatextremeleftreferto thosein Appendix 2> AR-11 HB(opacite)-aug-hyp andesite,Iava from Volcan Pichupichu. "Cerro Y anaorco" 1 TU-OI Hb-biot andesite.,M aso Pillone,Characato on high way Arequipa-O mate,50krn ESE Quad. from Arequipa. CH-OI Hyp-hb andesite, Barroso Group. 8km E 15 AR-12 Ol-aug-hb-hyp andesite, Lava flow from ofChiuata. Pichuchu. Cerro Tim pore. 2 CH-02 Aug-hb-hyp ahdesite, 13 kn ENE ofChi- A R-13 O1-aug andesite, Lava from Pichupichu. Volcanicrocks oftheA ndes 227 "Cerro Aqua Buena," 45kn ESE of flow from Cerro Antapuna. Arequipa. 26 OP-05 Aphyric andesite, Iava flow from Cerro A R-14 W el ded rh yolitic tuff (eutaxitic), quarry Antapuna. 5kn Se of Cerro Antapuna. OP-06 of sillar. 4km NW of Arequipa airport. Aphyric andesite,Iava from Cerro A nta- 16 A R-15 P lag r hyolit e,reddish pumi ce. 4.5k m N W puna. I .8 kn S SW o fOP-05. ofA requipaairport. OP-07 Aphyric andesite, possibly TacazaGroup. 1km NE of Orcop am p a, on the road . AR-16 Biot rhyolite, welded tuff,a sillar. Near Can tera d el Huyac o" 100kn W of center 27 OP-08 Aphyric dacite, ?boul der . SW part of ofArequpa. Orcop am pa. OP-09 And esite boulder on river bed of Rio 17 AR-17-01 A ug-hb-hyp andesite,S flank of E1Misti. AR-17 -0 2 H yp-hb a ndesite, Ia vaflow. Sam elocali ty Andah ua,SE ofCerro Paiche Loma. asabove. OP-I0-01 Hb(?)-biot(?) andesite, thick (>100m ) flow. E ban k of Ri o An dah ua, 13 krn 18 CV-OI Biot-aug- hyp an desite, youngerlava flow fr om Nevado H ualka H u alk a. Chiv ay - NNW of Andah ua. Huam bo high way. 28 OP-10-02 Hb(?)-aug an desite. Sam e locality as CV-02 Biot-aug- hyp andesite, sam e as above. above. 0. 5km W of Chirinu evo , on high way OP-11-01 A phyric andesite, probably lava from Ch iva i-Huam bo. Cerro Ticsho. 1 .2km SE of Latom a, CV-03 Biot-aug- hyp andesite, similar to CV-02. 4km NW of Andahua. OP-11-02 A phyric andesit e, d ark gray, sligh tly Sof Pujro. CV-04 B iot ande site (carbonate alteration), a altered. Sarn e asabove. OP-12 O pac ite an desite, a thick lava flow of block in lahar dep. frorn Hualkah ualka. A tPi ncholl o. Barro so Gr oup . I kn SW of Cerro Ticsho. CV-05 Hyp- biot andesite, older lava flow of N ev ado H ualk ah ualka. Q uarry S of OP-13 Aphyric an desite, m argin oflava flow 10 m th ick.1.3 kn WN W of And ah ua. M adrigal, on high way Chivay-Huam bo. 19 CV-06 Hb ( ?) - biot(?)-aug a nde site, Barroso OP-14-01 Aphyric andesite. 0.8kn W of center Group. 4 kn NN W ofChivay. of Andah ua. CV-07-01 Aphyri c andesite, d ark . N of Chivay. 29 OP-14-02 O1-aug andesite Center ofA ndauha. 20 CV-0 7-0 2 Aphy ric andesi te, gray. N of Chivay. OP-15-01 Andesite, Barroso Group (?). 2.3km NNW of Cerro Pu caylla on Andah ua- CV-08 Opacite andesite,glassy. AtCcayacha pe, 7kn N of C hivay. Arma high way. CS-O1-01 Hb (?)-au g-hyp andesite, Iava flow prob- 21 CM -OI Aphyric andesite, SE part of Caillom a 30 Caldera.W ofCe rr o Pillun es. ably from Nevado Coropuna. N flank CM-02 Aug -opacite an desite, Iava fiow from ofCerro Fiah uamani. Cerro Cosana, at the center of Caillom a CS-O1-02 Hb- aug-hyp andeiste. Sam e as above. CS-O1-03 Caldera. 0.3 kn W of Muyurina. Hb-aug-hyp ande site. S am e as ab o ve. CM-03 De nsely- welded tuff, underly ing flatlava CS-02 O pacit e-aug-hyp andesite,Iava flow from flo w of Ba rroso Group. 0.4 kn SW of Nevado Corop una . 7. 5km EN E ofArm a. San A ntonio, 5 km SW of Cail lom a. 31 CS-03-O1 Hb- aug-hyp andesite , Iava fl ow from 22 CM-04 Aug and esite, N W oart of C aillom a Cal - Cerro Cc orecah uana. N foot of Cerro dera. 7 ku W ofCaillorna. Ocoruro. CS-03-02 Plag andesite, Iava from Cerro Ccore- 23 CM-05- 01 Ol andesite. N flank ofCerro Antaym ar- ca, a s coria cone . 14kn SSW o f Caill o- cahuan a. 1 .7 kn ENE of Arm a. CS-04 Aug -h yp-hb andes ite,Iav a probably from ma. OP-OI A phyric andesite, pseudobrookite, hb, Cerro Antapuna. 1.7 kn ENE of Arma. biot, K-feldsparin dru se. Lava flow from 32 CS-05 Aphyric ancLebit e,Ia va of Ba rroso Gr oup. Cerr o Cajchay a. N E of L aguna C or ec o- 4.5 km SE ofCotah uasi. CS-06 Aug-hyp and esit e, sam e lava flow as cha. 24 OP-02 A p hyric andesite,Iava flow from Cerro abo ve. 4km SSE ofCotah uasi. Cajchaya. CS-07-01 Hyp-hb and esit e,in m orane fr o m Ne va do OP-03 A ph yric andesite, colum nar lava of Solim ana. 2.1 kn W of Huaytap am paand 1.5kn SE of Visca Grande . Barroso Group. N edge ofCerro M arcani, 2.8k m SE of Pueblo Arca ta. 33 CS-08 Plag andesite, Iava flow from Nevado 25 OP-04 A ug-hyp an desite, Barroso Group. Lava Solim ana. 1.7lcm SE of Huaytapam pa. 228 S.A RAM AKIetal. 34 CS-09 A phyric andesite. 1.4km NW of Arm a, 48 PU-05 Aug-ol "shoshonite",Iava flow of Cerro on Rio Arm a. Chupi. 4.5krn W ofPuno. 35 CS- 10- 01 A ug-hb-hyp andesi te, older flow from 49 PU-06 O1-aug "shoshonite", Iava flow from Nev ado Coropuna. 4krn S ofArm a. Cerr o Azoq uine. 2kn N ofPuno. CS- 10-02 H yp-hb-augandesite. Sam e asabove. 50 PU-07 Aug- biot-hb- hyp andesite, E flank of C S-11 A ug-hyp-hb and esite,I ava do me ofC erro Cerro Ti cani. 10km S of Puno. Kencho. 7km SSW ofA rma. PU-08 Biot-hb-aug-hb andesite, Iava flow from CS-12-01 H b-biot-hyp andesite, very young lava C erro Ca ctiri. On Pu no -M oq uegu a high - flow from Nevado Coropuna. NW of way. Cer ro Sepult ur ay oc, 1.5 kn N of Cam- 51 PU-09 Aug- hyp-hb-biotandesite,Barroso Group, pam ento S ique. altered . Lava flo w fro m C err o Cactiri(? ). CS-12-02 Sam e asab ov e. 3km SE ofQuimsachata. 36 CS-12-03 Hb-aug an desite. Sam eas above. 52 A ug-ol basa nite,Iava flow from unnamed AC-Ol 37 CS-14 Aug-hyp andesite. S of Cerro Reyusja Cerro. C e rro Chiana on Lago Ti ticaca , and 2 km NW o f Laguna Pallacoc ha . 15 kn N of Ac ora. CS-15 Hyp-hb- biot dacit e,weld ed tuffofSenc a AC-02 Aug-ol basan ite, Iava flow from Cerro Group. W est of Santa Rosa,6km NNW Paco. Ikm S o fAC -O1. ofChuquibam ba. AC-03 O1-aug basanite. 2kn NW of Chuchito, PA-OI Hb- hyp andesite,Iava from Nevado Sara on Puno-Ilave highway. Sa ra. I kn W ofH uall hu a. 53 AC-04 A ug-hyp andesite,partly altered. 0.5km 38 PA-02 Hb(?)-aug-hyp andesite, Sara Sara Group S ofC huchi to. (?). NE flan k ofNev ad o Sara Sar a. Ik m JL-OI-O1 Biot rhyolite, Iava flow ofCerro Pucara. W ofHuallhu a. On S fla nk of Cerro Oucar a,4kn SW of PA-03 B iot-h b-hyp andesite, Iava from Nevado Juli. Sar aSara. Ikm E ofQ uilcata ,onIncuyo- 54 JL-O1-02 Aug-hyp andesite, boulder on bank of Pausaroad. R io Sal ado. Sam easa bove. PA-04 Aug-hyp andesite, Iava from Cerro JL-O1-03 Aug-hyp andesite. Sam e asabove. Asccase. 4 kn N W ofQuil cata. JL-OI-04 Biot rhyolite,Iava flow similar to JL-O1- 39 PA-05 Aug-hyp andesite, Barroso Group. 2km O1 . S ofH uaculla. 55 JL-02 Aug- hyp- hb andesite, Barroso Group. PA-06 Hb-hyp-biot-aug an desite. Ikrn W ofPA- Between Cerro Pucar a and Cerro C aba llu- 05. n e. 40 CZ-OI A ug-hyp "shoshonite", relatively young JL-03 O1-aug andesite, probably from Cerro block lava. P lagan d qu artz xeno crysts Tu t acane. 5 km NE o fJuli. and abundant xenoliths. 2km W of San JL-04 H b-bio t da cite, Iava flow from Cerro P ed ro ,n e arSiqu ani. Tok ok cahua. 2.5kr n N W of Pom ate. 41 CZ-02-01 Hyp(?)-ol-aug "shoshonite," rich in 57 JL-IO Biot-h b-aug-hyp an desit e,Iava flow from granitic xen oliths u p t o 30cm across . C e rro P ueara. 1 4kn SE ofPom a te. 0 .2km W ofAnansaya,W ofSan Pedro. 58 JL-11 A ltered py roxene andesi te. 25km SE of C Z-02-02 Sam easabove. Pom ate. 42 CZ-03 A ug- hyp "sh oshonite",rich in xenoliths. 59 TA-O1 Aug-hb andesite,Iava from Nevado Chu- Q uellcocunca,2kyn SE ofTinta. qui ananta. Qu ebrr adal chupam pa. 43 CZ- 04 A phyri c andesite, valley- filling flow. On TA-02 Hb-biot dacite, Iava from Nevado Chu- Puno -Cuzco highw ay betwee n Andah ua y- q uianan ta. I km W of Tacala ya-Lag una lillas an d Oropesa. S uches. 44 PU-OI A ug-h yp-hb "sh oshonite". N foot of TA-03 Aug-biot-hb andesite, Iava flow from Cerro Atojllane,5.5km NW ofPu no. V olcan Tutupa ca. N W fl ank o f V. T utu- PU-02-01 O xyho rnb le nde "sho shonite". S fla nk of paca,on Tac alaya-Laq una Suchesroad. Cerro Coronado,6kn NW ofPuno. 60 TA-04 Hb-aug-hyp andesite, Iava flow of Rio 45 PU-02- 02 Ol-aug-hb "shoshonite ". Same as above. Tacalaya. Quilcata on the carretera 46 PU -03 O1 -aug "sho shonite". S flank o f Cerro Tacala ya-La gu na Suc hes. Pilchane,11km NW of Pu no. TA-05-01 A ug-biot-hyp an desite, Iava flow from 47 PU-04 Hb (?)-o l-hyp "shosh onite", Iava flow Pam pa Turun Turun. Huayllani, on from Cerro Coronado. 8km NW of Quilieata-H u aylla niroad. Pu no. TA-05-02 A ug-biot-hyp andesite, Iava flow over- VolcanicrocksoftheA ndes 229 lying TA-05-02. OM-14 Plag rhyolite, Iava flow of Cerro Ques- TA-06 Biot-hb-aug-hyp andesite,Iava flow from 1lam po. Apaceta Organune, on thecarre- Cerro Estr one. Cerr o P agrilaca on tri ple tera o f Candar ave-M az o Cruz. junction Candarave-Huanuara- Cairani. OM-15 Aug-hyp andesite, Iava from Cerro 61 TA-07 Hb- aug-hyp an desite, Iava fl ow of Cerro Chiapujo. On Cuajone-M azo Cruz road. Totorani. Ikr n NW of Cerro Totorani. 72 OM-16 A ug-h yp-hb andesite, Iava flo w fro m 62 TA-08 Biot -hb dacite, Iava fl ow from Cerro Cerro Anconaza. On the carretera of Calientes. O n the carretera Aranane - Can darave-M a zo Cruz. NinaYuca ma n e. 73 M C-O1 Biot(?)- hb andesite,Barroso Group. 3km TA-09 Hb-biot andesite, Iava flow from Cerro N W o fS allacruza. Ca lient es. M C-02 Biot- hb-hyp-aug andesite, Iava flow from 63 TA-10 Hb-aug-hyp andesite, Iava flow from C erro Huenqu e. 6km E of M azo Cr uz. Cerro Nazaparco. Ikn E of Aranane. 74 M C-03 A ug- hb-hyp andesite, Iava flow ov erlying T A-11 Aug=hyp-hb an desite, Iava flow from the Capillune Form ation. N flank of Volca n Tutupaca. Quebrada H uayjaq u e, Cerro San Francisco de Pachapaque. 0.2km W from Candarave-Lagu na Suches M C-04 H b-h yp ande site,Barroso Grou p (?) . On road. W flank ofCerro Taruja,15km S ofM az o 64 TA-12 H b-biot-aug-hyp andesite, Iava flow of Cruz. Tutupaca. Qu ebrada Zuripujo. 75 M C-05 H b andesite, probably Barroso Group. 65 OM-OI A ug -hyp-h b and esite ,Iav a flow of Cerro E flank ofa hill along Rio Llusta, 15 kn Laram calane. N flank ofCerro Laeram- S o fM azo Cru z. calane, along the road from Cuajone to 76 M C-06 A ug(?)-hb( ?) dacite, Iava flow of Cerro M azo Cr uz. Acsatata Grande. 28km S ofM azo Cruz. 66 OM-02 Hb andesite,1avaflow ofCerro Camillata. M C-07-01 Au g-hyp andesite, on E flank o f Cerro A longth er oad from Cuajoneto Carum as. Huallpanasa, 0.1 krn E of Rio Hum also. 67 O M-03 Biot-hb dacite, possibly older lava of M C-07-02 B iot-a ug-hyp andes ite. Sarne as abov e. V olcan Tiscani. M C-08 Biot-aug andesite, Barroso Group. E O M-04-01Biot-hb (opacitized) dacite, on SE flank flank of Cerro M urm untane. On M az o of C erro Toro Bravo. Ikm SE of La gu na Cruz-Taratahighway. Toro Bravo. M C-09 Biot-hb -hyp andesit e,Iava flow ofCerro O M-04-02Same asabove. Huancure. On N W flank of Cerro Huan- 68 O M-05 Aug- hb an des ite, Iava flow from Cerro cure,on M azo Cruz- Tarataroad. Chinilaca. N of Pam pa de Huamajals o. M C-10 A ug-hy p andesite, Iava flo w of Cerro O M-06 A ug-h y p andesit e, Iav a fr om V olcani co Capaca. 2 kn SW ofChila. Chil a. 4kn W of sum mit of C erro 77 MC-11 A u g-h yp andesite,bo ulder of Cerro Tifiri J u m ajalso. overthe Pleistocene m oraines. Along the OM-07 Aug-biot-hb andesite, Iava flow from road between M azo Cruza nd Ta rata. Nevado Ar unda ne . At Ojo s de Agu a i n M C-12 Green biot-hb dacite,Iava flow ofCerro the ParnpaTitijones. An tajave. Near Ce rro Azufr e,76km S o f 69 OM-08 Biot-aug-hyp a ndesite,Iava flow of Cerro Mazo Cruz. Carin ani. S side ofLagu naS uches. 78 M C-13 Biot-hb dacite, boulder probably from OM-09 Aug-hyp-hb andesite,Iava flow pr obably Ce rro Purupuru ni. Along the ro ad be- from Cerro Baajnani. On Lagu na Su- tween M azo Cruzand Tarata. che s,2k m N E ofSuches. 79 M C-14 H b andesite,Iava flow ofCe rro Quequesa- 70 OM-10 Aug- hyp andesite,Volcanica Chila(?), E ni. Along the road betw een M azo Cruz flank of Cerro Y unca ne. Ik m N of and T arat a. Condori. M C-15 Hb- aug-ol-hyp andesite, Iava flow of OM-11 Aug- hb andesite, Iava flow from Cerro Cerro Puti na. On M azo Cru z-Tacna Pac chiangui. I km E ofChallam oc o. highway, IO kn N E ofTarata. OM-12 Biot-hb-hyp-aug andesite, Iava flow of 80 PPD-IO H b(?)-aug andesite, Barroso Gro up. S Cerro Viz cacha s. 5k m E of La gu na flank ofCerro Y a nasaya. Ol ba salt, B arros o G roup. E flank of Viscachao Canocota. 81 PPD-3O OM-13 Au g-hyp an d esite, Iava flow from Cerro Ce rro Chucch urani, very close of the lchi pat a. At Acha cp ujo, on C uaj one- village ofChucc h urani. M as o Cru z highway. PPD-47 O l-a ug basalt,B arroso Group. E flank of 230 S.A RAM AKIetal. Cerro Chucchurani, very close to the vil- km N ofSatica. lage ofChucchuran i. A-I07 Opacite dacite, Barroso Group. 0.3km S 82 PPD 48 Biot rhyolite, B arroso Group. N part of ofA-IOO. Pam pa Am aruybe. 86 A-113 Aphyric basaltic andesite,Barroso Group PPD-56 O1-aug basa lt, Barroso Group. On NW (?). Anchochuasi, on E bank of Rio flank ofCerro Huancaram a. Vinchos,nearA nchochuasi. 83 PPD-101 Aug ande site, Barroso Group. NW flank A-116 Biotite rhyolite, welded tuff, Senca ofCerro Huacaram a. Group. Ikm N of Ocayhuacancha,3km 84 PPD-108 Hb(?)-ol andesite, Barroso Group. N SW ofAnchachuasi. flank of Cerro Marampata. 4kn SW of 87 HPA-54 Oliv(?)-aug-hy andesite, Barroso Group. Upah uacho. 1km NW of Quispicancha. E flank of 85 A-100 Biot(?)-hb andesite, Barroso Group. 0.5 CerroChaupiorcco. A ppENDIX 2 M ajorelem entcom positions ofthe volcanicrocksinsouthern Peru. TotalFeexpressedasFe203. Numbersrefertothosein APPENDIX I. No. 1 2 3 4 6 7 8 9 10 Si02 69.06 61.54 60.43 58.44 60.68 60.45 60.92 62.59 58.40 57.64 Ti02 O.45 0.71 0.70 0.96 0.88 O.94 0.90 0.82 0.99 1.07 A1203 16.05 17.92 18.32 19.18 l8.06 17.96 17.53 17.17 18.79 17.35 Fe203 3.28 5.84 6.21 6.52 6.36 6.44 6.65 5.18 7.00 7.48 MnO O.02 0.09 0.13 0.09 0.09 0,09 0.09 0.07 0.09 0.09 MgO 0.97 2.50 2.59 2.73 2.54 2.42 2.53 2.62 2.60 4.16 CaO 2.66 5.21 5.60 6.14 4.96 5.03 5.36 4.65 5.55 6.49 Na2O 3.37 3.64 3.43 3.48 3.39 3.58 2.98 3.79 3.76 3.13 K2O 4.05 2.36 2.40 2.23 2.81 2.91 2.56 2.34 2.80 2.88 P205 O.09 0.18 O.18 O.24 O.25 0.29 O.17 0.21 0.26 0.24 No. 11 12 13 14 15 16 17 18 19 20 Si02 54.07 63.00 60.76 68, 54 75,22 63.00 64.47 57.82 58,20 56.58 Ti02 1.35 0.68 0.91 0,43 0,20 0.73 O,80 0.87 1.37 1.21 A1203 17.04 18.16 17.08 16.46 14.40 17.13 16,18 17.85 17.47 17.81 Fe203 8.72 5.43 6.31 3,34 1.10 5.44 4,85 6.87 6.73 7.52 MnO 0.11 0.08 0.07 0,05 0.06 0.06 0,05 0.10 0.07 0,09 MgO 5.11 l.45 3.28 1,12 0.35 2.37 2.22 3.77 2.74 3.57 CaO 7.90 4.11 5.28 2,78 0.92 4.69 3.83 6.66 5.66 6.72 Na2O 3.52 3.87 3.56 3.15 3.45 3.60 3,83 3.63 4.57 4.02 K2O 1.83 3.01 2.53 4.04 4.29 2.79 3,55 2.21 2.70 2.11 P205 0.35 0.22 0.23 O.08 O.03 0.19 O,22 0.23 0.50 0.37 No. 21 22 23 24 25 16 27 28 29 30 Si02 57.93 54.99 59.39 67.61 57.54 67.64 63,54 59.11 56.73 64.85 Ti02 1.10 1.50 1.11 0.54 1.36 O.83 0,94 1.15 1.30 0.80 A1203 17.08 17.28 17.74 l7.71 17.45 14.67 16.39 17.47 17,69 16.76 Fe203 6.55 8.39 6.40 2,63 7.23 4.71 5.06 6.33 7.49 4.52 MnO O.08 0.10 O.06 0.02 0.07 0.05 0,07 0.06 0.06 0.06 MgO 4.OO 4.60 2.50 0.50 3,15 1.77 1,97 2.63 3.95 l.50 CaO 6.48 6.80 4.82 2.29 5.77 4.15 4.21 5.64 6.64 3.69 Na2O 3.98 3.73 4.35 3.73 4.38 3.15 4,36 4.47 3.95 3.92 K2O 2.38 2.13 3.17 4.88 2,55 2.69 3,11 2.70 1.88 3.64 P205 0.41 0.47 O.44 O.08 O.49 0.34 0,34 0.45 0.31 0.27 Volcan icrocksofthe Andes 231 No. 31 32 33 34 35 36 37 38 39 40 Si02 63,85 55,82 60.17 56.83 61.65 63.38 62.21 61.25 60.41 59.20 Ti02 0.83 1,65 1.10 1,33 O.93 O.88 0.93 0.85 O.90 1.14 A1203 17.64 17,59 17.25 18,06 17.19 16.97 16.95 17.17 17.07 15.48 Fe203 4.55 8,38 6.13 7,33 5.68 5.10 5.45 5.98 6.54 6.19 MnO O.06 0,09 0.06 0,08 O.06 0.06 O.06 0.07 0.08 0.08 MgO 1.76 3.48 2.75 3,34 2.57 1.99 2.34 2.98 2.88 5.29 CaO 3,61 6,36 5.08 5,91 4.70 4.07 4.51 5.15 5.89 4.97 Na2O 3.70 4,19 4.08 4,43 3.91 4.11 4.17 3.86 3*77 2.76 K2O 3.72 1.91 3.01 2,24 3.06 3.18 3.10 2.48 2.27 4.45 P205 0.28 0,53 0.36 0,46 0.25 0.26 0.28 0.20 0.19 0.44 No. 41 42 43 44 45 46 47 48 49 50 Si02 56.52 60.83 63.73 59,48 54.10 54.97 53,83 54,18 54.69 62.88 TiO2 1.32 1.06 0.85 1.49 1.94 1.94 1.84 1,88 2.52 0,87 A1203 15.62 15.87 17.32 16.88 16.45 16.11 15.51 15,55 14.82 17.17 Fe203 7.07 5.87 4.62 7,21 9.18 8.53 8,81 9,35 9.41 6.29 MnO 0.09 0.07 0.06 0.11 O.08 0.12 0,12 0,13 0.11 0.05 MgO 6.18 4.68 2.35 2.43 4.58 4.07 5.75 5,43 4.43 1,36 CaO 5.81 4.34 4.21 4.74 6.65 e.~1 ~.05 6,60 6.6e 4,61 Na2O 2.62 2.63 2.61 3.55 3.17 3.68 3.41 3.23 3.08 3.28 K2O 4.24 4.27 3.97 3,58 3.12 3.22 2.97 3,06 3.29 3.29 P205 0.52 0.38 0.29 0.53 0.74 0.79 O,71 0,59 0.97 0.19 No. 51 52 53 54 55 56 57 58 59 60 Si02 62.25 49,78 61.01 63.76 61.10 58,94 63.65 54.94 58.31 57.69 Ti02 0.91 1.39 1.38 1.08 0.96 1.39 0.93 1.35 0.87 0.97 A1203 17,09 13,31 16.4O 16.08 17.62 16,59 16.11 15.48 18.08 17.64 Fe203 6.32 8.62 6.33 5.35 5.89 7.51 5.51 8.06 7.08 7.77 MnO O.08 0.15 O.06 0.07 0.25 0,09 0.06 0.12 0.09 0.13 MgO 2.25 10,44 2.86 2.17 2.42 2.61 2.58 6.05 3.57 3.73 CaO 4.73 8.48 4.19 3.49 4.43 5.52 3.83 7.31 6.12 6.47 Na2O 2.83 2,87 3.40 2.58 3.20 3,38 3.18 3.20 3.71 3.28 K2O 3.33 4,11 3.95 5.07 3.81 3,54 3.81 2.92 2.00 2.12 P205 0.20 0,84 0.42 0.35 0.32 0,45 0.33 0.56 0.18 O.20 No. 61 62 63 64 65 66 67 68 69 70 Si02 59.58 64.67 60.75 62.86 58,28 61.74 65.63 60.66 61.41 61,92 Ti02 0.88 0.70 0.64 0.72 0,82 0.80 0.64 O.76 0.93 0,62 A1203 17,76 16.22 18.30 16.73 19.07 17.37 16.66 17.46 16.46 17,44 Fe203 6.85 5.35' 6.35 5.62 6,86 6.01 4.35 6.14 6.29 5,88 MnO 0.09 0,09 0.08 0.06 0.09 0.09 0.05 0.08 0.08 0,08 MgO 2.99 2,16 2.27 2.61 3.07 2.66 1.78 3.26 3.05 2.54 CaO 5.60 4,03 5.33 4.49 5,87 4.92 3.56 5.43 4.86 4,93 Na2O 3.67 3.36 3.36 3.75 3.82 3.70 4.01 3.76 3.80 3,28 K2O 2.38 3.24 2.76 2.98 1.89 2.52 3.15 2.28 2.87 3.16 P205 O.20 0.19 0.16 0.17 0.22 O.19 0.17 0.17 0.24 0,14 No. 71 72 73 74 75 76 77 78 79 80 Si02 77.01 60.60 63,77 61.88 61.94 67.91 57.34 64.36 58.57 56,05 TiO2 0.08 O.77 0,71 0.86 0.96 O.48 0.86 0.80 0.82 0.99 A1203 13.51 16.52 l5,94 16.76 17.04 16.20 18.98 16.68 17.55 17.17 Fe203 0.53 6,47 5,33 5.87 6.33 3.24 7.99 5.06 7.41 7.87 MnO 0.20 0.12 0,05 0.07 0.08 0.08 0.10 0.06 0.12 0.11 MgO 0.13 3.54 2,80 2.33 2.00 0,78 2.43 2.10 3.20 4.62 CaO 0,32 5.31 4,45 4.19 4,45 2,10 6.51 3.97 6.56 7.44 Na2O 3.82 3.26 2.86 3.17 3.62 4.00 3.36 3.48 3.19 3.06 K2O 4.39 3,24 3.91 4.61 3.27 5.13 2.17 3.29 2.41 2.46 P205 0.00 0,17 0,18 0.27 O.31 0.09 0.26 O.211 0.18 0.23 232 S.A RAMAKIetal. No. 81 82 83 84 85 86 87 Si02 51.68 74.14 54.92 60.04 65.46 52.22 55.92 Ti02 2.01 0.25 l.35 0.98 0.82 1.90 1.36 A1203 16.33 14.21 16.73 17.11 17.34 17.58 17.43 Fe203 10.08 1.49 7.36 6.41 4.15 11.41 8.09 MnO 0.12 0.lO 0.11 0.10 0.02 0.23 0.08 MgO 6.53 0.46 3.80 2.95 1.03 5.96 4.25 CaO 7.89 1.08 7.32 5.97 3.48 4.17 6.83 Na2O 3.27 3.84 3.42 3.72 4.33 3.68 3.38 K2O 1.59 4.36 4.03 2.50 3.14 2.06 2.31 P205 0.50 0.06 0.97 0.23 0.24 0.77 0.35