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Economic GeologyVol. 79 1984, pp. 172-176

AGE AND REGIONAL TECTONIC AND METALLOGENETIC IMPLICATIONS OF IGNEOUSACTIVITY AND MINERALIZATION IN THE ANDAHUAYLAS-YAURI

BELT OF SOUTHERN PERU

DONALD C. NOBLE,

Department of Geological ciences, ackay School f Mines, University f Nevada-Reno, eno, Nevada 89557

EDWIN H. MCKEE,

U.S. Geological urvey, 345 Middlefield Road, Menlo Park, California 94025

V. RA(3LEYZAGUIRRE,

Mauricio Hochschild CornpaVia tda., S. A., Avenida Reptlblica e Panarnd 055, Lima 27, Perd

AND REN MAROCCO

Oce de la Recherche cientifique utre-Mer, Mission u Pdrou, La Mariscala 115, Lima 27, Peril

Introduction

The evolution of the Andes of Peru is characterized

by a number of distinct episodes f compressional ec-tonics, ertical movement, nd gneous ctivity M/-gard, 1978; Noble et al., 1974) hat provide evidenceabout the nature of subduction beneath the continent

at various imes n the past. One important pulse ofigneous ctivity is represented y voluminous nter-mediate to silicic volcanic rocks of late Eocene and

early Oligocene ge that overlie he post-Incaic ro-sional urface n central Peru Noble et al., 1979b). nthis paper we present adiometric ages hat, in con-junction with other data, suggest hat the late Eocene-

early Oligocene olcanic rc of central Peru continuesto the southeast s he Andahuaylas-Yauri elt, a chainof high-level stocks and batholiths characterized bythe presence f Cu-Fe skarn mineralization t least npart of early Oligocene age. We also discuss ometectonic mplications f the fact that the Andahuaylas-Yauri belt lies at least 100 km farther inland from thepresent rench than does he coeval magmatic arc incentral Peru.

Andahuaylas-Yauri BeltGeologic setting

More than two dozen mineral districts located west,south, nd southwest f Cuzco, Peru, define an elongateprovince extending or more than $00 km from An-dahuaylas n the northwest o southeast f Yauri Fig.1) and covering n area of some 5,000 km2 TerronesL., 1958; Bellido t al., 1972; Santa Cruz et al., 1979).We refer to this province as the Andahuaylas-Yauribelt, following he usage f Bellido et al. (1972).

Mineralization within the Andahuaylas-Yauri eltconsists ainly of copper-bearing karn bodies nd a

smaller number of iron skarns. hey are not porphyrycopper deposits, s stated n many papers and bookspublished n English. mportant and better known dis-tricts nclude Tintaya, Sulfobamba, Charcas, Chalco-bamba, Ferrobamba, Katanga, Atalaya, Corocco-huayco, Quechua, and Huancabamba. At least fivebase and precious metal vein districts also are locatedwithin the Andahuaylas-Yauri elt, and zones of baseand precious metal vein mineralization efine a south-east extension f the belt (Bellido et al., 1972).

The skarn deposits mostly occur at or near he contactof quartz monzonite plutons with carbonate-bearingstrata f Late Jurassic nd Cretaceous ges.Appreciablevolumes of diorite and granodiorite lso are presentbut are not generally associated ith skarn deposits.On the geologic ap of Peru Instituto e GeologlaMinerla del Per6, 1975) hese ranitic ocks re shownas of Cretaceous nd/or early Tertiary age.

Age of igneous activity and rnineralization atTintaya and Chalcobarnba

The geology nd mineral deposits f the Tintayaand Chalcobamba istricts Fig. 1) are described yTerrones . (1958) and Santa Cruz et al. (1979). Cop-per-bearing mineralization of skarn type is spatiallyrelated to irregular bodies of quartz monzonite hat,

along with older but probably closely elated dioriteand granodiorite lutons, ntrude imestone f the Up-per Cretaceous errobamba Formation. n most placesthe quartz monzonite as undergone ervasive otas-sium-silicate alteration and carries variable amounts

of pyrite and copper-bearing ulfide minerals. Halite-bearing luid inclusions re common. Proven eservesat Tintaya consist f 50 million metric tons of ore with2.3 percent Cu, mainly as hypogene halcopyrite ndbornite.

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SCIENTIFIC COMM UNICA TIONS 178

FiG. 1. Map showing ocation f selected agmatic rcs n central nd southern eru.The Andahuaylas-Yauri belt s outlined y a dot-dashed ine. Middle o late Miocenemagmatic rc and Cretaceous-Paleocenecoastal atholith re indicated y stipple and cross atterns, espectively. he long dashed ine indicatesQuaternary volcanic rc.

Dikes of biotite- and hornblende-bearing acite,probably closely elated to the quartz monzonite, areexposed n the southern part of the Tintaya district.These dikes, essentially naltered at the southernmostends, become progressively ore altered oward thecentral part of the district.

Potassium-argon ge determinations ave been ob-tained on fresh magmatic hornblende rom one of the

prealteration dacite dikes at Tintaya and on secondarybiotite rom quartz monzonite hat has undergone o-tassium silicate alteration; this latter sample was ob-tained from drill core from two holes that passedthrough he skarn mineralization. he secondary iotiteappears resh but the mineral separates ated containsome ntergrown hlorite. The radiometric ges f 825_+_, 88.4 _ 1, 88.7 _+_ , and 84.7 _+_ m.y. (Table 1),identical within the limits of analytic reproducibility,show hat the quartz monzonite and dacite were em-placed, and the skarn mineralization ormed, about 88to 84 m.y. ago.

We have also obtained a single age of $2.6 _+_ m.y.

on biotite from a specimen of quartz monzonite por-phyry from Chalcobamba Table 1). This specimen,containing phenocrysts f plagioclase, uartz, alkalifeldspar, iotite, and amphibole n a fine-grained pliticmatrix, has undergone potassium-silicate lteration.Sulfide rains re common nd he quartz phenocry.stscontain numerous hypersaline luid inclusions.

No ages were obtained on the bodies of diorite andgranodiorite t Tintaya and Chalcobamba Fat are cutby the dated units of quartz monzonite and dacite.

These plutons may have been emplaced as much asseveral million years or more earlier.Age of igneous ctivity of theAndahuaylas-Yauri belt

Many plutonic provinces nd volcanic ields n theinterior of western North America of comparable izeto the Andahuaylas-Yauri elt were active over a periodof about 10 m.y. or less. Examples nclude he southwest

porphyry province of Arizona, New Mexico, and So-nora, Mexico Livingston, 978), he San Juan olcanicfield of southwestern olorado Steven nd Lipman,1976), and the Boulder batholith of Montana Tilling,1974). Drawing on these and similar examples--par-ticularly the southwest orphyry province--as ana-1ogues, t is reasonable o conclude hat the bulk ofthe granitic ocks of the Andahuaylas-Yauri elt wereemplaced etween ate Eocene and middle Oligocenetime.

An early Oligocene age is supported by geologicrelations seen about 50 km south of Cuzco, whereplutons within the Andahuaylas-Yauri elt cut coarse

conglomerates eposited fter Eocene ncaic ectonism(Marocco, 978a, b). Provisionally orrelative tratawithin the Puno Group in southernmost eru havebeen dated as Oligocene on the basis of fossil evidence(Chanove t al., 1969), and conglomerates verlyingthe post-Incaic nconformity n central Peru are over-lain by volcanic ocks as old as 40 to 41 m.y. (Nobleet al., 1979b). The batholith s in turn overlain un-conformably y volcanic ocks of probable early Mio-cene age.


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174 SCIENTIFIC COMMUNICATIONS

TABLE 1. K-Ar Age Determinations on Rocks from Tintaya and Chalcobamba, Peru

Sample Field K20 4Ar* Agenumber number Mineral dated (wt %) (mole/gm X 10 ) Ar*/2Ar (m.y._ r)

1 CHB-75-75 Biotite 6.41 3.2332 0.69 34.7 _ 1.02 INF-613-75 Biotite 6.26 3.0663 0.63 33.7 _ 1.03 TIN-D1 Hornblende 1.015 0.4796 0.44 32.5 _ 1.0

Hornblende impure) 2.37 1.1480 0.51 33.4 _ 1.04 CHALCOB Biotite 9.32 4.4187 0.62 32.6 _ 1.0

Specimens: 1) potassium ilicate-altered uartz monzonite, drill hole 75-75, Chabuca zone, Tintaya, depth 127 to 131 m; (2) potassiumsilicate-altered uartz monzonite, drill hole 613-75, Inflexi6n zone, Tintaya, depth 159 to 164 m; (3) unaltered ike of hornblende- ndbiotite-bearing acite, Tintaya, surface ample, district coordinates 37, 510 N, 233, 790 E; (4) potassium ilicate-altered uartz monzoniteporphyry, Chalcobama, surface sample

Constants: K = 0.581 X 10-/yr; Ko = 4.962 X 10-1/yr; tomic bundance K= 1.167 X 10 4* Indicates radiogenic argon

Accepting he above nterpretation, he many skarnand associated ein deposits f the Andahuaylas-Yauribelt represent newly recognized eriod of middleCenozoic mineralization in the Andes of Peru. Almostall mineral districts previously dated have belongedto one of two age groups: n older group of Paleoceneage, which includes he major porphyry deposits fsouthern eru, and a younger group hat includes e-posits anging n age from middle Miocene o Qua-ternary e.g., McKee et al., 1979, and references itedtherein; E. H. McKee and D.C. Noble, unpub. data).

Relation of the Andahuaylas-auri elt toContemporaneous Volcanic Activity

in Central Peru

The presence and position of calc-alkalic gneous

activity n active margin settings s conventionally n-terpreted as being related o the geometry of the sub-ducting plate and its interaction with the aestheno-sphere nd/or the overlying plate. The absence f ig-neous ctivity along active margins may relate o shal-low-subhorizontal subduction with little or no aes-

thenosphere resent etween he two plates Mgardand Philip, 1976; Dickinson and Snyder, 1978). Ig-neous activity at relatively great distances rom thetrench implies that a shallowly subducting plate hasreached sufficient depth to trigger magma generation,that a subhorizontally oving plate has--at some pointinland from the trench--bent and descended at a

steeper ngle, or that the igneous ctivity s unrelatedto subduction. n the first two models, a shift in thelocus f igneous ctivity elative o the trench mpliesa change n the geometry f the subducting late.

The Andahuaylas-Yauri elt lies 150 to 200 km in-land northeast) rom he Cretaceous-Paleocene oastalbatholith and approximately 50 km inland from thepresently ctive volcanic chain (Fig. 1). The belt islocated about 100 km farther inland from the trench

than the axis of middle to late Miocene 10_+ m.y.)igneous ctivity n central Peru (Fig. 1) (Noble et al.,

1975; McKee et al., 1979; McKee and Noble, 1982).Nevertheless, t seems easonable, ecause f its markedelongation arallel o the trench, ts calc-alkalic har-acter, and because of abundant evidence for variablesubduction eometries n the central Andes Stauder,1975; Mgard and Philip, 1976; Barazangi nd sacks,1976; 1979; Noble and McKee, 1977; Hasagawa ndSachs, 981) to interpret he belt as related o sub-duction cf., e.g., Sillitoe, 1975).

Several ines of evidence, ncluding he radiometricages btained t Tintaya and Chalcobamba, he strati-graphic onstraints n he age of plutonic ctivity outhof Cuzco, and the geologic similarity of the igneousrocks nd mineralization hroughout he Andahuaylas-Yauri belt, suggest hat the belt is a southeast ontin-uation of the late Eocene-early Oligocene olcanic rc

recognized n central Peru (Noble et al., 1979b). Al-though he vents rom which the late Eocene-earlyOligocene olcanic ocks n central Peru were eruptedare not known, facies relations and the absence ofvolcanic and intrusive ocks of this age o the northeastindicate that the vents for the thick volcanic section

that mantles he post-Incaic rosion urface re ocatedbetween the axis of middle to late Miocene igneousactivity and the coastal batholith Fig. 1). This is atleast 100 km closer o the trench han he Andahuaylas-Yauri belt. Volcanic rocks of Eocene and Oligoceneage are absent along he western margin of the highAndes south of lat 14 S (Noble et al., 1979a; Tosdal

et al., 1981), and t is reasonable o place he ocus figneous ctivity at this latitude appreciably artherinland (Noble et al., 1979a).

An obvious difference between the Andahuaylas-Yauri belt and he late Eocene-early ligocene olcanicbelt in central Peru is the absence of known miner-alization within the latter. Possible xplanations ncludeexposure--no ntrusive bodies of this age are knownin central Peru--and a change n eruptive style and/or magma chemistry along he magmatic arc.

Although well-defined olcanic elt of early Neo-


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gene age is known n central Bolivia (Grant et al.,1979), the middle Cenozoic magmatic arc does notappear to remain inland south of Lake Titicaca. Al-though not known n southermost eru, rocks of latestEocene-early Oligocene ge are present n northern-most Chile only 250 to $00 km inland rom the trench

(Sillitoe, 1981).Available vidence lso suggests hat the magmaticarc was ocated nland during early Eocene nd perhapsPaleocene ime. Early Eocene gneous ctivity east ofthe Andahuaylas-Yauri elt is documented y a po-tassium-argon ge of 52.7 _ 2 m.y. obtained on thegranite f La Raya E. Audebaud, ers. ommun., 981)and by ages on uranium mineralization n the Cor-dillera Vilcabamba northeast of Cuzco (Lenz andWendt, 1969). The inland ocation f these ocks on-trasts with the near-coast osition of Paleocene-earlyEocene gneous activity in central and southernmostPeru Pitcher, 978; Stewart t al., 1974).

Implications for Paleogene SubduerionThe interpretation resented ere requires sig-

nificant ifference n subduction eometry rom centralto southern eru during middle and possibly arlyCenozoic time. Subduction in northern Peru wouldhave been of inclined geometry. n southern eru heplate may have descended t a low angle rom thetrench nland, although he relatively narrow natureof the Andahuaylas-Yauri elt suggests hat subhori-zontal ubduction oward he rench ave way at somepoint nland o a steeper ode f subduction cf.Has-agawa nd Sachs, 981, ig. 11). A warp n the sub-

ducting late, comparable o those ecognized n theTonga-Kermadec ubduction one Davies, 980) andtoday n central and southern eru (Hasagawa ndSachs, 981), could have existed. ssuming hat theIncaic tectonic phase eflected a change n the rateand/or direction f subduction nd/or he ntegrity fthe subducting late, onset f igneous ctivity n theAndahuaylas-Yauri eltasmuch s several illion earslater han n central Peru about 1 m.y. ago) mayhave been caused y the greater ime required orlithosphere o reach he depth beneath he belt nec-essary o trigger magmatic activity (cf. Noble andMcKee, 1977).

In southern eru here was shift of gneous ctivityof about 150 km or more oward he trench hroughmiddle and ate Cenozoic ime after an even argernortheastward hiftduring he early Tertiary. n centralPeru, on he other hand, Cretaceous hrough eogeneigneous ctivity has almost entirely been constrainedto a belt ess han 100 km wide. We find t significantthat the inland shift of late Eocene-early ligocene,and probably lder, magmatic ctivity ook place atapproximately he same atitude ecause 1) the highAndean lateau, he zone of Cenozoic gneous ctivity,

the continental crust below 50 km, and the negativeBouguer ravity nomaly ll widen markedly Institutode Geologla MinerVa el Per6, 1975: James, 971);(2) folds and other structural eatures n Paleozoic ndyounger rocks change to an east-west rend at theAbancay deflection Marocco, 1978a, 1978b, 1979);

and $) a regional lectrical onductivity nomaly hiftsinland Schmucker t al., 1966).The correspondence mong crustal features and

patterns f subduction nd magmatic ctivity eads othe speculation hat long-established eatures of thecontinental ithosphere may have influenced he be-havior of oceanic plates subducting eneath hem, asdiscussed y Mgard (1978). Such ontrol, f present,apparently was ncomplete, or Paleogene gneous c-tivity in southernmost eru and northern Chile appearsto have been localized near the coast.

AcknowledgmentsThis study was partly supported y grants rom the

National Science oundation. MINERO-PERU pro-vided ogistical upport or the work at Tintaya. Wethank Ings. Mariano berico, Jos Me]ia, and ElmerVidal or facilitating his phase f the project. rancoisMigard nd Ulrich Petersen ffered elpful ommentson an early draft of the manuscript.April 6, 1983

REFERENCES

Barazangi, .,and sacks, .,1976, patial istribution fearthquakesand ubduction f heNazca late eneath outh merica: eology,v. 4, p. 686-692.

-- 1979, Subduction f the Nazca plate beneath eru: Evidence

from patial istributionfearthquakes: eophys.our. oyal stron.Soc., v. 57, p. 557-555.Bellido, ., Girard, ., and Paredes, ., 1972,Mapametallogenico

del Per6: Peru, Servicio Geol. y Minerla.Chanove, ., Mattauer, ., and Mgard, F., 1969, Precisions ur a

tectonique angentielle des terraines secondaires u massif Pirin(nord-ouest u lac Titicaca, rou): Acad. ci. Paris], omptesRendus, er. D, v. 368, p. 1698-1701.

Davies, .F., 1980.Mechanics fsubducted ithosphere:our. eophys.Research, . 85, p. 6g04-6518.

Dickinson, W. R., and Snyder, W. S., 1978, Plate ectonics f theLaramide rogeny: eol. Soc. America Mem. 151, p. 355-366.

Grant, . N., Halls, C., Avila Salinas,W., and Snelling, .J., 1979,K-Arages f gneous ocks nd mineralization n parts f he Boliviantin belt: ECON.GEOL., . 74, p. 858-851.

Hasagawa, ., and Sachs, . S., 1981, Subduction f the Nazca platebeneath eru, determined rom seismic bservations: our.Geophys.Research, . 86, p. 4971-4986.

Instituto e Geologla Minerla del Per6, 1975, Mapa geol(gico elPer6: Peru, Ministerio nergia Minas.

James, . E., 1971, Andean rustal nd upper mantle tructure: our.Geophys. Research, . 85, p. $246-8271.

Lenz, H., and Wendt, J., 1969, Pb/U-Altersbestimmungen n per-uanischen Uran-Erzen aus dem Gebiet yon Vilcabamba, ProvinzConvencion, eru: Zeitschr. eutsch. Geol. Gesell. ahrgang 966,p. 368-376.

Livingston, . E., 1975, A plate ectonic ypothesis or the genesisof porphyry opper eposits f the southern asin nd Range rov-ince: Earth Planet. Sci. Letters, . 20, p. 171-179.


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176 SCIENTIFIC COMM UNICA TIONS

Marocco, R., 1978a, Un segment -W de la chane des Andes -ruviennes: a defiexion 'Abancay. tude ologique e a Cordill'reoriental des hauts plateaux entre Cuzco et San Miguel. Sud duPros 1230'S 1400'S): rance, Office Recherche ci. Tech.Outre-Mer., Traveaux Docs., 195 p.

-- 1978b, Estudio eolgico e la Cordillera e Vilcabamba: nst.Geologla Minerla del Per6, Bol. 4, set. D (Estudios speciales),157 p.

-- 1979, Corte estructural de la cordillera de los Andes Peruanosal nivel de la defiexibn e Abancay. Ensayo e interpretacibn eesta defiexin: Soc. Geol. Per6 Bol., v. 63, p. 51-68.

McKee, E. H., and Noble, D.C., 1982, Miocene volcanism and de-formation n the Western Cordillera and high plateaus f south-central Peru: Geol. Soc. America Bull., v. 93, p. 657-662.

McKee, E. H., Noble, D. C., Scherkenbach, . A., Drexler, J. w.,Mendoza, os, and Eyzaguirre, . R., 1979, Age of porphyry n-trusion, potassic lteration, and related skarn mineralization, An-tamina district, northern Peru: ECON.GEOL.,v. 74, p. 928-930.

Mgard, F., 1978, Etude gologique es Andes du Prou central:France, Office Recherche Sci. Tech. Outre-Mer Mem. 86, 310 p.

Mgard, F., and Philip, H., 1976, Plio-Quaternary ectonic-magmaticzonation and plate tectonics n the central Andes: Earth Planet.Sci. Letters, v. 33, p. 231-238.

Noble, D.C., and McKee, E. H., 1977, Spatial distribution f earth-quakes nd subduction eneath outh America: omment: eology,v. 5, p. 576-579.

Noble, D.C., McKee, E. H., Farrar, E., and Petersen, U., 1974,Episodic enozoic olcanism nd tectonism n the Andes f Peru:Earth Planet. Sci. Letters, v. 21, p. 213-221.

Noble, D.C., Bowman, H. R., Hebert, A. J., Silberman, M. L., Her-opoulos, . E., Fabbi, B. P., and Hedge, C. E., 1975, Chemicaland sotopic onstraints n he origin of low-silica atite and andesitefrom the Andes of central Peru: Geology, . 3, p. 501-504.

Noble, D.C., Farrat, E., and Cobbing, . J., 1979a, The Nazca Groupof south-central eru: Age, source, nd regional volcano-tectonicsignificance: arth. Planet. Sci. Letters, v. 45, p. 80-86.

Noble, D.C., McKee, E. H., and Mgard, F., 1979b, Early TertiaryIncaic tectonism, plift, and volcanic ctivity, Andes of central

Peru: Geol. Soc. America Bull., v. 90, p. 903-907.Pitcher, W. S., 1978, The anatomy f a batholith: Geol. Soc. London

Jour., v. 135, p. 157-182.Santa Cruz, S., Guerrero, T., Castilia, F., Caro, E., and Candiotti, H.,

1979, Geologla e yacimientos e cobre en skarn en la regionsur-oriental el Per6: Soc. Geol. Per6 Bol., v. 60, p. 153-174.

Schmucker, U., Forbush, S., Hartmann, O., Giesecke, A., Casaverde,M., Castillo, J., Salgueiro, R., and Del Pozo, S., 1966, Electricalconductivity nomaly nder he Andes: arnegie nst. Washington,Year Book 65, p. 11-28.

Sillitoe, R. H., 1975, Subduction nd porphyry copper deposits nsouthwestern orth America; a reply to recent obiections: CON.GEOL., v. 70, p. 1474-1477.

-- 1981, Regional spects f the Andean porphyry opper belt inChile and Argentina: nst. Mining Metallurgy Trans., v. 90, sec.B, p. B15-B36.

Stauder, W., 1975, Subduction f the Nazca plate under Peru asevidenced by focal mechanisms nd by seismicity: our. Geophys.Research, . 81, p. 1053-1064.

Steven, T. A., and Lipman, P. W., 1976, Calderas of the San Juanvolcanic ield, southwestern olorado: U.S. Geol. Survey Prof.Paper 958, 35 p.

Stewart, J. w., Evernden, J. F., and Snelling, N.J., 1974, Age de-terminations rom Andean Peru--a reconnaissance urvey: Geol.Soc. America Bull., v. 85, p . 1107-1116.

Terrones ., A. J., 1958, Structural ontrol of contact metasomaticdeposits n the Peruvian cordillera: Am. Inst. Mining Metall. Pe-troleum Engineers, . 211, p. 365-372.

Tilling, R. I., 1974, Composition nd time relations f plutonic andassociated olcanic ocks, Boulder atholith egion, Montana: Geol.Soc. America Bull., v. 85, p. 1925-1930.

Tosdal, . M., Farrar, E., and Clark, A.M., 1981, K-Ar geochronologyof the late Cenozoic volcanic rocks of the Cordillera Occidental,southernmost eru: Jour. Volcanol. Geotherm. Research, . 10, p.157-174.

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