317

CRYPTIC CIND PFIRTIFILLY BURIED CCILDERM &LONG CI STRIKE-SLIP FAULT SYSTEM IN THE CENTRCIL CINDES.

Jose German Viramontea and Ivan Alejandro Petrinovic*

1 CONICET - Universidad National de Salta, Facul tad de Ci enci as Natural es Buenos &ire5 177 - 4.400 Sal ta Republica Argentina.

Resumen.

Se descr i ben una serie de cal deras cripticas Y/o parci al mente soterradas, de edad Cenozoica, asoci adas a lineamientos tect6nicos de orientacidn NS y ONO-ESE en 105 Andes Centrales.

Key words: cal deras - Central (Sndes - ignimbrites - strike- slip fault.

In the Central Andes (16°S-2G0S) a major calcalkaline volcanic province (CVZ) developed from lower Miocene to the Present related to the subduction of the Nazca plate be1 ow the South American Plate. One of the 1 argest volumes of ash-f 1 ow sheet e. in the world is exposed in the Puna -Altiplano plateau (CVZ) ; but few of them are evidently related with known emission La Pacana Cal der a” ; Gonz al et Ferran et al 1985 “Wheelwright Caldera”; Coira et al 1987; Ort et al, 1997 “Cerro Panizos Caldera”; Seggiaro et al 1986 “Pair i que and Coranzuli complex”; Viramonte et al. 1984a “Ramadas Caldera” ; Llambias, 1971 “Farall6n Negro complex”, etc). On the other hand, a close relationship betwFen Cenoz oi c volcani 5m and major N-S structures and WNW-ESE transcurrent fault system between 2,305-2805 were established by Vi ramonte et al (1984) and Gonzalez Ferrdn et al. (1985) for the Ojos de1 Sal ado area. FIGURE la

REFERENCES

Yak are Caldora rim

WNW-ESE mgcfmcturn

N-s hOId kctonlo owucl

Eati valcanlc ahain

Troavonal VOIWIIC chair

3. La RJcom mIdem 4. Awas Colientcs c&era s.Cdan ~ldrro 6. Cnro E4oncacoldcra 7.WMtigM cdderci 8. Faral!on Negro cddcra _.“__ . -lcI”II..

319

This relationship produced: a) the N-S trend main magmatic arc along the Argentine-Chilean-Bolivian boundary (principal volcanic range), b) the secondary volcanic range, located on the Puna-Western Cordilleran border and c) the WNW-ESE Transversal Volcanic Chains that developed to the east of the first one (Viramonte et al 1984b) (fig la) such as: 1) Liper Megafracture, related to Paniros-Coranruli Transverse Volcanic Chain. 2) Calama-Olacapato-El Toro (COT) left lateral Transcurrent fault with Puntas Negras- Puevar volcanic chain. 3) Archibarca-Galan megafractures with Archibarca- Beltran-Galan Volcanic chain. 4) Culampaja tlegafracture with Carachipampa-Farall6n Negro Volcanic chain. 5) Tucuman-Aconquija megafracture with Ojos de1 Salado- Wheelwright volcanic chain. A detailed analysie of this volcano-tectonic relationship, suggest5 that the main ignimbrite 5ources (caldera complex) in the CVZ, are in the transversal volcanic chain system and-or in the NS-volcanic arcs-Transversal volcanic chain intersections (figure la). Altough the Puna-Altiplano region is highly preserved in its geology, in several case5 the above described situation produces a darkening of the true ignimbrite source structures, because of beheading, deformation, lack of caldera rim, covering by younger volcanic units, avalanches, etc., due to the movement5 of the megafractures. i.e.: strong deformation in the north end of the resurgent La Pacana dome and lack of it5 northern caldera rim (see Gardeweg and Ramirez, 1987, pp. 549, fig.2 and 9), lack of the northern rim and beheading of the Aquas Calientes caldera complex (figure lb) and deformation in the Acay subvolcanic qranitic complex (see Llambias et al, 1985 pp. 160), due to transurrent movement of the COT meqafracture. Keeping this in mind, we found a good example of cryptic and partially buried calderas in the central area of COT megafracture where at least five ignimbrite 5ource5 exist (figure lb): Aquas Calientes Caldera complex ;El Mot-t-o caldera; Organullo caldera; Rupasca shield and Ramada5 caldera. An overview of the CVZ reveals that such examples should be quite common. Considering the large volumes of iqnimbrites in the Central Andes, we believe that over one hundred associated caldera structures must be present, such a5 Smith (1979) has showed for western United States. At last, we point out the importance of the recognition of this type of caldera complex and its evolutive history because many large epi thermal Au-Sb;Pb-Ag-Zn and Cu ore deposits are associated to them.

Ref er ences .

BAKER, M.C.W. (1981): The nature and distribution of Upper Cenozoic iqnimbrites centre5 in the Central Andes.3,Vglc,Gepth.Res, 11:293-315. 320

CDIRA, 8, AND PARIS, R. (1991): Estratigrafia de1 Area volcanica de1 Cerro Tuzgle. _e: CoDg,.egl,~rgL 3: 659-671. COIRA, 8.. MAZZONI, M. y J.C. MERODIO (19871: Cerro Paniros: un centre emisor daci tico, Jujuy, Argentina. Dogim!? !&CgC_esg Ge@_ogisg Ar-ge_ntinp. Actas 4: 338-340. DAVILA, M.S. (19811: Cailioma:caldera tipo Valle.@glekFD '&g:GggL, _PeCg. 68:25-35. FRANCIS, P.W., HAMIIILL, M., KRETZSCHtlAR, G., THORPE, R.S. (1978): The Cerro Gal&n Caldera, NW Argentina and its tectonic setting. y&u_r_p 274: 749-751. GARDEWEG, M. y RAMIREZ, C.F. (1995): Hoja Rio Zapaleri. C_art_a _G3glgLi_a 9% Cl=1119. Serv. Nac. de Geol y Miner n066. GARDEWEG, M. y RAMlREZ, C.F. (19871: La Pacana caldera and the Atana ignimbrite. A major ash-flow and resurgent caldera complex in the Andes of northern Chile. Bul_L, !!olg_an!QlL: 49:547-566. GONZALEZ FERRAN, 0.. BAKER, P.E. L REX. D.C., (1985): Tectonic-volcanic discontinuity at latitude 27O S Andean range associated with Nazca plate subduction. IggtgngghY~~gs 112: 423-441. GUEST, J.E. (1969): Upper Tertiary ignimbrites in the Andean Cordil lera, Antofagasta provicnce, North Chile. Geol: _SQg: _and l+llz 80:337-362. KUSSMAUL, S., HORMANN, P.K., PLOSKONKA, E, and SUBIETA. T. (1977): Volcanism and structure of southwestern Bolivia. J-5 Volcano1--~-----'__--~_--'-_-~ Geotherm Res 2:73-111. LLAMBIAS,E.J. (1970): Geologia de 10s yacimientos mineros de Aqua de Dionisio. -__:Rev d_e l_a !%%-c: AC9: d!? MBCQC_al,, Petroll y Sedi_m_e.e&, l(l-21: 2-32. MARINOVIC, N. & LAHSEN, A., (1984): Hoja Calama, Regibn de Antofagasta. SeCy- l$~, gg GeQi, y uiCgC_air c_aCt_a &gl, de Crlil_e. 58 pp 140. NOBLE, D.C. FARRAR, E. b COBBING, E.J., (1979): The Narca group of South-Central Peru: Age, source and regional Volcanic and Tectonic siqnificance.EaZLel-~~~:~~~4S:SO-06 NOBLE, D.C., MCKEE, E.H., (1982): Nevado Portugueza volcanic center, Central Peru: a Pliocene central volcano collapse-caldera complex with associated si 1 ver mineralization. EcoD, Geol--.__I 77:1893-1900. ORT, M., COIRA,B., MAZZONI ,M., F1SHER.R.V. y MATT I NSON, J.M., (1987): Volcanismo ignimbritico de1 Cerro Panizos, Juj uy Argentina. Dcime_Cnngreso_Gn~Lbg~~g_ Ayge_ct_Lng, Actas 4: 335-337. SEGGIARO, R., GORUSTOVICH, A. y MARTI, F., (1986): Las ignimbritas de1 cornplejo volcanico Coranzuli (Puna Argentina- Andes Centrales). E_sf,~gg~L 43(5-6):345-X9. VIRAMONTE, J.G., OMARINI, R.H., ARAKA, V., APARICIO, A., GARCIA CACHO, L. y PARICA, P., (1984a): Edad. Genesis y met an i 5mos de erupci6n de las riolitas qranatiferas de San Antoni 0 de 10s Cobres. provincia de Salta. Noveno-----_ Congreso Ggglgg,ip ACgeptino. Actas III: 216-233. VIRAMONTE, J.G., GALtISlc.1, M.A., ARAr;A, V.. APARICIO, A., GARC I A CACHO, L. y MART IN ESCORZA. C., (1984b): El finivulcanismo bdsico de la depresi6n de Arizaro, provi nci a de Salta. Ng_ve_ng Congreso Geol69'gg F\rgentino, Actas III: 234-251.