Late Tertiary Volcanic Episodes in the Area of the City of Santiago De Chile: New Geochronological and Geochemical Data

Journal of South American Earth Sciences 17 (2004) 227–238 www.elsevier.com/locate/jsames

Late tertiary volcanic episodes in the area of the city of Santiago de Chile: new geochronological and geochemical data

M. Vergaraa,*,L.Lo´pez-Escobarb, J.L. Palmaa, R. Hickey-Vargasc, C. Roeschmannd

aDepartamento de Geologıá, Universidad de Chile, Casilla 13518, Correo 21, Santiago, Chile bGrupo Magma´tico, Instituto GEA, Universidad de Concepcioń, Casilla 160-C, Concepcioń 3, Chile cDepartment of Earth Sciences, Florida International University, Miami, FL 33199, USA dServicio Nacional de Geologıá y Mineralogia

Received 1 February 2002; accepted 1 June 2004

Abstract

In the area of the city of Santiago de Chile, it is possible to distinguish at least three subvolcanic episodes. The ﬁrst is late Oligocene (30.9–25.2 Ma), and its products range from basalt to rhyolite. The second episode is early Miocene (22.3–20.3 Ma), and its products are two-pyroxene basalts to basaltic andesites. The third episode, though also early Miocene, is slightly younger than the second (20.3–16.7 Ma) and produces mainly amphibole-bearing dacitic porphyries. Samples from the three episodes are medium- to low-K calk-alkaline rocks. All are enriched in LILE relative to N-MORB and have La/Nb ratios O1.6 and Ba/La ratios O20. Each episode differs from the others in heavy REE concentrations and La/Yb ratios. Sr-, Nd-, and Pb-isotope ratios for the early Miocene rocks are similar to those of Quaternary volcanic rocks from the central SVZ (378–41.58S) of the Andes and unlike those of the Quaternary of the northern SVZ. Three samples reported here have nearly identical isotope ratios, though the La/Yb ratios range from 3 to 35. q 2004 Elsevier Ltd. All rights reserved.

Keywords: Central Chile; Geochemistry; Geochronology; Miocene volcanism; Sr-, Nd-, and Pb isotopes Resumen

En el a´rea de la ciudad de Santiago se distinguen, al menos, tres episodios subvolcańicos. El primero es del Oligoceno Tardıó (30,9 a 25,2 Ma) y la composicioń de sus rocas varıá de basaltos a riolitas. El segundo episodio es del Mioceno Temprano (22,3 a 20,3 Ma) y la composicioń de sus rocas es del tipo de basaltos de dos piroxenas a andesitas basa´ltica. El tercer episodio es tambien del Mioceno Temprano, pero un poco ma´s joven que el anterior (20,3 a 16,7 Ma) y su tipo de roca asociado corresponde a po´rfidos de anfı´bola. Las muestras de rocas de los tres episodios son calcoalcalinas con contenidos de K bajo a medio. Todas las muestras estań enriquecidas en LILE relativas a la concentracioń del N-MORB, y tienen razones La/Nb O1,6 y de Ba/La O20. Cada episodio es diferente de los otros en sus concentraciones de HREE y razoń La/Yb. Las razones isoto´picas de Sr, Nd y Pb de las rocas del Mioceno Temprano son similares a las rocas volcańicas del Cuaternario de la parte central del SVZ (378–41, 58S) de los Andes de Chile y son diferentes a las del extremo norte del SVZ. Los tres ana´lisis isoto´picos aquı´ presentados, tienen casi identicas razones a pesar de su amplio rango de la razoń La/Yb que cambia de 3 a 35. q 2004 Elsevier Ltd. All rights reserved.

1. Introduction rocks that make up the cluster of hills within and adjacent to Santiago, the capital city of Chile (Figs. 1 and 2). We present new geochronological, geochemical, and We discuss four principal belts or clusters of hills (Fig. 1): isotopic data for Tertiary volcanic and shallow plutonic (1) the Manquehue–San Cristo´bal–Santa Lucıá belt, which has a northeast direction. Its southwestern end (Cerro Santa Lucıá) extends into the middle of the city. It stands out, * Corresponding author. E-mail addresses: [email protected] (M. Vergara), llopez@ like a keel, above the alluvial fill of the Mapocho river; udec.cl (L. Lo´pez-Escobar), hickey@fiu.edu (R. Hickey-Vargas). (2) the Conchalı´ belt to the north includes Cerro Gordo

Fig. 1. Satellite image of the area of Santiago de Chile. and Cerro Las Canteras, whose rocks were used to pave the The hills consist principally of volcanic and subvolcanic streets of Santiago in colonial times; (3) Cerro Renca, rocks of Tertiary age. Volcanic and volcanoclastic rocks south of the Conchalı´ belt, is an isolated hill that also rises occur in the Abanico–San Ramoń–Provincia and Conchalı´ above the alluvial fill of the Mapocho river; and (4) the belts, as well as Cerro San Cristo´bal and Cerro Renca. The Abanico–San Ramoń–Provincia belt, which is the highest subvolcanic rocks are represented by porphyritic stocks, elevation dominating the Santiago landscape. The last belt dykes, and necks, most of which are of a basaltic to basaltic represents the eastern boundary of the city and is separated andesite composition. Subvolcanic rocks of dacitic compo- from the central valley, or central depression, where the sition occur at Cerro Manquehue, which limits the northern city is located, by the San Ramoń fault (Rauld, 2002). part of the city, and at Rinconada de Conchalı´. According to gravimetric data (Avendanõ and Araneda, 1994), the alluvial fill of the central valley varies from 400 to 800 m thick. Its age is probably Pliocene–Quaternary. 2. Regional geology The alluvial deposits overlie a concealed basement that, at depth, exhibits irregular relief and is formed by volcanic and The regional geology of the Santiago area has been studied subvolcanic rocks similar in lithology to the nearby hills. by several investigators. On the geological map of Santiago, M. Vergara et al. / Journal of South American Earth Sciences 17 (2004) 227–238 229

Fig. 2. Geological sketch map of the studied area, including the age of the different units. at 1:250,000 scale, Thiele (1980) distinguishes two units: (1) with the first petrologic data for its rocks, and Thiele et al. the Abanico Formation (late Cretaceous–Oligocene) and (2) (1980) study the geology of Cerro Renca. Recent strati- subvolcanic rocks, mainly volcanic necks and stocks, of graphic and geochemical studies of the volcanic rocks of Miocene age. Wall et al. (1999) provide a geological map of Santiago have been carried out by Selle´s (1999) and the Tiltil–Santiago area at a scale of 1:100,000, and Selle´s Nystro¨m et al. (2003). (1999) has published a geological map of the Santiago The Abanico–San Ramoń–Provincia belt limits the quadrangle at a scale of 1:50,000. These two works, eastern part of Santiago. The mountains comprise a huge supported by Ar/Ar dating, corroborate the presence of two stratified pile that reaches more than 3000 m, is intruded by age clusters of Oligocene and Miocene ages only. many stocks and porphyry dikes, and is much larger and Geological works at larger scales, carried out in local more heterogeneous than the cluster of hills north of the areas, include those of Mo¨rike (1896), Katsui and Vergara city. Nystro¨m et al. (2003) have studied the stratigraphy and (1966), Vergara (1971) and Thiele et al. (1980). Mo¨rike geochemistry of the Abanico Formation, which consists of (1896) determines the petrographic characteristics of units basaltic lava flows, silica-rich pyroclastic flows, and that crop out in the Manquehue–San Cristo´bal–Santa Lucıá continental lacustrine deposits. and Conchalı´ belts. Katsui and Vergara (1966) and Vergara Cerro San Cristo´bal (899 m a.s.l.) represents the center of (1971) provide a geological map of Cerro San Cristo´bal, the Manquehue-San Cristo´bal–Santa Lucıá belt (Fig. 1), 230 M. Vergara et al. / Journal of South American Earth Sciences 17 (2004) 227–238 which has a NE–SW direction. This hill rises 300–370 m Cerro Renca (900 m a.s.l.) is located at the NNW above the central valley. Katsui and Vergara (1966) periphery of Santiago (Fig. 2), rises 400 m above the describe two superimposed units of dacitic to rhyolitic Quaternary valley fill, and is an isolated hill (‘Cerro testigo,’ welded tuffs (ignimbritic pyroclastic flow deposits) that are Thiele et al., 1980). It is a subvolcanic stock, consisting of dark reddish-brown in color. They have a combined two-pyroxene basaltic andesite porphyry. This subvolcanic thickness of 120 m, strike 208–408 eastward, and dip body intrudes continental volcanic strata (andesitic lava 158–208 southward. The lower unit is more continuous flows, conglomerates, tuff, and breccia) that belong to the than the upper and contains pumice fragments (90%) and same rock unit that outcrops at the Manquehue–San accidental clasts of andesitic composition that can reach 2 m Cristo´bal–Santa Lucıá belt (Selle´s, 1999). in diameter (possible lag breccias). The lower unit is cut by The Conchalı´ belt (Fig. 1), comprised of Cerro Gordo and dykes and intrusive domes of dacitic to rhyolitic compo- Cerro Las Canteras, is located in the NNW part of the studied sition. The upper welded tuff unit is restricted to small areas area. Both Cerro Gordo (1481 m a.s.l.) and Cerro Las and exhibits glassy fiammes, altered to zeolites and other Canteras (750 m a.s.l.) are subvolcanic basaltic andesite clay minerals. The latter unit was named ‘San Cristo´bal porphyries that intrude the El Carrizo basaltic andesite lavas. welded tuffs’ by Selle´s (1999), who suggests the tuffs also outcrop in the isolated hills of the Chicureo Valley, northwest of the San Cristo´bal exposure, where they are 3. Petrography known as Las Rodrı´guez welded tuffs. In Cerro Las Rodriguez (Fig. 2), the welded tuffs present a N308–508W/ Vergara and Lo´pez-Escobar (1980) and Lo´pez-Escobar 308–608NE direction and delineate, in conjunction with the and Vergara (1997) have determined the petrographic and San Cristo´bal welded tuffs, the margins of a possible geochemical characteristics of subvolcanic rocks from the collapse caldera (Selle´s, 1999). Overlying the welded tuffs, Andean precordillera between Pocuro (338S) and Santiago there is an approximately 500-m thick packet of aphanitic (338300S). According to these features, the intrusive bodies basaltic andesite lavas (El Carrizo; Gana and Wall, 1997), were subdivided into two units consisting of two-pyroxene- breccia tuffs, and continental sedimentary rocks. Gana and bearing basaltic to basaltic andesite porphyries and their Wall (1996, 1997) subdivide them into three units, whereas fine-grained equivalents (dikes and chilled borders) and Selle´s (1999) suggests two units, Conchalı´ and Colina. amphibole-bearing dacitic porphyries and their fine-grained Herein, we combine the latter two units into a single unit equivalents. (basic lavas and lacustrine deposits, Fig. 2). Two-pyroxene-bearing basaltic to basaltic andesite Field relationships show that the San Cristo´bal welded porphyries occur at Cerro Las Canteras, Cerro Gordo, tuffs are intruded by three major subvolcanic bodies that Cerro Renca, Cerro San Cristo´bal, and Cerro Santa Lucıá. consist of two pyroxene porphyries, aligned along the same They are commonly microcrystaline rocks, dark grey to direction of the whole belt (Katsui and Vergara, 1966): Cerro black in color, and have phenocrysts of (1) plagioclase San Cristo´bal, Cerro El Salto, and La Pira´mide. In addition, (40–30%), generally zoned, with a composition of Cerro San Cristo´bal is intruded by an orthopyroxene andesite An65–An90; (2) augite (15–10%); and (3) orthopyroxene dyke that outcrops at the base of the monument to the Virgin (5–10%). The groundmass has a microgranular texture and Mary, which is located at the summit of the hill. is formed by plagioclase microlites, augite, orthopyroxene, Cerro Santa Lucıá, at the southwest end of the magnetite, and secondary minerals such as small veins and Manquehue–San Cristo´bal–Santa Lucıá belt in the middle amigdules of zeolites, calcite, chlorite, and quartz. Olivine of Santiago (Fig. 1), is a 300-m thick dyke with a N468E/ has not been found as either phenocryst or microcryst in the 608NW orientation (Selle´s, 1999). Its composition corre- groundmass. sponds to a two-pyroxene basaltic andesite. It may have Porphyritic orthopyroxene andesites are also present but been a feeder for a larger edifice at the foot of Cerro San are sparse. They appear as dykes that cut the two-pyroxene Cristo´bal. porphyritic stock of Cerro San Cristobal and contain Cerro Manquehue (1638 m a.s.l.), which rises approxi- phenocrysts of plagioclase (An40–An60, 30%) and micro- mately 1000 m above the central valley, represents the phenocrysts of orthopyroxene (20%). Their groundmass is northeast extreme of the Manquehue–San Cristo´bal–Santa intergranular and formed by plagioclase microlites and Lucıá belt. It is a stock consisting of a hornblende-bearing micrograins of orthopyroxene and magnetite. dacitic porphyry. The facies present at the summit are fine The amphibole-bearing dacitic porphyries and their grained, but rocks that outcrop at the lowest topographic fine-grained equivalents are found at Cerro Manquehue, levels (e.g. Agua del Palo valley, Rinconada de Conchalı´ Cerro El Penõń, Cerro El Buitre, and Rinconada de quarries) are coarse grained. Conchalı´ (Fig. 2). They are holocrystalline rocks, clear to Cerro El Penõń is located approximately 2 km NE of the dark grey in color, with phenocrysts of plagioclase top of Cerro Manquehue (Fig. 2). It also is a stock that (25–35%; An25–An40) and hornblende (5–10%). The consists of a hornblende-bearing dacitic porphyry. Its petro- groundmass is formed by micropegmatites of alkali graphic composition is similar to that of Cerro Manquehue. feldspar and quartz. M. Vergara et al. / Journal of South American Earth Sciences 17 (2004) 227–238 231

4. Geochronology 1999)(Fig. 2), which support an Oligocene age for these volcanic rocks. K/Ar and Ar/Ar ages have been obtained for samples from Two K/Ar age determinations for samples from the the following localities: Cerro El Abanico, Morro Las Cerro San Cristobal welded tuff also have been made. A´ guilas, Cerro San Cristo´bal, Cerro Las Canteras, Cerro Drake et al. (1976) measured plagioclase and obtained an age Renca, Cerro Gordo, Cerro Santa Lucıá, Cerro Manquehue, of 28.3G0.7 Ma; for biotite, Selle´s (1999) obtained an age of and Cerro El Penõń. We show the localities in Fig. 2 and 25.2G1.4 Ma. Also, two plagioclase Ar/Ar ages of 26.6G provide data in Table 1. 1.2 and 23.6G0.8 Ma were determined for samples from the Lava flows of the lower member of the Abanico–San Morro Las A´ guilas basaltic-andesite lavas, which overlie Ramoń–Provincia belt (Fig. 1) were dated. Three plagio- the Cerro San Cristobal welded tuff (Selle´s, 1999). According clase Ar/Ar age determinations (total fussion) for basaltic- to these radiometric data, the San Cristo´bal welded tuffs and andesite samples from Cerro El Abanico give values of Morro Las A´ guilas aphanitic lavas, similar to the Abanico– 30.9G1.9; 25.7G1.0, and 25.6G0.6 Ma (Vergara et al., San Ramoń–Provincia belt, are Oligocene in age.

Table 1 K/Ar and 40Ar/39Ar ages of samples from nearby Santiago hills

Sample Lithology Sample Mineral Age (Ma) %K Ar rad %Ar atm Reference location (ml/g) K/Ar Ages DS-168 Amphibole El Penõn Amphibole 11.6G1.3 0.353 0.160 71 Selle´s (1999) dacitic porphyry SnCr-03 Orthopyrox- San Cristo´bal Whole rock 13.1G0.9 0.576 0.294 70 This work ene Andesite GM-1181 Amphibole Manquehue Whole rock 16.7G0.9 0.884 0.578 66 Gana and Wall dacitic (1997) porphyry AG-451 Amphibole Manquehue Plagioclase 19.5G0.5 0.697 0.532 68 Drake et al. dacitic (1976) porphyry StaL-01 Basaltic Santa Lucıá Whole rock 20.3G1.9 0.481 0.382 55 This work andesite AP-01 Amphibole Manquehue Amphibole 20.3G5.4 0.198 0.157 90 This work dacitic porphyry LS-1 Pyroxene Santa Lucıá Whole rock 21.1G3.7 0.480 0.396 69 Selle´s (1999) andesitic porphyry DS-191 OpxCCpx Cerro Gordo Whole rock 21.2G1.0 0.721 0.599 54 Selle´s (1999) andesitic porphyry TH-11 OpxCCpx Cerro Renca Whole rock 21.8G0.5 0.530 0.466 70 Thiele (1980) basaltic-andesite porphyry H-157 OpxCCpx Cerro Las Whole rock 22.3G1.8 0.540 0.470 70 This work basaltic-ande- Canteras site porphyry DS-243 Ash tuff San Cristo´bal Biotite 25.2G1.4 0.484 0.478 63 Selle´s (1999) SCr-01 Rhyolitic San Cristo´bal Plagioclase 28.3G0.7 0.353 1.743 66 Drake et al. welded tuff (1976) 40Ar/39Ar Ages GM-1188 Basaltic Morro Las Plagioclase 23.7G0.8 95 Gana and Wall andesite A´ guilas (1997) DE-21 Basaltic Morro Las Plagioclase 26.6G1.2 56 Gana and Wall andesite A´ guilas (1997) Rb-07 Basalt Cerro El Plagioclase 30.9G1.9 Vergara et al. Abanico (1999) Rb-9B Basalt Cerro El Plagioclase 25.6G0.6 Vergara et al. Abanico (1999) Rb-6A Andesite Cerro El Plagioclase 25.7G1.0 Vergara et al. Abanico (1999) Table 2 232 Major and trace element abundances in the Tertiary volcanic and subvolcanic rocks from the Santiago hills

Sample Rb-07 Rb-9B Rb-6A SCr-01 DS-205 DS-229 StaL-01 TH-11 H-157 LS-1 SCr-02 AP-01 AG-451 DS-241 DS-072 Age 30.9 Ma 25.6 Ma 25.7 Ma 28.3 Ma 25–28 25–28 20.3 Ma 21.8 Ma 22.3 Ma 21.1 Ma 20.3 Ma 19.5 Ma 19 Ma 11.6 Ma Ma(?) Ma(?) Abanico Abanico Abanico San Cerro Las Santa Cerro Las Can- Santa San Manque- Manque- San El Penõń Fm Fm Fm Cristo´bal Blanco Rodrı´- Lucıá Renca teras Lucıá Cristo´bal hue hue Cristo´bal guez (dyke)

SiO2 49.94 50.54 58.54 69.97 68.87 72.15 49.20 51.22 52.01 54.62 57.80 61.10 61.18 55.19 57.63 TiO2 1.40 1.55 0.73 0.22 0.17 0.15 0.73 0.60 0.72 0.60 1.00 0.61 0.65 0.78 0.80 Al2O3 16.97 16.30 15.53 14.67 15.18 12.09 19.10 19.02 17.60 17.10 16.94 16.05 17.52 18.80 19.20 227–238 (2004) 17 Sciences Earth American South of Journal / al. et Vergara M. Fe2O3 (T 13.00 12.96 8.25 5.05 4.93 2.18 13.94 13.57 13.18 11.75 9.71 5.85 5.95 7.36 6.48 calc) MnO 0.19 0.22 0.13 0.08 0.15 0.06 0.12 0.14 0.14 0.13 0.10 0.06 0.06 0.08 0.08 MgO 3.80 3.77 3.59 0.37 0.67 0.46 2.70 3.59 3.67 2.10 2.33 2.32 2.28 3.13 2.57 CaO 9.14 8.78 6.17 2.68 2.43 2.32 9.09 7.22 7.37 7.95 6.30 5.67 5.55 6.81 6.46 Na2O 3.07 3.55 3.42 4.21 4.89 1.65 3.66 3.90 3.71 3.58 3.38 4.91 4.62 5.77 4.89 K2O 0.60 0.54 2.04 1.51 1.30 2.86 0.62 0.70 0.54 0.67 1.34 1.30 1.23 0.58 1.29 P2O5 0.33 0.36 0.27 0.12 0.13 0.08 0.18 0.22 0.22 0.20 0.18 0.16 0.15 0.19 0.17 LOI 1.50 1.42 1.84 1.24 2.36 5.63 0.98 1.46 1.32 1.42 1.34 1.98 1.77 3.08 1.70 Total 99.95 100.00 100.51 100.10 101.08 99.63 100.32 101.64 100.48 100.12 100.42 100.01 100.96 101.77 101.27 Rb 25 61 16 9 17 Sr 300 372 107 518 517 460 580 290 750 723 792 776 Ba 520 476 432 205 260 211 220 210 480 454 232 379 Ga Pb 9 13 55 Sc 5 3 4 25 17 19 11 24 5 7 12 9 V 5 13 20 235 127 152 60 175 100 113 166 125 Cr 54 3 4 22 120 15 85 61 19 17 Co 5 6 5 20 19 26 12 13 10 5 20 17 Ni 5 9 11 19 9 3 17 18 15 14 Cu 15 24 13 173 86 61 48 16 53 65 117 79 Zn 83 87 42 75 82 86 88 92 72 84 72 77 Y 16222016151413286556 Zr 102 120 160 43 56 54 50 95 76 74 44 57 Nb 5.6 3 5 4 4 2.2 3.2 4 5 Hf 2.3 4.2 1.8 2.1 1.8 1 2.1 Ta Th 3 11 1 2 1 2 La 13.03 14.70 14.74 13 10 12 6 96799 38 Ce 33.5 38.97 39.41 30 26 28 13 21 15 17 21 22 8 20 Nd 17.22 18.57 19.79 17 16 12 7 12 10 11 13 10 6 12 Sm 4.59 5.03 5.19 3.45 3.15 2.06 1.76 2.41 2.70 2.80 3.50 1.76 0.92 1.75 Eu 1.27 1.39 1.02 0.94 0.95 0.40 0.97 1.01 0.95 0.95 1.25 0.59 0.51 0.69 Gd 4.42 4.95 5.01 3.10 3.10 2.65 2.30 2.65 2.90 2.82 4.24 0.85 0.86 1.50 Dy 4.44 4.91 5.15 2.90 3.34 2.78 2.73 2.81 2.76 2.58 4.90 0.73 0.93 1.16 Ho 0.62 0.75 0.78 0.57 0.59 0.56 0.53 1.03 0.14 0.21 0.26 Er 2.56 2.84 3.16 1.75 2.16 2.47 1.57 1.70 1.63 1.54 3.07 0.34 0.41 0.52 Yb 2.38 2.70 3.14 1.79 2.14 2.38 1.55 1.69 1.65 1.48 3.02 0.26 0.39 0.53 M. Vergara et al. / Journal of South American Earth Sciences 17 (2004) 227–238 233

n No age has been determined for the Cerro San Cristo´bal ´ o ˜ main stock. Presumably, its age is similar to that of Cerro Santa Lucı´a. As we mentioned previously, the Cerro San El Pen Cristo´bal stock is intruded by an orthopyroxene andesitic

bal dyke that outcrops at the base of the monument to the Virgin ´

. The Sr, Nd, and Pb Mary, which is located at the summit of the hill. This dyke

San Cristo (dyke) gives a whole-rock K–Ar age of 13.1G0.9 Ma (Table 1). G

s (1999) The first K/Ar dating of Cerro Santa Lucıá (21.1 ´ 3.7 Ma) was reported by Sua´rez (1989, Revista del Selle Domingo, El Mercurio newspaper, Santiago de Chile, Manque- hue October 8, 1989, in Selle´s, 1999). We present a new whole-rock K/Ar age of 20.3G1.9 Ma for a basaltic- andesite sample (Table 1), which corroborates, within Manque- hue hile. Those labeled Rb-07, Rb-9b, and Rb-6A were analytical error, the age reported by Sua´rez and supports an early Miocene age for Cerro Santa Lucıá. bal

´ One sample from the summit of Cerro Manquehue gives spectrometry at the Carnegie Institution, Washington (USA). a plagioclase K/Ar age of 19.5G0.5 Ma; one from the base San Cristo (Agua del Palo valley) gives an amphibole K/Ar age of 20.3G5.4 Ma (Drake et al., 1976). A third sample collected a ´

0.7037710.512911 0.703786 0.512896 0.703745 0.512892 north of the Cerro Manquehue summit, probably a younger 18.45115.590 18.44638.351 15.593 18.472 38.366 15.581 38.317 Santa Lucı satellite intrusion of similar lithology, indicates a whole- rock K/Ar age of 16.7G0.9 Ma (Gana and Wall, 1996). These radiometric data indicate that Cerro Manquehue and its satellite intrusion are both early Miocene, though slightly Las Can- teras younger than Cerro Santa Lucıá. Another sample from Cerro El Penõń, of similar composition to those of Cerro Manquehue, provides an amphibole K/Ar age of 11.6G

Cerro Renca 1.3 Ma (Selle´s, 1999). We postulate that the latter Middle Miocene age and the age of the Cerro San Cristo´bal dyke

a represent subsequent subvolcanic activity unrelated to the ´ main volcanic events of the Manquehue–San Cristo´bal– Santa Lucı Santa Lucı´a belt. A whole-rock K/Ar age of 21.8G0.5 Ma has been - ´ reported for an andesitic porphyry from the summit of Cerro

Las Rodrı guez Renca (Thiele et al., 1980). As we mentioned previously, this subvolcanic body intrudes continental volcanic strata of Oligocene age. ochimiques de Nancy, France. Those labeled DS-205, DS-229, AG-451, DS-241, and DS-072 are from ´ mA two-pyroxene porphyritic sample of andesitic com- Cerro Blanco Ma(?) Ma(?) position from Cerro Gordo, which belongs to the Conchalı´ belt, has a whole-rock K/Ar age of 21.2G1.0 Ma (Selle´s, bal ´ 1999); another sample of similar composition from the Cerro

San Cristo Las Canteras quarry, which belongs to the same belt, gives a whole-rock K/Ar age of 22.3G1.8 Ma. These ages indicate that the Conchalı´belt is early Miocene. Both Cerro Gordo and Cerro Las Canteras also intrude continental volcanic and Abanico Fm volcaniclastic stratiﬁed rocks of Oligocene age.

Abanico Fm 5. Geochemistry

Fifteen samples were selected to characterize the geochemistry of the volcanic and subvolcanic rocks of Abanico Fm the hills near Santiago de Chile. Table 2 shows their major and trace element contents and includes data obtained by Selle´s (1999). We group chemical analyses according to the isotopic compositions (samples LS-1, SCr-02, and AP-01) were obtained at Florida International University and analyzed by thermal ionization mass Lu87/86 Sr 143/144 Nd 0.37206/204 Pb 207/204 0.42Pb 208/204 Pb 0.49The chemical data labeled SCr01, SnLu-01,obtained Th-11, H-157, by LS-1, INAA SCr-02, at and the AP-01 0.28 were Centre obtained de by Recherches ICP-AES Petrographiques at the et Department Ge of Geology, University of C 0.34 0.44 0.25 0.26volcanic 0.26 episodes 0.23 0.46 suggested 0.04 for the area. 0.06Samples 0.09 SCr-01, 234 M. Vergara et al. / Journal of South American Earth Sciences 17 (2004) 227–238

Fig. 3. K2O–SiO2 variation diagram of the Oligocene and Miocene samples discussed herein. Labels of the samples are as in Table 2. SnLu-01, TH-11, H-157, LS-1, Scr-02, and AP-01 were analyzed at the Departamento de Geologıá de la Universi- dad de Chile by ICP-AES. Chemical analyses Rb-07, Rb-9b, and Rb-9A were obtained by INAA at the Centre de Recherches Petrographiques et Geóchimiques de Nancy, France. Samples DS-205, DS-229, AG-451, DS-241, and DS-072 are from Selle´s (1999). Most samples from the three volcanic cycles exhibit medium- to low-K contents (Fig. 3). Those from the Oligocene volcanic episode range in SiO2 from basalt to Fig. 5. N-MORB incompatible trace element patterns of (a) Oligocene and rhyolite. The two-pyroxene-bearing samples from the early (b) Miocene samples. The N-MORB composition used for the normal- Miocene episode range from basalt to basaltic andesite, and ization is from McDonough and Sun (1995). the amphibole-bearing porphyries of the third episode are Fig. 5a and b show trace element abundances in these silicic andesite to dacite. rocks normalized relative to N-MORB. Regardless of SiO According to the AFM diagram (Fig. 4), the analyzed 2 content, samples from the three volcanic cycles are enriched samples are calc-alkaline. However, most basaltic rocks of in K, Rb, Sr, Ba, and Th relative to N-MORB, and all are the early Miocene volcanic cycle show tholeiitic affinities, depleted in high field strength elements with respect to light despite being MgO poor (MgOZ3.72% for SiO Z49.84%). 2 rare-earth elements (REE). These geochemical features are Samples from Cerro Santa Lucıá are Al O rich (O20%) and 2 3 similar to those exhibited by southern volcanic zone (SVZ) could be classified as high alumina basalts because they are Quaternary Andean lavas and typical of magmas associated aphanitic, relatively poor in MgO, and rich in total Fe. with subduction zones. Most of the studied samples have La/Nb ratios O1. 6 and Ba/La ratios O20, which are also typical of Andean lavas (Hildreth and Moorbath, 1988; Stern and Skewes, 1995). Significant differences are observed, however, in the concentration of the trivalent elements Y, Yb, and Sc and in the La/Yb ratios (Oligocene rocksZ3.0–5.3, early Miocene basaltic rocksZ4.6–7.2,

Fig. 6. Chondrite-normalized REE patterns of San Cristo´bal (basalt), Santa Fig. 4. AFM diagram showing that most of the analyzed samples are calc- Lucıá (andesite; 20 Ma), and Manquehue (dacite; 19 Ma) samples. alkaline. The boundaries between the tholeiitic and calc-alkaline fields are Chondrite composition used for normalization is that of McDonough and from Kuno (1968) and Irvine and Baragar (1971). Sun (1995). M. Vergara et al. / Journal of South American Earth Sciences 17 (2004) 227–238 235 and early Miocene amphibole-bearing subvolcanic rocksZ 7.6–15). As we show in Fig. 6, in the Manquehue-San Cristo´bal-Santa Lucıá volcanic chain, there is a significant increase in the La/Yb ratios, in correlation with decreasing ages, from San Cristo´bal–Santa Lucıá (21–20 Ma) to Manquehue (20–16 Ma). Table 2 includes Sr, Nd, and Pb isotope ratios for three subvolcanic rocks: a basaltic sample from Cerro San Cristo´bal, an andesitic sample from Cerro Santa Lucıá, and a dacitic sample from Cerro Manquehue. Sr isotope ratios range between 0.703745 and 0.703786, and Nd isotope ratios range between 0.512892 and 0.512911. These values are similar to those reported by Lo´pez-Escobar and Vergara (1997) for three subvolcanic samples collected at Pocuro, Colina, and Pan de Azućar hills, which are located at latitudes 338–33.58S. The Sr and Nd isotope ratios (Fig. 7) of all six samples are respectively lower and higher than those of Quaternary rocks from the northern province of the SVZ of the Andes (NSVZ; 338–34.58S) but similar to the Sr and Nd isotopes ratios of Quaternary rocks from the central SVZ (CSVZ; 378–41.58S). In Fig. 7, we define the mantle array on the basis of isotopic data from the east Pacific ridge, Chile ridge, Easter Island, and Juan Fernańdez archipelago (Lo´pez-Escobar and Vergara, 1997). The six samples have higher Sr and lower Nd isotope ratios than N-MORB, similar to Sr and Nd isotopic ratios from the Juan Fernańdez archipelago oceanic island basalts (OIB) and E-MORB from the Chile ridge. 206Pb/204Pb ratios (Fig. 8) are 18.45–18.47, and similar to many subduction-related rocks, the samples, together with Quaternary volcanic rocks from throughout the SVZ, are enriched in 207Pb and 208Pb compared with mantle-derived rocks with similar 206Pb/ 204Pb (Fig. 8).

Fig. 8. (A) 207Pb/204Pb versus 206Pb/204Pb; (B) 208Pb/204Pb versus 206Pb/204Pb; (C) 208Pb/204Pb versus 207Pb/204Pb diagrams for the Miocene samples in comparison with the Pb isotope composition of previous studied Miocene samples from 338 and 33. 58S; Quaternary rocks from the SVZ of the Andes between 338 and 41. 58S; oceanic rocks from the east Paciﬁc ridge and Chile ridge (MORB); and Nazca plate OIB from Easter Island, Juan Ferna´ndez archipelago, San Ambrosio, and San Fe´lix. Data used for comparison appear in Lo´pez-Escobar and Vergara (1997).

6. Volcanic episodes recorded in the hills near Santiago

The geochronological data for volcanic rocks from the hills near Santiago record volcanic activity from 30.9 to 16.7 Ma with some gaps of 2–3 Ma. The ages of 13.1 and Fig. 7. 143Nd/144Nd versus 87Sr/86Sr diagram of San Cristo´bal (basalt; 20 Ma(?)), Santa Lucıá (andesite; 20 Ma), and Manquehue (dacite; 19 Ma) 11.6 Ma reported for two small igneous bodies have not samples in comparison with the Nd–Sr isotope composition of previously been taken into consideration, because they do not seem studied Miocene samples from 338 and 33. 5-S; Quaternary rocks from the related to the main magmatic episodes. The radiometric SVZ of the Andes between 338 and 41. 58S; oceanic rocks from the east ages, together with the structure and lithology of the Pacific ridge and Chile ridge (MORB); and Nazca plate OIB from Easter Island, Juan Fernańdez archipelago, San Ambrosio, and San Fe´lix. Data volcanic rocks, suggest the existence of at least three main used for comparison appear in Lo´pez-Escobar and Vergara (1997). volcanic episodes, geographically superimposed and deeply 236 M. Vergara et al. / Journal of South American Earth Sciences 17 (2004) 227–238 eroded. The first is late Oligocene, and the second and third andesitic dyke (11.3 Ma) that outcrops at the base of the are early Miocene in age. monument to the Virgin Mary at Cerro San Cristo´bal and the The Oligocene episode is represented by lava flows of the amphibole dacitic porphyry near Cerro El Penõn could Abanico–San Ramoń–Provincia belt (30.9–25.6 Ma), the belong to a later volcanic event with no other expression in San Cristo´bal welded tuff (28.3–25.2 Ma), and the Morro the studied area. Las A´ guilas aphanitic lavas (26.3–23.6 Ma). According to Selle´s (1999), the areal distribution of the San Cristo´bal and Cerro Las Rodrı´guez deposits looks like an hemicircle, 7. Geochemical features of the volcanic units approximately 13 km in diameter, that dips radially. He interprets these features as the result of a caldera collapse, Overall, the geochemical characteristics of the volcanic with the outcrops representing the outflow sheets surround- and subvolcanic rocks are typical of subduction-related ing the Oligocene caldera. On the basis of their lithology magma. The isotopic characteristics are similar to volcanic and age, the San Cristo´bal welded tuffs can be correlated rocks from the Quaternary CSVZ and many intraoceanic with the lava flows of the Abanico–San Ramoń–Provincia island arcs, and the Sr and Nd isotope ratios are similar to belt stratified rocks. The bimodal composition of the some OIB from the Nazca plate and E-MORB from the volcanic rocks (ca. 3100 m) of Cerro Abanico, basic lavas, Chile ridge. According to the mantle-like isotopic values, it and acid pyroclastic flows and the structural studies and is likely that crustal contamination was not a major factor in facies analysis in the Maipo valley of the same rocks suggest the evolution of the magmas. The relative enrichment in deposition in a extensional basin (Aguirre, 1999; Zurita, 207Pb, as well as the enrichment in large ion lithophile 1999; Charrier et al., 2002; Nystro¨m et al., 2003) with a high elements, exhibited by these Miocene rocks suggests that subsidence rate, as deduced from the thermal state of the material derived from the subducted oceanic crust, notably organic material. The voluminous pyroclastic flows of the from pelagic sediments, was introduced as mantle source Cerro El Abanico area (400–500 m thick) are consistent contaminants. with a caldera-forming eruption. The presence of calderas is The major difference among the units and samples is the supported by the intercalation of lacustrine deposits in the extent of heavy REE depletion, as reflected by the La/Yb pyroclastic sequence and by lateral changes in secondary ratios. La/Yb is highest in 19–20 Ma rocks from Cerro mineral assemblages (yugawaralite and wairakite), which Manquehue (Figs. 5 and 6), and there is an overall increase reflect steep temperature gradients (Nystro¨m et al., 2003). in La/Yb over time among the Miocene rocks (Selle´s, 1999). Intrusive bodies of Oligocene age have not been found. Several reasons for this change have been proposed, such as The second volcanic episode is early Miocene, rep- (1) crustal thickening in the early Miocene, accompanied by resented by the Cerro Las Canteras (22.3 Ma), Cerro San the increased contamination of mantle-derived magma by Cristo´bal, Cerro Renca (21.8 Ma), Cerro Gordo (21.1 Ma), melts of garnet-bearing lower crust (e.g. Kay et al., 1991; and Cerro Santa Lucıá (21.2–20.3 Ma) two-pyroxene Kay and Mpodozis, 2002); (2) incorporation into the magma basaltic to basaltic andesite porphyries. These hills represent of tectonically eroded forearc crust at subduction zone the roots of eruptive centers that overlie the products of the depths (Kay and Mpodozis, 2002); and (3) partial melting of Oligocene volcanic episode. The actual distribution of their the subducted slab (Selle´s, 1999). On the basis of the similar outcrops suggests that they belonged to big dome or Sr, Nd, and Pb isotopic ratios reported here for rocks with stratavolcano complexes, whose locations would corre- widely varying La/Yb ratios from the early Miocene Cerros spond to the actual locations of Cerros Las Canteras, Renca, Santa Lucia, Santa San Cristobal, and Manquehue, we Gordo, and San Cristo´bal–Santa Lucıá. On the basis of its believe it is not likely that the increase in heavy REE structure and facies, Selle´s (1999) interprets the Cerro Las depletion was caused by a major change in magma source Canteras porphyry as the eruptive center of the Conchalı´ materials, at least initially. One probable scenario is that by unit lavas. approximately 20 Ma, the crust had thickened to the extent The third and last volcanic episode is also early Miocene that garnet was just stabilized in underplated gabbroic lower but slightly younger than the second episode. It is crust. Partial melting of both the mantle and gabbroic lower represented by the amphibole-bearing dacitic porphyries crust produced basaltic to basaltic andesitic and andesitic to of Cerro Manquehue (20.3–19.5 Ma) and its satellite dacitic magmas, respectively, with widely varying La/Yb intrusion (16.7 Ma). These could have been large strato- ratios but similar isotopic ratios. volcanoes that currently are deeply eroded and show a relatively wide range of ages. In the slopes of Cerro Manquehue, Selle´s (1999) finds cylindric bodies that he 8. Discussion and conclusion interprets as feeder dykes. These geochronological data suggest that the three On the basis of these geochronological data, the area volcanic episodes overlapped in space and were almost where Santiago de Chile is now located and its nearby hills continuous in time, with some gaps of 1–2 my, from the late were the site of almost continous volcanic activity from the Oligocene to the early Miocene. The orthopyroxene-bearing late Oligocene to the early Miocene. M. Vergara et al. / Journal of South American Earth Sciences 17 (2004) 227–238 237

According to Charrier et al. (2002) and Nystro¨m et al. been only 1.5 mm/year. The first exhumation event (19.6– (2003), during the late Oligocene, the Chilean continental 16.2 Ma) coincides with an intensity decrease of the margin was characterized by a low rate of subduction that volcanic activity, and the second is subsequent to any favored the extension and formation of volcanic sedimen- volcanic activity registered in the area. These tectonic tary basins. movements probably generated the San Ramoń fault, which During the early Miocene, new volcanic activity started separates the Abanico–San Ramoń–Provincia belt from the in the same area as Oligocene volcanism. At least five big central valley and the Manquehue–San Cristo´bal–Santa dome complexes or their (very shallow) intrusive equiva- Lucıá belt. lents, emplaced within the cores of eroded stratified volcanic edifices, grew in this area: Cerro Las Canteras (22.3 Ma), Cerro San Cristo´bal, Cerro Renca (21.8 Ma), Cerro Gordo (21.1 Ma), and Cerro Santa Lucıá (21.2– Acknowledgements 20.3 Ma). They mainly were located north of the Mapocho River and their rocks were essentially two-pyroxene bearing This work was made possible by Proyecto Fondecyt basalts and basaltic andesites. Of these volcanic edifices, 1020809. LLE acknowledges the support given by Proyecto only their necks remain; their covers, which probably Fondecyt (Lıńeas Complementarias) 800-0006, Proyecto consisted of pyroclastic material G lava flows, were ECOS-CONICYT C97U04 and ECOS-CONICYT CO3 destroyed by erosion. VO1. RHV acknowledges support from NSF:EAR During the early Miocene (20.3–16.7 Ma), volcanic 9725366. activity continued in this same area, though with less intensity, and induced a large stratovolcano, Cerro Man- quehue. This stratovolcano currently is reduced to only the References major neck that outcrops in the summit and some feeder dykes, whose lithologies correspond to amphibole-bearing Aguirre, R., 1999. Depositacioń y deformacioń de las secuencia volcańicas silicic andesite to dacitic porphyries. terciaria en el sector cordillerano de Pata del Diablo, Cajoń del Maipo. By this stage of volcanism, crustal thickness in the area Thesis, Departamento de Geologıá, Universidad de Chile, Santiago, had increased sufficiently to stabilize garnet in lower crustal 60pp. lithologies. Thus, whereas the early Miocene basaltic rocks Avendanõ, M., Araneda, M., 1994. Gravimetrıá de la cuenca de Santiago. Congreso Geolo´gico Chileno 7 (Actas 1), 571–575. Concepcioń. were generated in an extensional environment, the early Charrier, R., Baeza, O., Elgueta, S., Flynn, J.J., Gans, P., Kay, S.M., Miocene dacitic rocks mark the beginning of the compres- Wyss, A.R., Zurita, E., 2002. Evidence for Cenozoic extensional basin sional phase that affected this Andean region between the development and tectonic inversion south of the flat-slab segment, Miocene and the Quaternary. southern Central Andes, Chile, (338–368SL). Journal of South American The existence of Oligocene caldera systems in the Earth Sciences 15, 117–139. Drake, R., Curtis, G., Vergara, M., 1976. Potassium–Argon dating of Andean Cordillera near Santiago (e.g. Abanico Formation, igneous activity in the central Chilean Andes-latitude 338S. Journal of w60 km east of Santiago) has been suggested by Levi et al. Volcanology and Geothermal Research 1, 285–295. (1989), Thiele et al. (1980) and Vergara et al. (1993, 1999), Gana, P., Wall, R., 1996. Geocronologıá de los eventos magma´ticos del and Nystro¨m et al. (2003). They support this hypothesis with Cretaćico Superior-Terciario en el borde occidental de la Cordillera 0 the presence of thick packs of silicic pyroclastic flows, Principal, al sur de la Cuesta de Chacabuco (338–33830 S). Informe registrado IR-96-97, Servicio Nacional de Geologıá y Minerıá 1996;, 57 lacustrine deposits, basic lava flows, and alteration miner- un mapa 1100.000. alogy typical of a geothermal field (yugowaralite-type Gana, P., Wall, R., 1997. Evidencias geocrono´logicas Ar/Ar y K/Ar de un zeolite and wairakite) in the rims of the paleocalderas. hiatus Cretaćico Superior-Eoceno en Chile central (338–338300S). Reflectancy determinations in vitrinite from the Abanico Revista Geolo´gica de Chile 24 (2), 145–163. Formation (Zurita, 1999; Charrier et al., 2002) reveal a high Hildreth, W.E., Moorbath, S., 1988. Crustal contribution to arc magmatism in the Andes of Central Chile. Contributions to Mineralogy and heat flow during deposition, consistent with extension and a Petrology 98 (4), 455–489. low rate of subduction. Irvine, T.N., Baragar, W.R.A., 1971. A guide to the chemical classification The terrains that conform the hills near the city of of the common volcanic rocks. Canadian Journal of Earth Sciences 8, Santiago underwent tectonic uplift and exhumation, which 523–548. eroded most of the volcanic cover, so that they display a Katsui, Y., Vergara, M., 1966. Antecedentes petrolo´gicos del cerro San Cristo´bal. Revista Minerales 92, 9–25. basement formed by Oligocene rocks. On the basis of Kay, S.M., Mpodozis, C., 2002. Magmatism as a probe to the Neogene geochronological studies, Kurtz et al. (1997) show the shallowing of the Nazca plate beneath the modern Chilean flat-slab. existence of two exhumation events in the Andean Journal of South American Earth Sciences 15, 39–57. Cordillera of central Chile: 19.6–16.2 Ma, with an exhuma- Kay, S.M., Mpodozis, C., Ramos, V.A., Munizaga, F., 1991. Magma source tion rate of 0.55 mm/year, and 8.4–7.7 Ma, with an variations for mid-late Tertiary magmatic rocks associated with a shallowing subduction zone and a thickening crust in the central Andes exhumation rate of 3 mm/year. On the basis of fluid (28to338S), in: Harmon, R.S., Rapela, C.W. (Eds.), Andean inclusion determinations, Skewes and Holmgren (1993) Magmatism and its Tectonics Setting Geological Society of America, note that the exhumation rate during the last 4.9 Ma has Special Paper, 265, pp. 113–117. 238 M. Vergara et al. / Journal of South American Earth Sciences 17 (2004) 227–238

Kuno, H., 1968. Differentiation of basalt magmas, in: Hess, H.H., Stern, C.R., Skewes, M.A., 1995. Miocene to present magmatic evolution at Poldervaart, A. (Eds.), Basalts: the Poldervaart Treatise on Rocks of the northern end of the Andean Southern Volcanic Zone. Revista Basaltic Composition 2. Interscience, New York, pp. 623–688. Geolo´gica de Chile 22 (2), 261–272. Kurtz, A.C., Kay, S.M., Charrier, R., Farrar, E., 1997. Geochronology of Suarez, M., 1989. Revista del Domingo, El Mercurio newspaper, Santiago Miocene plutons and exhumation history of El Teniente region, Central de Chile. Chile (348–358S). Revista Geolo´gica de Chile 24 (1), 75–90. Thiele, R., 1980. Hoja Santiago. Carta Geolo´gica de Chile N8 39, Instituto Levi, B., Aguirre, L., Nystro¨m, J.O., Padilla, H., Vergara, M., 1989. Low grade de Investigaciones Geolo´gicas, 21pp., 1 map. regional metamorphism in the Mesozoic–Cenozoic volcanic sequences of Thiele, R., Bobenrieth, L., Boric, R., 1980. Geologıá de los cerros de Renca, the central Chile Andes. Journal of Metamorphic Geology 7, 487–495. Ruiz y Colorado (Santiago): Contribucioń a la estratigrafıá de Chile Lo´pez-Escobar, L., Vergara, M., 1997. Eocene–Miocene longitudinal central. Revista Comunicaciones 30, 1–14. depression and Quaternary volcanism in the Southern Andes (33– Vergara, M., 1971. Antecedentes petrogra´ficos y petrolo´gicos del Cordoń 42.58S): a geochemical comparison. Revista Geolo´gica de Chile 24 (2), del Cerro Manquehue, Santiago Universidad de Chile, Facultad de 227–244. Ciencias Fı´sicas y Matema´ticas. Departamento de Geologıá, Publica- McDonough, W.F., Sun, S., 1995. The composition of the Earth. Chemical cioń 16 1971. 31pp. Geology 120, 223–253. Vergara, M., Lo´pez-Escobar, L., 1980. Geologıá y Petrologıá de los Mo¨rike, W., 1896. El distrito eruptivo del San Cristo´bal, cerro de Santiago intrusivos subvolcańicos de la precordillera andina entre Santiago y Boletıń de la Sociedad Nacional de Minerıá(RevistaMinera; Colina. Revista Comunicaciones 29, 1–21. translation from German), Santiago, vol. 93 1896. 131-135pp. Vergara, M., Levi, B., Villarroel, R., 1993. Geothermal-type alteration in a Nystro¨m, J.O., Vergara, M., Morata, D., Levi, B., 2003. Tertiary volcanism burial metamorphosed volcanic pile, central Chile. Journal of in central Chile (338150-338450S): a case of Andean Magmatism. Metamorphic Geology 11, 449–454. Geological Society of America Bulletin 115, 1523–1537. Rauld, R.A., 2002. Ana´lisis morfoestructural del frente cordillerano Vergara, M., Morata, D., Villarroel, R., Nystro¨m, J., Aguirre, L., Santiago oriente entre el rıó Mapocho y Quebrada de Macul Memoria 1999. 40Ar/39Ar ages, very low grade metamorphism and para optar al tı´tulo de Geo´logo. Departamento de Geologıá, Universidad geochemistry of the volcanic rocks from Cerro El Abanico, 0 0 de Chile 2002. 57pp. Santiago, Andean Cordillera (33830 S–70825 W). In: International Selle´s, D., 1999. La Formacioń Abanico en el cuadrańgulo Santiago Symposium on Andean Geodynamics (ISAG) 4, Go¨ttingen Actas, (338150–338300S/708450W), Chile central: Estratigrafıá y Geoquı´mica. 785–788. MSc Thesis. Departamento de Geologıá, Universidad de Chile, 154pp. Wall, R., Selle´s, D., Gana, P., 1999. Mapa geolo´gico Tiltil-Santiago, Skewes, M.A., Holmgren, C., 1993. Solevantamiento andino, erosiońy Regioń Metropolitana. Mapa geolo´gico 9. Servicio Nacional de emplazamiento de brechas mineralizadas en el depo´sito de cobre Geologıá y Minerıá 9, xx. porfı´dico Los Bronces, Chile central (338S); aplicaciońde Zurita, E.A., 1999. Historia de enterramiento y exhumaciońdela geotermometrıá de inclusiones fluidas. Revista Geolo´gica de Chile Formacioń Coya-Machalı´, Cordillera Principal, Chile Central. Thesis. 20 (1), 71–84. Departamento de Geologıá, Universidad de Chile, 156pp.