The Cretaceous Iron Belt of Northern Chile_ Role of Oceanis Plate a Superplume Event and a Major Shear Zone

Mineralium Deposita (2003) 38: 640–646 DOI 10.1007/s00126-003-0359-y

L E T T ER

Roberto Oyarzun Æ Jorge Oyarzu´n Æ Jean Jacques Me´nard Æ Javier Lillo

The Cretaceous iron belt of northern Chile: role of oceanic plates, a superplume event, and a major shear zone Received: 18 November 2002 / Accepted: 3 March 2003 / Published online: 17 May 2003
Springer-Verlag 2003

Abstract The Cretaceous constitutes a turning point in the tectonic, magmatic, and metallogenic history of Chile. The geological evidence indicates that a major change occurred in late Neocomian time when superplume emplacement (Mid-Pacific Superplume) and plate reorganization processes took place in the Pacific. The superplume event resulted in a major ridge-push force resulting in increased coupling between the subducting and overriding plates. This completely changed the tectonic setting of Chile ending the Early Cretaceous extensional period (aborted rifting in the back-arc basin), and increasing stress at a crustal scale. As a consequence, overpressurized dioritic magmas were pushed up mainly along the best possible structural path in northern Chile, i.e., the Atacama Fault Zone, eventually forming a +500-km-long belt of Kiruna-type iron deposits with reserves of
2,000 Mt (60% Fe), a unique case in Chile’s geological history. Keywords Iron belt Æ Cretaceous Æ Chile Æ Shear zone Æ Superplume

Editorial handling: Robert King R. Oyarzun (&) Departamento de Cristalografı´ a y Mineralogı´ a, Facultad de Ciencias Geolo´gicas, Universidad Complutense, 28040 Madrid, Spain E-mail: [email protected] J. Oyarzu´n Departamento de Ingenierı´ a de Minas and CEAZA, Facultad de Ingenierı´ a, Universidad de La Serena, Casilla 554 La Serena, Chile J. J. Me´nard Institut Pe´dagogique National, BP 616, Nouakchott, Mauritanie J. Lillo Escuela Superior de Ciencias Experimentales y Tecnologı´ a, Universidad Rey Juan Carlos, Tulipa´n s/n, 28933 Mo´stoles Madrid, Spain

Introduction Although Chile is usually regarded as a ‘‘copper country’’ (largely due to the presence of giant porphyry copper deposits), other ores including iron are also present in important economic concentrations. Most of the Chilean iron deposits are of the Kiruna type, and occur along a narrow N–S trending belt stretching for over 500 km between 25 and 30S (Fig. 1). These deposits formed by the end of the Late Cretaceous, and from a structural point of view, can be regarded as shear zone related. The deposits have been largely studied petrologically, geochemically, and economically; however, no specific attempts have been made in order to relate the origin of the Chilean Iron Belt (CIB) to the Pacific plate tectonic scenario. In this paper, we present a brief account of the northern Chilean case, a realm that underwent profound changes in tectonic, magmatic, and metallogenic style during Cretaceous time (Oyarzu´n 2000). We suggest that this change happened in response to major, distal tectonic events taking place in the Pacific, involving the emplacement of a plate-wide superplume (Mid-Pacific Superplume; Larson 1991a, 1991b; Vaughan 1995). In the following, we present a summarized geologic account of these processes and their probable influence on the development of the unique iron metallogenic belt in northern Chile.

The tectonomagmatic scenario The Jurassic-Early Cretaceous plate tectonic setting of Chile was intimately linked to the southeastward directed subduction of the ancient Aluk plate (Fig. 2A). The geological evolution of northern Chile during this time span was characterized by a tectonic setting involving a magmatic-arc and a back-arc basin. This setting underwent minor readjustments by the Late Jurassic (Oxfordian), when the marine basin was uplifted giving rise to evaporitic facies. By the Tithonian, the basin had deepened again and the system arc basin had undergone

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Fig. 1 The Lower Cretaceous Chilean Iron Belt (CIB) along the southern segment of the Atacama Fault Zone (AFZ). The five large iron deposits (28–30S) have reserves (before mining) in the order of 200–400 Mt (60% Fe): Boquero´n Chan˜ar (BO), Los Colorados (CO), Algarrobo (AL), Cristales (CR), and El Romeral (RO). The rest of the deposits are in the order of 100–20 Mt and even less. Lower Cretaceous Cu–(Fe) deposits/districts: Talcuna (TAL), Candelaria (CAN), Punta del Cobre (PC), Manto Verde (MV). The Domeyko Fault System (DFS) and the southern segment of the Late Eocene–Early Oligocene porphyry copper belt (PCB) can be observed on the upper right of the figure. Porphyry copper deposits: El Salvador (ES), Potrerillos (PO). According to Me´nard (1995), Sillitoe et al. (1996), Vila et al. (1996), Taylor et al. (1998), Oyarzu´n (2000). See inset for location (SA South America)

minor changes in orientation. However, by the end of the Late Cretaceous, a drastic modification occurred. The magmatic activity along the arc decreased dramatically and the basin was uplifted; and, since then there has been no more record of marine episodes in northern Chile. This marked the onset of the cooling and uplifting of the arc which eventually shifted to an eastward position by Mid-Cretaceous time (Scheuber et al. 1995). These processes occurred when a major superplume event was taking place in the Pacific (Fig. 2B; Table 1). The superplume event developed during the Early–MidCretaceous (Larson 1991a; Vaughan 1995) and led to Table 1 Age constraints for major geologic processes during Neocomian–Mid-Cretaceous time. AFZ Atacama Fault Zone; CIB Chilean Iron Belt

Fig. 2 Configuration of continental and oceanic plates just before 130 Ma (A) and at 120 Ma (B). Plates: Aluk, Africa (AFR), Antarctic (ANT), Farallon (FAR), Pacific (PAC), South America (SA). CIB Chilean Iron Belt. As shown in the legend, the area depicted for the superplume is the maximum, and has been superimposed on plate configuration at 120 Ma for simplification. Observe the disruption of spreading centers and plate reorganization (Aluk-Farallon-Pacific) from 130 Ma (A) to 120 Ma (B), and the onset of plate breakdown-drifting (Africa–South America) (B). Plate configuration according to Zonenshayn et al. (1984) and Turner et al. (1994). Mid-Pacific Superplume (B) according to Larson (1991a)

the formation of the Earth’s most outstanding submarine volcanic plateaus, including among others those of Ontong Java, Manihiki, and Nauru (Larson 1991a). For example, Ontong Java alone, involved the extrusion of >50·106 km3 of basalts, i.e., more than five times the volume of the Deccan basalts in India (Coffin and Eldholm 1993). Plateau formation in the area affected by the Mid-Pacific Superplume (Fig. 2B) began at 130 Ma (Mid-Pacific Mountains) and ended at 75 Ma (Mid-Pacific Mountains, Line Islands; Larson 1991a). This time

Geologic events

Age (Ma)

Reference

Mid-Pacific Superplume; older and younger oceanic plateaus Peak production rates of oceanic crust Opening of the South Atlantic (onset) Ductile (d) and brittle (b) behavior of the AFZ Iron deposits (CIB): range (r), peak (p)

130–75

Larson (1991a)

120–100 120–100 130–125 (d)125–105 (b)

Larson (1991a) Turner et al. (1994) Taylor et al. (1998)

128–100 (r)115–110 (p)

See Table 2

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span can also be regarded as a period of high production of oceanic crust at mid ocean ridges (Larson 1991a; Vaughan 1995). Along the circum-Pacific rim, the superplume event also had far-reaching tectonic effects including uplift, deformation, and metamorphism (Vaughan 1995). The superplume may have affected an area as large as 6,000·10,000 km (Larson 1991a) (Fig. 2B) and induced increased ridge-push force and coupling between the subducting and overriding plates (Vaughan 1995). At a regional scale, the main Late Jurassic-Cretaceous structural element in northern Chile, with major metallogenic implications, is the so-called Atacama Fault Zone (AFZ; Fig. 1), a N–S trending megashear zone extending for about 1,000 km along the coastal block (Scheuber and Andriessen 1990; Scheuber and Reutter 1992; Taylor et al. 1998; among others). This megashear zone formed in response to SE-directed, oblique subduction of the ancient Aluk plate (Scheuber and Andriessen 1990; Fig. 2).

Magmatic and metallogenic implications: basis for a discussion At 128–100 Ma numerous intrusion-related Kiruna-type Fe deposits and stratabound Cu deposits (several of them rich in magnetite or hematite) were formed in volcanic or sedimentary rocks of the Neocomian magmatic arc and basin. The tectonomagmatic setting of the Neocomian basin corresponds to a case of aborted rifting (Levi and Aguirre 1981). Magmatism along the arc was characterized by extrusion of the so-called Ocoite Group (Berriasian-Albian), consisting of a ca. 3–13 km thick sequence of marine and continental sedimentary rocks, and high-K calc-alkaline and shoshonitic basalts and basaltic andesites, morphologically equivalent to flood lavas (Levi et al. 1987; Aguirre et al. 1989). Mineralization during this time span comprises the iron deposits of the coastal belt in Chile (Fig. 1) such as Los Colorados, El Algarrobo (Table 2), and several stratabound copper deposits such as El Soldado and Lo Aguirre in central Chile (Munizaga et al. 1988), and Punta del Cobre, Candelaria, and Talcuna in the northern part of the country (Marschick and Fontbote´ 1996; Oyarzun et al. 1998; Fig. 1).

Table 2 Age of iron deposits along the Chilean Iron Belt

From a metallogenic point of view, the most important magmatic activity was of the plutonic type (dioritic magmatism), and led to formation of the Chilean Iron Belt (CIB; Kiruna-type deposits) (Fig. 1). The CIB forms a +500-km-long and narrow N–S trending belt along the Coastal Range, and the largest deposits, Boquero´n Chan˜ar, Los Colorados, El Algarrobo, Cristales, El Romeral, are located between 28–30S (Fig. 1). Their reserves (before mining) are in the order of 200–400 Mt (60% Fe), whereas the reserves for the whole belt are about 2,000 Mt (60% Fe). The mineralized complexes consist of volcanic and subvolcanic andesitic rocks intruded by dioritic bodies (Oyarzu´n and Frutos 1984; Me´nard 1995). At the regional scale, the alignment of the CIB coincides with the Atacama Fault Zone (AFZ) (Fig. 1). Mineralization processes along the CIB took place between
128 and 100 Ma, with a peak at
115–110 Ma (Tables 1, 2). An important point regarding iron mineralization in the CIB relates to the type of magmatism. Intermediate magmatism is one of the typical features of the early evolution of the Chilean arc (Jurassic-Early Cretaceous), and may be one of the key factors that led to Kiruna-type iron mineralization along the AFZ. For example, as indicated by Hildebrand (1986), Kirunatype deposits are typically associated with high-level plutons of intermediate composition (dioritic magmatism), and affected by sodic metasomatism, which matches the CIB case. Additionally, it is worth also mentioning here the spatial relationships between the dioritic intrusive bodies and the volcanic rocks in the CIB case. Although the host-rocks for the iron mineralization in the CIB are andesites, more differentiated volcanic rocks may be also present, for example rhyolites at Los Colorados (Fig. 1). In this respect, a similar setting is observed at Great Bear (Canada) (Hildebrand 1986), and at Bafq (central Iran), although the latter represents a much more complex scenario (Fo¨rster and Jafarzadeh 1994). Whether this spatial relationship between ‘co-magmatic’ dioritic-andesitic/rhyolitic rocks has genetic connotations or not goes beyond the scope of this paper. However, one may not only speculate about the need for mafic magmas as a primary source of iron, but also about the need of a certain degree of differentiation as to liberate the iron from the parent magmatic source. For a comprehensive discussion on these topics, see for example Hildebrand (1986).

Ore deposit

Whole rock/mineral

Age (Ma)

Reference

Boquero´n Chan˜ar Cerro Ima´n El Algarrobo

Biotite Greisen Monzodiorite Diorite Diorite Biotite Post mineral dyke Andesite Diorite

128±4 102±3 99.6±5 115.6±5.8 128±6.4 110±3 110 111 108

Zentilli (1974) Zentilli (1974) Montecinos (1985) Montecinos (1985) Montecinos (1985) Munizaga et al. (1985) Oyarzu´n and Frutos (1984) Pichon (1981) Pichon (1981)

El Romeral Los Colorados

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The CIB andesitic host-rocks are rich in FeO(tot) (9–12 wt%; Me´nard 1988, 1995), and the main mineralogy includes labradorite and augite-diopside. The major part of the primary iron is in the form of Ti-magnetite, which was later partly remobilized during mineralization and deposited as Ti-poor hydrothermal magnetite (Ruiz et al. 1965; Me´nard 1995). The mineralization (Bookstrom 1977, Oyarzu´n and Frutos 1986; Pincheira 1986, Me´nard 1988; Me´nard 1995, among others) consists of veins and veinlets of magnetite, breccias, disseminations, and massive replacements of the andesites by magnetite ore. The mineral paragenesis includes magnetite ± tremolite ± apatite, followed by albite/oligoclase ± clinozoisite ± chlorite ± sphene ± scapolite ± tourmaline ± pyrite, and pyrophyllite. According to Me´nard (1995), the hydrothermal system evolved under high oxygen fugacity, high water pressure, and high temperature. Iron was leached from the host rock, transported as FeCl2 and deposited as Fe3O4. Deposition took place when P–T conditions dropped to allow for dissociation of the chloride complex at relatively shallow depths (
4 km) and temperatures of 450–550 C. The supercritical fluid phase was exsolved during cooling and consolidation of the plutons (800–900 C), which resulted in hydrogen, chlorine, and sodium metasomatism, and in the sequential leaching of Fe (at less than 700 C), and Ca and Mg (between 600 and 500 C) from minerals of the primary magmatic diorite assemblage: titanomagnetite-ilmenite, plagioclase, augite, and hypersthene. The residual altered dioritic rocks present a mineral assemblage evolving down to boundary conditions of the greenschistamphibolite facies (450 C). Similar to the leaching process, deposition is also selective: first Fe deposition occurs at less than 550 C, which is followed by Ca and Mg down to 450 C. The precipitation of magnetite may be represented as follows: 3 FeCl2 þ4 H2 O ! 6 HCl þ Fe3 O4 þH2 Meteoric and magmatic sources have been suggested for the origin of the Cl brines that allowed iron leaching and transport (Me´nard 1995). Recent studies (Kelley and Fru¨h-Green 2001) indicate that the mafic differentiated plutonism has a high potential for generating brines (up to 50 wt% NaCl). Since the iron deposits formed along the main magmatic arc, it is difficult to envisage major participation of fluids from the eastward located Early Cretaceous basin. A problematic fact regarding iron mineralization along the CIB is its ‘late’ character in the Neocomian evolution of the extensional back-arc setting. To provide a working hypothesis for the CIB, we must first review the series of events that took place in the Lower Cretaceous time (Fig. 2; Table 1). At a very large scale, the central Pacific was recording the largest known superplume event in ‘modern’ times of the Earth’s history (Fig. 2B). As suggested by Vaughan (1995), this event resulted in a major ridge-push force, with the final result of increased coupling between the subducting and

overriding plates, i.e., increased convergence rates. Thus, we may infer that a drastic change in stress conditions must have begun operating in Chile by the end of Late Cretaceous time. We suggest that this process may have been enhanced by the beginning of the opening of the South Atlantic (Hauterivian), and the consequent onset of the westward drifting of the South American plate (Turner et al. 1994) (Fig. 2B; Table 1). The change in stress conditions along the Cretaceous arc is well-supported by stratigraphic data (Mid-Cretaceous unconformity; Charrier et al. 2002), fission tracks (Coastal Cordillera; 130–100 Ma) and radiometric data for the AFZ (126–125 Ma) (Scheuber et al. 1995). In turn, these compressional conditions can adequately explain the emplacement of the plutonic rocks along the AFZ, which eventually led to Kiruna-type iron mineralization in northern Chile. Buoyancy and transpressional dynamics induce magma overpressuring, which in turn expels plutonic bodies upwards following the vertical pressure gradient along the shear zone (Saint Blanquant et al. 1998; Fig. 3A). In other words, within a compressional regime, a vertical shear zone becomes the main structural path along which magmas can ascend. The higher the pressure, the more pronounced the vertical gradient. This would explain why the iron belt formed by the end of Early Cretaceous, a time when enough pressure had accumulated in the continental crust as to channelize magma emplacement mainly along the AFZ (Fig. 3A). A decisive factor contributing to transpressional conditions along part of the iron belt is the curvature of the AFZ. The system formed an arc (concave seaward), which under the oblique SE-directed subduction of the Aluk plate, created both transtensional and transpressional conditions (for example see Lin and Jiang 2001; Fig. 3B). In this respect, Taylor et al. (1998) describe transtensional conditions along the AFZ in the N to NNW striking segment of 27–25S during the time span of
130 to 105 Ma. Based on the geometry of the AFZ, the obvious result is that a drastic change in the stress conditions must have occurred from Copiapo´ southward (Copiapo´ inflexion point: transtension— transpression) (Fig. 3B). This change coincides with the southern appearance of the CIB’s five large deposits (
200 Mt at 60% Fe): Boquero´n Chan˜ar, Los Colorados, El Algarrobo, Cristales, and El Romeral, which crop out within a short segment of the belt between 28– 30S (Figs. 1, 3B). Another structural factor that may have decisively contributed to mineralization processes, was the passage from ductile to brittle conditions along the AFZ at
125 Ma, a regime that prevailed until
105 Ma (Taylor et al. 1998), coinciding with the peak in formation of iron deposits along the CIB (Table 1). Given the depth of formation of the CIB deposits (
4 km; Me´nard 1995), we may infer suprahydrostatic fluid pressures (
60 MPa) resulting from the combined action of tectonic loading, plutonism-enhanced metamorphic dehydration (Sibson 1990), and the expulsion of magmatic brines (Kelley and Fru¨h-Green 2001). Brittle conditions imply a seismogenic regime, which

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ting greater chances of generating copper deposits (Me´nard 1992). This idea is supported by the presence of major copper deposits/districts immediately to the east of the AFZ (Punta del Cobre, Candelaria, Talcuna; Fig. 1). Alternatively, we may speculate about the possibility that shallow-seated copper deposits (porphyry copper type?) formed along the CIB, but, however, cannot be observed at present because they were wiped out by erosion. This would imply that the CIB was also a copper system, an idea supported by the presence of the fault-related Manto Verde copper–(iron) deposit (Vila et al. 1996; Fig. 1). However, although Manto Verde can be regarded as a ‘transitional’ Cu–Fe deposit, its position in the CIB (northern segment), and its tectonic conditions of emplacement (transtensional), make it a difficult case to compare with the large iron deposits of the southern segment of the belt.

Conclusions

Fig. 3 A Block diagram depicting the tectonomagmatic scheme for the end of the Late Cretaceous, and the ascent of overpressurized magmas along the shear zone. B Schematic view of the Atacama Fault Zone depicting relationships between size of iron mineralization and zones of transpression/transtension. AFZ Atacama Fault Zone, CIB Chilean Iron Belt. Upper block diagram and magma ascent based on Saint Blanquant et al. (1998). For the relationships between curved shear zones and transpression– transtension, see Lin and Jiang (2001). Box A in B Location of zone depicted in A

together with suprahydrostatic fluid pressure gradients are the key prerequisites for ‘‘fault valve’’ type mechanisms that allow for both the upward pumping of fluids in fault systems, and mineralizing processes (Sibson 1990). A last point relates to the Early Cretaceous copper deposits located either within or immediately to the east of the CIB, some of which are very rich in magnetite (Candelaria; Ryan et al. 1995; Fig. 1). Although a full discussion on the relationships between the CIB and these deposits is beyond the scope of this paper, we would like to suggest that the Fe and Cu signatures may be related to the structural setting. While the iron deposits developed within a highly fractured environment (AFZ; increased ‘crustal permeability’), the copper deposits formed within a zone where the intensity of fracturing was of lesser importance (as compared to that of the AFZ) (Fig. 1). Reduced fracturing (i.e., decreased crustal permeability) would have resulted in increased retention of the gaseous sulfur phase at depth, permit-

The relationships between plate-wide tectonic processes (e.g., superplume events) and ore deposits may look obscure or even non-existent in many cases. However, a recognized guiding principle of science tells us that ‘‘the absence of evidence is not evidence of absence’’ (Carl Sagan). We believe that the Chilean case proves this to be true. If the different pieces of the tectonic, magmatic, and metallogenic puzzle are put together, we may conclude that unique global tectonic events may in turn lead to unique results. For example, no deposits equivalent to those of the CIB formed before or after in the geological history of Chile. This is curious for a country in which metallogeny tends to be recurrent (Oyarzu´n 2000). The Mid-Cretaceous constitutes a turning point in the geologic history of central and northern Chile, defining a ‘before’ and an ‘after’. We suggest that the ultimate cause of the major tectonic processes that operated at that time, was the emplacement of the Mid-Pacific Superplume (Fig. 2B). This superplume played a crucial role in the geologic evolution of Chile, increasing convergence rates between Aluk and South America and therefore increasing the stress regime along the Chilean margin. As a consequence of the latter, the magmas were pushed up mainly along the main structural feature of the magmatic arc: the AFZ (Fig. 3A), thus creating a long and narrow belt of intrusions and associated Kiruna-type iron deposits. Curvature of the AFZ, brittle conditions, and transpression along the southern segment of the CIB are the key geodynamic elements that controlled formation of the large iron deposits (Boquero´n Chan˜ar, Los Colorados, El Algarrobo, Cristales, El Romeral; Figs. 1, 3B). Finally, although at another scale and magmatic setting, the CIB case resembles the tectonic structural framework of the Late Eocene–Early Oligocene porphyry copper belt of northern Chile (Sillitoe 1988; Maksaev and Zentilli 1988, Davidson and Mpodozis

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1991; Oyarzun et al. 2001) (Fig. 1). Both formed under compressional conditions along major shear zones, just before major magmatic shifts to the east. These conditions led to large-scale mineralization processes: one associated with dioritic plutonism (Fe, along the southern, compressional segment of the CIB), and the other with felsic, granodioritic intrusive bodies (Cu-Mo) along the Domeyko Fault System (Fig. 1). Although highly speculative, we may further suggest that the events that led to formation of the latter may have also been triggered by another major plate tectonic reorganization process that took place in the Pacific, leading, for example, to the sharp bend in the Hawaiian-Emperor seamount chain about 43 million years ago (Richards and Lithgow-Bertollini 1996). This further stresses the importance of major plate reorganization events in the geologic evolution of active margins, and sheds light on the origin of their final outputs, e.g., the development of mega shear zones, magmatism, and metallogenic processes (among others). Acknowledgments We would like to thank Bernd Lehmann and Robert W. King for their constructive reviews of the manuscript.

References Aguirre L, Levi B, Nystro¨m JO (1989) The link between metamorphism, volcanism and geotectonic setting during the evolution of the Andes. In: Daly JS, Cliff RA, Yardley BWD (eds) Evolution of metamorphic belts. Geol Soc Spec Publ 43, London, pp 223–232 Bookstrom AA (1977) The magnetite deposits of El Romeral. Econ Geol 72:1101–1130 Charrier R, Baeza O, Elgueta S, Flynn JJ, Gans P, Kay SM, Mun˜oz N, Wyss AR, Zurita E (2002) Evidence for Cenozoic extensional basin development and tectonic inversion south of the flat-slab segment, southern central Andes, Chile (33-36S.L.). J S Am Earth Sci 15:117–139 Coffin MF, Eldholm O (1993) Scratching the surface: estimating dimensions of large igneous provinces. Geology 21:515–518 Davidson J, Mpodozis C (1991) Regional geologic setting of epithermal gold deposits, Chile. Econ Geol 86:1174–1186 Fo¨rster H, Jafarzadeh A (1994) The Bafq mining district in central Iran – a highly mineralized Infracambrian volcanic field. Econ Geol 89:1697–1721 Hildebrand RS (1986) Kiruna-type deposits: their origin and relationship to intermediate subvolcanic plutons in the Great Bear magmatic zone, northwest Canada. Econ Geol 81:640–659 Kelley DS, Fru¨h-Green GL (2001) Volatile lines of descent in submarine plutonic environments: insights from stable isotope and fluid inclusion analyses. Geochim Cosmochim Acta 65:3325–3346 Larson RL (1991a) Latest pulse on Earth: evidence for a midCretaceous superplume. Geology 19:547–550 >Larson RL (1991b) Geological consequences of superplumes. Geology 19:963–966 Levi B, Aguirre L (1981) Ensialic spreading-subsidence in the Mesozoic and Paleogene Andes of central Chile. J Geol Soc 138:75–81 Levi B, Nystro¨m JO, Thiele R, A˚berg G (1987) Geochemical polarities in Mesozoic-Tertiary volcanic rocks from the Andes in central Chile and tectonic interpretation. J S Am Earth Sci 1:63–74

Lin S, Jiang D (2001) Using along-strike variation in strain and kinematics to define the movement direction of curved transpressional shear zones: an example from northwestern Superior province, Manitoba. Geology 29:767–770 Maksaev V, Zentilli M (1988) Metallogenic framework of the large porphyry copper deposits of the Andes of northern Chile. Proc 5th Chilean Geol Congr, Santiago, Chile, vol 1, pp 181–212 Me´nard JJ (1988) Les relations volcanism, plutonism et mine´ralisation dans la Ceinture de Fer du Chile: la re´gion d’El Algarrobo. The`se d’e´tat Universite´ Paris XI, 370 pp Me´nard JJ (1992) Comparaison entre les roches plutoniques associe´es a` la Ceinture de Fer du Chili et aux porphyres cuprife`res: arguments pe´trologiques. C R Acad Sci Paris 315: 725–731 Me´nard JJ (1995) Relationships between altered pyroxene diorite and the magnetite mineralization in the Chilean Iron Belt, with emphasis on the El Algarrobo iron ore deposits (Atacama region, Chile). Miner Deposita 30:268–274 Marschick R, Fontbote´ L (1996) Copper–(iron) mineralization and superposition of alteration events in the Punta del Cobre belt, northern Chile. In: Camus F, Sillitoe RH, Petersen R (eds) Andean copper deposits: new discoveries, mineralization, styles and metallogeny. Soc Econ Geol Spec Publ 5, pp 171–190 Montecinos P (1985) Pe´trologie des roches intrusives associe´es au gisement de fer El Algarrobo (Chile). The`se de Dr-Ing, Universite´ de Paris-Sud, 191 pp Munizaga F, Huete C, Herve´ F (1985) Geocronologı´ a K-Ar y razones iniciales Sr87/Sr86 de la ‘‘Faja Pacı´ fica’’ de ‘‘Desarrollos Hidrotermales’’. Proc 4th Chilean Geol Congr, Antofagasta, Chile, vol 4, pp 357–379 Munizaga F, Holmgren C, Huete C, Kawashita K (1988) Geocronologı´ a de los yacimientos de cobre El Soldado y Lo Aguirre, Chile central. Proc 5th Chilean Geol Congr, Santiago, Chile, vol 3, pp 177–193 Oyarzu´n J (2000) Andean metallogenesis: a synoptical review and interpretation. In: Cordani UG, Milani EJ, Thomaz Filho A, Campos DA (eds) Tectonic evolution of South America. 31st International Congress, Rio de Janeiro, pp 725–753 Oyarzu´n J, Frutos J (1984) Tectonic and petrological frame of the Cretaceous iron deposits of northern Chile. Mining Geol 34:21– 31 Oyarzu´n J, Frutos J (1986) Los depo´sitos ferrı´ feros del Norte de Chile. In: Frutos J, Oyarzun R, Pincheira M (eds) Geologı´ a y recursos minerales de Chile. University of Concepcio´n Press, pp 691–713 Oyarzun R, Ortega L, Sierra J, Lunar R, Oyarzu´n J (1998) Cu, Mn, and Ag mineralization in the Quebrada Marquesa Quadrangle, Chile: the Talcuna and Arqueros districts. Miner Deposita 33:547–559 Oyarzun R, Ma´rquez A, Lillo J, Lo´pez I, Rivera S (2001) Giant versus small porphyry copper deposits of Cenozoic age in northern Chile: adakitic versus normal calc-alkaline magmatism. Miner Deposita 36:794–798 Pichon R (1981) Contribution a` l’e´tude de la ceinture de fer du Chili. Les gisements de Bandurrias (Province d’Atacama) et Los Colorados Norte (Province de Huasco). The`se 3e`me cycle. Univ Paris XI, 326 pp Pincheira M (1986) Resen˜a de las caracterı´ sticas geolo´gicas de los principales yacimientos de hierro del Norte de Chile. In: Frutos J, Oyarzun R, Pincheira M (eds) Geologı´ a y recursos minerales de Chile. University of Concepcio´n Press, pp 715–737 Richards MA, Lithgow-Bertollini C (1996) Plate motion changes, the Hawaiian-Emperor bend, and the apparent success and failure of geodynamic models. Earth Planet Sci Lett 137:19–27 Ruiz C, Aguirre L, Corvala´n J, Klohn C, Klohn E, Levi B (1965) Geologı´ a y yacimientos metalı´ feros de Chile. Instituto de Investigaciones Geolo´gicas, Santiago (Chile), 305 pp Ryan PJ, Lawrence AL, Jenkins RA, Matthews JP, Zamora JC, Marino E, Urqueta I (1995) The Candelaria copper–gold deposit. In: Pierce FW, Bolm JG, (eds) Porphyry copper deposits of the American cordillera. Arizona Geol Soc Digest 20:625– 645

646 Saint Blanquant M, Tikoff B, Teyssier C, Vigneresse JL (1998) Transpressional kinematics and magmatic arcs. In: Holdsworth RE, Strachan RA, Dewey JF (eds) Continental transpressional and transtensional tectonics. Geol Soc Spec Publ 135, London, pp 327–340 Scheuber E, Andriessen PAM (1990) The kinematic and geodynamic significance of the Atacama fault zone, northern Chile. J Struct Geol 12:243–257 Scheuber E, Reutter KJ (1992) Magmatic arc tectonic in the central Andes between 21º and 25ºS. Tectonophysics 205:127–140 Scheuber E, Hammerschmidt K, Friedrichsen H (1995) 40Ar/39Ar and Rb–Sr analyses from ductile shear zones from the Atacama fault zone, northern Chile: the age of deformation. Tectonophysics 250:61–87 Sibson RH (1990) Faulting and fluid flow. In: Nesbitt BE (ed) Short course on fluids in tectonically active regimes of the continental crust. Mineralogical Association of Canada, Vancouver, pp 93–132 Sillitoe RH (1988) Epochs of intrusion-related copper mineralization in the Andes. J S Am Earth Sci 1:89–108 Sillitoe RH, Marquardt JC, Ramı´ rez F, Becerra H, Go´mez M (1996) Geology of the concealed MM porphyry copper deposit, Chuquicamata district, northern Chile. In: Camus F, Sillitoe RH, Peteresen R (eds) Andean copper deposits: new discoveries, mineralization, styles and metallogeny. Soc Econ Geol Spec Publ 5, pp 59–70

Taylor GK, Grocott J, Pope A, Randall DE (1998) Mesozoic fault systems, deformation and fault block rotation in the Andean forearc: a crustal scale strike-slip duplex in the Coastal Cordillera of northern Chile. Tectonophysics 299:93–109 Turner S, Regelous M, Kelley S, Hawkesworth C, Mantovani M (1994) Magmatism and continental break-up in the South Atlantic: high precision 40Ar-39Ar geochronology. Earth Planet Sci Lett 121:333–348 Vaughan, APM (1995) Circum-Pacific mid-Cretaceous deformation and uplift: a superplume-related event ? Geology 23:491– 494 Vila T, Lindsay N, Zamora R (1996) Geology of the Manto Verde copper deposit, northern Chile: a specularite-rich, hydrothermal tectonic breccia related to the Atacama fault zone. In: Camus F, Sillitoe RH, Peteresen R (eds) Andean copper deposits: new discoveries, mineralization, styles and metallogeny. Soc Econ Geol Spec Publ 5, pp157–169 Zentilli M (1974) Geological evolution and metallogenic relationships in the Andes of northern Chile between 26 and 29. Dissertation, Queens University Zonenshayn LP, Savostin LA, Sedov AP (1984) Global paleogeodynamic reconstructions for the last 160 Ma. Geotectonics 18:181–195