IntroductionWhereas the study of the volcanic products of modern volcanic chains allows indirect inferences on lithospheric processes, the eroded roots of these arcs offer a unique opportunity to examine, in the field, the processes of arc building, emplacement of magmas and their interaction with deformation in the arc. The Andean margin is a type convergent oceanic/continental plate boundary zone. This is in part because it has had a continuous record of subduction, since at least Mesozoic times. There has been a switch from extension to contraction- dominated deformation during the mid to Upper Cretaceous as a consequence of rapid sea-floor spreading in the Atlantic Ocean. Obliquity of subduction has generated major trench/orogen parallel strike-slip fault systems and the extensional and contractional deformation phases are often best considered as transtensional or transpressional. A major feature of such plate margins is the emplacement of voluminous magmatic arc plutonic suites as giving rise to trench-parallel plutonic suites (batholiths), comprising numerous individual plutons. In the Coastal Cordillera of northern Chile the late Triassic - Early Tertiary plutonic suites are exposed continuously between 33° and 18°S (Valparaiso to Iquique). In the Huasco province, to the south of the Atacama region, the Coastal Cordillera and western Precordillera is dominated at outcrop by very well exposed plutonic belts. These young eastward and are of Late Triassic to Early Tertiary age and are separated by screens of volcanic rocks, volcaniclastic rocks and limestones. These screen of country rock, are the remains of the overlying roof, underlying floors or lateral walls. They are important because they can be used to give the relative age of the plutons and they contain a record of emplacement-related and pre- and post-plutonic regional deformation. Careful examination of these structures allows inferences about the emplacement mechanism of magmas and the overall tectonic deformation in the arc to be made. This field trip will make a complete traverse across the Coastal Cordillera and the western Precordillera of the Huasco Province (Coastal Cordillera and Precordillera of Vallenar, Fig. 1). The first and the last day will be almost all used to travel to and from our operation centre, the city of Vallenar - capital of the Huasco province. The second, third and fourth days will be completely devoted to the itinerary described in this guide. Following the sequence in which the Mesozoic plutonic arc was built, we will examine the plutonic complexes from west to east and from old to young. During day 2 we will visit the Pacific coast and the Upper Triassic Carrizal Bajo and the Lower Jurassic Algodones plutonic complexes. On day 3 we will make a traverse across the Lower Cretaceous Infiernillo, Retamilla and La Higuera complexes to finish the day with a visit the Los Colorados iron mine, one of the most productive Chilean iron deposits. During day 3 we will go to the western Precordillera of Vallenar to visit its fold and thrust belt and the Upper Cretaceous-Palaeocene Chehueque Plutonic Complex. Over these five days we hope to maintain fruitful discussions on new concepts on magma transport and emplacement and, examine field evidence for the 3D geometry of plutons. We will discuss the emplacement mechanisms and the respective relationships within the context of the overall tectonic regime of the overriding plate as it evolved through Mesozoic and Palaeocene time. Fig. 1. Map of the sothern Atacama Region showing the main itinerary of the 5 days field work 1 margin-parallel normal faults (Tigrillo Fault System. Lying conformably on top of the Punta del Cobre strata. Bell. Basicsiliceous volcanic rocks. This marked a period of extensive crustal melting in the absence of subduction at the start of the rupture of the Gondwana continent and the Andean cycle (Mpodozis and Kay. Infiernillo Shear Zone) linked by NW-trending dextral transfer faults.Geology of the Coastal Cordillera of Vallenar (Fig. 1987. 700 m thick homogeneous sequence of well layered red to brownish calcilutites interbedded with fine grained conglomerates assigned to Sierra La Bandera Formation (Valanginian. Early Jurassic.000 m long belt. 1992). 2. plutonic belts are exposed. Suárez and Bell. Moscoso and Covacevich. limestones. from Antofagasta to the Magellan Strait. a ca. a 1200-3000 m thick clastic and volcanic sequence of quartzrich conglomerates. 1982) during the Late Palaeozoic at the western margin of the South-America subcontinent (Gondwana cycle). lutites. Upper Triassic to Early Cretaceous intrusions were emplaced into the stratified rocks. In the Chilean-Argentinean border these rocks culminate in extensive Upper Carboniferous-Triassic silicic volcanic and plutonic rocks formed as a result of crustal anatexis due to underplating of basalts. and marine carbonate rocks of Early Jurassic to Early Cretaceous in age represent the westernmost units of arc and back-arc sequences (Coira et al. most of them separated by a screen of country rock. the existence of southwest vergent folding in these rocks together with the emplacement of meta. Late Jurassic. Steeply-dipping. 1982). mid Early Cretaceous and latest Early Cretaceous in age. of sedimentary derived metamorphic rocks that represent the remains of accretionary prisms and/or fore-arc basin associations (Bell. 1986. metasedimentary rocks of Devonian-Carboniferous age (Las Tórtolas Formation.. Segerstrom and Ruiz. 1981) is exposed. are indicate the initial stages of volcanism of the Andean Cycle and the renewing of subduction along much of the South-American western margin (Mpodozis and Kay.to peraluminous intrusions have been interpreted as indications of the initiation of a north-easterly. 1967) is a ca. en preparation). 1982). García. 1992. Retamilla and La Higuera plutonic complexes) will be visited during the excursion (Fig. Main stratified units in yellow and intrusive rocks in pink (From Arévalo et al . 1992). A section in the lower part of the Punta del Cobre Fig. Stratigraphic chart of the Coastal Cordillera and Precordillera from the CopiapóVallenar region. The Triassic Carrizal Bajo Plutonic Complex and three Cretaceous complexes (Infiernillo. Pincheira. Formation (Upper Jurassic to Lower Valanginian. 1991). acidic tuffs and limestones. sandstones. 1962) lies to east of La Negra exposures. This is formed by 300 to 700 m of andesitic lava flows alternating with volcanic breccias. These rocks are considered to be the infill of a system of rift basins developed during a phase of extension during the break-up of the Gondwana supercontinent. Six main NNE trending 2 . Rapid facies changes suggest active tectonics throughout the sediment deposition. were also active during Triassic to early Cretaceous and gives the main overall extensional setting under which the plutonic complexes may all have been emplaced. Complejo Epimetamórfico de Chañaral (Godoy and Lara 1998) form part of a 3. The lowest sequence belongs to La Negra Formation (Early Jurassic. 2) In the Coastal Cordillera of the Atacama Region. From west to east they are: Late Triassic. including alkaline basalts. Brown. continental volcanic and volcaniclastic rocks.. In Atacama. The metamorphic rocks are unconformably overlain by the Canto del Agua Formation (Anisian-Sinemurian. fine grained conglomerates.1). Unconformably above the Canto del Agua Formation. 7002200 m thick homogeneous pile of aphanitic to porphyrithic andesitic lava flows interbedded with minor breccias and limestones. earliest Early Cretaceous. rhyolitic tuffs and pyroclastic breccias. subduction-induced underthrusting during the CarboniferousPermian boundary (Brook et al. Naranjo and Puig 1984. 2003) confirm an exhumation stage of this province during the Cerrillos deposition. In both cases the subsidence is accommodated by either down and outward ductile flow of the underlying crust or downward displacement into a deflating deep magma reservoir (Fig 4). imply that the base of the formation is an erosion surface although there is no angular unconformity. which probably led to the plutonic unroofing. 3). Since then the orogen has been characterised by progressive shortening alternating with every time less lasting extensional stages. Two end-member models are predicted: (1) cantilever and (2) piston (Fig. 2002). They developed a model involving four end-member cases of pluton emplacement by roof uplift/ floor depression during reactivation of pre-existing. 4000 of mainly clastic and volcaniclastic sediments within a narrow continental basin built on the Lower Cretaceous sequences. room for magmas can be created by two mechanisms to produce tabular plutons: roof uplift to create a laccolith or floor depression to create a lopolith type intrusion. Grocott and Taylor. Equivalent rocks in Central Chile reached more than 10000 m in thickness. and (3) Pabellón Formation (Upper Barremian to Aptian. The deposition of the Cerrillos Formation marks a major change in the Andean subduction regime during the Mesozoic. is compounded. 5).to high crustal levels because where finite strain have been determined in the adjacent wall rocks measured values are too small to support diapirism. The scarcity of contemporaneous volcanic rocks at the base indicates that the basin received sedimentary supply almost exclusively from the erosion of pre-existing volcanic rocks. Models for emplacement via fault dilation are also often debateable in that the many plutons either do not provide convincing evidence of structural control or are not located in local dilation sites of fault systems. They are formed by a lower sequence of acidic volcanic breccias. Biese-Nickel in Hoffstetter et al. 1957). The Chañarcillo Group (Late Valanginian to Aptian. This enormous accumulation and the common existence of interbedded shallow marine sediments scarce in volcanic components indicate high basin subsidence (Scheuber and Gonzalez. plutonic and acidic volcanic rocks thrust westward by the Vicuña Fault System at the latitude of the Alto del Carmen town. steeply dipping faults in extension or contraction (Fig. elongated parallel to inferred axis of magmatic arcs like those which form the Mesozoic plutonic arcs of North and South-America (Cordilleran Plutons). 1989) suggest that these rocks were deposited as extensional basins within a context of a decoupled margin or a retreating subduction boundary (Russo and Silver.Geology of the Precordillera of Vallenar (Fig. These characteristics together with mantle affinities of La Negra (Rogers and Hawkesworth. within the lowermost part of the sequence. a well layered sequence of laminated red to yellow calcilutites alternating with massive green volcarenites. 1988). 2) To the east of the Central Depression volcanic and sedimentary rocks of the Punta del Cobre Formation and marine carbonate rocks from the Chañarcillo Group are exposed. fluvial and colluvial sedimentary sheets cover the Coastal Cordillera and Precordillera rocks. a homogeneous package of well layered of grey mudstones with upper evaporitic breccias. According to Cruden (1998). This region. Segerstrom and Ruiz. The facies of the Punta del Cobre Formation (Late Jurassic to Early Valanginian. Biese-Nickel in Hoffstetter et al. Extensive Miocene (Atacama Gravels) to Miocene-Pliocene alluvial. 1989) and shoshonitic trends from Lower Cretaceous lava flows from Central Chile (Aguirre et al. 1999). This sequence widely exposed in the Atacama region. represent the accumulation of ca. Higher in the sequence volcanic breccias and lava flows are dominant. deeper plutons. Uyeda. These deposits were formed during a large scale period of regional aggradation caused by a generalized uplift of the Andes since the Middle Miocene. 1957). At the base it contains fluvial conglomerates and sandstones of volcanic origin and freshwater limestones. between Chañaral (26º 20` S) and Vallenar. by three formations. Short Review of Emplacement Mechanisms for Cordilleran Plutons Frequently cited emplacement mechanisms of plutons are: (1) diapirs or ballooning diapirs. Fossils derived from the underlying formations. Biese-Nickel in Hoffstetter et al. 1959) a type sequence for the Lower Cretaceous in northern Chile. are mostly emplaced by floor depression.. particularly during the Early Cretaceous. 1959). and an upper sequence of well bedded lava flows. Grocott and Taylor (2002) recently evaluated emplacement mechanisms for tabular intrusions from the Costal Cordillera of the Chañaral region. (2) emplacement at dilational sites in fault systems. (2) Totoralillo Formation (Barremian. 1962) exposed in the Precordillera are stratigraphicaly higher than those in the Coastal Cordillera. While laccoliths are shallow level intrusions and mostly occurs to less than 3 km of palaeodepth (Corry. 1982) changes to a “Chilean” type mode of subduction where a magmatic arc exists without development of backarc basin. related dome complexes and derived epiclastic conglomerates and sandstones interlayered with limestones. Segerstrom and Parker. batholithic in size. From old to young: (1) Nantoco Formation (Hauterivian. here in Vallenar. The Punta del Cobre and Chañarcillo units together with the La Negra and Sierra La Bandera formations. a coarse thickly-bedded sequence of brown bioclastic calcarenites. 1957). is bounded to the east by a crystalline block of Lower Paleozoic to Triassic metamorphic. represent a total thickness of 4000 to 7000 m accumulated during the Early Jurassic to Early Cretaceous. The Jurassic-Lower Cretaceous arc/back-arc pair (“Mariana” type of subduction. 3 . 1996. possibly from the volcanic rocks above the plutonic roofs farther west. informally denominated here as Vallenar Precordillera. In a field based study. Fission track ages between 108 and 86 Ma from the Copiapó Coastal Cordillera (Griest in Godoy et al. in the Coastal Cordillera. The hypothesis for the emplacement of granites as diapirs can no longer be sustained for mid. Segerstrom and Parker. The Chañarcillo rocks are overlain by the epiclastic to volcaniclastic Cerrillos Formation (Albian-Turonian. Pluton emplacement by roof uplift/ floor depression during reactivation of pre-existing. Geometry and parameters for floor depression models (Cruden. 5. steeply dipping faults in extension or contraction (Grocott and Taylor. 3. 1998) Fig. 4.Fig. Accomodation of deep crust in a floor depression model (Cruden. 2002) 4 . 1998) Fig. 1996). c. The pluton .country rock boundary at the SE side of the pluton is marked by a strongly foliated outward -dipping high-temperature hornblende. PLUTON MARGIN MONOCLINES Stop 1. biotite shear belt.f. This is a fairly homogeneous pluton with an ellipsoidal view plan and a 26 km NS-trending major axis. 6.197. Stretching lineations from these rocks are subvertical and kinematic indicators (σ-type porphyroclast) contained in them and S-C’ shear band cleavage developed in limestones to the south indicate pluton down sense of shear suggesting a floor depression emplacement mechanism. 2004a) 5 . the easternmost intrusive of the Coastal Batholith at this latitude. 6) This short stop is to point out a magnificent example of the characteristics normally observed in the study of plutons in the coastal range of Atacama. It was emplaced within volcanic and volcaniclastic rocks of the Jurassic-Lower Cretaceous Punta del Cobre Formation which comprise the massive green strata exposed to the east and south. Sierra Fritis. The volcanic rocks and the overlying Chañarcillo Group limestones (Nantoco Formation) that surround the intrusion are deformed into antiformal monoclines where the strata dip towards the pluton margin. Geological map of the area to the noth of Sierra de Fritis (Arévalo. Dallmeyer et al. Fig. The Pan American Highway passes through the core of the Sierra de Atacama diorite.Day 1 (9 November) CRETACEOUS SIERRA DE ATACAMA PLUTONIC COMPLEX HIGH-LOW TEMPERATURE MYLONITES. depending on the arrival time (N6. E355. One of these folds is exposed on the Sierra Fritis to the south.938. Hornblende and biotite 40Ar/39Ar ages from the deformed host rocks and the pluton coincide within error and confirm that these are synplutonic mylonites (emplacement-related mylonites.048) (Fig. optional. 5±0. An 40Ar/39Ar age from biotite is ca. Detailed mapping of the plutonic complex has revealed that granite and diorite units are constrained to layers bounded by sharp contacts or by horizons of mingling breccias which involve rocks from the two compositions.620) (Fig. The felsic fragments range from biotite-hornblende syenogranites to tonalites and have an U/Pb zircon age of 208. 1988). 2004). These volcanic rocks are overlain by resistant outcrops of a brown horizon that marks the base of the Lower Cretaceous carbonate rocks of the Chañarcillo Group.DAY 2 (10 November) UPPER TRIASSIC CARRIZAL BAJO PLUTONIC COMPLEX AND LOWER JURASSIC ALGODONES PLUTON PLUTON ARCHITECTURE. A visit to the Los Colorados Mine has been scheduled for the day 3.4 Ma. They are interpreted as mingling breccias whose fragments. in some cases become a mappable unit. are exposed as either decimetre scale blocks of gabbros and quartz diorites immersed in a granitic matrix or as a network of small dykes and irregular veinlets of felsitic material injected in the mafic rocks. show a broad variety in size and shape. the peaks Chehueque. Dark grey diorites. 8) From a headland between a small shell-fish farm and the Carrizal Bajo village a general view to the east reveals the bimodal nature of the Triassic Carrizal Bajo Plutonic Complex (CBPC). The Barril hill itself is made up of a compact package of Triassic granodiorite-diorite mingling breccias which underlies layer 1 and defines a steeply NW-dipping sheeted dyke complex interpreted to be part of the feeder system of the CBPC. To the west the view is of the easternmost Coastal Cordillera.853. Peineta and Pie de Gallo. Stop 2. Composite fabrics like the Carrizal Bajo mingling breccias occur when the felsic material that is partially or entirely liquid is intruded by contemporaneous mafic magma (Blake..5 and 207. while the mafic fragments range from olivine gabbros to biotite quartz monzodiorites and have an U/Pb zircon age of 208. The temperature gradient of the magmas results in a rapid cooling of the mafic material leading to the formation of angular gabbroic fragments. In the middle distance. Road to Carrizal Bajo.2±0. In the foreground diorites from the ca. The rough exposures between are a dacitic dome complex belonging to the Punta del Cobre Formation overlain by well-stratified limestones of the Sierra La Bandera Formation. E323. of fault propagation faults. smooth outcrops in dark green are of the Lower Cretaceous Punta del Cobre Formation. The main displacements on this system accumulated during the mid-Cretaceous. On the whole. The breccias are heavily intruded by a swarm of Jurassic andesitic dykes. reddish exposures of granite (unit 2) underlie dark grey diorites (unit 1b). These rocks form part of the eastern limb of an upright NS-trending syncline whose gently-dipping western limb occupies the foreground.480) (Fig.2 ± 0. The breccias which. these observations suggest that both felsic and mafic fractions are contemporaneous. 6 .4 ± 1. to the north of the Quebrada Carrizal are separated from reddish granites. to the south of this valley. E288.3 Ma). from N to S. Granitic rocks of the Palaeocene plutonic arc are exposed on Peineta and Pie de Gallo. 7) To the east is a view of the Precordillera and. 7) To the left are the main installations of the Compañía Minera Huasco (Mina Los Colorados) which exploit an iron ore body in volcanic rocks of Punta del Cobre Formation close to a branch of the Atacama fault System (Thiele and Pinchiera.2 Ma (Cruden et al. FEEDER SYSTEMS.360. This is equivalent of the northern (north of 27ºS) and southern (south of 33ºS) central valleys. E331.891.550) (Fig. Right at the sky-line. 126. Small hill at a side of the Panamerican highway (N6. 2004). either granitic or dioritic. 123 Ma La Higuera Plutonic Complex are exposed. Moreover.. 1981). The granitic layer on the near side of the fold is thinner and is also underlain by diorite indicating that the granite is a sheet that tapers to the W. granodiorite and tonalite rocks from the ca. To the far southeast.2 ± 0. Cerro Barril (N6. The presence of internal fragmentation and jig-saw textures within the mafic lobes could therefore indicate a rapid quenching of the pillow. probably correspond to a post-Miocene reactivation of a crustal-scale structural system located at the Coastal Cordillera-Precordillera boundary and also recognised for 70 km further northwards to the Inca de Oro and Copiapó districts. near Los Colorados Mine (N6. Such blind structures.3 Ma) were intruded into a pre-existing dioritic layer (207. Stop 3.6 Ma and coincide with the age of the Retamilla Pluton of 126. 1987). the existence of apatite needles together with fine grain textures in the gabbroic fragments also suggest a rapid cooling after pillows were formed (Vernon et al. The contact dips 40-50º to the W. A NS alignment of smooth hills made up of semi consolidated gravels (Atacama Gravels) lies parallel to the main highway. 126 Ma Retamilla Plutonic Complex crop out. Separating the Coastal Cordillera and Precordillera is a wide plain (Llano Chacritas) which forms part of a NS alignment of isolated depressions which extend between the Copiapó and Vallenar regions.. The reserves are 245 million metric tonnes with a mean grade of 48% Fe. The existence of pillow-like mafic bodies with crenulate-contacts within the felsic material indicates the simultaneous existence of the bimodal components in a liquid state. probably the surface expression.5 ± 0.5 Ma (Cruden et al. In the background.110. These Miocene sediments are deformed into a series of anticlines.650. MINGLING BRECCIAS. the cone-shaped Chehueque peak is made up of hornfelsic conglomerates and lavas of the continental mid-Cretaceous Cerrillos Formation.872. MIGMATITES Stop 1.7 ± 1. (2004) from the granodiorites and diorites confirm that the granodiorites (206. U/Pb zircon ages by Cruden et al. Geological map of the area to the south of Los Colorados Mine (from Arévalo and Welkner.7.Fig. in preparation) 7 . E290. This pluton is made up of granites and granodiorites with subordinate quartz diorites and has an elliptical shape in plan view. In the background massive reddish outcrops belong to unit 2. in the eastern part of the CBPC. The intense foliation present in the shear zone gradually diminishes toward the pluton and the Metamorphic Complex. This might be because the diorites were already crystallised at the time of granite emplacement. In the outcrop itself the shear zone defines a ENE to WNW trending foliation that dips 75-85º to the E and S respectively.8) Strongly hornfelsified metamorphic rocks (metapelites and metapsamites) pervasively intruded by NE and ENE trending granitic and dioritic dykes and sills. the second littoral terrace marks the top of the dyke complex which at this site intrudes heavily hornfelsitised phyllites and schists of the Devonian-Carboniferous basement (Complejo Epimetamórfico de Chañaral).175) (Fig. Stop 4. Mingling breccias at the contact between granitic and dioritic dykes like those in Cerro Barril are absent. E290. To the north. East of Quebrada El Carrizo (N6. A stretching lineation is defined by an alignment of flattened lumps that plunges steeply to the S.896. 8 . 8) In this point the eastern border of the ca. To the west this is in contact with the Carrizal Bajo Intrusive Complex in which a discrete alteration halo is developed. 8) To the north-east the foreground is formed by massive outcrops of dioritic rocks of unit 1a. σ-type elements (quartz dioritic fragments) contained in it indicate west (pluton) down sense of shear.650.887. Southern side of Quebrada La Higuera (N8. 8.375. in the western part of the CBPC. To the east the contact with metapelites and metapsamites of the Metamorphic Complex is marked by a subvertical cureved envelope of mylonites and migmatites with a quartz dioritic and metamorphic protolith. Some of the granitic bodies appear to cut and extend laterally toward the floor of the CBPC (to the top of the cliff ).375) (Fig. E295.225. Geological map of the area to the east of Carrizal Bajo (from Arévalo and Welkner. in preparation).775) (Fig. a process probably helped by the sedimentary nature of pre-existing rocks. Quebrada La Higuera (N6. This surface corresponds to the gentlydipping floor of the CBPC above which diorites of unit 1a crop out.894. Stop 5. This suggests an emplacement mechanism by depression of the pluton floor. Stop 6. 197 Ma Algodones Pluton is exposed.Fig. Sheared and unsheared short veins of granitic rock coexist in the shear zone and are evidence of melting during the deformation. NNE-trending. the remains of the ore body can be seen. an old (active up to year 1950) iron deposit where almost pure magnetite (magnetite-apatite) dykes (red) can be distinguished from surrounding actinolite haloes (green). All the remaining stops are located to the east which will help us to have an appropriate light during the return. melted. high temperature foliation.858.type porphyroclasts and S-C shear bands are consistent and indicate east down (pluton) sense of shear. To the west. is seen from which the Cerro Chehueque and the Cerro La Peineta stand out. strongly actinolitised andesite----dacite host rocks are exposed in which up to 10 cm-long actinolite crystal known as “piedra palo” (stick stone) by the local miners can be seen. This boundary and the contact of the diorite with rocks of the Punta del Cobre Formation in the pluton roof. Overlying these rocks. The pluton-down sense of shear shown by the shear zones in the host rocks and the granitic rocks is consistent with the “roll-over” of the layering towards the contact in the antiformal monocline in the host rocks. The closest exposures are made up of an enclave-rich dark granodiorite with a strong subvertical to W dipping. optional (N6. of almost pure magnetite cross cutting the country rock. Stop 2. Rounded. subsidiary to the main ore body. To the east.960) (Fig. If we are lucky we will be able to see on the skyline some of the highest peaks of the High Andes Chilean Puna). Although Punta del Cobre volcanics underlie the Sierra La Bandera limestones stratigraphically. granodiorite from the ca.164. Thin sections indicate that the plagioclase and hornblende foliation have a magmatic state alignment of crystals upon which a coplanar crystalplastic fabric was superimposed.855. so that the diorite has a tabular geometry. imply that the pluton was emplaced along the line of a pre-existing fault with a normal-slip separation down to the east. we assume the granodiorite body also has a layered shape. E319. Immediately to the south is the old open pit of the Sosita mine. a massive panel of Lower Jurassic volcanics deformed into a 40-50º east-dipping antiformal monocline is exposed. Sosita Pass (N6.855. With a bit of luck. strong linear element made up of hornblende and plagioclase alignments plunging steeply down-dip to the west can also be observed. 9 . in places. The host rocks dip steeply towards the pluton margin. The master fault of this structural system (Los Colorados Fault) cannot be seen from this point. The mylonites have a NNE trending foliation dipping 75-85º to the west. In the foreground granodiorites from the ca. whitish outcrops of granodiorite-granite from the lowermost unit of the Infiernillo Plutonic Complex (IPC) are exposed. The contact between these two end member components of the IPC is a sharp surface which steepens to the east. To the west is a general view of a series of NS trending ranges which coincide with the different plutonic belts and their respective country rocks. Stratigraphic separation across the pluton roof further north. Farther to the west. Llano El Sauce (N6. granitic back-veins. Stop 3. To the west. blocky and flattened. E307. At stop 5 we will be return to this point in detail. These characteristics suggest an emplacement mechanism by depression of the pluton floor during fault reactivation. Observe the short. although its trace marks the western boundary of the Retamilla Pluton and coincides with minor mining activity and the Tatara Pass. in Sierra La Bandera they remain structurally below the limestones in the thrust system due to out-of sequence-thrusting that leaves the structure in a young-over-old relationship. 9) The northern end of the main open pit of the Sosita mine. whitish outcrops of granodioritegranite from the lowermost unit of the Infiernillo Plutonic Complex (IPC) are exposed. a coarse grained diorite forms part of the peaks Sierra Los Helados. in the low-lying foreground. the same kinematic indications are shown by the crystalplastic fabric in the granites. E319. Although the floor of the granodiorite cannot be seen. To the east.773) (Fig. Farther west. PRE AND SYN-EMPLACEMENT EXTENSIONAL FAULTING. A subtle to. in the Astillas mine area.DAY 3 (11 November) LOWER CRETACEOUS INFIERNILLO AND RETAMILLA PLUTONIC COMPLEXES PLUTON ARCHITECTURE. Jurassic-Cretaceous volcanics crop out (Punta del Cobre Formation) stratigraphicaly underlying Valanginian marine limestones of Sierra La Bandera Formation. in brown. in the low-lying foreground. The pass itself is built on volcanics and volcaniclastics of the JurassicLower Cretaceous Punta del Cobre Formation. POST EMPLACEMENT CONTRACTIONAL FAULTING Stop 1. A stretching mineral lineation defined by biotite flakes and hornblende needles plunges 70 to 85º to the north. up to 1 cm thick pyramidal crystals of apatite can still be found. It is horizontal near Sierra Los Helados and steepens up to 50º to the east.849) (Fig. Farther east the Vallenar Precordillera. in reddish colours. In this case the ore is made up of pure magnetite (red by oxidation in surface) and apatite (scarce). Beautifully exposed σ. NNE trending andesitic dykes.150. These rocks form a series of thrust sheets tectonically transported to the west forming a positive flower structure (Los Colorado Fold and Thrust Belt). 130 Ma belt of granodiorites from the Infiernillo Plutonic Complex and farther still to the west a view of the outcrop of the Lower Jurassic volcanics (La Negra Formation).375. 9) To the east is a general view of the central depression (hopefully visible and not obscured by the Camanchaca (poor man’s mantle). Cerro Colorado and Cerro Infiernillo. the local name for the coastal mist). To the east. 9) At this point the western border of the 130 Ma Infiernillo Plutonic Complex is exposed. decimetre to meter scale. Conjugate S-C’ (shear band) type fabrics imply that there has been a late bulk flattening strain in the shear zone. jigsaw and lobate margins. Sosita Mine. K-feldspar hornblende-rich veins orthogonal to the stretching lineations. This face also displays a 5 m thick dyke. fine grained dioritic enclaves show all types of heat transference features: mingling textures. 100 m to the west the plutonic rocks have a sharp boundary with strongly foliated andesitic protomylonites cut by undeformed. are coplanar. 126 Ma Retamilla Plutonic Complex are coloured in yellow by albitic alteration. σ-type shear-sense indicators in high-temperature fabrics in thin section consistently show an east (pluton)-down shear sense. in preparation) Stop 4. This extensional faulting would have occurred prior the emplacement of the Retamilla Plutonic Complex and it has been documented farther to the south. The nearby upper diorites are actinolitised and intruded by granite dykes. slightly silicified well layered calcareous mudstones from Sierra La Bandera are interbedded with a thick package of conglomerates and sandstones crops out. The eastern limb of this structure has been truncated by the Los Colorados fault. Stop 4a.855. Visit to the Los Colorados Mine (Fig. the western limb is shared by a broad syncline whose western limb has been thrust over older volcanics and volcaniclastics from Punta del Cobre Formation (the syncline hinge. Sierra La Bandera (N6. but the pre-emplacement stratigraphic separation has been neutralised during subsequent inversion as the fold-thrust belt developed. in Quebrada Chañaral. To the south the western limb of an anticline is observed. South Cerro Colorado.952.317) Stop 5. blocky in surface.Fig. The “young over old” thrust relationship implies out-of-sequence faulting and is evidence for precontractional. E312. Stop 6. half a way to the top of the Sierra Los Helados and Cerro Los Colorados a strong contrast between upper reddish.043) (Fig.857. The boundary. There.944. The anticline can also be traced to the north. optional (N6.619) (Fig. The emplacement of the Retamilla Plutonic Complex probably occurred through the subsidence of the pluton floor via the normal-slip reactivation of a pre-existing Los Colorados Fault. appears flat and sharp to the south. This sequence has been deformed by a series of folds and thrusts to the west. whose trace can be followed southward to the Tatara pass. E316. though not clearly exposed. 9) An overview to the east towards Sierra Sosita and the pass visited during the morning (stop point 1). diorites (layer 2) and lower whitish. This magnificent view shows the flat roof of the ca. granodiorites (layer 1) can be observed. smooth in surface.855. At this side of the Retamilla Plutonic Complex. 9) Looking to the east. Geological map of the area to the west of Sosita Mine (from Arévalo and Welkner. E311. 7) 10 . in a similar way that the IPC was emplaced. preserved at the bottom of the valley. has been displaced westward by a minor thrust). 9. 126 Ma Retamilla Plutonic Complex indicated by the sharp contact between lower smooth whitish to yellowish outcrops of plutonic rocks and silicified and mined volcanic and volcaniclastics rocks of Punta del Cobre Formation and limestones of Sierra La Bandera above exposed to the far NE. Front of Cerro Colorado (N6.606. east-down displacements along the fault surfaces. 662. This out-of-sequence relationship implies that the shear zone correspond to a pre-existing extensional fault reactivated later as a W vergent reverse thrust. We will make a decision on the itinerary that we will follow on the day. steeply-dipping cleavage in calcareous mudstones. are exposures of well layered pale-yellow calcilutites from the Totoralillo Formation (Chañarcillo Group) interstratified with green sandstones lying on top of the Punta del Cobre volcanic and volcaniclastic rocks. This is a tip-line fold related to a thrust that outcrops along strike to the N. Quebrada Jilguero (N6. Asymmetric boudins of the chert bands and S-C’ fabrics also reveal an E-down sense of shear. E343. Both sections reveal an increase in the general dip of the rocks from c. E343373). depending on weather conditions. Further east. A (thrust) faulted contact is suspected. rather massive. and access to the exposures there is straightforward. well-layered granitic units of the Chehueque plutonic complex with cooling joints (Cerro La Peineta) over and underlie volcanic and volcaniclastic rocks from the Cerrillos Formation. 98 Ma Jilguero biotite monzodiorite is exposed intruding volcanics from Punta del Cobre Formation. the ca. Stop 2b. EMPLACEMENT V/S POST EMPLACEMENT CONTRACTIONAL STRUCTURES Stop 1.373. weak disjunctive cleavage in the hinge zone of the anticline. This surface forms part of the Atacama Pediment: an erosional surface that extends throughout the Atacama Region and marks a period of relative calm after a vigorous aggradational stage during the Andean Uplift during the Middle Miocene. Access involves a walk of +/.838. Stop 2. Observe the flat erosion surface that dissects the top of the gravels and partially erodes the granites. Dykes up to 1m-thick are disrupted into asymmetric pods with a east-down shear sense. the highest unit of the Chañarcillo Group. toward the skyline.838. 1988). The strong planar fabric in the limestones is axial planar to the folds. The intensely foliated mudstones contain spectacular boudinaged meta-andesite dykes. It does not involve steep inclines but may not be practicable if it is very warm.965 to N6. Observe folding of the Totoralillo limestones in the Sierra Los Pirpiques. recrystallised limestones interlayered within Punta del Cobre Formation are folded by an open.717) The Qda narrows to a gorge here. clean water-washed exposures (in 2003) show isoclinal folds in thin chert bands interpreted to represent transposed bedding. To the east. On the N side of the Qda. E339. End of Quebrada Tranca Azul (N6. between weakly/uncleaved rocks and intensely cleavage rocks.837. The maintained gravel road to Las Morteros follows Quebrada El Carbón. In the immediate foreground on the south side of the Qebrada.373) In the lower part of the quebrada massive. E343.662. The intensity of the fabric reinforces the interpretation that the contact to the west. It corresponds to minor asymmetric folds associated with fault-propagation and short-cut thrusts at the footwall of the Agua de los Burros Fault (“donkey spring.837. 339. Stop 2a. Cleavage development has obscured bedding in the mudstones. On top of the calcilutites massive thick-bedded brownish limestones from Pabellón Formation. 25º in the west to vertical in the east near the western margin of the Palaeocene plutonic suite. outcrops of the bimodal volcanic and volcaniclastic Punta del Cobre Formation with some impure calcareous horizons interbedded into the sequence can be seen. 10) This stop gives an overview of an E-W section through the JurassicLower Cretaceous sequences deformed into a 20-30º E dipping homocline. There is a steeply-dipping.water fault”) (Moscoso and Mpodozis. To the west brownish.284.837. west-vergent fold pair. is a structural and metamorphic break.446) (Fig. A traverse along either branch takes in a section through the Chañarcillo foldthrust belt in the Vallenar district and crosses the steeply-dipping belt which lies at the eastern margin of the Palaeocene plutonic arc (Agua de los Burros Fault). Quebrada Tranca Azul boasts some spectacular exposures but is not accessible by vehicle. Immediately to the front a thin bed of Miocene gravels (Atacama Gravels) covers the plutonic rocks. 10) Quebrada Jilguero divides in its upper part into the Quebrada Tranca Azul (northern branch) and Quebrada El Carbón to the south. but is difficult to demonstrate. Quebrada Tranca Azul (N6. Individual boudins show large separations demonstrating that the intense fabric does indeed represent a very high strain. recrystallised limestones (N6. Strongly cleaved calcareous mudstones and volcaniclastic rocks (Totoralillo Formation) overlie the massive. Impressive cliffs on the S side exhibit intense.10 km. Shear sense indicators in down-dip lineations within the calcareous mylonites show that the young Cerrillos rocks were thrust to the west over older Chañarcillo limestones. There are vague traces of bedding which appears to be folded but it is difficult to recognise the structures.965) (Fig. a major steeply E-dipping shear zone marked by calcareous mylonites at the Chañarcillo-Cerrillos boundary.838284.130. Quebrada Tranca Azul (N6.DAY 4 (12 November) CHEHUEQUE PLUTONIC COMPLEX ARCHITECTURE OF TERTIARY PLUTONS. 11 . E339. The contact between strongly cleaved and weakly/uncleaved rocks is sharp and dips gently E. The asymmetry of the boudins is consistently east-side-down. The foliation in the limestone is a penetrative mylonitic foliation with a down-dip lineation. On the other hand. Just upstream from this waypoint the Cerrillos Formation is exposed. The Cerrillos Formation below the limestone comprises massive andesites containing silicified lumps. An intense mylonitic foliation has reappeared and is parallel to the bedding. The rock contains a prominent S-C’ fabric with an E-down shear sense. The contact with overlying Cerrillos Formation is not exposed in the quebrada floor. Near the upper contact there is a 20m-wide belt of extremely-platy limestones with an intense down-dip stretching fabric. but were originally presumably basaltic andesites. in preparation) Stop 2c Quebrada Tranca Azul (N6. and going structurally up the section. Geology of the area to the east of Vallenar (from Arévalo and Chávez. 344. In any case. fine-grained limestone which is very impure (volcanogenic component?). anastomosing. The andesite is either intrusive or a flow within the Cerrillos Formation but its margin is affected by the cleavage. The stratigraphic and structural relationships imply that cleaved and uncleaved/non-metamorphic panels of Chañarcillo group have been duplicated by thrusting to the west. Separation between the boudins is extreme and is consistent with very high strain. The black shales contain chert bands characteristic of the Pabellón Formation of the Chañarcillo Group.511) Traversing east from Stop 2b.838. the foliation is more planar.839. Both the upper an lower contacts of the limestone horizon can be examined at this Stop. red cherts (possibly derived from the 12 . The significance of this strip of limestone within the Cerrillos Formation is debated.Fig. At Stop 2c. a 50 m-wide horizon of recrystallised limestone is present within the Cerrillos Formation. freshwater limestones have been described from the Cerrillos Formation in the Copiapó area. The andesite is in contact with strongly-foliated. to the east. there is no evidence that the contact is faulted. Away from the contact. disjunctive cleavage. 50m farther east up the quebrada there are spectacular water-washed (in 2003) exposures of polymict conglomerates. strongly foliated bioclastic limestones contain a strong. The rocks are polymict conglomerates with a strong ductile fabric defined by clasts flattened parallel to the bedding. Stop 2d Quebrada Tranca Azul (N6. The rocks contain spectacular asymmetric boudinaged dykes like those at Stop 2b. immediately beyond a small gap in the exposure. Cobbles of brown limestone (Chañarcillo Group).125. E346. The dykes are chlorite-actinolite schists. 10. down-dip stretching lineation.830. the intensity of the fabric decreases and bedding becomes more obvious in shales with thin calcareous mudstones.025) Two km farther east along Quebrada Tranca Azul a steeply-dipping. It may be a thrust-repeated slice of the Chañarcillo Group within the Cerrillos Formation. The contact between the essentially non-metamorphic shales and cherts of the Pabillón Formation a few metres to the west implies that the mylonitic and metamorphic limestones have been thrust to the west over a nonmetamorphic footwall. Asymmetric fold and cleavage vergence is to the west. but a few metres to the east of the platy limestones volcaniclastic sandstones contain only a weak. and this could be an example of such a horizon. La Negra Formation). From this view point two first order compositional layers can easily be appreciated. microgranite and diorite (from the Cretaceous plutonic arc) show that the Coastal Cordillera was progressively exhumed during deposition of the Cerrillos Formation. monzodiorite (layer 1) with a coarse layering (second order) immediately overlies the volcanics. In the closest of the two peaks.708. E344. Stop 4. Its base is parallel to bedding in the Cerrillos.837. Farther east and at the top of the microgranites three more compositionally distinctive layers (not visible from this point) have been recognised and mapped. optional (N6.836. The cobbles are well-rounded but poorly-sorted. Stop 3a. E343. In the foreground there is an E-dipping homocline formed by well layered mainly yellow Lower Cretaceous Chañarcillo limestones underlying mid-Cretaceous continental clastic and volcanic Cerrillos Formation in green tones. The rocks young to the east. The Cerrillos contains horizons of conglomerates and brecciated volcanics with a feldspar-phyric matrix. optional (N6. Stop 3c Quebrada El Carbón. 9) To the west is a view of the Rio Huasco valley.023) To the east the rocks become progressively more highly cleaved.697. To the west the strong contrast between multicoloured Cerrillos rocks and massive brownish Chañarcillo limestones marks the Agua de los Burros Fault. Cobble imbrication indicates current transport to the south. optional (N6.996. Although less spectacular than in the Qda Tranca Azul section. To the east. probably hidden by the Camanchaca in its lower part.269) (Fig. This latter “comb type” characteristic gives the name to the hill (Peineta=comb).836. A thick. Above is a much lighter microgranite layer (layer 2) with well-developed granite layers (second order layering) in which a characteristic vertical jointing develops. Farther up the quebrada propylitic alteration is prominent which has largely replaced the volcanic cobbles by epidote.856) From Stop 1 in Qda Jilguero the dip gradually increase eastward. the cobbles are supported by a coarse sandstone matrix. steeply-inclined. E347. the southern part of the Palaeocene Chehueque Plutonic Complex lies above a thick sequence of conglomerates and volcaniclastic rocks of Cerrillos Formation. The volcanic rocks contain a rough. and the Coastal Ranges to the far west. There is one clear example of an asymmetric boudin with a east-down sense of shear. tight to isoclinal minor folds with the planar fabric in the axial plane demonstrate that the planar fabric is a foliation. 345. disjunctive foliation but in conglomeritic horizons. clear layering in the granitic rocks can be appreciated. the clasts are flattened with a weak down-dip elongation in the foliation plane. At many localities. At this locality. Stop 3b Quebrada El Carbón. 13 . the limestones contain boudinaged andesite dykes implying a large amout of down-dip extension. blocky in outcrop. Quebrada El Carbón. strongly foliated limestones within the Cerrillos stands out in the distance.385. yellow package of subvertical. The minor fold vergence is consistently to the west. Sierra La Peineta (N6. to the north (Cordón El Cura) and to the south (Cerro La Peineta) of Quebrada Veladero. Often the calcareous mudstones are very finely laminated and it can be difficult to recognise whether this is a ductile fabric or a fine bedding lamination.838. The exposures in the Chañarcillo Group are rather dust-covered near the road but are calcareous mudstones with an intense foliation. steeply-dipping limestones of the Chañarcillo Group on the N-side of the road with discordances at a steeply-dipping (thrust?) fault can be seen. A lower pinkish.625) Steeply-dipping contact between Cerrillos Formation and the Chañarcillo Group. In the coarse beds. Notice the perfect concordance between the plutonic layering and the bedding in the volcanic rocks in the northern hill. Fig. The deformation has been described as produced by a mid-Cretaceous (90-80 Ma) leftlateral transpression stage mainly recorded at the boundary between the Coastal Cordillera and Copiapó Precordillera in the Copiapó region (Arévalo and Grocott. E383.DAY 5 (13 November) ARCHITECTURE OF CRETACEOUS PLUTONS LA BORRACHA PLUTONIC COMPLEX Stop 1.969) (Fig. This old track was used by tax officers. El Cuzco. To the west is exposed the Sierra Partida pericline (double plunging anticline) made up by white and red coloured marls of the Upper Valanginian to Barremian Bandurrias Formation. To the east are outcrops of the eastern most pluton of the Costal Batholith at this latitude (La Borracha Plutonic Complex) and one of the best examples of multilayered intrusion within the Costal Cordillera. and dipping 22º to the E above green monzodiorites from layer 4. This body is internally made up of at least 5 different compositional layers all dipping 22-28º to the ESE.145. a mostly continental. A further two layers have recently been mapped to the west. Two kilometres down the road a pre-Columbus trail known as the “Camino del Inca” (Inca Trail) cross cut the road. The boundary is marked by the strong colour change from whitish upper rocks to greenish lower rocks. 1997) and correlated with the fold-thrust belt in the Vallenar region. To the south there is a clear view of the uppermost layer of microgranite (layer 5) with a pinkish colour. 2004b) 14 . Farther east the microgranites underlie conformably sediments from the Bandurrias Formation. depending on the departure time (N6. laterally equivalent unit of the Chañarcillo Group. Geology of the area to the north of Copiapó (from Arévalo. messengers (called chasquis in old “quechua”) and llama caravans from the capital of the old Inca Empire. 11) General view of one of the most beautiful isolated plains (llanos) at the boundary between the Coastal Cordillera and Copiapó Precordillera. optional. 2. Pampa Medanosa.992. 11. The compositions varies from granite (to the bottom) to monzodiorite. located ca.100 km further north in the neighbouring country. Peru. . 5. 19-40. 1997. Dallmeyer. SERNAGEOMIN... Antofagasta. North Chile: Constraints from 40Ar/39Ar Mineral Ages. 1-11. 271-285. 189-196. G. 265. Ruiz. Instituto de Investigaciones Geológicas. Arévalo and Chávez. Shape and microstructure of microgranitoid enclaves: indicators of magma mingling and flow. Pincheira. Taylor. A. Chile. Pincheira. 1962.). 599-610. 31. Chile. Moscoso. Carta Los Loros.. S.A. Shephard. Santiago. 32 IGC. 1... Regiones de Atacama y Coquimbo. 20. Puig. Andean geochronology and metallogenesis. 33. J. 15 . Atacama Region. 1967. north Chilean Andes (25° 30´ S to 27° 00´ S). (en prep. Provincia de Atacama. 109-121. Late Paleozoic to Triassic evolution of the Gondwana margin: Evidence from Chilean Frontal Cordilleran batholiths (28˚-31˚S). 18. Arévalo. 2004b. 999-1014. Journal of the Geological Society.H. 1998.. Levi.000.R. Santiago. 133-159. 2004a. Chile. And Wall. Bell.. Segerstrom....J. Naranjo.. D. A. Servicio Nacional de Geología y Minería. Tectonic of the Jurassic-Early Cretaceous magmatic arc of the north Chilean Coastal Coprdillera (22º-26ºS): A story of crustal deformation along a convergent plate boundary. In: Proceedings ofVIII Congreso Geológico Chileno. Revista Geológica de Chile. 144. Covacevich. 1988. 1 mapa escala 1:100. Intrusive felsic-mafic net-veined complexes in north Queensland. volcanism and geotectonic setting during the evolution of the Andes. 1-83. 1982. C. Tectonics. 1992. 1 mapa escala 1:100. Scheuber. Triassic rift-related sedimentary basins in northern Chile (24˚-29˚S). V. J. Journal of the Geological Society. Magmatic Migration and Pluton Construction Rates in the Mesozoic Chilean Coastal Cordillera Batholith (27º To 29º S). W. Chile: descripción de la Formación Canto del Agua. 6. R. Región de Atacama.000 scale. C. 1981. Geological Society of America. Segerstrom. Suárez. M. Cecioni. C. Carta Carrizal Bajo-Chacritas. M. Journal of Geology. B. SERNAGEOMIN. B. D.. F. Vernon. magmatic arc fault systems and emplacement of granitic complex in the Coastal Cordillera. C. Florence. T. 104. 15.. Arévalo.K..M. Etheridge. 1988. The link between metamorphism. R. 1982. R. Cordillera formation.E. L. The lower Palaeozoic metasedimentary basement of the Coastal Range of Chile between 25º30’ and 27º S. (en prep. Earth and Science Review. S. 1987.. On the emplacement of tabular granites. 154. 1989. Hojas Taltal y Chañaral.L. Treloar. Memoria para optar al título de Geólogo. Hoffstetter. The tectonic setting of the Chañarcillo Group and the Bandurrias Formation: an early-Late Cretaceous Transpresive Belt between the Coastal Cordillera and Precordillera.S..000. Fuenzalida.. 263 p. Godoy. 2004.000. Cuadrángulo Copiapó. SERNAGEOMIN. M. M. R. Russo. Tectonic and magmatic evolution of Northern Argentina and Chile. Journal of the Geological Society.O.000. J. P.J. 2. Brook. Cuadrángulo Cerrillos. Subduction zones: an introduction to comparative subductology. Mpodozis. C. Blake. Moscoso. 91. 3. Carta Geológica de Chile. Parker. G. J. C. Deformation partitioning. 17.M. 6. Revista Geológica de Chile.M. Mpodozis. G. Arévalo. Grocott. 1959. 1987. Mesozoic Magmatic and Tectonic Events Within the Andean Plate Boundary Zone. 1996. 1. Taylor. R. 1:100.. Corry. Welkner. Uyeda. 511-514. 303-332. 24. 26º-27º 30’. 223-232. J. Arévalo. C. 22. Lara.. BMR Journal of Australian Geology and Geophysics. E. 853-862. Davis. Kay.Diego de Almagro. Geological Society of America Bulletin. Nyström. Geology .J. London. L. 1 mapa escala 1:100. 18. C.J. Carta Vallenar-Domeyko. 1986. B. 62-63. 104. R. Overseas Development Agency Open-file Report.. Mapa Geológico de las Hojas Chañaral . 2002. V. . 895-910. C.. 1992.. Ramos V. 2.. In: Symposium sobre el Geosinclinal Andino. Pankhurst. E. Comparitive geochemical interpretation of Permian-Triassic plutonic complexes of the Coastal Range and Altiplano (25º30’-26º30’S).000. Arevalo.. M. Cordillera de la Costa.. Revista Geológica de Chile. 1981.000. . Cruden. C. 1988. R. Concepción. Geological Society of London. Grocott. Journal of South American Earth Sciences. In Evolution of Metamorphic Belts (Daly. Presencia de sedimentitas triásico-jurásicas al sur de Canto del Agua. Amerique Latine. 3. Geologia de la mitad oriental del cuadrángulo Astillas: nuevos antecedentes de la franja ferrifera principal entre los 28º15’ y 28º30’ latitud sur. Bell.. 43. 1989. 157-177. 21-29. Tectónica transpresiva y movimiento de desgarre en el segmento sur de la zona de Falla Atacama. Coira. Laccoliths: Mechanics of emplacement and growths. 444. editors). 138. Geological Society of America Special Paper. SERNAGEOMIN. M. 1984. 1998. In: Actas III Congreso Geológico Chileno.G. 1999. Cruden. scala 1:250. 1604-1607. Spiro.. Silver P.. G. A geochemical tracerse across the north Chilean Andes: evidence for crust generation from the mantle wedge. Geología del Norte Grande de Chile. D. mantle dynamics and the Wilson Cycle. C. 77-94. K. 1957. Italy. Davidson.. Grocott. Lithos..S. Mpodozis. K.M. Cliff. escala 1: 50. Bell. M. J. Earth Planetary Science Letters. Brown. R. García. Chile. Special Publications. 115. Hawkesworth. 1982.. Tectonophysics. D.. J. escala 1: 50. Brown. A.M. G. 151-166. C. The origin of the upper Palaeozoic Chañaral melange of northern Chile. Carta Copiapó.References Aguirre... Instituto de Investigaciones Geológicas. 1982. C. Gonzalez. 95-99. 1991. Rogers. 1996. C. Thiele. 1 mapa escala 1:100.000... B. R. Grocott. Estilos Estructurales en el Norte Chico de Chile (28º-31º L. Universidad del Norte.. ANDCHRON. Sociedad Geológica de Chile.)..A. Yardley. Provincia de Atacama. 1.). 81. SERNAGEOMIN. Lexique Stratigraphique International.