Andes Of Northern Chile Research Articles

El Zorro: early Jurassic intrusion-related gold (IRG) mineralization in the oldest, western-most segment of the Andean Cordillera of Northern Chile

AbstractThe El Zorro gold district is the most recent gold discovery in the Coastal Cordillera of northern Chile. Ternera is the largest deposit in the district with total resources currently estimated at 1.282 Moz. New geology, geochemistry and geochronology data indicate that hydrothermal mineralization is mostly hosted within felsic to intermediate, ilmenite-bearing calc-alkaline dikes and stocks of the Upper Triassic to Lower Jurassic Relincho Pluton, and some of the adjacent Devonian to Carboniferous metasediments of the Chañaral Epimetamorphic Complex. Sheeted veins, veinlets, and fault zones with quartz, low amounts of pyrite, pyrrhotite and arsenopyrite, and local calcite are surrounded by narrow haloes of albite-biotite-quartz ± sulfides-K-feldspar-sericite-chlorite. Gold (mostly in the veins) is associated with elevated W-Bi and also As-Te-Sn, and not with iron enrichment or base metals, even though this system is proximal (~ 20 km) to IOCG and IOA deposits of the Coastal Cordillera. The main phase of gold mineralization occurred soon after emplacement of tonalitic dikes and granodiorite from the Relincho and Cuevitas plutons (U–Pb zircon between ~ 205 and 190 Ma), about 80 m.y. later than the development of orogenic fabrics. An absolute upper age limit is provided by compositionally distinct ore-cutting mafic dikes dated at 175–170 Ma (U–Pb apatite). The deposit falls into the intrusion-related gold category, as indicated by the cutting of earlier orogenic fabrics, the metal and alteration associations, and the spatial and temporal connection to reduced ilmenite-series intrusions, which are also very similar geochemically to the ‘type-locality’ IRG intrusions of the Tintina Belt in Yukon/Alaska. The El Zorro gold district represents the oldest and geologically western-most mineralizing event in the Central Andes of northern Chile, consistent with its time–space placement within the tectonic framework of easterly-younging mineralization and igneous activity in the Chilean Cordillera.

A new Sperchon species from the high Andes of northern Chile (Acari: Hydrachnidia: Sperchontidae)

A new Sperchon species from the high Andes of northern Chile (Acari: Hydrachnidia: Sperchontidae)

Volcano tectonic setting of the Salares Norte Au–Ag epithermal belt, central Andes of northern Chile

The Salares Norte (SN) Au–Ag belt is here defined as an Upper Miocene-Pliocene metallogenic area, extending for nearly 200 km, located NE of the northern end of the Upper Oligocene-Lower Miocene Maricunga Belt in the central Andes of northern Chile. The belt is located just east of the main reverse NS fault systems which are part of the Sierra Castillo, Potrerillos Mine and Claudio Gay Cordillera faults, limited to the north and south by the NW-striking oblique to the arc Imilac and Wheelwright-Incahuasi regional faults systems.The epithermal deposits within the SN belt are intimately associated with the occurrence of Middle Miocene volcaniclastic basins and Middle to Upper Miocene phreatomagmatic vents and their related high-sulfidation hydrothermal systems. The volcanostratigraphy of the SN epithermal belt comprises volcaniclastic sequences, subvolcanic and volcanic rocks ranging between the Lower Miocene and the Pliocene. High-angle NS reverse faults involving Paleozoic and lower Cenozoic units form the western-southwestern limit of the belt. Folded and faulted Middle Miocene volcaniclastic and volcanic sequences form the main host rock of at least 4 phreatomagmatic events that generated maar-diatreme fields and discrete maar vents, with their related subvolcanic facies, within the widespread Upper Cenozoic volcanic arc, ranging in age between ca. 15 and ca. 4 Ma. These four phreatomagmatic events are spatially and temporarily associated to 4 main high-sulfidation hydrothermal events which have altered both the phreatomagmatic rocks and the Cenozoic country rock of the explosive activity. These hydrothermal systems have formed dozens of discrete hydrothermally altered areas where argillic, advance argillic, silicification and steam-heated alteration are common. Most of the maar fields and the hydrothermal alteration systems are emplaced within a strike-slip tectonic regime with NE-trending shortening which is accommodated in the NW-striking sinistral-normal faults and NE-striking extension structures. These fault systems crosscutting interaction favor the hydrothermal fluid circulation and migration, as well as mineral precipitation on structural and/or primary lithological traps and on NE-striking tension cracks.In summary, the SN epithermal belt is an almost 200 km long and 60 km wide area, mainly NNE-oriented, where epithermal deposits have formed during the Upper Miocene and Pliocene (ca. 13-4 Ma), emplaced within Middle to Upper Miocene volcanic and volcaniclastic sequences associated to small volcanotectonic basins oriented in NS, NE-SW and NW-SE directions, in which most of the high-sulfidation systems are associated to discrete or repetitive structurally-controlled Upper Miocene-Pliocene phreatomagmatic vents and maar fields.

On Ypsolopha micromoths (Lepidoptera, Ypsolophidae) associated with Adesmia shrubs (Fabaceae) in the arid western slope of the central Andes.

Ypsolopha Latreille, 1796 (Lepidoptera, Ypsolophidae) is a genus comprised mostly of Holarctic micromoth species with a fairly broad range of larval hosts (e.g. Aceraceae, Rosaceae, and Fagaceae). The only previous record of herbivory on a representative of the South American genus Adesmia DC. (Fabaceae) was based on the discovery of Ypsolophamoltenii Vargas, 2018 larvae feeding on Adesmiaverrucosa Meyen in the Andes of northern Chile. Further surveys revealed Adesmiaatacamensis Phil. as another host for Y.moltenii, and Adesmiaspinosissima Meyen as the single host of Ypsolopha sp. The genetic distance between DNA barcodes of the two micromoth species was 7.9-8.1% (K2P). These results suggest narrow host ranges for Adesmia-feeding Ypsolopha and highlight the need to further explore the taxonomic diversity of these micromoths in other South American environments.

Argyrotaeniasocoromaensis sp. nov. (Lepidoptera, Tortricidae), a sexually dimorphic micromoth with polyphagous larvae from the arid Andes of northern Chile.

Argyrotaeniasocoromaensissp. nov. (Lepidoptera, Tortricidae, Tortricinae, Archipini) from the arid Andes of northern Chile is described and illustrated. Adults are sexually dimorphic, with differences in wing size, shape and pattern. The larvae feed on Steviaphilippiana Hieron. (Asteraceae) and Lupinusoreophilus Phil. (Fabaceae). Genetic distance between DNA barcodes of male and female adults reared from larvae collected on the two hosts was 0-0.2% (K2P). The discovery of A.socoromaensissp. nov. represents the first record of the genus Argyrotaenia Stephens, 1852 and the tribe Archipini for the Chilean fauna of Tortricidae.

Emplacement and accumulation of magmatic products in contractional structures: How does it occur? Insights from Central Andes of northern Chile

Structural and stratigraphic data demonstrate that the magmatism in northern Chile was accompanied by shortening related to the development of fold and thrust belts. However, how magmatic products were emplaced and accumulated in the contractional structures is an unresolved question. We, therefore, integrated field and seismic data from the regions of the Pampa del Tamarugal, Salar de Punta Negra Basin, and the Hornitos Fold and Thrust Belt to determine the main structures that facilitated the magma accumulation. The syn-kinematic granitic intrusions in the Hornitos Fold and Thrust Belt were preferably emplaced along fold-related thrusts. In this region, magma migrated along thrust ramps and finally accumulated into the core of the anticlines and broken synclines. Subsidiary and vertical tensional fractures controlled the magma accumulation in the hinge zone and at the axis of the folds. The seismic data from the Pampa del Tamarugal and Salar de Punta Negra Basin present evidence of buried volcanoes on inversion anticlines. During the tectonic inversion of the pre-existing Late Paleozoic to Mesozoic half-graben structures in the regions, magma migrated along the master faults and finally accumulated into the core of the inversion anticlines as sills or was expulsed to the surface as volcanoes, as evidenced by the Punta Negra Monogenetic Volcano.

Flightless Females in the Neotropical Moth Genus Cataspilates Warren (Lepidoptera: Geometridae) †.

Although adults are winged and able to fly in most Lepidoptera species, they are apterous or brachypterous and unable to fly in others, such as the flightless females of some geometrid moths. Records of flightless females in the highly diverse and widespread tribe Boarmiini (Geometridae: Ennominae) are mainly restricted to some Nearctic and Palearctic genera. The aim of this study is to provide the first record of flightless females for Cataspilates Warren, 1897, a Boarmiini genus endemic to the Neotropical Region, through the description of Cataspilates marceloi sp. nov. from the arid highlands of the western slopes of the Andes of northern Chile. DNA barcodes confirmed the conspecificity of brachypterous females and winged males reared from larvae collected on the native shrub Adesmia spinosissima (Fabaceae). This contribution represents the first female description for Cataspilates and provides a new opportunity to improve the understanding of the evolution of flightlessness in geometrid moths.

Comparing isotopic estimates of paleoelevation from carbonates and volcanic glass from the Miocene-age Chucal Formation in northern Chile

Paleoaltimetry reconstructions of the Central Andes based on stable isotope data indicate variable timing and rates of uplift, reflecting the operation of multiple geodynamic mechanisms. There are a range of isotopic methods and proxies involved in these reconstructions, and it may be that biases inherent in some of these methods has led to misinterpretations. Here we explored the limitations of carbonate archives in reconstructing past elevations, including underestimation of paleoelevations by oxygen-isotope evaporative enrichment and carbonate formation in the subsurface. To conduct our test, we obtained stable isotope values of carbonates from the Western Cordillera in northern Chile at ~18.5–19.5°S, where previously published paleoaltimetry results from the same sections, based on the hydrogen stable isotope composition of volcanic glass, indicate that this region of the Andes has remained at high elevations (>4.4 km) since at least ~23 Ma. We present new oxygen and carbon isotopic, and clumped isotopic results, petrographic and sedimentologic observations, as well as major element abundance (ICP-MS and microprobe analyses) from lacustrine carbonates (marlstones) and cements in sandstones of the early Miocene Chucal Formation in the central Andes of northern Chile. The clumped isotope paleotemperature estimates range from 26 to 45 °C in lacustrine carbonates and 27 to 54 °C in cements. These results indicate that carbonates from this section do not reflect surface temperatures, suggesting clumped isotope resetting in a rock-buffered setting for marlstones and carbonate formation at depth in the presence of groundwater for cements in sandstones. In contrast, the oxygen and carbon isotopic values from carbonates appear to be primary and combined with Mg/Ca ratios and Na concentrations document the transition from lake deposition into a dominantly fluvial environment within the Chucal Formation, also indicating variable evaporative conditions during deposition. The paleoaltimetry estimates in carbonates significantly underestimate the results determined in volcanic glass, with paleoelevation results ranging between 1.4 km and 2.6 km in marlstones and from 2.6 and 3.6 km in cements.. The results presented in this study highlight the importance of using multiple proxies for paleoaltimetry reconstructions, especially in arid land settings where meteoric waters have been modified by evaporation.

The spatial and trophic ecology of culpeo foxes (Lycalopex culpaeus) in the high Andes of northern Chile

ABSTRACT The spatial and trophic ecology of the culpeo fox (Lycalopex culpaeus) was studied in the Salar de Punta Negra basin and the Llullaillaco National Park, in the high Andes of the Region of Antofagasta in northern Chile. The objectives of this study were to understand the feeding ecology, habitat use, and home range and activity pattern of culpeo fox. The study was conducted in an area of approximately 2800 km2 inside the Punta Negra salt flat basin, Llullaillaco NP, the surrounding mountains, and within areas of mining operations. We used methodologies including camera trapping, live trapping and satellite monitoring of L. culpaeus individuals, and diet analysis. Fifteen captures and five recaptures of culpeos were made, and three of them were equipped with satellite tracking collars. The home ranges estimated using the Minimum Convex Polygon (MPC 95%) were: 1029 km2 (female), 809 km2 (female) and 215 km2 (male). Culpeo foxes were nocturnal animals. A larger sample of 282 fecal scats was collected, with the main trophic prey in culpeo fox diet by frequency of occurrence being rodents (74.3%), arthropods (48%), camelids carrion (43.6%), birds (16.3%), vegetation (13.8%) and reptiles (2.5%). Niche breadth was low (0.367).

A new species of Eupithecia Curtis (Lepidoptera, Geometridae) from the Andes of northern Chile

Eupithecia copaquillaensissp. nov. (Lepidoptera, Geometridae, Larentiinae, Eupitheciini) is described and illustrated. Adults of this new species were discovered using a light trap in the Copaquilla ravine, at about 2800 m elevation on the western slope of the Andes of northern Chile. The morphology of the genitalia of E. copaquillaensis resembles that of E. atacama (Vojnits, 1985), which is also Chilean. However, the shape of the smaller cornutus and the signa in the male and female genitalia respectively enable accurate differentiation of the two species. DNA barcodes are used to associate male and female E. copaquillaensis.

Ypsolophachicoi sp. n., the second representative of the widespread micromoth genus Ypsolopha Latreille (Lepidoptera, Ypsolophidae) from the Andes of northern Chile.

BackgroundThe largest number of species of the widespread and highly diverse micromoth genus Ypsolopha Latreille, 1796 (Lepidoptera, Yponomeutoidea, Ypsolophidae) is known from the Northern Hemisphere. Only seven species have been described from the Neotropical Region, two of which occur in Chile.New informationThe adult stage of Ypsolophachicoi sp. n. from the arid highlands of the western slopes of the Andes of northern Chile is described and illustrated. Its larvae feed on the native shrub Muehlenbeckiafruticulosa (Walp.) Standl. (Polygonaceae). The morphology of the genitalia of Y.chicoi sp. n. resembles that of the only congeneric known to occur in the same geographic area, Y.moltenii Vargas, 2018, whose larvae feed on Adesmiaverrucosa Meyen (Fabaceae). Besides using different host plants, the two species can be accurately separated, based on morphological differences in female and male genitalia.

Magnetotelluric image of the Chilean subduction zone in the Salar de Atacama region (23°-24°S): Insights into factors controlling the distribution of volcanic arc magmatism.

The Salar de Atacama region (23°-24°S) in the Central Andes of northern Chile represents an anomalous segment of the Andes, where a very large forearc basin is present (Salar de Atacama) and the axis of the active volcanic chain is deflected to the east from its regional trend. Here we used magnetotelluric (MT) data to infer the distribution of partial melts and hydrothermal fluids in order to better understand the mechanism controlling the magmatism in this subduction zone.Our 3-D inversion model shows a complex electrical resistivity structure, with several mid crustal conductors (<5 Ωm) imaged around the Salar de Atacama basin (SdAb). Although the forearc is dominated by high resistivities (>1000 Ωm), conductors were imaged below the Precordillera and in the northern SdAb, where major trench-parallel and transverse fault systems are present. We interpret these forearc conductors as evidence of active and fossil hydrothermal systems hosted by the Precordillera Fault System and the Calama-Olacapato-El Toro transverse fault. Conductors found along the arc are spatially coincident with active volcanoes likely representing partial melting in the continental crust. A large conductor was imaged in the backarc, indicating the presence of a significant volume of partial melts below the Altiplano-Puna plateau, as many previous geophysical studies have suggested. The model shows that the mid-lower crust and subcontinental mantle (i.e., >15 km depth) below the SdAb is dominated by resistivity values >100 Ωm., suggesting the presence of a relatively poorly hydrated continental crust and mantle wedge in this segment of the northern Chile subduction zone. These results, together with petrophysical interpretations derived from previous seismic and gravimetric studies, suggest that the lithosphere below the SdAb represents an impermeable block, which inhibits the upward flow of fluids and melts derived from deeper parts of the subduction system.

Electrical conductivity as a driver of biological and geological spatial heterogeneity in the Puquios, Salar de Llamara, Atacama Desert, Chile

Reputed to be the driest desert in the world, the Atacama Desert in the Central Andes of Northern Chile is an extreme environment with high UV radiation, wide temperature variation, and minimum precipitation. Scarce lagoons associated with salt flats (salars) in this desert are the surface expression of shallow groundwater; these ponds serve as refugia for life and often host microbial communities associated with evaporitic mineral deposition. Results based on multidisciplinary field campaigns and associated laboratory examination of samples collected from the Puquios of the Salar de Llamara in the Atacama Desert during austral summer provide unprecedented detail regarding the spatial heterogeneity of physical, chemical, and biological characteristics of these salar environments. Four main lagoons (‘Puquios’) and more than 400 smaller ponds occur within an area less than 5 km2, and are characterized by high variability in electrical conductivity, benthic and planktonic biota, microbiota, lagoon bottom type, and style of mineral deposition. Results suggest that electrical conductivity is a driving force of system heterogeneity. Such spatial heterogeneity within the Puquios is likely to be expanded with temporal observations incorporating expected seasonal changes in electrical conductivity. The complexity of these Andean ecosystems may be key to their ability to persist in extreme environments at the edge of habitability.

Buried thrust belt front of the western Central Andes of northern Chile: Style, age, and relationship with basement heterogeneities

We present a regional-scale study combining field, seismic, and limited borehole information to analyze the structural characteristics of the thrust belt front of the western Central Andes at 21°S. This region, located in northern Chile, consists of the easternmost part of the Coastal Cordillera, the Pampa del Tamarugal, and the western Domeyko Cordillera (or Chilean Precordillera). On the surface, a series of N–S-oriented folds alternating between monoclines and narrow anticline and syncline folds containing Mesozoic, Upper Cretaceous, and Cenozoic rocks form part of the main structural styles, which are frequently bound by west-verging reverse faults that form the basement of the deeper structural levels of the upper crust. The interpretation of a regional seismic grid composed of N–S, NE–SW, and WNW–ESE-oriented 2-D seismic profiles revealed the presence of several blind west-verging inversion anticlines that define the orogenic front of the Central Andes at this latitude. These anticline folds are related to the partial and/or total positive reactivation of ancient east-dipping Jurassic normal basement faults bounding half-graben structures and sub-basins developed within the Tarapacá Basin. Our results suggest that the thrust belt front in this region is preferably located under the Pampa del Tamarugal, and not along the topographic culmination of the western Precordillera as traditionally proposed. New tectonic restorations of 2-D structural models suggest that, during tectonic inversion, between 3 and 4 km of crustal shortening were accommodated by vertical motion along the inverted normal faults. The presence of Upper Cretaceous synorogenic deposits covering the Jurassic syn-rift deposits on the inversion anticlines indicates that both basin inversion and formation of the western thrust belt front began during the Late Cretaceous, and not during the Eocene “Incaic” tectonic phase as previously suggested by regional studies developed in the area.

A New Remarkable Dwarf Sedge (Carex phylloscirpoides, Cyperaceae) from Northern Chile, with Insights on the Evolution of Austral Carex section Racemosae

Abstract—We describe a new remarkable dwarf and apparently acaulescent species of Carex (Cyperaceae) from the Andes of northern Chile: Carex phylloscirpoides. Morphological and molecular data (two nuclear and three plastid DNA regions) were used to study the phylogenetic placement and systematic relationships of this species, which resulted in its assignment to Carex section Racemosae. However, despite being related to the other three species of the section present in the Southern Cone based on phylogenetic evidence, it displays a number of unusual morphological features. In addition, it is geographically disjunct and genetically differentiated from them. A preliminary conservation assessment was performed which resulted in the proposal of the Critically Endangered category at the global level under IUCN guidelines. We discuss the biogeographic and ecological peculiarities of the new species and its allies, with emphasis in the high number of acaulescent sedges present in South America. The features of C. phylloscirpoides emphasize its unique evolutionary position and its rarity highlights its conservation importance, especially in the context of the South American Andean flora.

Iridopsis socoromaensis sp. n., a geometrid moth (Lepidoptera, Geometridae) from the Andes of northern Chile.

BackgroundIridopsis Warren, 1894 (Lepidoptera: Geometridae: Ennominae: Boarmiini) is a New World moth genus mainly diversified in the Neotropical Region. It is represented in Chile by two described species, both from the Atacama Desert.New informationIridopsis socoromaensis sp. n. (Lepidoptera: Geometridae: Ennominae: Boarmiini) is described and illustrated from the western slopes of the Andes of northern Chile. Its larvae were found feeding on leaves of the Chilean endemic shrub Dalea pennellii (J.F. Macbr.) J.F. Macbr. var. chilensis Barneby (Fabaceae). Morphological differences of I. socoromaensis sp. n. with the two species of the genus previously known from Chile are discussed. A DNA barcode fragment of I. socoromaensis sp. n. showed 93.7-94.3% similarity with the Nearctic I. sanctissima (Barnes & McDunnough, 1917). However, the morphology of the genitalia suggests that these two species are distantly related. The discovery of I. socoromaensis sp. n. highlights the need for additional surveys in underexplored areas to understand better the taxonomic diversity and evolutionary relationships of the mainly Neotropical moth genus Iridopsis.

Systematics of Helioandesia tarregai gen. et sp. nov. (Lepidoptera: Yponomeutoidea: Heliodinidae) from the Andes of Northern Chile

The adult stage of Helioandesia tarregai gen. et sp. nov. (Lepidoptera: Yponomeutoidea: Heliodinidae) is described and illustrated from the arid western slopes of the Andes of northern Chile. The larvae of H. tarregai gen. et sp. nov. feed as leaf skeletonizers on Mirabilis acuta (Reiche) Heimerl (Nyctaginaceae). The mostly gray forewing of H. tarregai gen. et sp. nov., ornamented with strongly bulging metallic spots, resembles that of the representatives of the mainly Nearctic Lithariapteryx Chambers, 1876. However, the latter lacks CuP in the forewing, has a single bristle in the female frenulum, and lacks a well-developed cornutus. Helioandesia gen. nov. clustered as sister to Neoheliodines Hsu, 2004 in a cladistic analysis, although no synapomorphies were found for this cluster, while Lithariapteryx was sister to Helioandesia gen. nov. + Neoheliodines based on two synapomorphies. The genetic distance between a DNA barcode sequence of H. tarregai gen. et sp. nov. and representatives of other genera of Heliodinidae Heinemann, 1877 was 9.0–12.5% (K2P), and a maximum likelihood analysis based on this molecular marker confirmed the placement of H. tarregai gen. et sp. nov. as a member of this micromoth family. This contribution represents the first confirmed record of Heliodinidae for Chile.

First observations of invertebrate communities in Lauca bogs (18° S, Arica and Parinacota región, Chile)

Freshwaters of northern Chilean Andes include many bogs referred to as "bofedales". streams of snowmelt origin feed these endor-heic water bodies at high altitudes in the arid mountain zone. Our knowledge of biota inhabiting these ecosystems is rudimentary due to their marked geographical isolation. The present study aimed to do a first characterization of invertebrate fauna in Lauca bogs (18° S, Chile) using species co-occurrence and niche sharing null models. The results revealed the presence of non-structured patterns in co-occurrence considering each site as well as all sites that is most probably an effect of the presence of many repeated species in the studied sites.

A New Species of Scrobipalpomima Povolný (Lepidoptera: Gelechiidae) Reared from Stem Galls of Adesmia spinosissima Meyen (Fabaceae) in the Andes of Northern Chile

The micromoth genus ScrobipalpomimaPovolný, 1985, mainly distributed in southern South America, is one of the more diverse Neotropical genera of Gonorimoschemini (Lepidoptera: Gelechiidae: Gelechiinae). The adult stage of Scrobipalpomima agustini sp. nov. is described and illustrated from the Andes of northern Chile. Larval feeding and pupation of S. agustini occur inside fusiform stem galls on the native spiny shrub Adesmia spinosissima Meyen (Fabaceae). The larva and pupa of S. agustini are illustrated and briefly described. This discovery expands the northern limit of Scrobipalpomima and represents the first record of immature stages and host plant for this genus of micromoths

Adaina jobimi sp. nov., a plume moth (Lepidoptera, Pterophoridae) associated with Baccharis alnifolia (Asteraceae) in the Andes of northern Chile

The adult stage of the plume mothAdaina jobimisp. nov.(Lepidoptera: Pterophoridae: Pterophorinae: Oidaematophorini) from the arid highlands of the western slopes of the Andes of northern Chile is described and illustrated. The wing pattern and genitalia ofA. jobimiresemble those ofA. excretaMeyrick, 1930, from Argentina, Ecuador and Peru andA. coquimboaeGielis, 2012, the only representative of the genus previously known from Chile. Morphological differences ofA. jobimiwith these two congenerics are discussed. Larval feeding and pupation ofA. jobimioccur on inflorescences of the native shrubBaccharis alnifoliaMeyen &amp;amp; Walp. (Asteraceae). The discovery ofA. jobimiprovides the first record of the genus in a long distribution gap in mainland South America west of the Andes Range, suggesting that the taxonomic diversity ofAdainain this area deserves further attention.