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1.
Life spans and thermal evolution of hydrothermal systems are of fundamental metallogenic importance. We were able to establish
the chronology and cooling history of the Zaldívar porphyry copper deposit (Northern Chile) by applying a combination of different
isotopic dating methods in minerals with different closure temperatures, including 40Ar/39Ar geochronology and zircon fission track thermochronology, together with fluid inclusion thermometry and previous published
U–Pb zircon geochronology. The hydrothermal mineralization in the Zaldívar deposit is genetically related to the Llamo Porphyry
unit. Samples of igneous biotites from this intrusion yielded 40Ar/39Ar plateau ages between 35.5 ± 0.7 and 37.7 ± 0.4 Ma defining a weighted average of 36.6 ± 0.5 Ma (2σ). In contrast, one sample from the Zaldívar porphyry, one from the andesites, and two from the Llamo porphyry yielded considerably
younger fission track ages of approximately 29 Ma with a weighted mean for all ages of 29.1 ± 1.7 Ma (2σ). Thermal and compositional constraints for the hydrothermal system in the Zaldívar deposit from fluid inclusions thermometry
show that at least three fluid types broadly characterize two main hydrothermal episodes during the evolution of the deposit.
The main mineralization and alteration event is characterized by high temperature (above 320°C) hypersaline fluids (salinity
between 30 and 56 wt.% NaCl equivalents) coexisting with low-density gas-rich inclusions (salinity less than 17 wt.% NaCl
equivalents) that homogenizing into the gas phase at temperatures above 350°C. The second episode corresponds to a low-temperature
event which is characterized by liquid-rich fluid inclusions that homogenize into the liquid phase at temperatures ranging
from 200°C to 300°C with salinities lower than 10 wt.% NaCl equivalents. The 40Ar/39Ar data (36.6 ± 0.5 Ma, weighted average) obtained from igneous biotites represent the minimum age for the last high-temperature
(above 300°C) hydrothermal pulse. When compared with previously published U–Pb ages (38.7 ± 1.3 Ma) in zircons from the Llamo
porphyry, a close temporal relationship between crystallization of the parental intrusion and the thermal collapse of the
last high-temperature hydrothermal event is evident. Cooling took place from approximately 800°C (crystallization of the intrusive
complex defined by zircon U–Pb ages) to below 300 ± 50°C (biotite 40Ar/39Ar closure temperature) within approximately 1.5 m.y. Because the thermal annealing of fission tracks in zircons occurs at
temperatures of 240 ± 30°, the zircon fission track (ZFT) ages of 29.1 ± 1.7 Ma (2σ) mark the end of the thermal activity in the Zaldívar area, specifically the time when the whole area cooled below this temperature,
well after the collapse of the main hydrothermal event in the Zaldívar porphyry copper deposit. This cooling age roughly coincides
with the age defined for the emplacement of dacitic dikes at 31 ± 2.8 Ma (2σ) (published K–Ar whole rock), 5 km south of the Zaldívar deposit, in the Escondida area. This late magmatic pulse probably
is responsible for high heat flow in the Zaldívar deposit as late as 29 Ma. There is no evidence that the low temperature
hydrothermal pulse recognized by fluid inclusion studies is related to this thermal event. The zircon fission track cooling
ages are interpreted to be related to the time lag required for complete relaxation of the perturbation of the isotherms in
the geothermal field imposed by the intrusion of magmatic bodies, with or without any association with low temperature hydrothermal
activity. 相似文献
2.
Natalia Astudillo Pierrick Roperch Brian Townley Cesar Arriagada Annick Chauvin 《Mineralium Deposita》2010,45(1):23-41
El Teniente porphyry copper deposit, the world’s greatest intrusion-related Cu–Mo ore body, is hosted within basaltic–andesitic
volcanic and gabbroic rocks (mafic complex). This ore body is strongly affected by multiple events of alteration/mineralization
with pervasive potassic and chloritic alteration and coetaneous with associated copper mineralization. We present paleomagnetic
results obtained from oriented samples at four locations within the mine and from two drill cores, 200 and 400 m long, respectively.
Samples are representative of all the main hydrothermally altered rock units, with emphasis on the mafic host rock and dacitic
(Teniente dacite porphyry) and dioritic porphyry intrusions. Magnetic experiments [hysteresis loop, isothermal remanent magnetization
(IRM), k–T curves, thermal, and alternating field demagnetization] show the presence of prevailing magnetite. Microscope and SEM observations
show two families of magnetite, (a) large multidomain magnetite grains, associated with biotite and chlorite of various different
hydrothermal alteration events, and (b) abundant small to medium grain-size magnetite (<10 μm) contained within plagioclase,
either related to an early Na–Ca–Fe alteration or included within plagioclase during magmatic crystal growth. While the Teniente
dacite porphyry and the quartz diorite–tonalite have low magnetic susceptibility (<0.0005 SI) and low natural remanent magnetization
(NRM, 10−4–10−3 Am−1), the mineralized mafic host rocks have usually high susceptibility (>0.01 and up to 0.2 SI) with NRM in the range 0.1–2 Am−1. Most mafic complex rock samples have univectorial magnetizations during alternating field or thermal demagnetization. Within
the mine, the magnetic polarity is spatially distributed. In the northern part of the deposit, the Teniente dacite porphyry,
the associated hydrothermal breccias, and the hosting mafic complex record a reverse polarity magnetization, also observed
in the El Teniente sub-6 mine sector immediately to the east and southeast. In the eastern part of the deposit, a normal polarity
is observed for samples of the mafic complex from the two long drill cores. There is no evidence for superimposed magnetizations
of opposite polarities in samples of the mafic complex. Anhysteretic remanent magnetization (ARM) in a DC field of 40 μT and
NRM have similar magnitude and comparable behavior upon alternating field demagnetization. The well-defined strong remanent
magnetizations associated with high unblocking temperatures (>500°C) indicate an acquisition of remanent magnetization during
mineralization by circulating high temperature fluids related with ore deposition. Paleomagnetic results and the recorded
polarity zonation suggest multiple mineralization events occurred at El Teniente, each one with its own evolution stages,
superimposed within the district. These results indicate that a simplified broad four-stage model for El Teniente, as presented
and overly employed by many authors, divided in (1) late magmatic, (2) main hydrothermal, (3) late hydrothermal, and (4) posthumous
stage, does not recognize various short-lived single mineralization events, some superimposed and some distinctly separated
in time and space. There is no paleomagnetic evidence for post-mineralization deformation 相似文献
3.
What do people think about the flood risk? An experience with the residents of Talcahuano city,Chile
In the province of Concepción (Chile), floods are considered one of the main natural hazards. One of the most important cities of this area is Talcahuano. During the last years, Talcahuano has been affected by a number of flood episodes, as a consequence of an increase in the frequency of extraordinary atmospheric events, along with a higher exposure to the flood risk caused by an intense urban development. On 27 February 2010, an 8.8° earthquake (Richter scale) occurred in central southern Chile and originated the tsunami which flooded a large percentage of the residential area and military base of the Talcahuano city. This flood event affected a population higher than 180,000 people (including 23 casualties and invaluable economic and environmental losses). The objective of this study is to investigate the social perception and knowledge of Talcahuano residents affected by different types of flood, including tsunami, emphasizing which are their risks, vulnerability, resilience and coping capacity concepts. In addition, the kind of measures that have been proposed to improve their capacity to face floods after having suffered the natural disaster will be determined. This social assessment has been carried out based on a survey to permanent residents. Research results reveal that their endogenous and exogenous characteristics have resulted determinant to explain their perception. 相似文献
4.
《International Geology Review》2012,54(12):1466-1483
Chromitites (>80% volume chromite) hosted in two ultramafic bodies (Lavanderos and Centinela Bajo) from the Palaeozoic metamorphic basement of the Chilean Coastal Cordillera were studied in terms of their chromite composition, platinum-group element (PGE) abundances, and Re-Os isotopic systematics. Primary chromite (Cr# = 0.64–0.66; Mg# = 48.71–51.81) is only preserved in some massive chromitites from the Centinela Bajo ultramafic body. This chemical fingerprint is similar to other high-Cr chromitites from ophiolite complexes, suggesting that they crystallized from arc-type melt similar to high-Mg island-arc tholeiites (IAT) and boninites in supra-subduction mantle. The chromitites display enrichment in IPGE (Os, Ir, Ru) over PPGE (Rh, Pt, Pd), with PGE concentrations between 180 and 347 ppb, as is typical of chromitites hosted in the mantle of supra-subduction zone (SSZ) ophiolites. Laurite (RuS2)-erlichmanite (OsS2) phases are the most abundant inclusions of platinum-group minerals (PGM) in chromite, indicating crystallization from S-undersaturated melts in the sub-arc mantle. The metamorphism associated with the emplacement of the ultramafic bodies in the La Cabaña has been determined to be ca. 300 Ma, based on K-Ar dating of fuchsite. Initial 187Os/188Os ratios for four chromitite samples, calculated for this age, range from 0.1248 to 0.1271. These isotopic compositions are well within the range of chromitites hosted in the mantle section of other Phanaerozoic ophiolites. Collectively, these mineralogical and geochemical features are interpreted in terms of chromite crystallization in dunite channels beneath a spreading centre that opened a marginal basin above a supra-subduction zone. This implies that chromitite-bearing serpentinites in the metamorphic basement of the Coastal Cordillera are of oceanic-mantle origin and not oceanic crust as previously suggested. We suggest that old subcontinental mantle underlying the hypothetical Chilenia micro-continent was unroofed and later altered during the opening of the marginal basin. This defined the compositional and structural framework in which the protoliths of the meta-igneous and meta-sedimentary rocks of the Eastern and Western Series of the Chilean Coastal Cordillera basement were formed. 相似文献
5.
《地学前缘(英文版)》2019,10(3):1073-1099
Compositionally zoned plutons, both layered and concentrically arranged, provide granitic exposures where the mechanisms and timing of the magmatic emplacement processes can be studied. The importance of in-situ geochemical differentiation and the magma replenishment rates are revealed by geochemistry and field relations, together with the increasingly accurate U–Pb geochronology, which has promoted the knowledge about the pluton incremental assembly theories.The Flamenco pluton, located in the Coastal Range of northern Chile, is part of the Upper Triassic to Early Cretaceous Andean intrusives formed in the western active margin of South America, and present a normal zoned structure with mafic magmatic facies (mostly gabbros and Qtz-diorites) close to the contacts with the host metasediments, and tonalites, granodiorites and granites in the inner areas. A combined study of the field relations, geochemistry and zircon geochronology of the magmatic facies was applied to determine the emplacement sequence of the Flamenco pluton, revealing three distinguishable domains separated by metasedimentary septa. The SW area is constituted by mostly homogeneous leucocratic granodiorites that yielded an age of 213 Ma as the best estimation for their emplacement age. Distinctive geochemical characteristics, such as the absence of an Eu anomaly, the depletion in HREE, or the highest Sr, Sr/Y and Ce/Yb values among the granodioritic facies of the pluton, involve lower T and/or higher P conditions at the magmatic source according to experimental studies. These conditions were established during an early stage of the Andean magmatic arc building that is firstly defined here as Upper Triassic. The NW and E domains of the pluton were sequentially emplaced between 194 Ma and 186 Ma and both the field relations and the detailed geochronological results suggest that the mafic facies intruded latter in the emplacement sequence. To the NW, Qtz-dioritic and gabbroic externally emplaced pulses gave a younger crystallization age of 186.3 ± 1.8 Ma, and promoted the granoblastic textures and metamorphic zircon overgrowths that characterize the granodiorites located in the contact with the intermediate and felsic inner magmas, which yielded a best estimation of their emplacement age of 192 ± 1.5 Ma. On the other hand, in the eastern domain, magma-magma relations are observed between gabbros and previously intruded tonalites and granodiorites. Both the mafic and intermediate facies show two main subgroups of ages that yielded 194.7 ± 1.5 Ma to 188.3 ± 2.1 Ma and 193.1 ± 2.2 Ma to 185.5 ± 1.4 Ma respectively. These differences are related to the variations in the magmatic addition rates, which may extend the super-solidus conditions in the eastern domain of the magmatic reservoir as is confirmed by the wider age ranges yielded by these magmatic facies. Zircon overgrowths in the host rocks yield similar ages (around 220 Ma and 205 Ma) than the oldest results obtained in the intrusive facies, indicating that metamorphism correlates with the initial stages of plutonic emplacement.Geochronological results differ between 9 Myr and 41 Myr in the eight studied samples for non-inherited ages and gave very close mean ages (within analytical uncertainty) for all the intrusive units. However, we examine other characteristics such as zircon morphology, internal structure, geochemistry and statistical data to assess if the scattering of the geochronological data may be related to the different processes involved in the construction of the Flamenco pluton. We concluded that this detailed study of U–Pb zircon ages, including individual and significative groups of analyses, is useful to determine accurately the emplacement sequence and the genetic relation between the intrusive units, together with the evidences depicted by the geochemistry and field relations. 相似文献
6.
The Lluta collapse of northern Chile is one of the oldest recognizable landslides (>2.5 Ma) in a hyperarid continental setting. This paper develops a conceptual landscape evolution model of the Lluta collapse and analyzes the controls of mass wasting and erosion/sediment transport in channels on the topographic development. The data presented here imply that high relief along a topographic scarp, surface fracturing, elevated groundwater table during a more humid climate and an aquitard underlying permeable ignimbrites are preparatory causal factors for landsliding >2.5 Ma ago. A strong seismic event then possibly resulted in the displacement of ca. 26 km3 of mass. Subsequent modification of the landslide scar occurred by backward erosion, resulting in the establishment of a dendritic drainage network and the removal of an additional ca. 24 km3 of material. It appears that this mass was produced by mass wasting in the headwaters, and exported by high-concentrated debris flows in channels. In addition, morphometric information suggest that whereas the geometrical development of the Lluta collapse has been controlled by gravitational mass wasting, the rates of the development of this geomorphic unit have been limited by the export rates of mass and hence by the transport capacity of the flows. 相似文献
7.
Rabbia Osvaldo M. Correa Karen J. Hernández Laura B. Ulrich Thomas 《International Journal of Earth Sciences》2017,106(8):2687-2711
International Journal of Earth Sciences - The El Abra porphyry copper deposit belongs to the Late Eocene—Early Oligocene metallogenic belt of northern Chile, which host several world-class... 相似文献
8.
The San Ramón Fault is an active west-vergent thrust fault system located along the eastern border of the city of Santiago, at the foot of the main Andes Cordillera. This is a kilometric crustal-scale structure recently recognized that represents a potential source for geological hazards. In this work, we provide new seismological evidences and strong ground-motion modeling from hypothetic kinematic rupture scenarios, to improve seismic hazard assessment in the Metropolitan area of Central Chile. Firstly, we focused on the study of crustal seismicity that we relate to brittle deformation associated with different seismogenic fringes in the main Andes in front of Santiago. We used a classical hypocentral location technique with an improved 1D crustal velocity model, to relocate crustal seismicity recorded between 2000 and 2011 by the National Seismological Service, University of Chile. This analysis includes waveform modeling of seismic events from local broadband stations deployed in the main Andean range, such as San José de Maipo, El Yeso, Las Melosas and Farellones. We selected events located near the stations, whose hypocenters were localized under the recording sites, with angles of incidence at the receiver <5° and S–P travel times <2 s. Our results evidence that seismic activity clustered around 10 km depth under San José de Maipo and Farellones stations. Because of their identical waveforms, such events are interpreted like repeating earthquakes or multiplets and therefore providing first evidence for seismic tectonic activity consistent with the crustal-scale structural model proposed for the San Ramón Fault system in the area (Armijo et al. in Tectonics 29(2):TC2007, 2010). We also analyzed the ground-motion variability generated by an M w 6.9 earthquake rupture scenario by using a kinematic fractal k ?2 composite source model. The main goal was to model broadband strong ground motion in the near-fault region and to analyze the variability of ground-motion parameters computed at various receivers. Several kinematic rupture scenarios were computed by changing physical source parameters. The study focused on statistical analysis of horizontal peak ground acceleration (PGAH) and ground velocity (PGVH). We compared the numerically predicted ground-motion parameters with empirical ground-motion predictive relationships from Kanno et al. (Bull Seismol Soc Am 96:879–897, 2006). In general, the synthetic PGAH and PGVH are in good agreement with the ones empirically predicted at various source distances. However, the mean PGAH at intermediate and large distances attenuates faster than the empirical mean curve. The largest mean values for both, PGAH and PGVH, were observed near the SW corner within the area of the fault plane projected to the surface, which coincides rather well with published hanging-wall effects suggesting that ground motions are amplified there. 相似文献
9.
《Applied Geochemistry》2004,19(11):1855-1864
The Coquimbo region has been one of the richest producers of Cu, Au and Hg in Chile, and some of the deposits have been mined almost continuously since the 16th century. To assess the potential environmental contamination in this region, the authors measured the concentration of Cu, As, Cd, Zn and Hg in samples of stream and mine waters, stream sediments, soils, flotation tailings, and mine wastes in the Andacollo (Cu, Au, Hg) and Punitaqui (Cu–Au, Hg) districts. The concentration of Hg in the atmosphere in these districts were also measured. Although contamination is strongly controlled by the ore in each district, metal dispersion is modified by the degree of metallurgical processing efficiency as shown by the outdated Cu flotation system at Andacollo (stream sediments Cu 75–2200 μg/g). Conversely, more efficient procedures at Punitaqui resulted in less stream contamination, where stream sediments contained Cu ranging from 110–260 μg/g. However, efficient concentration by flotation of a given metal (e.g. Cu) may lead to the loss of another (e.g. Hg up to 190 μg/g in the tailings at Punitaqui), and therefore, to contamination via erosion of the tailings (downstream sediments Hg concentrations up to 5.3 μg/g). Continued use of Hg for Au amalgamation at Andacollo has led to significant contamination in stream sediments (0.2–3.8 μg/g Hg) and soils (2.4–47 μg/g Hg). Communities in this region are underdeveloped, and decades of inefficient treatment of flotation tailings and waste-rock stock piles has resulted in significant contamination of the surrounding landscape. 相似文献
10.
We investigated the Sm–Nd systematics of mafic granulite and undeformed layered gabbro, which form a midcrustal section of the Jurassic magmatic belt in the North Chilean Coast Range, south of Antofagasta. Mineral isochrons indicate ages between ca. 171 and 150?Ma for the granulite and an age of ca. 161 Ma for the gabbro. These ages are interpreted as closure time of the Sm–Nd system in the area. The age of metamorphism is Late-Jurassic. The minimum intrusion age of the protolith of the granulite is likely Early Jurassic (ca. 200?Ma), but an exact intrusion age could not be derived from the data. The intrusion age of the gabbro is ca. 185 Ma. Granulite generated from mantle-derived gabbroic magmas has ?Nd200 between 6.28 and 7.05 and the gabbro that intruded the granulite has ?Nd185 between 5.89 and 6.09. 相似文献
11.
Fernando Barra Hugo Alcota Sergio Rivera Victor Valencia Francisco Munizaga Victor Maksaev 《Mineralium Deposita》2013,48(5):629-651
The recently discovered Toki cluster, which includes the Toki, Quetena, Genoveva, Miranda, and Opache porphyry Cu–Mo prospects, is located 15 km south–southwest of the Chuquicamata–Radomiro Tomic mines in northern Chile. These prospects occur in an area of 5?×?6 km and are completely covered with Neogene alluvial deposits. Inferred resources for the cluster are estimated at about 20 Mt of fine copper, with Toki and Quetena contributing ～88 % of these resources. Mineralization in these deposits is associated with tonalite porphyries that intruded andesites and dacites of the Collahuasi Group and intrusions of the Fortuna–Los Picos Granodioritic Complex. Hypogene mineralization in the Toki cluster consists mainly of chalcopyrite–bornite with minor molybdenite with mineralization grading outward to a chalcopyrite–pyrite zone and ultimately to a pyrite halo. Alteration is dominantly of the potassic type with K-feldspar and hydrothermal biotite. Sericitic alteration is relatively restricted to late quartz–pyrite veins (D-type veins). Previous K–Ar geochronology for the cluster yielded ages within a range of 34 to 40 Ma. Four new Re–Os ages for Toki indicate that molybdenite mineralization occurred in a single pulse at ～38 Ma. Re–Os ages for three different molybdenite samples from Quetena are within error of the Toki mineralization ages. These ages are concordant with a new zircon U–Pb age of 38.6?±?0.7 Ma from the tonalite porphyry in Quetena. Two Re–Os ages for Genoveva (38.1?±?0.2 and 38.0?±?0.2 Ma) are also within error of the Toki and Quetena molybdenite ages. Four Re–Os molybdenite ages for Opache range between 36.4 and 37.6 Ma. The Miranda prospect is the youngest with an age of ～36 Ma. Four new Re–Os ages for the Chuquicamata deposit range between 33 and 32 Ma, whereas nine new 40Ar/39Ar ages of biotite, muscovite, and K-feldspar range between 32 and 31 Ma. Analyzed molybdenites have Re and Os concentrations that vary between 21–3,099 ppm and 8–1,231 ppb, respectively. The highest Re and Os concentrations are found in the Toki prospect. Three new 40Ar/39Ar ages for the Toki cluster are younger than the Re–Os mineralization ages. The age spectra for these three samples show evidence of excess argon and have similar inverse isochron ages of 35 Ma that probably reflect a late hydrothermal phyllic event. The new geochronological data presented here for the Toki cluster indicate that molybdenite mineralization occurred within a very short period, probably within 2 Ma, and synchronously (at ～38 Ma) in three mineralization centers (Toki, Quetena, and Genoveva). Furthermore, mineralization at the Toki cluster preceded the emplacement of the Chuquicamata deposit (35–31 Ma) and indicates that porphyry Cu–Mo mineralization occurred episodically over a period of several million years in the Chuquicamata district. 相似文献
12.
Jiménez Martínez Maribel Jiménez Martínez Mónica Romero-Jarén Rocío 《Natural Hazards》2020,104(2):1481-1533
Natural disasters are one of the main channels through which ecological and socio-economic systems interact. In particular, the severe impacts of earthquakes could disrupt activities in the labour market. However, the literature barely researched the long-term effects of such events. To investigate this issue, this article is concentrated in Chile that is subject to recurring seismic movements. The 27 February 2010 Bío-Bío Chile earthquake (Mw 8.8) was the second strongest in the history of the country. This natural disaster can be used to evaluate the response of the labour market to an exogenous shock. Besides, the capacity for resilience in the labour market is crucial for people who rely on their job. This document analyses the impacts of the 2010 Bío-Bío earthquake and tsunami on Chilean labour market outcomes, in particular, the quality of employment. With this objective, different data are combined for analysing the effect in the short and long term. Also, distinct econometric techniques and exogenous measurements of seismic acceleration are used. The evidence shows that these catastrophes harmed the labour market in the short term. However, in the long term, the government’s reconstruction efforts and other factors could have attenuated the adverse effects over some variables in the most affected zones.
相似文献13.
The aim of this study is to quantify the crustal differentiation processes and sources responsible for the origin of basaltic
to dacitic volcanic rocks present on Cordón El Guadal in the Tatara-San Pedro Complex (TSPC). This suite is important for
understanding the origin of evolved magmas in the southern Andes because it exhibits the widest compositional range of any
unconformity-bound sequence of lavas in the TSPC. Major element, trace element, and Sr-isotopic data for the Guadal volcanic
rocks provide evidence for complex crustal magmatic histories involving up to six differentiation mechanisms. The petrogenetic
processes for andesitic and dacitic lavas containing undercooled inclusions of basaltic andesitic and andesitic magma include:
(1) assimilation of garnet-bearing, possibly mafic lower continental crust by primary mantle-derived basaltic magmas; (2)
fractionation of olivine + clinopyroxene + Ca-rich plagioclase + Fe-oxides in present non-modal proportions from basaltic
magmas at ∼4–8 kbar to produce high-Al basalt and basaltic andesitic magmas; (3) vapor-undersaturated (i.e., P
H2O<P
TOTAL) partial melting of gabbroic crustal rocks at ∼3–7 kbar to produce dacitic magmas; (4) crystallization of plagioclase-rich
phenocryst assemblages from dacitic magmas in shallow reservoirs; (5) intrusion of basaltic andesitic magmas into shallow
reservoirs containing crystal-rich dacitic magmas and subsequent mixing to produce hybrid basaltic andesitic and andesitic
magmas; and (6)␣formation and disaggregation of undercooled basaltic andesitic and andesitic inclusions during eruption from
shallow chambers to form commingled, mafic inclusion-bearing andesitic and dacitic lavas flows. Collectively, the geochemical
and petrographic features of the Guadal volcanic rocks are interpreted to reflect the development of shallow silicic reservoirs
within a region characterized by high crustal temperatures due to focused basaltic activity and high magma supply rates. On
the periphery of the silicic system where magma supply rates and crustal temperatures were lower, cooling and crystallization
were more important than bulk crustal melting or assimilation.
Received: 2 July 1997 / Accepted: 25 November 1997 相似文献
14.
Paula C. Ugalde Calogero M. Santoro Eugenia M. Gayo Claudio Latorre Sebastin Maldonado Ricardo De Pol‐Holz Donald Jackson 《Geoarchaeology》2015,30(4):352-368
Archaeological sites composed only of surficial lithics are widespread in arid environments. Numerical dating of such sites is challenging, however, and even establishing a relative chronology can be daunting. One potentially helpful method for assigning relative chronologies is to use lithic weathering, on the assumption that the most weathered artifacts are also the oldest. Yet, few studies have systematically assessed how local environmental processes affect weathering of surficial lithics. Using macroscopic analyses, we compared the weathering of surficial lithic assemblages from seven mid‐to‐late Holocene archaeological sites sampled from four different microenvironments in the Atacama Desert of northern Chile. Changes in polish, texture, shine, and color were used to establish significant differences in weathering between two kinds of locations: interfluves and canyon sites. Lithics from interfluve sites were moderately to highly weathered by wind and possessed a dark coating, whereas canyon lithics were mildly weathered despite greater exposure to moisture, often lacked indications of eolian abrasion, and lacked dark coatings. Our results show that lithic weathering can be used as a proxy for relative age, but only after considering local environmental factors. The power of such chronologies can be improved by combining archaeological, paleoenvironmental, geomorphological, and taphonomic data. 相似文献
15.
Catastrophic,rainfall-induced debris flows in Andean villages of Tarapacá, Atacama Desert,northern Chile 总被引：1，自引：0，他引：1
Sergio A. Sepúlveda Sofía Rebolledo James McPhee Marisol Lara Mauricio Cartes Eduardo Rubio David Silva Nicolle Correia Juan P. Vásquez 《Landslides》2014,11(3):481-491
In March 2012, during the rainy season in the Altiplano plateau, a >100-year return period rainfall event affected the deeply incised valleys of the Precordillera of the Tarapacá Region, northern Chile. This extreme event in a very arid region triggered a number of debris and mud flows that caused severe damage and destruction in several small villages along the Camiña and Tarapacá valleys. The highly vulnerable location of the villages on top of alluvial fans due to socioeconomic and cultural reasons is a key factor to explain the level of destruction in most villages. In this paper, this unusual, remarkable landslide event is described, and the hazard faced by these settlements for future rainfall episodes and possible mitigation measures are discussed. 相似文献
16.
《Journal of South American Earth Sciences》2009,27(4):412-423
Recent work in the central Andean Main Range of Chile near Laguna del Laja (∼37.5°S, 71°W) has produced the first mammal fossils for the region. Fossils, locally abundant and well preserved, occur patchily across a wide area southeast of the lake. Mammalian remains are derived from generally strongly folded (kilometer-scale) exposures of the locally ∼1.8 km thick, early to middle Miocene Cura-Mallín Formation; two identifiable specimens have been recovered from the overlying Trapa Trapa Formation as well. Both formations consist primarily of well-stratified (1–5 m thick layers) volcaniclastic and volcanic strata, deposited predominantly in fluviatile systems. The Cura-Mallín Formation is possibly the southern continuation of (or lateral equivalent to) the richly fossiliferous Abanico Formation mapped between ∼32°S and 36°S. Intensive sampling in a series of localities east and south of Laguna del Laja has yielded diverse faunas, in addition to radioisotopically dateable horizons. The new fossil mammal faunas represent as many as six South American Land Mammal “Ages” (SALMAs). Fossils, together with preliminary 40Ar/39Ar radioisotopic dates, ranging from ∼9 to 20 Ma across the exposed thickness of the Cura-Mallín Formation and into the overlying Trapa Trapa Formation, provide a robust geochronological framework for middle Cenozoic strata in the Laguna del Laja region. The sequence of directly superposed mammalian assemblages at Laguna del Laja is one of the longest in all of South America, rivaled only by the classic Gran Barranca section of Patagonian Argentina. These data illuminate the geological history of the area and its record of mammalian evolution. The potential to isotopically date these diverse faunas with high precision (error ± 0.5 Ma) presents a rare opportunity to calibrate related portions of the SALMA sequence. 相似文献
17.
《Journal of South American Earth Sciences》1999,12(2):183-199
The gneisses and metabasites of the Sierra de Limón Verde were investigated by P–T–t determinations. The rocks are unique in the Central Andes because of their high pressure metamorphic conditions with P≈13±1 kbar at T≈660–720°C. Their age of metamorphism is ≈270 Ma, based on Sm–Nd mineral isochrons. Final uplift of the isolated basement block occurred in the Triassic with a K–Ar age of biotite at ca 235 Ma. In our interpretation, the protolith of the Permian metamorphic rocks is the crust that formed and stabilized during Early Paleozoic. The Sierra de Limón Verde rocks give insight into the lowermost part of the crust in Early Mesozoic. Its Sm–Nd isotopic composition is indistinguishable from the composition of the crust that formed in the Early Paleozoic metamorphic–magmatic cycle (ca 500 Ma) in northern Chile and NW Argentina. The tectonic-geodynamic setting that triggered the high P (∼45 km depth) metamorphism and the locally restricted exhumation of the rocks remains speculative. Continental collision or a subduction related accretionary complex is unlikely considering the regional geological situation. Transpression–transtension in a strike slip system along the continental margin is suggested as a hypothesis for future investigations. 相似文献
18.
Castro-Correa Carmen-Paz Aldunce Ide Paulina Wyndham Vásquez Katherine Mena Maldonado Dania Pérez Tello Sonia 《Natural Hazards》2020,103(2):2427-2440
Natural Hazards - This article analyzes the impact of socio-natural disasters on social capital at a local level, studying the cases of the communities of Chañaral and Diego de Almagro after... 相似文献
19.
This paper discusses a well-represented fossil record of cartilaginous fishes (Chondrichthyes) from southern South America. The recovered samples allow the recognition of three assemblages with chronostratigraphic and paleogeographic value: i) typical Maastrichtian sharks and rays with affinities to eastern Pacific fauna, including the taxa Ischyrhiza chilensis, Serratolamna serrata, Centrophoroides sp. associated to Carcharias sp., and Dasyatidae indet.; ii) a scarce reworked assemblage of Paleocene–Early Eocene age including the taxa Otodus obliquus and Megascyliorhinus cooperi; iii) a rich assemblage with reworked taxa of Early to Middle Eocene age, together with autochthonous deposited Middle to Late Eocene taxa with close affinities to paleoichthyofaunas recovered from the North Atlantic, represented by Carcharias ‘hopei’, Odontaspis winkleri, Carcharoides catticus, Macrorhizodus praecursor, Carcharocles auriculatus, Striatolamia sp., Striatolamia macrota, Hexanchus agassizi, Notorhynchus sp., Myliobatis sp., Abdounia sp., Pristiophorus sp., Squatina sp., cf. Rhizoprionodon sp., Ischyodus sp., and one new species, Jaekelotodus bagualensis sp. nov. The studied samples include for the first time taxa with well established chronostratigraphic resolutions as well as taphonomic information that help clarifying the age of the fossil-bearing units. In addition, they provide relevant information about the evolution of the Magallanes (=Austral) Basin from the Upper Cretaceous to the Paleogene, suggesting a probable connection with the Quiriquina Basin of south-central Chile during the latest Cretaceous. Finally, the studied assemblages indicate a latitudinal pattern of distribution that provides valuable data on the environmental evolution and temperature of southern South America during the Paleogene. 相似文献
20.
Cecilia M. Spagnuolo Augusto E. Rapalini Ricardo A. Astini 《International Journal of Earth Sciences》2011,100(2-3):603-618
Early Paleozoic paleomagnetic data from NW Argentina and Northern Chile have shown large systematic rotations within two domains: one composed of the Western Puna that yields very large (up to 80°) counter-clockwise rotations, and the other formed by the Famatina Ranges and the Eastern Puna that shows (~40°) clockwise rotations around vertical axes. In several locations, lack of significant rotations in younger rocks constrains this kinematic pattern to have occurred during the Paleozoic. Previous tectonic models have explained these rotations as indicative of rigid-body rotations of large para-autochthonous crustal blocks or terranes. A different but simple tectonic model that accounts for this pattern is presented in which rotations are associated to crustal shortening and tectonic escape due to the collision of the allochthonous terrane of Precordillera in the Late Ordovician. This collision should have generated dextral shear zones in the back arc region of the convergent SW Gondwana margin, where systematic domino-like clockwise rotations of small crustal blocks accommodate crustal shortening. The Western Puna block, bordering the Precordillera terrane to the north, might have rotated counterclockwise as an independent microplate due to tectonic escape processes, in a fashion similar to the present-day relationship between the Anatolia block and the Arabian microplate. 相似文献