Diego Morata

Elemental concentrations of ambient particles and cause specific mortality in Santiago, Chile: a time series study

BackgroundThe health effects of particulate air pollution are widely recognized and there is some evidence that the magnitude of these effects vary by particle component. We studied the effects of ambient fine particles (aerodynamic diameter < 2.5μm, PM2.5) and their components on cause-specific mortality in Santiago, Chile, where particulate pollution is a major public health concern.MethodsAir pollution was collected in a residential area in the center of Santiago. Daily mortality counts were obtained from the National Institute of Statistic. The associations between PM2.5 and cause-specific mortality were studied by time series analysis controlling for time trends, day of the week, temperature and relative humidity. We then included an interaction term between PM2.5 and the monthly averages of the mean ratios of individual elements to PM2.5 mass.ResultsWe found significant effects of PM2.5 on all the causes analyzed, with a 1.33% increase (95% CI: 0.87-1.78) in cardiovascular mortality per 10μg/m3 increase in the two days average of PM2.5. We found that zinc was associated with higher cardiovascular mortality. Particles with high content of chromium, copper and sulfur showed stronger associations with respiratory and COPD mortality, while high zinc and sodium content of PM2.5 amplified the association with cerebrovascular disease.ConclusionsOur findings suggest that PM2.5 with high zinc, chromium, copper, sodium, and sulfur content have stronger associations with mortality than PM2.5 mass alone in Santiago, Chile. The sources of particles containing these elements need to be determined to better control their emissions.

Tertiary volcanism during extension in the Andean foothills of central Chile (33°15′–33°45′S)

This lithologic and geochemical study treats two Tertiary volcanic formations in the Andean foothills of central Chile deposited during and after an inferred culmination of crustal attenuation. The Abanico and Farellones Formations, which are described in their type localities just east of Santiago, formed from volcanic arcs in continental basins during the Oligocene and Early Miocene, respectively. Aphyric basic lavas of tholeiitic affinity, acid pyroclastic rocks, and lacustrine deposits constitute the >3100-m-thick Abanico Formation. The overlying >2100-m-thick Farellones Formation consists of calc-alkaline lavas (basalts absent) with thick pyroclastic deposits at the base. Both formations have Nd-Sr isotope signatures within the mantle array; the Abanico rocks (eNd ≈ +5.7) plot closer to N-MORB (normal mid-oceanic-ridge basalt) than the Farellones rocks (eNd = +3.9 to +5.1). The REE (rare earth element) patterns indicate greater depth to the mantle source and a smaller degree of partial melting with time. The Abanico lavas segregated within the stability field of spinel, whereas the lavas of the upper Farellones member show residual garnet in their source. Geochemical changes with time are systematic: the greatest contrast is between the middle and upper Farellones members in 1–2 m.y., e.g., for basaltic andesites, La/Yb increases from 4.3 (Abanico) to 5.6, 6.0, and 11.6 (lower, middle, and upper Farellones members). The bimodal composition of the Abanico Formation and the lower Farellones member indicates that volcanism took place during episodes of extensional conditions. Extension with subsidence is independently shown by the burial metamorphic pattern. Voluminous pyroclastic flows, structural relationships, and other evidence suggest recurrent caldera collapse. The first extensional episode ended with contraction and folding of the Abanico rocks, and the second episode resulted in uplift of the lower and middle Farellones members, followed by a more passive tectonic regime. Sequences showing many similarities with the Abanico and Farellones Formations occur along the Andean foothills of Chile. They decrease in age from Late Cretaceous– Paleocene at 23°S to Early Miocene–late Miocene at 35°S and might be explained by oblique subduction of oceanic ridge.

Early Evidence (ca. 12,000 BP) for Iron Oxide Mining on the Pacific Coast of South America

Iron oxides have been used extensively in the Americas from the Paleoindian period up to the ethnographic present. But, because archaeological mining sites are extremely rare in this continent, we still know very little about how indigenous groups exploited and processed these minerals. Here we report finds from the San Ramón 15 site, located on the arid coast of northern Chile, where our research revealed a prehistoric mine with associated tailings and mining debris that was exploited by hunter-gatherer-fisher groups. The mine was first exploited during the Pleistocene-Holocene transition (ca. 12,000–10,500 calibrated years before present [cal yr BP]) and then again during the Late Archaic (ca. 4300 cal yr BP), representing the earliest known mining activity in the Americas. This discovery has important implications, including (1) the record of undisputed mining activity in the continent is extended by several millennia, showing the first insights into Early Archaic mining techniques and technologies; (2) the earliest inhabitants of the Pacific Coast of South America had a well-developed mining knowledge, that is, they were hunter-gatherer-fisher-miner communities; and (3) mobility patterns of early nomadic maritime adaptations in northern Chile were influenced by repeated access to iron oxide pigments used mainly for symbolic purposes.

Time interval between volcanism and burial metamorphism and rate of basin subsidence in a Cretaceous Andean extensional setting

40Ar/39Ar ages were obtained from basaltic flows belonging to a 9-km-thick sequence generated in an extensional ensialic setting of an arc/back-arc basin type during the Early Cretaceous and presently exposed along the Coastal Range of central Chile. The basalts have been affected by very low- to low-grade burial metamorphism, mostly under prehnite–pumpellyite facies. Age values obtained from primary (volcanic) and secondary (metamorphic) minerals permit to quantify the time interval between volcanism and burial metamorphism. A plateau age of 119±1.2 Ma from primary plagioclase represents the best estimation of the age of the volcanism, whereas adularia, in low-variance assemblages contained in amygdules, gave a plateau age of 93.1±0.3 Ma which is interpreted as the age of the metamorphism. Considering the P–T conditions estimated for this metamorphic event, the c. 25 Ma time interval between volcanic emplacement and prehnite–pumpellyite facies metamorphism, the rate of basin subsidence in this extensional geodynamic setting would be comprised in the interval 150–180 m/Ma.

Formation of cristobalite nanofibers during explosive volcanic eruptions

High-resolution transmission electron microscopy (HRTEM) observations of unaltered volcanic air-fall deposits from the ongoing lava dome explosive eruption at Chaiten Volcano, Chilean Patagonia, revealed the presence of highly crystalline silica nanofibers in the respirable fraction of the volcanic ash ( 240 °C), beta form of cristobalite, with average lengths of hundreds of nanometers and widths on the order of tens of nanometers. We propose that the beta-cristobalite nanofibers are formed during explosive eruptions by the reduction of amorphous silica by carbon monoxide to its reactive suboxide SiO, which is later oxidized to form one-dimensional crystalline silica nanostructures. Nucleation and growth of the nanofibers are enhanced by the high surface area of the micrometer- to nanometer-sized fragments of silica glass in the volcanic column. The formation of nanocrystalline cristobalite fibers during explosive lava dome eruptions poses new challenges for the assessment of the short- and long-term health hazards associated with the respirable nanofibrous components of volcanic ash.

Ages and cooling history of the Early Cretaceous Caleu pluton: testimony of a switch from a rifted to a compressional continental margin in central Chile

The Caleu pluton, in the Coastal Range of central Chile, represents the last magmatic event related to the Early Cretaceous rifting along the western margin of South America. The pluton was emplaced into a c. 10 km thick pile of mainly basalts and basaltic andesites deposited in an Early Cretaceous subsiding basin, and affected by very low-grade metamorphism. The cooling history of the pluton is documented on the basis of U–Pb, 40Ar/39Ar step-heating and fission-track dating. The U–Pb date suggests an age of emplacement in the interval 94.2–97.3 Ma. Rapid subsolidus cooling between 550–500 °C and 250 °C is documented by 40Ar/39Ar plateau ages on amphibole, biotite and plagioclase between 94.9 ± 1.8 and 93.2 ± 1.1 Ma. Slower subsolidus cooling to c. 100 °C is identified at the 94–90 Ma interval by the fission-track thermal model. The geochronological data show that the emplacement of the pluton is coeval with the very low-grade metamorphism of the host rocks. Therefore, this metamorphism is probably not the result simply of burial, but also of a regional thermal gradient related to the plutonism. Exhumation of the pluton started coevally with its emplacement and continued to about 90 Ma, being associated with the closure of the Early Cretaceous rifting. The Caleu plutonism represents an asthenospheric-derived event during maximum extension, and marks a turning point between extensional- and compressional-related magmatism.

A low‐grade metamorphic model for the Miocene volcanic sequences in the Andes of central Chile

Abstract Calc‐alkaline basic volcanic rocks in a c. 600 m thick sequence of Miocene age, the Valle Nevado stratified sequence (VNSS), have been affected by very low grade metamorphism characterised by mineral assemblages of the zeolite facies. Metastable conditions prevailed, most of the igneous minerals being wholly or partially preserved. The main metamorphic phases are mafic phyllosilicates and zeolites of calco‐sodic and calcic composition. The intensity of the metamorphism was controlled by depth and by hydrothermal activity related to volcanic centres. From top to bottom of the sequence, the zeolites vary from heulandite‐clinoptilolite through mordenite to laumontite, whereas the phyllosilicates show a compositional transition from tri‐smectite to smectite/chlorite with up to 75% chlorite layers. Strong fluid/rock interaction took place only at flow levels with a high primary porosity and permeability as illustrated by: (a) the similarity of the REE patterns of the basaltic host flows and the secondary zeolites; and (b) the contrast in composition observed between phyllosilicates in vesicular tops as opposed to the massive (central) parts of the same flow. The thermal gradients acting during the metamorphic event were high and are estimated at 150–175°C/km. The metamorphic zonation is interpreted as the result of a rapid accumulation of considerable volumes of rock generated by volcanic centres connected with geothermal field activity and characterised in places by caldera collapse.

Subduction of an Active Spreading Ridge Beneath Southern South America: A Review of the Cenozoic Geological Records from the Andean Foreland, Central Patagonia (46–47°S)

The Chile-Argentina Patagonian Cordillera is a natural laboratory to study the interactions between oceanic and continental lithosphere during the subduction of an active spreading ridge beneath a continent. Subduction of the South Chile spreading ridge, which separates the Nazca plate from the Antarctic plate, started around 15–14 Ma at the southern tip of Patagonia. Presently, the southernmost segment of the Chile Ridge enters the Peru-Chile trench at 46°S, at the site of the Chile Triple Junction (CTJ). We review the main events which occurred on land in the CTJ region (46–47°S), related with processes of ridge subduction. We summarize tectonic, sedimentary, and magmatic features in a 30 Ma-to Present chronological table. A preridge subduction stage, from 30 to 15 Ma, is characterized by the onset and growth of Patagonian relief and by a shift from marine to continental detrital sedimentation in the foreland at 20–22 Ma. The change from pre-ridge subduction to ridge subduction is marked on land by a transition from calc-alkaline to alkaline volcanism, at 14–12 Ma, and by the onset of eruption of very large fl ood basalt provinces (future volcanic plateaus) following rapid erosion of the eastern foreland belt. Post-plateau basaltic volcanism (<4 Ma) is coeval with a period of tectonic and morphological rejuvenation during which the eastern foreland of the Cordillera has been affected by extensional/transtensional tectonics. We place these events in the framework of a tectonomagmatic model involving the opening of slab windows due to both slab tear and ridge axis subduction.

Contrasting geochemistry and metamorphism of pillow basalts in metamorphic complexes from Aysén, S. Chile

Abstract The geochemistry of pillow basalts from the Chonos Metamorphic Complex (CMC) and the Eastern Andes Metamorphic Complex of Aysen (EAMC) indicates contrasting tectonic environments for these basic lavas. They have E-MORB and continental alkaline affinities, respectively. The MORB-like basalts are metamorphosed in the pumpellyite–actinolite metamorphic facies, with mineral associations indicative of relatively high P/T metamorphism. The continental alkali basalts exhibit pumpellyite–chlorite assemblages developed in a low to intermediate P/T regime. These contrasting eruptive and metamorphic settings agree with recently established age differences between the complexes, and invalidate direct correlation between them.

Late Jurassic terrane collision in the northwestern margin of Gondwana (Cajamarca Complex, eastern flank of the Central Cordillera, Colombia)

Medium-grade metabasites and metapelites from the Cajamarca Complex (Central Cordillera of Colombia) are in fault contact with the Jurassic Ibague batholith and show a penetrative foliation, locally mylonitic, suggesting intense dynamic–thermal metamorphism. The amphibolites are composed of calcic amphibole + epidote + plagioclase + quartz plus rutile + titanite + apatite + carbonate as accessory phases. Chlorite and albite appear as retrograde replacements. The metapelites are mainly composed of phengite + quartz + garnet + chlorite, plus epidote + albite + apatite + titanite + haematite as accessory phases. Bulk geochemistry of the amphibolites indicates basaltic protoliths with a mid-ocean ridge basalt (MORB) signature, although enrichment in the mobile large-ion lithophile elements compared to MORB suggests pre- and/or syn-metamorphic alteration by fluids. Peak pressure–temperature determinations for both types of rocks are similar, ranging 550–580°C and 8 kbar (approximately 26 km depth and an apparent geothermal gradient of 22°C/km). 40Ar-39Ar dating of amphibole from two amphibolite samples and one phengitic mica from a pelitic schist yielded plateau ages of 146.5 ± 1.1 Ma and 157.8 ± 0.6 Ma, and 157.5 ± 0.4 Ma, respectively. These Late Jurassic ages contrast with previously published (Permian)Triassic ages of metamorphism in the Cajamarca Complex. Taken together, our data indicate tectonic-driven burial of oceanic supracrustal sequences down to mid-crustal depths during Late Jurassic times and are best explained as the result of terrane collision-related metamorphism and deformation in a fore-arc/volcanic-arc environment of the active western margin of Gondwana rather than as a result of Jurassic thermal–metamorphic resetting of a (Permian)Triassic metamorphic sequence during intrusion of the Jurassic Ibague batholith. Our results represent the first report of Jurassic terrane collision tectonics involving supracrustal oceanic rocks in the northwestern margin of Gondwana in Colombia.