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Christian Pin Eladio Lin Emilio Pascual Teodosio Donaire Alfonso Valenzuela 《Tectonophysics》2002,352(1-2)
Because the Hercynian overprint was extremely weak, the Sierra de Córdoba (southeastern Ossa-Morena Zone, OMZ) provides an excellent opportunity to study the tectonic evolution of sequences deposited close to the Late Neoproterozoic–Early Palaeozoic boundary. In order to put constraints on the sources and geodynamic significance of the Late Proterozoic magmatism, a representative set of 18 igneous rocks, and 3 interbedded sedimentary rocks from the San Jerónimo Formation have been studied for major and trace element geochemistry and for the Sm–Nd isotopic systematics. The igneous rocks are generally porphyritic to microporphyritic andesites, with abundant plagioclase (±amphibole) phenocrysts. With the exception of two intrusive rocks, possibly not related to the Late Proterozoic episode, all the samples display positive Nd550 Ma values, ranging from +2.9 to +7.6. Most of them, with +4<Nd550 Ma<+6, exhibit LREE enrichment, high La/Nb ratios, and elevated Zr/Nb ratios ranging from 21 to 32. There is no obvious correlation between the shape of REE patterns, La/Nb ratios and Nd550 Ma values, precluding simple models of late-stage interaction with typical crustal components having low Nd and high LREE/HREE and La/Nb ratios. Based on their major element composition and enriched, continental crust-like trace element characteristics, combined with distinctly positive Nd initial values, the Córdoba andesites document an episode of crustal growth through the addition of calc-alkaline magmas, extracted from a mantle reservoir which was strongly depleted in LREE on a time-integrated basis. The occurrence of interlayered sediments of continental provenance (negative Nd values) does not favour a purely ensimatic arc setting, remote from continental land masses, for this subduction-related magmatism, but the geochemical data suggest an active margin environment located on relatively juvenile crust. In any case, the Córdoba andesites document the addition of materials chemically similar to the bulk continental crust which were extracted from mantle sources with strong time-integrated LREE depletion. Therefore, they provide evidence for crustal growth related to Cadomian orogenic events during Late Proterozoic times. 相似文献
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Jose Villanueva-Diaz David W. Stahle Brian H. Luckman Julian Cerano-Paredes Mathew D. Therrell Malcom K. Cleaveland Eladio Cornejo-Oviedo 《Climatic change》2007,83(1-2):117-131
The understanding of historic hydroclimatic variability is basic for planning proper management of limited water resources
in northeastern Mexico. The objective of this study was to develop a network of tree-ring chronologies to reconstruct hydroclimate
variability in northeastern Mexico and to analyze the influence of large-scale circulation patterns, such as ENSO. Precipitation
sensitive tree-ring chronologies of Douglas-fir were developed in mountain ranges of the Sierra Madre Oriental and used to
produce winter-spring precipitation reconstructions for central and southern Nuevo Leon, and southeastern Coahuila. The seasonal
winter-spring precipitation reconstructions are 342 years long (1659–2001) for Saltillo, Coahuila and 602 years long (1400–2002)
for central and southern Nuevo Leon. Both reconstructions show droughts in the 1810s, 1870s, 1890s, 1910s, and 1970s, and
wet periods in the 1770s, 1930s, 1960s, and 1980s. Prior to 1800s the reconstructions are less similar. The impact of ENSO
in northeastern Mexico (as measured by the Tropical Rainfall Index) indicated long-term instability of the Pacific equatorial
teleconnection. Atmospheric circulation systems coming from higher latitudes (cold fronts or `nortes’) and others developed
in the Gulf of Mexico (tropical storms, hurricanes) also influence the climatic conditions characterizing this region. The
recent development of new and longer tree-ring chronologies for the region will contribute to a better understanding of the
interannual and multidecadal climatic variability of northeastern Mexico. 相似文献
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Matthew D. Therrell David W. Stahle Jose Villanueva Diaz Eladio H. Cornejo Oviedo Malcolm K. Cleaveland 《Climatic change》2006,74(4):493-504
Maize was domesticated more than 6,000 years ago in central Mexico, and remains a vital staple food and cultural symbol in
Mesoamerica. Maize yield in the central highlands is strongly dependant on adequate rainfall early in the growing season (April–June)
because late maturation of the crop may result in damage from autumn frost. Climate-induced crop failures with profound socioeconomic
impacts have punctuated Mexican history. However, reliable records of maize harvest have not been available until very recently,
and historical records of crop yield and price are discontinuous and can be difficult to interpret. We have developed a continuous,
exactly dated, tree-ring reconstruction of maize yield variability in central Mexico from 1474 to 2001 that provides new insight
into the history of climate and food availability in the heartland of the Mesoamerican cultural province. The reconstruction
indicates that seven of the most severe agricultural crises in Mexican history occurred during decadal-scale episodes of reconstructed
maize shortfalls. 相似文献
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