Isotope and trace element evidence for three component mixing in the genesis of the North Luzon arc lavas (Philippines)   总被引：5，自引：0，他引：5  

F. McDermott  M. J. Defant  C. J. Hawkesworth  R. C. Maury  J. L. Joron 《Contributions to Mineralogy and Petrology》1993,113(1):9-23

Post-3Ma volcanics from the N Luzon arc exhibit systematic variations in ⁸⁷Sr/⁸⁶Sr (0.70327–0.70610), ¹⁴³Nd/¹⁴⁴Nd (0.51302–0.51229) and ²⁰⁸Pb^*/²⁰⁶Pb^* (0.981–1.035) along the arc over a distance of about 500 km. Sediments from the South China Sea west of the Manila Trench also exhibit striking latitudinal variations in radiogenic isotope ratios, and much of the isotopic range in the volcanics is attributed to variations in the sediment added to the mantle wedge during subduction. However, Pb-Pb isotope plots reveal that prior to subduction, the mantle end-member had high 8/4, and to a lesser extent high 7/4, similar to that in MORB from the Indian Ocean and the Philippine Sea Plate. Th isotope data on selected Holocene lavas indicate a source with unusually high Th/U ratios (4.5–5.5). Combined trace element and isotope data require that three end-members were implicated in the genesis of the N Luzon lavas: (1) a mantle wedge end-member with a Dupal-type Pb isotope signature, (2) a high LIL/HFS subduction component interpreted to be a slab-derived hydrous fluid, and (3) an isotopically enriched end-member which reflects bulk addition (<5%) of subducted S China Sea terrigenous sediment. The ⁸⁷Sr/⁸⁶Sr ratios in the volcanics show a restricted range compared with that in the sediments, and this contrasts with ¹⁴³Nd/¹⁴⁴Nd and ²⁰⁸Pb^*/²⁰⁶Pb^*, both of which have similar ranges in the volcanics and sediments. Such differences imply that whereas the isotope ratios of Nd, Pb and Th are dominated by the component from subducted sediment, those of Sr reflect a larger relative contribution from the slab-derived fluid.  相似文献   

Andesite and dacite genesis via contrasting processes: the geology and geochemistry of El Valle Volcano,Panama   总被引：3，自引：0，他引：3  

Mare J. Defant  Lee F. Clark  Robert H. Stewart  Mark S. Drummond  Jelle Z. de Boer  René C. Maury  Hervé Bellon  Thomas E. Jackson  Juan F. Restrepo 《Contributions to Mineralogy and Petrology》1991,106(3):309-324

The easternmost stratovolcano along the Central American arc is El Valle volcano, Panama. Several andesitic and dacitic lava flows, which range in age 5–10 Ma, are termed the old group. After a long period of quiescence (approximately 3.4 Ma), volcanic activity resumed approximately 1.55 Ma with the emplacement of dacitic domes and the deposition of dacitic pyroclastic flows 0.9–0.2 Ma. These are referred to as the young group. All of the samples analyzed are calc-alkaline andesites and dacites. The mineralogy of the two groups is distinct; two pyroxenes occur in the old-group rocks but are commonly absent in the young group. In contrast, amphibole has been found only in the young-group samples. Several disequilibrium features have been observed in the minerals (e.g., oscillatory zoning within clinopyroxenes). These disequilibrium textures appear to be more prevalent among the old- as compared with the young-group samples and are most likely the result of magma-mixing, assimilation, and/or polybaric crystallization. Mass-balance fractionation models for major and trace elements were successful in relating samples from the old group but failed to show a relationship among the young-group rocks or between the old- and young-group volcanics. We believe that the old-group volcanics were derived through differentiation processes from basaltic magmas generated within the mantlewedge. The young group, however, does not appear to be related to more primitive magmas by differentiation. The young-group samples cannot be related by fractionation including realistic amounts of amphibole. Distinctive geochemical features of the young group, including La/Yb ratios〉15, Yb〈1, Sr/Y〉150, and Y〈6, suggest that these rocks were derived from the partial melting of the subducted lithosphere. These characteristics can be explained by the partial melting of a source with residual garnet and amphibole. Dacitic material with the geochemical characteristics of subducted-lithosphere melting is generated apparently only where relatively hot crust is subducted, based on recent work. The young dacite-genesis at El Valle volcano is related to the subduction of relatively hot lithosphere.  相似文献   

Magma mixing in alkaline series: an example from Sancy volcano (Mont-Dore,Massif Central,France)     

A. Gourgaud  R. C. Maury 《Bulletin of Volcanology》1984,47(4):827-847

Three magmatic units (Grande Cascade pyroclastic deposits, Grande Cascade lava flow, Durbise nuée ardente deposits) from the Quaternary volcano Sancy (Mont-Dore area, Auvergne, France) show textural evidences of magma mixing between a silica undersaturated basic magma (alkali basalt and hawaiite) and an acid magma (quartz-bearing trachyte). Three kinds of mixed rock types are described: basic inclusions within an acid host, « emulsified rocks » showing infracentimetric basic globules disseminated within an acid groundmass, and « banded rocks » in which elongated acid and basic zones alternate. The chemical compositions of mixed rocks plot systematically onto linear trends in petrographic diagrams. Microprobe analyses of the groundmass show similar linear variations between basic and acid end-members. The mineralogical associations of these mixed rocks are highly complex and present many disequilibrium features. Olivine is stable in the basic component and becomes rimmed by orthopyroxene in the acid one. Zoning patterns of feldspars are complex. Clinopyroxene, kaersutite and phlogopite phenocrysts have increasing component Mg contents from core to rim both in the basic and the acid. Titanomagnetite and hemoilmenite phenocrysts were equilibrated at 900-800° C under high oxygen fugacities.Mixing results primarily from a mechanical disintegration of partly liquid basic inclusions within their acid host, and also from a mechanical transfer of phenocrysts from one component to the other, in which they often remain surrounded by a coating of their original groundmass. Chemical data on the groundmass indicates that some « true » hybridization between coexisting acid and basic liquids may also have occurred. The extent of mixing is controlled by the type of emplacement. For pyroclastic deposits a chemical gap exists between basic inclusions and their acid hosts; in contrast, mechanical mixing was enhanced during the emplacement of the viscous Grande Cascade lava flow, and complete transitions occur between basic and acid components. The two end-members are genetically associated, the latter deriving from the former by crystal fractionation. Mixing appears as a late-stage phenomenon in the petrogenetic history of the Mont-Dore series; in the case of the Grande Cascade lava flow, its extent is primarily dependent on emplacement modalities.  相似文献   

Etude des minéralisations sulfurées du gisement de Salau,Pyrenées (France) et de ses environs     

C. Derré  M. Lafitte  R. Maury 《Mineralium Deposita》1984,19(3):176-182

Résumé Les minéralisations du gisement de Salau, Pyrénées (France) comportent, outre la pyrrhotite et la scheelite, de la chalcopyrite, de l'arsénopyrite et de la sphalérite en phases accessoires. Ces sulfures ont été analysés à la microsonde électronique. — Les pyrrhotites sont les seuls sulfures à avoir subi l'influence de la mise en place de la rhyodacite. Les autres sulfures présentent une grande homogénéité et n'ont pas subi de modification liée à la mise en place du pluton. Les teneurs en fer des sphalérites, homogènes à l'intérieur d'un même niveau stratigraphique, mais différentes d'un niveau à l'autre, suggèrent une mise en place à plusieurs périodes sans remaniement ultérieur à leur dépôt.

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Mineralisation of Salau deposit, Pyrénées (France) contain massive pyrrhotite and scheelite associated with chalcopyrite, arsenopyrite and sphalerite. Electron microprobe analyses of these sulfides have been systematically performed. — Pyrrhotites show a zonation with regard to the rhyodacite settlement. Other sulfides show a great homogeneity and are not disturbed by this settlement. Iron content of sphalerites, homogeneous inside a given stratigraphical level but different when the age of layers change, suggest several origins without further modification.

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14C dating of buried soils in the volcanic chaine des puys (France)     

J. M. Hetier  B. Guillet  R. Brousse  G. Delibrajs  R. C. Maury 《Bulletin of Volcanology》1983,46(2):193-201

Apparent ages of the paleosoils buried under ash deposits or lava flows cannot be used without a correct understanding of the soil type buried by the volcanic event. Considering the apparent ages measured in the French «Massif Central» we can accept the rejuvenation of 500 years generally used if mollisols (sol bruns) are concerned. The rejuvenation can reach 4,000 years or more in the case of buried andosoils whose mean residence time of carbon is generally of 2,000 to 6,000 years. These observations have to be taken into account in the future to establish more accurate chronosequences of the volcanic events using paleosoil¹⁴C datations.  相似文献   

Evolution comparée de deux séries alcalines du Pacifique Central: Rôle de la fugacité d’oxygène et de la pression d’eau     

R. C. Maury  R. Andriambololona  C. Dupuy 《Bulletin of Volcanology》1978,41(2):97-118

A comparative mineralogical and geochemical study of two alkali-basalt series from French Polynesia (Rapa and Nuku-Hiva islands) reveals several important differences, particularly in the degree of Fe enrichment in ferromagnesian minerals and the behaviour of Ti, V and Zn. These differences appear to be connected with the onset of magnetite crystallization, which is early in the Nuku-Hiva suite but later in that of Rapa. The variable influence of this phase is ascribed to differences in IO₂, which is probably ultimately dependent on variations in P_{H 2 O}. In both cases, observed chemical variations may be explained in terms of fractional crystallization, with the occurrence of some oversaturated residual liquids resulting from the separation of mica.  相似文献   

Comparative magma/xenolith relationships in some volcanic and plutonic rocks from the french massif central     

R. C. Maury  J. Didier  J. Lameyre 《Contributions to Mineralogy and Petrology》1979,69(1):95-95

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Pliocene extensional tectonics in the Eastern Central Patagonian Cordillera: geochronological constraints and new field evidence     

Yves Lagabrielle  Manuel Surez  Jacques Malavieille  Diego Morata  Felipe Espinoza  Ren C. Maury  Bruno Scalabrino  Luis Barbero  Rita de la Cruz  Eduardo Rossello  Herv Bellon 《地学学报》2007,19(6):413-424

Recent field work and review of radiometric data obtained from Neogene lavas and plutonic rocks exposed in the Eastern Central Patagonian Cordillera (46–48ºS), which overlie subducted segments of the South Chile Ridge, suggest important Late Miocene to Pleistocene morphological changes in relation to base level variations and/or tectonic events. We present new field observations from a region south of Lago General Carrera‐Buenos Aires, between the main Cordillera and the Meseta del Lago Buenos Aires, demonstrating that normal faulting controlled valley incisions and occurred during lava emplacement at 5–4 Ma and after 3 Ma. We also show that the 12 Ma basaltic flows of the Meseta del Lago Buenos Aires (∼2000 m a.s.l.) have been subjected to deep incision, with younger lavas dated at 1.2 Ma partially filling the valleys. These incisions are thought to reflect progressive eastward tilting of the entire meseta. Our new observations, together with additional features from Central Patagonia, strongly suggest that tectonic events led to a regional widespread morphological change after 5 Ma. The coincidence in time and space between the subduction of segments of the South Chile Ridge at 6 and 3 Ma causing opening of a slab window, and strong base level variations in the studied area, suggests a cause‐and‐effect relationship. In Central Patagonia, compressional tectonics ended well before extensional events reported here. Causes of uplift and further extension are probably completely disconnected. The uplift is purely tectonic in origin and occurred prior to the subduction of the South Chile Ridge. Extension should be a consequence of this subduction.  相似文献   

The implementation of Bayesian structural additive regression models in multi-city time series air pollution and human health studies   总被引：2，自引：2，他引：0  

Lung-Chang Chien  Shrikant I. Bangdiwala 《Stochastic Environmental Research and Risk Assessment (SERRA)》2012,26(8):1041-1051

In this study, a novel Bayesian semiparametric structural additive regression (STAR) model is introduced in multi-city time series air pollution and human health studies. This modeling approach can simultaneously take into account the fixed effects, random effects, nonlinear smoothing functions and spatial functions in an integrated model framework. This study focuses on examining the powerful functionalities of this approach in modeling air pollution and mortality data of 100 U.S. cities from 1987 to 2000. Compared with previous studies, the modeling approach used in this study yields consistent findings of nation-level and city-level PM₁₀ (particulate matter less than 10?μm) effects on mortality. Notably, cities with significantly elevated mortality rates were concentrated in the Northeastern U.S. This modeling approach also emphasizes the important functionality of the spatial function in visualizing disease mapping. Model diagnostics were performed to confirm the availability of the STAR model. We also found consistent findings by using different hyperparameters in the sensitivity analysis. To sum up, the implementation of this modeling approach has achieved the goals of applying a spatial function and obtaining robust results in the multi-city time series air pollution and human health study.  相似文献   

Complex origin for the south-western Zamboanga metamorphic basement complex, Western Mindanao, Philippines     

Rodolfo A. Tamayo JR    Graciano P. Yumul JR    René C. Maury  Hervé Bellon  Joseph Cotten  Mireille Polvé  Thierry Juteau and  Cliff Querubin 《Island Arc》2000,9(4):638-652

Abstract Amphibolites unconformably overlain by a metasedimentary sequence of quartz-muscovite-feldspar-kyanite schists, metagraywackes and epidote-bearing amphibolites occur in the northern portion of the south-western Zamboanga metamorphic basement complex, western Mindanao. These amphibolites (here identified as the Mount Dansalan amphibolites) display relict magmatic textures inherited from cumulate gabbro protoliths. Bulk-rock major and trace-element data are consistent with this hypothesis. Together with the chemistry of relict igneous clinopyroxenes, they indicate a magmatic arc-related signature for the gabbro protoliths. Geochemical data allow us to identify various sources for the associated metasediments: the gabbro themselves for the metagraywackes and a continental basement for the quartz-muscovite-feldspar-kyanite schists. Both sources contributed to the genesis of the epidote-amphibolite metasediments. The compositions of the metamorphic mineral assemblages suggest that the rocks have undergone metamorphism at temperatures ranging from 550°C to 700°C and pressures probably in the range of 5–9 kbar. ⁴⁰K–⁴⁰Ar isotopic study of amphibole separates from the Mount Dansalan samples document a metamorphic event dated at 24.6 ± 1.4, 22.2 ± 1.4 and 21.2 ± 1.2 Ma. Our results are in agreement with plate tectonic models which describe the south-western Zamboanga metamorphic basement as a continental terrane. However, its evolution was not as simple as it was usually considered. In particular the basement incorporated slivers of magmatic arc crust, which cannot be unambiguously related to any of the Tertiary arcs documented in the area.  相似文献