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101.
Petrology and geochemistry of Camiguin Island, southern Philippines: insights to the source of adakites and other lavas in a complex arc setting 总被引:72,自引:1,他引:71
Paterno R. Castillo Philip E. Janney Renato U. Solidum 《Contributions to Mineralogy and Petrology》1999,134(1):33-51
Camiguin is a small volcanic island located 12 km north of Mindanao Island in southern Philippines. The island consists of
four volcanic centers which have erupted basaltic to rhyolitic calcalkaline lavas during the last ∼400 ka. Major element,
trace element and Sr, Nd and Pb isotopic data indicate that the volcanic centers have produced a single lava series from a
common mantle source. Modeling results indicate that Camiguin lavas were produced by periodic injection of a parental magma
into shallow magma chambers allowing assimilation and fractional crystallization (AFC) processes to take place. The chemical
and isotopic composition of Camiguin lavas bears strong resemblance to the majority of lavas from the central Mindanao volcanic
field confirming that Camiguin is an extension of the tectonically complex Central Mindanao Arc (CMA). The most likely source
of Camiguin and most CMA magmas is the mantle wedge metasomatized by fluids dehydrated from a subducted slab. Some Camiguin
high-silica lavas are similar to high-silica lavas from Mindanao, which have been identified as “adakites” derived from direct
melting of a subducted basaltic crust. More detailed comparison of Camiguin and Mindanao adakites with silicic slab-derived
melts and magnesian andesites from the western Aleutians, southernmost Chile and Batan Island in northern Philippines indicates
that the Mindanao adakites are not pure slab melts. Rather, the CMA adakites are similar to Camiguin high-silica lavas which
are products of an AFC process and have negligible connection to melting of subducted basaltic crust.
Received: 27 February 1998 / Accepted: 27 August 1998 相似文献
102.
When performing the seismic risk assessment of new or existing buildings, the definition of compact indexes able to measure the damaging and safety level of structures is essential, also in view of the economic considerations on buildings rehabilitation. This paper proposes two series of indexes, named, respectively, Global Damage Indexes (GDIs), which are representative of the overall structure performance, and Section Damage Indexes (SDIs), which assess the conditions of reinforced concrete (RC) beam‐column sections. Such indexes are evaluated by means of an efficient numerical model able to perform nonlinear analyses of the RC frame, based on the continuum damage mechanics theory and fiber approach. An improvement of a two‐parameter damage model for concrete, developed by some of the authors, which guarantees a better correlation between the Local Damage Indexes (LDIs) and the material's mechanical characteristics, is also presented. For the reinforcement, a specific LDI, named ‘steel damage index’, which takes into account the plastic strain development and the bar buckling effect, is proposed. The numerical model has been employed to simulate several experimental tests, in order to verify the accuracy of the proposed approach in predicting the RC member's behavior. Nonlinear static and dynamic analyses of two RC frames are carried out. The robustness of the method, as well as the effectiveness of the GDIs in assessing the structural conditions, are demonstrated here. Finally, comparisons between the evolution of GDIs and the achievement of the performance levels as proposed in FEMA 356 are reported. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
103.
Francine A. Kalas Renato S. Carreira Stephen A. Macko Angela L. R. Wagener 《Continental Shelf Research》2009
The present work aimed at studying the origin of particulate organic matter in Guanabara Bay and in some rivers of the Guanabara basin by using elemental composition, isotopic ratios (δ13C and δ15N) and molecular markers (sterols) in samples collected in two periods (winter and summer). Elemental and isotopic compositions were determined by dry combustion and mass spectrometry, respectively, while sterols were investigated by GC–FID and GC–MS. Higher sterol concentrations were present in the north-western part of the bay in winter (5.10–23.5 μg L–1). The high abundance of algal sterols (26–57% of total sterols), the elemental composition (C/N=6–8) and the isotopic signatures (δ13C=−21.3‰ to −15.1‰ and δ15N=+7.3‰ to +11.1‰) suggested the predominance of autochthonous organic matter, as expected for an eutrophic bay, although seasonal variation in phytoplankton activity was observed. Coprostanol concentration (fecal sterol) was at least one order of magnitude higher in the particulate material from fluvial samples (4.65–55.98 μg L–1) than in the bay waters (<0.33 μg L–1). This could be ascribed to a combination of factors including efficient particle removal to sediments in the estuarine transition zone, dilution with bay water and bacterial degradation during particle transport in the water column. 相似文献
104.
Mount Etna volcano was shaken during the summer 2001 by one of the most singular eruptive episodes of the last centuries.
For about 3 weeks, several eruptive fractures developed, emitting lava flows and tephra that significantly modified the landscape
of the southern flank of the volcano. This event stimulated the attention of the scientific community especially for the simultaneous
emission of petrologically distinct magmas, recognized as coming from different segments of the plumbing system. A stratigraphically
controlled sampling of tephra layers was performed at the most active vents of the eruption, in particular at the 2,100 m
(CAL) and at the 2,550 m (LAG) scoria cones. Detailed scanning electron microscope and energy dispersive x-ray spectrometer
(SEM-EDS) analyses performed on glasses found in tephra and comparison with lava whole rock compositions indicate an anomalous
increase in Ti, Fe, P, and particularly of K and Cl in the upper layers of the LAG sequence. Mass balance and thermodynamic
calculations have shown that this enrichment cannot be accounted for by “classical” differentiation processes, such as crystal
fractionation and magma mixing. The analysis of petrological features of the magmas involved in the event, integrated with
the volcanological evolution, has evidenced the role played by volatiles in controlling the magmatic evolution within the
crustal portion of the plumbing system. Volatiles, constituted of H2O, CO2, and Cl-complexes, originated from a deeply seated magma body (DBM). Their upward migration occurred through a fracture network
possibly developed by the seismic swarms during the period preceding the event. In the upper portion of the plumbing system,
a shallower residing magma body (ABT) had chemical and physical conditions to receive migrating volatiles, which hence dissolved
the mobilized elements producing the observed selective enrichment. This volatile-induced differentiation involved exclusively
the lowest erupted portion of the ABT magma due to the low velocity of volatiles diffusion within a crystallizing magma body
and/or to the short time between volatiles migration and the onset of the eruption. Furthermore, the increased amount of volatiles
in this level of the chamber strongly affected the eruptive behavior. In fact, the emission of these products at the LAG vent,
towards the end of the eruption, modified the eruptive style from classical strombolian to strongly explosive. 相似文献
105.
Geomorphic influence on small glacier response to post‐Little Ice Age climate warming: Julian Alps,Europe 下载免费PDF全文
Renato R. Colucci 《地球表面变化过程与地形》2016,41(9):1227-1240
The evolution of glaciers and ice patches, as well as the equilibrium‐line altitude (ELA) since the Little Ice Age (LIA) maximum were investigated in the Julian Alps (south‐eastern European Alps) including ice masses that were previously unreported. Twenty‐three permanent firn and ice bodies have been recognized in the 1853 km2 of this alpine sector, covering a total area in 2012 of 0.385 km2, about one‐fifth of the area covered during the LIA (2.350 km2). These features were classified as very small glaciers, glacierets or ice patches, with major contribution to the mass balance from avalanches and wind‐blown snow. Localized snow accumulation is also enhanced in the area due to the irregular karst topography. The ice masses in the region are at the lowest elevations of any glaciers in the Alpine Chain, and are characterized by low dynamics. The ELAs of the two major LIA glaciers (Canin and Triglav) have been established at 2275 ± 10 m and 2486 ± 10 m, respectively, by considering the reconstructed area and digital elevation model (DEM) and using an accumulation area ratio (AAR) of 0.44 ± 0.07, typical of small cirque glaciers. Changes in the ELA and glaciers extension indicate a decoupling from climate. This is most evident in the smallest avalanche‐dominated ice bodies, which are currently controlled mainly by precipitation. The damming effect of moraine ridges and pronival ramparts at the snout of small ice bodies in the Julian Alps represents a further geomorphological control on the evolution of such ice masses, which seem to be resilient to recent climate warming instead of rapidly disappearing as should be expected. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
106.
In this paper, we discuss high‐resolution coherence functions for the estimation of the stacking parameters in seismic signal processing. We focus on the Multiple Signal Classification which uses the eigendecomposition of the seismic data to measure the coherence along stacking curves. This algorithm can outperform the traditional semblance in cases of close or interfering reflections, generating a sharper velocity spectrum. Our main contribution is to propose complexity‐reducing strategies for its implementation to make it a feasible alternative to semblance. First, we show how to compute the multiple signal classification spectrum based on the eigendecomposition of the temporal correlation matrix of the seismic data. This matrix has a lower order than the spatial correlation used by other methods, so computing its eigendecomposition is simpler. Then we show how to compute its coherence measure in terms of the signal subspace of seismic data. This further reduces the computational cost as we now have to compute fewer eigenvectors than those required by the noise subspace currently used in the literature. Furthermore, we show how these eigenvectors can be computed with the low‐complexity power method. As a result of these simplifications, we show that the complexity of computing the multiple signal classification velocity spectrum is only about three times greater than semblance. Also, we propose a new normalization function to deal with the high dynamic range of the velocity spectrum. Numerical examples with synthetic and real seismic data indicate that the proposed approach provides stacking parameters with better resolution than conventional semblance, at an affordable computational cost. 相似文献
107.
108.
Renato L. Prado Isabel C. Espin Fenoll Irfan Ullah Gianna C. Maciel Miura Alvaro P. Crsta Roberto P. Zanon dos Santos Wolf Uwe Reimold Vagner R. Elis Erico Imbernon Claudio Riccomini Liliana Alcazar Diogo 《Meteoritics & planetary science》2019,54(10):2357-2372
The origin of the nearly circular Colônia structure, located at the southwestern edge of the city of São Paulo, Brazil, has been the subject of a long‐standing debate, ever since the 1960s when the structure was first investigated by geophysical methods. The structure still raises interest for geological research, as its sedimentary infill holds important paleoclimatic information about the evolution of the tropical rainforest, as well as the interplay between the South American summer monsoon, the Intertropical Convergence Zone, and the southern Westerly wind belt—for possibly as long as several million years. In addition, the search for evidence to conclusively establish the origin of this structure continues, and the answer most likely lies in the lower portions of the basin's sedimentary infill, which also holds a significant potential for underground water resources. Here, we present the results from recent seismic (reflection and HVSR), gravimetric, and geoelectrical surveys. They have provided a reliable image of the sedimentary infill, and the maximum depth to basement within the structure has been constrained consistently by the different methods to approximately ?400 m. The geophysical data have also allowed to map the lateral contact between the crystalline basement rocks and the sedimentary infill, which indicates a diameter of approximately 2.8 km for the sedimentary basin, with 3.6 km being the diameter of the outermost limit of the structure. A total of six seismic stratigraphic boundaries were identified within the sedimentary infill, providing a framework for the planning of a deep drilling campaign and subsequent sampling program aimed at geological and paleoclimatology studies. 相似文献
109.
110.
Di Franco A Graziano M Franzitta G Felline S Chemello R Milazzo M 《Marine pollution bulletin》2011,62(5):926-933
Many human activities add new structures to the marine landscape. Despite the fact that human structures cause some inevitable impacts, surprisingly little information exists on the effects of marina on natural marine assemblages. The aim of this paper is to assess habitat-specific response of benthic sessile organisms of rocky shores in relation to the presence of a small marina. Sampling was carried out at three coastal habitats (midshore, lowshore and subtidal) by means of visual censuses adopting an after-control-impact (ACI) experimental design. It appears that the marina affects the structure and composition of benthic communities of both the midshore and the lowshore. Little effect was evident on shallow subtidal assemblage structure. The results of the present study clearly show habitat-specific responses of coastal benthic assemblages to the presence of infrastructure. 相似文献