排序方式: 共有37条查询结果,搜索用时 15 毫秒
1.
Adakitic lavas in the Central Luzon back‐arc region,Philippines: lower crust partial melting products? 总被引:6,自引:0,他引:6
Graciano P. Yumul JR Carla Dimalanta Herve Bellon Decibel V. Faustino Joel V. De Jesus Rodolfo A. Tamayo JR Ferdinand T. Jumawan 《Island Arc》2000,9(4):499-512
Abstract Volcanism in the back-arc side region of Central Luzon, Philippines, with respect to the Manila Trench is characterized by fewer and smaller volume volcanic centers compared to the adjacent forearc side-main volcanic arc igneous rocks. The back-arc side volcanic rocks which include basalts, basaltic andesites, andesites and dacites also contain more hydrous minerals (ie, hornblende and biotite). Adakite-like geochemical characteristics of these back-arc lavas, including elevated Sr, depleted heavy rare earth elements and high Sr/Y ratios, are unlikely to have formed by slab melting, be related to incipient subduction, slab window magmatism or plagioclase accumulation. Field and geochemical evidence show that these adakitic lavas were most probably formed by the partial melting of a garnet-bearing amphibolitic lower crust. Adakitic lavas are not necessarily arc–trench gap region slab melts. 相似文献
2.
Early Miocene adakite-like volcanism in the Balkuyumcu region, central Anatolia, Turkey: Petrology and geochemistry 总被引:1,自引:0,他引:1
Elif Varol Abidin Temel Alain Gourgaud Herve Bellon 《Journal of Asian Earth Sciences》2007,30(5-6):613-628
The Balkuyumcu region, located in the southwestern part of Ankara in the Izmir-Ankara suture zone (central Anatolia, Turkey), consists of basic andesitic, andesitic, dacitic and rhyolitic rocks extruded during the Early Miocene (20–22 Ma) as a result of post-collisional volcanism. Balkuyumcu volcanic rocks can be divided into two groups on the basis of their mineralogy and composition: The basic andesitic (BA) and andesitic, dacitic and rhyolitic (ADR) groups. The ADR and BA group of rocks have adakite-like and calc-alkaline characteristics, respectively. The ADR group has higher SiO2 content, Sr/Y and La/Yb ratios and low MgO, Mg#, Y and Yb contents than the BA group. Both groups have nearly the same Sr, Nd isotopic compositions and display similar normalized multi-element patterns with enrichments in LILE and LREE, depletions in Nb, Ti, Zr, P and a lack of Eu anomalies. Major, trace element and Sr, Nd isotopic data indicate that both groups of rocks were derived from the same source but affected by different magmatic processes during ascent. The adakite-like rocks may have been produced by partial melting of thickened lower continental crust. Fractional crystallization also played a major role in their formation. However, the BA group rocks were derived from partial melting of lower continental crust that was probably delaminated. These rocks appear to have had limited interaction with mantle peridodite during ascent to the surface. 相似文献
3.
4.
Zhixue Zhao Xiaoguang Wang Yonghong Hao Tongke Wang Abderrahim Jardani Herve Jourde Tian‐Chyi Jim Yeh Ming Zhang 《水文研究》2019,33(19):2551-2560
The study on the hydraulic properties of coastal aquifers has significant implications both in hydrological sciences and environmental engineering. Although many analytical solutions are available, most of them are based on the same basic assumption that assumes aquifers extend landward semi‐infinitely, which does not necessarily reflect the reality. In this study, the general solutions for a leaky confined coastal aquifer have been developed that consider both finitely landward constant‐head and no‐flow boundaries. The newly developed solutions were then used to examine theoretically the joint effects of leakage and aquifer length on hydraulic head fluctuations within the leaky confined aquifer, and the validity of using the simplified solution, which assumes the aquifer is semi‐infinite. The results illustrated that the use of the simplified solution may cause significant errors, depending on joint effects of leakage and aquifer length. A dimensionless characteristic parameter was then proposed as an index for judging the applicability of the simplified solution. In addition, practical application of the general solution for the constant‐head inland boundary was used to characterize the hydraulic properties of a leaky confined aquifer using the data collected from a field site at the Seine River estuary, France, and the versatility of the general solution was further justified. 相似文献
5.
6.
Fernando Munizaga Luis Aguirre Francisco Herve 《Earth and Planetary Science Letters》1973,18(1):87-92
Eleven whole rock Rb/Sr age determinations from the Chilean metamorphic basement — formerly considered as Precambrian — define two limiting reference isochrons of 342 and 273 my. Analized rocks are phyllites and schists of sedimentary origin with mineralogical assemblages mainly corresponding to the greenschist facies.Two metamorphic series characterize the Chilean metamorphic basement: an eastern low P/T series, and a western high P/T series. Four of the analyzed samples belong to the former and seven to the latter.The obtained age is interpreted as the age of a main metamorphic episode of the basement. This episode would have taken place in the Upper Paleozoic. 相似文献
7.
The basaltic volcanism which finishes the eruptive activity of the Cantal volcano shows various patterns of the continuous transition from a lava flow to a pyroclastic flow. These sub-aerial deposits can exibit either a laminar or turbulent aspect. The affected lavas show neither mineralogical nor chemical differences from other basalts which did not present this behaviour. The outpouring was along fissures, in the central area of the volcano, as well as the margins; in this last case, it may have involved phreatomagmatic events. Study of the conditions of fragmentation is possible in the case of these basic lavas, because it was delayed until the magma reached the surface. It leads to a better understanding of a phenomenon that, for acid lavas, usually takes place in the feeding channel. 相似文献
8.
Betchaida D. Payot Victor B. Maglambayan Carla B. Dimalanta Graciano P. Yumul Jr. Rodolfo A. Tamayo Jr Toshihiko Matsuda Shigeyuki Suzuki Herve Bellon 《Resource Geology》2005,55(3):155-162
Abstract. The Pantingan Gold System (PGS) is a vein-type epithermal prospect exposed within the summit caldera of Mount Mariveles, Bagac, Bataan (Luzon), Philippines. It consists of nine major veins, eight of which trend NW-WNW and distributed in an en echelon array. The eastern tips of these veins appear to terminate near the NE-NNE trending Vein 1, which is located in the easternmost portion of the prospect. Metal assay results on vein and wall rock samples indicate concentrations of 0.01 to 1.1 g/ton Au, trace to 34 g/ton Ag and 0.003 to 0.02 % Cu. Andesite lava flow deposits host the PGS. Potassium-Argon isotopic dating of these andesites yields anarrow age range of 0.88± 0.13 to 1.13 ± 0.17 Ma. The surface exposures of the veins (up to 5 m wide) are encountered at different levels between 590–740 masl. These commonly display a massive texture although banding prominently occurs in Vein 1. The veins consist of gray to cream-colored crystalline and chalcedonic quartz and amorphous silica. Pyrite is the most ubiquitous sulfide mineral. It occurs either as fine-grained disseminations and aggregates in quartz or as infillings in vugs. Calcite, marcasite and bornite are also occasionally noted in the deposit. The prospect shows silicic, argillic, propylitic and advanced argillic alteration zones. Silicic and argillic alterations are confined in the immediate wall rocks of the quartz veins. Argillic alteration grades to a propylitic zone farther away from the veins. The advanced argillic alteration zone, indicated by a suite of acidic clay minerals that include kaolin-ite, dickite, pyrophyllite and alunite, might have been imprinted during the late stages of gold deposition. As a whole, the PGS displays geological and mineralogical features typical of gold mineralization in a low sulfidation, epithermal environment. It is also representative of a young, tectonically undisturbed gold deposit. 相似文献
9.
Michael Mutz Herve Pigay Kenneth J. Gregory Dietrich Borchardt Michael Reich Klaus Schmieder 《Limnologica》2006,36(2):110-118
Dead wood is a significant element of natural streams and rivers in temperate climate zones. Established stream management removes wood, whereas some scientists recently promoted the reintroduction of wood in stream rehabilitation and restoration. It is desirable to know if wood in streams and rivers would be accepted. A survey was therefore conducted in order to assess the spontaneous visual perception of 10 stream and 10 river scenes with and without wood in terms of naturalness, risk, aesthetics and need for improvement using visual analog scales. Three hundred and sixty-five German students from five subjects related to water management and from one subject without any professional association to running waters were surveyed before their first contact to teaching of aquatic ecology. They clearly perceived wood in streams and rivers as natural. Scenes with wood were most frequently associated with danger for sport activities while scenes without wood were most frequently associated with danger by flooding. When comparing scenes with and without wood, scenes with wood were clearly considered more positive as significantly more aesthetic, less dangerous and needing less improvement. The disciplinary groups showed variations in the absolute evaluation scores but the relative evaluation of scenes with wood versus scenes without wood was similar among all groups. The results indicate an acceptance for the reintroduction of wood in stream rehabilitation and restoration by young students who are potential future players in water management. 相似文献
10.
Richard A. Marston Jacky Girel Guy Pautou Herve Piegay Jean-Paul Bravard Chris Arneson 《Geomorphology》1995,13(1-4)
The purpose of this paper is to describe and explain channel metamorphosis of the Ain River in east-central France and the effects of this metamorphosis on floodplain disturbance and vegetation development. The Ain River is a 195 km long stream originating in the Jura Mountains which flows into the Rhône River between Lyon, France, and Geneva, Switzerland. The lower 40 km of the Ain River, beyond the mountain front, are situated in a valley of outwash deposits where the floodplain is 0.2 to 1.2 km wide. A complex mosaic of floodplain landscape units has developed. Maps dating back to 1766 and six sets of aerial photographs dated between 1945 and 1991 were used to document changes in channel pattern. Aerial photos and field surveys were used to compile maps of landscape units based on dominant vegetation life-forms, species, and substrate. Six maps dated between 1945 and 1991 were digitized in ARC/INFO and an overlay was generated to determine the changes in landscape units as related to channel disturbance. Change from a braided to a single-thread meandering channel probably took place in the period 1930–1950. The process of river entrenchment has occurred throughout the Holocene but has accelerated in the present century due to shortening of the river course, construction of lateral embankments, and vegetation encroachment following reservoir construction and cessation of wood-cutting and grazing. The increase in horizontal channel stability coupled with channel entrenchment have decreased floodplain disturbance and lowered the water table by approximately one meter. Pioneer and disturbance-dependent landscape units have experienced a more terrestrial-like succession to an alluvial forest. Abandoned channels have also been replaced by alluvial forests. On poorly drained soils, shrub-swamp communities of willow and hydrophytic herbaceous plants have been replaced by mixed forests of ash, alder, black poplar, and oak. On well drained alluvial soils, ash and oak dominated hardwood forests have declined in favor of mesophytic stands of black poplar. All types of vegetation, but particularly dry grasslands-shrublands, have been cleared for mines, campgrounds, agriculture, and other types of development. Using several measures, landscape diversity decreased between 1945 and 1991. 相似文献