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1.
We investigated the distribution of Cl, F, Li, and Be in pumices, obsidians, and crystallized dome rocks at Chaitén volcano in 2008?C2009 in order to explore the behavior of these elements during explosive and effusive volcanic activity. Electron and ion microprobe analyses of matrix and inclusion glasses from pumice, obsidian, and microlite-rich dome rock indicate that Cl and other elements were lost primarily during crystallization of the rhyolitic dome after it had approached the surface. Glass in pumice and microlite-free obsidian has 888?±?121?ppm Cl, whereas residual glass in evolved microlite-rich dome rock generally retains less Cl (as low as <100?ppm). Estimated Cl losses were likely >0.7?Mt Cl, with a potential maximum of 1.8?Mt for the entire 0.8-km3 dome. Elemental variations reflect an integrated bulk distribution ratio for Cl?>?1.7 (1.7 times more Cl was degassed or incorporated into crystals than remained in the melt). Because Cl is lost dominantly as the very last H2O is degassed, and Cl is minimally (if at all) partitioned into microlites, the integrated vapor/melt distribution ratio for Cl exceeds 200 (200 times more Cl in the evolved vapor than in the melt). Cl is likely lost as HCl, which is readily partitioned into magmatic vapor at low pressure. Cl loss is accelerated by the change in the composition of the residual melt due to microlite growth. Cl loss also may be affected by open-system gas fluxing. Integrated vapor-melt distribution ratios for Li, F, and Be all exceed 1,000. On degassing, an unknown fraction of these volatiles could be immediately dissolved in rainwater.  相似文献   

2.
General inverse of Stokes, Vening-Meinesz and Molodensky formulae   总被引：1，自引：0，他引：1  
The undulation of the geoid, the gravity anomaly and the deflection of the vertical are the three basic observations describing the shape and the gravity field of the earth. The Stokes’ formula that computes the undulation of the geoid using the gravity anomaly on the geoid under spherical approximate conditions was first put forward by Stokes[1]. According to Stokes’ theory, The Vening-Meinesz formula that computes the meridian and the prime vertical components of the deflection of the ve…  相似文献   

3.
Mantle convection results in plate movement.Large-scale mantle convection causes the migration of materials between the mantle and the crust,which leads to the variation of Earth's rotation following the law of conservation of angular momentum.When the Earth's rotation varies,relative movements occur among the plates due to their inertia and different degrees of coupling with the mantle.These relative movements inevitably cause tensile development of fractures,folds,faults and earthquakes along plate boundaries.As a result,several seismic belts have formed along these boundaries.The boundary of the Pacific Plate is the largest seismic belt in the world.Each plate has been cut up into blocks of various sizes by faults.It is the relative movement of the blocks that acts as the major driving force of intraplate earthquakes.These earthquakes are distributed mainly in areas of intermediate latitudes in the Northern Hemisphere.In short,mantle convection,variation of the Earth's rotation and plate movement are  相似文献   

4.
The Temté basement in North Cameroon is crosscut by dyke swarms with N 20°–40° trending,including dykes 15–30 m wide, up to 3 km-long. Representative rocks exhibit intersertal to sub-ophitic textures.Electron microprobe analyses identified diopside, augite,pargasite, biotite, Ti-magnetite, plagioclase, and sanidine.Whole-rock ICP-MS and ICP-AES chemical analyses showed compositions of basaltic andesite, basaltic trachyandesite and trachyandesite in composition. Igneous differentiation was likely governed by fractional crystallization associated with limited fluid metasomatism. Some lavas could have been moderately contaminated by crustal materials during feeding of local cracks through turbulent magma flows. Discrimination geochemical diagrams and immobile trace and REE element ratios show that the mantle source of Temté dolerites was a deep phlogopitebearing EMII mantle component and has undergone moderate to high partial melting rate. Correlations of fieldwork and analytical data with previous results evidence the Temté dolerite dyke swarms as fingerprints of crustal extension accompanying regional uplift in an active continental margin when early rifting led to the formation of the Poli marginal basin.  相似文献   

5.
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6.
Apoyeque volcano, located 9 km northwest of Managua city, erupted explosively at 12.4 ka. The Plinian eruption deposited a widespread pumice fall deposit known as the Upper Apoyeque Tephra (UAq). The UAq is massive, reversely graded, and consists of white juvenile pumice (~78 vol.%), a variety of cognate lithics and accidental altered lithics. The whole-rock pumice composition is rhyodacitic (SiO2?=?66.9–68.5 wt.%) with a mineral paragenesis of plagioclase, orthopyroxene, clinopyroxene, amphibole, titanomagnetite, and ilmenite in a rhyolitic glass groundmass (SiO2?=?74.4?±?0.6 wt.%). The deposit’s dispersal axis is to the south, with the deposit covering a minimum area of 877 km2 within the 50 cm isopach and has a total volume of 3 km3 (dense rock equivalent, 1.15 km3). The eruption column reached a maximum height of ca.28 km. The eruption ejected a total mass of 3?×?1012 kg at an average rate of 2?×?108 kg/s, and based on available models, we infer duration of almost 4 h. Petrographic and geochemical characteristics suggest that the eruption was triggered by magma mixing.  相似文献   

7.
In this work,the vertical deformation,horizontal displacement,and stress fields of arcuate tectonics are theoretically derived from the horizontal tectonic stress; then the characteristics of tectonic movement,seismicity,and focal mechanism of arcuate tectonics of the entire world are explained.It is pointed out that the island arc and other arcuate tectonics are gradually developed under the displacement and stress fields of the arcuate tectonics and that the under-thrusting action of the ocean plate is secondary.The distance formulas between the volcanic arc and the trench are suggested and also that theoretical results are consistent with actual data.  相似文献   

8.
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9.
Bitumen from the Nanpanjiang Basin occurs mainly in the Middle Devonian and Upper Permian reef limestone paleo-oil reservoirs and reserves primarily in holes and fractures and secondarily in minor matrix pores and bio-cavities. N2 is the main component of the natural gas and is often associated with pyrobitumen in paleo-oil reservoirs. The present study shows that the bitumen in paleo-oil reservoirs was sourced from the Middle Devonian argillaceous source rock and belongs to pyrobitumen by crude oil cracking under high temperature and pressure. But the natural gas with high content of N2 is neither an oil-cracked gas nor a coal-formed gas generated from the Upper Permian Longtan Formation source rock, instead it is a kerogen-cracked gas generated at the late stage from the Middle Devonian argilla- ceous source rock. The crude oil in paleo-oil reservoirs completely cracked into pyrobitumen and methane gas by the agency of hugely thick Triassic deposits. After that, the abnormal high pressure of methane gas reservoirs was completely destroyed due to the erosion of 2000--4500-m-thick Triassic strata. But the kerogen-cracked gas with normal pressure was preserved under the relatively sealed condition and became the main body of the gas shows.  相似文献   

10.
An ASKANIA borehole tiltmeter which consists of a vertical pendulum with two degrees of freedom was installed in Xiangshan station,Beijing,in May 1989 in order to monitor the earthquake-reiated crustal deformations.The preliminary results indicate that the resolution of the instrument is better than 0.05 msec for tidal amplitudes.The daily total tidal amplitude is about 20 msec.The spectral analysis of the first four months data provides a signal-to-noise ratio of > 100 for the main semi-diurnal waves.The non-tidal tilts for one year data are dominated by a long term drift with the rate of 0.9 msec/day for X-component and 1.1 msec/day for Y-component.In addition,the tilt observations are affected by meteorological factors,especially by rainfall.The results of modelings of the fault-creep related tilts and responses of tilts to earthquakes suggest that the tilt measurements are very sensitive to the change in tectonic strain and stress fields near the site where the tiltmeter is installed.The fault-creep  相似文献   

11.
Geometry,kinematics and evolution of the Tongbai orogenic belt   总被引：2，自引：0，他引：2  
1 Introduction spectively[2,3]. Several tectonic units such as the Bei- The Qinling-Dabie orogenic belt has attracted huaiyang, north Dabie, south Dabie and Susong belts worldwide attention by its very complex and abundant have been recognized in eastern Dabie[4]. Nine tec- geological characters, and has been a “hot point” of tonic units have been recognized in western Dabie and international geological research[1]. A vast amount of a more detailed division has been suggested especially …  相似文献   

12.
In this paper,a historical review of the seismic network of Vietnam and the ability of the network to monitor earthquakes is presented.The seismic activity of Vietnam as a country of high seismictiy in the last century and since the beginning of the new century is described.The current state of seismological research in Vietnam and cooperation with institutions outside of Vietnam is outlined.  相似文献   

13.
The results of original experiments performed with a ground-based geophysical laser interferometer and a GPS-based satellite ionospheric profilometer are given. Synchronous growth was recorded for deformations of the Earth’s surface and variations in the atmospheric pressure and in the level of spatiotemporal modifications of the electron content within the ionospheric F2 layer with characteristic space scales of 102–103 km and periods of 102–103 s. The relationship between the revealed phenomena and the Earth’s seismic activity is analyzed.  相似文献   

14.
The unique ecological landscapes are composed of the mountain systems with the obviousvertical differentiation, vast natural desert systems, and oasis systems on which the human beings rely for the existence in the arid areas in West China. Oases are the …  相似文献   

15.
Tumuli are positive topographic features that are common on Hawaiian pahoehoe lava flow fields, particularly on shallow slopes, and 75 measured examples are presented here to document the size range. Tumuli form by up-tilting of crustal plates, without any crustal shortening, and are thus distinguished from pressure ridges which are up-buckled by laterally directed pressure. The axial or star-like systems of deep clefts that characterize tumuli are defined here as lava-inflation clefts; their tips advanced into red-hot lava and they widened as uplift proceeded and while the lava crust was thickening. Flat-surfaced uplifts, formed like tumuli by injection of lava under a surface crust, were previously called pressure plateaus, but lava rise is proposed instead. The pits that abound among lava rises, previously attributed to collapse or subsidence, are generally formed because the lava around them rose, and the name lava-rise pit is proposed. Unique examples of tumuli and lava rises, from which lava drained out under a surface crust 1.5 to 2.5 m thick, are described from Kilauea caldera. These examples show that in tumuli and lava rises the crust floats on considerable bodies of fluid lava, and is able to do so because of its higher vesicle content: the fluid lava loses many of its gas bubbles during residence beneath the crust. The bulk densities of samples from tumuli show a general downward increase. The form of the density profile is consistent with the relationship that for any given crustal thickness the density of fluid lava closely matched the average density of that crust, suggesting that the lava was stably density-stratified. It is inferred that stable stratification was regulated by out-flows of the more vesicular lava fractions, loss of bubbles through the lava-inflation clefts, and entry of injected lava at its level of neutral buoyancy. Below the uppermost meter the downward decrease in vesicularity closely conforms with that expected by compression of a uniform mass of gas per unit mass of lava.  相似文献   

16.
Pyrite is a common sulfide mineral, particularly abundant in mining waste. It is a focus of mine envi-ronmental concern because the oxidation of exposed pyrite may lead to acid drainage and poisonous mate-rials (like As and heavy metals) release. In the United States, approximately $1000000 per day is spent in alleviating acid mine drainage[1], while the Canadian mining community has environmental liabilities that exceed $2 billion for disposal, management, and rec-lamation of mine waste[2]. …  相似文献   

17.
Using the four phases (1996～1999) of re-surveying data from the GPS network along the Shanxi fault zone, the recent state of horizontal movement of the fault zone and its relation with the Datong-Yanggao M5.6 earthquake (November 1, 1999), which took place on the north end of the monitored area, are analyzed. In the focal region, three areas with relatively higher strain (1×10 -6) appeared in Xinzhou and to the northeast of Jiexiu. The Shanxi fault zone is mainly controlled by the WNW-ESE-trending compressive stress field and the NNE-SSW-trending tensile stress field, and it does not have strike-slip movement. When examined for long-term tendency, attention should be paid to the junctures between the three moving elements.  相似文献   

18.
Geochemistry, zircon U–Pb geochronology, and Hf isotope data for the Early Paleozoic granites in the Baoshan Block reveal the Early Paleozoic tectonic evolution of the Proto-Tethys. The samples are high-K, calcalkaline, strongly peraluminous rocks with A/CNK values of 1.37–1.46, are enriched in SiO2, K2O, and Rb, and are depleted in Nb, P, Ti, Eu, and heavy rare earth elements,which indicates the crystallization fractionation of the granitic magma. Zircon U–Pb dating indica...  相似文献   

19.
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20.
This paper reports geochemical and Pb-Sr-Nd isotopic compositions of the Indosinian Yangba (215 Ma),Nanyili (225 Ma) and Mopi granitoids from the Bikou block of the northwestern margin of the Yangtze plate. These granitoids are enriched in Al (Al2O3:14.56%―16.48%) and Sr (352 μg/g―1047 μg/g),and depleted in Y (<16 μg/g) and HREE (e.g. Yb<1.61 μg/g),resulting in high Sr/Y (36.3―150) and (La/Yb)N (7.8―36.3) ratios and strongly fractionationed REE patterns. The Indosinian granotoids show initial Sr isotopic ratios (ISr) from 0.70419 to 70752,εNd(t) values from-3.1 to -8.5,and initial Pb isotopic ratios 206Pb/204Pb=17.891-18.250,207Pb/204Pb=15.494-15.575,and 208Pb/204Pb=37.788-38.335. Their geochemi-cal signatures indicate that the granitoids are adakitic. However,they are distinct from some adakites,generated by partial melting of subducted oceanic slab and/or underplated basaltic lower crust,be-cause they have high K (K2O: 1.49%―3.84%) and evolved Nd isotopic compositions,with older Nd iso-topic model ages (TDM=1.06―1.83 Ga). Geochemical and Sr-Nd isotopic compositions suggest that the magmas of the Insoninian adakitic rocks in the Bikou block were derived from partial melting of thick-ened basaltic lower crust. Combined with regional analyses,a lithospheric delamination model after collision between the North China and South China plates can account for the Indosinian adakitic magma generation. On the other hand,based on the Pb-Sr-Nd isotopic probing to the magma sources of the adakitic rocks,it is suggested that there is an unexposed continent-type basement under the exposed Bikou Group volcanic rocks. This can constrain on the Bikou Group volcanic rocks not to be MORB-or OIB-type.  相似文献   

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