俯冲带的锂同位素特征     

李真真  田世洪  侯增谦  苏嫒娜  侯可军  高延光  李延河  杨竹森 《岩石矿物学杂志》2010,29(4):431-438

近年来,由于分析手段的不断改进,锂同位素的精确测试才得以实现。锂以其分馏大、中度不相容、易随流体迁移、地表环境与地幔锂同位素特征差异明显等优势,被认为是极具潜力的示踪元素。目前,锂同位素在壳幔物质循环、风化作用、岩浆作用、流体(热液)活动等方面研究中已得到广泛的应用,其中又以俯冲带锂同位素的研究程度最高。本文主要从锂同位素分馏机理、俯冲带锂的行为特征、岛弧岩浆的锂同位素研究以及深俯冲作用过程中锂的行为等方面总结了当前国内外锂同位素的研究进展。  相似文献   

Sulfur dioxide emissions from Popocatépetl volcano (Mexico): case study of a high-emission rate, passively degassing erupting volcano     

H. Delgado-Granados  L. Crdenas Gonzlez  N. Piedad Snchez 《Journal of Volcanology and Geothermal Research》2001,108(1-4)

Popocatépetl volcano in central Mexico has been erupting explosively and effusively for almost 4 years. SO₂ emission rates from this volcano have been the largest ever measured using a COSPEC. Pre-eruptive average SO₂ emission rates (2–3 kt/d) were similar to the emission rates measured during the first part of the eruption (up to August 1995) in contrast with the effusive–explosive periods (March 1996–January 1998) during which SO₂ emission rates were higher by a factor of four (9–13 kt/d). Based on a chronology of the eruption and the average SO₂ emission rates per period, the total SO₂ emissions (up to 1 January 1998) are estimated to be about 9 Mt, roughly half as much as the SO₂ emissions from Mount Pinatubo in a shorter period. Popocatépetl volcano is thus considered as a high-emission rate, passively degassing eruptive volcano. SO₂ emission rates and SO₂ emissions are used here to make a mass balance of the erupted magma and related gases. Identified excess SO₂ is explained in terms of continuous degassing of unerupted magma and magma mixing. Fluctuations in SO₂ emission rate may be a result of convection and crystallization in the chamber or the conduits, cleaning and sealing of the plumbing system, and/or SO₂ scrubbing by the hydrothermal system.  相似文献   

Discovery of a recurrent lava lake on Saunders Island (South Sandwich Islands) using AVHRR imagery     

T. Lachlan-Cope  J. L. Smellie  R. Ladkin 《Journal of Volcanology and Geothermal Research》2001,112(1-4)

Monitoring of the remote South Sandwich Islands volcanic arc, using advanced very high resolution radiometer (AVHRR) data, has identified a radiant pixel on channels 3 (3.55–3.93 μm) and (rarely) 4 (10.3–11.3 μm). The position of the pixel is coincident with Mount Michael, Saunders Island, the active summit crater of a snow-covered basaltic stratovolcano with a persistent steam plume. The radiant pixel was continuously present in successive AVHRR images acquired during intervals of several months in the period examined (March 1995–February 1998), although apparently disappearing for similar time intervals. More than 5000 images were examined during this study. The radiant pixel is interpreted to indicate that the crater has contained a lava lake, the first to be recorded in the South Sandwich Islands. The lake appears to persist in the crater for several months at a time, at least. It may have drained completely at times and was probably absent when the crater was viewed briefly during an overflight in January 1997. Persistent or recurring lava lakes are very uncommon world-wide and that at Mount Michael is one of only two recorded in the Antarctic region.  相似文献   

Emplacement of xenolith nodules in the Kaupulehu lava flow,Hualalai Volcano,Hawaii     

J. E. Guest  P. D. Spudis  R. Greeley  G. J. Taylor  S. M. Baloga 《Bulletin of Volcanology》1995,57(3):179-184

The basaltic Kaupulehu 1800–1801 lava flow of Hualalai Volcano, Hawaii contains abundant ultramafix xenoliths. Many of these xenoliths occur as bedded layers of semi-rounded nodules, each thinly coated with a veneer (typically 1 mm thick) of lava. The nodule beds are analogous to cobble deposits of fluvial sedimentary systems. Although several mechanisms have been proposed for the formation of the nodule beds, it was found that, at more than one locality, the nodule beds are overbank levee deposits. The geological occurrence of the nodules, certain diagnostic aspects of the flow morphology and consideration of the inferred emplacement process indicate that the Kaupulehu flow had an exceptionally low viscosity on eruption and that the flow of the lava stream was extremely rapid, with flow velocities of at least 10 m s^-1 (more than 40 km h^-1). This flow is the youngest on Hualalai Volcano and future eruptions of a similar type would pose considerable hazard to life as well as property.  相似文献   

古特提斯造山带在华南两广交界地区的新证据   总被引：27，自引：0，他引：27       下载免费PDF全文

张伯友  杨树锋 《地质论评》1995,41(1):1-6

作者等在两广交界罗定一带新发现了中晚克生代的枕状熔岩和二叠－三叠纪的构造混杂岩，结合区域构造，分析并提出了钦州－岑溪－罗定－云浮构造混杂带的存在。它与全球古特提斯构造域的发育演化联系，故提出了两广交界地区存在古特提斯构造的分支带。  相似文献   

Radon anomalies on three kinds of faults in California   总被引：1，自引：0，他引：1  

Ch-Yu King  Wei Zhang  Bi-Shia King 《Pure and Applied Geophysics》1993,141(1):111-124

Radon emanation is known to be anomalously high along active faults in many parts of the world. We tested this relationship in California during July and early August 1992, using a portable radonmeter to conduct soil-air radon surveys at 5 sites across three kinds of faults: Creeping, locked, and freshly broken.Along a 350-m long survey line across a creeping segment of the San Andreas fault at Nyland Ranch in San Juan Bautista, we found anomalous radon concentrations not in the creep zone itself as determined by a creepmeter, but on the adjacent sides, 10 and 30 meters from the center line of the fault. The anomalous values were 5 times higher than the background values measured farther away from the fault. A similar radon anomaly was observed along a 420-m long survey line across a creeping segment of the Calaveras fault near 7th Street in Hollister. There, the anomalous values were about 6 to 11 times the background values and about 40 and 50 m from the center line of the fault. The double-peaked featire of the anomalies may be indicative of a relatively low gas permeability of the fault-gouge materials in the creeping zones and high permeability of fractured rocks in the adjacent shear zones.Along a 144-m survey line across the currently locked segment of the San Andreas fault at the Earthquake Trail near Olema, the radon concentration was indeed anomalously high in the fault zone, by a factor of two above background values. However, the maximum values (3 to 6 times background) again were recorded about 10 meters from the center line.Three weeks after the magnitude 7.5 Landers earthquake of 28 June 1992, we conducted a survey along a 300-m line across the earthquake fault alongside Encantado Road in the epicenter area. The radon values measured at the two main fault breaks were an order of magnitude higher than the background values. A similar result was found along a 420-m line alongside Reche Road about 1.7 km south of Encantado Road.  相似文献   

The Laki (Skaftár Fires) and Grímsvötn eruptions in 1783–1785     

Th Thordarson  S Self 《Bulletin of Volcanology》1993,55(4):233-263

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Simple stochastic modelling of the eruption history of a basaltic volcano: Nyamuragira,Zaire     

M. L. Burt  G. Wadge  W. A. Scott 《Bulletin of Volcanology》1994,56(2):87-97

Three simple models of the behaviour of a series of basaltic eruptions have been tested against the eruptive history of Nyamuragira. The data set contains the repose periods and the volumes of lava emitted in 22 eruptions since 1901. Model 1 is fully stochastic and eruptions of any volume with random repose intervals are possible. Models 2 and 3 are constrained by deterministic limits on the maximum capacity of the magma reservoir and on the lowest drainage level of the reservoir respectively. The method of testing these models involves (1) seeking change points in the time series to determine regimes of uniform magma supply rate, and (2) applying linear regression to these regimes, which for models 2 and 3 are the determinsstic limits to those models. Two change points in the time series for Nyamuragira, in 1958 and 1980, were determined using a Kolmogorov-Smirnov technique. The latter change involved an increase in the magma supply rate by a factor of 2.5, from 0.55 to 1.37 m³s^-1. Model 2 provides the best fit to the behavior of Nyamuragira with the ratio of variation explained by the model to total variation. R², being greater than 0.9 for all three regimes. This fit can be interpreted to mean that there is a determinstic limit to the elastic strength of the magma reservoir 4–8 km below the summit of the volcano.  相似文献   

Morphology and propagation styles of Miocene submarine basanite lavas at Stanley, northwestern Tasmania, Australia   总被引：2，自引：0，他引：2  

Yoshihiko Goto  Jocelyn McPhie 《Journal of Volcanology and Geothermal Research》2004,130(3-4):307-328

Miocene submarine basanite pillows, lava lobes, megapillows and sheet lavas in the Stanley Peninsula, northwestern Tasmania, Australia, are well-preserved in three dimensions. The pillows have ropy wrinkles, transverse wrinkles, symmetrical wrinkles, contraction cracks and three types of spreading cracks on their surfaces, and concentric and radial joints in the interior. The lava lobes have ropy wrinkles and contraction cracks on their surfaces. The megapillows are cylindrical with a smoothly curved upper surface and steep sides, and are characterized by distinct radial columnar joints in the interior. They are connected to pillows that propagate radially from its basal margin. The sheet lavas are tabular and have vertical columnar joints in the interior. The largest sheet lava shows a remarkable gradation from a lower 5-m-thick pillow facies to an upper massive facies. The pillows, lava lobes, megapillows and sheet lavas are inferred to have been emplaced completely below sea level but in a shallow marine environment. Their morphological features suggest that the pillows grew by episodic rupture of a near-solid crust and emergence of hot lava, whereas the lava lobes propagated by continuous stretching of the outer skin at the flow front. The megapillows and sheet lavas were master feeder channels by which molten lava was conveyed to the advancing pillows. The sheet lavas propagated by repeated processes of pillow formation and overriding by an upper massive part. Alternating pillow and massive facies commonly found in ocean-floor drill cores and exposed in cross-section in many subaqueous volcanic successions may have formed by propagation of pillows from the basal margins of advancing sheet lavas.  相似文献   

Periodic pumping tests     

Jörg Renner  Mareike Messar 《Geophysical Journal International》2006,167(1):479-493

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