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In autumn of 1966 on the northern slope of Kliuchevskoy volcano a chain of new adventive craters broke out at the height of about 2200 m. Eighty-four hours before the beginning of the eruption a swarm of preliminary volcanic earthquakes had appeared. The number of preliminary shocks was 457 with total energy of 4 × 1017 erg. With the beginning of the lava flow the earthquakes stopped and a continuous volcanic tremor appeared. The total energy of volcanic tremor amounts to 1016 erg. During the eruption numerous explosive earthquakes with the energy of 1015–1016 erg were recorded and besides the microbarograph of the Volcanostation recorded 393 explosions with an energy more than 1013 erg and their total energy was equal to 1017 erg. All together it has been formed 8 explosive craters and the lowest 9th crater was effusive. The slag cone was formed round this effusive crater, the lava effusion of basaltic-andesite composition (52,5% SiO2) tooke place from the lava boccas at the cone base and from the crater. The lava flow covered a distance of 10 km along the valley of the Sopochnoy river and descended to a height of about 800 m. The lava flow velocity at the outflow reached 800 m/hr, the lava temperature was 1050°C. The effused lava volume amounts to 0.1 km3. The eruption stopped on December 25–26, 1966. 相似文献
3.
Tanna, one of the southernmost islands of the New Hebrides volcanic arc, is made of Late Pliocene to Recent island arc tholeiitic basalts and andesites, with SiO2 contents ranging from 45 to 57%. These lavas are highly porphyritic (30–50% in volume): phenocrysts of plagioclase are the most abundant, together with olivine and clinopyroxene. The groundmass contain plagioclase, augite, olivine, magnetite and glass; pigeonite, tridymite, sanidine and, rarely, biotite may also occur. The olivines and clinopyroxenes show an iron enrichment from the cores of phenocrysts to their rims and the groundmass crystals, but their compositional variations are not correlated with the Mg/Fe ratio of bulk host rocks, the most Fe-rich compositions being found in Mg-rich lavas. Plagioclase compositions range from An95 to An60 in the basalts and An60 to An50 in the andesites, but, within each group, they are not correlated with SiO2 or Na2O contents of host lavas. Consequently, the bulk major element compositions of Tanna volcanic rocks cannot be considered as primarily controlled by crystal separation from successive liquids. The oxyde-SiO2 variations diagrams, and the modal compositions and mineral chemistry show that crystal accumulation is the predominant mechanism accounting for bulk rock compositions. However, this does not exclude fractional crystallization: the variation of the calculated groundmass mineralogy strongly suggest the occurrence of crystal removal mainly clinopyroxene and magnetite. 相似文献
4.
Pumiceous pyroclastic products are present as flows and falls at several stages of the evolution of the southern Guadeloupe volcanic island. An understanding of this volcanism had to rely on detailed petrochemical data of these products to complement similar data for effusive rocks so as to yield complete stratigraphical coverage. On the other hand most pumiceous rocks are more or less conspicuousily banded suggesting that mixing phenomena occurred to different degrees in their genesis. Three major classes of pumiceous products are found: (1) the Axial Chain deposits (2.0–0.5 My) are characterized by An90, 75-55 + En55 + Wo42En37 + Usp35-37 ± Fo68 ± Hble, SiO2 60%, SiO2/Th 35.6, and La/Th 3.9. Banded samples have components that differ in evolution indices by about 50%; (2) the Bouillante Chaine pyroclastics (0.3–0.1 My) consist of scattered deposits with variable mineralogical and geochemical compositions that seem to have erupted from a number of small eruptive centers. Qz-dacitic pumice is common with An90, 70-45 + En66-56 + Usp32-38 + Ilm94 + Hble ± Wo40-42En40-42, SiO2 62%, SiO2/Th 22.9, and La/Th >4. Mixed pumice samples have highly contrasted evolution indices differing by up to 120%; (3) the Pintade pumice flows and falls correspond to the major pyroclastic event (approx. 10 km3) in the southern Basse Terre area. They are characterized by An85-70 + En66-56 + Usp32-37 ± Wo42En42, SiO2/Th 18.7-22?6, and La/Th 3.0-4.0. Banded pumice lumps are scarce and show slight compositional contrasts; differences in evolution indices do not exceed 38%. Axial and Bouillante chain pyroclastics and Grande Découverte volcano pumice respectively, form two different families in trace element plots. Minor elements in pyroxenes also are distinctive. These trends are similar to those obtained for effusive rocks and define comagmatic series. Major and trace element data for the separated components of inhomogeneous pumice in each formation always plot in the corresponding series. These chemical discriminants can be used to attribute samples of unknown provenance to a given volcanic ensemble. An inverse relationship between differences in evolution indices in inhomegeneous pumice and the volume of any single eruptive sequence is noted. This is an indication that pumiceous pyroclastic rocks were erupted from a zoned magma chamber. We favor an interpretation where zonation is produced by influx of less envolved magma in superficial differentiated chambers which is a direct cause for eruption. 相似文献
5.
The 2.1 b.y. old Rooiberg Felsite roofs and is intruded by the mafic layered rocks and granites of the Bushveld Complex. The felsite unit, which locally exceeds 5 km in thickness and may represent an originally erupted volume of more than 300,000 km3, is dominated by rhyolitic to dacitic lavas with minor pyroclastic and sedimentary rock types. Volcanic rocks of more mafic composition occur towards the base of the sequence. The Rooiberg episode essentially terminated the volcanic activity in the Transvaal basin and heralded the emplacement of the Bushveld Complex. Despite the close spatial and temporal relationships between the Rooiberg Felsite and the Bushveld Complex, the precise nature of the petrogenetic link is obscure. Chemical analyses of felsite have been variously interpreted to suggest cyclic differentiation along a comagmatic trend or to demonstrate anomalous enrichment in SiO2. Several characteristics delineate the Rooiberg Felsite as a possibly unique occurrence of rhyolitic magmatism, notably the immense volume of the unit, the marked preponderance of lavas over pyroclastic types, and the unusually great thickness and lateral extent of the flows. The thesis that the Rooiberg Felsite represents a shock-produced, meteorite-impact melt cannot be supported on the available evidence. 相似文献
6.
K. Laing Bladh 《Bulletin of Volcanology》1980,43(1):155-171
The rhyodactic O’Leary Porphyry which forms the Pleistocene (0.233±0.37 m.y.) volcanic domes of O’Leary Peak and Darton Dome in the San Francisco Volcanic Field (northern Arizona, U.S.A.) contains sanidine phenocrysts with oligoclase mantles (rapakivi texture). Rapakivi texture occurs worldwide in silicic rocks of many ages and has been attributed to various igneous and metamorphic processes. The O’Leary Porphyry contains both mantled and unmantled sanidine (both are Or63–69 Ab30–36An1), oligoclase and quartz phenocrysts, labradorite (An53Ab45Or2) and kaersutite xenocrysts and andesite xenoliths. The compositional range of oligoclase is the same (An11–26Ab70–80Orr–10) for the rapakivi mantles, the oligoclase phenocrysts, and the oligoclase crystals poikilitic within sanidines. Most mantles are discontinuous. The sanidine appears to have been resorbed prior to mantling. Experimental melting studies on the O’Leary Prophyry show that, for a 15 wgt.% water system, plagioclase crystallized prior to sanidine and quartz crystallized last. The O’Leary Porphyry, although inhomogeneous, plots on a Q-Or-Ab-An diagram well within the plagioclase stability field. Poikilitic plagioclases within sanidines further support crystallization of plagioclase prior to sanidine in the O’Leary Porphyry. Exsolution of a ternary feldspar to form a plagioclase mantle is the most commonly accepted igneous theory of rapakivi texture formation but has been eliminated as the origin of the O’Leary Porphyry rapakivi. Petrologic models by Tuttle and Bowen and by Stewart are rejected for the O’Leary rapakivi because of inconsistencies with the O’Leary occurrences. Two theories are viable for the O’Leary rapakivi texture. First, is a decrease in water vapor pressure which would enlarge the plagioclase stability field possibility causing mantling of metastable sanidines. The second and preferred theory is that of an addition of sodium and calcium by basification (chemical assimilation without melting) of the xenoliths within the O’Leary Porphyry. This would move the bulk composition of the melt into the plagioclase field possibly resulting in crystallization of plagioclase on sanidine crystals. Diffusion of sodium and calcium from the xenoliths to sanidine would result in mantling only those crystals near to the xenoliths. Later, convection would result in distribution throughout the melt of rapakivi, unmantled sanidines, and xenolithic kaersutite as is seen in the porphyry. Basic xenoliths are extremely common in rapakivi-bearing rocks. Those within the O’Leary Porphyry are andesitic and show resorption, and in some areas of O’Leary Peak itself, have been drawn out into schlieren. 相似文献
7.
The simultaneous eruption of Mt. Pelée, Martinique and Soufrière, St. Vincent are regarded as the first recognized examples of Pelean-type and St. Vincent-type pyroclastic eruptions. Both produced nuées ardentes, the former usually laterally directed because of the presence of a dome and the latter vertically directed from an open crater. Both volcanoes have subsequently erupted for a second time this century. The 1902–05 and 1929–32 eruptions of Mt. Pelée produced andesite lava of almost identical composition and mineralogy. Both contain two generations of plagioclase, orthopyroxene, Fe-Ti oxide, corroded brown amphibole and olivine rimmed by pyroxene. In contrast, the Soufrière material is more basic in composition varying from basaltic andesite to basalt in 1902–03 and basaltic andesite in 1971–72. The Soufrière material contains two generations of plagioclase (with those of 1971–72 having additional zones of labradorite), clinopyroxene, orthopyroxene, olivine and Fe-Ti oxide. The pyroclastic deposits are strikingly different, those from the Pelean-type eruption are termed «block and ash deposits» being characterised by poorly vesicular lava blocks up to 7 m in diameter, while the St. Vincent-type eruption produced «scoria and ash deposits» containing vesicular ropey blocks or bombs no larger than 1 m in diameter. The differences in styles of eruption are attributed to differences in viscosity and mechanism of eruption of the magmas. Stratigraphic studies of Mt. Pelée reveal that the volcano has produced basaltic andesite scoria and ash deposits from St. Vincent-type eruptions. It is concluded that the recent eruptions of Pelée tapped a deep level magma during both eruptions releasing magma of similar composition, while the 1971 Soufrière magma is thought to be a remnant of the 1903 basaltic magma which remained at a high level within the volcano where it underwent enrichment in plagioclase and loss of olivine and oxide. 相似文献
8.
To give an indication on the influence of the dynamics and behavior of lake plankton on the seston composition in the outlet, four 24-hour sampling sessions were made in the Greifensee (situated near Zürich, Switzerland) and its outlet (River Glatt). The most important crustacean species studied wereEudiaptomus gracilis, Cyclops abyssorum, Cyclops vicinus, Mesocyclops leuckarti andDaphnia spp.Leptodora kindtii was found during one sampling only. No evidence of shore avoidance was found. The vertical migration in the lake especially in the upper layer (0–6 m) is believed to have an influence on the amount of plankton which is flushed into the outlet. Although the composition and concentration of the plankton at the deepest point of the lake have been known, no accurate predictions on the quality of the plankton close to shore or in the outlet were possible. 相似文献
9.
The volcanic centre of Monte Seda Oro, N. W. Sardinia, representative of a Cenozoic calc-alkaline andesitic suite of rocks is composed of a variety of rocks ranging from high alumina basalts to dacites. The minerals of basaltic, andesitic and dacitic rocks show only limited variation in chemical composition. The geochemical data suggest that the various rock-types are related by a crystal-liquid fractionation. Least-squate numerical calculations, using major element data, support the derivation of andesites with SiO3 content ranging from 53.8 to 59.0% from basalts having about 48.7% of SiO2 by low pressure crystal fractionation of the phenocryst phases present in these rocks. However, the origin of dacites cannot be readily explained by this mechanism. 相似文献
10.
Ceboruco is a major composite volcano at the western end of the Mexican Volcanic Belt, near the junction between the North American and Pacific plates. The volcano is built from successive eruptions of andesite lavas and pyroclastic rocks, and major eruptions during its history have resulted in the formation of two concentric calderas. The youngest volcanic activity has included the extrusion of dacites within the inner caldera and a voluminous flank eruption of andesite during 1870–72. Fumarolic activity persists to the present day. Chemical analyses show that the lavas are of cale-alkaline type and rangs from andesite (SiO2=58–61%) to acid dacite (SiO2=68%) in composition. The rate of increase of K2O relative to SiO is greater than that in volcanic rocks from the Mexican Volcanic Belt as a whole. This indicates that simple models based on the application of such relationships may not be adequate to explain the petrogenesis of calc-alkaline lavas. 相似文献
11.
The 10-km diameter Mule Creek caldera is the youngest felsic eruptive center in the Mogollon-Datil volcanic field of southwestern New Mexico. The caldera forms a topographic basin surrounded by a raised rim. The caldera wall is well displayed on the south and west sides of the structure where it dips 20–30 degrees toward the center of the basin. Mudflow breccia fills the caldera and is banked up against the caldera wall. Post-caldera porphyritic quartz latite domes and flows crop out along the ring-fracture zone. The caldera is superimposed upon an older volcanic complex of flow-banded rhyolite and porphyritic andesite lava. The Mule Creek caldera probably originated by explosive eruption of about 10 km3 of pumice and ash, in part preserved in the matrix of the mudflow breccia. Periods of explosive volcanism during the deposition of mudflow breccia are documented by tuffaceous beds interbedded with the breccia. A thin rhyolite ash-flow sheet originated in the caldera and overlies the mudflow breccia. The youngest felsic rocks around the caldera are (1) domes and flows of crystal-rich porphyritic quartz latite of variable mineralogy, interpreted as a defluidized magma, and (2) widespread crystal-poor, flow-banded rhyolite, dated at 18.6 m.y., which is not directly related to the caldera sequence. The Mule Creek caldera and other volcanic features farther south represent the only documented overlap of felsic volcanism with early stages of Basin-Range tectonism in the Mogollon-Datil field. 相似文献
12.
The Society Islands of French Polynesia (south-central Pacific Ocean) are formed predominatly by basaltic lavas of alkaline affinities. These intraplate rocks are either Ne- or Hy-normative. Ne-normative basaltic lavas are lower in Si and heavy rare earth elements and higher in Ti, V and Sr than Hy-normative. The differences are attributed to the contrasting behaviour of amphibole during melting of the upper mantle, which, in turn, may be related to the variation in the depth of melting. Compared to pyrolite, the upper mantle source of the lavas was enriched in incompatible elements. 相似文献
13.
The Tertiary and Recent volcanics of Mexico occur in two provinces. The Cordillera Province is made up of about 1700 m of ignimbrite sheets overlain and intercalated in the upper part by olivine basalt and basaltic andesite. The Rio Lerma Province extends transversely across Mexico and in the Valley of Mexico the lavas consist mainly of andesite and dacite, 68 % of those analysed having 62 | 4.7 % SiO2. A total of 108 chemical analyses were made for the major elements, 90 of these including determinations of Cr, Ni, Cu, Zn, Rb, Sr, Ba, Th and Pb for two areas, the Valley of Mexico in the Rio Lerma Province and the Guadalajara region which lies at the intersection of the two provinces. Computer constructions of normative components in the basalt tetrahedron and other projections support an origin of partial melting of tholeiitic to pyrolitic material for the production of andesite. The Guadalajara lavas have consistently higher K/SiO2 and K/Rb ratios and lower Mg/SiO2 ratio than the Valley of Mexico rocks suggesting generation at greater depth. 相似文献
14.
The last 300 years of Vesuvius history are reconstructed as a chronological succession of 4 phenomenological states: i) repose, ii) persistent activity, iii) intermediate eruption and iv) final eruption. It turns out that the times of permanence in each state are distributed according to the same exponential law. Vesuvius activity is then described by a Markov chain of these 4 states, with transition probabilities determined from the previous phenomenological analysis. The model reproduces the Vesuvius activity between 1694 and 1872 and possibly also in the 1872–1944 period. It turns out that, at least between 1694 and 1872, the volcano was behaving like a quasistationary system with 4 equilibrium states, perturbed by a stochastic noise responsible for occasional transitions from an equilibrium state to another. Major physical or structural changes of the volcanic system around 1872 and possibly in the whole subsequent period, are clearly shown by the statistical analysis. 相似文献
15.
D. A. Swanson W. A. Duffield D. B. Jackson D. W. Peterson 《Bulletin of Volcanology》1972,36(1):105-126
Since February 1969 Alae Crater, a 165-m-deep pit crater on the east rift of Kilauea Volcano, has been completely filled with about 18 million m3 of lava. The filling was episodic and complex. It involved 13 major periods of addition of lava to the crater, including spectacular lava falls as high as 100 m, and three major periods of draining of lava from the crater. Alae was nearly filled by August 3, 1969, largely drained during a violent ground-cracking event on August 4, 1969, and then filled to the low point on its rim on October 10, 1969. From August 1970 to May 1971, the crater acted as a reservoir for lava that entered through subsurface tubes leading from the vent fissure 150 m away. Another tube system drained the crater and carried lava as far as the sea, 11 km to the south. Much of the lava entered Alae by invading the lava lake beneath its crust and buoying the crust upward. This process, together with the overall complexity of the filling, results in a highly complicated lava lake that would doubtless be misinterpreted if found in the fossil record. 相似文献
16.
We apply a newly developed numerical method to improve the Moho geometry by the implementation of gravity data. This method utilizes expressions for the gravimetric forward and inverse modeling derived in a frequency domain. Methods for a spectral analysis and synthesis of the gravity field and crust density structures are applied in the gravimetric forward modeling of the consolidated crust-stripped gravity disturbances, which have a maximum correlation with the (a priori) Moho model. These gravity disturbances are obtained from the Earth’s gravity disturbances after applying the topographic and stripping gravity corrections of major known anomalous crust density structures; in the absence of a global mantle model, mantle density heterogeneities are disregarded. The isostatic scheme applied is based on a complete compensation of the crust relative to the upper mantle density. The functional relation is established between the (unknown) Moho depths and the complete crust-stripped isostatic gravity disturbances, which according to the adopted isostatic scheme have (theoretically) a minimum correlation with the Moho geometry. The system of observation equations, which describes the relation between spherical functions of the isostatic gravity field and the Moho geometry, is defined by means of a linearized Fredholm integral equation of the first kind. The Moho depths are determined based on solving the gravimetric inverse problem. The regularization is applied to stabilize the ill-posed solution. This numerical procedure is utilized to determine the Moho depths globally. The gravimetric result is presented and compared with the seismic Moho model. Our gravimetric result has a relatively good agreement with the CRUST2.0 Moho model by means of the RMS of differences (of 3.5 km). However, the gravimetric solution has a systematic bias. We explain this bias between the gravimetric and seismic Moho models by the unmodelled mantle heterogeneities and uncertainties in the CRUST2.0 global crustal model. 相似文献
17.
A brief report is made of current laboratory investigations on phase relations among olivine, pyroxene, anorthite, magnetite, tridymite, liquid and gas in the system Mg2SiO4-CaAl2Si2O8-FeO-Fe2O2-SiO2 over a wide range of oxygen partial pressures. Courses of fractional crystallization under various conditions of oxygen partial pressure are depicted using an anorthite saturation diagram. Starting with a basalt-like composition in the system, fractional crystallization at a moderate oxygen partial pressure (10 atm.) results in an andesite-like residual liquid of composition 55 SiO2, 14 iron oxide, 6 MgO, 9 CaO, 16 Al2O3 at a temperature of 1155°C. With fractional crystallization in a closed system, the end liquid approaches the composition of 45 SiO2, 38 iron oxide, 6 CaO and 11 Al2O3, at a temperature of 1050°C and oxygen partial pressure of about 10?12 atm. The andesitic final liquid in this system would be expected to further differentiate toward dacitic and rhyolitic compositions if alkalies and water were present in the system. On the basis of these studies, the derivation of liquids of andesitic, dacitic or rhyolitic composition from primary basalts by fractional crystallization seems entirely possible if the oxygen partial pressure is maintained at a moderate or high level. 相似文献
18.
The results of a ground deformation study (1) of Vesuvius are reported. The study is a part of the geophysical program for the surveillance of this extremely dangerous active volcano. The results obtained in the period 1977–1981 show no significant changes in the dynamic state of the volcano. Corresponding to the southern Aapennines Nov. 23, 1980 earthquake a modification of the zenithal distance between the rim and bottom of the Vesuvius crater was observed which was likely connected with fairly shallow effects. 相似文献
19.
E. Ibarrola 《Bulletin of Volcanology》1969,33(3):729-777
More than two hundred new analyses of basaltic rocks from the Canary Islands are presented. The available data show that the earlier successions have similar variation trends throughout the archipelago; these trends represent all the intermediate types between basic differentiates (oceanites, ankaramites) and more salic differentiates (trachy-basalts, hawaiites). In the more recent volcanic series, the study shows that there is a magmatic diversification with different variation trends in the Eastern than in the Central Canary Islands. In the latter the alkaline character becomes stronger in the successive periods of volcanic activity which have been established in each island. In the Eastern islands the basaltic evolution is, on the contrary, towards basaltic rocks with tholeiitic affinities. 相似文献
20.
E. E. Larson R. L. Reynolds R. Merrill S. Levi M. Ozima Y. Aoki H. Kinoshita S. Zasshu N. Kawai T. Nakajima K. Hirooka 《Bulletin of Volcanology》1974,38(1):361-377
Volcanic rocks from six of the currently or recently active volcances of the Mariana Island are show little variation in major element abundances. SiO2 content averages 51.5 wt.%. The flows are high in Al2O (mean 17.7 wt.%) and Fe oxides (mean 10.1 wt.% calculated as FeO only), and moderate in MgO content (mean 4.7 wt.%), Na2O (mean 2.7 wt.%), and K2O (mean 0.7 wt.%). Only the rocks from Farallon de Pajaros, the northernmost of the Mariana Islands, deviate slightly from the average of the analyses. Three analyses from this island are slightly higher in SiO2 (about 54 wt.%) and Al2O3, and are lower in total Fe oxides and MgO. According to preferred classification, the lavas of the Mariana Islands can be termed mela-andesites, high-alumina basalts, or calc-alkaline (orogenic) basalts. The K2O values (mean 0.7 wt.%) obtained from lavas of the Mariana Islands are significantly higher than the K2O values (about 0.33 wt.%) from volcanics of the Izu chain to the north. Inasmuch as the substantial scatter in location of earthquake foci beneath both arcs prevents accurate delineation of the upper boundary of the Benioff zone, it presently cannot be determined whether this discrepancy in K2O values reflects a difference in depth from the volcanic are to the dipping seismic zone or relates to other phenomena. The older volcanic islands within the Mariana-Bonin island chain apparently defined an island arc system during Eocene to Miocene time. This indicates that the present plane of convergence between the Pacific plate and the Philippine Sea plate has defined the convergence between these plates since Eocene time. 相似文献