排序方式： 共有78条查询结果，搜索用时 999 毫秒
1.
破火山内出露的火山岩与浅成侵入岩为硅质岩浆演化研究提供了一个重要窗口，从而备受关注。小雄破火山内的火山-侵入杂岩是中国东南沿海晚白垩世岩浆活动的典型代表，包括小雄组火山岩（K2x）与两类侵入岩（花岗斑岩、正长斑岩）。本文以小雄火山-侵入杂岩为研究对象，开展了系统的锆石U-Pb年代学、岩石学和地球化学研究，旨在深入探讨破火山内火山岩与侵入岩之间的成因联系和岩浆演化过程。系统的LA-ICP-MS 锆石U-Pb年代学研究表明，小雄组火山岩形成于98~88Ma，并具有多期次喷发的特点，可分为下段、中段和上段，年龄分别为98~96Ma（K2x1）、95~92Ma（K2x2）、~ 88Ma（K2x3）。小雄花岗斑岩形成年龄为90Ma；正长斑岩形成稍晚，约88Ma。与下段流纹质玻屑凝灰岩的Nd-Hf同位素组成[εNd（t）=-8.3~-7.2， εHf（t）=-11.8~-7.2]相比，中段流纹岩要更为亏损[εNd（t）=-5.84~-5.32， εHf（t）=-10.1~-0.5]。研究表明，小雄组流纹质火山岩的母岩浆可能起源于发生在深部岩浆房中渐进的壳幔相互作用，中段流纹岩的源区混入了更多的亏损幔源组分。中段流纹岩与花岗斑岩具有相似的Nd-Hf同位素组成，以及 "互补"的微量元素地球化学特征，由发生在浅部岩浆房的分离结晶作用和堆晶作用所制约。值得注意的是，正长斑岩与花岗斑岩并不存在直接的成因演化关系，两者应是不同的起源。不同的正长斑岩岩株具有高度一致的结晶年龄、微量元素特征以及Nd-Hf同位素组成，以上特征均表明小雄破火山内的正长斑岩具有相同的起源。正长斑岩母岩浆起源于富集岩石圈地幔的部分熔融，岩浆源区混入了来自亏损的软流圈地幔组分，其地球化学成分变化主要受"普通辉石+磷灰石+钛铁矿"的分离结晶所控制。 相似文献
2.
中朝边境天池破火山口湖底地形多波束测深探测 总被引：4，自引：3，他引：1
为调查天池破火山口湖的基本参数和湖底地形特征,研究破火山口的内部构造、破火山口的组合样式和垮塌堆积分布,本文采用多波束测深方法,对天池湖底地形进行了探测。探测结果显示:天池最大水深值为373.2m,天池水域边界实测周长为13.44km,天池湖水面面积9.4km~2,天池总蓄水量约为19.88×10~8m~3。天池周边分布4个温泉,温度为7~47℃。根据湖底地形推断,现今的天池破火山口形成于千年大喷发。其后,在天池西侧形成一个喷火口,东侧形成一个熔岩丘。天池湖底存在5个较大的破火山口内壁垮塌堆积区,但在湖底未见熔岩流。天池边缘出露的温泉点对应环状断裂,同时反映深部存在岩浆体。 相似文献
3.
A. M. F. Lagmay K. S. Rodolfo F. P. Siringan H. Uy C. Remotigue P. Zamora M. Lapus R. Rodolfo J. Ong 《Bulletin of Volcanology》2007,69(7):797-809
The 1991 Pinatubo eruption left 5–6 km3 of debris on the volcano slopes, much of which has been mobilized into large lahars in the following rainy seasons. Also
during the eruption, collapse, localized in part along preexisting faults, left a caldera 2.5 km in diameter that almost immediately
began to accumulate a 1.6 × 108 m3 lake. By 2001, the water had risen to the fault-controlled Maraunot Notch, the lowest, northwestern portion of the caldera
rim comprising the physiographic sill of the Caldera Lake. That year, a narrow artificial canal dug into an old volcanic breccia
underlying the outlet channel failed to induce a deliberate lake breakout, but discharge from heavy rains in July 2002 rapidly
deepened the notch by 23 m, releasing an estimated 6.5 × 107 m3 of lake water that bulked up into lahars with a volume well in excess of 1.6 × 108 m3. Lakes in other volcanoes have experienced multiple breakouts, providing practical motivation for this study. Fieldwork and
high-resolution digital elevation models reveal andesites and ancient lacustrine deposits, strongly fractured and deformed
along a segment of the Maraunot Fault, a prominent, steeply dipping, left-lateral fault zone that trends N35°–40°W within
and parallel to the notch. Seismicity in 1991 demonstrated that the Maraunot Fault is still active. The fault zone appears
to have previously been the erosional locus for a large channel, filled with avalanche or landslide deposits of an earlier
eruption that were exhumed by the 2002 breakout floods. The deformed lacustrine sediments, with an uncalibrated 14C age of 14,760 ± 40 year BP from a single charcoal sample, attest to the existence of an earlier lake, possibly within the
Tayawan Caldera, rim remnants of which survive as arcuate escarpments. That lake may well have experienced one or more ancient
breakouts as well. The 2002 event greatly reduced the possibility of another such event by scouring away the erodible breccia,
leaving less erodible fractured andesites and lacustrine rocks, and by enlarging the outlet channel and its discharge capacity.
Several lines of evidence indicate, however, that future lahar-generating lake breakouts at the notch may keep populations
of Botolan municipality downstream at risk: (1) a volume of 9.5 × 107 m3 of lake water remains perched 0.8 km above sea level; (2) seismicity in 1991 demonstrated that the Maraunot Fault is still
active and movements of sufficient magnitude could enlarge the outlet and the discharge through it; (3) more likely, however,
with or without earthquake activity, landslides from the steep to overhanging channel walls could block the channel again,
and a major rainstorm could then cause a rise in lake level and sudden breakouts; (4) intrusion of a new dome into the bottom
of the lake, possibly accompanied by phreatic explosions, could expel large volumes of lahar-generating water. 相似文献
4.
New deformation data from the Askja volcano, Iceland, show that the volcano's caldera has been deflating continuously for over 20 years, and confirm that the rate of subsidence is slowing down. The decay in subsidence rate can be fitted with a function of the form e
−
t
/
τ
, where τ is 39 years. Reanalysis of GPS data from 1993–1998 show that these data can be fitted with a model calling for two Mogi point sources, one shallow, and another one much deeper (16.2 km depth). Pressure decrease occurs in both sources. The deeper source is responsible for observed horizontal contraction towards Askja at distances that cannot be explained by the shallower source. Plate spreading of 19 mm/year distributed evenly over about 100-km-wide zone is also favoured by the data. 相似文献
5.
Rowe M. C.; Wolff J. A.; Gardner J. N.; Ramos F. C.; Teasdale R.; Heikoop C. E. 《Journal of Petrology》2007,48(11):2063-2091
The Miocene–Quaternary Jemez Mountains volcanic field(JMVF) is the site of the Valles caldera and associated BandelierTuff. Caldera formation was preceded by > 10 Myr of volcanismdominated by intermediate composition rocks (57–70% SiO2)that contain components derived from the lithospheric mantleand Precambrian crust. Simple mixing between crust-dominatedsilicic melts and mantle-dominated mafic magmas, fractionalcrystallization, and assimilation accompanied by fractionalcrystallization are the principal mechanisms involved in theproduction of these intermediate lavas. A variety of isotopicallydistinct crustal sources were involved in magmatism between13 and 6 Ma, but only one type (or two very similar types) ofcrust between 6 and 2 Ma. This long history constitutes a recordof accommodation of mantle-derived magma in the crust by meltingof country rock. The post-2 Ma Bandelier Tuff and associatedrhyolites were, in contrast, generated by melting of hybridizedcrust in the form of buried, warm intrusive rocks associatedwith pre-6 Ma activity. Major shifts in the location, styleand geochemical character of magmatism in the JMVF occur withina few million years after volcanic maxima and may correspondto pooling of magma at a new location in the crust followingsolidification of earlier magma chambers that acted as trapsfor basaltic replenishment. KEY WORDS: crustal anatexis; fractional crystallization; Jemez Mountain Volcanic Field; Valles Caldera; radiogenic isotopes; trace elements 相似文献
6.
A first-order leveling survey across the northeast part of the Yellowstone caldera in September 1998 showed that the central
caldera floor near Le Hardy Rapids rose 24±5 mm relative to the caldera rim at Lake Butte since the previous survey in September
1995. Annual surveys along the same traverse from 1985 to 1995 tracked progressive subsidence near Le Hardy Rapids at an average
rate of –19±1 mm/year. Earlier, less frequent surveys measured net uplift in the same area during 1923–1976 (14±1 mm/year)
and 1976–1984 (22±1 mm/year). The resumption of uplift following a decade of subsidence was first detected by satellite synthetic
aperture radar interferometry, which revealed approximately 15 mm of uplift in the vicinity of Le Hardy Rapids from July 1995
to June 1997. Radar interferograms show that the center of subsidence shifted from the Sour Creek resurgent dome in the northeast
part of the caldera during August 1992 to June 1993 to the Mallard Lake resurgent dome in the southwest part during June 1993
to August 1995. Uplift began at the Sour Creek dome during August 1995 to September 1996 and spread to the Mallard Lake dome
by June 1997. The rapidity of these changes and the spatial pattern of surface deformation suggest that ground movements are
caused at least in part by accumulation and migration of fluids in two sill-like bodies at 5–10 km depth, near the interface
between Yellowstone's magmatic and deep hydrothermal systems.
Received: 30 November 1998 / Accepted: 16 April 1999 相似文献
7.
Application of synthetic aperture radar (SAR) imagery to volcano mapping in the humid tropics: a case study in East Java, Indonesia 总被引：3，自引：0，他引：3
Simon A. Carn 《Bulletin of Volcanology》1999,61(1-2):92-105
Volcanoes in humid tropical environments are frequently cloud covered, typically densely vegetated and rapidly eroded. These
factors complicate field and laboratory studies and even the basic identification of potentially active volcanoes. Numerous
previous studies have highlighted the potential value of radar remote sensing for volcanology in equatorial regions. Here,
cloud- and vegetation-penetrating LHH-band (λ≈24 cm) synthetic aperture radar (SAR) data from the Japanese Earth Resources Satellite (JERS-1) are used to investigate
persistently active volcanoes and prehistoric calderas in East Java, Indonesia. The LHH-band JERS-1 SAR produces high-spatial-resolution (18 m) imagery with relatively high incidence angle that highlights structures
and topographic variations at or greater than the wavelength scale while minimising geometrical distortions such as layover
and foreshortening. These images, along with Internet browse data derived from the Canadian RADARSAT mission, provide new
evidence relating regional tectonics to volcanism throughout East Java. Volcanic events, such as caldera collapse at the Tengger
caldera, appear to have been partly controlled by northwest-aligned faults related to intra-arc sedimentary basins. Similar
regional controls appear important at historically active Lamongan volcano, which is encircled by numerous flank maars and
cinder cones. A previously undocumented pyroclastic sheet and debris avalanche deposit from the Jambangan caldera complex
is also manifested in the synoptic radar images. At the currently active Semeru volcano these data permit identification of
recent pyroclastic flow and lahar deposits. Radar data therefore offer a valuable tool for mapping and hazard assessment at
late Quaternary volcanoes. The criteria developed in the analysis here could be applied to other regions in the humid tropics.
Received: 25 June 1998 / Accepted: 20 January 1999 相似文献
8.
在乔治王岛中部的阿德默勒尔蒂湾 ,凯勒半岛、于尔曼山嘴和埃内坎角是第三纪火山岩集中分布区。野外地质调查和同位素年代学研究表明 ,凯勒半岛发生了三期火山喷发 (三个火山喷发旋回 ) ,同时伴随着火山活动中心的不断北移 ;在第二期火山喷发之后 ,火口塌陷 ,形成破火山 ,之后在半岛北部又发生火山喷发 ,并向东迁移到于尔曼山嘴。因此凯勒半岛是一复活破火山 ,火山活动具有随时间迁移的特性。埃内坎角火山活动虽与上述两地区大致同时 ,但化学成分上不存在明显演化关系 ,应属另一相对独立的火山活动中心 相似文献
9.
Three major rhyolite systems in the northeastern Davis and adjacent Barrilla Mountains include lava units that bracketed a
large pantelleritic ignimbrite (Gomez Tuff) in rapid eruptions spanning 300,000 years. Extensive silicic lavas formed the
shields of the Star Mountain Formation (37.2 Ma-K/Ar; 36.84 Ma 39Ar/40Ar), and the Adobe Canyon Formation (37.1 Ma-K/Ar; 36.51-39Ar/40Ar). The Gomez Tuff (36.6 Ma-K/Ar; 36.74-39Ar/40Ar) blanketed a large region around the 18×24 km diameter Buckhorn caldera, within which it ponded, forming sections up to
500 m thick. Gomez eruption was preceded by pantelleritic rhyolite domes (36.87, 36.91 Ma-39Ar/40Ar), some of which blocked movement of Star Mountain lava flows. Following collapse, the Buckhorn caldera was filled by trachyte
lava. Adobe Canyon rhyolite lavas then covered much of the region. Star Mountain Formation (~220 km3) is composed of multiple flows ranging from quartz trachyte to mildly peralkalic rhyolite; three major types form a total
of at least six major flows in the northeastern Davis Mountains. Adobe Canyon Formation (~125 km3) contains fewer flows, some up to 180 m thick, of chemically homogenous, mildly peralkalic comendite, extending up to 40 km.
Gomez Tuff (~220 km3) may represent the largest known pantellerite. It is typically less than 100 m thick in extra-caldera sections, where it
shows a pyroclastic base and top, although interiors are commonly rheomorphic, containing flow banding and ramp structures.
Most sections contain one cooling unit; two sections contain a smaller, upper cooling unit. Chemically, the tuff is fairly
homogeneous, but is more evolved than early pantelleritic domes. Overall, although Davis Mountains silicic units were generated
through open system processes, the pantellerites appear to have evolved by processes dominated by extensive fractional crystallization
from parental trachytes similar to that erupted in pre- and post-caldera lavas. Comparison with the Pantelleria volcano suggests
that the most likely parental magma for the Buckhorn series is transitional basalt, similar to that erupted in minor, younger
Basin and Range volcanism after about 24 Ma. Roughly contemporaneous mafic lavas associated with the Buckhorn caldera appear
to have assimilated or mixed with crustal melts, and, generally, may not be regarded as mafic precursors of the Buckhorn silicic
rocks, They thus form a false Daly Gap as opposed to the true basalt/trachyte Daly gap of Pantelleria.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
This paper constitutes part of a special issue dedicated to Bill Bonnichsen on the petrogenesis and volcanology of anorogenic
rhyolites. 相似文献
10.
New insights into Late Pleistocene explosive volcanic activity and caldera formation on Ischia (southern Italy) 总被引：2，自引：1，他引：1
A new pyroclastic stratigraphy is presented for the island of Ischia, Italy, for the period ∼75–50 ka BP. The data indicate
that this period bore witness to the largest eruptions recorded on the island and that it was considerably more volcanically
active than previously thought. Numerous vents were probably active during this period. The deposits of at least 10 explosive
phonolite to basaltic-trachyandesite eruptions are described and interpreted. They record a diverse range of explosive volcanic
activity including voluminous fountain-fed ignimbrite eruptions, fallout from sustained eruption columns, block-and-ash flows,
and phreatomagmatic eruptions. Previously unknown eruptions have been recognised for the first time on the island. Several
of the eruptions produced pyroclastic density currents that covered the whole island as well as the neighbouring island of
Procida and parts of the mainland. The morphology of Ischia was significantly different to that seen today, with edifices
to the south and west and a submerged depression in the centre. The largest volcanic event, the Monte Epomeo Green Tuff (MEGT)
resulted in caldera collapse across all or part of the island. It is shown to comprise at least two thick intracaldera ignimbrite
flow-units, separated by volcaniclastic sediments that were deposited during a pause in the eruption. Extracaldera deposits
of the MEGT include a pumice fall deposit emplaced during the opening phases of the eruption, a widespread lithic lag breccia
outcropping across much of Ischia and Procida, and a distal ignimbrite in south-west Campi Flegrei. During this period the
style and magnitude of volcanism was dictated by the dynamics of a large differentiated magma chamber, which was partially
destroyed during the MEGT eruption. This contrasts with the small-volume Holocene and historical effusive and explosive activity
on Ischia, the timing and distribution of which has been controlled by the resurgence of the Monte Epomeo block. The new data
contribute to a clearer understanding of the long-term volcanic and magmatic evolution of Ischia. 相似文献