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排序方式: 共有856条查询结果,搜索用时 31 毫秒
71.
腾冲火山活动监测,预测与对策研究中的若干重要问题 总被引:2,自引:1,他引:1
《膳冲火山活动监测、预测与对策研究》项目是一项集火山活动监测研究、防灾及资源综合开发与利用为一体的系统工程。需要火山地质、地震、地球化学、地球物理、地壳形变及地热等诸多相关学科的合理配置和联合攻关。在过去的30年,众多学和研究实体对腾冲火山进行 大量的观察和研究获得一批与火山活动的相关的基础研究成果。其中也不乏说明腾冲火山存在在喷发危险性的证据。为了保证本重大项目能在有限时间内及有限的人力、财务 相似文献
72.
73.
STUDY ON TRANSMISSION MECHANISM OF THERMAL INFRARED REMOTE SENSING FOR ABRUPT GEOTHERMAL ANOMALY IN VOLCANIC REGION 总被引:2,自引:0,他引:2
Geothermalanomalyisaphenomenonthatundergroundtemperatureandgeothermalgradientincreasesmuchmoreintheareathanitssurroundings(Xia,1979).Abruptgeothermalanomalymeansthatundergroundtemperatureonsomespotsaswellastheaffectedtemperatureofsurroundingareaabr… 相似文献
74.
T. Feseker T. Pape K. Wallmann S.A. Klapp F. Schmidt-Schierhorn G. Bohrmann 《Marine and Petroleum Geology》2009
The sediment temperature distribution at mud volcanoes provides insights into their activity and into the occurrence of gas hydrates. If ambient pressure and temperature conditions are close to the limits of the gas hydrate stability field, the sediment temperature distribution not only limits the occurrence of gas hydrates, but is itself influenced by heat production and consumption related to the formation and dissociation of gas hydrates. Located in the Sorokin Trough in the northern Black Sea, the Dvurechenskii mud volcano (DMV) was in the focus of detailed investigations during the M72/2 and M73/3a cruises of the German R/V Meteor and the ROV Quest 4000 m in February and March 2007. A large number of in-situ sediment temperature measurements were conducted from the ROV and with a sensor-equipped gravity corer. Gas hydrates were sampled in pressurized cores using a dynamic autoclave piston corer (DAPC). The thermal structure of the DMV suggests a regime of fluid flow at rates decreasing from the summit towards the edges of the mud volcano, accompanied by intermittent mud expulsion at the summit. Modeled gas hydrate dissociation temperatures reveal that the gas hydrates at the DMV are very close to the stability limits. Changes in heat flow due to variable seepage rates probably do not result in changes in sediment temperature but are compensated by gas hydrate dissociation and formation. 相似文献
75.
Volcan Popocatépetl is a Quaternary stratovolcano located 60 km southeast of Mexico City. The summit crater is the site of
recent ash eruptions, excess degassing, and dacite dome growth. The modern cone comprises mainly pyroclastic flow deposits,
airfall tephras, debris flows, and reworked deposits of andesitic composition; it is flanked by more mafic monogenetic vents.
In least-degassed fallout tuffs and mafic scoria, transition metals are concentrated in phases formed before eruption, during
eruption, and after eruption. Preeruptive minerals occur in both lavas and tephra, and include oxides and sulfides in glass
and phenocrysts. The magmatic oxides consist of magnetite, ilmenite, and chromite; the sulfides consist of both (Fe,Ni)1-xS (MSS) and Cu–Fe sulfide (ISS). Syn- and posteruptive phases occur in vesicles in both lavas and tephra, and on surfaces
of ash and along fractures. The mineral assemblages in lavas include Cu–Fe sulfide and Fe–Ti oxide in vesicles, and Fe sulfide
and Cu–Fe sulfide in segregation vesicles. Assemblages in vesicles in scoria include Fe–Ti oxide and rare Fe–Cu–Sn sulfide.
Vesicle fillings of Fe–Ti oxide, Ni-rich chromite, Fe sulfide, Cu sulfide, and barite are common to two pumice samples. The
most coarse-grained of the vesicle fillings are Cu–Fe sulfide and Cu sulfide, which are as large as 50 μ in diameter. The
youngest Plinian pumice also contains Zn(Fe) sulfide, as well as rare Ag–Cu sulfide, Ag–Fe sulfide, Ag bromide, Ag chloride,
and Au–Cu telluride. The assemblage is similar to those typically observed in high-sulfidation epithermal mineralization.
The fine-grained nature and abundance of syn- and/or posteruptive phases in porous rocks makes metals susceptible to mobilization
by percolating fluids. The abundance of metal compounds in vesicles indicates that volatile exsolution prior to and/or during
eruption played an important role in releasing metals to the atmosphere.
Received: March 1997 · Accepted: 27 May 1997 相似文献
76.
Laser line scan imaging and chirp sub-bottom profiling were used to detail the morphology of a submarine mud volcano and brine-filled crater at 652 m water depth in the northern Gulf of Mexico. The mud volcano has a relief of 6 m and a basal diameter of about 80 m. The feature comprises a central, brine-filled crater (253 m2) surrounded by a continuous bed of methanotrophic mussels (Bathymodiolus childressi) covering 434 m2 and a patchy bed covering an additional 214 m2 of the periphery. The brine pool was mostly <2 m deep, but there were two holes of >28 m and 12 m deep, respectively at the northern end of the pool which emitted continual streams of small clear bubbles. Sub-bottom profiles indicated three distinct strata beneath the present surface of the mud volcano. Integration of 17 profiles shows that the mud volcano has been built in at least three successive stages: the lowest stage deposited 35,400 m3, while the middle and upper stages deposited 7700 and 20,400 m3, respectively. Piston cores were taken at the northern edge of the mussel bed and a site ∼100 m southwest of the pool. Mussel and lucinid shells were recovered from the closer core, lucinid shells from the distant core. A mussel shell from 3.4 m sub-bottom had a Δ14C age of 16.2 ka. Mixture of modern carbon with “carbon dead” reservoir material would produce actual ages ∼2 ka less than the radiocarbon ages. 相似文献
77.
Partial melting of subducting oceanic crust expressed as high-Mg volcanic rocks such as adakites and boninites has been actively studied for decades, and Lee and King (2010) reported that time-evolving subduction parameters such as the age and the subduction rate of the converging oceanic plate play important roles in transient partial melting of the subducting oceanic crust (e.g., Aleutians). However, few subduction model experiments have considered time-evolving subduction parameters, posing problems for studies of transient partial melting of subducting oceanic crust in many subduction zones. Therefore, we constructed two-dimensional kinematic–dynamic subduction models for the Izu–Bonin, Mariana, Northeast Japan, Kuril, Tonga, Java–Sunda, and Aleutian subduction zones that account for the last 50 Myr of their evolution. The models include the time-evolving age and convergence rate of the incoming oceanic plate, so the effect of time-evolving subduction parameters on transient partial melting of oceanic crust can be evaluated. Our model calculations revealed that adakites and boninites in the Izu–Bonin and Aleutian subduction zones resulted from transient partial melting of oceanic crust. However, the steady-state subduction model using current subduction parameters did not produce any partial melting of oceanic crust in the aforementioned subduction zones, indicating that time-evolving subduction parameters are crucial for modeling transient eruption of adakites and boninites. Our model calculations confirm that other geological processes such as forearc extension, back-arc opening, mantle plumes and ridge subduction are required for partial melting of the oceanic crust in the Mariana, Northeast Japan, Tonga, and southeastern Java–Sunda subduction zones. 相似文献
78.
粤北大宝山矿区加里东期火山岩的厘定及其地质意义 总被引:6,自引:2,他引:4
粤北大宝山矿区一带出露一套与层状Fe-Cu-Pb-Zn矿化紧密共生的层状火成岩。层状火成岩产状与上覆页岩及大理岩和下伏碳质页岩基本一致。本文通过层状火成岩显微特征及锆石年龄探讨火成岩形成环境及时代。层状火成岩为斑状结构,块状构造,局部发育条带状构造及流动构造。层状火成岩的斑晶主要由火山喷发形成的棱角明显石英、斜长石、钾长石、少量角闪石、黑云母及黄铁矿等晶屑及少量岩屑组成,基质为火山熔浆凝结形成的全晶质矿物,主要由粒度极细的石英、钾长石、绢云母、白云母及少量黑云母等组成,石英和钾长石构成典型的霏细结构。层状火成岩含大量火山碎屑及具流动构造等现象表明其为火山碎屑熔岩类,主要为英安质凝灰熔岩、流纹质凝灰熔岩及角砾熔岩。大宝山矿区中部流纹质凝灰熔岩和东部丘坝一带英安质凝灰熔岩的锆石LA-ICP-MS U-Pb年龄分别为436.4±4.1Ma,MSWD=0.94和434.1±4.4Ma,MSWD=1.9,是加里东期形成的。据大宝山矿区熔岩锆石U-Pb年龄,结合层状熔岩和灰岩及碳质页岩紧密共生及区域深大断裂构造活动特征,我们认为大宝山与层状矿化关系密切的层状火成岩为加里东期海相火山熔岩,粤北一带加里东期海相火山活动可能和形成于加里东期的吴川-四会深大断裂活动有关。 相似文献
79.
海底扩张的潮汐模式 总被引:3,自引:0,他引:3
杨学祥 《大地测量与地球动力学》2003,23(2):77-80
2000年6月底,东京以南的伊豆岛开始发生火山与地震活动。此后,在伊豆岛观测到异常的地壳变形,8月底,火山与地震活动达到高潮。对潮汐与火山和地震活动的关系进行了分析,认为:地壳变形是由伊豆岛的岩脉侵入引起的,并且与强潮汐天文条件相对应。根据观测和计算数据提出了海底扩张的潮汐模式。 相似文献
80.