Geometry and growth of sill complexes: insights using 3D seismic from the North Rockall Trough   总被引：1，自引：0，他引：1  

K.?ThomsonEmail author  D.?Hutton 《Bulletin of Volcanology》2004,66(4):364-375

Doleritic sill complexes, which are an important component of volcanic continental margins, can be imaged using 3D seismic reflection data. This allows unprecedented access to the complete 3D geometry of the bodies and an opportunity to test classic sill emplacement models. The doleritic sills associated with basaltic volcanism in the North Rockall Trough occur in two forms. Radially symmetrical sill complexes consist of a saucer-like inner sill at the base with an arcuate inclined sheet connecting it to a gently inclined, commonly ragged, outer rim. Bilaterally symmetrical sill complexes are sourced by magma diverted from a magma conduit feeding an overlying volcano. With an elongate, concave upwards, trough-like geometry bilaterally symmetrical sills climb away from the magma source from which they originate. Both sill complex types can appear as isolated bodies but commonly occur in close proximity and consequently merge, producing hybrid sill complexes. Radial sill complexes consist of a series of radiating primary flow units. With dimensions up to 3 km, each primary flow unit rises from the inner saucer and is fed by primary magma tube. Primary flow units contain secondary flow units with dimensions up to 2 km, each being fed by a secondary magma tube branching from the primary magma tube. Secondary flow units in turn are composed of 100-m scale tertiary flow units. A similar branching hierarchy of flow units can also be seen in bilaterally symmetrical sill complexes, with their internal architecture resembling an enlarged version of a primary flow unit from a radial sill complex. This branching flow pattern, as well as the interaction between flow units of varying orders, provides new insights into the origin of the structures commonly seen within sill complexes and the hybrid sill bodies produced by their merger. The data demonstrate that each radially symmetrical sill complex is independently fed from a source located beneath the centre of the inner saucer, grows by climbing from the centre outwards and that peripheral dyking from the upper surface is a common feature. These features suggest a laccolith emplacement style involving peripheral fracturing and dyking during inner saucer growth and thickening. The branching hierarchy of flow units within bilaterally symmetrical sill complexes is broadly similar to that of primary flow units within a radially symmetrical sill complex, suggesting that the general features of the laccolith emplacement model also apply.Editorial responsibility: J. Stix  相似文献   

An Upper Pliocene coarse pumice breccia generated by a shallow submarine explosive eruption,Milos, Greece     

Andrew?L.?StewartEmail author  Jocelyn?McPhie 《Bulletin of Volcanology》2004,66(1):15-28

The Filakopi Pumice Breccia (FPB) is a very well exposed, Pliocene volcaniclastic unit on Milos, Greece, and has a minimum bulk volume of 1 km³. It consists of three main units: (A) basal lithic breccia (4–8 m) mainly composed of angular to subangular, andesitic and dacitic clasts up to 2.6 m in diameter; (B) very thickly bedded, poorly sorted pumice breccia (16–17 m); and (C) very thick, reversely graded, grain-supported, coarse pumice breccia (6.5–20 m), at the top. The depositional setting is well constrained as shallow marine (up to a few hundred metres) by overlying fossiliferous and bioturbated mudstone. This large volume of fine pumice clasts is interpreted to be the product of an explosive eruption from a submarine vent because: (1) pumice clasts are the dominant component; (2) the coarse pumice clasts (>64 mm) have complete quenched margins; (3) very large (>1 m) pumice clasts are common; (4) overall, the formation shows good hydraulic sorting; and (5) a significant volume of ash was deposited together with the coarsest pyroclasts.The bed forms in units A and B suggest deposition from lithic-rich and pumiceous, respectively, submarine gravity currents. In unit C, the coarse (up to 6.5 m) pumice clasts are set in matrix that grades upwards from diffusely stratified, fine (1–2 cm) pumice clasts at the base to laminated shard rich mud at the top. The coarse pumice clasts in unit C were settled from suspension and the framework was progressively infilled by fine pumice clasts from waning traction currents and then by water-settled ash. The FPB displays important features of the products of submarine explosive eruptions that result from the ambient fluid being seawater, rather than volcanic gas or air. In particular, submarine pyroclastic deposits are characterised by the presence of very coarse juvenile pumice clasts, pumice clasts with complete quenched rims, and good hydraulic sorting.Electronic Supplementary Material Supplementary material is available for this article if you access the article at . A link in the frame on the left on that page takes you directly to the supplementary material.Editorial responsibility: J. Donelly-Nolan  相似文献   

Doppler radar sounding of volcanic eruption dynamics at Mount Etna     

G.?Dubosclard  F.?DonnadieuEmail author  P.?Allard  R.?Cordesses  C.?Hervier  M.?Coltelli  E.?Privitera  J.?Kornprobst 《Bulletin of Volcanology》2004,66(5):443-456

Besides their common use in atmospheric studies, Doppler radars are promising tools for the active remote sensing of volcanic eruptions but were little applied to this field. We present the observations made with a mid-power UHF Doppler radar (Voldorad) during a 7-h Strombolian eruption at the SE crater of Mount Etna on 11–12 October 1998. Main characteristics of radar echoes are retrieved from analysis of Doppler spectra recorded in the two range gates on either side of the jet axis. From the geometry of the sounding, the contribution of uprising and falling ejecta to each Doppler spectrum can be discriminated. The temporal evolution of total power backscattered by uprising targets is quite similar to the temporal evolution of the volcanic tremor and closely reproduces the overall evolution of the eruption before, during and after its paroxysm. Moreover, during the sharp decrease of eruptive activity following the paroxysm, detailed analysis of video (from camera recording), radar and seismic measurements reveals that radar and video signals start to decrease simultaneously, approximately 2.5 min after the tremor decline. This delay is interpreted as the ascent time through a magma conduit of large gas slugs from a shallow source roughly estimated at about 500 m beneath the SE crater. Detailed analysis of eruptive processes has been also made with Voldorad operating in a high sampling rate mode. Signature of individual outburst is clearly identified on the half part of Doppler spectra corresponding to rising ejecta: temporal variations of the backscattered power exhibit quasi periodic undulations, whereas the maximum velocity measured on each spectrum displays a sharp peak at the onset of each outburst followed by a slow decay with time. Periodicity of power variations (between 3.8 and 5.5 s) is in agreement with the occurrence of explosions visually observed at the SE vent. Maximum vertical velocities of over 160 m s^–1 were measured during the paraoxysmal stage and the renewed activity. Finally, by using a simplified model simulating the radar echoes characteristics, we show that when Voldorad is operating in high sampling rate mode, the power and maximum velocity variations are directly related to the difference in size and velocity of particles crossing the antenna beam.Editorial responsibility: A. Woods  相似文献   

Nonlinear Time Series Analysis of Volcanic Tremor Events Recorded at Sangay Volcano,Ecuador     

K. I.?Konstantinou  C. H. ?LinEmail author 《Pure and Applied Geophysics》2004,161(1):145-163

The assumption that volcanic tremor may be generated by deterministic nonlinear source processes is now supported by a number of studies at different volcanoes worldwide that clearly demonstrate the low-dimensional nature of the phenomenon. We applied methods based on the theory of nonlinear dynamics to volcanic tremor events recorded at Sangay volcano, Ecuador in order to obtain more information regarding the physics of their source mechanism. The data were acquired during 21–26 April 1998 and were recorded using a sampling interval of 125 samples s^–1 by two broadband seismometers installed near the active vent of the volcano. In a previous study Johnson and Lees (2000) classified the signals into three groups: (1) short duration (<1 min) impulses generated by degassing explosions at the vent; (2) extended degassing chugging events with a duration 2–5 min containing well-defined integer overtones (1–5 Hz) and variable higher frequency content; (3) extended degassing events that contain significant energy above 5 Hz. We selected 12 events from groups 2 and 3 for our analysis that had a duration of at least 90 s and high signal-to-noise ratios. The phase space, which describes the evolution of the behavior of a nonlinear system, was reconstructed using the delay embedding theorem suggested by Takens. The delay time used for the reconstruction was chosen after examining the first zero crossing of the autocorrelation function and the first minimum of the Average Mutual Information (AMI) of the data. In most cases it was found that both methods yielded a delay time of 14–18 samples (0.112–0.144 s) for group 2 and 5 samples (0.04 s) for group 3 events. The sufficient embedding dimension was estimated using the false nearest neighbors method which had a value of 4 for events in group 2 and was in the range 5–7 for events in group 3. Based on these embedding parameters it was possible to calculate the correlation dimension of the resulting attractor, as well as the average divergence rate of nearby orbits given by the largest Lyapunov exponent. Events in group 2 exhibited lower values of both the correlation dimension (1.8–2.6) and largest Lyapunov exponent (0.013–0.022) in comparison with the events in group 3 where the values of these quantities were in the range 2.4–3.5 and 0.029–0.043, respectively. Theoretically, a nonlinear oscillation described by the equation ++g(x)=fcost can generate deterministic signals with characteristics similar to those observed in groups 2 and 3 as the values of the parameters ,,f, are drifting, causing instability of orbits in the phase space.  相似文献   

松辽盆地徐家围子断陷火山岩气藏天然气成因类型和气源对比   总被引：6，自引：0，他引：6       下载免费PDF全文

刘伟  刘安英 《地质科学》2009,44(2):571-584

松辽盆地徐家围子断陷发育营城组火山岩气藏.钻井统计、地球化学特征及天然气组份分析和碳同位素研究表明徐中和徐东地区天然气源岩有机质偏腐泥型,生气潜力更大.对主力源岩层沙河子组和次要源岩层营城组源岩分布有了新的认识.对营城组天然气的烃类气体和CO₂气的来源进行对比和探讨,认为烃类气受气源的控制,CO₂气藏受深大断裂的控制,与火山岩分布关系不大.连通地幔的气藏中,也没有发现无机烃类气体聚集.徐家围子断陷营城组天然气以烃类气占绝对优势,而且主要为甲烷,二氧化碳成藏并不普遍.天然气甲烷成因类型以煤型气为主,甲烷碳同位素变化范围较小.乙烷、丙烷和丁烷碳同位素均有较大的变化范围,而且具有较好的相关性,说明母质类型多样,乙烷、丙烷和丁烷具有相同的来源.含量大于50%的二氧化碳来源于地幔,属无机成因.含量小于50%的二氧化碳既有无机成因,也有有机成因.  相似文献   

松辽盆地北部安达断陷营城组火山岩岩相的地震识别   总被引：4，自引：0，他引：4       下载免费PDF全文

于晶  刘大锰  文瑞霞  金圣爱 《地质科学》2009,44(2):595-604

安达断陷营城组的火山岩岩相分为火山通道相、爆发相、溢流相、次火山岩相和火山-沉积相,每种火山岩岩相的地震特征各不相同.根据各种岩相的地震反射特征,逐条测线解释出火山岩相,结合相干体技术和振幅属性预测了安达断陷内研究区的火山岩岩相分布,圈出3个爆发相发育区.据此讨论了地震识别方法在识别火山岩岩相和火山岩储层物性中的应用.  相似文献   

2021年3—5月全球火山活动简报     

关升  康建红  贾若  顾国辉 《中国地震》2021,37(3):745-748

正1)吉林省地震局,长春1301172)中国地震局火山研究所,长春130117  相似文献   

Vortical mechanism for generation of astrophysical jets     

M. G. Abrahamyan 《Astrophysics》2008,51(2):163-180

A vortical mechanism for generation of astrophysical jets is proposed based on exact solutions of the hydrodynamic equations with a generalized Rankine vortex. It is shown that the development of a Rankine vortex in the polar layer of a rotating gravitating body creates longitudinal fluxes of matter that converge toward the vortex trunk, providing an exponential growth in the angular rotation velocity of the trunk and a pressure drop on its axis. The increased rotational velocity of the vortex trunk and the on-axis pressure drop cease when the discontinuity in the azimuthal velocity at the surface of the trunk reaches the sound speed. During this time, ever deeper layers of the gravitating body are brought into the vortical motion, while the longitudinal velocity of the flow along the vortex trunk builds up, producing jet outflows of mass from its surface. The resulting vortices are essentially dissipationless. Dedicated to the 100-th birthday of Academician V. A. Ambartsumyan __________ Translated from Astrofizika, Vol. 51, No. 2, pp. 201–218 (May 2008).  相似文献   

春风油田石炭系火山岩油气层综合判识研究     

庄圆  杨凤丽 《新疆地质》2019,(2):231-236

火山岩油气藏是一种特殊类型油气藏,受岩性、岩相、储集空间类型等因素影响较大。常规测井仅能对储层进行评价,录井仅能对岩性及油气显示进行评价。利用测录井资料无法快速判识油气层现状,制约了现场完井方式及试油方案的及时决策,并影响钻井周期、成本及对区块的潜力评价。通过岩心描述、镜下薄片储集空间及含油性观察,结合测井解释和试油结果,总结了春风油田石炭系火山岩油藏岩石类型及含油性特征;火山岩储集空间类型、影响因素、识别方法及物性有效性;孔隙、裂缝等储集空间有效性电性识别方法;建立了春风油田石炭系油气层综合判识准则。本次研究可快速对该区石炭系完钻探井进行油气层综合判识,指导现场完井方式决策,提高勘探效益。  相似文献   

Paleoproterozoic volcanic rocks in the southern margin of the North China Craton,central China:Implications for the Columbia supercontinent   总被引：1，自引：0，他引：1  

Changming Wang  Xinyu He  Emmanuel John M.Carranza  Chengmin Cui 《地学前缘(英文版)》2019,10(4):1543-1560

The volcanic rocks of the Xiong'er Group are situated in the southern margin of the North China Craton(NCC).Research on the Xiong er Group is important to understand the tectonic evolution of the NCC and the Columbia supercontinent during the Paleoproterozoic.In this study,to constrain the age of the Xiong'er volcanic rocks and identify its tectonic environment,we report zircon LA-ICP-MS data with Hf isotope,whole-rock major and trace element compositions and Sr-Nd-Pb-Hf isotopes of the volcanic rocks of the Xiong'er Group.The Xiong'er volcanic rocks mainly consist of basaltic andesite,andesite.dacite and rhyolite,with minor basalt.Our new sets of data combined with those from previous studies indicate that Xiong'er volcanism should have lasted from 1827 Ma to 1746 Ma as the major phase of the volcanism.These volcanics have extremely low MgO.Cr and Ni contents,are enriched in LREEs and LILEs but depleted in HFSEs(Nb,Ta,and Ti),similar to arc-related volcanic rocks.They are characterized by negative zircon ε_(Hf)_(t) values of-17.4 to 8.8,whole-rock initial ~(87)Sr/~(86)Sr values of 0.7023 to 0.7177 andε_(Nd)(t) values of-10.9 to 6.4.and Pb isotopes(~(206)Pb/~(204)Pb =14.366-16.431,~(207)Pb/~(204)Pb =15.106-15.371,~(208)Pb/~(204)Pb= 32.455-37.422).The available elemental and Sr-Nd-Pb-Hf isotope data suggest that the Xiong'er volcanic rocks were sourced from a mantle contaminated by continental crust.The volcanic rocks of the Xiong'er Group might have been generated by high-degree partial melting of a lithospheric mantle that was originally modified by oceanic subduction in the Archean.Thus,we suggest that the subduction-modified lithospheric mantle occurred in an extensional setting during the breakup of the Columbia supercontinent in the Late Paleoproterozoic,rather than in an arc setting.  相似文献