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Tectonic setting of the Azores Plateau deduced from a OBS survey 总被引:1,自引:0,他引:1
Miranda J.M. Mendes Victor L.A. Simões J.Z. Luis J.F. Matias L. Shimamura H. Shiobara H. Nemoto H Mochizuki H. Hirn A. Lépine J.C. 《Marine Geophysical Researches》1998,20(3):171-182
The studies of Azores seismicity generally show shocks with either normal faulting or right-lateral strike-slip along the ESE direction, compatible with a eastward relative motion of the Eurasian (EU) relative to the African (AF) plate. However, the 1 January 1980 earthquake was interpreted as a clear left-lateral strike-slip shock along the N150E direction. This pattern is difficult to explain in terms of the relative motion between the EU, AF and North American (NA) plates: all available models for the present day movement of this triple junction fail to explain the regional variability in the stress conditions of the area. Here we present data from a 34-day long Ocean Bottom Seismograph array deployment. We show that the seismicity is distributed along a band aligned with the island chain itself, and is concentrated along several faults with an approximate N150E strike, cutting the Azores plateau in all the area covered by the OBS network. The combination of these new results with other geophysical data permits us to conclude that the tectonic setting of the Azores plateau is characterised by the existence of two sets of faults, in the N120E and N150E directions, defining several crustal blocks, whose relative motion accommodates the interaction of the three megaplates. The deformation of these tectonic blocks is probably driven by the shear between the EU and AF plates. This model explains well the spatial variability of the stress conditions in the Azores domain, the combination of dextral and sinistral strike slip mechanisms and the observed seismotectonics of the Azores islands. 相似文献
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Anthony Hildenbrand Pedro Madureira Fernando Ornelas Marques Inês Cruz Bernard Henry Pedro Silva 《Earth and Planetary Science Letters》2008,273(3-4):289-298
New K/Ar dating and geochemical analyses have been carried out on the WNW–ESE elongated oceanic island of S. Jorge to reconstruct the volcanic evolution of a linear ridge developed close to the Azores triple junction. We show that S. Jorge sub-aerial construction encompasses the last 1.3 Myr, a time interval far much longer than previously reported. The early development of the ridge involved a sub-aerial building phase exposed in the southeast end of the island and now constrained between 1.32 ± 0.02 and 1.21 ± 0.02 Ma. Basic lavas from this older stage are alkaline and enriched in incompatible elements, reflecting partial melting of an enriched mantle source. At least three differentiation cycles from alkaline basalts to mugearites are documented within this stage. The successive episodes of magma rising, storage and evolution suggest an intermittent re-opening of the magma feeding system, possibly due to recurrent tensional or trans-tensional tectonic events. Present data show a gap in sub-aerial volcanism before a second main ongoing building phase starting at about 750 ka. Sub-aerial construction of the S. Jorge ridge migrated progressively towards the west, but involved several overlapping volcanic episodes constrained along the main WNW–ESE structural axis of the island. Mafic magmas erupted during the second phase have been also generated by partial melting of an enriched mantle source. Trace element data suggest, however, variable and lower degrees of partial melting of a shallower mantle domain, which is interpreted as an increasing control of lithospheric deformation on the genesis and extraction of primitive melts during the last 750 kyr. The multi-stage development of the S. Jorge volcanic ridge over the last 1.3 Myr has most likely been greatly influenced by regional tectonics, controlled by deformation along the diffuse boundary between the Nubian and the Eurasian plates, and the increasing effect of sea-floor spreading at the Mid-Atlantic Ridge. 相似文献
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豫陕鄂交界区县域综合发展水平测度及障碍因子分析 总被引:1,自引:0,他引:1
以豫陕鄂交界区为研究对象,测度2000—2017年豫陕鄂交界区县域的综合发展水平,探析其空间分异特征、演化趋势和障碍因素。结果表明:① 2000—2017年,豫陕鄂交界区县域综合发展水平逐步提升,年均增速为6.08%,县域间发展的空间差异逐渐增大;② 县域综合发展水平在空间上呈正相关性,热点显著区呈现由东南部向西南部再向东南部迁移变化特征,冷点显著区在2005年前主要分布在安康市和商洛市,之后主要聚集在南阳市;③ 人文和经济要素为中度和中高障碍水平,资源和环境要素为极低和低障碍水平;随着时间的推移,障碍因子在不同县域空间阻力的分异特征更加显著。④ 豫陕鄂交界区县域发展空间阻力模式可划分为3种类型,其中人文资源要素制约型是主要的空间阻力模式。最后,基于不同空间阻力模式特征解析,提出了分区发展策略。 相似文献
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史生才 《紫金山天文台台刊》2003,(1)
为了研制亚毫米波射电天文用超导SIS(超导 -绝缘体 -超导 )接收机 ,我们重点开展了如下研究 ,1 )Nb超导SIS结在其能隙频率附近的量子混频特性 ,及其结合高能隙超导薄膜 (NbTiN)和高电导率金属薄膜 (Al)分布结阵在 780 - 950GHz频率区间的量子混频特性 ;2 )亚毫米波超导混频器嵌入阻抗的数值和实验表征 ;3)高电流密度小面积Nb超导SIS结的制备和特性表征 ;4)一个 60 0 - 72 0GHz超导SIS混频器的研制和特性表征。本文详细介绍了相关的数值分析和实验测量结果。 相似文献
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The Woodlark triple junction region, a topographically and structurally complex triangular area of Quaternary age, lies east of Simbo Ridge and southwest of the New Georgia island group, Solomon Islands, at the junction of the Pacific, Australian and Solomon Sea plates. SeaMARC II side-scan imagery and bathymetry in conjunction with seismic reflection profiles, 3.5 kHz records, and petrologic, magnetic and gravity data show that the active Woodlark spreading centre does not extend into this region.South of the triple junction region, the Woodlark spreading centre reoriented at about 2 Ma into a series of short ESE-trending segments. These segments continued to spread until about 0.5 Ma, when the lithosphere on their northern sides was transferred from the Solomon Sea plate to the Australian plate. Simultaneously the Simbo transform propagated northwards along the western side of the transferred lithosphere, forming a trench-trench-transform triple junction located NNW of Simbo island and a new leaky plate boundary segment that built Simbo Ridge.As the Pacific plate approached, the area east of northern Simbo Ridge was tilted northwards, sheared by dominantly right-lateral faults, elevated, and intruded by arc-related magmas to form Ghizo Ridge. Calc-alkalic magmas sourced beneath the Pacific plate built three large strato-volcanic edifices on the subducting Australian plate: Simbo at the northern end of Simbo Ridge, and Kana Keoki and Coleman seamounts on an extensional fracture adjoining the SE end of Ghizo Ridge.A sediment drape, supplied in part from Simbo and Kana Keoki volcanoes, mantles the east-facing slopes of northern Simbo and Ghizo Ridges and passes distally into sediment ponded in the trench adjoining the Pacific plate. As a consequence of plate convergence, parts of the sediment drape and pond are presently being deformed, and faults are dismembering Kana Keoki and Coleman seamounts.The Woodlark system differs from other modern or Tertiary ridge subduction systems, which show wide variation in character and behaviour. Existing models describing the consequences of ridge subduction are likely to be predictive in only a general way, and deduced rules for the behaviour of oceanic lithosphere in ridge subduction systems may not be generally applicable. 相似文献
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目的 探讨阿霉素性心肌病大鼠发生心律失常的发病机制。方法 健康wistar雄性大鼠20只,体重200g,适应周围环境1周后,随机将20只wistar雄性大鼠分为对照组(n=10)和阿霉素(ADR)组(n=10)。ADR组的大鼠在1周内进行3次腹腔注射ADR 2mg/kg;同时对照组则进行3次腹腔注射0.9%NaCl (2ml/kg),停药后让两组大鼠自由饮食4周。7周后对两组大鼠行心脏彩超检测,左心室舒张末径(LVEDd)与左心室收缩末期内径(LVESd)及左心室射血分数(LVEF),行VG染色观察各组大鼠心肌纤维化情况;扫描电镜染色观察左心室心肌细胞闰盘病理学变化;两组大鼠心肌结缔组织生长因子(CTGF)、转化生长因子β1(TGF-β1)、N型钙黏蛋白(N-cad)、桥粒芯糖蛋白(DSG2)表达应用ELISA法检测;采用Western blot法检测两组大鼠的心肌细胞Cx40 、Cx43、p-Cx43蛋白表达。结果 与对照组相比,阿霉素组大鼠明显出现心室重构,并易出现心律失常;电镜下观察ADR组大鼠心肌细胞闰盘破损严重,间隙增宽,VG染色显示ADR组大鼠病理积分明显高于对照组(P<0.05);ADR组大鼠相较于对照组大鼠心室肌中CTGF、TGF-β1的表达升高显著,N-cad、DSG2、Cx40、Cx43及p-Cx43的表达明显减低(P<0.05)。结论 ADR组大鼠可能由于心室肌细胞纤维化、闰盘结构受损、缝隙连接重构等原因导致心律失常。 相似文献
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班公湖-怒江结合带中段上三叠统确哈拉群与下伏岩系角度不整合关系的发现及意义 总被引:9,自引:9,他引:9
在位于班公湖-怒江结合带中段的西藏班戈县白拉乡拉纳沟一带,首次发现上三叠统确哈拉群与下伏岩系呈角度不整合接触。该接触关系的发现,证实在班公湖-怒江结合带内有古特提斯蛇绿岩的存在,说明以班公湖-怒江结合带为代表的新特提斯域是在古特提斯域基础上继承和发展起来的。 相似文献