Deformation of a young salt giant: regional topography of the Red Sea Miocene evaporites   总被引：1，自引：0，他引：1       下载免费PDF全文

Neil C. Mitchell  Marco Ligi  Peter Feldens  Christian Hübscher 《Basin Research》2017,29(Z1):352-369

The deformational behaviour of ‘salt giants’ during and shortly after their deposition is difficult to decipher in ocean margin settings where the original evaporites have been deeply buried and strongly mobilized. Here, we examine seismic reflection data from the Red Sea, where evaporites deposited until the end of the Miocene (~5.3 Ma), are generally covered by only 200–300 m of low‐density sediments and where the presence of an axial spreading centre allows us to observe how they have responded to a varied configuration of underlying basement. The regional morphology of the S‐reflection, representing the evaporite surface, is mapped out from seismic data from 13 cruises. The S‐reflection is locally rugged and commonly angular. It is either underlain by layered reflectivity, suggestive of layered evaporite beds, or by more transparent seismic character, suggestive of massive halite. On average, the depth of the reflection on the flanks of the axial rift systematically declines from 700 to 1100 m below sea level (mbsl) going northwards from 16 to 23°N. In the central Red Sea, the S‐reflection has 100‐ to 200‐m‐deep depressions, extending towards the coasts in places. In the southern Red Sea, the S‐reflection forms a surface at 300–800 mbsl that appears less disrupted. We suggest that the evaporites originally had a flat, horizontal surface at the end of the Miocene and have subsequently been distorted by isostatic effects and axial rifting, which in turn promoted evaporite flowage. Off‐axis evaporite depressions correspond with flows identified with multibeam sonar. Furthermore, across‐rift lows in Bouguer gravity anomalies represent valleys in the underlying basement. The off‐axis evaporite depressions overlie those valleys, as would be expected if halokinetic movements were greatest where the evaporites are locally thick, leading to deflation of the evaporite surface. The thickness of post‐Miocene sediment, also mapped out as part of this procedure, confirms the generally pelagic nature of this interval and increases on average from ~250 to 300 m from the central to the southern Red Sea, mimicking the variation in pelagic productivity observed in the present water column.  相似文献   

Robustness and the Paradox of Bridging Organizations: The Exit Problem in Regional Water Governance Networks in Central America     

Jacob Hileman  Marco T. A. Bastos  Mark Lubell 《社会与自然资源》2018,31(6):683-697

Bridging organizations facilitate a range of governance processes, including cooperation and social learning, and are theorized to be a key component of robust governance systems. In this article, we use node removal simulations to test structural hypotheses of robustness in a regional water governance network in Central America. We investigate the response of network measures supporting core governance processes to the targeted removal of bridging organizations and other actors, which we compare to random and centrality-based simulations. The results indicate removing bridging organizations has a greater impact on the network than any other type of actor, suggesting bridging organizations are critical to the robustness of the governance system. Furthermore, network structures supporting cooperation may be less robust than structures facilitating social learning. We conclude with policy implications of the research findings as they relate to the exit problem in governance systems with a large presence of international development actors.  相似文献   

中等传输距离下的无线功率传输链路第1部分:实现工作状态最优化     

Alessio De ANGELIS  Marco DIONIGI  Paolo CARBONE  Mauro MONGIARDO  车文荃  王清华  Franco MASTRI  Giuseppina MONTI 《南京气象学院学报》2017,9(1):64-72

中程无线功率传输（WPT）可以采用几种不同的方式实现,如通过电感或电容耦合、谐振或非谐振网络实现.本文主要研究了通过感应耦合谐振器实现的WPT链路,而且只着重研究了利用2个谐振器的链路（直接链路）并工作在主谐振频率下的情况.研究结果表明,当工作在主谐振频率下,可以根据网络参数来对传输效率或负载功率进行优化.  相似文献   

Unravelling the evolution of an Alpine to post-glacially active fault in the Swiss Alps     

Michaela Ustaszewski  Marco Herwegh  Alastair F. McClymont  O. Adrian Pfiffner  Robyn Pickering  Frank Preusser 《Journal of Structural Geology》2007,29(12):1943-1959

The Gemmi fault is a prominent NW–SE striking lineament that crosses the Gemmi Pass in the central Swiss Alps. A multidisciplinary investigation of this structure that included geological mapping, joint profiling, cathodoluminescence and scanning electron microscopy, stable isotope measurements, luminescence- and U-TH-dating, 3D ground penetrating radar (GPR) surveying and trenching reveals a history of fault movements from the Miocene to the Holocene. The main fault zone comprises a 0.5–3 m thick calcite cataclasite formed during several cycles of veining and brittle deformation. Displaced Cretaceous rock layers show an apparent dextral slip of 10 m along the fault.A detailed study of a small sediment-filled depression that crosses the fault provides evidence for a post-glacial reactivation of the fault. A trench excavated across the fault exposed a Late-Glacial-age loess layer and late Holocene colluvial-like slope-wash deposits that showed evidence for fault displacement of a few centimeters, indicating a recent strike-slip reactivation of the fault. Focal mechanisms of recent instrumentally recorded earthquakes are consistent with our findings that show that the fault at the Gemmi Pass, together with other parallel faults in this area, may be reactivated in today's stress field. Taking together all the observations of its ancient and recent activity, the Gemmi fault can be viewed as a window through geological space and time.  相似文献   

M4–18: the planetary nebula and its WC10 central star     

Orsola De Marco  Paul A. Crowther 《Monthly notices of the Royal Astronomical Society》1999,306(4):931-942

We present a detailed analysis of the planetary nebula M4–18 (G146.7+07.6) and its WC10-type Wolf–Rayet (WR) central star, based on high‐quality optical spectroscopy (WHT/UES, INT/IDS, WIYN/DensPak) and imaging ( HST /WFPC2). From a non-LTE model atmosphere analysis of the stellar spectrum, we derive T _eff=31 kK,     v _∞=160 km s⁻¹ and abundance number ratios of H/He<0.5, C/He=0.60 and O/He=0.10. These parameters are remarkably similar to those of He 2–113 ([WC10]). Assuming an identical stellar mass to that determined by De Marco et al. for He 2–113, we obtain a distance of 6.8 kpc to M4–18 [ E ( B−V )=0.55 mag from nebular and stellar techniques]. This implies that the planetary nebula of M4–18 has a dynamical age of ∼3100 yr, in contrast to ≥270 yr for He 2–113. This is supported by the much higher electron density of the latter. These observations may be reconciled with evolutionary predictions only if [WC]-type stars exhibit a range in stellar masses.
Photoionization modelling of M4–18 is carried out using our stellar WR flux distribution, together with blackbody and Kurucz energy distributions obtained from Zanstra analyses. We conclude that the ionizing energy distribution from the WR model provides the best consistency with the observed nebular properties, although discrepancies remain.  相似文献   

Droughts,food and culture: Ecological change and food security in Africa's later prehistory     

Marco Madella 《Geoarchaeology》2004,19(8):809-811

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Mg-metasomatism of oceanic gabbros and its control on Ti-clinohumite formation during eclogitization   总被引：1，自引：0，他引：1  

Marco Scambelluri  Elisabetta Rampone 《Contributions to Mineralogy and Petrology》1999,135(1):1-17

In the high-pressure meta-ophiolites of Western Liguria (Italy), serpentinized ultramafites host bodies of eclogite, metarodingite and Ti-clinohumite ± Ti-chondrodite-bearing rocks. The latter contain relics of augite, ilmenite and apatite, which suggest derivation from pristine Fe-Ti-rich gabbros. The composition of relict mantle clinopyroxene in the host serpentinites indicates primary depleted peridotite compositions. Compared with their inferred protoliths, the Ti-clinohumite dikelets and the host serpentinites display significant changes in their major and trace element concentrations, indicating element exchange between the two rock systems. In particular, the Fe-Ti-rich gabbros were depleted in CaO and FeO and were strongly enriched in MgO. Analogous compositional variations are shown by altered gabbros enclosed in serpentinized peridotites from the obducted ophiolite sequences of the Northern Apennine. This evidence suggests that the observed Mg-enrichment recorded by the Ti-clinohumite metagabbros occurred in oceanic environments as the result of diffusive exchange between ultramafites and gabbros in presence of fluids related to serpentinization of the ultramafic country rocks. Alteration of the gabbro and concomitant Mg-uptake mostly caused extensive chloritization of the igneous plagioclase. Survival of igneous ilmenite and augite and their reaction with the hydrothermal chlorite during high-pressure metamorphism produced the observed Ti-clinohumite and Ti-chondrodite assemblages. The data presented thus indicate that crystallization of Ti-clinohumite assemblages was facilitated by a stage of oceanic alteration leading to Mg-enrichment of original Fe-Ti-rich gabbros. We suggest that during alteration, Mg-metasomatism occurred prior to rodingitization and was related to the earlier stages of peridotite serpentinization. Survival of oceanic chemical heterogeneities in the Ti-clinohumite rocks, indicates that element mobility during high-pressure recrystallization of these rocks was on a limited scale. This allowed preservation of their pre-subduction alteration features. Received: 13 July 1998 / Accepted: 3 November 1998  相似文献   

A watershed on the Rhine: Changing approaches to international environmental cooperation     

Marco Verweij 《GeoJournal》1999,47(3):453-461

Since the 1950s, the governments of the riparian countries of the Rhine have attempted to protect the ecosystems of the river basin through international cooperation. Before 1987, their relations were unproductive and antagonistic. International programs for the protection of Rhine were far less effective than domestic policies. From 1987 onwards, international cooperation on the protection of the Rhine has been exemplary, and has led the way in domestic and international water protection policies. Many existing frameworks of international relations are not able to offer an adequate account of this wholesale change. In this article, an attempt is undertaken with the help of grid-group theory. This revised version was published online in August 2006 with corrections to the Cover Date.  相似文献   

1990s长江流域降水趋势分析   总被引：2，自引：0，他引：2  

苏布达  姜彤  施雅风  Stefan BECKER  Marco GEMMER 《湖泊科学》2003,15(Z1):38-48

依据国家气象局提供的实测月降水和日降水资料,运用Mann-Kendall(M-K)非参数检验法验证了降水趋势,并通过空间插补法,由点扩展到面,分析了1990s长江流域降水变化特征,发现1990s长江流域降水变化以降水在时间和空间分布上的集中度的增加为主要特点:时间上,年降水的增加趋势以冬季1月和夏季6月降水的集中增加为主;一日降水量大于等于50mm的暴雨日数和暴雨量在1990s也有了较明显的增加.空间上,年降水、夏季降水、冬季降水的增加都以中下游区的增加为主,尤其以鄱阳湖水系、洞庭湖水系的降水增加为主.1990s长江流域春季和秋季降水的减少以5月和9月两个汛期月份的降水减少为主,除金沙江水系和洞庭湖水系等少数地区外,流域大部分地区降水呈减少趋势.上述1990s出现的降水趋势明显与近年来全球变暖背景下长江流域各地区不同的温度及水循环变异有关.  相似文献   

长江流域降水变化及其趋势演变   总被引：1，自引：0，他引：1  

Stefan BECKER  Marco GEMMER  姜彤 《湖泊科学》2003,15(Z1):123-130

本文对中国长江流域降水趋势进行了分析.指出对月降水量而言,20世纪后50年不同区域出现1不胃的降水趋势变化特征.趋势插补法研究表明中国降水时空分布趋势十分明显.对长江流域长期降水资料分析研究指出夏季月份降水时间更集中,而对年降水而言在一些站则表现出明显的周期变化.  相似文献