From stormy seas to the doldrums: The challenges of navigating towards an ecologically coherent marine protected area network through England's Marine Conservation Zone process     

《Marine Policy》2016

There is an on-going process to establish Marine Conservation Zones (MCZs) in England, to form part of a coherent and representative network of marine protected areas under national and EU legislation. From 2009 to 2011, the MCZ process included strong participatory elements. Four regional multi-sector stakeholder groups developed MCZ recommendations collaboratively, in line with ecological guidance provided by the Government's nature conservation advisers. This guidance was based on Government policy principles, including that MCZs should be designated based on ‘best available evidence’. This paper analyses the multi-dimensional conflicts that emerged within the stakeholder group in south-west England, which were magnified by uncertainty about future MCZ management. In September 2011, after working through these conflicts through trade-offs and negotiations, the stakeholder groups jointly recommended 127 MCZs to Government. The process subsequently shifted to a top-down approach, with further stakeholder engagement limited to bilateral consultation. There was a concurrent shift in policy, from a broad-scale network-level focus towards single-feature conservation. A lengthy series of evidence reviews concluded that the existing evidence at the time was insufficient to progress with the designation of most sites, marking a clear departure from the policy principle of proceeding with the designation of a representative network based on ‘best available evidence’, and effectively undermining the work carried out by stakeholder groups. Though MCZ designation was originally timetabled for 2012, in November 2013 just 27 of the recommended 127 MCZs were designated in a first tranche. At the time, no clear timetable was in place for subsequent tranches.  相似文献   

The Mesoproterozoic mantle plume beneath the northern part of the Siberian craton     

《Russian Geology and Geophysics》2016,57(5):672-686

The study of the Mesoproterozoic (1473 ± 24 Ma) dolerites of the Olenek uplift of the Siberian craton basement has shown their petrologic and geochemical similarity to typical OIB produced with participation of a mantle plume. The dolerites are characterized by variations in the geochemical composition explained by different degrees of melting of the same source. A conclusion is drawn that the parental melts of the rocks were slightly modified by crustal contamination, as evidenced from their Nd isotope composition (£_Nd(T) = + 0.6 to − 0.8) and the presence of inherited zircons of four ages (2564, 2111, 2053, and 1865 Ma). Since the Siberian craton in the structure of the Nuna supercontinent (Columbia) was located relatively close to the Baltic continent and the Congo and Sao Francisco cratons, we assume that the Early Mesoproterozoic mafic intrusions (1500–1470 Ma) of all these cratons belong to the same large igneous province (LIP). The province formation was related to the activity of superplume (or mantle hot field), which supplied mantle matter to the lithosphere basement. The superplume core was probably located beneath the northern part of the Siberian craton, where basites are compositionally most similar to the primary mantle source.  相似文献   

Thermo-mechanical modeling of the obduction process based on the Oman Ophiolite case     

《Gondwana Research》2016

Obduction emplaces regional-scale fragments of oceanic lithosphere (ophiolites) over continental lithosphere margins of much lower density. For this reason, the mechanisms responsible for obduction remain enigmatic in the framework of plate tectonics. We present two-dimensional (2D) thermo-mechanical models of obduction and investigate the possible dynamics and physical controls of this process. Model geometry and boundary conditions are based on available geological and geochronological data and numerical modeling results are validated against petrological and structural observations of the Oman (Semail) Ophiolite. Our model reproduces the stages of oceanic subduction initiation away from the Arabian margin, the emplacement of the Oman Ophiolite on top of it, and the domal exhumation of the metamorphosed margin through the ophiolitic nappe. A systematic study indicates that 350–400 km of bulk shortening provides the best fit for both maximum pressure–temperature conditions of the metamorphosed margin (1.5–2.5 GPa/450–600 °C) and the dimension of the ophiolitic nappe (~ 170 km width). Our results confirm that a thermal anomaly located close to the Arabian margin (~ 100 km) is needed to initiate obduction. We further suggest that a strong continental basement rheology is a prerequisite for ophiolite emplacement.  相似文献   

Late Triassic alkaline complex in the Sulu UHP terrane: Implications for post-collisional magmatism and subsequent fractional crystallization     

《Gondwana Research》2016

Continental subduction and its interaction with overlying mantle wedge are recognized as fundamental solid earth processes, yet the dynamics of this system remains ambiguous. In order to get an insight into crust–mantle interaction triggered by partial melting of subudcted continental crust during its exhumation, we carried out a combined study of the Shidao alkaline complex from the Sulu ultrahigh pressure (UHP) terrane. The alkaline complex is composed of shoshonitic to ultrapotassic (K₂O: 3.4–9.3 wt.%) gabbro, pyroxene syenite, amphibole syenite, quartz syenite, and granite. Field studies suggest that the mafic rocks are earlier than the felsic ones in sequence. LA-ICPMS zircon U–Pb dating on them gives Late Triassic ages of 214 ± 2 to 200 ± 3 Ma from mafic to felsic rocks. These ages are slightly younger than the Late Triassic ages (225–210 Ma) of the felsic melts from partial melting of the Sulu UHP terrane during exhumation. The alkaline rocks have wide ranges of SiO₂ (49.7–76.7 wt.%), MgO (8.25–0.03 wt.%), Ni (126.0–0.07 ppm), and Cr (182.0–0.45 ppm) contents. The contents of MgO, total Fe₂O₃, CaO, TiO₂ and P₂O₅ decrease with increasing SiO₂ contents. The contents of Na₂O, K₂O, and Al₂O₃ increase from gabbro to amphibole syenite, and decrease from amphibole syenite to granite, respectively. The alkaline rocks have characteristics of an arc-like pattern in trace element distribution, e.g., enrichment of LREE, LILE (Rb and Ba), Th and U, depletion of HFSE (Nb, Ta, P and Ti), and positive Pb anomalies. From the mafic rocks to the felsic rocks, the (La/Yb)_N ratios and the contents of the total REE, Sr and Ba decrease but the Rb contents increase. The alkaline rocks with high SiO₂ contents also display features of an A2-type granitoids, e.g., high contents of total alkalis, Zr and Nb and high ratios of Fe₂O₃^T/MgO, Ga/Al, Yb/Ta and Y/Nb, suggesting a post-collisional magmatism during exhumation of the Sulu UHP terrane. The alkaline rocks have homogeneous initial ⁸⁷Sr/⁸⁶Sr ratios (0.7058–0.7093) and negative ε_Nd(t) values (− 18.6 to − 15.0) for whole-rock. The Sr–Nd isotopic data remain almost unchanged with varying SiO₂ and MgO contents, suggesting a fractional crystallization (FC) process from the same parental magma. Our studies suggest a crust–mantle interaction in continental subduction interface as follows: (1) hydrous felsic melts from partial melting of subducted continental crust during its exhumation metasomatized the overlying mantle wedge to form a K-rich and amphibole-bearing mantle; (2) partial melting of the enriched lithospheric mantle generated the Late Triassic alkaline complex under a post-collisional setting; and (3) the alkaline magma experienced subsequent fractionational crystallization mainly dominated by olivine, clinopyroxene, plagioclase and alkali feldspar.  相似文献   

From convergent plate margin to arc–continent collision: Formation of the Kenting Mélange,Southern Taiwan     

《Gondwana Research》2016

The Kenting Mélange on the Hengchun Peninsula, Taiwan, formed through tectonic shearing of subduction complex lithologies, probably within the plate boundary subduction channel between the Eurasian and Philippine Sea plates, with further deformation and exhumation in the Pliocene–Pleistocene during arc–continent collision. Field relations reveal a structural gradation from normal stratified turbidite sequence (Mutan Formation) through broken formation to highly sheared Kenting Mélange containing allochthonous polygenic blocks. This gradation is consistent with an increase of average vitrinite reflection values from ~ 0.72% in the Mutan Formation through ~ 0.93% in the broken formation to ~ 0.99% in the mélange, suggesting temperatures of at least 140 °C during formation of the Kenting Mélange. Zircons from gabbro in the Kenting Mélange are dated as 25.46 ± 0.18 Ma, which together with geochemical data constrains the source to South China Sea oceanic lithosphere. In combination with the field relationships, vitrinite reflectance values, microfossil stratigraphy, and offshore geophysical data from S and SE Taiwan, we propose that the Kenting Mélange initially formed at the subduction plate boundary from off-scraped trench deposits. Minor Plio–Pleistocene microfossils (< 5%) occur within the mélange in proximity to slope basin of equivalent age and were likely sheared into the mélange during out-of-sequence thrusting associated with active arc–continent collision, which in the Hengchun Peninsula commenced after 6.5 Ma.  相似文献   

Comparison of water-level,extensometric, DInSAR and simulation data for quantification of subsidence in Murcia City (SE Spain)     

S. Tessitore  J. A. Fernández-Merodo  G. Herrera  R. Tomás  M. Sanabria  J. Duro  J. Mulas  D. Calcaterra 《Hydrogeology Journal》2016,24(3):727-747

Subsidence due to groundwater overexploitation has been recognized in the metropolitan area of Murcia (25 km²) in south-eastern Spain since the early 1990s. Previous published works have focused their attention on land subsidence that occurred during the drought period between 1995 and 2008. This work first analyzes the groundwater recovery that has occurred since 2008 and then determines the kind of associated ground deformation detected by the new extensometric data. Subsequently, subsidence time series are computed on 24 geotechnical boreholes scattered throughout the study area by means of a hydro-mechanical finite element code and a linear-elastic constitutive law. A spatio-temporal interpolation of the numerically modeled surface displacements is performed over the whole domain and compared with extensometers and DInSAR-derived displacement maps in two different periods: the drought period from 2004 to 2008, and the recovery period from 2008 to 2012. In spite of the limited information on the geomechanical parameters characterizing the modelled geological formations, the proposed approach is able to discriminate areas where the soils have an elastic behavior (small differences in the comparisons) or an elasto-plastic behavior (large differences in the comparisons). This zonation enhances the understanding of the subsidence phenomenon in Murcia City and could prevent, from a quantitatively point of view, future severe subsidence due to aquifer overexploitation.  相似文献   

Middle Permian U–Pb zircon ages of the “glacial” deposits of the Atkan Formation,Ayan-Yuryakh anticlinorium,Magadan province,NE Russia: Their significance for global climatic interpretations     

《Gondwana Research》2016

The Atkan Formation in the Ayan-Yuryakh anticlinorium, Magadan province, northeastern Russia, is of great interest because of the occurrence of deposits of apparent “dropstones” and “ice rafted debris” that have been previously interpreted as glacial. Two high-precision U–Pb zircon ages, one for an intercalated volcanic tuff (262.5 ± 0.2 Ma) and the other for a boulder clast (269.8 ± 0.1 Ma) within a diamictite of the Atkan Formation, constrain the age of the Atkan Formation as Guadalupian (middle Permian). Sedimentologic study of the Atkan Formation casts doubt on the glacial nature of the diamictites. Deposition of rocks of the Atkan Formation temporally correlates with the Capitanian interglacial event in the southern hemisphere that recently was calibrated with high precision CA-TIMS. The previously proposed climate proxy record based upon warm-water foraminifera, which corresponds closely to global climate fluctuations, is compared with the glacial record of eastern Australia and indicates that the Capitanian was a time of globally warm climate. The sedimentology of Atkan Formation, the record of diversification of both fusulinids and rugosa corals, global sea-water temperature, and sea-level fluctuations agree well with high latitude paleoclimate records in northeastern Russia and eastern Australia. Major components of the Atkan Formation, the volcanic rocks, are syngenetic with the sedimentation process. The volcanic activity in the nearby regions during middle–late Permian was quite extensive.  相似文献   

Using a Thermal Proxy to Examine Sediment–Water Exchange in Mid-Continental Shelf Sandy Sediments     

William B. Savidge  Alicia Wilson  Gwendolyn Woodward 《Aquatic Geochemistry》2016,22(5-6):419-441

Fluid exchange across the sediment–water interface in a sandy open continental shelf setting was studied using heat as a tracer. Summertime tidal oscillation of cross-shelf thermal fronts on the South Atlantic Bight provided a sufficient signal at the sediment–water interface to trace the advective and conductive transport of heat into and out of the seabed, indicating rapid flushing of ocean water through the upper 10–40 cm of the sandy seafloor. A newly developed transport model was applied to the in situ temperature data set to estimate the extent to which heat was transported by advection rather than conduction. Heat transported by shallow 3-D porewater flow processes was accounted for in the model by using a dispersion term, the depth and intensity of which reflected the depth and intensity of shallow flushing. Similar to the results of past studies in shallower and more energetic nearshore settings, transport of heat was greater when higher near-bed velocities and shear stresses occurred over a rippled bed. However, boundary layer processes by themselves were insufficient to promote non-conductive heat transport. Advective heat transport only occurred when both larger boundary layer stresses and thermal instabilities within the porespace were present. The latter process is dependent on shelf-scale heating and cooling of bottom water associated with upwelling events that are not coupled to local-scale boundary layer processes.  相似文献   

P–T–t evolution of eclogite/blueschist facies metamorphism in Alanya Massif: time and space relations with HP event in Bitlis Massif,Turkey     

Mete Çetinkaplan  Amaury Pourteau  Osman Candan  O. Ersin Koralay  Roland Oberhänsli  Aral I. Okay  Fukun Chen  Hüseyin Kozlu  Fırat Şengün 《International Journal of Earth Sciences》2016,105(1):247-281

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Effect of antecedent-hydrological conditions on rainfall triggering of debris flows in ash-fall pyroclastic mantled slopes of Campania (southern Italy)     

E. Napolitano  F. Fusco  R. L. Baum  J. W. Godt  P. De Vita 《Landslides》2016,13(5):967-983

Mountainous areas surrounding the Campanian Plain and the Somma-Vesuvius volcano (southern Italy) are among the most risky areas of Italy due to the repeated occurrence of rainfall-induced debris flows along ash-fall pyroclastic soil-mantled slopes. In this geomorphological framework, rainfall patterns, hydrological processes taking place within multi-layered ash-fall pyroclastic deposits and soil antecedent moisture status are the principal factors to be taken into account to assess triggering rainfall conditions and the related hazard. This paper presents the outcomes of an experimental study based on integrated analyses consisting of the reconstruction of physical models of landslides, in situ hydrological monitoring, and hydrological and slope stability modeling, carried out on four representative source areas of debris flows that occurred in May 1998 in the Sarno Mountain Range. The hydrological monitoring was carried out during 2011 using nests of tensiometers and Watermark pressure head sensors and also through a rainfall and air temperature recording station. Time series of measured pressure head were used to calibrate a hydrological numerical model of the pyroclastic soil mantle for 2011, which was re-run for a 12-year period beginning in 2000, given the availability of rainfall and air temperature monitoring data. Such an approach allowed us to reconstruct the regime of pressure head at a daily time scale for a long period, which is representative of about 11 hydrologic years with different meteorological conditions. Based on this simulated time series, average winter and summer hydrological conditions were chosen to carry out hydrological and stability modeling of sample slopes and to identify Intensity-Duration rainfall thresholds by a deterministic approach. Among principal results, the opposing winter and summer antecedent pressure head (soil moisture) conditions were found to exert a significant control on intensity and duration of rainfall triggering events. Going from winter to summer conditions requires a strong increase of intensity and/or duration to induce landslides. The results identify an approach to account for different hazard conditions related to seasonality of hydrological processes inside the ash-fall pyroclastic soil mantle. Moreover, they highlight another important factor of uncertainty that potentially affects rainfall thresholds triggering shallow landslides reconstructed by empirical approaches.  相似文献