Classical structural analysis, in combination with new techniques including pyroxene thermobarometry and recrystallized-grain- and subgrain-size paleopiezometry, has been used to deduce the tectonic history of the Vourinos Ophiolite Complex, Greece. Results can be used to infer the variation with depth of differential stress in the upper mantle and indicate that these rocks were subjected to an initial stress level of 10–100 bar over a depth interval from 100 to 40 km, respectively. Subsequently, they underwent mylonitization, associated with stresses of about 2500 bar at 30 km depth. Rocks equilibrated at the deepest levels commonly have the highest structural positions within the ultramafic tectonites and also show appreciable Al depletion. Lack of annealing recrystallization in the mylonitic rocks, together with low stress levels and an abnormally high pyroxene geotherm for the Complex lead to the interpretation of the Complex being the remnant of a mantle diapir, with an overlying magma chamber, located at a spreading ridge. 相似文献
In the South Rifian ridges (SRR), the dominated structures correspond to the faulted anticline characteristic of a foreland orogeny context, front of the Rif Alpine belt. These anticlines correspond to thrust propagation folds. Geometric model of these structures shows that the normal faults have controlled the Mesozoic sedimentation during extensive episodes and participated in determining areas of thrusting during Miocene compressional phases. However, the normal fault strike which is relative to the direction of the shortening determined the geometry of diverse folds whether into the frontal ramps, lateral, or oblique. In the meantime, the systematic fracturing study in the Jurassic limestone beds, in different parts of the folds with axes oriented E-W, NW-SE, and NE-SW, permits to propose a relative fracturing chronology and tries investigating the relationship between folding and fracturing. The three main fracture families, oblique, transversal, and axial, appear simultaneously during the amplification of the fold. The simple shear in the limb contributes the latest to the folding reactivation and the density of the intensification of these microfractures. Likewise, given the important downslope fold limb dip of the ramp propagation folds, theoretically the shear intensity is more important, and micro-fractures are more important in the downslope fold limb, thus the uphill one. 相似文献
As the world’s largest fossil fuels exporter, Russia is one of the key countries for addressing global climate change. However, it has never demonstrated any significant ambitions to reduce greenhouse gas (GHG) emissions. This paper applies ideational research methodology to identify the structural differences in economic, political, and social normative contexts between industrialized fossil fuel importing economies and Russia that lead to the fundamental gap in motivations driving decarbonization efforts. Russia is unlikely to replicate the approach to the green transition and climate policy instruments of energy-importing countries. In order to launch decarbonization in Russia, interested stakeholders need to frame climate policies in Russia differently. Specifically, the framing must address the priority of diversification as a means to adapting the national economy to a new green landscape, the combination of diverse channels for decarbonization, the promotion of energy-efficiency, closer attention to climate-related forest projects, and linkage of climate change with other environmental problems. Moreover, considering Russia’s emissions as a part of the global economic system and shifting from a simplistic national focus on GHG emissions reduction would help coordinate policies through dialogue between exporters and importers of fossil fuel energy-intensive goods, which is essential for the global movement towards a net-zero future.
The Middle Palaeolithic chronology of the Maghreb region of North Africa is poorly known because of the paucity of sites with a long stratigraphy and the limited number of available radiometric dates. In this paper, we report the age-estimates obtained by the TL and OSL methods on sediments and burnt lithic samples from the Rhafas Cave in Eastern Morocco. Our results indicate that the Mousterian is largely earlier than 100 ka, that the latest Mousterian dates to OIS 5 between 90–80 ka and the Mousterian to Aterian transition occurred about 70–80 ka, at the end of OIS 5 or during OIS 4. These dates will be most useful in the construction of a chronological framework of this unique sequence and for the interpretation of paleoenvironmental information. 相似文献
A careful re-examination of the well-known written documents pertaining to the 2,750-year-long historical period of Mount
Etna was carried out and their interpretation checked through the high-accuracy archeomagnetic method (>1,200 large samples),
combined with the 226Ra-230Th radiochronology. The magnetic dating is based upon secular variation of the direction of the geomagnetic field (DGF) and
estimated to reach a precision of ±40 years for the last 1,200 years, and ±100 to 200 years up to circa 150 B.C. Although
less precise, the 226Ra-230Th method provides a unique tool for distinguishing between historic and prehistoric lavas, which in some cases might have
similar DGFs. We show that despite the abundance of details on ancient historical eruptions, the primary sources of information
are often too imprecise to identify their lava flows and eruptive systems. Most of the ages of these lavas, which are today
accepted on the geological maps and catalogues, were attributed in the 1800s on the basis of their morphology and without
any stratigraphical control. In fact, we found that 80% of the “historically dated” flows and cones prior to the 1700s are
usually several hundreds of years older than recorded, the discrepancies sometimes exceeding a millennium. This is proper
the case for volcanics presumed of the “1651 east” (actually ∼1020), “1595” (actually two distinct flows, respectively, ∼1200
and ∼1060), “1566” (∼1180), “1536” (two branches dated ∼1250 and ∼950), “1444” (a branch dated ∼1270), “1408” (lower branches
dated ∼450 and ∼350), “1381” (∼1160), “1329” (∼1030), “1284” (∼1450 and ∼700), “1169 or 812” (∼1000) eruptions. Conversely,
well-preserved cones and flows that are undated on the maps were produced by recent eruptions that went unnoticed in historical
accounts, especially during the Middle Ages. For the few eruptions that are recorded between A.D. 252 and 750 B.C., none of
their presumed lava flows shows a DGF in agreement with that existing at their respective dates of occurrence, most of these
flows being in fact prehistoric. The cinder cones of Monpeloso (presumed “A.D. 252”) and Mt. Gorna (“394 B.C.”), although
roughly consistent magnetically and radiochronologically with their respective epochs, remain of unspecified age because of
a lack of precision of the DGF reference curve at the time. It is concluded that at the time scale of the last millennia,
Mount Etna does not provide evidence of a steady-state behavior. Periods of voluminous eruptions lasting 50 to 150 years (e.g.,
A.D. 300–450, 950–1060, 1607–1669) are followed by centuries of less productive activity, although at any time a violent outburst
may occur. Such a revised history should be taken into account for eruptive models, magma output, internal plumbing of the
volcano, petrological evolution, volcano mapping and civil protection. 相似文献
Total variation diminishing (TVD) advection schemes are known to produce results that are free from some of the numerical
artifacts (no overshooting, no spurious oscillation, small diffusion) that can spoil the physical significance of the results.
When two or more tracers are advected separately using a TVD scheme, the sum of these variables can however exhibit some inappropriate
behaviors. The total variation of the sum will not necessarily be non- increasing and local artificial oscillations and extrema
can appear. We show that these can be avoided with only minor perturbations of the original solution by adjusting the slope
limiters used for the different variables. If the sum of these variables has some physical significance, for instance as refinement
of a larger model compartment, the correction procedure introduced in this paper should be used to ensure a physically meaningful
solution. 相似文献
Tropical volcanic islands are biodiversity hotspots where the Critical Zone (CZ) still remains poorly studied. In such steep topographic environments associated with extreme climatic events (cyclones), deployment and maintenance of monitoring equipment is highly challenging. While a few Critical Zone Observatories (CZOS) are located in tropical volcanic regions, none of them includes a Tropical Montane Cloud Forest (TMCF) at the watershed scale. We present here the dataset of the first observatory from the French network of critical zone observatories (OZCAR) located in an insular tropical and volcanic context, integrating a ‘Tropical Montane Cloud Forest’: The ERORUN-STAFOR observatory. This collaborative observatory is located in the northern part of La Réunion island (Indian Ocean) within the 45.0 km2 watershed of Rivière des Pluies (i.e., Rainfall river) which hosts the TMCF of Plaines des Fougères, one of the best preserved natural habitats in La Réunion Island. Since 2014, the ERORUN-STAFOR monitoring in collaboration with local partners collected a multidisciplinary dataset with a constant improvement of the instrumentation over time. At the watershed scale and in its vicinity, the ERORUN-STAFOR observatory includes 10 measurement stations covering the upstream, midstream and downstream part of the watershed. The stations record a total of 48 different variables through continuous (sensors) or periodic (sampling) monitoring. The dataset consists of continuous time series variables related to (i) meteorology, including precipitation, air temperature, relative humidity, wind speed and direction, net radiation, atmospheric pressure, cloud water flux, irradiance, leaf wetness and soil temperature, (ii) hydrology, including water level and temperature, discharge and electrical conductivity (EC) of stream, (iii) hydrogeology, including (ground)water level, water temperature and EC in two piezometers and one horizontally drilled groundwater gallery completed by soil moisture measurements under the canopy. The dataset is completed by periodic time series variables related to (iv) hydrogeochemistry, including field parameters and water analysis results. The periodic sampling survey provides chemical and isotopic compositions of rainfall, groundwater, and stream water at different locations of this watershed. The ERORUN-STAFOR monitoring dataset extends from 2014 to 2022 with an acquisition frequency from 10 min to hourly for the sensor variables and from weekly to monthly frequency for the sampling. Despite the frequent maintenance of the monitoring sites, several data gaps exist due to the remote location of some sites and instrument destruction by cyclones. Preliminary results show that the Rivière des Pluies watershed is characterized by high annual precipitation (>3000 mm y−1) and a fast hydrologic response to precipitation (≈2 h basin lag time). The long-term evolution of the deep groundwater recharge is mainly driven by the occurrence of cyclone events with a seasonal groundwater response. The water chemical results support existing hydrogeological conceptual models suggesting a deep infiltration of the upstream infiltrated rainfall. The TMCF of Plaine des Fougères shows a high water storage capacity (>2000% for the Bryophytes) that makes this one a significant input of water to groundwater recharge which still needs to be quantified. This observatory is a unique research site in an insular volcanic tropical environment offering three windows of observation for the study of critical zone processes through upstream-midstream-downstream measurements sites. This high-resolution dataset is valuable to assess the response of volcanic tropical watersheds and aquifers at both event and long-term scales (i.e., global change). It will also provide insights in the hydrogeological conceptual model of volcanic islands, including the significant role of the TMCFs in the recharge processes as well as the watershed hydrosedimentary responses to extreme climatic events and their respective evolution under changing climatic conditions. All data sets are available at https://doi.org/10.5281/zenodo.7983138 . 相似文献