Complex origin for the south-western Zamboanga metamorphic basement complex, Western Mindanao, Philippines     

Rodolfo A. Tamayo JR    Graciano P. Yumul JR    René C. Maury  Hervé Bellon  Joseph Cotten  Mireille Polvé  Thierry Juteau and  Cliff Querubin 《Island Arc》2000,9(4):638-652

Abstract Amphibolites unconformably overlain by a metasedimentary sequence of quartz-muscovite-feldspar-kyanite schists, metagraywackes and epidote-bearing amphibolites occur in the northern portion of the south-western Zamboanga metamorphic basement complex, western Mindanao. These amphibolites (here identified as the Mount Dansalan amphibolites) display relict magmatic textures inherited from cumulate gabbro protoliths. Bulk-rock major and trace-element data are consistent with this hypothesis. Together with the chemistry of relict igneous clinopyroxenes, they indicate a magmatic arc-related signature for the gabbro protoliths. Geochemical data allow us to identify various sources for the associated metasediments: the gabbro themselves for the metagraywackes and a continental basement for the quartz-muscovite-feldspar-kyanite schists. Both sources contributed to the genesis of the epidote-amphibolite metasediments. The compositions of the metamorphic mineral assemblages suggest that the rocks have undergone metamorphism at temperatures ranging from 550°C to 700°C and pressures probably in the range of 5–9 kbar. ⁴⁰K–⁴⁰Ar isotopic study of amphibole separates from the Mount Dansalan samples document a metamorphic event dated at 24.6 ± 1.4, 22.2 ± 1.4 and 21.2 ± 1.2 Ma. Our results are in agreement with plate tectonic models which describe the south-western Zamboanga metamorphic basement as a continental terrane. However, its evolution was not as simple as it was usually considered. In particular the basement incorporated slivers of magmatic arc crust, which cannot be unambiguously related to any of the Tertiary arcs documented in the area.  相似文献   

The ophiolite of Oman and United Arab Emirates     

Boudier  Françoise  Juteau  Thierry 《Marine Geophysical Researches》2000,21(3-4):145-146

Marine Geophysical Research -  相似文献   

UV Spectroscopic Dating of Stars and Galaxies     

Sara Heap  Thomas Brown  Thierry Lanz  Sukyoung Yi 《Astrophysics and Space Science》1999,265(1-4):531-532

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Lagged rejuvenation of groundwater indicates internal flow structures and hydrological connectivity     

Tamara Kolbe  Jean Marçais  Jean-Raynald de Dreuzy  Thierry Labasque  Kevin Bishop 《水文研究》2020,34(10):2176-2189

Large proportions of rainwater and snowmelt infiltrate into the subsurface before contributing to stream flow and stream water quality. Subsurface flow dynamics steer the transport and transformation of contaminants, carbon, weathering products and other biogeochemistry. The distribution of groundwater ages with depth is a key feature of these flow dynamics. Predicting these ages are a strong test of hypotheses about subsurface structures and time-varying processes. Chlorofluorocarbon (CFC)-based groundwater ages revealed an unexpected groundwater age stratification in a 0.47 km² forested catchment called Svartberget in northern Sweden. An overall groundwater age stratification, representative for the Svartberget site, was derived by measuring CFCs from nine different wells with depths of 2–18 m close to the stream network. Immediately below the water table, CFC-based groundwater ages of already 30 years that increased with depth were found. Using complementary groundwater flow models, we could reproduce the observed groundwater age stratification and show that the 30 year lag in rejuvenation comes from return flow of groundwater at a subsurface discharge zone that evolves along the interface between two soil types. By comparing the observed groundwater age stratification with a simple analytical approximation, we show that the observed lag in rejuvenation can be a powerful indicator of the extent and structure of the subsurface discharge zone, while the vertical gradient of the age-depth-relationship can still be used as a proxy of the overall aquifer recharge even when sampled in the discharge zone. The single age stratification profile measured in the discharge zone, close to the aquifer outlet, can reveal the main structure of the groundwater flow pattern from recharge to discharge. This groundwater flow pattern provides information on the participation of groundwater in the hydrological cycle and indicates the lower boundary of hydrological connectivity.  相似文献   

Mitigating the effects of sand dunes on seismic data from the Rub al Khali basin,Saudi Arabia     

Mustafa Al-Marzooq  Mamadou S. Diallo  Vincent Etienne  Thierry Tonellot  SanLinn I. Kaka 《Geophysical Prospecting》2019,67(7):1825-1837

The Rub Al Khali region in Saudi Arabia is characterized by the presence of sand dunes separated by salt flats, also called Sabkhas. In general, the elevation of dunes in this region varies between 90 and 250 m above sea level. The presence of these sand dunes, along with the rapidly changing surface topography poses challenges for seismic data acquisition and processing. The high contrast in acoustic impedance between the dune base and the underlying formation often results in amplification of seismic waves that are recorded at stations located on the surface of sand dunes. Attempts to address the issue using conventional surface-consistent amplitude scaling methods without reducing these amplification effects generally fail, thus compromising the suitability of the processed data for amplitude versus offset analysis. In this study, we propose a new reference site technique to reduce the effects of sand dune amplification, enabling the production of data sets that are suitable for amplitude versus offset processing. The proposed technique uses a deterministic approach to derive surface-consistent, frequency-dependent de-amplification functions for shots and stations located on the dunes only. Two-dimensional synthetic and field data examples show that the technique significantly reduces the effects of sand dune amplification.  相似文献   

Seafloor seismic acquisition using autonomous underwater vehicles     

Constantinos Tsingas  Thierry Brizard  Abdulaziz Al Muhaidib 《Geophysical Prospecting》2019,67(6):1557-1570

Although narrow-azimuth towed-streamer data provide good image quality for structural interpretation, it is generally accepted that for wide-azimuth marine surveys seabed receivers deliver superior seismic reflection measurements and seismically derived reservoir attributes. However, seabed surveys are not widely used due to the higher acquisition costs when compared to streamer acquisition. In recent years, there have been significant engineering efforts to automate receiver deployment and retrieval in order to minimize the cost differential and conduct cost-efficient seabed receiver seismic surveys. These engineering efforts include industrially engineered nodes, nodes on a rope deployment schemes and even robotic nodes, which swim to and from the deployment location. This move to automation is inevitable, leading to robotization of seismic data acquisition for exploration and development activities in the oil and gas industry. We are developing a robotic-based technology, which utilizes autonomous underwater vehicles as seismic sensors without the need of using a remotely operated vehicle for deployment and retrieval. In this paper, we describe the autonomous underwater vehicle evolution throughout the project years from initial heavy and bulky nodes to fully autonomous light and flexible underwater receivers. Results obtained from two field pilot tests using different generations of autonomous underwater vehicles indicate that the seismic coupling, and navigation based on underwater acoustics are very reliable and robust.  相似文献   

Long-term (10⁵) or short-term (10³) δ¹³C excursion near the Palaeocene-Eocene transition: evidence from the Tethys     

Gangyi Lu  Gerta Keller  Thierry Adatte  Nieves Ortiz  Eustoquio Molina 《地学学报》1996,8(4):347-355

Expanded sedimentary records from the Tethys reveal unique faunal and isotopic changes across the Palaeocene-Eocene (P-E) transition. Unlike in the open oceans, the Tethys exhibits a gradual decrease of 1.5% in δ¹³C values prior to the rapid δ¹³C excursion. Associated with the 6¹³C excursion is a decrease in calcite burial, increase in detrital content and appearance of a unique opportunistic planktic foraminifera1 assemblage (e.g. compressed acarininids). The existence of a prelude decrease in δ¹³C values in the Tethys suggests that the P-E δ¹³C excursion may have occurred in two steps and over a few hundred thousand years, rather than as one step over a few thousand years as previously suggested. This slower excursion rate is readily explained by changing organic carbon weathering or burial rates and avoids the need of invoking ad hoc scenarios.  相似文献   

The landscape-unit approach applied to geology, on SPOT images, in temperate climate zones using a test-area in the Cévennes (Massif Central, France)     

Jean-Paul Deroin  Jean Chorowicz  Thierry Deroin  Phillippe Dutarte  Jean-Yves Scanvic  Andr Simonin 《ISPRS Journal of Photogrammetry and Remote Sensing》1990,45(5-6)

Classification image processing is based mainly upon spectral features but this information alone is inadequate for drawing comprehensive maps or reliably distinguishing lithological or structural targets, especially in vegetation-covered areas. It is therefore of interest to explore an approach in which subtle features of the image are matched with field data in a variety of parameters either measured or assessed qualitatively. This approach is necessarily multidisciplinary, the three basic aspects being geomorphological, botanical and geological.The Cévennes massif, in southern France, with its sedimentary margins was selected as a test area, having both varied geology, giving a variety of landscapes, and a range of climatic zones, from Mediterranean to sub-Alpine.The present work is distinguished by its use of the landscape unit, which is rarely considered in geology. Landscapes units are recognized and defined, and the spectral homogeneity of the units is then assessed. They are combined with satellite and other data in order to improve the digital processing for geological purposes.The parameters characterising each landscape unit define the various elements contributing to the landscape, the most important of which are morphology, vegetation and geology, and their interactions. Our results using these parameters show the interest of the management of both the satellite (SPOT in this case) and non-satellite (exogenous) data.  相似文献   

The Var turbidite system (Ligurian Sea, northwestern Mediterranean)—morphology, sediment supply, construction of turbidite levee and sediment waves: implications for hydrocarbon reservoirs     

Sébastien Migeon  Thierry Mulder  Bruno Savoye  Françoise Sage 《Geo-Marine Letters》2006,26(6):361-371

The Var turbidite system is a small sandy system located in the Ligurian Basin. It was deposited during the Pliocene-Quaternary in a flat-floored basin formed during the Messinian salinity crisis. The system was fed through time by the Var and Paillon canyons that connect directly to the Var and Paillon rivers. It is still active during the present sea-level highstand. Two main mechanisms are responsible for gravity-flow triggering in the Var turbidite system: (1) mass-wasting events affect mainly the upper part of the continental slope, in areas where volumes of fresh sediment delivered by rivers are highest, and result from the under-consolidation state of slope sediments and earthquakes, and (2) high-magnitude river floods resulting from melting of snow and convective rainfall during fall and spring seasons, and generating hyperpycnal turbidity currents at river mouths when the density of freshwater transporting suspended particles exceeds that of ambient seawater. Failure- and flood-induced gravity flows are involved through time in the construction of the Var Sedimentary Ridge, the prominent right-hand levee of the Var system, and sediment waves. Processes of construction of both the Var Ridge and sediment waves are closely connected. Sandy deposits are thick and abundant in the eastern (downchannel) part of the ridge. Their distribution is highly constrained by the strong difference of depositional processes across the sediment waves, potentially resulting through time in the individualization of large and interconnected sand bodies.  相似文献   

Sea ice evolution over the 20th and 21st centuries as simulated by current AOGCMs   总被引：5，自引：1，他引：5  

Olivier Arzel  Thierry Fichefet  Hugues Goosse 《Ocean Modelling》2006,12(3-4):401-415

Outputs from simulations performed with current atmosphere-ocean general circulation models for the Fourth Assessment Report of Intergovernmental Panel on Climate Change (IPCC AR4) are used to investigate the evolution of sea ice over the 20th and 21st centuries. We first use the results from the “Climate of the 20th Century Experiment” to assess the ability of these models to reproduce the observed sea ice cover changes over the periods 1981–2000 and 1951–2000. The projected sea ice changes over the 21st century in response to the IPCC Special Report on Emission Scenarios A1B are then examined. Overall, there is a large uncertainty in simulating the present-day sea ice coverage and thickness and in predicting sea ice changes in both hemispheres. Over the period 1981–2000, we find that the multimodel average sea ice extent agrees reasonably well with observations in both hemipsheres despite the wide differences between the models. The largest uncertainties appear in the Southern Hemisphere. The climate change projections over the 21st century reveal that the annual mean sea ice extent decreases at similar rates in both hemispheres, and that the reduction in annual mean sea ice volume is about twice that of sea ice extent reduction in the Northern Hemisphere, in agreement with earlier studies. We show that the amplitude of the seasonal cycle of sea ice extent increases in both hemispheres in a warming climate, with a larger magnitude in the Northern Hemisphere. Furthermore, it appears that the seasonal cycle of ice extent is more affected than the one of ice volume. By the end of the 21st century, half of the model population displays an ice-free Arctic Ocean in late summer.  相似文献