Validation and comparison of Advanced Differential Interferometry Techniques: Murcia metropolitan area case study

This paper is focused on the analysis of the performance of Stable Point Network (SPN) and Coherent Pixel Technique (CPT), which are Advanced Differential Interferometry Techniques (A-DInSAR) that estimate, among other results, mean deformation velocity maps of the ground surface and displacement time series from a SAR dataset. The test site is the metropolitan area of the city of Murcia (Spain) where a moderate slow subsidence induced by the overexploitation of aquifers is present. SAR data acquired between July 1995 and August 2005 from ERS and ENVISAT sensors have been processed by the SPN and CPT techniques and compared with in situ instrumental measurements assumed as reference. Experimental results have shown that both SPN and CPT techniques provide estimates of the deformation evolution in time with an absolute difference below 6 mm consistently in all comparisons: SPN vs extensometer, CPT vs extensometer and SPN vs CPT. The proposed validation and comparison experiment between both A-DInSAR techniques has been useful to observe their differences and complementarities.     

The relationship of anchovy and sardine to water masses in the Peruvian Humboldt Current System from 1983 to 2005

The Humboldt Current System (HCS) is dominated by two pelagic species; Peruvian anchovy or anchoveta (Engraulis ringens) and sardine (Sardinops sagax). Using data from 43 acoustic surveys conducted from 1983 through 2005 by the Peruvian Marine Institute (IMARPE), we examined the distribution of these two species relative to water masses. We tested the hypothesis that anchovy was found more frequently in upwelled cold coastal water (CCW) and mixed waters (MCW) than in other water types and that sardine was more associated with more offshore oceanic surface subtropical water (SSW). Surface temperature, salinity, latitude, season and distance to the coast data were used to define water masses. Results using generalized additive models (GAM), modelling sardine and anchovy presence–absence as a function of year, water body, bottom depth and latitude, showed that anchovy were primarily found in CCW and MCS, while sardine were more ubiquitous relative to water masses with some predilection for SSW. These results were supported by various indexes of anchovy and sardine distribution versus water mass as well as temporal and location variables.     

Zooplankton and forage fish species off Peru: Large-scale bottom-up forcing and local-scale depletion

The Humboldt Current System, like all upwelling systems, has dramatic quantities of plankton-feeding fish, which suggested that their population dynamics may ‘drive’ or ‘control’ ecosystem dynamics. With this in mind we analysed the relationship between forage fish populations and their main prey, zooplankton populations. Our study combined a zooplankton sampling program (1961–2005) with simultaneous acoustic observations on fish from 40 pelagic surveys (1983–2005) conducted by the Peruvian Marine Research Institute (IMARPE) and landing statistics for anchoveta (Engraulis ringens) and sardine (Sardinops sagax) along the Peruvian coast from 1961 to 2005. The multi-year trend of anchoveta population abundance varied consistently with zooplankton biovolume trend, suggesting bottom-up control on anchovy at the population scale (since oceanographic conditions and phytoplankton production support the changes in zooplankton abundance). For a finer-scale analysis (km) we statistically modelled zooplankton biovolume as a function of geographical (latitude and distance from the 200-m isobath), environmental (sea surface temperature), temporal (year, month and time-of-day) and biological (acoustic anchovy and sardine biomass within 5 km of each zooplankton sample) covariates over all survey using both classification and regression trees (CART) and generalized additive models (GAM). CART showed local anchoveta density to have the strongest effect on zooplankton biovolume, with significantly reduced levels of biovolume for higher neighbourhood anchoveta biomass. Additionally, zooplankton biovolume was higher offshore than on the shelf. GAM results corroborated the CART findings, also showing a clear diel effect on zooplankton biovolume, probably due to diel migration or daytime net avoidance. Apparently, the observed multi-year population scale bottom-up control is not inconsistent with local depletion of zooplankton when anchoveta are locally abundant, since the latter effect was observed over a wide range of overall anchoveta abundance.     

Survival of eclogite xenolith in a Cretaceous granite intruding the Central Dabieshan migmatite gneiss dome (Eastern China) and its tectonic implications

Investigation of an eclogite xenolith, discovered in a Cretaceous granite from the Central Domain of the Dabieshan massif in eastern China, yields new petrological insights into the high to ultrahigh-pressure metamorphism, experienced by the Qinling-Dabie orogen. Prior to inclusion as a xenolith in the granite during the Early Cretaceous, this eclogite xenolith had recorded a complex metamorphic evolution that complies with subduction and exhumation processes experienced by the continental crust of the South China Block. Well-preserved mineral parageneses substantiate the prograde and retrograde stages revealed by inclusions in porphyroblastic garnet and zoned minerals such as garnet, omphacite and amphibole in the matrix. The relatively low P/T re-equilibration during a late metamorphic stage was textually inferred by the presence of aluminous and calcic-subcalcic amphiboles such as katophorite, edenite, taramite and pargasite as main matrix phases. According to our U/Pb, Rb/Sr and new ⁴⁰Ar/³⁹Ar geochronological results, namely109 ± 1 and 112 ± 2 Ma plateau ages for muscovite and amphiboles, respectively, two successive but distinct cooling stages account for the thermal history of the granite–migmatite gneiss dome that forms the Central Dabieshan Domain. We argue that prior to the Cretaceous doming, the Central Dabieshan Domain experienced a tectono-metamorphic evolution similar to that observed in the high-pressure to ultra high-pressure units developed in the Southern Dabieshan Domain and Hong’an massif.     

Experimental soft‐sediment deformation caused by fluidization and intrusive ice melt in sand

Identifying the driving mechanisms of soft‐sediment deformation in the geological record is the subject of debate. Thawing of ice‐rich clayey silt above permafrost was proved experimentally to be among the processes capable of triggering deformation. However, previous work has failed so far to reproduce similar structures in sand. This study investigates fluidization and intrusive ice formation from soil models in the laboratory. Experimental conditions reproduce the growth of ice‐cored mounds caused by pore water pressure increase during freeze‐back of sand in a permafrost context. Excess pore water pressure causes hydraulic fracturing and the development of water lenses beneath the freezing front. Later freezing of the water lenses generates intrusive ice. The main structures consist of sand dykes and sills formed when the increase in pore water pressure exceeds a critical threshold, and soft‐sediment deformations induced by subsidence during ice melt. The combination of processes has resulted in diapir‐like structures. The experimental structures are similar to those described in Pleistocene sites from France. These processes constitute a credible alternative to the seismic hypothesis evoked to explain soft‐sediment deformation structures in other European regions subjected to Pleistocene cold climates.     

40Ar/39Ar temporal framework for the Alleret maar lacustrine sequence (French Massif-Central): Volcanological and paleoclimatic implications

The Alleret maar (Massif Central, France) is part of the few Western European early middle Pleistocene lacustrine sequences. In the AL3 core several new ash layers were recovered in the 10 first meters of the sedimentary filling. We obtained three ⁴⁰Ar/³⁹Ar ages, which range from 683 ± 5 ka (MSWD: 1.2, n = 17) to 722 ± 6 ka (MSWD: 3.2, n = 18). All the studied ash layers belong to the Super-Besse eruptive cycle of the Sancy volcano. Based on the chronostratigraphy that we have derived we estimate that the age of the main eruption could correspond to the Sancy volcano caldera formation at 725 ka close to the end of MIS 18 and that the Super-Besse explosive episode duration lasted only about 40 ka. The time framework we build evidences that the Alleret lacustrine sequence represents a time interval of probably 180 ka spanning from MIS 18 to MIS 14. This sequence offers the first well constrained comparison between terrestrial environmental history and that preserved in marine sediments during the Mid-Pleistocene Revolution.     

Geoarchaeological simulation of meandering river deposits and settlement distributions: A three‐dimensional approach

Fluvial processes have the potential to obscure, expose, or even destroy portions of the archaeological record. Floodplain aggradation can bury and hide archaeological features, whereas actively migrating channels can erode them. The archaeological record preserved in the subsurface of a fluvial system is potentially fragmented and is three‐dimensionally complex, especially when the system has been subjected to successive phases of alluviation and entrenchment. A simulation model is presented to gain insight into the threedimensional subsurface distribution, visibility, and preservation potential of the archaeological record in a meander‐floodplain system as a function of geomorphic history. Simulation results indicate that fluvial cut‐fill cycles can strongly influence the density of archaeological material in the subsurface. Thus, interpretation of floodplain habitation based solely upon features visible in the shallow subsurface (through traditional techniques such as aerial photography and geophysical prospection) can be misleading. In the examples, the loss of archaeological record by channel migration ranges between 45% and 90% over 12,000 years for channel belt‐dominated systems, decreasing to 10 to 30% for rivers where the floodplain width is a multiple of channel belt width. The modeling presented can be used to test excavation strategies in relation to hypothesized scenarios of stratigraphic evolution for archaeological sites. © 2006 Wiley Periodicals, Inc.     

Marble-hosted ruby deposits from Central and Southeast Asia: Towards a new genetic model

Marble-hosted ruby deposits represent the most important source of colored gemstones from Central and South East Asia. These deposits are located in the Himalayan mountain belt which developed during Tertiary collision of the Indian plate northward into the Eurasian plate. They are spatially related to granitoid intrusions and are contained in platform carbonates series that underwent high-grade metamorphism. All occurrences are located close to major tectonic features formed during Himalayan orogenesis, directly in suture zones in the Himalayas, or in shear zones that guided extrusion of the Indochina block after the collision in South East Asia. Ar–Ar dating of micas syngenetic with ruby and U–Pb dating of zircon included in ruby gives evidence that these deposits formed during Himalayan orogenesis, and the ages document the extensional tectonics that were active, from Afghanistan to Vietnam, between the Oligocene and the Pliocene.The petrography shows that ruby-bearing marbles formed in the amphibolite facies (T = 610 to 790 °C and P ~ 6 kbar). A fluid inclusion study defines the conditions of gem ruby formation during the retrograde metamorphic path (620 < T < 670 °C and 2.6 < P < 3.3 kbar) for the deposits of Jegdalek, Hunza and northern Vietnam.Whole rock analyses of non-ruby-bearing marbles indicate that they contain enough aluminum and chromiferous elements to produce all the ruby crystals that they contain. In addition, (C, O)-isotopic analyses of carbonates from the marbles lead to the conclusion that the marbles acted as a metamorphic closed fluid system that were not infiltrated by externally-derived fluids. The carbon isotopic composition of graphite in marbles reveals that it is of organic origin and that it exchanged C-isotopes with the carbonates during metamorphism. Moreover, the O-isotopic composition of ruby was buffered by metamorphic CO₂ released during devolatilisation of marble and the H-isotopic composition of mica is consistent with a metamorphic origin for water in equilibrium with the micas. The (C, O, H)-isotopic compositions of minerals associated with marble-hosted ruby are all in agreement with the hypothesis, drawn from the unusual chemistry of CO₂–H₂S–COS–S₈–AlO(OH)-bearing fluids contained in fluid inclusions, that gem ruby formed at P ~ 3 kbar and 620 < T < 670 °C, during thermal reduction of evaporite by organic matter, at high temperature-medium pressure metamorphism of platform carbonates during the Tertiary India–Asia collision. The carbonates were enriched in Al- and chromiferous-bearing detrital minerals, such as clay minerals that were deposited on the platform with the carbonates, and in organic matter. Ruby formed during the retrograde metamorphic path, mainly by destabilization of muscovite or spinel. The metamorphic fluid system was rich in CO₂ released from devolatilisation of carbonates, and in fluorine, chlorine and boron released by molten salts (NaCl, KCl, CaSO₄). Evaporites are key to explaining the formation of these deposits. Molten salts mobilized in situ Al and metal transition elements contained in marbles, leading to crystallization of ruby.     

Optical extinction due to aerosols in the upper haze of Venus: Four years of SOIR/VEX observations from 2006 to 2010

The variability of the aerosol loading in the mesosphere of Venus is investigated from a large data set obtained with SOIR, a channel of the SPICAV instrument suite onboard Venus Express. Vertical profiles of the extinction due to light absorption by aerosols are retrieved from a spectral window around 3.0 μm recorded in many solar occultations (～200) from September 2006 to September 2010. For this period, the continuum of light absorption is analyzed in terms of spatial and temporal variations of the upper haze of Venus. It is shown that there is a high short-term (a few Earth days) and a long-term (～80 Earth days) variability of the extinction profiles within the data set. Latitudinal dependency of the aerosol loading is presented for the entire period considered and for shorter periods of time as well.