Plio-Quaternary geodynamic evolution of a segment of the Peruvian Andean Cordillera located above the change in the subduction geometry: the Cuzco region

The Cuzco region, which is located above a change in subduction geometry, appears to be characterized by a variable Plio-Quaternary tectono-sedimentary evolution essentially located along the major fault system that separates the High Plateaux from the Eastern Cordillera. After the higher surface formation of the High Plateaux, a set of Neogene basins were filled by Miocene “ fluvio-torrential” series and by Plio-Pleistocene fluvio-lacustrine deposits. The Neogene series have been affected by compressional tectonic forces attributed to the Late Miocene. This compression is followed by roughly E-W trending syn-sedimentary extensional tectonics attributed to the Pliocene; it is related to reactivation of the pre-existing major faults, basin evolution, and volcanic activity concentrated along the faults. In the Early Pleistocene, fluvio-lacustrine deposits are affected by syn- and post-sedimentary compressional tectonism it is characterized by shortening that trends both N-S and E-W and produces folding and faulting of the sedimentary cover. Extensional tectonism trending roughly N-S has been taking place from the Middle Pleistocene to the Present; it is coeval with shoshonitic volcanic activity, and with sedimentation of fluvio-lacustrine terraces, torrential fans and moraines. Quaternary and active normal faults due to this tectonism, are located in a narrow zone more than 100 km-long between the High Plateaux and the Eastern Cordillera, and two 15 km-long fault sectors in the Eastern Cordillera. Characteristic Pleistocene scarps, 400 m or more high, are due to the cumulative normal offset, and there are also little scarps, with heights ranging between 2 and 20 m, which are related to Holocene fault reactivations. Recent fault reactivation on the Cuzco fault system, during the April 5, 1986 earthquake (m_b = 5.3), is due to the N-S trending extension. This state of stress, located at a mean elevation of roughly 3730 m, is generally homogeneous to different scales. The active Cuzco normal faults may be a consequence of adjustment between the compensated Western Cordillera and the undercompensated Eastern Cordillera, this latter being uplifted higher than its isostatic equilibrium due to compression acting on its eastern edge. The variation of the state of stress, during the Plio-Quaternary is in agreement with the variations of the compressional boundary forces. It may be explained by variation of the convergence rate or by the variation of pull-slab forces.     

Methane release and the carbon cycle on Mars

It has been suggested that the present release rate of methane to the Martian atmosphere could be the result of serpentinization in the deep subsurface, followed by the conversion of H₂ to CH₄ in a CO₂-rich fluid. Making this assumption, we show that the cryosphere could act as a buffer storing, under the form of micron-size methane clathrate particles, the methane delivered from below by hydrothermal fluids and progressively releasing it to the atmosphere at the top. From an extrapolation of the present CH₄ release rate back to the past, we calculate that up to several hundred millibars (～200–2000 mbar) of CO₂, resulting from the oxidation of the released CH₄, in addition to the volcanic supply (～400 mbar), should have accumulated in the atmosphere in the absence of a CO₂ sink. We reassess the capability of escape to have removed CO₂ from the atmosphere by C non-thermal escape and show that it is not significant. We suggest that atmospheric carbon is recycled to the crust through an active subsurface hydrological system, and precipitates as carbonates within the crust. During episodic periods of magmatic activity, these carbonates are decomposed to CO₂ dissolved in running water, and CO₂ can react with H₂ formed by serpentinization to build CH₄. CH₄ is then buffered in the subsurface cryosphere, above the water table, and finally released to the atmosphere, before being recycled to the subsurface hydrological system, and converted back to carbonates. We propose a typical evolution curve of the CO₂ pressure since the late Noachian based on our hypothesis. Contrary to the steady state carbon cycle at work on Earth, a progressive damping of the carbon cycle occurs on Mars due to the absence of plate tectonics and the progressive cooling of the planet.     

A data‐mining approach for assessing consistency between multiple representations in spatial databases

When different spatial databases are combined, an important issue is the identification of inconsistencies between data. Quite often, representations of the same geographical entities in databases are different and reflect different points of view. In order to fully take advantage of these differences when object instances are associated, a key issue is to determine whether the differences are normal, i.e. explained by the database specifications, or if they are due to erroneous or outdated data in one database. In this paper, we propose a knowledge‐based approach to partially automate the consistency assessment between multiple representations of data. The inconsistency detection is viewed as a knowledge‐acquisition problem, the source of knowledge being the data. The consistency assessment is carried out by applying a proposed method called MECO. This method is itself parameterized by some domain knowledge obtained from a second method called MACO. MACO supports two approaches (direct or indirect) to perform the knowledge acquisition using data‐mining techniques. In particular, a supervised learning approach is defined to automate the knowledge acquisition so as to drastically reduce the human‐domain expert's work. Thanks to this approach, the knowledge‐acquisition process is sped up and less expert‐dependent. Training examples are obtained automatically upon completion of the spatial data matching. Knowledge extraction from data following this bottom‐up approach is particularly useful, since the database specifications are generally complex, difficult to analyse, and manually encoded. Such a data‐driven process also sheds some light on the gap between textual specifications and those actually used to produce the data. The methodology is illustrated and experimentally validated by comparing geometrical representations and attribute values of different vector spatial databases. The advantages and limits of such partially automatic approaches are discussed, and some future works are suggested.     

Late Mesozoic compressional to extensional tectonics in the Yiwulüshan massif,NE China and its bearing on the evolution of the Yinshan–Yanshan orogenic belt: Part I: Structural analyses and geochronological constraints

With a cratonic nucleus, the North China Craton (NCC) experienced a complex tectonic evolution with multiphase compressional and extensional events during Mesozoic times. Along the northern part of the NCC, the Yinshan–Yanshan fold and thrust belt was a typical intraplate orogen. Jurassic and Cretaceous continental sedimentation, magmatism, widespread intraplate characterize the Yinshan–Yanshan orogenic belt. The geodynamic significance of these tectonic events is still in dispute. In the western part of the Liaoning province, the Yiwulüshan massif crops out at the eastern end of the Yinshan–Yanshan orogenic belt. The Yiwulüshan massif presents an elliptical domal shape with a NE–SW striking long axis. The structural evolution of this massif brings new insights for the understanding of the Mesozoic plutonic–tectonic history of the NCC. A multidisciplinary study involving structural geology, geochronology, Anisotropy of Magnetic Susceptibility (AMS) and gravity modeling have been carried out. The presentation of the new results splits into two parts. Part I (this paper) deals with field and laboratory structural observations, and presents the main geochronological results. The AMS, gravity modeling data will be provided in a companion paper (Part II). The early compressional deformation (D₁) corresponds to a Late Jurassic to Early Cretaceous southward thrusting. The subsequent deformation is related to the Early Cretaceous exhumation of the Yiwulüshan massif. A detailed structural analysis allows us to distinguish several deformation events (D₂, D₃, and D₄). The Cretaceous extensional structures, such as syntectonic plutons bounded by ductile normal faults, metamorphic core complexes, and half-graben basins are recognized in many places in East Asia. These new data from the Yiwulüshan massif constitute a link between Transbaikalia, Mongolia, North China and South China, indicating that NW–SE extensional Mesozoic tectonics occurred throughout the entire region.     

Polybrominated diphenyl ethers and their methoxylated analogs in mullet (Mugil cephalus) and sea bass (Dicentrarchus labrax) from Bizerte Lagoon, Tunisia

Concentrations of ten polybrominated diphenyl ethers (PBDEs) and eight methoxylated polybrominated diphenyl ethers (MeO-PBDEs) in mullet (Mugil cephalus) and sea bass (Dicentrarchus labrax) collected from the Bizerte Lagoon and the Mediterranean Sea were investigated. To the best of our knowledge, this is the first report of these compounds in marine fishes from Tunisia. The PBDE mean concentrations in fish from Bizerte Lagoon were 45.3 and 96.2 ng g(-1) lw respectively in mullet and sea bass, while the concentrations of these compounds in mullet and sea bass from Mediterranean Sea were 7.80 and 27.9 ng g(-1) lw respectively. MeO-PBDE concentrations in mullet and sea bass from Bizerte Lagoon ranged from 6.46 to 286 ng g(-1) lw and from 49.4 to 798 ng g(-1) lw respectively, while the concentrations of these compounds in mullet and sea bass from Mediterranean Sea ranged from 190 to 401 ng g(-1) lw and from 353 to 578 ng g(-1) lw respectively. The total PBDEs and total MeO-PBDEs concentration in fish from Bizerte Lagoon were similar or slightly lower than those reported for other species from other locations around the world.     

Amphibole as an archivist of magmatic crystallization conditions: problems,potential, and implications for inferring magma storage prior to the paroxysmal 2010 eruption of Mount Merapi,Indonesia

Amphibole is widely employed to calculate crystallization temperature and pressure, although its potential as a geobarometer has always been debated. Recently, Ridolfi et al. (Contrib Mineral Petrol 160:45–66, 2010) and Ridolfi and Renzulli (Contrib Mineral Petrol 163:877–895, 2012) have presented calibrations for calculating temperature, pressure, fO₂, melt H₂O, and melt major and minor oxide composition from amphibole with a large compositional range. Using their calibrations, we have (i) calculated crystallization conditions for amphibole from eleven published experimental studies to examine the problems and the potential of the new calibrations; and (ii) calculated crystallization conditions for amphibole from basaltic–andesitic pyroclasts erupted during the paroxysmal 2010 eruption of Mount Merapi in Java, Indonesia, to infer pre-eruptive conditions. Our comparison of experimental and calculated values shows that calculated crystallization temperatures are reasonable estimates. Calculated fO₂ and melt SiO₂ content yields potentially useful estimates at moderately reduced to moderately oxidized conditions and intermediate to felsic melt compositions. However, calculated crystallization pressure and melt H₂O content are untenable estimates that largely reflect compositional variation in the crystallizing magmas and crystallization temperature and not the calculated parameters. Amphibole from Merapi’s pyroclasts yields calculated conditions of ~200–800 MPa, ~900–1,050 °C, ~NNO + 0.3–NNO + 1.1, ~3.7–7.2 wt% melt H₂O, and ~58–71 wt% melt SiO₂. We interpret the variations in calculated temperature, fO₂, and melt SiO₂ content as reasonable estimates, but conclude that the large calculated pressure variation for amphibole from Merapi and many other arc volcanoes is evidence for thorough mixing of mafic to felsic magmas and not necessarily evidence for crystallization over a large depth range. In contrast, bimodal pressure estimates obtained for other arc magmas reflect amphibole crystallization from mafic and more evolved magmas, respectively, and should not necessarily be taken as evidence for crystallization in two reservoirs at variable depth.     

Superdense CO2 inclusions in Cretaceous quartz–stibnite veins hosted in low-grade Variscan basement of the Western Carpathians, Slovakia

CO₂ inclusions with density up to 1,197 kg m⁻³ occur in quartz–stibnite veins hosted in the low-grade Palaeozoic basement of the Gemericum tectonic unit in the Western Carpathians. Raman microanalysis corroborated CO₂ as dominant gas species accompanied by small amounts of nitrogen (<7.3 mol%) and methane (<2.5 mol%). The superdense CO₂ phase exsolved from an aqueous bulk fluid at temperatures of 183–237°C and pressures between 1.6 and 3.5 kbar, possibly up to 4.5 kbar. Low thermal gradients (∼12–13°C km⁻¹) and the CO₂–CH₄–N₂ fluid composition rule out a genetic link with the subjacent Permian granites and indicate an external, either metamorphogenic (oxidation of siderite, dedolomitization) or lower crustal/mantle, source of the ore-forming fluids.According to microprobe U–Pb–Th dating of monazite, the stibnite-bearing veins formed during early Cretaceous thrusting of the Gemeric basement over the adjacent Veporic unit. The 15- to 18-km depth of burial estimated from the fluid inclusion trapping PT parameters indicates a 8- to 11-km-thick Upper Palaeozoic–Jurassic accretionary complex overlying the Gemeric basement and its Permo-Triassic autochthonous cover.