Effect of frictional heating and thermal advection on pre-seismic sliding: a numerical simulation using a rate-, state- and temperature-dependent friction law

Laboratory experiments on simulated faults in rocks clearly show the temperature dependence of dynamic rock friction. Since rocks surrounding faults are permeable, we have developed a numerical method to describe the thermo-mechanical evolution of the pre-seismic sliding phase which takes into account both the rate-, state- and temperature-dependent friction law and the heat advection term in the energy equation. We consider a laminar fluid motion perpendicular to a vertical fault plane and assume that fluids move away from the fault plane. A semi-analytical temperature solution which accounts for the variability of slip velocity and stress on the fault has been found. This solution has been generalized to the case of a time varying fluid velocity and then was used to include the thermal pressurization effect. After discretizing the temperature solution, the evolution of the system is obtained by the solution of a system of first order differential equations which allows us to determine the evolution of slip, slip rate, friction coefficient, effective normal stress, temperature and fluid velocity. The numerical solutions are found using a Runge-Kutta method with an adaptative stepsize control in time. When the thermal pressurization effects can be neglected, the heat advection effect gives rise to a delay, with respect to the purely conductive case, of the earthquake occurrence time. This delay increases with increasing permeability H of the system. When the thermal pressurization effects are taken into account the situation is opposite, i.e. the onset of instability tends to precede that of the purely conductive case. The advance in the time of occurrence of instability increases with increasing coefficient of thermal pressurization. In the small permeability range (H ≤ 10^?18 m²), the seismic moment and nucleation length of the pre-seismic phase are significantly smaller than those predicted by the purely conductive model.     

Calculating the two-dimensional magnetotelluric Jacobian in finite elements using reciprocity

To speed up the calculation of the field Jacobian for 2-D magnetoteliuric inversion using finite elements, the principle of electromagnetic reciprocity is applied. The governing relationship for the Jacobian of the field along strike is obtained by differentiating the Helmholtz equation with respect to the resistivity of each region in the finite-element mesh. The result is a similar Helmholtz equation for the Jacobian, with new sources distributed over all nodes within the parameter medium. However, according to the principle of electromagnetic reciprocity, the roles of sources and receivers are interchangeable. Utilizing reciprocity, the field values obtained from the original forward problem and for new unit sources imposed at the receivers are then utilized in the calculation of the Jacobian by simple multiplication and summation with finite-element terms at each rectangle in the mesh. For the auxiliary (across-strike) fields, the Jacobian terms are obtained by solving source vectors loaded with parabola coefficients used in the approximation to Maxwell's equations. Jacobian terms for the apparent resistivity ( p _a), the impedance phase (φ) and the vertical magnetic field ( K _zy) are then calculated utilizing the parallel- and auxiliary-field Jacobians. Comparison of Jacobian values obtained from reciprocity calculations and by differencing two forward solutions show that the reciprocity method is accurate and can be used to decrease the number of calculations required to obtain sensitivities by one to two orders of magnitude.     

EXERCISE IN DOWNSCALING ON SEA SURFACE TEMPERATURE ALONG CHINESE COAST

ＩＮＴＲＯＤＵＣＴＩＯＮＴｈｅｍｏｎｓｏｏｎｈａｓａｃｉｒｃｕｌａｔｉｏｎｆｅａｔｕｒｅｔｈａｔｉｓｐｌａｎｅｔａｒｙｉｎｓｃａｌｅａｎｄａｎｉｄｅｎｔｉｆｉａｂｌｅｓｉｇｎａｌｒｅｇａｒｄｉｎｇｉｔｓｓｕｂｓｅｑｕｅｎｔｉｎｔｅｎｓｉｔｙｓｏｍｅｎｉｎｅｍｏｎｔｈｓｐｒｉｏｒｔｏｔｈｅａｃｔｉｖｅｓｔａｇｅｏｆｔｈｅｓｕｍｍｅｒｍｏｎｓｏｏｎ(ＷｅｂｓｔｅｒａｎｄＹａｎｇ,1992).Ｆｕｒｔｈｅｒｍｏｒｅ,ｔｈｅｍａｇｎｉｔｕｄｅｏｆｔｈｅｍｏｎｓｏｏｎｖａｒｉａｂｉｌｉｔｙｉｓｓｕｂｓｔａｎｔｉａ…     

Corona textures in Proterozoic olivine melanorites of the Equeefa Suite,Natal Metamorphic Province,South Africa

Summary Olivine-plagioclase and phlogopite-plagioclase coronas have been identified from olivine melanorites of the Mid- to Late Proterozoic Equeefa Suite in southern Natal, South Africa. Olivine, in contact with plagioclase, is mantled by a shell of clear orthopyroxene, in turn rimmed by pale green (pargasitic) clinoamphibole. Locally a third rim, composed of a fine pargasite-spinel symplectite is developed adjacent to the plagioclase. The second corona reaction has produced greenish-brown pargasite at phlogopite-plagioclase interfaces. A third, less obvious reaction, between olivine and phlogopite is also noted. Analytical data of all the mineral phases present, along with the coronas, are given. Two-pyroxene thermometry yields magmatic core temperatures ( 1120°C), with rim compositions indicating equilibration at 850°C. Consistent with this, the modelled olivine-plagioclase reaction occurs between 830–1050°C with a_waterbetween 0.1 and 1.0 at 7 kbar. The three reactions took place during a prolonged history of cooling and partial hydration of the magmatic olivine melanorites from over 1000°C down to 600°C. The P-T conditions indicated by the reactions suggest this cooling process was essentially isobaric, indicating that the area was not subjected to rapid uplift or burial throughout this entire period.

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Korona-Texturen in proterozoischen Olivin-Melanoriten der Equeefa Suite, Natal Metamorphic Province, Südafrika

Zusammenfassung Aus Olivin-Melanoriten der mittel- bis spätproterozoischen Equeefa Suite im südlichen Natal, Südafrika, wurden Olivin-Plagioklas und Phlogopit-Plagioklas-Koronartexturen beobachtet. Olivin, der mit Plagioklas im Kontakt steht, wird von einem klaren Saum vom Orthopyroxen ummantelt, der seinerseits von blaßgrünem (pargasitischem) Klinoamphibol umsäumt wird. Stellenweise ist ein dritter Saum, bestehend aus feinkörnigem symplektitischem Pargasit-Spinell im Kontakt mit Plagioklas ausgebildet. Die zweite koronabildende Reaktion resultiert in Bildung eines grünbraunen Pargasites an Phlogopit-Plagioklas Kornkontakten. Eine dritte, weniger auffällige Reaktion zwischen Olivin und Phlogopit wurde ebenfalls beobachtet. Zwei-Pyroxen-Thermometrie ergab magmatische Temperaturen der Kernbereiche ( 1120°C) und belegt eine Gleichgewichtseinstellung in den Randzonen bei ca. 850°C. Olivin-Plagioklas-Modellreaktionen liegen ebenfalls in einem Temperaturbereich von 830–1050°C bei Wasseraktivitäten von 0.1 bis 1.0 und einem Druck von 7 kbar. Die drei Reaktionen liefen im Zuge einer länger andauernden Abkühlung unter teilweiser Hydratisierung der magmatischen Melanorite in einem Temperaturbereich von 1000°C bis ca. 600°C ab. Die aus den Reaktionen ableitbaren P-T-Bedingungen sprechen für eine im wesentlichen isobare Abkhlungsgeschichte und zeigen, daß dieses Gebiet wáhrend dieser gesamten Periode keiner raschen Hebung bzw. keiner Versenkung unterworfen worden ist.

     

Comparative study of sampling methods and in situ and laboratory analysis for shallow-water submarine hydrothermal systems

A primary aim for sampling of submarine hydrothermal vents is to minimize inclusion of ambient seawater. Here, we compare the results of three different sampling methods (air displacement, two-valve bottle, and syringes) for shallow submarine systems. Mixing of hydrothermal fluid with seawater is unavoidable; however, calculations based on linear mixing models allow estimation of the hydrothermal fluid end-member composition. The results show that sampling with a two-valve bottle and syringes are the best options because they allow collection of samples with a large proportion of hydrothermal fluid. Additionally, we compare the results of in situ and laboratory analyses of the fluid samples, and demonstrate that determination of chemical composition in situ is the best option for some components, as re-equilibration affects some component concentrations (i.e. bicarbonate). Conversely, silica determination in situ usually underestimates the concentration in the fluid, as it does not account for polymeric silica. Other components can be measured either in the field or in the laboratory.     

Low-grade metamorphic rocks from the Pulur complex,NE Turkey: implications for the pre-Liassic evolution of the Eastern Pontides

In the Pulur complex (Sakarya Zone, Eastern Pontides, Turkey) a low-grade tectonometamorphic unit (Doankavak) is exposed in three tectonic windows beneath a complex medium-pressure high-temperature metamorphic unit of late Carboniferous age. The thrust plane between both units is transgressively covered by Liassic conglomerates. The Doankavak unit comprises a sequence of metabasites with MORB-type chemical compositions and phyllites, with subordinate calcareous phyllites, marbles, quarzofeldspathic schists and metacherts. This sequence is interpreted as a former accretionary complex related to the consumption of the Palaeotethys. Mineral parageneses in the metabasites allow for the distinction of two domains with slightly different peak metamorphic conditions, i.e. 375–425 °C/0.5–0.8 GPa (greenschist facies) and 400–470 °C/0.6–1.1 GPa (albite-epidote amphibolite facies). The age of metamorphism is constrained at ~ 260 Ma (early Late Permian) by two Rb-Sr mineral-whole rock ages (hornblende, phengite) and one ⁴⁰Ar/³⁹Ar single step total fusion age (phengite). In conjunction with previous data on other accretionary complexes in the Sakarya zone in Northern Turkey, the data presented in this study suggest a continuous subduction of the Palaeotethys at least from Early/Late Permian to Late Triassic and a discontinuous preservation of accretion complexes in both space and time.     

Paleoenvironment and sea-level change in the early Cretaceous Barents Sea—implications from near-shore marine sapropels

The late Volgian (early "Boreal" Berriasian) sapropels of the Hekkingen Formation of the central Barents Sea show total organic carbon (TOC) contents from 3 to 36 wt%. The relationship between TOC content and sedimentation rate (SR), and the high Mo/Al ratios indicate deposition under oxygen-free bottom-water conditions, and suggest that preservation under anoxic conditions has largely contributed to the high accumulation of organic carbon. Hydrogen index values obtained from Rock-Eval pyrolysis are exceptionally high, and the organic matter is characterized by well-preserved type II kerogen. However, the occurrence of spores, freshwater algae, coal fragments, and charred land-plant remains strongly suggests proximity to land. Short-term oscillations, probably reflecting Milankovitch-type cyclicity, are superimposed on the long-term trend of constantly changing depositional conditions during most of the late Volgian. Progressively smaller amounts of terrestrial organic matter and larger amounts of marine organic matter upwards in the core section may have been caused by a continuous sea-level rise.     

等离子体发射光谱法测定大气颗粒物中的无机元素

建立了用等离子体发射光谱（ＩＣＰ－ＡＥＳ）测定大气颗粒物中无机元素的分析方法,包括样品消解体系的选择,仪器的操作条件及采样滤膜的选择,产对自行采样分析测得的无机元素数据作了初步的讨论。实验结果表明：采用ＨＮＯ３－ＨＣｌＯ４消解体系,操作方便,样品消解较完全;选用石英滤膜查减低空白值,保证测定质量以及同时在一张滤膜上测定大气颗粒物中的有机碳、元素碳及无机元素;内标法可有效降低由于仪器漂移等因素对测定     

Hydrothermal plume mapping as a prospecting tool for seafloor sulfide deposits: a case study at the Zouyu-1 and Zouyu-2 hydrothermal fields in the southern Mid-Atlantic Ridge

Seafloor hydrothermal polymetallic sulfide deposits are a new type of resource, with great potential economic value and good prospect development. This paper discusses turbidity, oxidation–reduction potential, and temperature anomalies of hydrothermal plumes from the Zouyu-1 and Zouyu-2 hydrothermal fields on the southern Mid-Atlantic Ridge. We use the known location of these vent fields and plume data collected in multiple years (2009, 2011, 2013) to demonstrate how real-time plume exploration can be used to locate active vent fields, and thus associated sulfide deposits. Turbidity anomalies can be detected 10 s of km from an active source, but the location precision is no better than a few kilometers because fine-grained particles are quasi-conservative over periods of many days. Temperature and oxidation–reduction potential anomalies provide location precision of a few hundred meters. Temperature anomalies are generally weak and difficult to reliably detect, except by chance encounters of a buoyant plume. Oxidation–reduction potential is highly sensitive (nmol concentrations of reduced hydrothermal chemicals) to discharges of all temperatures and responds immediately to a plume encounter. Real-time surveys using continuous tows of turbidity and oxidation–reduction potential sensors offer the most efficient and precise surface ship exploration presently possible.     

Cotton Fiber/ZrO2, A New Material for Adsorption of Cr(VI) Ions in Water

The natural cotton fiber was used to synthesize an anion exchange, containing ZrO₂ film on its surface, NCFZC (natural cotton fiber/ZrO₂ composite). This anion exchanger was produced by the reaction of the zirconium oxychloride and hydroxyl groups on surface of the natural cotton fiber. The material was used for Cr(VI) ions adsorption studies. Adsorption equilibrium time and optimum pH for Cr(VI) adsorption were found to be 6 h and 4.0, respectively. The Langmuir and Temkin isotherms were used to models adsorption equilibrium data. The adsorption capacity of NCFZC was found to be 1.33 mmol/g. Kinetic studies showed that the rate of adsorption of Cr(VI) on NCFZC obeyed a pseudo‐second‐order kinetic model.