Timescale of open-reservoir evolution beneath the south Cleft segment, Juan de Fuca ridge

Lavas erupted at the southern end of the intermediate Juan de Fuca ridge (Cleft segment) are mostly cogenetic and their chemical diversity results from melt evolution in an open magma system. In the present study, we apply a theoretical model allowing the time evolution of this periodically recharged and tapped magma chamber to be estimated. In our mathematical procedure, the melt quantity supplied to the reservoir varies through time following a sinusoidal function. The rare earth element concentrations in the refilling melt were calculated on the basis of the REE distribution in lavas. This theoretical composition is akin to that previously estimated for a Mg#70 MORB from mineralogical and chemical data. Then, we approached the temporal evolution of the reservoir using a set of suitable parameters deduced from the geometry of the crust and magma system beneath the Cleft segment. Particularly, we considered two end-members scenarios for the melt repartition through the magma reservoir beneath the Cleft segment: the “gabbro glacier” model (crystal nucleation and growth occur within one single melt lens and crystals subside vertically and laterally) and the “sheeted sill” model (crystallization takes place within a network of connected sills located at various depths within the crust). We estimated that the magma chamber is refilled every thousand years and that the melt resides approximately one hundred years within the reservoir.     

Total individual ion activity coefficients of calcium and carbonate in seawater at 25°C and 35%. salinity,and implications to the agreement between apparent and thermodynamic constants of calcite and aragonite

We have calculated the total individual ion activity coefficients of carbonate and calcium, and , in seawater. Using the ratios of stoichiometric and thermodynamic constants of carbonic acid dissociation and total mean activity coefficient data measured in seawater, we have obtained values which differ significantly from those widely accepted in the literature. In seawater at 25°C and 35%. salinity the (molal) values of and are $\text{0.038 ± 0.002}$ and $\text{0.173 ± 0.010}$, respectively. These values of and are independent of liquid junction errors and internally consistent with the value . By defining and on a common scale (), the product is independent of the assigned value of and may be determined directly from thermodynamic measurements in seawater. Using the value and new thermodynamic equilibrium constants for calcite and aragonite, we show that the apparent constants of calcite and aragonite are consistent with the thermodynamic equilibrium constants at 25°C and 35%. salinity. The demonstrated consistency between thermodynamic and apparent constants of calcite and aragonite does not support a hypothesis of stable Mg-calcite coatings on calcite or aragonite surfaces in seawater, and suggests that the calcite critical carbonate ion curve of Broecker and Takahashi (1978, Deep-Sea Research25, 65–95) defines the calcite equilibrium boundary in the oceans, within the uncertainty of the data.     

Least-squares center-to-center and mean object ellipse fabric analysis

The subjectivity of ellipse fitting in many strain techniques has hindered the determination of fabric anisotropy and tectonic strain. However, many sets of x, y co-ordinates can be approximated as an ellipse using a least-squares algorithm to calculate a best-fit ellipse and associated average radial error. For instance, the two dimensional shape of many objects can be approximated as an ellipse by entering digitized co-ordinates of the object margin into the ellipse algorithm.The rim of maximum point density in a normalized Fry diagram is defined by normalized center-to-center distances between touching or nearly touching objects. The enhanced normalized Fry (ENFry) method automates ellipse fitting by entering center-to-center distances between these “touching” objects into the least-squares ellipse algorithm. For homogeneously deformed populations of 200 objects, the ENFry method gives an accurate and precise measure of whole-rock fabric anisotropy, particularly for low ellipticities. When matrix strain exceeds clast strain, manual ellipse fitting of normalized Fry plots gives more accurate matrix anisotropies.The mean object ellipse (MOE) method calculates the best-fit ellipse from the geometry of the objects. Three points from the margin of each object ellipse, centered at the origin and expanded or reduced to unit volume, are used to calculate the best-fit fabric ellipse. The MOE method is very precise for small data sets, making it a good method for mapping heterogenous object strain. However, least-squares calculations maximize the influence of distal and spurious ellipticities, causing the MOE method to overestimate the fabric ellipticity of most aggregates.     

Trace metals in sediments from the inner continental shelf of the western Beaufort Sea

Increased development and changing climate have enhanced global interest in the Arctic Ocean and adjacent seas. Using a large, 3-yr data base, we have determined the distribution of trace metals in sediments from the inner shelf of the western Beaufort Sea. Metal concentrations in these sediments reflect pristine conditions, consistent with those for most coastal areas in the Arctic and with predictions based on average continental crust. Geographic variations in metal values are primarily related to sediment grainsize distribution. However, grain-size patterns are a complex function of several variables including source areas, ice and water movement, as well as physical and chemical weathering. Future identification of any metal contamination in Beaufort Sea sediments will be simplified by understanding the predictable natural patterns.     

Instrumental neutron activation in geoanalysis

Theoretical aspects of instrumental neutron activation analysis (INAA) are discussed. Various applications of INAA to exploration geochemistry are described demonstrating its capabilities and its limitations.Cost, turnaround time, high sensitivity for certain elements, the non-destructive nature of analysis and its precision and accuracy have combined to make INAA an indispensible method for multielement determination on virtually all geological matrices. Humus, vegetation, heavy minerals, lake bottom sediments as well as rocks and soils comprise the major sample types analyzed by INAA. As many as 50 elements can be determined routinely and easily by INAA.     

不同气候变化情景下亚洲北山羊（Capra sibirica）的响应（英文）

目前很少见到关于气候变化影响亚洲北山羊物种栖息地的研究。通过调查气候变化对塔吉克斯坦东部亚洲北山羊(Capra sibirica)分布的影响,并采用生态位建模比较了亚洲北山羊的适宜栖息地的当前与未来分布情况。预计到2070年,现有适宜栖息地的18%(2689 km^2)将变得不适宜亚洲北山羊的生存,损失的区域主要位于研究区域的东南部和西北部地区。新的适宜栖息地可能会扩展到当前亚洲北山羊范围之外:到2070年将扩展30%(4595 km^2)的范围,这些区域与亚洲北山羊现有的分布有很强的相关性。东南部的损失与该地区当前大多数的亚洲北山羊栖息地重叠,主要出现在比研究区域海拔低得多的区域(3500–4000 m)。当同时考虑损失和收益时,亚洲北山羊可能会净扩展到新的适宜栖息地。到2070年,亚洲北山羊的平均栖息地增加量约为30%(1379 km^2),表明适宜栖息地已向北部低温栖息地转移。研究结果有助于规划气候变化情景下塔吉克斯坦东部山区对生物多样性保护的潜在影响。应该特别注意东南地区的高地山羊种群,那里的栖息地可能由于气候对山区生态系统的影响而变得不适合该物种继续生存。     

Geology and geochemistry of the Mammoth breccia pipe,Copper Creek mining district,southeastern Arizona: evidence for a magmatic–hydrothermal origin

The Copper Creek mining district, southeastern Arizona, contains more than 500 mineralized breccia pipes, buried porphyry-style, copper-bearing stockworks, and distal lead–silver veins. The breccia pipes are hosted by the Copper Creek Granodiorite and the Glory Hole volcanic rocks. The unexposed Mammoth breccia pipe, solely recognized by drilling, has a vertical extent of 800 m and a maximum width of 180 m. The pipe consists of angular clasts of granodiorite cemented by quartz, chalcopyrite, bornite, anhydrite, and calcite. Biotite ⁴⁰Ar/³⁹Ar dates suggest a minimum age of 61.5 ± 0.7 Ma for the host Copper Creek Granodiorite and ⁴⁰Ar/³⁹Ar dates on hydrothermal sericite indicate an age of 61.0 ± 0.5 Ma for copper mineralization. Fluid inclusion studies suggest that a supercritical fluid with a salinity of approximately 10 wt.% NaCl equiv. condensed to a dilute aqueous vapor (1–2.8 wt.% NaCl equiv.) and a hypersaline brine (33.4–35.1 wt.% NaCl equiv.). Minimum trapping temperatures are 375°C and trapping depths are estimated at 2 km. Sulfur isotope fractionation of cogenetic anhydrite and chalcopyrite yields a temperature of mineralization of 469 ± 25°C. Calculated oxygen and hydrogen isotope values for fluids in equilibrium with quartz and sericite range from 10.2‰ to 13.4‰ and −60‰ to −39‰, respectively, suggesting that the mineralizing fluid was dominantly magmatic. Evidence from the stable isotope and fluid inclusion analyses suggests that the fluids responsible for Cu mineralization within the Mammoth breccia pipe exsolved from a gray porphyry phase found at the base of the breccia pipe.     

Coseismic slip model of the 2007 August Pisco earthquake (Peru) as constrained by Wide Swath radar observations

The Pisco earthquake ( M _w 8.0; 2007 August 15) occurred offshore of Peru's southern coast at the subduction interface between the Nazca and South American plates. It ruptured a previously identified seismic gap along the Peruvian margin. We use Wide Swath InSAR observations acquired by the Envisat satellite in descending and ascending orbits to constrain coseismic slip distribution of this subduction earthquake. The data show movement of the coastal regions by as much as 85 cm in the line-of-sight of the satellite. Distributed-slip model indicates that the coseismic slip reaches values of about 5.5 m at a depth of ∼18–20 km. The slip is confined to less than 40 km depth, with most of the moment release located on the shallow parts of the interface above 30 km depth. The region with maximum coseismic slip in the InSAR model is located offshore, close to the seismic moment centroid location. The geodetic estimate of seismic moment is 1.23 × 10²¹ Nm ( M _w 8.06), consistent with seismic estimates. The slip model inferred from the InSAR observations suggests that the Pisco earthquake ruptured only a portion of the seismic gap zone in Peru between 13.5° S and 14.5° S, hence there is still a significant seismic gap to the south of the 2007 event that has not experienced a large earthquake since at least 1687.