西天山达巴特A型花岗岩的形成时代与构造背景

达巴特花岗斑岩侵入体位于西天山北部的赛里木湖北部,构造上属于准葛尔板块与伊犁.中天山板块之间的造山带.达巴特花岗岩斑岩具有A型花岗岩的特征,如高硅(SiO2=75.38%～77.61%)、碱(Na2O K2O=8.26%～10.10%)和Fe/(Fe Mg)(0.91～0.98),但低Al2O3(12.04～12.9%)和CaO(0.03%～0.42%),富集Rb、Th、U等大离子亲石元素和Nb、Ta、zr、Hf等高场强元素,(Ga/Al)×104值变化于3.19～3.40之间,具有明显的负Eu、Ba和Sr异常,稀土配分显示"海鸥型"特征.达巴特花岗岩斑岩具有较高的Rb/Nb和Y/Nb比值,显示了A2型花岗岩的特征.LA-ICP-MS锆石U-Pb测年结果显示达巴特岩体的侵位年龄为288.9±2.3Ma,并且一些锆石具有老的核(319.0±4.7),暗示花岗岩斑的源岩中可能包含有石炭纪的岩浆岩.结合区域地质和岩浆岩资料,我们认为西天山早二叠世处于伸展的背景中,可能与造山带后碰撞阶段的演化有关.     

Interpretation of tensor gravity data using an adaptive tilt angle method

Full Tensor Gravity Gradiometry (FTG) data are routinely used in exploration programmes to evaluate and explore geological complexities hosting hydrocarbon and mineral resources. FTG data are typically used to map a host structure and locate target responses of interest using a myriad of imaging techniques. Identified anomalies of interest are then examined using 2D and 3D forward and inverse modelling methods for depth estimation. However, such methods tend to be time consuming and reliant on an independent constraint for clarification. This paper presents a semi‐automatic method to interpret FTG data using an adaptive tilt angle approach. The present method uses only the three vertical tensor components of the FTG data (T_zx, T_zy and T_zz) with a scale value that is related to the nature of the source (point anomaly or linear anomaly). With this adaptation, it is possible to estimate the location and depth of simple buried gravity sources such as point masses, line masses and vertical and horizontal thin sheets, provided that these sources exist in isolation and that the FTG data have been sufficiently filtered to minimize the influence of noise. Computation times are fast, producing plausible results of single solution depth estimates t hat relate directly to anomalies. For thick sheets, the method can resolve the thickness of these layers assuming the depth to the top is known from drilling or other independent geophysical data. We demonstrate the practical utility of the method using examples of FTG data acquired over the Vinton Salt Dome, Louisiana, USA and basalt flows in the Faeroe‐Shetland Basin, UK. A major benefit of the method is the ability to quickly construct depth maps. Such results are used to produce best estimate initial depth to source maps that can act as initial models for any detailed quantitative modelling exercises using 2D/3D forward/inverse modelling techniques.     

The Development of a Web‐based Demographic Data Extraction Tool for Population Monitoring

The Internet contains a great wealth of information available online. People search engines, such as WhitePages ( http://www.whitepages.com ), gather personal‐level demographic data, including full name, address, age and household members. Requiring only a surname and locational reference (e.g. city or postal code) as the minimum search criteria, such people search engines can be perceived as a gigantic database of demographic records. The objective of this article is to outline the development of a web‐based demographic data extraction tool for population monitoring. In this study, a web prototype was developed to extract web demographics of the Vietnamese‐American (VA) population in Texas, an ethnic minority with unique migration history, from WhitePages. After post‐processing, the personal‐level demographic data represent 40.3% of 202,003 VA in Texas reported by the American Community Survey (ACS) 2009. While all enumeration strategies, the web approach included, have their own strengths and weaknesses, this study suggests an alternative approach that is complementary to existing enumeration strategies. More research and development are needed to validate the accuracy of web demographics and further enhance data navigation and extraction rules. The utilization and release of web demographics must be cautious with regards to privacy and integrity of personal identity.     

In situ cosmogenic exposure ages from the Isle of Skye,northwest Scotland: implications for the timing of deglaciation and readvance from 15 to 11 ka

We present 10 in situ cosmogenic exposure ages from two moraines on the Isle of Skye. The Strollamus medial moraine was deposited during deglaciation of the Devensian ice sheet and yields a mean exposure age from five samples of 14.3 ± 0.9 ka. The moraine age indicates that a significant ice mass existed on Skye at the time of a regional readvance recorded in Wester Ross, northwest Scotland. Taken at face value the ages suggest that deglaciation did not occur until well into Greenland Interstade 1. The Slapin moraine represents the local limit of the Loch Lomond Readvance (LLR) and yields a mean exposure age from five samples of 11.5 ± 0.7 ka, which is consistent with deposition relating to the LLR. These ages suggest that the maximum extent may have been reached late in the stadial and that some glaciers may have remained active until after the climatic amelioration that marks its end. This scenario is considered unlikely given the nature of the climate during this period, which leads us to call for a locally calibrated production rate. Copyright © 2011 John Wiley & Sons, Ltd.     

Timing,pace and controls on ice sheet retreat: an introduction to the BRITICE-CHRONO transect reconstructions of the British–Irish Ice Sheet

Motivated to help improve the robustness of predictions of sea level rise, the BRITICE-CHRONO project advanced knowledge of the former British–Irish Ice Sheet, from 31 to 15 ka, so that it can be used as a data-rich environment to improve ice sheet modelling. The project comprised over 40 palaeoglaciologists, covering expertise in terrestrial and marine geology and geomorphology, geochronometric dating and the modelling of ice sheets and oceans. A systematic and directed campaign, organised across eight transects from the continental shelf edge to a short distance (10s of kilometres) onshore, was used to collect 914 samples which yielded 639 new ages, tripling the number of dated sites constraining the timing and rates of change of the collapsing ice sheet. This special issue synthesises these findings of ice advancing to the maximum extent and its subsequent retreat for each of the eight transects to produce definitive palaeogeographic reconstructions of ice margin positions across the marine to terrestrial transition. These results are used to understand the controls that drove or modulated ice sheet retreat. A further paper reports on how ice sheet modelling experiments and empirical data can be used in combination, and another probes the glaciological meaning of ice-rafted debris.     

Timing and pace of ice-sheet withdrawal across the marine–terrestrial transition west of Ireland during the last glaciation

Understanding the pace and drivers of marine-based ice-sheet retreat relies upon the integration of numerical ice-sheet models with observations from contemporary polar ice sheets and well-constrained palaeo-glaciological reconstructions. This paper provides a reconstruction of the retreat of the last British–Irish Ice Sheet (BIIS) from the Atlantic shelf west of Ireland during and following the Last Glacial Maximum (LGM). It uses marine-geophysical data and sediment cores dated by radiocarbon, combined with terrestrial cosmogenic nuclide and optically stimulated luminescence dating of onshore ice-marginal landforms, to reconstruct the timing and rate of ice-sheet retreat from the continental shelf and across the adjoining coastline of Ireland, thus including the switch from a marine- to a terrestrially-based ice-sheet margin. Seafloor bathymetric data in the form of moraines and grounding-zone wedges on the continental shelf record an extensive ice sheet west of Ireland during the LGM which advanced to the outer shelf. This interpretation is supported by the presence of dated subglacial tills and overridden glacimarine sediments from across the Porcupine Bank, a westwards extension of the Irish continental shelf. The ice sheet was grounded on the outer shelf at ~26.8 ka cal bp with initial retreat underway by 25.9 ka cal bp. Retreat was not a continuous process but was punctuated by marginal oscillations until ~24.3 ka cal bp. The ice sheet thereafter retreated to the mid-shelf where it formed a large grounding-zone complex at ~23.7 ka cal bp. This retreat occurred in a glacimarine environment. The Aran Islands on the inner continental shelf were ice-free by ~19.5 ka bp and the ice sheet had become largely terrestrially based by 17.3 ka bp. This suggests that the Aran Islands acted to stabilize and slow overall ice-sheet retreat once the BIIS margin had reached the inner shelf. Our results constrain the timing of initial retreat of the BIIS from the outer shelf west of Ireland to the period of minimum global eustatic sea level. Initial retreat was driven, at least in part, by glacio-isostatically induced, high relative sea level. Net rates of ice-sheet retreat across the shelf were slow (62–19 m a⁻¹) and reduced (8 m a⁻¹) as the ice sheet vacated the inner shelf and moved onshore. A picture therefore emerges of an extensive BIIS on the Atlantic shelf west of Ireland, in which early, oscillatory retreat was followed by slow episodic retreat which decelerated further as the ice margin became terrestrially based. More broadly, this demonstrates the importance of localized controls, in particular bed topography, on modulating the retreat of marine-based sectors of ice sheets.     

Can sodium hypochlorite reduce the risk of species introductions from diapausing invertebrate eggs in non-ballasted ships?

Many transoceanic vessels enter the Great Lakes carrying residual ballast water and sediment that harbours live animals and diapausing eggs. In this study, we examine the potential for sodium hypochlorite (NaOCl) to reduce the risk of species introductions from diapausing invertebrate eggs in residual ballast sediment. We collected sediment from three transoceanic vessels and from Lake Erie and exposed them to NaOCl concentrations between 0 and 10,000 mg/L for 24 h. Hatching success was reduced by >89% in all four experiments at 1,000 mg/L relative to unexposed controls. Fewer species hatched at high than at low NaOCl concentrations. Based on an average residual ballast of 46.8 tonnes, the volume of NaOCl required to treat inbound vessels is 374 L. Impacts of NaOCl use could be minimized by neutralization of treated residuals with sodium bisulfite. Further research is needed, however, to evaluate the effect of NaOCl on ballast tank corrosion.     

The fine‐grained matrix of the Semarkona LL3.0 ordinary chondrite: An induced thermoluminescence study

Abstract— To investigate the nature, origin, and history of the fine‐grained matrix in Semarkona and develop techniques suitable for small samples, we have measured the induced thermoluminescence properties of six matrix samples 10 μm to 400 μm in size. The samples had TL sensitivities comparable with 4 mg of bulk samples of type 3.2–3.4 ordinary chondrites, which is very high relative to bulk Semarkona. The other induced TL properties of these samples, TL peak temperatures, and TL peak widths distinguish them from other ordinary chondrite samples where the TL is caused by feldspar. Cathodoluminescence images and other data suggest that the cause of the luminescence in the Semarkona fine‐grained matrix is forsterite. In some respects the matrix TL data resemble that of Semarkona chondrules, in which the phosphor is forsterite and terrestrial forsterites from a variety of igneous and metamorphic environments. However, differences in the TL peak temperature versus TL peak width relationship between the matrix samples and the other forsterites suggest a fundamentally different formation mechanism. We also note that forsterite appears to be a major component in many primitive materials, such as nebulae, cometary dust, and Stardust particles.     

Diurnal and Seasonal Trends in Convective Mixed-Layer Heights Estimated from Two Years of Continuous Ceilometer Observations in Vancouver,BC

Twenty-six months of continuous ceilometer data are used to estimate the convective mixed-layer height for 710 days by identifying backscatter gradients associated with the entrainment zone. To accomplish this, a semi-automatic procedure is developed that removes all non-applicable data before applying a mixed-layer height algorithm to the backscatter profiles. Two different algorithms for estimating the mixed-layer height are assessed: the minimum-gradient method and the ideal-profile method. The latter of these two algorithms is found to be more robust. Comparisons of mixed-layer height values estimated from the ceilometer agree with previous observations with slightly higher estimates in the mornings and evenings. For clear days with no cumulus cloud formation, the seasonal cycle in mixed-layer heights peaks in late June to early July. Daily maximum values are suppressed by the site’s coastal location, remaining below 800 m for all but a few days. The mean daily maximum mixed-layer height increases by 384 m for days with boundary-layer clouds. The mean summer diurnal trend is found not to differ greatly from that in spring on clear days, while days with boundary-layer clouds have higher spring values than in summer. Net surface heat flux and synoptic stability likely have the largest influence on the mixed-layer heights. Additionally, large intra-monthly variability suggests a strong influence from regional dynamics.     

An investigation of the presence and nature of phyllosilicates on the surfaces of C asteroids by an analysis of the continuum slopes in their near‐infrared spectra

Abstract– To understand the nature of C asteroid surfaces, which are often related to phyllosilicates and C chondrites, we report near‐infrared spectra for a suite of phyllosilicates, heated to 100–1100 °C in 100 °C intervals, and compare the results for telescope IRTF spectra for 11 C asteroids. As C asteroids have relatively featureless spectra, we focus on “continuum plots” (1.0–1.75 μm slope against 1.8–2.5 μm slope). We compare the continuum plots of the 11 C asteroids and our heated phyllosilicates with literature data for C chondrites. The CI, CR, CK, and CV chondrite meteorites plot in the C asteroid field, whereas CM chondrites plot in a close but discrete field. All are well separated from the large phyllosilicate field. Heating kaolinite and montmorillonite to ≥700 °C moves their continua slopes into the C asteroid field, whereas chlorite and serpentine slopes move into the CM chondrite field. Water losses during heating are generally 10–15 wt% and were associated with a 20–70% albedo drop. Our data are consistent with surfaces of the C asteroids consisting of the dehydration products of montmorillonite whereas the CM chondrites are the dehydration products of serpentine and chlorite. The presence of opaque minerals and evaporites does not provide quantitative explanations for the difference in continua slopes of the phyllosilicates and C asteroids. The CM chondrites can also be linked to the C asteroids by heating. We suggest that the CM chondrites are interior samples, and the presence of a 3 μm feature in C asteroid spectra also indicates the excavation of material.