基于深度加权的重力梯度数据联合相关成像反演

针对矿产勘查中相关成像反演存在的纵向分辨率较低的问题，提出了一种基于深度加权的重力梯度数据相关成像反演方法.通过联合多个重力梯度分量、引入基于先验信息的深度加权函数与地下空间分区加权等方法，提高反演的纵向空间分辨率.在数据试验中，利用立方体组合模型证实了提出的方法能够准确反演出目标体的空间位置，计算的密度数值范围与理论模型基本一致，且方法具有一定的抗噪能力.将反演应用于美国文顿盐丘地区的实测重力梯度数据，结果显示出的盖岩位置与已知地质资料相符，证明了本文方法具有可行性和实用性.     

Preliminary evidence indicating Dome A （Antarctica） satisfying preconditions for drilling the oldest ice core

Lowest temperature and snow accumulation rate are preconditions for retrieving the oldest ice core from the polar ice sheets. The 10-m depth firn temperature at Dome A, the summit of the Antarctic Ice Sheet, recorded by an automatic weather station （AWS） was -58.3℃ in 2005 and -58.2℃ in 2006, respectively. The 10-m firn temperature is an approximation of the annual mean air temperature （AMAT）, and this is the lowest AMAT that has been recorded on the surface of the Earth. The stable isotopic ratios （δ^18O and δD） of surface snow at Dome A are also lower than at other ice sheet domes along the East Antarctic Ice Divide such as Dome C, Dome F, Dome B and Vostok. These facts indicate that Dome A is the ＂pole of cold＂ on the Earth. The total amount of snow accumulation rate in 2005 and 2006 was only 0.16 cm, equaling 0.016 m water equivalent per year, the lowest precipitation ever recorded from Antarctica. Preliminary evidences indicate that Dome A is a candidate site for recovering the oldest ice core.     

Ice radar investigation at Dome A, East Antarctica: Ice thickness and subglacial topography

Dome A, located in the central East Antarctic ice sheet (EAIS), is the highest summit of the Antarctic ice sheet. From ice-sheet evolution modeling results, Dome A is likely to preserve over one million years of the Earth’s paleo-climatic and -environmental records, and considered an ideal deep ice core drilling site. Ice thickness and subglacial topography are critical factors for ice-sheet models to determine the timescale and location of a deep ice core. During the 21st and 24th Chinese National Antarctic Research Expedition (CHINARE 21, 2004/05; CHINARE 24, 2007/08), ground-based ice radar systems were used to a three-dimensional investigation in the central 30 km×30 km region at Dome A. The successfully obtained high resolution and accuracy data of ice thickness and subglacial topography were then interpolated into the ice thickness distribution and subglacial topography digital elevation model (DEM) with a regular grid resolution of 140.5 m×140.5 m. The results of the ice radar investigation indicate that the average ice thickness in the Dome A central 30 km×30 km region is 2233 m, with a minimal ice thickness of 1618 m and a maximal ice thickness of 3139 m at Kunlun Station. The subglacial topography is relatively sharp, with an elevation range of 949–2445 m. The typical, clear mountain glaciation morphology is likely to reflect the early evolution of the Antarctic ice sheet. Based on the ice thickness distribution and subglacial topography characteristics, the location of Kunlun Station was suggested to carry out the first high-resolution, long time-scale deep ice core drilling. However, the internal structure and basal environments at Kunlun Station still need further research to determine.     

Distribution of <Emphasis Type="Italic">δ</Emphasis><Superscript>18</Superscript>O in surface snow along a transect from Zhongshan Station to Dome A,East Antarctica

Surface snow samples were collected during the 14th (1997/1998) and 24th (2007/2008) Chinese National Antarctica Research Expeditions along a transect from Zhongshan Station to Dome A. The stable oxygen isotope ratios of these samples were measured to investigate their relationships with temperature and geographical parameters (latitude, longitude, altitude and distance to the coast). The results reveal a strong positive correlation (R=0.945) between δ¹⁸O and mean annual temperature, with a gradient of 0.84‰°C ^–1, which is a little higher than that in Terre Adelie Land. Regression analyses also show that the δ¹⁸O of surface snow is strongly correlated with distance to the coast (R=0.942), latitude (R=0.942), and altitude (R=0.941). But no significant correlation was found between δ¹⁸O and longitude in study area. Altitude should be the most important factor influencing the δ¹⁸O distribution because of distinctive topography. The δ¹⁸O-altitude and T-altitude gradients along this transect are determined to be –1.1‰/100 m and 1.31°C/100 m, respectively.     

Analyses on the air and snow temperatures near ground with observations of an AWS at Dome A, the summit of Antarctic Plateau

As the summit of the Antarctic Plateau, Dome A has been received international attentions.In this paper, observational data of an automatic weather station (AWS) at Dome A in 2005–2007 were used to analyze the seasonal variations of air temperatures near the ground and snow temperatures within a depth of 10 m. Analyses on the air temperatures show a typical feature of the coreless winter, and strong inversion maintains during the long winter. Accordingly the stratification near the ground is dominated by th...     

Recent accumulation rate at Dome A, Antarctica

Based on the horizon of β activity and the density profiles, recent accumulation rate at Dome A, Ant-arctica is calculated to be 0.023 m water equivalent per year. This value is comparative to the accumu-lation rates deduced from the other inland sites of Antarctica. Clear-sky precipitation (or diamond dust) dominates the total precipitation at Dome A region. We speculate Dome A as a potential site to discover the oldest ice in Antarctica due to its tremendous ice thickness (>3000 m), extremely low accumulation rate, and low ice velocity.     

复杂地下洞室群施工污染气体及粉尘通风运移

在地下洞室群的爆破施工过程中会产生大量污染气体及粉尘,对地下洞室群施工通风污染气体及粉尘运移的认识有助于优化洞室群施工通风设计,提高洞室群通风方案的合理性。本文针对某大型复杂地下储油洞室群穹顶施工过程中的通风问题,采用CFD数值模拟及现场实测的方法,对污染气体及粉尘在洞室内的运移进行了分析。结果表明：气流在洞室内的发展过程分为涡流区、回流区和碰撞区,涡流区和碰撞区是通风过程中较不利的位置。多洞室的情况下,洞室内的污染气体容易在主通道内聚集。粉尘在洞室与连接通道交叉的位置以及主通道左侧转弯处浓度较高。洞室穹顶内污染气体及粉尘运移的速率较高,并且粉尘相对于污染气体的运移存在滞后性。     

方向总水平导数法的改进和边界识别中的应用

为了提高重力勘探中边界识别方法的分辨率,增强对地质体边界的划分和检测能力,本文在方向总水平导数法的基础上进行了改进.提出了基于重力梯度数据的方向总水平导数与加强方向总水平导数的垂向导数、综合x,y和z方向的方向总水平导数及其垂直导数等6种新型边界探测器.通过理论模型与噪声试验,证明了改进的方法具有较好的边界划分能力;与原方法相比,改进后的方法识别出的边界与模型更好地吻合.将文顿盐丘地区的实测数据引入改进后的方法中,更清晰地识别出地下盖岩的边界,验证了方法的可行性.     

Preliminary results of ice radar investigation along the traverse between Zhongshan and Dome A in East Antarctic ice sheet: Ice thickness and subglacial topography

During the 24th Chinese National Antarctic Research Expedition (CHINARE 24, 2007/08), a ground-based ice radar was used to survey ice thickness and subglacial topography along the 1170 km traverse between Zhongshan and Dome A in East Antarctic ice sheet (EAIS). Ice-bedrock interface was detected along 82% of the traverse and data was collected at a horizontal resolution of <5.6 m. The data was processed to produce curves of ice thickness distribution and subglacial topography along the traverse. The results indicate that, along the traverse, the average ice thickness is 2037 m, smaller than the average ice thickness in EAIS; the thickest ice is at 730 km, and the thinnest ice (891 m) is at the edge of the ice sheet, but the slightly larger ice thickness (1078 m) in inland appears at 1020 km; the average subglacial topography elevation is 728 m, greatly larger than the average value in EAIS, and the largest elevation reaches up to 2650 m at 1034 km. The lowest terrain is located at 765 km. In further inland of 900–1170 km, the subglacial topography is relatively high due to the existence of the Gamburtsev Subglacial Mountains in the region. Generally, the influence of subglacial topography on ice surface is not significant, except at 900 km where great rise of subglacial topography causes evident uplift of ice surface. Where ice-bedrock interface was detected, the frequent and strong change of ice thickness and subglacial topography in small-scale means large bedrock roughness along the traverse, and is considered as the result of the integrated influence of ice flow, basal environments and geology. The segment where bedrock was not detected has very large ice thickness. The strong ice flow there also makes internal structure more complicated and induces serious attenuation of radar signals.     

Early Oligocene anatexis in the Yardoi gneiss dome, southern Tibet and geological implications

The Yardoi gneiss dome is located to the easternmost of the North Himalayan Gneiss Dome (NHGD), southern Tibet. It consists of metapelite, garnet amphibolite, granite and leucogranite, and is a key subject to constrain the formation and tectonic evolution of NHGD. SHRIMP zircon U/Pb data on the leucogranite yield an age of 35.3±1.1 Ma, which is substantially older than that of the similar leucogranites to the west. Sr and Nd isotope systematics indicate that this leucogranite was derived from partial melting of the mixed garnet amphibolite and metapelite. Our data suggest that (1) during the early stage of Himalayan magmatism, amphibolite dehydration melting overwhelmed that of the metapelite; and (2) such a melting at middle-lower crust might be a major factor that initiated the movement along the Southern Tibetan Detachment System (STDS). Supported by National Natural Science Foundation of China (Grant No. 40673027), the Outlay Research Fund of Chinese Academy of Geological Sciences (Grant No. 20071120101125), and the Hundred Talent Program of Chinese Academy of Sciences