Separation problem in satellite gravimetry

The problem of separating gravitation from inertia is discussed in very general sense, and the conclusion is positive: man can separate gravitation from inertia, if various observation techniques are applied for. The accelerometer’s position problem in satellite gravimetry is investigated, and the additional acceleration effect due to the position error of an instrument as well as the difference between the mass center and the gravity center is explored.     

腾冲火山岩年龄问题评述

腾冲火山及火山岩是国内新近纪火山及其喷发物九大分布区之一,研究程度较广较深,喷发序列岩石定岩及年龄值资料丰富,综合评述并指出今后研究方向。     

Geomorphology of carbonate platform‐marginal uppermost slopes: Insights from a Holocene analogue,Little Bahama Bank,Bahamas

As the product of a variety of sediment sources and sedimentation (and re‐sedimentation) and erosion processes, the geomorphology and sedimentology of carbonate slopes are highly variable. The purpose of this study is to describe sub‐bottom profiles and side‐scan sonar, multibeam and optical data acquired by an autonomous underwater vehicle to explore variability in geomorphological and sedimentological character of the present‐day platform‐marginal, uppermost slope environments (< 240 m water depth) on the north, open‐ocean facing flank of Little Bahama Bank, Bahamas. Although at time scales of greater than 100 ka this margin is progradational, the data illustrate a complex juxtaposition of erosional and depositional processes and features. Erosion is evidenced by two prominent escarpments (70 m and 120 m) that expose eroded, bedded rocky outcrops. These escarpments are interpreted to represent relict features, related to past sea‐level positions, although they still may be shedding debris. Aside from erosional remnants, sedimentation and active transport is indicated by several features, including active bedforms (especially above the 70 m escarpment, but ripples occur to depths of ca 200 m), several mass transport complexes that overlie and cover the lower escarpment, gravity flow deposits and rare slump features. Similarly, a thick (up to 20 m) onlapping sediment wedge, interpreted to be Holocene in age, suggests lateral accretion of the slope by more than 75 m in this period. Data illustrate that this open‐ocean margin is distinct from windward margins in the Bahamas, which typically include near‐vertical walls of erosion or bypass, flanked downdip by rubble and talus, and leeward margins, which have onlapping muddy wedges, but that lack marked terraces or escarpments. Collectively, the results provide perspectives into the nature and controls on complex geomorphological patterns of erosion and deposition in Holocene uppermost slope systems, concepts potentially applicable to ancient analogues.     

深水重要油气储层--琼东南盆地中央峡谷体系

南海北部海域琼东南盆地发育一个大型中央峡谷体系,平面上呈“S”型NE向展布,西起莺歌海盆地中央拗陷带东缘,横穿琼东南盆地中央拗陷带,向东延伸进入西沙海槽。通过2D及3D地震资料的精细解释和钻井资料综合分析,研究揭示该峡谷体系可以划分为4个区段,不同区段不仅具有明显不同的剖面形态,而且具有不同沉积物构成、沉积微相以及不同沉积物源。不同区域峡谷形态及充填分析表明,自西向东,中央峡谷下切深度越来越大,下切层位越来越老。其下切剖面形态发育有“V”、“U”、“W”和复合型。其中“V”型峡谷下切深度最大,冲刷、削截特征最明显。峡谷西段以浊积水道沉积为主,峡谷东段为浊积水道与块体流沉积互层沉积,但在不同区带不同沉积物所占比例有一定差异。浊积水道沉积的物源主要来自于盆地西侧,块体流沉积的物源主要来自于盆地北部陆坡体系,从而,来自于西部浊积水道沉积与来自于北部块体流沉积在中央峡谷内形成了多源多期发育的复杂的峡谷系统。     

Oxygen isotopes from Chinese caves: records not of monsoon rainfall but of circulation regime

Oxygen isotope variations in Chinese stalagmites have been widely interpreted as a record of the amount of East Asian summer monsoonal rainfall. This interpretation infers decreasing monsoonal rainfall from the mid‐Holocene and large, dipolar rainfall oscillations within glaciations. However, the speleothem δ¹⁸O variations conflict with independent palaeoclimate proxies (cave δ¹³C, loess/palaeosol magnetic properties, δ¹³C alkanes), which indicate no systematic decline in rainfall from the mid‐Holocene, and no glacial rainfall maxima. Using mass balance calculations (which incorporate seasonality effects in both δ¹⁸O concentration and amount of precipitation), we demonstrate that the cave δ¹⁸O variations cannot be accounted for by summer rainfall changes, or rainfall seasonality or winter cooling, but instead reflect changes in moisture source. A possible driver of the δ¹⁸O variations in Chinese stalagmites is precessional forcing of inter‐hemispheric temperature gradients, and resultant shifts in the position and intensity of the subtropical pressure cells. Through such forcing, Indian monsoon‐sourced δ¹⁸O may have dominated at times of high boreal summer insolation, and local Pacific‐sourced moisture at low insolation. Suppression of summer monsoonal rainfall during glacial stages may reflect diminished sea and land surface temperatures and the radiative impacts of increased regional dust fluxes. Copyright © 2012 John Wiley & Sons, Ltd.     

Nd–Sr isotopic constraint to the formation of metatexite and diatexite migmatites,Higo metamorphic terrane,central Kyushu,Japan

ABSTRACT

Metatexite and diatexite migmatites are widely distributed within the upper amphibolite and granulite-facies zones of the Higo low-P/high-T metamorphic terrane. Here we report Nd–Sr isotopic and whole rock composition data from an outcrop in the highest-grade part of the granulite-facies zone, in which diatexite occurs as a 3 m-thick layer between 2 m-thick layers of stromatic-structured metatexite within pelitic gneiss. The metatexite has Nd–Sr isotopes and whole rock compositions similar to those of the gneiss, but the diatexite shows the reverse. The diatexite has a higher ε_Nd(t) and ¹⁴⁷Sm/¹⁴⁴Nd ratio (ε_Nd(t) = ?0.5; ¹⁴⁷Sm/¹⁴⁴Nd = 0.1636) than the gneiss (ε_Nd(t) = ?2.1; ¹⁴⁷Sm/¹⁴⁴Nd = 0.1287) and metatexite (ε_Nd(t) = ?3.1; ¹⁴⁷Sm/¹⁴⁴Nd = 0.1188). The (⁸⁷Sr/⁸⁶Sr)_initial and ⁸⁷Rb/⁸⁶Sr of the diatexite ((⁸⁷Sr/⁸⁶Sr)_initial = 0.70568; ⁸⁷Rb/⁸⁶Sr = 0.416) are lower than those of the gneiss ((⁸⁷Sr/⁸⁶Sr)_initial = 0.70857; ⁸⁷Rb/⁸⁶Sr = 1.13) and metatexite ((⁸⁷Sr/⁸⁶Sr)_initial = 0.70792; ⁸⁷Rb/⁸⁶Sr = 1.11). The metatexite and gneiss show enrichment of Th and depletion of P and Eu and have a similar chondrite-normalized REE pattern, which shows steep LREE–MREE-enriched and gently declining HREE patterns and negative Eu anomalies, whereas the diatexite shows enrichment of Sr and depletion of Th and Y, and exhibits gently declining LREE and steeply declining HREE pattern and weak Eu depletion. The metatexite migmatite is interpreted to have formed by in situ partial melting in which the melt did not migrate from the source, whereas the diatexite migmatite included an externally derived melt with a juvenile component. The Cretaceous high-temperature metamorphism of the Higo metamorphic terrane is interpreted to reflect emplacement of mantle-derived basalts under a volcanic arc along the eastern margin of the Eurasian continent, and mass transfer and advection of heat via hybrid silicic melts from the lower crust.     

稀土元素对鲁西铜石、铜井、龙宝山杂岩体的同源性制约

20世纪80年代,在山东省平邑县发现归来庄大型金矿床,实现了鲁西黄金找矿的重大突破。此后,鲁西相继发现卓家庄、磨坊沟和龙宝山金矿。近年,又在沂南金矿的深部发现新的矿体,鲁西良好的金矿成矿前景引起了地质学界的广泛关注。目前,鲁西发现的金矿床主要分布在铜石、铜井和龙宝山等燕山期杂岩体的附近。这些岩体在成因上有什么关系值得研究。通过对上述岩体稀土元素的地球化学分析,每种岩体不同期次侵入的岩浆岩的稀土元素分布形式和3种岩体综合稀土元素分布形式均呈向右陡倾的弧形线,且配分曲线形态基本相似,都没有明显的Ce、Eu异常,指示了岩体之间存在同源性,均来自深部同一岩浆房。该认识对于指导鲁西黄金找矿具有一定的意义。     

浅析四川汶川索桥滑坡稳定性及治理措施

根据工程地质测绘及勘探成果资料,在对四川汶川县索桥滑坡产生的成因机理和破坏模式进行分析判断的基础上,对两个潜在滑移面在不同的工况下的稳定性进行了分析评价,确定岩土交界面为最危险滑面.在此前提下对边坡发展趋势及激发诱因进行科学预测,认为在暴雨或余震等诱发下边坡极有可能失稳,并有针对性的制定了应急防治与永久根治的综合治理方案.     

Nontectonic signals in reprocessed continuous GPS position time series of CMONOC

The nearly nine-year continuous GPS data collected since 1 March 1999 from the Crustal Motion Observation Network of China(CMONOC) were consistently analyzed.Most of the nonlinear movements in the cumulative position time series pro-duced by CMONOC data center disappeared;and more accurate vertical terms and tectonic signals were extracted.Displacements caused by atmospheric pressure loading,nontidal ocean loading,soil moisture mass loading,and snow cover mass loading using the National Centers for Environmental Prediction(NCEP) Reanalysis I/II models and Estimation of the Circulation and Climate of the Ocean(ECCO) data can explain most of the vertical annual terms at many stations,while only parts can be explained at Lhasa and southern coastal sites,indicating that there are some deformation mechanisms that are still unknown or not modeled accurately.The remarkable differences in vertical position time series for short-baseline sites reveal that GPS stations can be greatly affected by lo-cal factors;and attention should be paid when explaining observed GPS velocity vectors.     

Contemporary 14C radiocarbon levels of oxygenated polybrominated diphenyl ethers (O-PBDEs) isolated in sponge-cyanobacteria associations

Considerable debate surrounds the sources of oxygenated polybrominated diphenyl ethers (O-PBDEs) in wildlife as to whether they are naturally produced or result from anthropogenic industrial activities. Natural radiocarbon (¹⁴C) abundance has proven to be a powerful tool to address this problem as recently biosynthesized compounds contain contemporary (i.e. modern) amounts of atmospheric radiocarbon; whereas industrial chemicals, mostly produced from fossil fuels, contain no detectable ¹⁴C. However, few compounds isolated from organisms have been analyzed for their radiocarbon content. To provide a baseline, we analyzed the ¹⁴C content of four O-PBDEs. These compounds, 6-OH-BDE47, 2′-OH-BDE68, 2′,6-diOH-BDE159, and a recently identified compound, 2′-MeO-6-OH-BDE120, were isolated from the tropical marine sponges Dysidea granulosa and Lendenfeldia dendyi. The modern radiocarbon content of their chemical structures (i.e. diphenyl ethers, C₁₂H₂₂O) indicates that they are naturally produced. This adds to a growing baseline on, at least, the sources of these unusual compounds.