青藏高原东部多年冻土退化对环境的影响

退化是本区多年冻土变化的基本趋势，不同区段退化幅度有差异，影响退化的因素除了全球气候转暖外，还有局地气候和地下水迳流。在退化敏感的地带，工程建设，牧区生态平衡都有不可忽视的影响。     

对我国西南地区河谷深厚覆盖层成因机理的新认识

近年来,在我国水能资源开发过程中,发现各河流现代河床以下普遍堆积厚达数十米甚至上百米的松散堆积物。河谷深厚覆盖层的存在,不仅严重制约了工程坝址的选择,影响相关流域水电资源的开发利用,也给坝工设计带来巨大的困难。由于深厚覆盖层埋藏于现代河床之下,其形成年代一般先于一二级阶地,有悖于河流发育演化的常理,其成因一直令人费解。首次将河谷深切和深厚堆积事件与全球气候变化、海平面升降运动、地壳运动等有机地联系起来,并提出冰期、间冰期全球海平面大幅度升降,是导致河流深切成谷并形成深厚堆积的主要原因的新观点。在此基础上,引入层序地层学原理,从理论上较好地解释了全球气候变化导致海平面和河流侵蚀基准面大幅变化,并产生河谷深切和深厚堆积的原因和过程。最后,进一步将沿河大型古滑坡的孕育和发生与河谷深切事件相联系,提出沿河大型古滑坡是在河谷深切期因前缘临空较好而形成的新观点,从而对沿河古滑坡前缘剪出口高程往往低于现代河床数十米的原因给出了较合理的解释。     

RATIONAL UTILIZATION OF MOUNTAIN SOILS IN SOUTHEAST QINGHAI-XIZANG (TIBETAN)PLATEAU

ISoil-fo~gEnvironmentandMainSoilTrocsThesoLItheastQinghai-Xizang(Tibetan)PlateauwheretheHengduanMoUnains,eastempartoftheThmalayanandNyainqentanglhamoUnainsarelocatedextendsfrom25'to34"Nand92'to1O5'Ewithanareaof5OO,OOOkm',oraboutone-fiffooftheentireQinghai-XiZangPlateau.ItisatransitionalzoneofdeePdisseCtedmoUntainseXtendingsoutheastWardpenpherallowlandsandwichedin-betWeenSichuanBasinandcentralYunnanPlateau.Whletheterrainofthesmponinclinestosoutheast,thealtitudeofthevaIleysraises…     

Modes of raising northeastern Tibet probed by explosion seismology

New wide-angle reflection and refraction seismic data provide constraints on the structure of the upper lithosphere, and test models of its evolution to raise the northeastern part of the Tibetan Plateau. Amplitudes observed for reflections from the crust-mantle boundary are sufficiently large to suggest that there is no significant partial melt in the deep crust. The data show an increase of the crustal thickness between terranes from north of the Kun Lun Fault into the Qang Tang of central Tibet, and a contrast among their intracrustal images and compositions. In the north, P and S velocities are consistent with a dominantly felsic composition and show that only the upper crust thickened. South of the Kun Lun Fault a thicker crust made of two layers could result from the superposition of the originally thin crust of the Bayan Har terrane on the lower part of the crust of the domain to the north, which upper crust it shoved and thickened. Different modes of crustal thickening, either by thickening of individual layers or superpositions and imbrication among them appear to work jointly to raise the topography.     

The Darwin Rise demise: the western Pacific guyot heights trace the trans-Pacific Mendocino fracture zone

The Darwin Rise has been proposed so many times and in so many forms and places that the time has come to make a more comprehensive examination of the region. Lying on the NW Pacific Plate between the Geisha Guyots, the Mid-Pacific Mountains, the equator, and the trenches, the region is roughly bounded by magnetic anomaly M20 (147 Ma). It was subjected to a massive outpouring of lava about 105 to 120 Ma, which created the guyots and seamounts in that region. Guyots are excellent tools for studying events of long ago because they eroded in the same lowstand in the Cretaceous and guyot relief, therefore, is a surrogate for paleo-sealevel. The relief is derived by subtracting the break depth of the summit plateau of a guyot from the regional depth. Guyot relief would necessarily be less in the center than to the periphery if the feature formed on a pre-existing rise, as has been postulated. The existence of a paleo-Darwin Rise would give concentric contours for the region in question. Of the sixty guyots used in this study, thirty-seven of these guyots were surveyed using SASS multibeam in the Marcus-Wake seamount group. Twenty-three guyots were surveyed using random track single-beam sonar surveys. An entirely different scenario is shown. Data revealed a major fracture passing through the area coevally or after the guyots formed. Because the depths to the summit are not the same now, vertical tectonics occurred after subaerial erosion. This means the fracture formed during and after the erosion (roughly 105 Ma) and influenced the normal sequence of events in guyot formation. Depending on how one deciphers trends through the Hess Rise morass, SASS bathymetry shows a continuation of the Surveyor/Mendocino fracture zone swarm inside the M20 region to the NE of these data. The fracture swarm continues to the western Pacific trench system. Based on this information, if the Darwin Rise ever existed, it had to have done so elsewhere.     

Reconstruction of atmospheric CO2 from ice-core data and the deep-sea record of ontong Java plateau: the Milankovitch chron

We provide a reconstruction of atmospheric CO₂ from deep-sea sediments, for the past 625000 years (Milankovitch chron). Our database consists of a Milankovitch template of sea-level variation in combination with a unique data set for the deep-sea record for Ontong Java plateau in the western equatorial Pacific. We redate the Vostok ice-core data of Barnola et al. (1987). To make the reconstructions we employ multiple regression between deep-sea data, on one hand, and ice-core CO₂ data in Antarctica, on the other. The patterns of correlation suggest that the main factors controlling atmospheric CO₂ can be described as a combination of sea-level state and sea-level change. For best results squared values of state and change are used. The square-of-sea-level rule agrees with the concept that shelf processes are important modulators of atmospheric CO₂ (e.g., budgets of shelf organic carbon and shelf carbonate, nitrate reduction). The square-of-change rule implies that, on short timescales, any major disturbance of the system results in a temporary rise in atmospheric CO₂.     

青藏高原Pn波研究进展及问题

简要总结了青藏高原地区Pn波速度结构、各向异性研究进展；介绍了Pn波速度结构、各向异性等在岩石圈结构、构造背景反映等方面的应用研究进展。分析了目前青藏高原Pn波研究中存在的一些问题。     

Mafic Pegmatites Intruding Oceanic Plateau Gabbros and Ultramafic Cumulates from Bolivar, Colombia: Evidence for a 'Wet' Mantle Plume?

The fault-bounded Bolívar Ultramafic Complex (BUC) onthe eastern fringes of the Western Cordillera of Colombia wastectonically accreted onto the western coast of South Americain the late Cretaceous–early Tertiary, along with pillowbasalts of the Caribbean–Colombian Oceanic Plateau (CCOP).The complex consists of a lower sequence of ultramafic cumulates,successively overlain by layered and isotropic gabbroic rocks.The gabbros grade into, and are intruded by, mafic pegmatitesthat consist of large magnesiohornblende and plagioclase crystals.These pegmatites yield a weighted mean ⁴⁰Ar–³⁹Ar step-heatingage of 90·5 ± 0·9 Ma and thus coincidewith the timing of peak CCOP volcanism. The chemistry of theBUC is not consistent with a subduction-related origin. However,the similarity in Sr–Nd–Pb–Hf isotopes betweenthe CCOP and the BUC, in conjunction with their indistinguishableages, suggests that the BUC is an integral part of the plume-derivedCCOP. The parental magmas of the Bolívar complex wereprobably hydrous picrites that underwent 20–30% crystallization.The residual magmas from this fractionation contained     

Changes in soil organic carbon and other physical soil properties along adjacent Mediterranean forest, grassland, and cropland ecosystems in Turkey

Cultivation, overgrazing, and overharvesting are seriously degrading forest and grassland ecosystems in the Taurus Mountains of the southern Mediterranean region of Turkey. This study investigated the effects of changes on soil organic carbon (SOC) content and other physical soil properties over a 12-year period in three adjacent ecosystems in a Mediterranean plateau. The ecosystems were cropland (converted from grasslands in 1990), open forest, and grassland. Soil samples from two depths, 0–10 and 10–20 cm, were collected for chemical and physical analyses at each of cropland, open forest, and grassland ecosystems. SOC pools at the 0–20 cm depth of cropland, forest, and grassland ecosystems were estimated at 32,636, 56,480, and 57,317 kg ha⁻¹, respectively. Conversion of grassland into cropland during the 12-year period increased the bulk density by 10.5% and soil erodibility by 46.2%; it decreased SOM by 48.8%, SOC content by 43%, available water capacity (AWC) by 30.5%, and total porosity by 9.1% for the 0–20 cm soil depth (p<0.001). The correlation matrix revealed that SOC content was positively correlated with AWC, total porosity, mean weight diameter (MWD), forest, and grassland, and negatively with bulk density, pH, soil erodibility factor, and cropland. The multiple regression (MLR) models indicated that any two of the three ecosystems and one of the two soil depths accounted for 86.5% of variation in mean SOC values ((p<0.001).     

鄂尔多斯盆地南部的黄土塬区地震资料处理与解释,第一部分:地震资料处理

Branching river channels and the coexistence of valleys, ridges, hiils, and slopes＇as the result of long-term weathering and erosion form the unique loess topography. The Changqing Geophysical Company, working in these complex conditions, has established a suite of technologies for high-fidelity processing and fine interpretation of seismic data. This article introduces the processes involved in the data processing and interpretation and illustrates the results.