40Ar/39Ar geochronology and exhumation of mylonitized metamorphic complex in Changle-Nanao ductile shear zone

New⁴⁰Ar/³⁹Ar plateau ages from rocks of Changle-Nanao ductile shear zone are 107.9 Ma(Mus), 108.2 Ma(Bi), 107.1 Ma(Bi), 109.2 Ma(Hb) and 117.9 Ma(Bi) respectively, which are concordant with their isochron ages and record the formation age of the ductile shear zone. The similarity and apparent overlap of the cooling ages with respective closure temperatures of 5 minerals document initial rapid uplift during 107–118 Ma following the collision between the Min-Tai microcontinent and the Min-Zhe Mesozoic volcanic arc. The⁴⁰Ar/³⁹ Ar plateau ages, K-Ar date of K-feldspar and other geochronologic information suggest that the exhumation rate of the ductile shear zone is about 0.18–1.12 mm/a in the range of 107–70 Ma, which is mainly influenced by tectonic extension.     

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。     

被动微波遥感估算雪水当量研究进展与展望

被动微波遥感可以透过云层，全天候地提供地表一定深度的信息。星载被动微波遥感传感器的时间分辨率很高，在冰冻圈动态研究中有着重要的地位。在最近的二三十年中，大量被动微波遥感的应用都是在美国、加拿大、欧洲等地，而我国在这方面的研究相对较少。首先介绍了被动微波遥感数据在监测积雪方面的国内外研究进展，对现存的雪水当量（SWE）估算算法（和模型）的适用性进行讨论。然后，详细讨论了我国西部的青藏高原地区雪水当量的估算，阐明了利用SSM／I数据估算青藏高原地区雪水当量的复杂性，并指出了其复杂性产生的原因，提出了解决问题的方法，为该地区积雪动态的进一步研究提供了理论依据。     

2002年6月13日重庆区域大暴雨分析

通过对重庆西部“6 1 3”区域大暴雨的分析 ,发现此次天气过程是一次典型的高原涡与西南涡耦合 ,结合地面弱冷空气条件下产生的 ,同时对ECMWF和T2 1 3数值预报产品进行了简要的分析 ,发现ECMWF和T2 1 3的形势预报能力都比较好 ,但T2 1 3的部分物理量要素和降水量预报能力还有待提高。     

陕北砂黄土区公路地质灾害及防治对策

中国西北黄土的颗粒组成具有明显的地带性分布规律，自NW向SE可依次划分为砂黄土带、典型黄土带和粘黄土带。黄土高原北部地质灾害综合调查表明，砂黄土区公路地质灾害的主要类型包括黄土边坡滑塌灾害、路堤裂陷灾害、路桥变形和冲蚀灾害等。根据试验测试分析结果，公路地质灾害的形成主要受黄土本身的物质组成、结构及力学性质控制，人类工程活动的盲目性是诱发地质灾害的重要因素。文章在砂黄土公路地质灾害特征分析的基础上，提出加强边坡防护和冲蚀灾害防治是公路地质灾害防治的两个基本途径，并给出了针对性的防治对策。这不仅对该地区的公路建设具有重要的指导作用，而且对其它生命线工程如铁路、输油气管道、渠道等也具有重要的借鉴意义。     

Bio-climatic imprints on a Holocene loess palaeosol from China

Micromorphology, heavy minerals, pollen and soil properties were examined in a typical Holocene loess profile in the north of the Loess Plateau, consisting of a palaeosol (locally known as the Ansai palaeosol) underlain by the Malan loess and overlain by modern loess. The palaeosol consists of an upper humus-rich (AB) horizon over a clay-rich (Bt) horizon. The humus-rich horizon is intensely weathered, contains precipitated calcitic material derived from the overlying modern loess, and has both high pollen content and diversity. Clay coatings in the clay-rich horizon indicate formation by eluviation–illuviation of clay. Pedogenetic characteristics and pollen analysis imply that the vegetation during the time of most intensive soil development is likely to have been a warm-temperate forest. A complex interpretation of the loess–palaeosol sequence recognizes several development stages. The phase of soil development, maximum and minimum limiting ages for which are ca. 8800 and 4400 ¹⁴C years BP, involved continuing but reduced loess deposition, and successive Holocene bio-climatic environment overprinted new features on the palaeosol.     

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     

Geochemistry of Early Cretaceous Alkaline Ultramafic-Mafic Complex from Jasra, Karbi Anglong, Shillong Plateau, Northeastern India

An early Cretaceous alkaline ultramafic-mafic complex is emplaced within the Proterozoic rocks of Shillong plateau at Jasra, Karbi Anglong district of Assam. It is associated to the fracture system of Barapani-Tyrsad shear zone, Kopali faults, and Um Ngot lineaments and mainly comprises pyroxenite, gabbro and nepheline syenite. Few small mafic dykes, emplaced within pyroxenitic and granitic plutons, are also reported. No such dyke is reported to cut gabbros or nepheline syenites. Nepheline syenites occur either in the form of small dykes in pyroxenites or as differentiated bodies in the gabbros. Mineralogical and chemical composition of pyroxenite and gabbro clearly indicate their affinity to the alkaline magmatism. Syenitic samples show miaskitic character (agpaitic index <1), also indicates affinity with alkaline-carbonatite magmatism. Calcite is encountered in a number of pyroxenite samples. From the presented petrological and geochemical data it is difficult to establish any significant genetic relationship through simple differentiation process between these rocks. These data probably suggest that these rocks are derived from a primary carbonatite magma, generated by the low-degree melting of a metasomatized mantle peridotite. CO₂ released by this process also progressively metasomatizes the lherzolite to an alkaline wehrlite and melts derived from alkaline wehrlite (ultrabasic alkaline silicate magma) may be responsible for crystallization of Jasra alkaline ultramafic-mafic rocks.     

Cenozoic rifting and volcanism in eastern China: a mantle dynamic link to the Indo–Asian collision?

The Indo–Asian continental collision is known to have had a great impact on crustal deformation in south-central Asia, but its effects on the sublithospheric mantle remain uncertain. Studies of seismic anisotropy and volcanism have suggested that the collision may have driven significant lateral mantle flow under the Asian continent, similar to the observed lateral extrusion of Asian crustal blocks. Here we present supporting evidence from P-wave travel time seismic tomography and numerical modeling. The tomography shows continuous low-velocity asthenospheric mantle structures extending from the Tibetan plateau to eastern China, consistent with the notion of a collision-driven lateral mantle extrusion. Numerical simulations suggest that, at the presence of a low-viscosity asthenosphere, continued mass injection under the Indo–Asian collision zone over the past 50 My could have driven significant lateral extrusion of the asthenospheric mantle, leading to diffuse asthenospheric upwelling, rifting, and widespread Cenozoic volcanism in eastern China.     

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).