峨眉山玄武岩地幔源成分及其变化的微量元素标志

根据峨眉山玄武岩系岩石的稀土元素、不相容元素特征，估计了产生其母岩浆的地幔源成分，在讨论了地幔平衡部分熔融和岩浆分离结晶过程中强不相容元素与一般不相容元素的比值变化后，提出用双对数图解来判别地幔成分、元素总分配系数及母岩浆形成时地幔熔融度的原理。根据Ｌａ，Ｃｅ和Ｓｃ，Ｙｂ在地幔－岩浆过程中地球化学特征，运用上述原理，讨论了峨眉山玄武岩系母岩浆的地幔成分及其变化，计算了地幔矿物相组成和部分熔融度。     

Upper mantle SH velocity structure beneath Qiangtang Terrane by modeling triplicated phases

We constrain SH wave velocity structure for the upper mantle beneath western Qiangtang Terrane by comparing regional distance seismic triplicated waveforms with synthetic seismograms, based on an intermediate event （-220 km） recorded by the INDEPTH-Ⅲ seismic array. The ATIP model reveals a low-velocity anomaly with up to -4% variation at the depth of 190-270 km and a relatively small velocity gradient above the depth of 410 km in the upper mantle, which is in agreement with previous results. In combination with other geological studies, we suggest that the depth of top asthenosphere is 190 km and no large-scale lithosphere thinning occurs in western Qiangtang Terrane, besides, Qiangtang Terrane has the same kind of upper mantle structure as the stable Eurasia.     

含斜坡软弱夹层的路堤填筑过程数值模拟

基于拉格朗日差分方法,并结合现场类似地形的实测数据,研究了含斜坡软弱夹层的地基在路堤分层填筑的过程竖向及水平向位移的规律.分析表明,倾斜地基的水平向位移沿倾斜方向发展,变形明显,影响区域很广,地基的不均匀沉降情况严重,影响了路堤稳定性.由于表层硬壳层的作用,有效地限制了位移的发展,使得整体情况相对改善很多.数值模拟结果与现场实测数据吻合,为进一步研究该类软土地形提供有力的理论依据.     

南海玄武岩：扩张洋脊与海山

 南海存在两种火山岩：洋中脊玄武岩（MORB）和洋岛玄武岩（OIB）。国际大洋发现计划（IODP）第349、367、368、368X航次在南海海盆的成功钻取,获得了南海初始扩张（~34 Ma）和停止扩张（~15-16 Ma）前的洋壳样品。南海东部、西南次海盆及北缘洋-陆过渡带代表海盆发展的不同阶段,具有不同的地幔潜能温度、物质组成和洋脊扩张速度,因此产生的洋中脊玄武岩成分差异显著。南海地区在扩张晚期及停止扩张之后存在大规模地幔上涌,与其周缘地区的持续俯冲有关,产出的海山OIB不同于地幔柱活动产生的火山链。南海虽小,但蕴含的信息异常丰富,是窥探地球深部难得的天然窗口。     

Some basic concepts and problems on the petrogenesis of intra-plate ocean island basalts

Basaltic magmatism that builds intra-plate ocean islands is often considered to be genetically associated with ＂hotspots＂ or ＂mantle plumes＂. While there have been many discussions on why ocean island basalts （OIB） are geochemically highly enriched as an integral part of the mantle plume hypothesis, our current understanding on the origin of OIB source material remains unsatisfactory, and some prevailing ideas need revision. One of the most popular views states that OIB source material is recycled oceanic crust （ROC）. Among many problems with the ROC model, the ocean crust is simply too depleted （e.g., [La/Sm]PM 〈1） to be source material for highly enriched （e.g., [La/Sm]pM 〉〉 1） OIB, Another popular view states that the enriched component of OIB comes from recycled continental crust （RCC, i.e.; terrigenous sediments）. While both CC and OIB are enriched in many incompatible elements （e.g., both have [La/Sm]PM 〉〉1）, the CC has characteristic enrichment in Pb and deletion in Nb, Ta, P and Ti. Such signature is too strong to be eliminated such that CC is unsuitable as source material for OIB. Plate tectonics and mantle circulation permit the presence of ROC and RCC materials in mantle source regions of basalts, but they must be volumetrically insignificant in contributing to basalt magmatism. The observation that OIB are not only enriched in incompatible elements, but also enriched in the progressively more incompatible elements indicates that the enriched component of OIB is of magmatic origin and most likely associated with low-degree melt metasomatism. H2O and CO2 rich incipient melt may form in the seismic low velocity zone （LVZ）. This melt will rise because of buoyancy and concentrate into a melt rich layer atop the LVZ to metasomatize the growing lithosphere, forming the metasomatic vein lithologies. Erupted OIB melts may have three components： （1） fertile OIB source material from depth that is dominant, （2） the melt layer, and （3） assimilation of the metasomatic vein lithologies formed earlier in the growing/grown lithosphere. It is probable that the fertile source material from depth may be （or contain） recycled ancient metasomatized deep portions of oceanic lithosphere. In any attempt to explain the origin of mantle isotopic end-members as revealed from global OIB data, we must （1） remember our original assumptions that the primitive mantle （PM） soon after the core separation was compositionally uniform/homogeneous with the core playing a limited or no role in causing mantle isotopic heterogeneity; （2） not use OIB isotopes to conclude about the nature and compositions of ultimate source materials without understanding geochemical consequences of subduction zone metamorphism; and （3） ensure that models and hypotheses are consistent with the basic petrology and major/trace element geochemistry.     

Peridotite-melt interaction: A key point for the destruction of cratonic lithospheric mantle

This paper presents an overview of recent studies dealing with different ages of mantle peridotitic xenoliths and xenocrysts from the North China Craton, with aim to provide new ideas for further study on the destruction of the North China Craton. Re-Os isotopic studies suggest that the lithospheric mantle of the North China Craton is of Archean age prior to its thinning. The key reason why such a low density and highly refractory Archean lithospheric mantle would be thinned is changes in composition, thermal regime, and physical properties of the lithospheric mantle due to interaction of peridotites with melts of different origins. Inward subduction of circum craton plates and collision with the North China Craton provided not only the driving force for the destruction of the craton, but also continuous melts derived from partial melting of subducted continental or oceanic crustal materials that resulted in the compositional change of the lithospheric mantle. Regional thermal anomaly at ca. 120 Ma led to the melting of highly modified lithospheric mantle. At the same time or subsequently lithospheric extension and asthenospheric upwelling further reinforced the melting and thinning of the lithospheric mantle. Therefore, the destruction and thinning of the North China Craton is a combined result of per- idotite-melt interaction （addition of volatile）, enhanced regional thermal anomaly （temperature increase） and lithospheric extension （decompression）. Such a complex geological process finally produced a ＂mixed＂ lithospheric mantle of highly chemical heterogeneity during the Mesozoic and Cenozoic. It also resulted in significant difference in the composition of mantle peridotitic xenoliths between different regions and times.     

Trace element characteristics and origin of intergranular components in mantle peridotites

Leaching experiment has been carried out on mantle xenoliths with different petrographic features in order to directly characterize the nature of intergranular components. ICP-MS analyses of leachates show that they are characterized by high LREE concentrations with strong depletion of Ta. The total REE contents and whether the negative Rb, Ba and Nb anomalies are present or not in intergranular components are largely dependent upon the nature of mantle metasomatism experienced by its host rock. It is proposed that intergranular components may represent residues of small volume metasomatic melts.     

Discovery of mantle and lower crust xenoliths from early Cretaceous volcanic rocks of southwestern Tianshan, Xinjiang

In Tuoyun area of southwestern Tianshan, mantle and lower crust xenoliths are present in the volcanic rocks with ages of 101–123 Ma. Mantle xenoliths include mineral megacrysts such as kaersutite and pargasite, feldspar, biotite, and rare pyroxene and rock fragments such as perodotite, pyroxenite, amphibolite, and rare glimmerite. Lower crust xeno-liths are mainly banded and massive granulite. The volcanic rocks were produced by within-plate magmatism. Occurrence of hydrous and volatile mineral megacrysts, amphibolite, and some pyroxenite containing hydrous and volatile minerals indicates that mantle metasomatism was intense. Undoubtedly, this discovery is very important to understanding of the crust-mantle structure and geodynamic background in depth in southwestern Tianshan and geological correlation with adjacent regions.     

Helium isotopic study on mantle degassing in the Altay orogenic zone, China

New helium isotopic data of ores and rocks from the Altay orogenic zone, Xinjiang, China are reported, which show that the pegmatites from No. 3 vein in the Keketuohai area have high³He/⁴He ratios up to 1.795 × 10⁻⁶ and 2.54 × 10⁻⁶. Such a result suggests that the metallogenic process of rare metal deposits in the Altay orogenic zone might be related to mantle degassing.