Trace-element of Tuoyun clinopyroxene: Implication for the deep processes of lithospheric mantle beneath the southwest Tianshan, West China

Based on the LAM-ICPMS analytic results on the trace elements of clinopyroxenes in peridotitic xenoliths occurring in early-Cretaceous basalts from western Xinjiang, the properties and the deep processes, including partial melting and mantle metasomatism, of the subcontinental lithospheric mantle beneath the Tuoyun Basin are analyzed. In the northern edge of the Tarim Basin (southwest Tianshan), the Mesozoic subcontinental lithosphere which has experienced the effect of partial melting (<10%) and intricate mantle metasomatism is characterized by Phanerozoic ‘ocean-type’ mantle. The superposed influence of SiO₂-unsaturated silicate melt and carbonate melt probably results in the metasomatic medium which resembles the hydrous silicated carbonate melt in some aspects. By comparing Tuoyun mantle with Cenozoic main mantle beneath eastern China, the properties are similar, while the former shows finer grain and higher diopside content of the peridotites and more conspicuous modal metasomatism.     

Mantle metasomatism by P- and F-rich melt/fluids: evidence from phosphate glass in spinel lherzolite xenolith in Keluo, Heilongjiang Province

Spinel lherzolite xenoliths were found in phonolitic alkaline basalt in the Keluo area, Heilongjiang Province. Detailed electron-microprobe study revealed abundant phosphates and associated metasomatic minerals between primary phases in xenolith. The phosphates are considered special residual phases (coagulation) of P- and F-rich mantle melt/fluid, most of which were identified as glass phases based on Raman spectroscopic analyses. Such melt/fluid also further metasomatized primary minerals, thus leading to formation of reaction rims successively composed of Cr-spinel symplectitic zone and olivine diopside zone. Therefore, the P- and F-rich melt/fluid played an important role in the upper-mantle metasomatism in the Keluo area. It is suggested that this kind of metasomstism may occur in some other places of eastern China. The present results may also have significance in study-ing types of metasomatic melt/fluid and its evolution in the lithospheric mantle beneath eastern China.     

Carbon isotopic composition of mantle xenoliths in alkali basalt from Damaping, Hebei

The carbon isotopic composition of CO-2, CO and CH-4 extracted by pyrolysis from spinel lherzolite and black pyroxenolite xenoliths in alkali basalt from Damaping has been measured with GC_MS. The results show that, at heating temperatures from 400 to 1 140℃, the δ 13C of CO-2 and CO is -22‰--27‰, and that of CH-4 -30‰--50‰. The data imply that the magma which was generated in the upper mantle by partial melting in the area has experienced the multistage degassing process, and the δ 13C values represent the carbon isotopic composition of CO-2, CO and CH-4 remaining in it, respectively.     

下地幔深部压力条件下顽火辉石Perovskite(MgSiO3)的冲击诱导相变

最近的计算机模拟分析和静高压实验结果都证实了钙钛矿顽火辉石Perovsk ite(M g-S iO3)在下地幔条件下发生了后钙钛矿相变(post—perovsk ite)。通过对顽火辉石动态高压实验Hugon iot数据进行分析,结果发现Perovsk ite(M gS iO3)在冲击压力为120G pa时(相当于下地幔压力)密度发生了系统性跳跃,增大了1.5%,于是我们推测顽火辉石在冲击波实验中也可能出现后钙钛矿相变,进一步的分析得到在2500K和109GPa条件下的C lapeyron斜率为4.0±0.4M Pa/k,其值和最近所得到的静高压实验、分子动力学模拟以及地球物理观测所得到的数据有很好的一致性。     

Experimental study on electrical conductivity of dunite at high temperature and pressure

The electrical conductivities of the dunite from the Qinghai-Xizang (Tibetan) Plateau were measured with the impedance spectra method at 1.0-4.0 GPa and 643-1093 K. The experimental results indicated that activation enthalpies of the dunite are smaller than 0.9 eV, the conduction mechanism in dunite may be attributed to the mixed electrical conduction involving grain interiors and boundaries. On the basis of the results of this experiment, we can deduce that there exists cold mantle in the area of Gaize-Lugu in the Qinghai-Xizang (Tibetan) Plateau by reverse methods from the magnetotelluric sounding data (conductivity-depths profile) available for western Tibet. The result provides the present cold mantle viewpoint with strong proof on the basis of high temperature and pressure experiments.     

一种定量地消除波速横向变化影响的三叉震相一维波速结构反演计算方案

通过数值模拟分析,定量讨论震源区附近高速异常、接收区附近低速异常以及目标区浅部局地波速异常对三叉震相反演一维波速结构的影响, 结果说明波速横向变化在传统的一维波速结构反演中会产生与异常体相同量级的波速异常假象。提出一种借助区域或全球层析成像结果定量地消除波速横向变化对利用三叉震相走时进行一维波速结构反演影响的解决方案。利用射线追踪法进行的测试计算表明, 提出的计算方法能有效地消除波速横向变化对计算结果的影响, 使得反演结果更接近于真实结构。     

大地地磁测探——探测地球深部电性和物质状态的一种有效手段

作者全面综述了一种极具发展前景的探测地球深部结构和物质状态的手段,它是以天然大地电磁场为场源,以地球电磁感应效应为基础,可以面对多方面应用需求的一种方法,即大地电磁测深。介绍了地球电磁场的特征和方法的基本原理,随后评述了大地电磁测深提出以来几项突破性的进展。最后给出了大地电磁测深的几方面标志性应用。     

中亚造山带大陆动力学边程与成矿作用

本文简述了国家973计划项目“中亚造山带大陆动力学过程与成矿作用”（2007CB411300）的总体框架、研究思路和研究目标。对项目已开展的研究工作和研究进展进行了总结。目前,项目组已在以下4个方面展开了研究工作并取得了一系列重要进展：（1）中亚造山带增生、体制转换与改造大陆动力学过程;（2）中亚造山带壳幔相互作用与巨量金属堆积机理;（3）中亚造山带典型矿集区壳幔结构的深部地球物理探测;（4）大陆增生成矿理论框架的构建和矿集区预测与隐伏矿床识别。     

Re-Os isotopic system and formation age of subcontinental lithosphere mantle

The determination of the formation age of subcontinental Lithosphere Mantle (SCLM) is a widely concerned issue in mantle geochemistry. It is difficult to obtain the formation age of SCLM using lithophile isotopic systems such as Rb-Sr, Sm-Nd, U-Th-Pb, etc., but as siderophile elements, the Re-Os isotopic system provides a powerful tool for that work. Here a comprehensive review on the recent development in Re-Os dating for SCLM has been given.     

Characteristics of lateral heterogeneities with thermal and chemical origins in the pyrolitic lower mantle

The relative changes between shear and compressional velocities (R_SP = ∂ ln V_S/∂ ln V_P), bulk sound and shear velocities (R_CS = ∂ ln V_C/∂ ln V_S), and density versus shear wave velocity (R_ρS = ∂ ln ρ/∂ ln V_S) in response to thermal and chemical variations were investigated for the pyrolitic lower mantle. For heterogeneities with thermal origins, R_SP increases from 1.7 to 2.0 together with R_ρS decreasing from 0.4 to 0.2 and R_CS = ∼0.27 from the top to the bottom of the lower mantle. In comparison, chemical variations (bulk iron or silica contents) are characterized by R_SP < 1.5 and R_CS > 0.5 at lower mantle depths. Negative values of R_ρS and R_CS are indicative of chemical anomalies in the lower mantle, but a combination of thermal and chemical heterogeneities may be required to produce velocity and density anomalies at the magnitudes observed in seismic data. Further refinement of these characteristics requires data on the higher order pressure and temperature derivatives of the elastic moduli of the constituent phases.