当代造山带研究中值得重视的若干前沿问题

当代造山带研究正从以往以阐明板块运动历史和板块边界相互作用为主，转向并进入到了阐明造山带岩石圈及其之下地幔系统中各层圈相互作用过程和动力学的新阶段，大陆动力学正成为造山带研究的主要指导思想。在这种形势下，造山带研究正围绕着下列前沿问题展开工作：（１）碰撞后的造山过程：拆沉作用、伸展垮塌和深变质岩剥露；（２）造山带之下地幔的结构和演化；（３）壳内软层的性质和动力学作用；（４）造山带地壳的精细构造和演化；（５）巨量花岗岩的成因和侵位动力学；（６）沉积作用与造山过程：根据沉积特征对造山过程、造山事件的恢复再造；（７）新元古代超大陆。     

造山后伸展构造研究的最新进展

本文综合介绍和比较分析了全球范围内不同时期造山带中的伸展构造样式；地壳尺度的拆离带或低角度正断层的性质、几何学和运动学；拆离带下盘变质核杂岩的抬升机理及其中各种韧性组构的成因和发展演变；后造山伸展塌陷过程中的岩浆活动和热演化；伸展平行褶皱的成因和构造几何学；后造山伸展盆地的形成过程；造山带地球物理剖面解释和岩石圈动力学；后造山伸展构造的物理和数字模拟等方面，当前开展的主要研究内容、研究方法和趋势。     

横贯中国东南部的一条古断裂带

本文根据地质和物探资料,论证横贯中国东南部桂西、黔东南、湘西北、鄂东南、赣西北、皖东南和苏南的湘黔-江南古断裂带。中元古代为超壳断裂,古生代属壳断裂,是一条长期发展的控岩控矿的古断裂带。往东入海,延向济州岛和西南日本飞驒地区。     

物元可拓法在地下水水质评价中的应用

可以从定性、定量两个角度解决问题的物元可拓法已被广泛应用于各个领域,本文对物元可拓法进行了改进,并应用于地下水水质评价,同时采用模糊综合评判方法进行了验证。Piper-三线图显示,研究区地下水主要为HCO3—Na和HCO3—Ca·Na型水,水质本底条件较好。水质评价结果表明,上第三系馆陶组地下水水质显著优于明化镇组,1984~1999年间明化镇组和馆陶组的地下水水质均有变坏趋势,前者趋势较为明显。物元可拓法采用综合关联度与可拓指数判断地下水水质级别,不仅能反映其相对性,也能反映绝对性,可延拓连续的特点使其更有说服力。     

Graben width controlling syn-rift sedimentation: the Palaeogene southern Upper Rhine Graben as an example

Eocene to Early Oligocene syn-rift deposits of the southern Upper Rhine Graben (URG) accumulated in restricted environments. Sedimentation was controlled by local clastic supply from the graben flanks, as well as by strong intra-basinal variations in accommodation space due to differential tectonic subsidence, that in turn led to pronounced lateral variations in depositional environment. Three large-scale cycles of intensified evaporite sedimentation were interrupted by temporary changes towards brackish or freshwater conditions. They form three major base level cycles that can be traced throughout the basin, each of them representing a stratigraphic sub-unit. A relatively constant amount of horizontal extension (ΔL) in the range of 4–5 km has been estimated for the URG from numerous cross-sections. The width of the rift (L _f ), however, varies between 35 and more than 60 km, resulting in a variable crustal stretching factor between the bounding masterfaults. Apart from block tilting, tectonic subsidence was, therefore, largely controlled by changes in the initial rift width (L ₀). The along-strike variations of the graben width are responsible for the development of a deep, trough-like evaporite basin (Potash Basin) in the narrowest part of the southern URG, adjacent to shallow areas in the wider parts of the rift such as the Colmar Swell in the north and the Rhine Bresse Transfer Zone that delimits the URG to the south. Under a constant amount of extension, the along-strike variation in rift width is the principal factor controlling depo-centre development in extensional basins.     

Lithosphere formation in the central Slave Craton (Canada): plume subcretion or lithosphere accretion?

Major-element compositions of minerals in peridotite xenoliths from the Lac de Gras kimberlites provide constraints on the mode of lithosphere formation beneath the central Slave Craton, Canada. Magnesia contents of reconstructed whole rocks correlate positively with NiO and negatively with CaO contents, consistent with variable partial melt extraction. Alumina and Cr₂O₃ contents are broadly positively correlated, suggestive of melt depletion in the absence of a Cr–Al phase. Garnet modes are high at a given Al₂O₃ content (a proxy for melt depletion), falling about a 7 GPa melt depletion model. These observations, combined with high olivine Mg# and major-element relationships of FeO-poor peridotites (<7.5 wt%) indicative of melt loss at pressures >3 GPa (residual FeO content being a sensitive indicator of melt extraction pressure), and similar high pressures of last equilibration (∼4.2 to 5.8 GPa), provide multiple lines of evidence that the mantle beneath the central Slave Craton has originated as a residue from high-pressure melting, possibly during plume subcretion. Apparent low melt depletion pressures for high-FeO peridotites (>7.5 wt%) could suggest formation in an oceanic setting, followed by subduction to their depth of entrainment. However, these rocks, which are characterised by low SiO₂ contents (<43 wt%), are more likely to be the result of post-melting FeO-addition, leading to spuriously low estimates of melt extraction pressures. They may have reacted with a silica-undersaturated melt that dissolved orthopyroxene, or experienced olivine injection by crystallising melts. A secular FeO-enrichment of parts of the deep mantle lithosphere is supported by lower average Mg# in xenolithic olivine (91.7) compared to olivine inclusions in diamond (92.6).     

东准噶尔鲍尔羌吉——带热隆伸展构造的厘定

东准噶尔1：25万造山带填图方法研究过程中，在鲍尔羌吉一带发现较为典型的伸展构造，与许志琴等提出的热隆伸展构造有相似之处，其隆升与晚古生代造山后期抬升侵位的花岗岩有关，重熔花岗岩侵位上隆形成“热穹隆”构造，在岩体顶部垂直主应力作用下导致上部地壳伸展减薄，形成以晚古生代花岩为核心的伸展构造。     

正常固结饱和粘性土的不排水强度

本文以有效应力强度理论和Henkel孔隙水压力公式为基础,建立了各种类三轴与平面应变试验条件下正常固结饱和粘土的不排水强度公式及相互关系;初步估计了粘土强度随固结增长的计算公式.     

The longevity of subcontinental lithospheric mantle beneath Jiangsu-Anhui Region

The basalt-borne peridotite xenoliths from Jiangsu-Anhui provinces were analyzed for whole rock Os isotopic compositions in two laboratories of USTC, China and CRPG, France, respectively. The¹⁸⁷Os/¹⁸⁸Os ratio of the sample set ranges from 0.119 to 0.129 (25 samples, USTC) and from 0.117 to 0.131 (17 samples, CRPG). The Os isotopic compositions of most samples are less than 0.129 and depleted relatively to the primitive mantle, showing a good correlation with the major element compositions. With the¹⁸⁷Os/¹⁸⁸Os-Al₂O₃ alumichron, the samples yield a model age of 2.5 ± 0.1 Ga (data of USTC) and 1.9 ± 0.1 Ga (data of CRPG), late Archean to early Pro-terozoic. The two samples with the lowest¹⁸⁷Os/¹⁸⁸Os ratio (0.119 and 0.117) have the T_RD (Re depleted age) of 1.1 Ga (USTC) and 1.4 Ga (CRPG), mid-Proterozoic. The Os isotope model age shows that the peridotite xenoliths from Cenozoic alkali basalt in Jiangsu-Anhui provinces have an old formation age (early- to mid- Proterozoic). They are not newly produced mantle after the Phanerozoic replacement of the lithosphere mantle, but residual fractions of Proterozoic mantle.     

Faulting in zones of lithospheric extension: Quantitative analysis of natural and experimental data

Quantitative relationships between major fault parameters from geological observations and laboratory experiments are compared. Relationships are established between fault length, number, depth of fault penetration, amplitude of displacement and other characteristics. The width of destruction zones is estimated. Spacing between parallel faults of compatible length is evaluated. It is shown that there is a stable correlation between fault length and number, which is independent from the mode of loading the material under destruction. Destruction of the lithosphere is believed to occur according to the laws of deformation of Maxwell elasto-viscous body.