树根桩在厂房扩建工程地基处理中的应用

在苏南某工业厂房扩建工程中,为了妥善解决新旧熔炉区的不均匀沉降,通过多方案的比选,最终采用树根桩托换技术进行地基加固。并且对新旧熔炉区的基础进行了化学植筋连接和防渗漏处理。     

http://www.sciencedirect.com/science/article/pii/S1674987111000429

The three most crucial factors for the formation of large and super-large magmatic sulfide deposits are: (1) a large volume of mantle-derived mafic-ultramafic magmas that participated in the formation of the deposits; (2) fractional crystallization and crustal contamination, particularly the input of sulfur from crustal rocks, resulting in sulfide immiscibility and segregation; and (3) the timing of sulfide concentration in the intrusion. The super-large magmatic Ni-Cu sulfide deposits around the world have been found in small mafic-ultramafic intrusions, except for the Sudbury deposit. Studies in the past decade indicated that the intrusions hosting large and super-large magmatic sulfide deposits occur in magma conduits, such as those in China, including Jinchuan (Gansu), Yangliuping (Sichuan), Kalatongke (Xinjiang), and Hongqiling (Jilin). Magma conduits as open magma systems provide a perfect environment for extensive concentration of immiscible sulfide melts, which have been found to occur along deep regional faults. The origin of many mantle-derived magmas is closely associated with mantle plumes, intracontinental rifts, or post-collisional extension. Although it has been confirmed that sulfide immiscibility results from crustal contamination, grades of sulfide ores are also related to the nature of the parental magmas, the ratio between silicate magma and immiscible sulfide melt, the reaction between the sulfide melts and newly injected silicate magmas, and fractionation of the sulfide melt. The field relationships of the ore-bearing intrusion and the sulfide ore body are controlled by the geological features of the wall rocks. In this paper, we attempt to demonstrate the general characteristics, formation mechanism,tectonic settings, and indicators of magmatic sulfide deposits occurring in magmatic conduits which would provide guidelines for further exploration.     

偏序向量空间中集值映射的一类扩张定理

经典的Hahn-Banach扩张定理及其推广定理有着非常广泛的应用,但主要都是讨论单值映射的扩张性质。为了进一步讨论多值映射的扩张性质,通过构造的方法,利用了zorn引理及偏序向量空间的完备性,得到了当定义域空间是一个实向量空间,而值域空间是由锥引入序的Dedekind完备的偏序向量空间时集值映射的一类扩张性质,以及当给值域空间引入相应拓扑时连续集值映射的一类扩张性质。其结果进一步推广了Hahn-Banach扩张定理,扩大了其应用范围。     

Plate-driven extension and convergence along the East Gondwana active margin: Late Silurian–Middle Devonian tectonics of the Lachlan Fold Belt,southeastern Australia

The Lachlan Fold Belt of southeastern Australia developed along the Panthalassan margin of East Gondwana. Major silicic igneous activity and active tectonics with extensional, strike-slip and contractional deformation have been related to a continental backarc setting with a convergent margin to the east. In the Early Silurian (Benambran Orogeny), tectonic development was controlled by one or more subduction zones involved in collision and accretion of the Ordovician Macquarie Arc. Thermal instability in the Late Silurian to Middle Devonian interval was promoted by the presence of one or more shallow subducted slabs in the upper mantle and resulted in widespread silicic igneous activity. Extension dominated the Late Silurian in New South Wales and parts of eastern Victoria and led to formation of several sedimentary basins. Alternating episodes of contraction and extension, along with dispersed strike-slip faulting particularly in eastern Victoria, occurred in the Early Devonian culminating in the Middle Devonian contractional Tabberabberan Orogeny. Contractional deformation in modern systems, such as the central Andes, is driven by advance of the overriding plate, with highest strain developed at locations distant from plate edges. In the Ordovician to Early Devonian, it is inferred that East Gondwana was advancing towards Panthalassa. Extensional activity in the Lachlan backarc, although minor in comparison with backarc basins in the western Pacific Ocean, was driven by limited but continuous rollback of the subduction hinge. Alternation of contraction and extension reflects the delicate balance between plate motions with rollback being overtaken by advance of the upper plate intermittently in the Early to Middle Devonian resulting in contractional deformation in an otherwise dominantly extensional regime. A modern system that shows comparable behaviour is East Asia where rollback is considered responsible for widespread sedimentary basin development and basin inversion reflects advance of blocks driven by compression related to the Indian collision.     

Depth dependency of stress ratios during the sedimentation of NW Gyeongsang Basin (Cretaceous), southeast Korea: Estimate of stress parameters and timing of tectonic episodes

The natural stress state in the lithosphere consists of the vertical load and Poisson ratio, and then additional horizontal compression and extension (denoted by Δσ_H and Δσ_T, respectively) are assumed to be superimposed upon this gravitational stress field. The resulting stress state is composed of the maximum, medium and minimum stresses denoted by σ₁, σ₂, and σ₃, respectively. The stress ratio is given as Φ = (σ₂ − σ₃)/(σ₁ − σ₃). A linear relation is found between Φ or 1/Φ and the vertical load in wrench-faulting and extensional stress regimes, respectively. The slope and intercept of the linear relation result in the additional horizontal stresses and level of (average) paleo-surface, respectively. Stress ratio is also determinable by the stress tensor inversion of fault-slip data. The earliest tectonic event (T_1 Event) in the Cretaceous Gyeongsang Basin consists of coexisting E–W compression and N–S extensional faulting episodes. Plots of Φ or 1/Φ against the burial depth (or vertical load) display several linear trends: two clusters in extensional episodes, and two or three clusters in wrench-faulting episodes. Because Δσ_H is assumed to be null or negligible in the extensional regime, Δσ_T is determinable from the slopes of two linear clusters as being −2.5 to −4.0 MPa. In wrench-faulting episodes, the values of Δσ_H are given to be 61.6–101.4 MPa by applying determined additional horizontal extensions. Determined levels of average paleo-surfaces and those of syndepostional structures illustrate that more than five wrench-faulting or extensional episodes have occurred during the T_1 Event, whose active age, consequently, ranges from the Barremian to the Coniacian. This supports that the coexisting coaxial faulting episodes with the same extension may correspond to the alternation of wrench-faulting and extensional episodes.     

青藏高原腹地班戈—双湖一带晚新生代伸展构造 及动力学机制

在青藏高原腹地,晚新生代以来除发育南北向的伸展构造以外,还发现有一系列时代较新的近东西向正断层控制的伸展构造,空间上呈现出平行排列的宽缓凹槽及其间相对狭窄的山梁相互间隔的活动地貌结构特点,称这种地貌结构为"槽梁地貌"。数字高程模型(DEM)的研究表明,研究区近东西向的伸展构造在地貌上切割了近南北向的双湖盆地。结合断层运动学、年代学及盆地沉积作用的研究,认为近东西向的伸展构造的发育最早可能始于中新世,与近南北向的伸展构造交织发育,断裂的活动性在第四纪随着高原腹地海拔抬升得到了显著的增强。青藏高原隆升后重力作用导致了不同方向断陷盆地的发育。     

Late orogenic extension in the Bohemian Massif: petrostructural evidence in the Hlinsko region

Abstract

The tectonic contact between low-grade metase-dimentary series and high-grade rocks in the Hlinsko region (Bohemian Massif) is commonly interpreted as a thrust of the Barrandian sediments over the upper Moldanubian nappe.

The sediments occur in an E-facing synform that contains a tonalitic laccolith on its eastern boundary with the Moldanubian, and is truncated by a granodiorite pluton to the west. The synform represents a late deformational folding event related to the granodiorite intrusion. NW-oriented normal shear in the tonalite is indicated by S-C microstructures. Kinematic criteria associated with the major foliation and lineation development in the metasediments also indicate a north-westward, normal shear. In addition, Moldanubian gneiss display late shear bands due to north-westward, normal shear. Consequently, the presumed thrust is a low-angle, normal shear zone.

Low-pressure type metamorphism (3 < P < 4 x 10² MPa) coeval with the major deformational phase in pelites of the Hlinsko synform is attributed to both the tonalite aureole and the extensive HT metamorphism (under P > 6 x 10² MPa) that has affected the underlying Moldanubian.

The possibly polyphase normal fault is consistent with the meta-morphic pressure jump between the metasediments and the Moldanubian.

We suggest that the tonalite intruded syntectonically within the normal ductile shear zone active during waning stages of the Variscan orogeny.     

Evidence of two-stage extensional tectonics from the northern edge of the Edremit Graben,NW Turkey

Western Turkey is a place of active continental extension, characterized by the occurrence of several WNW-ESE-trending major grabens. The central part of the northern edge of the Edremit Graben is delineated by various geological units, namely the metamorphic Kazda? Massif, the Mid-Cretaceous Çetmi mélange, the sedimentary Küçükkuyu formation, and loose Plio-Quaternary deposits. Detailed structural and sedimentological study suggests a two-stage extensional evolution of the area, separated by a short break in the tectonic regime. The first stage, possibly related to back-arc extension and/or orogenic collapse, is marked by the activity of a newly described low-angle detachment fault, the ?elale detachment fault, from the latest Oligocene onward. The fault plane, separating the mylonitized rocks of the Kazda? Massif in the footwall from the unmetamorphosed Çetmi mélange and Küçükkuyu formation in the hanging wall, must have played a significant role in the initial exhumation processes of the Kazda? Massif at that time. The Lower Miocene syntectonic Küçükkuyu formation has recorded the initiation and filling up of a small basin, which has developed in a typical supra-detachment basin, above the detachment fault. After a short phase of possible compression and erosion, the second stage—which marks the onset of neotectonic activity—is marked by the development of Plio-Quaternary step-like normal faults, which cut through all the previous units. Coarse, loose sediments were deposited following the fault activity. These local results are extrapolated to apply to the entire Edremit Graben. In that case, its evolution is seen as the succession of two extensional stages, characterized by distinct structural and sedimentological patterns, and possibly separated by a short compressional phase.     

Late Variscan “Basin and Range” magmatism and tectonics in the Central Alps: evidence from U-Pb geochronology

Abstract

Towards the end of the Variscan orogeny, volcano-sedimentary basins were formed within the mountain hell. U-Pb age determinations on zircons of volcanic and plutonic rocks from intramontane basins of the Central Alps allows us to define the age of two volcano-sedimentary units: The former one was dated older than 333 Ma (probably Visean), the younger one was deposited in a short time span between 303 and 298 Ma (Stephanien). The latter contains tuffs (303 ± 4 Ma), ignimbrites and microgranites (299 ± 2 Ma) and intrusive rhyolites (300 ± 2 Ma) that are all coeval within analytical precision. Granitoid rocks intruded into the volcano-sedimentary rocks at 333 ± 2 Ma, 310 ± 3 Ma and 298 ± 2 Ma. An angular unconformity between the older and the younger units in the Tö di area (Aar massif) indicates uplift and erosion between 310 and 303 Ma.

Our results suggest the existence of two periods of late Variscan extension (or transtension) in the Alpine realm, both combined with magmatic activity. The extensional event of Stephaniun age is characterized by a short duration of only a few million years, between 303 and 298 Ma, comprising tectonic activity, volcanism and plutonism. The plutonic rocks are characterized by a dominant lithospheric mantle component, which was contaminated by different amounts of crostai material and might have been increasingly influenced by aslhcnos-pherie mantle melts in the course of crostai thinning. The ealc-alkaline geochemical characteristics of the granites may be explained as an inherited source feature.

The overall tectonic style and the mode of magmatism resembles the situation of the Basin-and-Kange Province (eastern USA). Consequently there is no need to invoke a late-Variscan Andean-type subduction to explain the geochemical composition of the magmatic rocks. We conclude that late-orogenic extension is an important tectonic stage of the Variscan orogeny, which lasted for some 50 million years. The extension led to thinning of the crust and upwelling of hot mantle, causing high heat flow, intrusion of mantle melts and formation of huge volumes of acid melts.     

Intra-arc extension in Central America: Links between plate motions, tectonics, volcanism, and geochemistry

This study revisits the kinematics and tectonics of Central America subduction, synthesizing observations of marine bathymetry, high-resolution land topography, current plate motions, and the recent seismotectonic and magmatic history in this region. The inferred tectonic history implies that the Guatemala–El Salvador and Nicaraguan segments of this volcanic arc have been a region of significant arc tectonic extension; extension arising from the interplay between subduction roll-back of the Cocos Plate and the ~ 10–15mm/yr slower westward drift of the Caribbean plate relative to the North American Plate. The ages of belts of magmatic rocks paralleling both sides of the current Nicaraguan arc are consistent with long-term arc-normal extension in Nicaragua at the rate of ~ 5–10mm/yr, in agreement with rates predicted by plate kinematics. Significant arc-normal extension can ‘hide’ a very large intrusive arc-magma flux; we suggest that Nicaragua is, in fact, the most magmatically robust section of the Central American arc, and that the volume of intrusive volcanism here has been previously greatly underestimated. Yet, this flux is hidden by the persistent extension and sediment infill of the rifting basin in which the current arc sits. Observed geochemical differences between the Nicaraguan arc and its neighbors which suggest that Nicaragua has a higher rate of arc-magmatism are consistent with this interpretation. Smaller-amplitude, but similar systematic geochemical correlations between arc-chemistry and arc-extension in Guatemala show the same pattern as the even larger variations between the Nicaragua arc and its neighbors.