Relationships between magmatism,metamorphism and deformation in the Fraser Complex,Western Australia: Constraints from new SHRIMP U–Pb zircon geochronology

SHRIMP U–Pb zircon isotopic data have been obtained for four samples collected from granitoids and paragneisses in the Fraser Complex, a large composite metagabbroic body cropping out in the Mesoproterozoic Albany‐Fraser Orogen of Western Australia. The data are combined with the results of field mapping and petrographic analysis to revise a model for the geological evolution of the Fraser Complex. Three main phases of deformation are recognised in the Fraser Complex (D_1–3) associated with two metamorphic events (M_1–2), which involve four distinguishable episodes of recrystallisation. The first metamorphic event recognised (M_1a/D₁) reached granulite facies and is characterised by peak T ≥800°C and P = 600–700 MPa. A syn‐M_1a/D₁ charnockite has a U–Pb SHRIMP zircon age of 1301 ± 6 Ma, which also provides an estimate for the age of intrusion of Fraser Complex gabbroic rocks. Disequilibrium textures comprising randomly oriented minerals (M_1b), consistent with approximately isobaric cooling, formed in various lithologies in the interval between D₁ and D₂. Post‐D₁, pre‐D₂ granites intruded at 1293 ± 8 Ma and were foliated during the D₂ event, which culminated in the burial of the Fraser Complex to depths equivalent to 800–1000 MPa. Following burial, pyroxene granulites on the western boundary of the complex were pervasively retrogressed to garnet amphibolite (M_2a). An igneous crystallisation age of 1288 ± 12 Ma from a syn‐M_2a aplite dyke suggests that retrogression may have occurred only a few millions of years after the peak of granulite facies metamorphism. Exhumation to depths of less than ～400 MPa occurred within ～20–30 million years of the M_2a pressure peak. Associated deformation (D₃) is characterised by the development of mylonite and transitional greenschist/amphibolite facies disequilibrium textures (M_2b).     

A tool to assess livelihood preparedness for disasters: a study of Kaikōura earthquake in New Zealand

Natural Hazards - Over the past decade, the cost of disasters on lives and livelihoods has increased many folds. However, there are few tools available that can be used to measure the level of...     

气候变化背景下欧洲中部水资源供给的不稳定性评估——以易北河流域为例

 欧洲中部的易北河流域是典型的湿润半湿润地区。夏季的水资源供给是限制农业生产的因素之一,特别是在具有较高农业生产力水平,而年降水量只有500 mm的黄土地区。通过总结气候变化与水文循环（GLOWA-Elbe）项目第一阶段的成果,根据气候和土地利用变化的各种情景并考虑其不确定性,对未来50 a德国易北河流域水资源供给稳定性作出综合评估。研究表明,欧洲中部必须从自然和社会角度应对未来气候变化情景下产生水资源供给短缺的可能情况。     

Poverty and Disasters in the United States: A Review of Recent Sociological Findings

This article synthesizes the literature on poverty and disasters in the United States and presents the results from a wide range of studies conducted over the past twenty years. The findings are organized into eight categories based on the stages of a disaster event. The review illustrates how people of different socioeconomic statuses perceive, prepare for, and respond to natural hazard risks, how low-income populations may be differentially impacted, both physically and psychologically, and how disaster effects vary by social class during the periods of emergency response, recovery, and reconstruction. The literature illustrates that the poor in the United States are more vulnerable to natural disasters due to such factors as place and type of residence, building construction, and social exclusion. The results have important implications for social equity and recommendations for future research and policy implementation are offered.     

Cavernous weathering,dynamical instability and self‐organization

Cavernous weathering may be conceptualized as a self‐reinforcing process, characterized by positive feedback within the weathering system. A morphometric study of caverns in the Valley of Fire State Park, Nevada, USA, demonstrates the applicability of a dynamically unstable, or conditionally unstable, model of cavernous weathering systems. Outcrop surfaces displaying caverns tend to show increasing fragmentation of the surface in the early stages of cavernous weathering, succeeded by convergent evolution of the surface in which caverns tend to grow and coalesce. A paradoxical relationship exists between the weathering system output at the scale of individual forms and the outcrop scale: caverns tend toward minimum interior surface area by developing a spheroidal form, yet the outcrop surface tends toward maximum exposed surface area by increasing the degree of fragmentation of the surface. Copyright © 2004 John Wiley & Sons, Ltd.     

Palaeomagnetic data from Ediacaran (Vendian) sediments of the Arkhangelsk region, NW Russia: An alternative apparent polar wander path of Baltica for the Late Proterozoic–Early Palaeozoic

The study area is situated along the Zolotica river in NW Russia, located within the Kola–Dvyna Rift System in the Baltic Shield that developed during Meso and Neoproterozoic times. A 9-m thick section made up of shallow marine sediments of Upper Ediacaran age was sampled in this locality. Two volcaniclastic levels from the middle part of the section yielded an age of 556 Ma. (U/Pb SHRIMP-II on zircons). Two magnetic components were successfully isolated, component A (Decl = 157.1, Incl = 68.0, ₉₅ = 1.9°, N = 575 in situ) carried by magnetite and component B (Decl = 120.3, Incl = − 31.7, ₉₅ = 3.9°, N = 57, bedding corrected), carried by haematite. While component A is thought to represent a younger overprint direction, the in situ direction for component B on the other hand, is dissimilar to any expected younger direction and is considered to be primary magnetisation in origin, acquired during or soon after deposition of the sediments in the Late Ediacaran. The corresponding palaeomagnetic pole for component A in situ is located at Lon = 55.4°E, Lat = 31°N, A₉₅ = 2.7° and for component B at Lon = 110°E, Lat = 28.3°S, A₉₅ = 3.8°, N = 57. Combined with other palaeomagnetic poles of the same tectonostratigraphic unit an alternative apparent polar wander path for the Late Proterozoic–Early Palaeozoic of Baltica is proposed. Such an alternative path shows that after the mid Cryogenian (750 Ma), the poles that were situated over South Africa (p.d.c.) moved to the east until they reached Australia during the Late Ediacaran (555 Ma) where they remained approximately stationary until the beginning of the Cambrian (545 Ma). Finally, they moved to the northwest until they reached the Arabian Peninsula in the Early Ordovician. Palaeolatitudes indicate that Baltica situated near the equator from the Cryogenian through to the Ediacaran moving gradually to the south at c. 1 cm/yr. During the Late Early Ediacaran, the plate suddenly began to drift northward at c. 8 cm/yr and in the boundary with the Cambrian it was positioned in low to intermediate latitudes. Finally, Baltica began to move back to the south at c. 13 cm/yr until in the Early Ordovician, reaching intermediate to high southern latitudes.     

从地震信息看中国东部垂直构造样式及油气

所讨论的垂直构造是石油勘探中最常见的小尺度局部升降作用所引起的各种构造 ,按成因可分为跨塌构造、压实构造、底辟构造三类样式。垮塌构造样式是碎屑岩沉积盆地基底的碳酸盐岩地层长期被地下水溶解形成地下大溶洞 ,造成上部地层垮塌而形成的堑背形构造样式 ;压实构造由沉积压实作用所致 ,可分为基底古隆起披覆构造样式和差异压实披覆构造样式等 ;底辟构造 (又称“挤入构造”)是塑性岩层在外力作用下发生底辟作用而产生的 ,分刺穿底辟和拱形底辟两种 ,或冷底辟和热底辟两类。莺歌海盆地发育众多的地震异常体 ,呈底辟状 ,但比较特殊 ,可称为气烟筒 ,与通常的底辟具本质之别。中国东部中、新生代盆地中普遍发育垂直构造 ,它们与沉积作用同步发生 ,一般无明显的挤压褶皱变形     

Influence of Mn oxides on the reduction of uranium(VI) by the metal-reducing bacterium Shewanella putrefaciens

The potential for Mn oxides to modify the biogeochemical behavior of U during reduction by the subsurface bacterium Shewanella putrefaciens strain CN32 was investigated using synthetic Mn(III/IV) oxides (pyrolusite [β-MnO₂], bixbyite [Mn₂O₃] and K⁺-birnessite [K₄Mn₁₄O₂₇ · 8H₂O]). In the absence of bacteria, pyrolusite and bixbyite oxidized biogenic uraninite (UO₂[s]) to soluble U(VI) species, with bixbyite being the most rapid oxidant. The Mn(III/IV) oxides lowered the bioreduction rate of U(VI) relative to rates in their absence or in the presence of gibbsite (Al[OH]₃) added as a non-redox-reactive surface. Evolved Mn(II) increased with increasing initial U(VI) concentration in the biotic experiments, indicating that valence cycling of U facilitated the reduction of Mn(III/IV). Despite an excess of the Mn oxide, 43 to 100% of the initial U was bioreduced after extended incubation. Analysis of thin sections of bacterial Mn oxide suspensions revealed that the reduced U resided in the periplasmic space of the bacterial cells. However, in the absence of Mn(III/IV) oxides, UO₂(s) accumulated as copious fine-grained particles external to the cell. These results indicate that the presence of Mn(III/IV) oxides may impede the biological reduction of U(VI) in subsoils and sediments. However, the accumulation of U(IV) in the cell periplasm may physically protect reduced U from oxidation, promoting at least a temporal state of redox disequilibria.     

云南地区上地幔各向异性研究

对云南23个数字地震台11次地震的SKS记录，采用理论切向分量与实测切向分量拟合的方法，确定了快S波的偏振方向和快、慢波之间的时间延迟．结果表明，除鹤庆台外，在各台都观测到了S波分裂现象；云南地区的快方向总体特征是北北东向，时间延迟变化范围为0.5～2.0ｓ．在地质构造复杂地区断层对分析的影响很大．分析表明，作为青藏高原与华南块体之间的过渡带，云南地区的S波快方向反映了印度板块向欧亚板块俯冲是该地区地球动力学的基本背景，而由于青藏高原隆起造成的康滇菱形块体的南东-南南东向运动是造成复杂构造、应力环境的重要因素．快方向与上地幔运动的方向存在差异，说明在云南地区低速层或者软流层的运动与地壳块体的运动之间存在着复杂的耦合作用，构造驱动力如同向北东方向张开的手掌．从时间延迟出发，推断各向异性层的厚度为60～225ｋｍ．其变化范围与低速层埋深的变化范围（104～260ｋｍ）相当，认为各向异性层顶面可能在地壳底部，也可能在低速层，且在不同地点是不相同的，这与云南及周边地区莫霍面变化剧烈有因果关系．进一步推断出上地幔的各向异性主要存在于岩石圈而不是整个上地幔．      

Variations in organic geochemistry and lithology of a carbonate sequence deposited in a backplatform basin (Triassic, Hungary)

The variations in the organic matter quantity and quality were studied with respect to the mineral composition of the carbonate sequences accumulated on a gentle slope (Zl-1 well) and at the toe of the slope (Rzt-1 well) located between a Late Triassic carbonate platform and a backplatform basin. Parallel variations observed in mineral composition and organic geochemical features of the successions appeared to be controlled by the change in climate and by sea-level fluctuations. The repetitive sea-level changes resulted in a variation in the carbonate-rich basin facies and in the mineralogically heterogenous slope and toe-of-slope ones. According to Rock Eval pyrolysis, organic petrography and carbon isotope ratios, the immature organic matter is of predominantly marine origin and composed of mainly liptinites in both of the studied boreholes. The results of the GC and GC/MS analyses of the saturated hydrocarbon fractions of bitumens together with the composition of kerogen pyrolysates reveal a predominant algal input with a minor variable bacterial and subordinate terrestrial contribution for the Rzt-1 borehole. In the Zl-1 borehole a significantly higher proportion of the bacterial biomass contributed to the organic precursors. The δ¹³C values and the composition of the kerogen pyrolysates together with the results of the maceral analysis and GC data suggest a relatively higher, but moderate, higher plant derived contribution in the slope facies and at the top of the toe-of-slope facies. The elementary composition of kerogens and Rock Eval data display type II-S kerogen in the basin and the slope facies, and type I-II-S one in the toe-of-slope facies. Variations in the hydrogen content of the organic matter mainly reflect variations in the preservation conditions and in primary productivity. The presence of the 2,6,10,15,19-pentamethyleicosane and the extremely low pristane/phytane ratios indicate a relatively high methanogenic bacterial activity and strongly anoxic depositional conditions in the Rzt-1 well, especially in two most organic-rich toe-of-slope facies.