玉华山高位侵入杂岩定位机制

高位侵入杂岩独特的成岩环境使其形成了一套与深成岩体不同的构造，这些构造为分析岩体的定位提供了依据。区域构造的演化与伴随早期超单元所形成的一系列构造，共同影响着超单元方式的选择。玉华山杂岩定位受到第一、第二和第三序次构造的控制，先后以隐爆拓宽、破火山口塌陷、岩墙扩张机制定位。     

中国区域地磁异常的提取及分析

区域地磁异常的提取对于研究地壳区域的、深部的情况是很有益的。为此,采用地磁台站的多分量磁场强度,经过处理获得了区域地磁异常,提供了丰富的地质信息。     

Evolution of an accretionary complex along the north arm of the Island of Sulawesi, Indonesia

Abstract Seismic reflections across the accretionary prism of the North Sulawesi provide excellent images of the various structural domains landward of the frontal thrust. The structural domain in the accretionary prism area of the North Sulawesi Trench can be divided into four zones: (i) trench area; (ii) Zone A; (iii) Zone B; and (iv) Zone C. Zone A is an active imbrication zone where a decollement is well imaged. Zone B is dominated by out‐of‐sequence thrusts and small slope basins. Zone C is structurally high in the forearc basin, overlain by a thick sedimentary sequence. The subducted and accreted sedimentary packages are separated by the decollement. Topography of the oceanic basement is rough, both in the basin and beneath the wedge. The accretionary prism along the North Sulawesi Trench grew because of the collision between eastern Sulawesi and the Bangai–Sula microcontinent along the Sorong Fault in the middle Miocene. This collision produced a large rotation of the north arm of Sulawesi Island. Rotation and northward movement of the north arm of Sulawesi may have resulted in southward subduction and development of the accretionary wedge along North Sulawesi. Lateral variations are wider in the western areas relative to the eastern areas. This is due to greater convergence rates in the western area: 5 km/My for the west and 1.5 km/My for the east. An accretionary prism model indicates that the initiation of growth of the accretionary prism in the North Sulawesi Trench occurred approximately 5 Ma. A comparison between the North Sulawesi accretionary prism and the Nankai accretionary prism of Japan reveals similar internal structures, suggesting similar mechanical processes and structural evolution.     

Geological framework and Paleozoic tectonic history of the Chinese Altai, NW China: a review

The Chinese Altai, as a key portion of the Central Asian Orogenic Belt (CAOB), is dominated by variably deformed and metamorphosed sedimentary rocks, volcanic rocks and granitic intrusions. Its Early Paleozoic tectonic setting has been variously considered as a passive continental margin, a subduction-accretion complex, or a Precambrian microcontinent, and two representative competing tectonic models have been proposed, i.e., open-closure versus subduction-accretion. Recent studies demonstrate that the high-grade metamorphic rocks previously considered as fragments of a Precambrian basement have zircon U-Pb ages (predominantly 528 to 466 Ma) similar to those of the widely distributed low-grade metasedimentary rocks named as Habahe Group in the region, and all these meta-sedimentary rocks were dominantly deposited in the Early Paleozoic. Petrological evidence and geochemical compositions further suggest that these meta-sedimentary rocks were probably deposited in an active margin, not a passive continental margin as previously proposed. The detrital zircons of sediments and igneous zircons from granitoids including the inherited ones (mainly 543–421 Ma) mostly give positive ?_Hf(t) values, suggesting significant contributions from mantle-derived juvenile materials to the lower crust. A modeling calculation based on zircon Hf isotopic compositions suggests that as much as 84% of the Chinese Altai is possibly made up of “juvenile” Paleozoic materials. Thus, available data do not support the existence of a Precambrian basement, but rather indicate that the Chinese Altai represented a huge subduction-accretion complex in the Paleozoic. Zircon U-Pb dating results for granitoids indicate that magmatism was active continuously from the Early to Middle Paleozoic, and the strongest magmatic activity took place in the Devonian, coeval with a significant change in zircon Hf isotopic composition. These findings, together with the occurrence of chemically distinctive igneous rocks and the high-T metamorphism, can be collectively accounted for by ridge-trench interaction during the accretionary orogenic process.     

Response of coastal plain rivers to falling relative sea-level: allogenic controls on the aggradational phase

This study combines mathematical modelling and supporting flume experiments to address the problem of how coastal plain rivers respond to a steady fall in relative sea-level. The theoretical component of the study focuses on the development of a moving boundary model of fluviodeltaic progradation that treats rigorously the dynamics of the shoreline and alluvial–basement transition (the upstream limit of the alluvial river system). Dimensional analysis and numerical solutions to the model governing equations together suggest that, at first order, coastal plain rivers will remain aggradational on a timescale that varies with allogenic sediment and water supply and the fall rate of relative sea-level. In natural fluviodeltaic systems, this intrinsic timescale is likely to vary by several orders of magnitude, suggesting that the aggradational phase of river response can be geologically long-lived. At second order, the duration of alluvial aggradation is controlled by two dimensionless numbers that embody system geometry and the kinematics of alluvial sediment transport. Model predictions were tested in a series of carefully scaled flume experiments. The level of agreement between predicted and measured trajectories for the shoreline and alluvial–basement transition strongly suggests that the moving boundary theory developed here successfully captures the response of small-scale fluviodeltaic systems to falling sea-level. The results of this study have several sequence-stratigraphic implications: a fall in relative sea-level at the shoreline is not a sufficient condition for river incision; the onset of alluvial degradation and sequence-boundary formation need not coincide with a maximum in the rate of sea-level fall; and the onset of sequence-boundary formation is sensitive to allogenic sediment supply.     

An Improved Gradual Deformation Method for Reconciling Random and Gradient Searches in Stochastic Optimizations

Constraining stochastic models of reservoir properties such as porosity and permeability can be formulated as an optimization problem. While an optimization based on random search methods preserves the spatial variability of the stochastic model, it is prohibitively computer intensive. In contrast, gradient search methods may be very efficient but it does not preserve the spatial variability of the stochastic model. The gradual deformation method allows for modifying a reservoir model (i.e., realization of the stochastic model) from a small number of parameters while preserving its spatial variability. It can be considered as a first step towards the merger of random and gradient search methods. The gradual deformation method yields chains of reservoir models that can be investigated successively to identify an optimal reservoir model. The investigation of each chain is based on gradient computations, but the building of chains of reservoir models is random. In this paper, we propose an algorithm that further improves the efficiency of the gradual deformation method. Contrary to the previous gradual deformation method, we also use gradient information to build chains of reservoir models. The idea is to combine the initial reservoir model or the previously optimized reservoir model with a compound reservoir model. This compound model is a linear combination of a set of independent reservoir models. The combination coefficients are calculated so that the search direction from the initial model is as close as possible to the gradient search direction. This new gradual deformation scheme allows us for reducing the number of optimization parameters while selecting an optimal search direction. The numerical example compares the performance of the new gradual deformation scheme with that of the traditional one.     

上海粘性土剪切带倾角的试验研究

采用可量测局部侧向应变的平面应变仪，对上海地区第（2）层褐黄色粉质粘土和第（6）层暗绿色粉质粘土的原状土样，进行固结不排水平面应变压缩试验，观察土样的局部化变形过程，量测剪切带倾角，研究剪切带倾角随固结压力的变化情况，计算剪切带倾角的传统土力学理论解并与实测值进行比较，根据剪切带内局部剪胀角的近似估算，初步研究剪切带内的变形机理，认为剪切带的形成与孔隙水的运动密切相关。     

古老造山带洋板块地层*

重点分析和总结了由前寒武纪增生复合体和造山带混杂岩重建的古老造山带洋板块地层,包括由英国威尔士安格尔西岛新元古代莫纳超群混杂岩重建的太平洋洋板块地层、由澳大利亚西北部皮尔巴拉早太古代克里夫维尔绿岩带重建的古印度洋洋板块地层。澳大利亚东皮尔巴拉地块大理石坝地区早太古代玄武岩-硅质岩-碎屑岩序列与日本二叠纪-三叠纪洋板块地层在岩石组成和地球化学特征方面具有高度的相似性,这一认识将为早太古代洋板块地层的沉积环境从高热流洋脊扩张区经过热点向低热流海沟陆源碎屑沉积区转变这一过程提供有力支持。从增生造山带洋板块地层保存的岩石记录看,不同年代洋板块地层的主要物质组成和岩石类型相似,因此在地球38亿年的演化进程中,洋壳扩张、海洋沉积、俯冲及增生的过程并没有显著变化;但随着时间推移,年轻造山带洋板块性质和洋板块地层组成与古老造山带相比,可能会发生一些变化。就古老造山带洋板块地层而言,前寒武纪的地幔温度略高,太古代局部熔融显著,熔融量大大超过洋壳扩张速率,因而没有形成席状岩墙群。     

Early Paleozoic accretionary orogens along the Western Gondwana margin

Early Paleozoic accretionary orogens dominated the Western Gondwana margin and were characterized by nearly continuous subduction associated with crustal extension and back-arc basin development.The southwestern margin is represented by Famatinian and Pampean basement realms exposed in South America,both related to the protracted Paleozoic evolution of the Terra Australis Orogen,whereas the northwestern margin is mainly recorded in Cadomian domains of Europe and adjacent regions.However,no clear relationships between these regions were so far established.Based on a compilation and reevaluation of geological,paleomagnetic,petrological,geochronological and isotopic evidence,this contribution focuses on crustal-scale tectonic and geodynamic processes occurring in Western Gondwana accretionary orogens,aiming at disentangling their common Early Paleozoic evolution.Data show that accretionary orogens were dominated by high-temperature/lowpressure metamorphism and relatively high geothermal gradients,resulting from the development of extended/hyperextended margins and bulk transtensional deformation.In this sense,retreating-mode accretionary orogens characterized the Early Paleozoic Gondwana margin,though short-lived pulses of compression/transpression also occurred.The existence of retreating subduction zones favoured mantle-derived magmatism and mixing with relatively young(meta)sedimentary sources in a thin continental crust.Crustal reworking of previous forearc sequences due to trenchward arc migration thus took place through assimilation and anatexis in the arc/back-arc regions.Therefore,retreating-mode accretionary orogens were the locus of Early Paleozoic crustal growth in Western Gondwana,intimately associated with major flare-up events,such as those related to the Cadomian and Famatian arcs.Slab roll back,probably resulting from decreasing convergence rates and plate velocities after Gondwana assembly,was a key factor for orogen-scale geodynamic processes.Coupled with synchronous oblique subduction and crustal-scale dextral deformation,slab roll back might trigger toroidal mantle flow,thus accounting for bulk dextral transtension,back-arc extension/transtension and a large-scale anticlockwise rotation of Gondwana mainland.     

阿拉伯海北部莫克兰增生楔天然气水合物浅表层识别标志

阿拉伯海北部的莫克兰增生楔是阿拉伯板块以低速、低角度俯冲到欧亚板块之下形成的主动陆缘构造,蕴藏着丰富的天然气水合物资源。依据2019年中国在莫克兰增生楔海域采集的高分辨率多道地震资料、浅地层剖面及多波束测深数据,并结合以往的调查成果,探讨莫克兰海域天然气水合物存在的浅表层识别标志。地震识别标志主要有似海底反射层(BSR)和振幅空白带2种标志,地形地貌标志包括海底麻坑、海底滑塌、丘状体、泥火山、冷泉系统等,水体标志主要为羽状流。在水深1000m和2900m的站位已分别钻获水合物样品。莫克兰增生楔丰富的水合物识别标志可能与低速、低角度的俯冲地质背景有关,使该区水合物存在指示兼具主动大陆边缘和被动大陆边缘的特征。综合研究区的异常标志分布特征,推测增生楔中部和西部的背斜脊及其附近区域是天然气水合物远景区。