东海陆架盆地构造反转特征及成因机制探讨

通过对东海陆架盆地各二级构造单元内反转构造的梳理与分析,认为盆内新生代反转构造以形态各异的背斜为主,伴有逆断层发育。主要存在瓯江运动(T80)、玉泉运动(T30)、花港运动(T20)和龙井运动(T12)4期构造反转,在时间和空间上具有明显的差异性。在时间演变上：西部坳陷带构造反转从瓯江运动(T80)到花港运动(T20)有相对减弱的趋势,龙井运动(T12)特征不明显;东部坳陷带构造反转从玉泉运动(T30)、花港运动(T20)到龙井运动(T12)有相对增强的趋势。在空间演变上：东部坳陷带西湖凹陷和钓北凹陷龙井运动(T12)构造反转具有显著的自北向南减弱的趋势。东海陆架盆地新生代构造反转强弱分布、迁移演化是太平洋板块与欧亚板块、印度板块与欧亚板块之间汇聚俯冲速率和方向的变化在盆内叠加的局部响应。     

Changes of Paleo-precipitation on the Sunda Shelf Since the Last Glacial Maximum Revealed by Hydrogen and Oxygen Isotopes

The Sunda Shelf, owing to its unique geographical location and roles, has attracted much attention on its changes during the glacial cycle. At present, there is a consensus about the change of temperature in the region, but the reconstruction of paleo precipitation has been disputed. The hydrogen and oxygen isotope records since the last glacial in the Sunda Shelf were collected, combining with other paleo climate record, we roughly divided the precipitation records in the region into the Northern and Southern areas. During the glacial, the precipitation changed little and climate remained moist in the northern area, while precipitation decreased greatly,and the climate became dry in the southern. Difference in the precipitation isotopes between the northern and southern areas might be related to the different controlling factors of the precipitation isotopes in the two areas and large-scale atmospheric circulation in the region. Limited by the collected hydrogen and oxygen records, the precise mechanism of division in regional hydrological changes of the region still needs more work to confirm.     

Resistivity of reservoir sandstones and organic rich shales on the Barents Shelf:Implications for interpreting CSEM data

Marine controlled source electromagnetic(CSEM)data have been utilized in the past decade during petroleum exploration of the Barents Shelf,particularly for de-risking the highly porous sandstone reservoirs of the Upper Triassic to Middle Jurassic Realgrunnen Subgroup.In this contribution we compare the resistivity response from CSEM data to resistivity from wireline logs in both water-and hydrocarbon-bearing wells.We show that there is a very good match between these types of data,particularly when reservoirs are shallow.CSEM data,however,only provide information on the subsurface resistivity.Careful,geology-driven interpretation of CSEM data is required to maximize the impact on exploration success.This is particularly important when quantifying the relative re-sistivity contribution of high-saturation hydrocarbon-bearing sandstone and that of the overlying cap rock.In the presented case the cap rock comprises predominantly organic rich Upper Jurassic-Early Cretaceous shales of the Hekkingen Formation(i.e.a regional source rock).The resistivity response of the reservoir and its cap rock become merged in CSEM data due to the transverse resistance equivalence principle.As a result of this,it is imperative to understand both the relative contributions from reservoir and cap rock,and the geological sig-nificance of any lateral resistivity variation in each of the units.In this contribution,we quantify the resistivity of organic rich mudstone,i.e.source rock,and reservoir sandstones,using 131 exploration boreholes from the Barents Shelf.The highest resistivity(＞10,000 Ωm)is evident in the hydrocarbon-bearing Realgrunnen Subgroup which is reported from 48 boreholes,43 of which are used for this study.Pay zone resistivity is primarily controlled by reservoir quality(i.e.porosity and shale fraction)and fluid phase(i.e.gas,oil and water saturation).In the investigated wells,the shale dominated Hekkingen Formation exhibits enhanced resistivity compared to the background(i.e.the underlying and overlying stratigraphy),though rarely exceeds 20Ωm.Marine mudstones typically show good correlation between measured organic richness and resistivity/sonic velocity log signatures.We conclude that the resistivity contribution to the CSEM response from hydrocarbon-bearing sandstones out-weighs that of the organic rich cap rocks.     

Crustal anatexis and formation of two types of granitic magmas in the Kontum massif, central Vietnam: Implications for magma processes in collision zones

Asia grew in the Late Permian by the collision of a number of micro-continents. Syn- to post-collisional magmatism occurred along the continental collision zones . In this study, we report two types of granitic rocks, garnet granite (Grt granite) and orthopyroxene granite (Opx granite), from the Kontum massif, central Vietnam, which is situated on the continental collision zone between the South China and Indochina cratons. These granitic rocks were formed at ca. 250 Ma when high-temperature (HT) and ultrahigh-temperature (UHT) metamorphism took place in the same zone. Based on the petrological and geochemical features compared with previously reported experimental results, garnet-bearing granite is derived from pelitic gneisses by partial melting, whereas orthopyroxene-bearing granite is produced by the partial melting of garnet-bearing mafic granulites. We inferred that a significantly high-geothermal gradient is required to produce Vietnamese granitic magmatism and related HT to UHT metamorphism. This geotherm may be attributed to upwelling mantle plume beneath the Kontum massif during the Late Permian.     

Paleoshorelines and lowstand sedimentation on subtropical shelves: a case study from the Fraser Shelf,Australia

Evidence of submerged paleoshorelines on tectonically stable continental shelves is represented by relict coastal depositional features that formed during periods of lower sea level. This study investigates two paleoshoreline features that extend 70?km from the Barwon Bank along the southeast Fraser Shelf, off eastern Australia. They are defined by well-lithified, mixed carbonate-siliciclastic deposits now at water depths of 60?m and between 80 and 100?m, located approximately 40?km seaward of the modern shoreline. High-resolution multibeam bathymetry data show geomorphic features that we interpret as paleodunes in the case of the 60?m feature, and paleobarriers in the case of the 80–100?m feature. Sub-bottom profiles also show evidence of prograded beach foresets and paleochannels as components of the Barwon Bank, which is a low and elongate bank that rises about 30?m above the surrounding shelf to a depth of 60?m. Carbonate cements in the rocks forming the paleoshoreline features reveal diagenetic influence of meteoric waters, suggesting that subaerial processes contributed to the formation and preservation of both features. Radiocarbon dating of bioclastic grains (coralline algae, benthic forams) yields an age range between 22.8 and 20.4?ka for the paleobarrier, and an age of 17.3?ka for the paleodune. The morphology of the submerged paleodunes is analogous to modern parabolic dunes on nearby Fraser and Moreton islands. The position and morphology of the paleodunes provide proxy information about the climate history of Australia during the late Quaternary, as these dunes are a likely consequence of the general continent-wide aridity during the Last Glacial Maximum. The preservation of the eolian dunes during marine transgression, despite their direct exposure to coastal hydrodynamic processes, suggests that the dunes were armoured, stabilised and lithified during the glacial lowstand, prior to drowning.     

Probabilistic landslide susceptibility mapping in the Lai Chau province of Vietnam: focus on the relationship between tectonic fractures and landslides

This study evaluates the susceptibility of landslides in the Lai Chau province of Vietnam using Geographic Information System (GIS) and remote sensing data to focus on the relationship between tectonic fractures and landslides. Landslide locations were identified from aerial photographs and field surveys. Topographic, geological data and satellite images were collected, processed, and constructed into a spatial database using GIS data and image-processing techniques. A scheme of the tectonic fracturing of crust in the Lai Chau region was established. Lai Chau was identified as a region with many crustal fractures, where the grade of tectonic fracture is closely related to landslide occurrence. The influencing factors of landslide occurrence were: distance from a tectonic fracture, slope, aspect, curvature, soil, and vegetative land cover. Landslide prone areas were analyzed and mapped using the landslide occurrence factors employing the probability–frequency ratio model. The results of the analysis were verified using landslide location data and showed 83.47% prediction accuracy. That emphasized a strong relationship between the susceptibility map and the existing landslide location data. The results of this study can form a basis stable development and land use planning for the region.     

The characteristics,formation and exploration progress of the potash deposits on the Khorat Plateau,Thailand and Laos,Southeast Asia

The giant potash deposit on the Khorat Plateau is one of the most promising targets for exploitation of potassium salts. So far, many researches and geologic survey have been conducted on the giant potash deposits. Hence, it is necessary to make an overall review on the potash deposits. The potash deposit on the Khorat Plateau was formed during the Middle to Late Cretaceous, during which seawater was enriched in Ca²⁺ and depleted in SO₄^2- compared with those of modem seawater. In addition to seawater, continental water and hydrothermal fluids could have affected the evaporite basins. The seawater was probably derived from Tethys ocean, and the brine should have evaporated to some extent before entering into the basin systems based on the evidence of absence of carbonates and unproportionate sulphate compared with chloride salts. The paleo-climate during Middle to Late Cretaceous was characterized as high temperature and extremely arid environment, which is favourable for deposition of potassium-magnesium saline minerals. The major saline minerals are of anhydrite, halite, camallite, sylvite and, tachyhydrite, with trace amounts of borates. The resources of the potash deposit on the Khorat Plateau could be approximately as much as 400×10⁹ t of camallite and 7×10⁹ t of sylvite. The evaporite sequences have been deformed and altered by postdepositinal processes, including tectonic movements and chemical alteration. Salt domes were formed in the postdepositional processes. Based on the analyses of geophysical surveys and drilling projects, high-quality sylvinite ores are commonly found at the flanks of those salt domes due to incongruent dissolution of camallite. The future potential prospecting areas for the high-quality sylvinite ores would be on the edges of the Khorat Plateau.     

Neoproterozoic Tectonic Setting of Southeast China: New Constraints from SHRIMP U-Pb Zircon Ages and Petrographic Studies on the Mamianshan Group

<正>Precambrian tectonic history of Zhejiang,Fujian,and Jiangxi provinces of south China is important for understanding the tectonic evolution of South China but its magmatic activity, petrogenesis,stratigraphic sequence of the Mamianshan Group is still strongly controversial.Here we present new sensitive high resolution ion micro-probe(SHRIMP) U-Pb zircon geochronological data for the Mamianshan Group and petrographical data to constrain the tectonic framework of the regions.Our results showed that the SHRIMP U-Pb zircon age of green schists of the Dongyan Formation is 796.5±9.3 Ma,the Daling Formation is 756.2±7.2 Ma,and mica-quartz schist of the Longbeixi Formation is 825.5±9.8 Ma.These data indicate that the Mamianshan Group was formed not in the Mesoproterozoic,but in the Neoproterozoic and its stratigraphic sequences should be composed of Longbeixi,Dongyan,and Daling Formations from the bottom to the top.Rocks from this Group, from Zhejiang,Fujian and Jiangxi provinces,constituted the upper basement of the Cathaysia Block that overlay the lower basement of the Mayuan Group.Detailed petrographic studies demonstrate that the amphibole schists of the Dongyan Formation in the Mamianshan Group were formed within an intra-arc rift setting rather than a continental rift as previously suggested.Rather,this island-arc type formation was developed by collision and/or subduction between various blocks resulting from the breakup of the supercontinent Rodinia at c.850-750 Ma.The Zhuzhou conglomerate,distributed near Dikou Town,Jian'ou City,Fujian Province and previously considered as evidence of the Mesoproterozoic Dikou movement,is shown here not to be the basal conglomerate above the angular unconformity between the upper and lower basements.Our conclusions have important implications for understanding the Precambrian tectonics of South China.     

火山碎屑密度流沉积机制研究——以松辽盆地东南隆起区九台地区白垩系营城组火山碎屑岩为例

火山碎屑密度流是一种危险的火山活动现象,也是一种重要的盆地物源供给方式,对其沉积机制的研究具有灾害预防和油气勘探的双重意义。松辽盆地东南隆起区九台营城煤矿地区白垩系营城组古火山机构保存良好,发育有典型的火山碎屑密度流沉积物。本文在精细刻画火山碎屑岩的岩石结构、沉积构造的基础上,运用薄片观察和沉积物粒度统计的方法,从物质来源、搬运机制和就位方式角度系统地分析了火山碎屑密度流的整个沉积过程,并结合国内外火山学、沉积学的研究进展探讨了不同浓度火山碎屑密度流的沉积机制。研究区内的火山碎屑密度流沉积物可以划分为五种微相:①块状熔结角砾凝灰岩微相;②无序含集块凝灰角砾岩微相;③逆粒序或双粒序角砾凝灰岩微相;④正粒序角砾凝灰岩微相;⑤韵律层理凝灰岩微相。第一种微相具有熔结结构,可能形成于高挥发分岩浆喷发柱的垮塌,火山碎屑密度流的就位温度较高;后四种微相具有正常火山碎屑岩结构,可能形成于火山口的侧向爆炸,火山碎屑密度流的就位温度中等。沉积块状熔结角砾凝灰岩微相的火山碎屑密度流具有黏性碎屑流的流体特征,沉积物整体冻结就位;沉积无序含集块凝灰角砾岩微相和逆粒序或双粒序角砾凝灰岩微相的火山碎屑密度流具有颗粒流的流体特征,沉积物整体冻结就位;沉积正粒序角砾凝灰岩微相和韵律层理凝灰岩微相的火山碎屑密度流具有湍流的流体特征,沉积物连续加积就位。火山碎屑密度流的颗粒浓度是一个连续变量,但流体性质可能会发生突变,稀释的火山碎屑密度流的沉积机制符合下部流动边界模型,稠密的火山碎屑密度流的沉积机制符合层流(碎屑流或颗粒流)模型。     

Conditions and mechanism for the formation of iron-rich Montmorillonite in deep sea sediments (Costa Rica margin): Coupling high resolution mineralogical characterization and geochemical modeling

Iron-rich smectite is commonly described in the diagenetic fraction of deep-sea sediment, as millimeter to centimeter aggregates dispersed in the sediment, or as a coating on sedimentary particles or nodules. This study examines several factors to elucidate formation mechanisms of a particular iron-rich smectite and its potential transformation to glauconite. The study combines a detailed mineralogical investigation on natural samples and a chemical modeling approach to assess mineralogical reactions and pathways.Transmission electron microscopy (TEM) observations and analytical electron microscopy (TEM-AEM) analyses were conducted on microtomed samples of millimeter- to centimeter-long green grains. These grains are widespread in pelagic calcareous sediment from the Costa Rica margin. They are composed of pyrites that are partially dissolved and are surrounded by amorphous or very poorly crystallized iron-rich particles. Iron-rich montmorillonite grows from an amorphous precursor and its formation requires the input of Si, O, Mg, K, Na and Ca; our results suggest that these inputs are supported by the dissolution of sedimentary phases such as volcanic glasses, siliceous fossils and silicates.Thermodynamic modeling of fluid-sediment interactions was conducted with the geochemical computer code PhreeqC, using mineralogical and pore fluid compositions from sediment samples and calculated estimates for thermodynamic constants of smectites that are not maintained by the computer code. Simulations confirm the possibility that the green grains are the product of pyrite alteration by seawater under oxidizing conditions. The extent of smectite production is controlled by the kinetics of pyrite dissolution and fluid migration. The absence of aluminum in the Costa Rica margin system explains the formation of an iron-rich montmorillonite instead of glauconite, whereas the presence of calcite that buffers the system explains the formation of an iron-rich montmorillonite instead of iron oxides.     

Granitoids in the Dalat zone,southern Vietnam: age constraints on magmatism and regional geological implications

The Dalat zone in southern Vietnam comprises a Cretaceous Andean-type magmatic arc with voluminous granitoids and contemporary volcanic rocks. On the basis of petrographical and mineralogical studies, the granitoids were subdivided into three suites: Dinhquan, Deoca and Cana. Rocks of the Dinhquan suite are hornblende–biotite diorites, granodiorites and minor granites. The Cana suite encompasses mainly leucocratic biotite-bearing granites with scarce hornblende. The Deoca suite is made up of granodiorites, monzogranites and granites. Geochemically, the granitoids are of subalkaline affinity, belong to the high-K, calc-alkaline series, and most of them display typical features of I-type granites. This paper presents the new Rb–Sr mineral and U–Pb zircon and titanite age data for the granitoids, which establish the ages of the plutonic suites as: the Dinhquan at ~112–100 Ma, Cana at ~96–93 Ma and Deoca at ~92–88 Ma. These ages are significantly different from earlier publications, and indicate that the earliest magmatism in the Dalat zone began at ~112 Ma ago, that is ~30–50 Ma later than previously thought. Our geochronological data are also support the continuation of an Andean-type arc running from SE China via southern Vietnam to SW Borneo.     

Zircon SHRIMP U-Pb ages and geochemistry of Late Mesozoic granitoids in Western Zhejiang and Southern Anhui: constraints on the model of lithospheric thinning of Southeast China

ABSTRACT

We report geochemical data and zircon SHRIMP U-Pb ages for Late Mesozoic granitoids from the western Zhejiang province and southern Anhui province (the WZSA region) from southeast China. In combination with published geochronological and geochemical data, the granitoids in the region can be divided into three stages: 171–141 Ma, 140–121 Ma, and 120–95 Ma. The first stage of these granitoids is mainly composed of granite porphyry and granodiorite which are similar to I-type granitoids, including having weakly negative Eu anomalies with enrichment in light rare earth elements (LREE), Rb, Th, and U. The second stage of granitoids consists of monzogranite, syenogranite, and granite with the characteristics of both A-type and I-type granitoids including strongly negative Eu anomalies; depletion of Ba, Sr, and Ti; and enrichment of K, Rb, and high field strength elements (HFSEs) (such as Th and U). The third stage of granitoids is mainly composed of granite, quartz monzonite, quartz diorite, and mafic rocks with weakly negative Eu anomalies and also enrichment in LREE, Rb, Th, U, and K. From our work, we propose a transition from compressional to extensional magmatism at ~141 Ma. Based on the geochemical characteristics of these granites and coeval mafic rocks, we propose that the formation of the A-type magmatism in the WZSA region formed as the result of lithospheric extension and asthenospheric upwelling during the Early Cretaceous.     

Channel formation by flow stripping: large-scale scour features along the Monterey East Channel and their relation to sediment waves

The Monterey East system is formed by large‐scale sediment waves deposited as a result of flows stripped from the deeply incised Monterey fan valley (Monterey Channel) at the apex of the Shepard Meander. The system is dissected by a linear series of steps that take the form of scour‐shaped depressions ranging from 3·5 to 4·5 km in width, 3 to 6 km in length and from 80 to 200 m in depth. These giant scours are aligned downstream from a breech in the levee on the southern side of the Shepard Meander. The floor of the breech is only 150 m above the floor of the Monterey fan valley but more than 100 m below the levee crests resulting in significant flow stripping. Numerical modeling suggests that the steps in the Monterey East system were created by Froude‐supercritical turbidity currents stripped from the main flow in the Monterey channel itself. Froude‐supercritical flow over an erodible bed can be subject to an instability that gives rise to the formation of cyclic steps, i.e. trains of upstream‐migrating steps bounded upstream and downstream by hydraulic jumps in the flow above them. The flow that creates these steps may be net‐erosional or net‐depositional. In the former case it gives rise to trains of scours such as those in the Monterey East system, and in the latter case it gives rise to the familiar trains of upstream‐migrating sediment waves commonly seen on submarine levees. The Monterey East system provides a unique opportunity to introduce the concept of cyclic steps in the submarine environment to study processes that might result in channel initiation on modern submarine fans.     

气候变化影响下高山区泥石流形成机制研究及展望

全球范围内高海拔或高纬度山区（以下简称高山区）,尤其高山冰川冻土急剧消退地区,广泛发育泥石流灾害。在全球气候变暖的大背景下,高山区泥石流的现实危害和潜在风险日渐凸显。与其他环境条件下泥石流过程主要由降雨激发不同,高山区泥石流的暴发多受降雨和温度条件的共同影响,其形成机制更为复杂,预测预警十分困难,因此加强高山区泥石流研究具有重要的科学价值和实践意义。通过述评近期高山区泥石流起动研究的主要进展,包括泥石流暴发与气象条件的关系,典型高山区泥石流事件成因,冰川冻土体消融破坏机制,以及冰碛土泥石流起动特征,认为未来高山区泥石流研究应加强高时空分辨率气象数据获取和物源动态变化分析研判,并从动力学机制层面进一步明晰高山区泥石流起动条件和发育过程。     

鞍山-本溪地区条带状铁矿的Fe同位素特征及其对成矿机理和地球早期海洋环境的制约

本文报道了鞍山-本溪地区晚太古代条带状铁建造的主量元素、微量元素、稀土元素和Fe同位素的分析结果.结果显示:铁矿主要由Fe2O3T和SiO2组成,具有较低的Al2O3和TiO2含量;微量元素含量和稀土总量均较低;经页岩标准化的稀土元素配分模式呈现轻稀土亏损、重稀土富集;具有明显的La、Eu、Y的正异常;较高的Y/Ho比值.这些特征均表明鞍山-本溪地区条带状铁矿是由极少碎屑物质加入的化学沉积岩,成矿物质主要来源于海底热液的贡献.相对于标准物质IRMM-014,条带状铁矿石的Fe同位素组成最突出的特征是均为正值,这是由于二价铁溶液经部分氧化和沉淀形成富集重铁同位素的三价铁氧化物或氢氧化物的结果,且沉淀程度的不同是控制Fe同位素组成变化的重要因素.条带状铁矿无明显的Ce负异常和Fe同位素组成为正值的特征暗示了铁矿沉淀时的海水为低氧逸度环境.     

全谱拟合定量研究气候对土壤成壤机制的约束:以鲁粤土壤剖面为例

以山东棕壤剖面和广东红壤剖面为研究对象,通过X射线衍射(XRD)和基于Rietveld技术的全谱拟合定量分析土壤中的矿物组成、在剖面上的含量变化并研究粘土矿物之间的相互转化关系,揭示气候对土壤成壤机制的约束。结果表明,2个剖面中的矿物组成不同:山东棕壤中非粘土矿物有长石、石英、方解石及少量的铁铝氧化物和闪石类矿物,粘土矿物有伊利石、绿泥石、高岭石和蒙脱石,且粘土矿物含量伊利石>绿泥石≈蒙脱石>高岭石;广东红壤的矿物组成为石英、赤铁矿、针铁矿、三水铝石、高岭石、伊利石和蛭石,其中高岭石>伊利石>蛭石。此外,两地的土壤中均含有少量的非晶质物质。山东气候干冷,以物理风化为主,化学风化较弱,原生闪石类原生硅酸盐矿物和易被溶蚀的方解石等仍有存留;广东气候湿热,化学风化强烈,存在明显的脱硅富铝作用,铁铝氧化物富集。3)利用定量结果计算的化学风化指数与矿物的变化是一致的。     

干旱、半干旱地区高砷地下水形成机理研究:以中国内蒙古河套平原为例

干旱、半干旱地区高砷地下水形成机理,是一较为复杂的地球化学和环境水文地球化学过程。通过多年来的实地调查、资料分析和试验测试等方法手段,详细研究了中国西部地区,特别是中国内蒙古河套平原,高砷地下水的分布特征及地质环境背景。研究并阐述了地下水中砷的来源,地层中砷的来源、聚集、溶出的地球物理、地球化学过程,提出了河套平原地层中砷聚集的3种模式,即断裂运移聚集模式,河、湖水胶体作用聚积模式和蒸发浓缩再聚集模式。研究表明：河套平原地下水中的砷,主要来源于地层,而地层中的砷主要来源于3个方面：周边的山区特别是存在高矿化带的西部山区、黄河上游和构造运移深部地下水;地层中砷的溶出主要与3个因素有关：地下封闭的还原环境、脱硫酸作用和大量灌溉水的入渗。     

5.12汶川地震对黄龙世界遗产地源泉水文地球化学的影响——高分辨率和高精度的水文地球化学监测证据

2008年5月12日的汶川特大地震不仅造成了惨重的人员伤亡和巨大的经济损失,而且对当地生态环境产生了严重的影响。本文根据黄龙钙华景观退化的人为和自然影响机理研究获得的部分高分辨率和高精度水文地球化学监测数据分析发现,大地震通过诱导控制黄龙源泉的深源断裂活动对源泉的水文地球化学产生了显著影响,主要表现为地震后泉流量、水温、电导率和CO2分压升高,反映出地震增加了地下向地表的水、热、钙离子和CO2通量。然而,地震对从泉水中沉积的钙华景观的后续影响以及汶川地震造成深源CO2向大气CO2释放对全球碳循环的影响,有待进一步的监测评估。