准噶尔盆地西北缘车拐地区侏罗系成藏动力学模拟

准噶尔盆地西北缘车拐地区目前已经在侏罗系发现了多个油气藏,分析这些油气藏形成的过程及其主要控制因素具有重要意义。基于成藏动力学的三维模拟结果表明,侏罗系油气藏的油气来源主要是二叠系风城组和乌尔禾组烃源岩,油气运移路径主要表现为由沙湾凹陷向车排子凸起、中拐凸起方向。从充注时间看,侏罗系八道湾组始于早侏罗世(178Ma),齐古组始于早白垩世(120Ma),充注过程一直持续到古近纪末期;白垩纪中期的构造运动使车拐地区的地形向现今的"南低北高"发展,改造了已经形成的圈闭,使此前形成的油气藏重新分配,并向北部重新聚集,从而形成现今侏罗系的油气藏主要分布在车拐地区北部和车排子断裂带附近区域,而在车拐地区南部仅存在一些残余油气藏的格局。     

Petrology, Mineralogy and Geochemisty of Antarctic Mesosiderite GRV 020175: Implications for Its Complex Formation History

<正>GRV 020175 is an Antarctic mesosiderite,containing about 43 vol%silicates and 57 vol% metal.Metal occurs in a variety of textures from irregular large masses,to veins penetrating silicates, and to matrix fine grains.The metallic portion contains kamacite,troilite and minor taenite.Terrestrial weathering is evident as partial replacement of the metal and troilite veins by Fe oxides.Silicate phases exhibit a porphyritic texture with pyroxene,plagioclase,minor silica and rare olivine phenocrysts embedded in a fine-grained groundmass.The matrix is ophitic and consists mainly of pyroxene and plagioclase grains.Some orthopyroxene phenocrysts occur as euhedral crystals with chemical zoning from a magnesian core to a ferroan overgrowth;others are characterized by many fine inclusions of plagioclase composition.Pigeonite has almost inverted to its orthopyroxene host with augite lamellae, enclosed by more magnesian rims.Olivine occurs as subhedral crystals,surrounded by a necklace of tiny chromite grains(about 2-3μm).Plagioclase has a heterogeneous composition without zoning. Pyroxene geothermometry of GRV 020175 gives a peak metamorphic temperature(～1000℃) and a closure temperature(～875℃).Molar Fe/Mn ratios(19-32) of pyroxenes are consistent with mesosiderite pyroxenes(16-35) and most plagioclase compositions(An_(87.5_96.6)) are within the range of mesosiderite plagioclase grains(An_(88-95)).Olivine composition(Fo_(53.8)) is only slightly lower than the range of olivine compositions in mesosiderites(Fo_(55-90)).All petrographic characteristics and chemical compositions of GRV 020175 are consistent with those of mesosiderite and based on its matrix texture and relatively abundant plagioclase,it can be further classified as a type 3A mesosiderite.Mineralogical, penological,and geochemical studies of GRV 020175 imply a complex formation history starting as rapid crystallization from a magma in a lava flow on the surface or as a shallow intrusion.Following primary igneous crystallization,the silicate underwent varying degrees of reheating.It was reheated to 1000℃,followed by rapid cooling to 875℃.Subsequently,metal mixed with silicate,during or after which,reduction of silicates occurred;the reducing agent is likely to have been sulfur.After redox reaction,the sample underwent thermal metamorphism,which produced the corona on the olivine, rims on the inverted pigeonite phenocrysts and overgrowths on the orthopyroxene phenocrysts,and homogenized matrix pyroxenes.Nevertheless,metamorphism was not extensive enough to completely reequilibrate the GRV 020175 materials.     

根据碎屑白云母40Ar/39Ar年龄追索喜马拉雅造山带的剥落历史——对青藏高原隆升过程的启示

对喜马拉雅前陆盆地和孟加拉海扇中各地层的碎屑白云母40Ar/39Ar资料的系统分析揭示了喜马拉雅造山带自印度-欧亚板块碰撞开始造山以来的整个剥落历史: 剥落速率开始较为稳定,然后开始上升,在22Ma左右达到峰值,为4~5mm/a,随后急剧下降,最终以2mm/a的速率保持平稳。喜马拉雅造山带与青藏高原周缘剥落历史的对比约束了印度-欧亚板块碰撞造成青藏高原东缘和北缘的不同反应方式。即开始时的挤压主要被青藏高原北缘的大规模左旋走滑吸收, 到30Ma左右,喜马拉雅造山带冷却、剥落速率显著增强,北缘左旋走滑造成的柴达木地块的向东运动被华北板块阻挡而停滞,因此在北缘发生了一些重要的冷却和抬升剥落事件。至18Ma左右,喜马拉雅造山带的冷却、剥落速率继续增高并维持在较高水平,而该时间段内无论是北缘还是东缘,均未发生显著的抬升剥落事件,因此青藏高原的整体隆升和地壳增厚可能发生在此期间。中新世末—上新世初开始至今,青藏高原东缘龙门山地区发生了一些显著的抬升剥落事件,导致了大量的山崩和河流侵蚀,即此时来自喜马拉雅的挤压主要被青藏高原向东方向的地壳逃逸所吸收。     

The role of climate variability and fire in early and mid Holocene forest dynamics of southern Sweden

The objective of this study was to investigate the possible links between regional climate, fire and vegetation at the small spatial scale during the early and mid Holocene in southern Sweden using pollen, plant macrofossil and charcoal records from a small bog. The fire history was compared with climate reconstructions inferred from various proxy records in the study region. High fire activity is related to dry and warm climate around 8550, 7600, 5500–5100 and 4500 cal. a BC. Low fire activity ca. 6500–6000 and 4750 BC may correspond to the widespread ‘8.2 k event’ (ca. 6200 BC) recorded across the North Atlantic region, and a later, brief period of increased precipitation, respectively. The decrease in broadleaved trees culminating ca. 6500–6000 BC correlates with the ‘8.2 k event’. A long mid Holocene period with low fire activity (ca. 4350–1000 BC) agrees with the pattern emerging for Europe from the global charcoal database, and may correspond to generally wetter and cooler conditions. High fire activity ca. 8550 BC probably triggered the local establishment of Corylus. Warmer and drier conditions (and high fire activity) ca. 7600 BC might have favoured the establishment of Alnus, Quercus and Tilia. The fire‐adapted Pinus maintained important populations throughout the early and mid Holocene. Copyright © 2008 John Wiley & Sons, Ltd.     

Millennial‐scale fire and vegetation history from a mesic hardwood forest of southeastern Wisconsin,USA

High‐resolution charcoal analysis of lake sediment cores was used to reconstruct the fire history from two sites in a mesic hardwood forest of south‐eastern Wisconsin located in the Kettle Moraine State Forest. Pollen data from the region indicate that the sites, which lie within 5 km of each other, have had a consistent presence of mesic hardwood forest for the last 6500 years. A pollen record from one of the sites confirmed the regional vegetation history and the charcoal analysis indicated that fire frequency at each site was temporally linked to regional drought. Periods of high fire occurrence occurred in connection with a region‐wide drought 4200 years ago and, over the last 2000 years, shorter‐scale regional droughts were centred at 1800, 1650, 1100, 1000, 800, 700 and 600 cal a BP. The fire histories indicate that the last 1000 years have had lower fire frequencies than the previous 6500 years and suggest that the mesic hardwood forests may be resilient to increases in fire that may result from future climate change. Copyright © 2011 John Wiley & Sons, Ltd.     

东濮凹陷桥口-白庙地区砂岩石英增生及其对流体活动的反映

对东濮凹陷下第三系储层砂岩石英增生边及其中的流体包裹体进行了鉴定和检测,结果表明东濮凹陷桥口-白庙地区共有3期石英增生现象,代表3期流体活动。第1期与第2期发生在盆地深陷期,当时埋深1700～3000m,年代28～37Ma,第3期增生边尚不能确定其形成条件,但可确定其形成于碳酸盐大规模交代石英颗粒之后。桥口地区第1期所代表的流体活动温度主要在110～115℃,第2期所代表的流体活动温度主要在130～135℃。白庙地区第1期所代表的流体活动温度主要在105～110℃,第2期所代表的流体活动温度主要在120～125℃。这3期流体活动的性质可能是粘土矿物转化过程中释放的晶格水通过泥岩的幕式压裂作用向砂岩中释放的结果。     

Cooling and inferred exhumation history of the Ryoke metamorphic belt in the Yanai district, south-west Japan: Constraints from Rb–Sr and fission-track ages of gneissose granitoid and numerical modeling

Abstract The Ryoke metamorphic belt in south-west Japan consists mainly of I-type granitoids and associated low-pressure/high-temperature metamorphic rocks. In the Yanai district, it has been divided into three structural units: northern, central and southern units. In this study, we measured the Rb–Sr whole-rock–mineral isochron ages and fission-track ages of the gneissose granodiorite in the central structural unit. Four Rb–Sr ages fall in a range of ca 89–87 Ma. The fission-track ages of zircon and apatite are 68.9 ± 2.6 Ma and 57.4 ± 2.5 Ma (1σ error), respectively. Combining the newly obtained ages with previously reported (Th–)U–Pb ages from the same unit, thermochronologic study revealed two distinctive cooling stages; 1) a rapid cooling (> 40°C/Myr) for a period (~7 Myr) soon after the peak metamorphism (~ 95 Ma) and 2) the subsequent slow cooling stage (~ 5°C/Myr) after ca 88 Ma. The first rapid cooling stage corresponds to thermal relaxation of the intruded granodiorite magma and its associated metamorphic rocks, and to the uplift by a displacement along low-angle faults which initiated soon after the intrusion of the magma. Uplift by the later stage deformation having formed large-scale upright folds resulted in progress of the exhumation during the first stage. The average exhumation velocity of the stage is ≥ 2 mm/yr. During the second stage, the rocks were not accompanied by ductile deformation and were exhumed with the rate of 0.1–0.2 mm/yr. The difference in the exhumation velocity between the first and second cooling stages resulted from the difference in the thickness of the crust and in the activity of ductile deformation between the early and later stages of the orogenesis.     

Records of natural fire and climate history during the last three glacial-interglacial cycles around the South China Sea Charcoal record from the ODP 1144

The history of natural fire and its relationship to climate during the last three gla cial-interglacial cycles in the Southern coast areas of China and the northern continental shelf of the South China Sea (SCS) are discussed based on the statistic study of charcoal particles and associated pollen data from ODP 1144 Site (20° 3′N, 117° 25′E, 2037 m in water depth). Accord ing to the results of the charcoal and pollen study, the sediments from the upper 225 m are divided into 8 zones (C1-8), which might be correlated with the Marine Isotope Stage 1-8 (MIS1-8)respectively. Our study indicates that during the last glacial period (MIS2, 4), the influx of charcoal particle was much higher than that from the interglacial period, suggesting strong occurrence of natural fire and dry climate. During MIS 6 and MIS 8 (C6, C8), although the influx of fine charcoal particles was quite high, the influx of the coarse and medium charcoal particle were much low,which might be due to the smaller source area of fire probably resulting from the limited exposure of the continental shelf before MIS5. During the interglacial period (MIS1, 5, 7), the influxes of charcoal particles were much lower, implying dropping of intensity of the natural fire and then a humid climate. Another reason is that the continental shelf was submerged into the sea during the interglacial periods, and the source areas of fire were reduced then. Although the influx of the fine charcoal particles was much lower during MIS3, the influx of the coarse and medium charcoal par ticles were almost equal to those of MIS4 (C4), which suggests that the intensity of the natural fire remained quite high and the climate was considerably dry during that period.     

华北、扬子板块碰撞后热演化史的初步研究

对采自苏北－胶南－大别高压变质构造混杂岩带的片麻岩、糜棱岩和郯庐断裂带上的片麻岩中９个钾长石进行了￣４０Ａｒ－￣３９Ａｒ年龄测定和多重扩散域（ＭＤＤ）模式处理，９个样品的热演化史表明上述地区存在５个不同的快速冷却时段，并就其可能的构造含义，提出了华北与扬子板块碰撞后的折返历史过程