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

WANG Linyan  HSU Weibiao  and MA Changqian 《《地质学报》英文版》2010,84(3):528-542

<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.  相似文献   

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   总被引：1，自引：1，他引：0  

段亮 《地质通报》2010,29(1):70-78

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。  相似文献   

东海西湖凹陷天外天二井热史恢复     

张洋 《海洋地质译丛》2009,(4):44-47

应用结合法和流体包裹体显微测温法对东海西湖凹陷浙东中央背斜带南部天外天二井的地热演化史进行了模拟恢复。结果表明，自渐新世至今，总体表现为古地温梯度呈逐渐降低的趋势，高的古地温梯度有利于烃源岩的成熟演化与烃类生成；坳陷演化阶段的古热流高于区域沉降阶段，升温速率与古热流具有较为明显的“镜像”变化关系。利用结合法与流体包裹体测温法能有效地恢复含油气盆地的热演化历史。  相似文献   

岩溶发育的物理化学模式     

赵景波  岳应利  袁道先 《地球科学与环境学报》1999,21(3)

根据大气降水化学成分和岩溶水化学成分的分析，认识到了陕西镇安、旬阳地区夏秋季岩溶水 Ｈ＋ 与 Ｈ Ｃ Ｏ－３ 含量高，岩溶作用活跃，冬春季的变化相反。根据该区及南桂林等地现代岩溶作用强弱变化规律，提出了补充的岩溶作用的物理化学模式。  相似文献   

广西那坡果提金矿成因新认识     

陆有德 《南方国土资源》1999,12(4):31-34

广西那坡县果提金矿是近年化探异常查证发现、并控制了一定储量且地质特征特殊的矿床 ,矿体产于下泥盆统郁江组下部硅化压碎岩中 ,受上寒武统博莱田组碳酸盐岩古侵蚀面控制。通过矿体分布特征和形态产状、矿石特点的研究 ,认为果提金矿属岩溶沉积间断面微细粒金矿。  相似文献   

规模型溶洞在电探上的反映特征初探     

雷旭友 《物探化探计算技术》1998,20(2):175-178

南宁～昆明铁路共进行了２３８ｋｍ路基、隧道、车站、桥址的岩溶综合物探，依据物探结果，进行了３５００多个钻孔的岩溶整治，钻孔资料为物探资料的再分析、总结、提高提供了极为丰富翔实的已知资料。本文通过了三个典型的厅状大溶洞电探信息分析，初步总结出该类异常的反映特征和规律。  相似文献   

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

Annica Greisman  Marie‐José Gaillard 《第四纪科学杂志》2009,24(6):593-611

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.  相似文献   

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

Colin J. Long  Mitchell J. Power  Breanne Mcdonald 《第四纪科学杂志》2011,26(3):318-325

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.  相似文献   

女性主义地理学观及其思想史意义   总被引：1，自引：0，他引：1  

孙俊  汤茂林  潘玉君  武友德 《地理科学进展》2019,38(3):332-345

论文从本体论、认识论和方法论3个层面讨论了女性主义地理学观的建构,并说明了女性主义地理学对更新地理学观的意义,以及对当代主流人文地理学思潮的潜在影响。在本体论层面上,女性主义地理学一直直面西方传统社会文化思想中的等级制性别化二元论,建构了主张女性和男性在建构社会及社会空间中具有交互性关系的本体论。在认识论和方法论层面上,女性主义地理学证明了女性及其空间在西方社会中处于弱势的认识论和方法论根源,动摇了实证主义地理学认识论和方法论中永恒性、普遍性、客观性的预设,阐释了地理学认知过程中情感等主观因素的可靠性,并建构了“去中心化”的认识论和方法论框架。无论在本体论还是在认识论和方法论层面上,当前的女性主义地理学主流思潮都有一定的中和性色彩,这一倾向使女性主义地理学在地理学观演进,以及以人文地理学思想为代表的地理学思想演进中,都具有重要的位置。西方女性主义地理学的兴盛,与其直面西方的社会文化思想根源问题不无关联。在中国女性主义地理学开始发展的当下,注重分析中国女性及其空间问题产生的社会文化思想根源,将有助于中国女性主义地理学的发展,并提升其潜在的价值。  相似文献   

Causes and consequences of life-history variation in North American stocks of Pacific cod     

Ormseth  Olav A.; Norcross  Brenda L. 《ICES Journal of Marine Science》2009,66(2):349-357

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