华南玻璃陨石的原生层位及其事件地层学意义

华南大玻璃陨石分布于广西、广东和海南。根据广东西部和海南岛实测的两类含玻璃陨石的地层剖面——第四系北海组与湛江组界线附近的连续剖面和与湛江组顶部剥蚀面相当的原始台地剖面。玻璃陨石从产状来看可分为埋藏的原生撒落型、暴露的原生撒落型和次生搬运型等几类,赋存的原生层位是北海组中-下部的组内剥蚀面,而不是北海组与湛江组的界面;发现了玻璃陨石及其层位附近的某些元素异常以及早更新世晚期-中更新世早期存在的环境事件与灾变,指出将华南玻璃陨石事件与华北黄土和南海深海盆沉积中的微玻璃陨石进行准确地层对比的必要性,并从玻璃陨石的研究中引入事件地层学及其与全球变化关联研究的新思路。谨以此文深切悼念我国第四纪地质及第四纪冰川地质的优秀科学家吴锡浩先生。      

识别冲击变质作用的岩石学和矿物学标志

自80年代初新突变学说兴起以来,陨击坑及冲击变质作用研究,已成为国际地学界的重大课题之一.本文归纳了国内外的大量资料,对岩矿识别标志进行简介和评述.主要涉及标志有:1.陨石碎块;2.玻陨石和微玻陨石;3.击变者和熔石玻璃;4.击变矿物;5.击变玻璃;6.冲击变形组构;7.冲击变质石英的光学常数变化;8.冲击微页理:9.冲击变质石英的结构变化和变形;10.陨击角砾岩;11.震裂锥;12.瞬变岩.     

海南白沙陨坑冲击变质岩岩石：地球化学特征初步研究

海南白沙陨石冲击坑是中国境内发现的第—个保存良好、可供直观的陨坑.经野外考察和室内分析鉴定工作,进一步对白沙陨坑内击变岩的岩石一地球化学特征进行了研究,证明堆积在底盘原岩之上的貌似“火成岩”的块状、角砾岩岩石,是长石石英砂岩受冲击变质而成的击变岩.现简介如下.     

西藏泽当地区的宇宙尘

宇宙尘也称微陨石、陨砂、微玻璃陨石,我国海南岛、雷州半岛产的玻璃陨石称为雷公墨,其中也有微玻璃陨石,或称为显微熔融石。 宇宙尘最早是1872—1876年英国“挑战”号考察船在大洋底淤泥中发现的,Murray根据这些宇宙尘球粒表面构造特征与铁质陨     

ODP 1144站钻孔沉积物中微玻璃陨石的元素地球化学特征

利用电子探针和激光探针等离子体质谱方法分析了取自南海北部的ODP1144钻孔沉积物中的微玻璃陨石和取自邻近的广东省湛江和吴川玻璃陨石的主元素和微量元素组成。结果显示，这些微玻璃陨石属于亚洲-澳大利亚散落区的普通微玻璃陨石。从成分上看，这些微玻璃陨石存在两种不同的类型，其中的绝大部分Al2O3含量在19.0%以上，属于高Al类型，相应的难熔微量元素含量也比较高；个别微玻璃陨石Al2O3含量（13.0%)和难熔微量元素含量较低，微量元素含量和特征比值都与邻近的广东省湛江和吴川的玻璃陨石相近。元素地球化学特征意味着，这些微玻璃陨石来源于同一靶源区，但靶区的物质组成并不均一。     

海南岛白沙陨击坑及其成坑陨石

海南岛白沙陨击坑是一个直径约３．５ｋｍ的环形镶边坳陷，组成陨击坑边缘的环形山连续性好，并具二元结构；下部是层理清晰的下白垩统紫红色砂岩，其中长石、石英等粒状矿物普遍受冲击破碎，发育有冲击微页理和击变玻璃，云母呈膝折状变形；上部是冲击角砾岩块杂乱堆垒成的溅射覆盖层，冲击角砾岩因冲击熔融结晶而貌似凝灰岩，但其中矿物成分十分复杂，含有镁橄榄石、镍纹石以及高密度石英等，岩石化学计算结果说明它是由砂岩变质而成的，与火成岩无关。坑内保留有回落角砾岩，常见到沿裂缝贯入的脉状角砾岩。在陨击坑内找到了重３．７５ｋｇ的石陨石碎块，其中含碱硅镁石、陨铁大隅石、四方镍纹石、陨硫钙石和陨硫铁等陨石标型矿物，但不具球粒结构，ＣａＯ含量为９．１９％，属富钙的无球粒陨石，认为是白沙陨石坑的成坑陨石。在陨击坑中找到富钙无球粒陨石，为陨击坑提供了最直接可靠的证据，也为石陨石撞击成坑提供了实例。     

陨石撞击构造作用的研究现状与前景

当陨石撞击地球表面时, 它所引起的瞬时(1秒至1微秒)动态高压(数十至数百个吉帕)和高温(大于1500℃), 必然导致陨石撞击坑(astroblems)的生成并使周围岩石发生变质作用, 这便是撞击变质作用(impact metamorphism)。目前关于撞击构造(impact tectonics)作用研究的主要进展涵盖如下四个方面:1.撞击坑的构造形貌及形成机制; 2.撞击变质作用及撞击变质岩; 3.撞击作用的数值模拟和实验研究; 4.撞击作用的经济地质意义。陨击作用研究不仅具有学术意义, 还具有实际的经济地质意义。南非的Vredefort-Witwatersrand是最老的撞击构造, 它以丰富的金铀矿床而闻名; 加拿大的肖德贝里(Sudbury)以同撞击作用期的大型铜镍矿床著称; 如今北美、中美不少地区正在探索与陨击期后构造有关的油气储集。此外, 许多陨击变质岩可以供作建筑材料。不少撞击坑已经辟为旅游胜地, 如德国的Nordlingen Ries撞击坑。我国撞击构造的研究已有不少进展。20世纪90年代初发现了海南白沙陨击坑, 此外内蒙古的多伦、江苏的太湖和辽宁的岫岩罗圈里等地也发现有陨击构造的证迹, 不过, 都尚待进一步的工作予以证实。全球撞击构造研究经验可以借鉴的是, 在长期构造稳定区较易于发现陨击坑; 不少撞击构造被隐伏在第四纪或更老的沉积物之下, 所以采用人造卫星发回资料解译地球表面的照片, 加上地球物理勘探, 可以有效地确定研究靶区, 在此基础上再加强岩石学、构造学研究予以确认。      

陨石熔壳研究

本文通过对毫县陨石熔壳的化学成分分析,Ｘ射线物相分析和红外光谱分析,并与一岩相互对照,讨论了熔壳中Ｆｅ的氧化状态的变化、击变玻璃及主要矿物结构参数的变化;研究了熔壳的氧化作用、击变作用、击变作用下矿物的变形机制,同时,熔壳的ＳＥＭ显微 貌像给出了熔壳的一套完整剖面,从而讨论了熔壳的烧蚀作用主要有破碎作用,熔融作用和抽蚀作用三种方式。此外,透射电观察敢证实了陨石熔壳中石英玻璃的存在。     

东太平洋573孔始新世末渐新世初地层特征及稀土元素地球化学

根据深海钻探样品分析,对东太平洋地区573孔始新世末渐新世初的地层特征进行了研究,尤其是研究了其稀土元素地球化学特征.各层球粒陨石标准化值曲线平缓,重稀土相对富集,各层Ce严重亏损(第2层轻度亏损),各层的Eu仅轻度亏损.始新世与渐新世的界线地层含金属粘土层的稀土元素含量明显比其它层含量高得多.此外,该层还富含Fe及指示地外成因的Ni、Co、Ir等元素,且底部富含微玻璃陨石.这些特征说明该含金属粘土层的形成与火山活动有明显关系,其底部可能还与陨击作用相联系.从区域地质情况来看,始新世末期有明显的生物灭绝和环境变化,微玻璃陨石广泛发育,说明该时期有明显的灾变事件发生.     

东太平洋573孔始新世末渐新世纪地层特征及稀土元素地球化学

根据深海钻探样品分析，对东太平洋地区573孔始新世末渐新世初的地层进行了研究，尤其是研究了其稀土元素地球化学特征。各层球粒陨石标准化值曲线平缓，重稀土相对富集，各层Ce严重亏损（第2层轻度亏损），各层的Eu仅轻度亏损。始新世与渐新世的界线地层含钨粘土层的稀土元素含量明显比其它层含量高得多。此外，该层还富含Fe及指示地外成因的Ni、Co、Ir等元素，且底部富含微玻璃陨石。这些特征说明该含金属粘土层的形成与火山活动有显关系，其底部可能还与陨击作用相联系。从区域地质情况来看，始新世末期有明显的生物灭绝和环境变化，微玻璃陨石广泛发育，说明该时期明显的灾变事件发生。     

湛江湾海域表层沉积物稀土元素特征及其物源指示意义

通过对湛江湾近海海域表层沉积物样品粒度和稀土元素(RE E)测试分析,系统地研究海域沉积物稀土元素地球化学特征并探讨其物质来源.结果表明,研究区沉积物的稀土元素含量变化较大,平均值为163.23μg/g,湾外的REE含量(168.61μg/g)高于湾内的REE含量(142.17μg/g);不同类型沉积物的稀土元素含量存...     

Goat Paddock,Western Australia: an impact crater near the simple – complex transition

Goat Paddock in northern Western Australia is a ～5 km-diameter impact crater of Eocene age excavated in gently dipping Proterozoic sandstones. Roughly radial gorges formed by post-impact erosion provide cross-sectional views of the wall and rim zone. The predominant structural theme is one of synclinal rim folding with broad zones in which bedrock strata were deformed by impact to steep, vertical and overturned attitudes. Impact breccia is found craterward of deformed bedrock, on top of it, and downdropped into fault troughs roughly concentric to the crater. The bedrock?–?breccia contact is sharp in some places and gradational in others. In at least one section, the entire mass of upturned bedrock and breccia was displaced radially over essentially undisturbed bedrock, as indicated by slickensides on the horizontal contact. Talus deposits are similar to breccia, but show rough size sorting and clast orientation that dips steeply craterward, indicating that the talus formed as slides down the oversteepened crater wall immediately after crater formation. Shatter cones in some clasts indicate that allogenic material is incorporated in these deposits. Suevite, characterised by ropy flow textures, and by microclasts of quartz with planar deformation features, planar fractures, and of vesiculated silica glass, was found overlying deformed bedrock at a point where the surface of the bedrock forms a nearly horizontal bench midway up the crater wall. The crater was at least partially filled by later sediments, represented by bedded conglomerate close to the crater wall grading inward to sand, silt and mudstone recovered by drillholes on the crater floor. Some of the talus and conglomerate occupy re-entrants in the crater walls, suggesting an original scalloped outline to the crater. Two drillholes, one central and one halfway to the wall, both reached brecciated sandstone after penetrating 210 m of lake sediments. Goat Paddock has a flat floor with no indication of a central uplift and a depth/diameter ratio of ～0.073. This crater form, coupled with the modification of the crater walls by slumping and the scalloped outline of the crater rim suggests that Goat Paddock bridges the two traditional classes of impact crater: simple and complex.     

塔里木盆地轮南地区奥陶系潜山古岩溶及其所控制的储层非均质性

低孔低渗的碳酸盐岩通过长期的地表风化淋滤、溶蚀之后可能会成为较好的油气储集岩体。本文通过钻井、测井及岩心等资料探讨轮南地区奥陶系灰岩中的古岩溶及其对储集的控制作用。研究表明,区内古岩溶主要形成于早石炭世,岩溶作用所形成的角砾岩相是重要的储集岩类,无论是在横向上或垂向上这种储集岩体均表现出强烈的非均质性。     

安徽巢湖地区早三叠世火山碎屑流的岩石学特征及其形成机理

安徽巢湖早三叠世青龙组南陵湖段中的火山碎屑流沉积物,由火山碎屑岩组成,可分为英安 质角砾岩、英安质晶屑－玻屑凝灰角砾岩、英安质玻屑－晶屑凝灰岩和凝灰质灰岩四种岩石类型。沉积 层序分为两个旋回,包括Ｂｏｕｍａ序列的Ａ—Ｃ、Ａ—Ｅ段。层序分析表明,是介于近源和远源之间的过渡 相,属于斜坡沉积环境,物质来源于巢湖以南的浅海区火山喷发物质。     

江西九瑞矿集区硅质断裂磨砾岩带的厘定及其成岩成矿意义

在九瑞矿集区研究叠合断裂和叠加成矿作用的基础上,我们进一步详细研究了出露在洋鸡山-丁家山-望夫山一线的硅质角砾岩,指出它们不是原先认为的石炭系沉积硅质岩,而应属于一种断裂磨砾岩,并深入探究其形成过程及与成矿之关系.断裂磨砾岩是断裂分带结构成熟的标志之一,多在剪切作用和热液作用下,断裂岩石经硅化-破裂-碎裂-粉碎-研磨,形成具有一定圆度和球度,大小差异较大的磨砾或磨粒,且又会反复的集结-破碎,不断拓宽断裂构造形成磨砾-角砾岩带.本文研究的断裂磨砾岩,呈北东向展布,延长达十几千米.成分上以硅化角砾岩为主,SiO2含量一般大于90％,石英颗粒由隐晶到显晶.一些角砾岩中含Fe2O3较高,有可能是原先的硫化物经氧化形成的褐铁矿.本区洋鸡山-丁家山-望夫山一线产出的断裂磨砾-角砾岩带,很可能是燕山期构造-岩浆-成矿事件的产物.在城门山和武山铜矿,我们之前的工作己发现存在产于泥盆系五通组和石炭系黄龙组层滑构造体系中的黄铁矿角砾岩,则有可能属于海西期同生断裂活动的产物.因此,这些不同的角砾岩具有多阶段活动和叠加成矿的特征.本文还进一步指出,九瑞地区其他层位(如泥盆系与志留系之间、志留系与奥陶系之间)发育的层滑构造体系和断裂角砾岩及热液蚀变岩,也很可能是成矿有利部位,值得今后找矿工作的关注.     

The Sudbury Structure (Ontario,Canada): a tectonically deformed multi-ring impact basin

The occurrence of shock metamorphic features substantiates an impact origin for the 1.85 Ga old Sudbury Structure, but this has not been universally accepted. Recent improvements in knowledge of large-scale impact processes, combined with new petrographic, geochemical, geophysical (LITHOPROBE) and structural data, allow the Sudbury Structure to be interpreted as a multi-ring impact structure. The structure consists of the following lithologies: Sudbury Breccia —dike breccias occurring up to 80 km from the Sudbury Igneous Complex (SIC); Footwall rocks and Footwall Breccia — brecciated, shocked crater floor materials, in part thermally metamorphosed by the overlying SIC; Sublayer and Offset Dikes, Main Mass of the SIC and Basal Member of the Onaping Formation (OF) — geochemically heterogeneous coherent impact melt complex ranging from inclusion-rich basal unit through a dominantly inclusion-free to a capping inclusion-rich impact melt rock; Grey Member of OF — melt-rich impact breccia (suevite); Green Member of OF — thin layer of fall back ejecta; Black Member of OF — reworked and redeposited breccia material; Onwatin and Chelmsford Formations — post-impact sediments. Observational and analytical data support an integrated step-by-step impact model for the genesis of these units. Analysis of the present spatial distribution of various impact-related lithologies and shock metamorphic effects result in an estimated original rim-to-rim diameter of the final crater of 200 or even 280 km for the Sudbury Structure, prior to tectonic thrusting and deformation during the Penokean orogeny.     

安徽宣城茶亭铜金矿床隐爆角砾岩特征及其成矿意义

安徽宣城茶亭铜金矿床是近年来在长江中下游浅覆盖区之南陵—宣城中—新生代火山—沉积盆地中新发现的一个大型矿床。文章以赋矿石英闪长玢岩侵入体内发育的隐爆角砾岩为对象,通过详细的钻孔岩心观察和显微岩相学研究,确定其地质特征并探讨其与成矿的关系。根据钻孔岩心观察确定的岩石构造特征及钻孔剖面圈定的角砾岩空间分布特征,茶亭铜金矿床发育的隐爆角砾岩呈上大下小的不规则筒状体,被隐伏的石英闪长玢岩侵入体包孕。根据角砾特征以及角砾间的裂隙和胶结物特征,可将隐爆角砾岩划分为隐爆浆屑角砾岩、隐爆热液角砾岩和隐爆破裂角砾岩三类,三类隐爆角砾岩空间上有规律地分布,以隐爆浆屑角砾岩为中心向外或向上依次过渡为隐爆热液角砾岩→隐爆破裂角砾岩→石英闪长玢岩。基于隐爆角砾岩与蚀变和矿化的关系推测,岩浆—气液隐蔽爆破作用所产生的大量裂隙为后期含矿岩浆热液和大气降水热液的运移、交代、混合乃至卸载、沉淀成矿提供了有利的构造空间。茶亭铜金矿床的矿体赋存于浅成斑岩侵入体中,其围岩蚀变类型与分带,以及矿化呈细粒浸染状和细脉—网脉状等地质特征显示其与斑岩型矿床极为相似,但矿化富集部位与隐爆角砾岩筒（体） 的一致,且矿床同时发育角砾状、脉状、团块状矿化,矿脉中发育热液硬石膏甚至形成硬石膏岩等地质特征又明显不同于斑岩型矿床。因此,文章将茶亭铜金矿床确定为一个与中酸性浅成斑岩侵入体密切相关的隐爆角砾岩型矿床。     

The chemical composition of metallic spheroids and metallic particles within impactite from Barringer Meteorite Crater,Arizona

Atomic absorption analyses of 25 metallic spheroids from Barringer Meteorite Crater have been carried out for Fe, Ni, Co and Cu. In addition, electron microprobe analyses of 58 impactite metallic particles have been carried out for Fe, Ni and Co from four different impactite samples. The normalized Ni, Co and Cu contents of the spheroids were from 13–22 per cent, 0.8–1.3 per cent and 260–430 μg/g, respectively. These figures represent enrichment factors of 2–3 in the spheroids compared to analyses of the bulk meteorite. The Co/Ni and Cu/Ni ratios in the spheroids are close to the respective ratios in the bulk meteorite. This suggests that the spheroids were formed by preferential removal of iron by oxidation from a chemically homogeneous liquid.The impactite metallic particles had Ni contents from 10 to 95 per cent and Co contents from 0·3 to 4 per cent. The Co contents of these particles showed a positive correlation with Ni up to 60 per cent Ni and a negative correlation beyond 60 per cent Ni. Reaction of the impactite metallic particles with SiO₂ of the target can explain these variations. Our findings show that extensive chemical reaction between projectile and target occurs at impact.     

Distribution of chemical elements in calc-alkaline igneous rocks,soils, sediments and tailings deposits in northern central Chile

This study follows the paths of 32 chemical elements in the arid to semi-arid realm of the western Andes, between 27° and 33° S, a region hosting important ore deposits and mining operations. The study encompasses igneous rocks, soils, river and stream sediments, and tailings deposits. The chemical elements have been grouped according to the Goldschmidt classification, and their concentrations in each compartment are confronted with their expected contents for different rock types based on geochemical affinities and the geologic and metallogenic setting. Also, the element behavior during rock weathering and fluvial transport is here interpreted in terms of the ionic potentials and solubility products. The results highlight the similarity between the chemical composition of the andesites and that of the average Continental Crust, except for the higher V and Mn contents of the former, and their depletion in Mg, Ni, and Cr. The geochemical behavior of the elements in the different compartments (rocks, soils, sediments and tailings) is highly consistent with the mobility expected from their ionic potentials, their sulfates and carbonates solubility products, and their affinities for Fe and Mn hydroxides. From an environmental perspective, the low solubility of Cu, Zn, and Pb due to climatic, chemical, and mineralogical factors reduces the pollution risks related to their high to extremely high contents in source materials (e.g., rocks, altered zones, tailings). Besides, the complex oxyanions of arsenic get bound by colloidal particles of Fe-hydroxides and oxyhydroxides (e.g., goethite), thus becoming incorporated to the fine sediment fraction in the stream sediments.     

Formation of mud clast breccias and the process of sedimentary autobrecciation in the hominin-bearing (Homo naledi) Rising Star Cave system,South Africa

Unconsolidated mud clast breccia facies in the hominin-bearing (Homo naledi) Rising Star Cave, Cradle of Humankind, South Africa, are interpreted to have formed through a process termed sedimentary autobrecciation in this study. This process, by which most of the angular mud clast breccia deposits are thought to have formed autochthonously to para-autochthonously via a combination of erosion, desiccation, diagenesis and microbial alteration of laminated mud deposits, is thought to have taken place under relatively dry (i.e. non-flooded) conditions inside the cave. Subsequently, gravitational slumping and collapse was the dominant mechanism that produced the mud clast breccia deposits, which commonly accumulate into debris aprons. The mud clast breccia is typically associated with (micro) mammal fossils and is a common facies throughout the cave system, occurring in lithified and unlithified form. This facies has not been described from other cave localities in the Cradle of Humankind. Additionally, sedimentary autobrecciation took place during the deposition of some of the fossils within the Rising Star Cave, including the abundant Homo naledi skeletal remains found in the Dinaledi Subsystem. Reworking of the mud clast breccia deposits occurs in some chambers as they slump towards floor drains, resulting in the repositioning of fossils embedded in the breccias as evidenced by cross-cutting manganese staining lines on some Homo naledi fossil remains. The formation of the unlithified mud clast breccia deposits is a slow process, with first order formation rates estimated to be ca 8 × 10⁻⁴ mm year⁻¹. The slow formation of the unlithified mud clast breccia facies sediments and lack of laminated mud facies within these deposits, indicates that conditions in the Dinaledi Chamber were probably stable and dry for at least the last ca 300 ka, meaning that this study excludes Homo naledi being actively transported by fluvial mechanisms during the time their remains entered the cave.