Sea level change: a philosophical approach

The present Cenozoic era is an icehouse episode characterized by a low sea level. Since the beginning of the industrial revolution, the human race has been emitting greenhouse gases, increasing the global atmospheric temperature, and causing a rise in sea level. If emissions continue to increase at the present rate, average global temperatures may rise by 1.5°C by the year 2050, accompanied by a rise of about 30 cm in sea level. However, the prediction of future climatic conditions and sea level is hampered by the difficulty in modelling the interactions between the lithosphere, kryosphere, biosphere and atmosphere; in addition, the buffering capacity of our planet is still poorly understood. As scientists cannot offer unambiguous answers to simple questions, sorcerer's apprentices fill in the gaps, presenting plans to save planet without inconveniencing us.The geological record can help us to learn about the regulation mechanisms of our planet, many of which are connected with or expressed as sea level changes. Global changes in sea level are either tectono-eustatic or glacioeustatic. Plate tectonic processes strongly control sea levels and climate in the long term. There is a strong feed-back mechanism between sea level and climate; both can influence and determine each other. Although high sea levels are a powerful climatic buffer, falling sea levels accelerate climatic accentuation, the growth of the polar ice caps and will hence amplify the drop in sea level. Important sources of fossil greenhouse gases are botanic CO₂ production, CO₂ released by volcanic activity, and water vapour. The latter is particularly important when the surface area of the sea increases during a rise in sea level (maritime greenhouse effect). A volcanogenic greenhouse effect (release of volcanogenic CO₂) is possibly not equally important, as intense volcanic activity may take place both during icehouse episodes as well as during greenhouse episodes. The hydrosphere, land vegetation and carbonate platforms are major CO₂ buffers which may both take up and release CO₂. CO₂ can be released from the ocean due to changes in the pCO₂ caused by growth of coral reefs and by uptake of CO₂-rich freshwater from karst provinces. Efficient sinks of CO₂ are the weathering products of silicate rocks; long-term sinks are organic deposits caused by regional anoxic events which preferrably develop during sea level rises and highstands; and coal-bearing strata. Deposition of limestone also removes CO₂ from the atmospheric-hydrospheric cycle at a long term. Biotic crises are often related to either sea-level lows or sea-level highs. Long-term sea-level lows, characteristic of glacial periods, indicate cooling as major cause of extinction. During verly long-lasting greenhouse episodes the sea level is very high, climate and circulation systems are stable and biotic crises often develop as a consequence of oxygen depletion. On land, niche-splitting, complex food web structures and general overspecialization of biota will occur. Whether the crisis is caused by a single anoxic event (e.g. in the Late Devonian) or a disturbance by an asteroid impact (e.g. the Cretaceous/Tertiary boundary), it will only trigger total collapse of an ecosystem if a large part of it was already in decline. The regulatory mechanisms and buffers are thermodynamically extremely efficient if they are given sufficient time in which to deploy their power. However, after major catastrophes the re-establishment of successful ecosystems will take millions of years. The present rate of sea level and associated temperature rise is much too fast to be compensated and buffered by the network of natural controls. It is likely that the transitional time towards a new steady state will be an extremely variable and chaotic episode of unpredictable duration. Correspondence to: H. Seyfried     

三江中段铜多金属矿床流体成矿作用:微量元素地球化学证据

研究区属"三江成矿带"中段,包含三个不同的地质构造单元,由西向东依次为金沙江混杂岩带、中咱地块、义敦岛弧带。本文通过对这三个构造单元中代表性铜多金属矿床中热液石英脉进行系统的采样和微量稀土元素分析,讨论了各构造单元中石英脉的微量及稀土元素地球化学特征及分布模式,在此基础上结合研究区的地质背景及演化,进一步讨论石英脉中微量元素的指示意义。结果表明:1)研究区石英脉中Cu、Zn等成矿元素与亲岩浆元素呈较好正相关,指示成矿与岩浆活动的联系,微量元素地球化学特征指示中咱地块成矿流体与岩浆活动的联系较为密切;2)中咱地块石英脉稀土元素地球化学特征与义敦岛弧带和金沙江混杂岩带成矿流体差异较大,中咱地块流体稀土元素接近于地幔的稀土组成特征,稀土元素配分曲线为近于水平的平缓曲线,稀土元素特征参数表明形成于相对还原的环境,反映出深部来源很可能是中咱地块成矿流体的主要物质来源;3)石英微量元素地球化学特征的研究为本区区域构造演化提供了佐证,金沙江混杂岩带和义敦岛弧带的成矿流体特征较为相似,而在中咱地块与扬子陆块夹持间形成的义敦岛弧带成矿流体与中咱地块存在较大的元素地球化学差异。本文通过对石英的微量元素、稀土元素地球化学特征的研究为该区的区域成矿特征、热液流体成因和构造演化提供了证据,并对西南三江地区的找矿理论提出了建议。     

吉林省区域成矿系列的讨论

本文根据吉林省内各个地史时期地质构造环境、演化规律及成矿特点,划分了10个区域性成矿系列,21个亚系列。同时,分析了各亚系列主要的成矿物质来源、生成顺序、不同成因类型的金属成矿系列的伴生规律,以及隶属这一构造环境控制的成因上有联系的非金属成矿系列。为在省内某一特定成矿地质背景条件下寻找系列矿产提供了依据。     

焦家深部金矿床成矿流体来源:来自黄铁矿微量元素及S-He-Ar同位素的约束

焦家金矿是胶东蚀变岩型金矿的典型代表，金储量超过200t。矿体受焦家主干断裂控制，呈脉状产出，发育钾化、绢英岩化、硅化和碳酸盐化等蚀变，矿石中主要载金矿物为黄铁矿。热液成矿期主要可分为四个阶段：黄铁矿-石英阶段（i）、金-石英-黄铁矿阶段（ii）、金-石英-多金属硫化物阶段（iii）和石英-碳酸盐阶段（iv）。本文选取焦家金矿床深部I号主矿体为研究对象，采集了不同标高（-600~-1100m）的钻孔岩心样品，分析了黄铁矿的微量元素和S-He-Ar同位素组成，以此讨论成矿流体的组成、性质及来源。研究发现：焦家深部I号矿体黄铁矿呈浅黄色，强金属光泽，自形-半自形粒状结构，粒度50~1000μm，呈浸染状-细脉状分布于黄铁绢英岩化碎裂岩中，为第ii成矿阶段的产物。黄铁矿的稀土元素含量较低，ΣREE为3.27×10^-6~38.5×10^-6，富集轻稀土元素，δCe值为0.81~1.05，δEu值为0.67~1.43，Th/La、Nb/La比值均小于1，指示成矿流体为富Cl的还原性流体。Co/Ni比值介于0.54~1.57之间，平均值为0.99，与变质流体相近；Y/Ho比值在21.9~35.5之间，与地幔值（25~30）和中国东部大陆地壳值（20~35）接近，指示成矿流体与壳-幔相互作用有关。Y/Ho值、Zr/Hf值和Nb/Ta值变化范围较大，表明成矿热液体系发生了交代作用或有外来热液加入。与大陆地壳相比，黄铁矿富集Cu、Pb、Zn、Cd、Co、Ni等亲硫、铁族元素，亏损高场强元素。焦家深部金矿床黄铁矿的δ³⁴S值介于7.5‰~9.8‰之间，平均值为8.7‰，低于浅部矿床δ³⁴S值，呈现出由浅到深δ³⁴S值逐渐降低的特点。胶东金矿硫同位素组成整体一致，绝大多数矿床δ³⁴S值均为正值，变化范围主要集中在6‰~12‰，其来源与古老的变质基底岩系、中生代花岗岩以及幔源流体具有继承演化关系。δ³⁴S值整体呈现出：石英脉型 < 硫化物石英脉型 < 蚀变岩型的变化规律，说明矿化类型的差异是造成硫同位素组成差别的最主要因素。黄铁矿的³He/⁴He值为1.6±0.1Ra~1.8±0.1Ra，⁴⁰Ar/³⁶Ar值为750~3106，均显示混合来源特征。幔源He所占比例为20%~22%，表明幔源流体可能参与了成矿过程。焦家金矿成矿与燕山晚期中国东部强烈的壳幔相互作用密切相关。     

湘东北正冲金矿床成矿物质来源的S-Pb同位素示踪

长沙-平江(长-平)成矿带位于江南造山带中段,金资源储量达250余吨。该区金矿床是典型的沉积变质岩容矿的热液脉状金矿床,构造控矿特征清晰,然而巨量金来源与矿床成因尚不明确。正冲金矿床主体赋存于新元古代变质沉积岩中,矿区内同时发育少量花岗岩体,是识别不同地质体对成矿贡献的理想选择。因此,本文选取正冲金矿床,在野外宏观地质工作基础上,系统开展了成矿阶段划分与载金硫化物同位素地球化学测试等工作。正冲金矿床严格受控于NNE-NE向的长-平断裂及其次级断裂系统,矿体呈脉状,走向NW或NNE,蚀变分带不明显。正冲金矿床矿物组合简单:早阶段发育有乳白色贫矿石英与白云母;成矿主阶段为石英细脉与自然金黄铁矿毒砂-多金属硫化物-少量绿泥石;成矿晚阶段发育有石英-方解石脉。其中,黄铁矿与毒砂是矿床内自然金与不可见金重要的载体。为弱化毒砂和黄铁矿裂隙中细粒多金属硫化物对同位素地球化学结果的干扰,本次研究挑选自形、未变形的毒砂、黄铁矿颗粒测试研究。实验结果表明载金毒砂铅同位素组成~(208)Pb/~(204)Pb、~(207)Pb/~(204)Pb与~(206)Pb/~(204)Pb分别为37.867～38.285、15.555～15.663与17.743-18.073,略高于黄铁矿铅同位素组成37.774～38.268、15.547～15.660与17.670～18.021;毒砂δ~(34)S变化幅度较小(-4.7‰～-0.9‰,均值为-3.0%),略高于黄铁矿δ~(34)S值(-9.1‰～-1.1‰,均值为-4.4‰),成矿流体氧逸度约为10~(-30.7)。正冲金矿床硫、铅同位素组成与赋矿围岩、区域内岩体和斑岩型矿床同位素特征具有较大差异,说明区内岩体与赋矿地层并不是正冲金矿床成矿物质的主要来源。金矿床成矿物质具有深源特征,可能来源于比冷家溪群地层变质程度更高、沉积位置更深的变质沉积岩。结合区域地质背景、金矿床地质-地球化学特征与成矿年代学资料,推断正冲金矿床为造山型金矿床。     

江西414矿床矿物包裹体研究

重点研究了４１４矿床石英流体包裹体特征及成矿物理化学条件，其成矿温度４９０～５３０℃；成矿压力为１０８０×１０￣５Ｐａ；成矿溶液的ｐＨ值为４．８２～４．８３；Ｅｈ值为－０．４２５～－０．４３６伏特，ｆｏ＿２：为１０￣（－３０．４４）～１Ｏ￣（－３０．０９）。     

粤西-桂东四套成矿系统地质特征、成因类型及构造启示

粤西-桂东地区是我国重要的矿产资源基地,是研究区域成矿作用和大地构造演化耦合关系的理想地区。本文基于粤西-桂东地区四套主要成矿系统的地质特征的研究,结合区域内矿床精确定年和构造演化的研究成果,探讨四套主要成矿系统的成因类型、成矿构造背景及其对钦杭结合带构造演化的启示。其中,广东云浮硫铁矿产于震旦系大绀山组,块状和条带状矿石呈层状产于火山沉积岩系中,是一套与海底热液活动密切相关的VMS成矿系统,形成于新元古代俯冲相关的弧后(间)拉张盆地;盘龙铅锌矿产于泥盆系上伦组,角砾状和胶状矿石产于浅海相白云质碎屑岩中,是一套加里东期被动大陆边缘的SEDEX型铅锌成矿系统;河台金矿田赋存于震旦系乐昌组,脉状矿体严格受断裂和蚀变带控制,是一套变质热液主导的造山型金矿成矿系统,形成于印支-燕山期陆内走滑或陆陆碰撞背景;圆珠顶铜钼矿床形成与燕山期(155Ma)二长花岗斑岩密切相关,细脉浸染状矿石赋存于岩体的内外接触带,是一套陆内伸展背景的斑岩铜钼成矿系统。总体而言,粤西-桂东地区经历了新元古代俯冲、加里东期被动大陆边缘、印支期陆内走滑(或陆陆碰撞)和燕山期陆内伸展四个重要的构造事件,这与钦杭结合带总体构造演化过程一致。     

Pre-eruptive physical conditions of El Reventador volcano (Ecuador) inferred from the petrology of the 2002 and 2004–05 eruptions

A petrological study of the eruptive products of El Reventador allowed us to infer the magmatic processes related to the 2002 and 2004–05 eruptions of this andesitic stratovolcano. On November 3, 2002, El Reventador experienced a highly explosive event, which was followed by emplacement of two lava flows in November–December 2002. Silica contents range from 62 to 58 wt.% SiO₂ for the November 3 pyroclastic deposits to 58–56 and 54–53 wt.% SiO₂ for the successive lava flows. In November 2004 eruptive activity resumed supplying four new lava flows (56–54 wt.% SiO₂) between November 2004 and August 2005.     

西藏班公湖-怒江成矿带西段拿厅斑岩Cu(Au)矿床的火成岩岩石成因与成矿物质来源

位于西藏班公湖-怒江成矿带西段多龙矿集区内的拿厅斑岩Cu(Au)矿床是近年来开展勘查取得重大找矿突破的矿床之一,控制Cu资源量已达到大型规模。但目前对该矿床的地质特征、成矿岩石成因及成矿物质来源还缺乏深入的了解和研究。本文基于系统的野外地质观察、岩相学研究,结合精细的锆石SIMS U-Pb定年、锆石Hf-O同位素、岩石地球化学和蚀变-矿石矿物的H-O-S同位素分析,认为该矿床是形成于121～118Ma的斑岩型Cu(Au)矿床,与多龙Cu(Au)矿集区内多不杂、波龙、拿顿、色那、拿若和铁格隆南(荣那)矿床为同一期岩浆-热液成矿事件,其成岩-成矿峰期为120～118Ma。拿厅斑岩铜(金)矿床成矿岩体显示轻稀土富集的分配型式和缺少Eu异常,且富集大离子亲石元素(如Rb、Ba等),而亏损高场强元素(如Nb、Ta等),显示弧岩浆的特征,形成于班公湖-怒江洋向北俯冲的大陆边缘弧背景。锆石Hf-O同位素模拟结果显示,矿区早期的安山-英安质次火山岩(ε_(Hf)(t)=-2. 0～10. 3;δ~(18)O=5. 07‰～6. 77‰)具有早期幔源岩浆和经历MASH过程混入壳源的岩浆(10%～20%壳源物质)的特征;而二长花岗斑岩和成矿花岗闪长斑岩(ε_(Hf)(t)=1. 7～3. 3;δ~(18)O=6. 40‰～6. 95‰)则是MASH过程逐渐演化(壳源-幔源混合,约20%～40%壳源物质)的产物。在形成拿厅斑岩铜金矿成矿岩浆的过程中,没有发生陆壳加厚的过程;岩浆演化过程中有较少斜长石分离结晶,主要为角闪石和钛铁氧化物结晶分异。另外,热液蚀变(石英、磁铁矿)和硫酸盐-硫化物(硬石膏、黄铜矿、黄铁矿)的H-O-S同位素结果显示,拿厅成矿流体和成矿物质主要来源于岩浆,与岩浆流体出溶过程密切有关。     

新疆和田团结峰铅锌矿床勘查模型初论

新疆和田县团结峰铅锌矿床是西昆仑地区新发现的一处重要MVT型铅锌矿床,铅锌规模达中型,伴生银。在勘查工作实践及综合研究矿床模型基础上,总结了矿床的成矿地质条件、地球物理勘查模型、地球化学勘查模型和地质找矿标志。研究表明:赋矿地层为中侏罗统龙山组二段灰岩,次级NW向断裂控制了铅锌矿体的分布,硅钙面之上的层间构造是矿体的赋存部位。1∶50万水系沉积物测量勘查模型显示:矿区及周边主要异常元素有Au,Ag,Pb,Zn,Mn,Hg,Sb,Cu,Co等,矿区为Ag-Zn-Cu-Pb-Au-As-Sn-Cr-Fe-F异常范围内,元素异常套合较好。1∶5万水系物测量勘查模型显示:成矿元素Ag,Zn,Cu,As,Sn,Sb,Pb浓度分带明显,异常套合好,有明显的浓集区;1∶1万瞬变电磁测量勘查模型显示:矿区内主要岩层的电阻率差异很大,含铅锌矿化地层电阻率为4 660～6 030Ω·m,可形成中高阻异常;遥感蚀变信息勘查模型显示:矿区遥感异常以羟基为主,铁染零星,异常与构造套合较好。除了物化遥异常标志外,铁帽、次级NW向断裂、围岩蚀变也是重要的找矿标志。