蒙阴盆地早白垩世火山岩地球化学特征及其岩石成因

蒙阴盆地早白垩世火山岩主要出露于青山群八亩地组和方戈庄组中。火山岩SiO₂含量为53.71%~69.08%,主要为安山质岩石和流纹岩,以钙碱性系列为主(σ平均3.42);富集Rb、Ba等大离子亲石元素和轻稀土元素,相对亏损Nb、Ta、P、Ti等高场强元素和重稀土元素;具有富集的Sr-Nd-Pb同位素组成(⁸⁷Sr/⁸⁶Sr(t)=0.7051~0.7110,ε_Nd(t)=-5.16~-16.4)。根据MgO含量和Mg^﹟值,可将安山质火山岩划分为高镁(Mg^﹟>60)和低镁(Mg^﹟<60)两个系列。高镁安山质岩石的MgO、Cr、Ni及不相容元素的含量明显高于低镁安山质岩石,且具有相对高的⁸⁷Sr/⁸⁶Sr(t)和较低的ε_Nd(t)值,Sr-Nd同位素组成趋向于EMⅡ型富集地幔端元。低镁安山质岩石地球化学特征类似于埃达克岩,其同位素组成介于EMⅠ型富集地幔端元与华北麻粒岩相下地壳之间。流纹岩具有较低的MgO、Cr、Ni含量和明显的负Eu、Sr异常,同位素组成类似于扬子中、上地壳。研究表明,蒙阴盆地高镁安山质岩石由曾遭受俯冲扬子陆壳熔体改造的华北岩石圈地幔部分熔融形成,且岩浆在上升 过程中经历了华北下地壳物质一定程度的混染或混合作用;低镁安山质岩石主要由华北下地壳部分熔融形成;流纹岩为岩石圈伸展减薄背景下仰冲至华北克拉通之上的扬子中、上地壳部分熔融的产物。地质现象显示,郯庐断裂带的伸展活动控制着蒙阴断陷盆地的发育,与蒙阴盆地早白垩世火山岩的成因有着密切的联系,在华北克拉通破坏中可能起到了重要的作用。     

沂沭断裂带北段早白垩世高钾钙碱性火山岩地球化学特征与岩石成因

沂沭断裂带内发育了大量的中生代火山岩,其成因研究对剖析断裂带活动规律具有重要意义。本文对断裂带北段潍坊、安丘、鄌郚地区中生代火山岩进行了详细的岩石学、锆石U-Pb年代学和主量元素、微量元素、Sr-Nd-Pb同位素分析。探讨了沂沭断裂带中生代火山岩成因及其形成的地球动力学过程。断裂带北段火山岩年龄集中在131~124Ma之间,喷发于早白垩世。岩石为一套高钾钙碱性火山岩,包括玄武安山岩、粗安岩、粗面岩、英安岩。火山岩富集Rb、Ba等大离子亲石元素,相对亏损Nb、Ta、Ti等高场强元素。稀土元素含量高（∑REE=140.5×10^-6~433.1×10^-6）,富集轻稀土、亏损重稀土（∑LREE/∑HREE=9.8~31.0）,无明显的Eu负异常。火山岩具有富集且变化范围较大的Sr-Nd-Pb同位素组成,（⁸⁷Sr/⁸⁶Sr）_i=0.708054~0.711692,ε_Nd（t）值为-15.3~-7.4,（²⁰⁶Pb/²⁰⁴Pb）_i=17.213~17.962,（²⁰⁷Pb/²⁰⁴Pb）_i=15.425~15.590,（²⁰⁸Pb/²⁰⁴Pb）_i=37.597~38.365。研究表明,高钾钙碱性火山岩的源区与区域基性岩源区一致,均为富集岩石圈地幔。玄武安山岩、粗安岩、粗面岩经基性岩浆分离结晶作用形成,英安岩则遭受了华北下地壳强烈混染。三叠纪末期,由于扬子板块向华北克拉通俯冲,扬子地壳析出的流体/熔体交代了华北古老岩石圈地幔,形成富集岩石圈地幔。早白垩世,受古太平洋板块俯冲和后撤作用,富集岩石圈地幔部分熔融形成基性岩浆,岩浆在上升过程中发生分离结晶作用,受沂沭断裂深切作用影响,部分地区遭受华北下地壳混染,最终形成区内各类高钾钙碱性火山岩。     

海拉尔盆地基底晚古生代adakite的发现及其地质意义

海拉尔盆地的前中生代基底隶属中亚造山带东段的兴蒙造山带。 在盆地基底地层中发现了具有adakite成分特征的粗面安山岩、英安岩和闪长玢岩。 这些火成岩与晚古生代沉积地层交互或伴生, 共同构成晚中生代裂陷盆地的基底。 地球化学研究表明, 这些火成岩基本上属于高钾钙碱性和准铝质岩石系列, 具有高SiO₂和Al₂O₃含量, 高Sr、Sr/Y和La/Yb值, 富集轻稀土(LREE), 亏损重稀土(HREE)、Y和高场强元素(HFSE),Eu表现弱的负异常或轻微的正异常, 相容元素Mg、Cr和Ni含量低, 这些特征与增厚下地壳部分熔融成因的adakite非常相似, 而明显不同于典型的由俯冲洋壳熔融形成的adakite。 样品的(⁸⁷Sr/⁸⁶Sr)_i值基本一致,为0.7041, (¹⁴³Nd/¹⁴⁴Nd)_i值为0.51243~0.51247, ε_Nd (t)为正值(+3.7~+4.5), 显示其岩浆源区可能源于弱亏损地幔, 或亏损地幔受到地壳物质混染。 本文认为海拉尔地区晚古生代adakite型岩浆很可能是由当时新底侵的玄武质下地壳在角闪岩相向榴辉岩相过度或榴辉岩相条件下部分熔融形成。 这些adakite岩石的出现反映了兴蒙造山带晚古生代受到了古亚洲洋的俯冲消减引起的强烈的地幔玄武质岩浆底侵作用, 并由此导致地壳垂向上显著的增生加厚过程。     

松辽盆地徐家围子营城组流纹岩地球化学特征及构造指示意义

松辽盆地徐家围子营城组发育一套以流纹岩为主的中酸性火山岩。岩石薄片观察和主量、微量元素研究发现,后期热液蚀变、区域埋深及低温水合作用对流纹岩的Si、K、Rb等元素含量产生一定影响; 流纹岩明显富集Rb、Th、U、Pb等强不相容元素,Ba、Sr、Ti、Eu、P 负异常,暗示其经历了斜长石、磷灰石和钛铁矿分离结晶作用。流纹岩的(⁸⁷Sr/⁸⁶Sr)_i(0.705265 ~ 0.711895)值变化范围较大,大多数ε_Nd(t)为正值(1.83 ~ 3.38),Pb同位素比值相对集中,(²⁰⁶Pb/²⁰⁴Pb)_i=18.09～18.32,(²⁰⁷Pb/²⁰⁴Pb)_i=15.50 ~ 15.54,(²⁰⁸Pb/²⁰⁴Pb)_i=37.80 ~ 38.10。研究表明,岩石的源区为大比例年轻成分与少量古老地壳的混合部分熔融,其演化过程中经历了不同程度的地壳混染。松辽盆地早白垩世火山岩为板内伸展环境喷发的产物,可能与太平洋板块俯冲导致的中国东部岩石圈减薄、软流圈上涌密切相关。     

新疆三塘湖盆地后碰撞火山岩的锆石SHRIMP U-Pb定年及其地质意义

新疆三塘湖盆地广泛出露哈尔加乌组地层,主要为陆相中性喷发岩夹火山碎屑岩。火山岩锆石SHRIMP U-Pb年龄为319.6±9.8Ma（MSWD=4.8）。地球化学分析表明,哈尔加乌组火山岩高钾富碱,属于高钾钙碱性系列;LREE强烈富集、大离子亲石元素（LILE）强烈富集、大多数高场强元素（HFSE）明显高于MORB,没有Ti的负异常和P的正异常,Nb、Ta负异常明显,基本没有Eu、Ce的异常,Ti/Y（467~494）、Nb/Y（0.41~0.43）值高。判别图解投入板内火山岩和岛弧火山岩区域,整体显示板内火山岩的特征又携带岛弧火山岩的地球化学痕迹。ε_Nd (t)值（+5.90~+6.31）为正值、Mg^#较高（0.54~0.57）,显示与亏损地幔相关的源区特点,(⁸⁷Sr/⁸⁶Sr) _i值（0.70397~0.70464）相对于亏损地幔高、La/Nb（3.12~3.39）、Nb/U（5.86~9.80）比值显示源区有陆壳组分的参与。综合区域地质特征和前人研究资料表明,三塘湖盆地哈尔加乌组火山岩是碰撞造山中增厚的岩石圈根部拆沉作用致使软流圈地幔上涌底侵,致使早期的陆壳组分和弧组分部分熔融而形成的火山喷发,形成于后碰撞伸展转换背景。     

非洲乍得盆地火山岩地球化学特征及成因

钻井揭示了乍得盆地中新生代有大量玄武岩喷发,主要为橄榄拉斑玄武岩,少数为石英拉斑玄武岩和碱性橄榄玄武岩。主量、微量元素及Sr-Nd-Pb同位素地球化学研究表明,乍得盆地玄武岩岩浆在上升过程中经历了橄榄石、单斜辉石的分离结晶作用,且未受到陆壳物质的混染;岩石明显富集轻稀土元素、大离子亲石元素和高场强元素,Nb、Ta、Zr、Hf具正异常。晚白垩世玄武岩(⁸⁷Sr/⁸⁶Sr) _i比值（0.704167~0.706564）高于古近纪玄武岩（0.703545~0.705380）,(¹⁴³Nd/¹⁴⁴Nd)_i比值（0.512451~0.512703）低于古近纪玄武岩（0.512690~0.512847）;晚白垩世玄武岩ε_Nd(t)u值变化范围较大（-1.4~3.5）,且明显低于古近纪玄武岩（2.6~5.6）。两者具有相似的Pb同位素比值,²⁰⁶Pb/²⁰⁴Pb=18.14~18.96,²⁰⁷Pb/²⁰⁴Pb=15.56~15.62,²⁰⁸Pb/²⁰⁴Pb=38.33~38.88。乍得盆地玄武岩主要来自于亏损地幔DM和富集地幔EMⅡ两种端元组分混合产生的,石榴石橄榄岩的母熔体可能是本区玄武岩产生的源区,是地幔高度部分熔融的结果（15%左右）。乍得盆地玄武岩的地幔组份随时间的演化可能与中生代以来中、西非地区软流圈上涌、岩石圈减薄作用密切相关。     

二连盆地北缘晚中生代火山岩Ar-Ar年代、地球化学及构造背景

中国东北二连盆地周缘分布有三组时代不同的晚中生代火山岩,其中早、中期为两套地球化学性质不同的流纹岩,晚期为玄武质火山岩。本文通过测定火山岩基质Ar-Ar同位素年龄,表明早期查干诺尔组流纹岩形成于142Ma,晚期不拉根哈达组基性火山岩形成于129Ma,可见二连盆地北缘晚中生代火山岩时代均为早白垩世。通过对主、微量元素地球化学特征和Sr-Nd-Pb同位素组成研究,以及与邻区同期满克头鄂博组英安岩和流纹岩、玛尼吐组英安岩、霍林河地区查干诺尔组英安岩、流纹岩对比,认为早期查干诺尔组流纹岩来源于新成下地壳,岩浆演化过程经历了强烈分异作用;中期流纹岩源区为中上地壳或下地壳岩浆经历了上地壳强烈同化混染作用;晚期不拉根哈达组基性火山岩则源于受俯冲洋壳流体交代的富集岩石圈地幔。结合早白垩世区域岩石圈减薄背景,本文认为研究区早白垩世火山岩形成于陆内伸展构造环境。     

浙西新路盆地晚白垩世钾玄岩的厘定及其地质意义

对浙西新路火山盆地发育的辉绿岩进行了激光显微探针⁴⁰Ar-³⁹Ar定年和系统的岩石地球化学特征研究。研究表明, 新路盆地辉绿岩成岩时代为(93±3) Ma, 属晚白垩世产物; 岩石中辉石有单斜辉石和斜方辉石两个种属, 斜长石为拉长石; SiO₂含量介于44.00%~50.09%之间, 具有富碱(平均为5.15%)、高钾(K₂O/Na₂O平均为1.08)、低TiO₂含量(平均为1.15%)等特征; 岩石具有原生岩浆特点, 显示典型的钾玄岩特征。钾玄岩富集LREE、大离子亲石元素和强不相容元素, 无Eu亏损; 锶初始值(Isr)介于0.70707~0.70870之间, (¹⁴³Nd/¹⁴⁴Nd)i介于0.512338~0.512407之间; Δ7/4Pb为6.0~9.2、Δ8/4Pb为48.5~68.0、DSr为70.73~87.04, 均表现出富集地幔特征。认为新路盆地钾玄岩的厘定对该区域岩石圈与构造岩浆演化的深入研究具有重要意义; 钾玄岩形成与造山带后碰撞期的热点活动相关; 钾玄岩侵位年龄基本限定了新路地区岩石圈大规模减薄的时限; 推测热点活动导致岩石圈减薄的动力学演化过程及其壳幔作用源区可能对火山岩型铀成矿起着重要的制约作用。     

西准噶尔巴音达拉地区卡拉岗组火山岩锆石U-Pb年代学、地球化学及其地质意义

西准噶尔巴音达拉地区发育一套酸性火山岩,被称为卡拉岗组,岩石组合以流纹岩、英安岩、流纹质熔结凝灰岩等酸性火山岩为主。本文对卡拉岗组火山岩进行高精度锆石LA-ICP-MS U-Pb测年,获得英安岩和流纹岩的加权平均²⁰⁶Pb/²³⁸U年龄分别为（294.4±1.3）Ma（n=9,MSWD=0.8）和（298.4±2.5）Ma（n=9,MSWD=3.4）,其形成于早二叠世。岩石地球化学特征表明,卡拉岗组火山岩岩具有高硅（66.69%~75.21%）,富碱（Na₂O+K₂O：6.98%~8.35%）,低MgO（0.18%~1.32%）,贫钙（0.24%~2.49%）的特征,均属过铝质（A/CNK：1.14~1.33）及高钾钙碱性系列。微量元素数据显示,稀土总量为∑REE为83.82×10^-6~197.61×10^-6,（La/Yb）_N=3.15~12.50,轻、重稀土元素分馏比较明显,轻稀土元素（LREE）较为富集,重稀土元素分布相对平坦,球粒陨石标准化配分模式为右倾型。微量元素富集大离子亲石元素（LILE）Rb、Th、U、K,并亏损高场强元素（HFSE）_Nb、Ta、P、Ti。综合最新区域资料及本文研究成果,文章认为研究区早二叠世卡拉岗组火山岩岩浆来源于壳源物质不同程度的部分熔融,残留相中有少量斜长石和角闪石,为后碰撞伸展阶段的产物。     

华北克拉通兴城早白垩世玄武玢岩锆石、金红石地球化学特征及其地质意义

华北克拉通在中生代时期发生大规模的岩石圈减薄,伴生的早白垩世火山岩为研究克拉通破坏提供了窗口,但其中镁铁质火山岩成因和岩浆源区性质的争议,制约了对克拉通破坏机制和中生代岩石圈减薄结束时间的认识。本文用激光剥蚀电感耦合等离子质谱（LA-ICP-MS）方法对兴城玄武玢岩中的锆石、金红石进行了系统的微量元素分析,以揭示岩浆源区性质及其演化,并进一步探讨了华北克拉通中生代岩石圈减薄的机制和结束时间。锆石t_Ti温度计计算结果表明,兴城玄武玢岩锆石结晶温度为695~779℃,平均温度为730℃,说明玄武玢岩可能起源于俯冲带地幔楔交代橄榄岩。微量元素分析结果显示,锆石富集HREE,LREE与HREE分异明显,Nb、Ti亏损,Th、U和Hf相对富集,Ce、Eu呈不同程度的正、负异常;金红石Nb、Ti、Hf等高场强元素呈不同程度富集,Sr明显亏损,无明显的Ce、Eu异常。微量元素特征也显示玄武玢岩岩浆起源于岩石圈地幔交代橄榄岩,后期经历了氧化作用和分离结晶作用。结合区域内相关地质资料,认为兴城玄武玢岩岩浆为古老岛弧型岩浆。华北克拉通中生代岩石圈减薄的结束时间可约束到早白垩世晚期（约105 Ma）,高角度俯冲的古太平洋板块回撤为华北克拉通岩石圈减薄的一级动力学机制,热化学侵蚀或拆沉为二级机制。     

摩擦桩基桩土间极限摩阻力取值问题探讨

通过对广珠东线高速公路横沥大桥的试桩及土体的工程地质条件分析,总结出影响摩擦桩基桩土间极限摩阻力取值的一般问题以及解决问题的方法和措施。     

从榴辉岩与围岩的关系论苏鲁榴辉岩的形成与折返

位于华北和扬子两板块碰撞带中的苏鲁榴辉岩形成的温压条件不但是超高压，而且是高温。榴辉岩的PTt轨迹表明其为陆-陆磁撞俯冲带的产物。榴辉岩的区域性围岩花岗质片麻岩为新元古代同碰撞期花岗岩，榴辉岩及其他直接围岩皆呈包体存在于其中，并见新元古代花岗岩呈脉状侵入榴辉岩包体中。区域性围岩新元古代花岗岩的锆石中发现有柯石英、绿辉石等包裹体，表明新元古代花岗岩的组成物质也经受过超高压变质作用，且榴辉岩与围岩新元古代花岗岩的锆石U-Pb体系同位素年龄基本相同。但新元古代花岗岩所记录的变质作用和变形作用期次（或阶段）却少于榴辉岩。椐上述可得如下推断：超高压榴辉岩与新元古代花岗岩岩浆是同时在碰撞带底部（俯冲板块前部）形成的；榴辉岩的第一折返阶段是由新元古代花岗岩岩浆携带上升的，其第二折返阶段是和新元古代花岗岩一起由逆冲及区域性隆起而上升，遭受剥蚀。     

The Importance of the Precipitation and the Susceptibility of the Slopes for the Triggering of Landslides Along the Roads

In order to characterise the influence of the heavyrains on the observed landslides during the 1996–1997hydrological cycle, rainfall records for the last 100years are analysed from 104 stations in easternAndalusia. Regarding the amounts of rain recordedbetween October 1996 and March 1997 in the 104stations studied, 31 presented new all-time records;15 presented values that were 80–100% of thepre-1995 record; 49 stations, 80–50%; and 9stations, < 50%. A map has been devised of thesusceptibility of the materials through which thesouth-eastern Andalusian road network crosses,together with an inventory of the damage caused byinstability phenomena on banks and cuttings of theroad network during the winter of 1996–1997. Therelationships between the rainfall during the studyperiod, the damage caused to the road network and thesusceptibility of the materials affected are analysed.The results indicate that there is a clearcorrespondence between the rainfall recorded and thesusceptibility of the materials with the inventorieddamage. It is concluded that the widespread seriousdamage caused in early 1997 to the roads andsurrounding areas in the Alpujarra region and thecoast of the Province of Granada was mainly caused bythe extraordinarily heavy rains. However, considerablyless damage was observed where the susceptibility ofthe terrain is low, thus highlighting the extremeusefulness of terrain-susceptibility maps for riskprevention and territorial planning.     

某高速公路下伏煤矿采空区稳定性分析

在论述某高速公路下伏砦脖煤矿采空区地质、采矿和工程地质特征的基础上, 进行了稳定性数值模拟分析, 定性与定量地分析与评价了该煤矿采空区的地表变形特征及稳定性。研究结果表明: 该煤矿采空区的变形尚未完成, 对拟建的高速公路将产生很大的危害, 必须采取相应的工程治理措施。      

混凝剂处理钻井废泥浆液的研究

通过烧杯搅拌实验对混凝剂处理钻井废泥浆液进行研究,从混凝剂适应p H值范围、混凝效果、沉降速度三方面研究比较,找出一种较为理想的混凝剂,并分析了影响混凝剂性能的主要因素,确定了混凝剂的最佳投放剂量。      

黄河源区水环境变化及黄河出现冬季断流的原因

自1954年有水文观测资料以来，黄河曾在青海省玛多县黄河沿水文站发生过3次断流。本文在分析黄河源区水环境特征及其影响因素的基础上指出，鄂陵湖、扎陵湖的环湖融区调节能力低，当遇到连续干旱、冬季其调节水量不足以维系黄河径流时便会发生断流，这是断流的主因。湖水位降低、开采沙金、过度放牧等自然和人为因素也会对黄河发生断流产生影响。鄂陵湖口附近黄河上修建的水电站开始蓄水，提高了两湖及环湖融区的调节能力，今后黄河冬季出现断流的可能性将大为降低。     

Unity of the national and the international in the socio-cultural development of the peoples of the USSR

International unity is becoming ever stronger in this country owing to an increasing similarity in the development of the cultural environment. This comprises the provision of all the country's republics with a sufficient number of schools, theatres, and other institutions and cultural information media in accordance with the needs of the population. An important part is played by the rise in ‘the general educational level, as well as the level of professional qualifications and skills. Among all the Soviet nations and nationalities, this rise being more rapid among formerly backward peoples. Prominent among the factors of internationalization is the progressive development of the nationalities’ cultural resources, while professional culture is being increasingly brought within the reach of the masses.The implementation of the nationalities policy promotes the all-round development of all Soviet nations and nationalities, their drawing together, the upsurge of the individual capabilities of every Soviet citizen.     

Artemia in the Salt Lakes of Russia:the Productivity of Populations,the Reserves of the Cysts and the Fisheries

正Artemia cysts are an extremely important component of aquaculture diets.It is well established that the cultivation of fish and shellfish derive substantial health and growth advantages when Artemia are included in the diets of the     

天山南坡科其喀尔冰川表碛区小气候特征研究

利用天山南坡科其喀尔冰川3号观测站2009年全年的气象观测资料,分析研究了科其喀尔冰川表碛区的小气候特征. 结果表明：总辐射和净辐射夏秋季较高、冬春季较低;反射辐射和地表反照率反之. 与其他地区不同,该区主要受积雪物理性质和下垫面状况的影响,冬春季地表反照率日变化表现为由大到小的变化过程,夏秋季表现为倒U型. 温度年变化表现为夏秋季高、冬春季低,最高月均值出现在8月,为9.4℃,最低月均值出现在1月,为-9.6℃. 受山谷风和冰川风的影响,全年的风向以西北风和西北偏西风为主,风向的日变化以11：00为界发生转向. 受降水和冰川消融等的影响,比湿夏秋季月均值较大,冬春季月均值较小.     

Climate: Is the past the key to the future?

 The climate of the Holocene is not well suited to be the baseline for the climate of the planet. It is an interglacial, a state typical of only 10% of the past few million years. It is a time of relative sea-level stability after a rapid 130-m rise from the lowstand during the last glacial maximum. Physical geologic processes are operating at unusual rates and much of the geochemical system is not in a steady state. During most of the Phanerozoic there have been no continental ice sheets on the earth, and the planet’s meridional temperature gradient has been much less than it is presently. Major factors influencing climate are insolation, greenhouse gases, paleogeography, and vegetation; the first two are discussed in this paper. Changes in the earth’s orbital parameters affect the amount of radiation received from the sun at different latitudes over the course of the year. During the last climate cycle, the waxing and waning of the northern hemisphere continental ice sheets closely followed the changes in summer insolation at the latitude of the northern hemisphere polar circle. The overall intensity of insolation in the northern hemisphere is governed by the precession of the earth’s axis of rotation, and the precession and ellipticity of the earth’s orbit. At the polar circle a meridional minimum of summer insolation becomes alternately more and less pronounced as the obliquity of the earth’s axis of rotation changes. Feedback processes amplify the insolation signal. Greenhouse gases (H₂O, CO₂, CH₄, CFCs) modulate the insolation-driven climate. The atmospheric content of CO₂ during the last glacial maximum was approximately 30% less than during the present interglacial. A variety of possible causes for this change have been postulated. The present burning of fossil fuels, deforestation, and cement manufacture since the beginning of the industrial revolution have added CO₂ to the atmosphere when its content due to glacial-interglacial variation was already at a maximum. Anthropogenic activity has increased the CO₂ content of the atmosphere to 130% of its previous Holocene level, probably higher than at any time during the past few million years. During the Late Cretaceous the atmospheric CO₂ content was probably about four times that of the present, the level to which it may rise at the end of the next century. The results of a Campanian (80 Ma) climate simulation suggest that the positive feedback between CO₂ and another important greenhouse gas, H₂O, raised the earth’s temperature to a level where latent heat transport became much more significant than it is presently, and operated efficiently at all latitudes. Atmospheric high- and low-pressure systems were as much the result of variations in the vapor content of the air as of temperature differences. In our present state of knowledge, future climate change is unpredictable because by adding CO₂ to the atmosphere we are forcing the climate toward a “greenhouse” mode when it is accustomed to moving between the glacial–interglacial “icehouse” states that reflect the waxing and waning of ice sheets. At the same time we are replacing freely transpiring C3 plants with water-conserving C4 plants, producing a global vegetation complex that has no past analog. The past climates of the earth cannot be used as a direct guide to what may occur in the future. To understand what may happen in the future we must learn about the first principles of physics and chemistry related to the earth’s system. The fundamental mechanisms of the climate system are best explored in simulations of the earth’s ancient extreme climates. Received: 7 November 1996/Accepted: 23 January 1997