中国东北地区显生宙岩浆作用和洋-陆格局及其与气候演变的关系SCIEI北大核心CSCD

显生宙期间,地球经历了温室-冰室气候的周期性交替变化。在数百万年的时间尺度,这种古气候的转变被认为是碳源和碳汇过程耦合的结果,但一直以来关于两者贡献程度的认识尚不明确。通过全球统计分析,不同学者提出大陆弧火山脱气模型和热带弧-陆碰撞模型用于解释整个显生宙古气候的演变,分别强调了碳源和碳汇的一级控制作用。为了检验上述模型,更好地理解古气候的转变机制和演化细节,本文系统总结了中国东北地区显生宙岩浆作用-矽卡岩型矿床的时空展布和构造背景,以及弧-陆碰撞的时代、规模和古地理位置,通过数据统计和作图对比,发现东北地区岩浆作用-矽卡岩成矿峰期、弧-陆碰撞缝合带的时空迁移与大气圈CO_(2)浓度和大陆冰川沉积有很好的对应关系,暗示东北显生宙构造-岩浆过程和古气候演变的内在联系。综合东北地区及全球的研究进展,本文提出如下倾向性认识:1)洋-陆俯冲过程中火山-变质脱气的强度决定了CO_(2)排放量,而热带区域弧-陆碰撞缝合带的规模决定了全球硅酸盐风化速率和CO_(2)吸收量,在地质演化过程中两者紧密联动,共同控制了显生宙古气候的演变;2)大陆弧岩浆作用的全球爆发不一定能造成温室气候的出现,如果缺乏充分矽卡岩变质脱碳反应,大陆弧CO_(2)排放通量与岛弧、大洋中脊和板内并无显著区别;3)SO_(2)属于短期效应气体,理论和实例研究均暗示爆发式火山作用难以诱发大冰期的形成,火山作用之于长期气候应该仍是促使地球升温而非变冷。     

云南老君山锡多金属成矿区含矿夕卡岩地质特征及原岩恢复

夕卡岩是滇东南老君山成矿区众多锡多金属矿床的主要赋矿围岩。本文在系统分析了夕卡岩的产状特征和矿物组成特征的基础上,采用岩石化学和微观结构、构造相结合的方法,进行了原岩恢复。认为该类夕卡岩的原岩中含有大量中-基性火山岩,其形成过程与海相火山活动有关。滇东南地区寒武纪为大陆边缘拗陷盆地构造环境,含矿夕卡岩微量元素组成特征与火山弧玄武岩类似,推测研究区在早加里东期区域拉张作用背景下,盆地地壳变薄导了混杂作用,最终在拗陷盆地中心形成海相中-基性火山喷发及成矿作用。研究区中、下寒武统均有火山喷流沉积岩分布,反映了该区海相火山活动的多期次性。该套含矿夕卡岩为火山喷流沉积岩与其它正常海相沉积物混杂后,经印支期区域变质作用形成。     

云南光明铁多金属矿与矽卡岩选择性成矿关系

详细论述两种不同类型石榴石矽卡岩和透辉石矽卡岩与铁矿及其共生、伴生矿铜、铅、锌、锡等的富集规律,总结出铁多金属矿与矽卡岩之间的选择性富集关系。     

Occurrence of Contrasting skarn formations in dolomites of the Traversella deposit (Ivrea,Italy)

Metasomatic columns hosted in dolomitic marbles in the thermal aureole of the Traversella monzodiorite (Ivrea, Italy) differ by their mineralogy and/or mineral composition. Three groups have been distinguished. In group A, the first zone always contains forsterite-calcite and the second zone contains clinopyroxene. The last zone is made of wollastonite (A1), andradite-rich garnet (A 2) or grossular-rich garnet (A 3). In group B, tremolite instead of forsterite occurs in the first two zones. In group C columns, there are only two zones and clinohumite or chondrodite characterize the first zone.Field, petrographic and chemical data demonstrate that the occurrence of contrasted mineral zonations in the same protolith has not been induced by local heterogeneities in the dolomitic marbles. The presence of tremolite in group B instead of forsterite is due to the lower temperature prevailing in the external part of the contact aureole. Chemical data as well as - diagrams suggest that the columns in groups A and C were formed through the interaction of the dolomitic marbles with fluids with different _{Fe 2}O₃, _{Al 2 O 3} and _F. A fluid with low _{Al 2 O 3} and _{Fe 2}O₃ is assumed for the metasomatic column with wollastonite (A 1) and different Al₂O₃/Fe₂O₃ values in the fluid are responsible for the formation of columns A 2 and A 3. The stability of clinohumite or chondrodite in group C columns has been induced by a higher _F of the fluid than in the other groups. The presence during the prograde metasomatic stage of distinct fluids differing by their _{Al 2 O 3}/_{Fe 2}O₃ (columns A 2 and A 3) is likely to have been induced by variations in the source composition. Moreover, the low A1 and Fe content in column A 1 could be due to the reaction of the dolomitic marble with a fluid previously depleted in these components during percolation and reaction with the country rocks.As shown by isocon diagrams and Gresens's equation, skarn formation has locally induced both mass and volume change. The volume decreased in the wollastonite zone of A 1 (19%) and in the Fo-Cc zone of A2 (17%). Mass is always increased except in the wollastonite of A 1 where it is decreased. Mass balance of major elements has shown that Ca is likely to be a perfectly inert component and that Si is always strongly increased. Moreover, Fe is increased in A 2 and A 3 whereas Al is only increased in A 3. Mg is leached in the internal part of column Al.Quantification of chemical potential diagrams using different values of _{Al 2 O 3 Fe 2 O 3}, X _F and T suggests that the successive zones observed in all types of columns can be obtained along an increase of _{SiO 2} towards the inner zones. A simultaneous decrease in _MgO is inferred for group A columns.     

江西香炉山钨矿床矽卡岩矿物和成矿花岗岩地球化学特征及其指示意义

江西香炉山大型钨矿床位于长江中下游成矿带南侧新识别的钨矿带西段,为一矽卡岩型白钨矿床.矽卡岩矿体主要产于中寒武统杨柳岗组含炭质灰岩和香炉山花岗岩接触部位.香炉山花岗岩具有细粒至中粗粒结构,主要由石英、钾长石、斜长石和黑云母组成,副矿物以钛铁矿为主.香炉山花岗岩的SiO2含量为66.37％～67.76％,并具有较高的Na...     

江西九瑞坳下地区矽卡岩的矿物化学、氧同位素特征及成矿潜力探讨

江西九瑞矿集区是长江中下游成矿带上重要的铜金资源产地,近年来地勘单位在该区西南部的坳下远景区发现物化探异常,并布置钻探工作,在奥陶系白云岩与隐伏黑云母花岗斑岩侵入体的接触带上,揭露了矽卡岩和矿化。本文以这些矽卡岩为研究对象,运用电子探针及同位素质谱仪测定矿物的化学成分和氧同位素组成,在此基础上探讨了热液的物理化学条件,流体来源及演化过程。结果表明,形成坳下矽卡岩的热液流体,进蚀变阶段温度为516~663℃,平均597℃,氧同位素值(δ~(18)O_(Fluid))为9.3‰,偏还原性;退蚀变阶段温度为263~317℃,平均290℃,氧同位素值(δ~(18)O_(Fluid))为-4.9‰,偏氧化性。与九瑞的武山、东雷湾、邓家山等矽卡岩矿床相比,坳下镁矽卡岩组分更高,发现了以往九瑞地区的矽卡岩矿床中未见的橄榄石、金云母。经综合分析,认为高盐度的、较热的、氧化性弱的岩浆热液,与稀释的、较冷的、氧化性强的大气降水的流体混合过程,是坳下矽卡岩及其矿化的形成机制。这一过程,对形成有价值的矽卡岩型矿床非常有利,在九瑞矿集区后续的勘查工作中,应关注侵入体与奥陶系白云岩接触带形成的镁矽卡岩相关矿床,以及志留系和奥陶系地层硅钙界面处受到岩浆热液叠加形成的层状矿体。