伊春东风经营所新元古代花岗质片麻岩U-Pb年代学和地球化学特征

张广才岭中段东风经营所一带发现新元古代花岗质片麻岩,岩石具有高硅、富碱和低钙、镁及偏铝质-过铝质特点,稀土元素配分模式中轻稀土元素富集且缓向右倾斜,重稀土元素曲线较为平坦,为具有铕亏损的海鸥型,富集高场强元素Th、Zr、Hf,亏损Ba、Sr、P、Ti、Nb、Ta等大离子亲石元素,微量元素特征指示其形成于大陆地壳的部分熔融。锆石LA--ICP MS U--Pb定年结果表明,岩石加权平均年龄为(850.2±2.0)Ma,形成于新元古代。构造环境显示研究区花岗质片麻岩形成于挤压造山环境,为造山期的深熔产物。新元古代花岗质片麻岩的发现,表明研究区之前存在一古老的微陆块。     

福建南平花岗伟晶岩型钽铌矿床地质特征与成因

福建南平钽铌矿是亚洲最大的花岗伟晶岩型钽铌矿床,也是中国钽铌金属矿的重要产地。南平钽铌矿在构造上位于闽西北隆起带东南缘,矿区内广泛发育有中—新元古界变质岩系。钽铌矿多呈脉体,沿变质岩系的片理或层理侵入,矿脉与围岩的关系清晰。这些脉体是在与加里东期花岗岩有成因联系的4类花岗伟晶岩分异—演化的基础上形成的。矿化伟晶岩中分带和交代蚀变作用均十分发育,稀土元素的矿化与伟晶熔体的结晶分异及后期热液蚀变作用有较密切的关系。稀土元素和磷酸盐矿物含量很多,这在国内外同类型伟晶岩中不常见。同时该地区也是新矿物——南平石的唯一产地。钽铌矿物是矿化伟晶岩中Ta和Nb元素的最主要载体,Ta含量大于Nb,还有其他可综合利用的稀土元素。闽西北地区具有进一步寻找此类型矿化伟晶岩的广阔前景。     

皖赣两省地质公园造景花岗岩的岩石特征、形成时代及景观成因

皖赣两省气候宜人,旅游资源丰富。黄山、三清山、天柱山、九华山、牯牛降等地质公园更是以独特的花岗岩地貌景观闻名于世。通过对地质公园内造景花岗岩进行年代学、岩石学、地球化学等方面的研究,证明上述地质公园内的花岗岩集中形成于135~125 Ma,属于早白垩世强烈岩浆活动的产物。这些花岗岩高硅、富碱、过铝,轻重稀土分馏不明显,Eu强烈亏损,稀土配分曲线呈海鸥型;强烈亏损Ba、Sr、P、Ti,形成四个明显的凹槽,具有造山后铝质A型花岗岩的岩石地化特征,属于铝质A型花岗岩或者高分异花岗岩。上述花岗岩主要形成于造山后伸展的构造背景。该构造背景下产出的花岗岩以浅色矿物为主,暗色矿物含量稀少,抗风化蚀变能力更佳;并具有多组密集的原生节理,对花岗岩地貌景观的形成起着极其重要的控制作用。     

吉林省桦甸市隆兴铁矿床深部地质特征

隆兴铁矿赋存于太古宙夹皮沟岩群三道沟岩组和腰抢子片麻岩中。认为矿床成因类型是属于受变质(火山沉积)铁硅建造铁矿。富矿部分则是混合岩化热液作用,使铁发生迁移而富集的。确定三道沟组内的火山铁硅质沉积建造岩层是寻找此类型矿床的地层标志,而地球物理标志是地面磁异常强度在1 000 n T以上的面积性异常即为矿致异常。     

Structural and metamorphic controls on the distribution of zircon in an evolving quartzofeldspathic migmatite: an example from the Reynolds Range, central Australia

Three types of zircon occur in a complexly deformed and variably migmatized quartzofeldspathic gneiss from the Reynolds Range, central Australia. The oldest type is inherited from the granitic precursor of the gneiss, and is overgrown by a second group of zircon grains that formed during prograde, granulite facies metamorphism. Partial melting of the gneiss resulted in solution of both the inherited and metamorphic zircon. No new zircon growth accompanied crystallization of the partial melt, suggesting loss of zirconium–rich residual fluids. Hydrous, amphibolite facies retrogression of the gneiss and its migmatized variants during late shearing produced new, idiomorphic zircon in both the shear zone and its wall rocks.
Important implications of this study are that (i) zircon has a tendency to dissolve if it comes into direct contact with a melt produced from anhydrous biotite breakdown in a quartzofeldspathic granulite, (ii) melt crystallization is not necessarily accompanied by zircon growth, and (iii) euhedral zircon can grow from a hydrous fluid phase under subsolidus, amphibolite facies conditions, e.g. within shear zones.     

胶南-威海造山带与罗迪尼亚(Rodinia)超大陆相关问题的初步探讨

胶南-威海造山带中的榴辉岩为晋宁早期板块俯冲作用的产物;沿造山带广泛分布的花岗质片麻岩,则为晋宁晚期板块由俯冲转为碰撞过程中同造山岩浆事件的产物.它们与全球性的格林威尔造山运动属同一事件范畴,但具有明显的穿时性.侵入于同造山花岗质片麻岩的片麻状花岗岩及震旦纪朋河石组,为后造山伸展机制下发生的岩浆及沉积事件的产物,与700～650Ma期间Rodinia超大陆的裂解作用密切相关.     

华北克拉通南缘小秦岭地区花岗质浅色脉体锆石U-Pb年龄、稀土元素特征及其地质意义

小秦岭地区发育有大量古元古代晚期的花岗质浅色脉体, 这为理解同时期华北克拉通南缘的深熔作用和构造演化提供了重要的窗口。本文对小秦岭地区三条花岗质浅色脉体中的锆石开展了CL图像、LA-ICP-MS U-Pb年代学及稀土元素的研究。浅色脉体中的锆石具有深熔成因锆石的斑杂状、平面状或弱振荡环带的内部结构及较为自形的外部形态特征, 测得的锆石207Pb/206Pb年龄分别为(1867±13) Ma (MSWD=0.22, n=21)、(1849±17) Ma (MSWD=0.79)和(1828±15) Ma (MSWD=0.33, n=20), 代表了该区深熔作用发生的时间。与上述三组年龄相对应, 其锆石稀土元素配分曲线由具较弱负Eu异常(Eu/Eu*=0.12~0.81)的重稀土相对富集型, 转变为中等负Eu异常(Eu/Eu*=0.29~0.61)的近平坦重稀土型、再到显著负Eu异常(Eu/Eu*=0.15~0.54)的重稀土富集型, 结合锆石Ti温度计获取其结晶温度为574~708 °C, 表明地壳深熔作用的发生可能与高角闪岩相-麻粒岩相的退变质作用有关。结合前人的变质年代学数据可知, 小秦岭地区1.87~1.82 Ga的深熔作用应与~1.95 Ga时东、西部陆块碰撞造山所致增厚地壳的长期抬升和冷却过程有关。     

Extensional Setting of Hainan Island in Mesoproterozoic: Evidence from Granitic Intrusions in the Baoban Group

The Mesoproterozoic Baoban Group is the oldest basement in Hainan Island and has played an important role in Columbia (Nuna) supercontinent reconstructions. The Mesoproterozoic granitic intrusions in the Baoban Group are the most widely-exposed Precambrian magmatic rocks and are the key to understanding the tectonic settings of Hainan Island and its relationship with the South China Block and the Columbia supercontinent. New LA-ICP-MS zircon U-Pb dating on three mylonitic granite samples from the Tuwaishan and Baoban areas yield ages ranging from 1447 Ma to 1437 Ma, representing the absolute timing of the emplacement of the granitic intrusions. Combined with previously published geochronological data for rocks from the Baoban Group and regional mafic intrusions, it is concluded that the Baoban Group formed at 1460–1430 Ma, coeval with the emplacement of the granitic and mafic intrusions. New in-situ zircon Lu-Hf isotope analyses for the three mylonitic granite samples yielded positive εHf(t) values, ranging from +0.49 to +8.27, with model ages (TCDM) ranging from 2181 Ma to 1687 Ma, suggesting that the granitic intrusions originated from a mixed source of Paleoproterozoic crust with juvenile crust. New zircon trace element data show characteristics of high Th/U values of 0.24–1.50, steep slopes from LREE to HREE and negative Pr, Eu anomalies with positive Ce, Sm anomalies, representing typical magmatic zircons formed in continental crust. Compared with available magmatic and detrital zircon ages from Precambrian rocks in the Cathaysia Block, Yangtze Block and western Laurentia, it is inferred that Hainan Island was separated from both the Cathaysia Block and the Yangtze Block, instead being connected with western Laurentia in the Columbia supercontinent. Considering the decreasing tendency of basin deposition time along the western margin of Laurentia, it is proposed that Hainan Island was located to the north or northwest of the Belt-Purcell Supergroup, along the western margin of Laurentia, during the breakup of the Columbia supercontinent.     

内蒙古大青山地区古元古代早期榴云片麻岩(大青山表壳岩)深熔作用:地质、锆石年代学和地球化学研究

大青山位于华北克拉通西部孔兹岩带中段,古元古代晚期孔兹岩系(上乌拉山岩群)十分发育。近年来,在上乌拉山岩群中分辨出一套古元古代早期变质碎屑沉积岩(大青山表壳岩,榴云片麻岩),它们遭受强烈变质变形和深熔作用改造,形成古元古代早期石榴石花岗岩。包头哈德门沟是古元古代早期榴云片麻岩典型出露区,并有古元古代早期石榴石花岗岩(哈德门沟石榴石花岗岩)形成。由榴云片麻岩经深熔榴云片麻岩再到石榴石花岗岩,浅色体增多,石榴石增多且颗粒增大,黑云母减少,石榴石包裹黑云母、石英、斜长石等矿物。石榴石岩的锆石呈浑圆状,普遍具核-幔-边或核-边结构,碎屑锆石年龄为~2.5Ga,变质锆石年龄为~2.45Ga和~1.90Ga。锆石形态、内部结构和年龄与榴云片麻岩、深熔榴云片麻岩和石榴石花岗岩中的锆石类似,但记录了古元古代晚期变质事件年龄。石榴石花岗岩与榴云片麻岩和深熔榴云片麻岩的地球化学组成特征总体上类似,高Al2O3含量和FeO T/MgO比值,CaO含量和K2O/Na2O比值存在较大变化,富集轻稀土和大离子亲石元素,亏损Nb、Ta、P和Ti。研究表明:1)浅色体和石榴石花岗岩中的石榴石是黑云母转熔的产物,并非岩浆结晶形成的;2)石榴石岩是在石榴石花岗岩岩浆形成之后进一步演化过程中石榴石不断地发生运移、分异和聚集的结果;3)尽管哈德门沟石榴石花岗岩具有一定或较大的规模,但具有深熔岩浆的性质;4)石榴石花岗岩地球化学组成变化与熔融母岩组成变化和深熔及岩浆演化过程中残余矿物相石榴石、锆石局部变化有关。     

西藏玉龙铜矿床成矿斑岩的厘定及地质意义

位于青藏高原东缘的玉龙铜矿是我国最大的斑岩铜矿之一,其形成一致认为与矿区中心产出的二长花岗质复式斑岩体有关,但成矿与复式岩体的确切关系并不清楚。本文通过详细的野外地质填图,特别是矿床8号勘探线12个钻孔的重新编录,在复式岩体中识别出一套花岗斑岩岩枝,岩枝中不规则状石英-钾长石脉广泛发育,同时还见有单向固结结构、粗晶及细晶结构,这些特征表明该岩浆中的流体曾经发生过饱和。同时结合矿床高品位(0.6%,质量分数)铜矿化紧密围绕花岗斑岩分布、含矿脉体自花岗斑岩向外围逐渐由高温石英-钾长石A脉过渡为中低温石英-硫化物脉、热液蚀变自花岗斑岩向外由高温钾硅酸盐化过渡为中低温石英-绢云母化的规律,最终确定这套花岗斑岩为玉龙矿床的成矿斑岩。玉龙铜矿成矿斑岩的厘定,较好地解释了矿床矿化类型及金属的分布规律,为进一步深入理解矿床形成过程提供了帮助。