湖南桂阳大义山南体(太坪山单元)花岗岩形成时代及物质来源探讨     

赵增霞  徐兆文  左昌虎  陆建军  王汝成  缪柏虎  路睿 《地质论评》2017,63(2):395-412

在详细的野外地质调查基础上,本文通过对湖南省桂阳县大义山南体(太坪山单元)黑云母二长花岗岩的岩石化学、锆石U-Pb定年和全岩Sm-Nd同位素以及锆石原位Hf同位素的综合研究,参照前人研究成果,探讨其岩石化学性质、形成时代、物质来源以及形成机制等。LA-ICP-MS锆石U-Pb定年结果显示其n(~(206)Pb)/n(~(238)U)加权平均年龄为153.4±1.1Ma,两颗继承锆石核n(~(207)Pb)/n(~(206)Pb)年龄分别为2449Ma和2498 Ma。岩石高硅、富碱、高钾钙碱性、准铝质到弱过铝质,富集轻稀土元素、部分大离子亲石元素(Rb、K等)和Th、U、Pb等元素,亏损部分高场强元素(Nb、Ta、Ti)和Ba、Sr、P等元素。该岩体zr+Nb+Ce+Y350×10~(-6),10000*Ga/Al2.6,显示出A型花岗岩的特征。全岩Sm-Nd同位素显示ε_(Nd)(t)=-6.94~-5.19,二阶段模式年龄T_(DM2)=1.37~1.51 Ga。锆石原位Hf同位素显示,锆石ε_(Hf)(t)=-9.35~-1.16,T_(DM2)=1.28~1.79 Ga。两颗继承锆石核ε_(Hf)(t)分别为-6.82和1.48。岩石化学和同位素特征表明岩石主要来源于元古代地壳变质杂岩的部分熔融,并可能有少量地幔物质的加入。燕山早期,由于俯冲的古太平洋板块后撤,研究区处于伸展的构造环境,岩石圈减薄,软流圈上涌,导致玄武质岩浆底侵,诱发上覆的古元古代下地壳部分熔融,形成花岗质岩浆,并沿着深大断裂带运移侵位,形成大义山南体(太坪山单元)黑云母二长花岗岩。  相似文献   

Depositional Age of a Fossil Whale Bone from São Paulo Ridge,South Atlantic Ocean,Based on Os Isotope Stratigraphy of a Ferromanganese Crust          下载免费PDF全文

Tatsuo Nozaki  Yutaro Takaya  Takashi Toyofuku  Ayaka Tokumaru  Kosuke T. Goto  Qing Chang  Jun‐ichi Kimura  Yasuhiro Kato  Katsuhiko Suzuki  Adolpho Herbert Augustin  Hiroshi Kitazato 《Resource Geology》2017,67(4):442-450

Whale carcasses (whale falls) deposited on the deep seafloor are associated with a distinctive biotic community. A fossil whale bone recovered from São Paulo Ridge, South Atlantic Ocean, during cruise YK13–04 Leg 1 of R/V Yokosuka was covered by a ferromanganese (Fe–Mn) crust approximately 9 mm thick. Here, we report an age constraint for this fossil bone on the basis of Os isotopic stratigraphy (¹⁸⁷Os/¹⁸⁸Os ratio) of the Fe–Mn crust. Major‐ and trace‐element compositions of the crust are similar to those of Fe–Mn crusts of predominantly hydrogenous origin. Rare earth element concentrations in samples of the crust, normalized with respect to Post‐Archean average Australian Shale, exhibit flat patterns with positive Ce and negative Y anomalies. These results indicate that the Fe–Mn crust consists predominantly of hydrogenous components and that it preserves the Os isotope composition of seawater at the time of its deposition. ¹⁸⁷Os/¹⁸⁸Os ratios of three Fe–Mn crust samples increased from 0.904 to 1.068 in ascending stratigraphic order. The value of 1.068 from the surface slice (0–3 mm depth in the crust) was identical to that of present‐day seawater within error (~1.06). The value of 0.904 from the basal slice (6–9 mm) equaled seawater values from ca. 4–5 Ma. Because it is unknown how long the bone lay on the seafloor before the Fe–Mn crust was deposited, the Os stratigraphic age of ca. 5 Ma is a minimum age of the fossil. This is the first application, to our knowledge, of marine Os isotope stratigraphy for determining the age of a fossil whale bone. Such data may offer valuable insights into the evolution of the whale‐fall biotic community.  相似文献   

基于岩石物理相的储集层分类评价:以北部湾盆地乌石凹陷东区始新统流沙港组三段Ⅱ油组为例^*          下载免费PDF全文

曾小明  张辉  邹明生  黄冬梅  莫冯阳 《古地理学报》2017,19(4):703-712

目前储集层分类方法多数只是从储集层的物性特征角度进行分类,而没有从储集层的成因机制进行分类。通过利用分析化验资料、钻测井资料和测试资料,对北部湾盆地乌石凹陷东区始新统流沙港组三段Ⅱ油组(L₃Ⅱ油组)的沉积特征、成岩作用和构造特征进行分析,进而研究其对储集层物性的影响,并对储集层进行分类。结果表明: L₃Ⅱ油组主要发育扇三角洲内前缘水下分流河道、外前缘水下分流河道和席状砂3种沉积微相;成岩相主要识别出泥质杂基充填相、不稳定组分溶蚀相和强压实致密相3种成岩相;裂缝相则以无裂缝相为主,局部可观察到高角度和网状裂缝相。在此基础上通过三者的叠加对储集层的岩石物理相进行分类命名,划分出内前缘水下分流河道—泥质杂基充填相—高角度裂缝相等9种不同的岩石物理相。根据不同的岩石物理相特征,总结归纳出了Ⅰ类好储集层、Ⅱ类中等储集层和Ⅲ类差储集层共3类储集层,实现了从储集层成因机制的角度对储集层进行分类和评价。  相似文献   

太平洋东马里亚纳海盆多金属结核成因及品位控制因素          下载免费PDF全文

曹德凯  任向文  石学法 《海洋学研究》2017,35(4):76-86

本文选取东马里亚纳海盆与CC区中国多金属结核合同区西区的多金属结核样品,采用ICP-OES、ICP-MS以及XRD等测试方法对结核表层进行了地球化学与矿物学分析,并探讨了东马里亚纳海盆结核成因以及其主要成矿元素含量的控制因素。结果表明,结核具备水成型结核的主、微量元素特征,并受到成岩作用的影响。结核上下表层各元素含量差异明显,上表层Fe、Co、P等多数主量元素及∑REYs含量均高于下表层,而Mn、Cu、Ni等元素含量在下表层明显增加。根据结核矿物学以及海洋环境特征,并结合前人数据统计分析认为,东马里亚纳海盆结核样品中Mn、Ni、Cu、Co、Fe、Ce的品位主要受控于Mn矿物组成、底层海水溶解氧和表层海水初级生产力,La、Y等稀土元素品位还受到洋中脊热液活动的制约。  相似文献   

Trace elements in ferromanganese nodules from the central indian ocean basin     

J. N. Pattan  G. Parthiban  Ankeeta Amonkar  Sufiyan A. Shaikh  S. Jai Sankar 《Marine Georesources & Geotechnology》2017,35(8):1147-1157

Thirty-three bulk ferromanganese nodules from the sediment–water interface of siliceous sediment domain from the Central Indian Ocean Basin were analyzed for 50 elements including 6 new (Be, As, Se, Sn, Sb, and Bi) using inductively coupled plasma–mass spectrometer. The Mn/Fe ratio and triangular plot (Fe-Mn-{Cu+Ni+Co?×?10}) suggest that ferromanganese nodules are of hydrogenetic, early diagenetic, and diagenetic origin. In the ferromanganese nodules, Mo, Sb, Bi, and As are highly enriched ～320, 160, 90, and 50 times compared with upper continental crust, respectively. A majority of the elements such as Be, Sc, Ti, V, Co, As, Se, Sr, Y, Zr, Nb, Sn, rare earth elements (REEs), Pb, Bi, P, Th, U, Hf, and Ta are associated with Fe, whereas, Cu, Ni, Zn, Mo, Li, Ga, Sb, Mg, and Cs are associated with Mn in the ferromanganese nodules. Redox proxies such as U/Th (0.14) and Mo/Mn (0.0019) ratio in the ferromanganese nodules suggest their formation under oxic conditions.  相似文献   

福建李家坊金矿区火成岩岩体锆石U-Pb年龄、地球化学特征及其地质意义   总被引：2，自引：2，他引：0  

赵骏峰  吴晓林  陈镜文  刘文元  卢林 《矿床地质》2022,41(2):273-302

福建李家坊金矿为何宝山矿田近年新发现的中型金矿床,矿区内广泛发育火成岩岩体,然而,由于缺少对其岩浆活动时限及地球化学特征的研究,各类岩体与金矿化的关系尚不明确.针对这一问题,文章通过全岩主微量元素分析和LA-ICP-MS锆石U-Pb定年及微量元素测试,约束李家坊金矿床内火成岩岩体成岩年龄,并讨论了其地球化学特征.研究表...  相似文献