Mesozoic radiolarian chert from the middle sector of the Yarlung Zangbo suture zone,Tibet and its tectonic implications

The middle sector of the Yarlung Zangbo suture zone stretches over 200 km long from Ngamring through Geding to Rinbung, roughly along Yarlung Zangbo River valley (Fig. 1). This belt resulted from the closure of the Tethyan ocean and the collision be- tween Indian plate and Lhasa block[1―8]. Lots of works demonstrated that rifting of the Tethyan basin in southern Tibet started from Triassic time. Initial oce- anic crust appeared in the Late Jurassic, and then ex- perienced a rapid sprea…     

Geochemical evidence for contribution of ore-forming materials from peraluminous granite basement —— Taking Fucheng pluton and No. 6722 uranium deposit in southern Jiangxi Province as examples

Source of ore-forming material is always one of the fundamental subjects in the study of mineral deposits. Recently, in order to probe deep sources of ore-forming materials, many interna-tional and Chinese investigators have paid much attention to the rel…     

内蒙古锡林浩特I型花岗岩的时代及构造意义

在内蒙古锡林浩特水库地区出露的花岗岩确定为I型花岗岩,具有较高的Cr、Co、Ni丰度。Ca、Al含量和N2O／K2O比值较高,Fe、Mg含量较低。微量元素蛛网图中显示出明显的Nb、Ta、P、Ti负异常。在SiO2-K2O及AFM图中,花岗质岩石投在钙碱性系列区;在构造环境判别图中,花岗质岩石样品都投在火山弧＋同碰撞花岗岩区。锆石测年结果显示平均年龄为317．0±4．0Ma,属晚石炭世。这套晚石炭世岛弧花岗岩的存在,表明加里东期古亚洲洋并未完全关闭,晚石炭世时仍然存在洋壳的俯冲消减事件。从区域上看,是北侧的贺根山洋盆向南俯冲的结果。     

贺兰山中段奥陶系米钵山组砂岩地球化学及构造背景分析

本文利用奥陶系米钵山组砂岩地球化学分析,结合区域地质研究,探讨贺兰山中、晚奥陶世的构造环境。贺兰山中段奥陶系米钵山组砂岩的地球化学研究表明,砂岩的siO2平均含量为81．3％;A120。／Si02值0．07～0．11,平均值为0．08;K20／Na20值变化较大,最大60．7,一般介于4．79～7．81;Fe2O3＋MgO含量较低,介于2．1％～2．81％。砂岩微量元素Nb丰度及V／（V＋Ni）与Ce／La、Sr／Ba值均较高,说明砂岩沉积于湿热、还原、低盐度环境,具有大陆型沉积特征。砂岩稀土元素富集,含量在116×10^-6～195×10^-6之间,平均值为158×10～;8Eu为0．52～0．58,具显著的负铕异常。这些数据指示了米钵山组具有重力流快速堆积的特征和大量陆源补给,浊流沉积作用是重力流携带陆源物质的主要途径。通过多种构造环境判别图解分析,显示物源区地质构造具有被动大陆边缘性质。     

西峡盆地含恐龙蛋化石剖面磁性地层学结果及其构造地质意义

通过对河南南阳西峡盆地含恐龙蛋化石的阳域—丹水剖面的岩石磁学与古地磁学研究表明,该陆相沉积地层的特征剩磁载体以赤铁矿与磁铁矿为主,特征剩磁通过了倒转检验,表明其很可能为岩石形成时期获得的原生剩磁.结合该剖面古生物资料,磁性地层学结果表明,剖面上部2973~3023 m处年代为83~79 Ma;该剖面蛋化石所在最高层位年龄不晚于83 Ma,暗示该地区大型爬行动物的绝灭可能与西峡地区当时的气候、环境变化有关.此外,自晚白垩世以来,该剖面所处位置相对华北和华南地块发生了约18°的顺时针旋转,可能由该地区的局部构造活动引起.     

Re-Os isotope dating of molybdenites in the Huang-shaping Pb-Zn-W-Mo polymetallic deposit, Hunan Province, South China and its geological significance

The large-scale Huangshaping Pb-Zn-W-Mo polymetallic deposit is located in the central Nanling min- eralization zone, South China. Six molybdenite samples from the Huangshaping deposit were selected for Re-Os isotope measurement in order to define the mineralization age of the deposit. It yields a Re-Os isochron age of 154.8±1.9 Ma (2σ ), which is in accordance with the Re-Os model ages of 150.9― 156.9 Ma. This age is about 7 Ma younger than their host granite porphyry, which was dated as 161.6±1.1 Ma by zircon U-Pb method using LA-ICPMS. All these ages demonstrate that the Huang- shaping granite and related Pb-Zn-W-Mo deposit occurred in the middle Yanshanian period, when many other granitoid and related ore deposits emplaced and formed, e.g. the Qitianling granite and Furong tin deposit, the Qianlishan granite and giant Shizhuyuan W-Sn-Mo-Bi deposit and Jinchuantang Sn-Bi deposit in the nearby area. They constitute the main part of the magmatic-metallogenic belt of southern Hunan, and represent the large-scale metallogeny in middle Yanshanian in the area. The lower rhenium content in molybdenite of Huangshaping deposit suggests that the ore-forming material was mainly of crust origin.     

Sr, Nd isotope geochemistry of volcanic rock series and its geological significance in the middle Okinawa Trough

There exists extensive basic-acidic volcanic rock series in the middle section of the Okinawa Trough. Different types of these volcanic rocks have their own average strontium ratios of 0.704 749, 0.705 062, 0.708 771, 0.704 840 and 0.720 301 with average¹⁴³Nd/¹⁴⁴Nd ratios of 0.512 820, 0.512 673, 0.512 413, 0.512 729 and 0.512 034. These ratios of Sr and Nd isotopes all fall on a theoretic hyperbolic curve of mixing between two end-members of MORB and rhyolitic magma. So we infer that these different kinds of volcanic rocks in the middle Okinawa Trough are the erupted product in different stages of formation and evolution of the trough crust. MORB magma, which had suffered assimilation, mixed with the early-formed crust-derived rhyolitic partial melt mass at different ratios; then, these mixed magma erupted and formed volcanic rock types of the trough. This study indicates that the Okinawa Trough is coming into a stage of submarine spreading from the stage of continental rift.     

Discovery and its geological significance of the mantle-derived helium in the inclusions of the Ordovician oil-bearing reservoir rocks in the Huanghua depression,China

The values of the helium isotopes in the inclusions of the Ordovician reservoir rocks in the Kongxi buried hill belt in the Huanghua depression were first measured and the source of helium and its geological significance were investigated in comparison with those of the helium isotopes in the conclusions in the Ordovician rocks in the Ordos basin and the Tarim basin. The input of the mantle-derived helium into the inclusions in the carbonate reservoir rocks was found from the Konggu 3 well, the Konggu 4 well, and the Konggu 7 well in the Kongxi buried hill belt. The 3He/4He and R/Ra in the conclusions in the Ordovician oil-bearing reservoir rocks in the Konggu 7 well average 2.54×10-6(3) (sample quantity, the same below) and 1.82(3), respectively. The percent of the mantle-derived helium in the inclusions of the reservoir rocks in the Konggu 7 well reaches up to an average of 23.0%(3). The age of the contribution of the mantle-derived helium to the inclusions in the Kongxi buried hill belt is in the La