Depositional age and correlation of the Oonah Formation: refining the timing of Neoproterozoic basin formation in Tasmania

The Proterozoic Oonah Formation comprises a thick sequence of turbidites and mafic rocks that is widely exposed in western and northern Tasmania. The regional significance of the Oonah Formation is poorly understood as its contacts are faulted and estimates of its depositional age range from 1450 Ma to 700 Ma. Here we refine the depositional age of the Oonah Formation and clarify its relationship to other Proterozoic sequences in Tasmania. Magmatic apatite from the syn-sedimentary Cooee Dolerite has a ²⁰⁷Pb-corrected ²³⁸U/²⁰⁶Pb age of 733 ± 9 Ma that provides a robust estimate of the depositional age of the Oonah Formation. The Oonah Formation contains abundant 750 Ma detrital monazite and has detrital zircon age populations at 1800–1700 Ma, 1590 Ma, and 1450 Ma. The new age and provenance data support the interpretation that the Oonah Formation is a lateral equivalent of the base of the Togari Group and correlatives in Tasmania. We demonstrate that the stratigraphy and provenance of Neoproterozoic strata in Tasmania differ from time-equivalent sequences in Adelaide Rift Complex but are similar to the Pahrump Group (Death Valley, California) and the Cobham Formation (Transantarctic Mountains), which supports a southwest Laurentia—Tasmania—East Antarctica connection within supercontinent Rodinia.     

湘东南太和仙铅锌矿床流体包裹体研究

太和仙铅锌矿床位于东南地洼区之南岭成矿带中段,为了了解其流体性质及演化,探讨成矿机制,通过现场调查,对矿区不同成矿阶段的矿石进行了流体包裹体岩相学、显微测温和激光拉曼探针分析。该矿区成矿作用分为3个阶段,依次为石英-黄铁矿毒砂阶段(早阶段)、石英-铅锌多金属硫化物阶段(中阶段)、石英-方解石-黄铁矿阶段(晚阶段)。包裹体研究表明:矿床中主要发育富液相水溶液包裹体(Ia型)、富气相水溶液包裹体(Ib型)、CO_2包裹体(Ⅱ型)、含CO_2的三相水溶液包裹体(Ⅲ型)4类。早阶段中均一温度为235~349℃,盐度为2.03%~7.44%(NaCleq,质量分数,下同);中阶段包裹体均一温度为159~272℃,盐度为1.39%~10.86%;晚阶段包裹体均一温度为128~205℃,盐度为1.39%~7.58%。激光拉曼探针测试表明,3个阶段中包裹体的组分主要为H2O,其次有少量CO_2和还原性气体CH4、N2。早阶段成矿流体在演化过程中发生了不混溶作用,表现为CO_2等气相成分的逸失是导致金属元素沉淀富集的主要因素。中阶段成矿流体在演化过程中发生不同流体间的混合作用,表现在以大气降水及层间水的混入是导致大量金属元素沉淀成矿的主要因素。晚阶段流体以大气降水为主,推测可能流体自然冷却致使成矿元素沉淀富集。     

琼东南海域天然气水合物地震反射特征

天然气水合物是一种新能源,目前,世界上许多国家都在进行天然气水合物研究。琼东南盆地是天然气水合物可能赋存的重点目标区,笔者针对琼东南海域二维地震资料进行以突出含天然气水合物地层地震反射特征为目的的处理,进一步识别含天然气水合物地层地震反射特征与分布。通过应用地震资料保幅处理技术,对该海域含天然气水合物地层地震反射特征,如似海底反射(BSR)、BSR强反射界面之上的高速异常带、BSR附近的振幅空白带、BSR的极性反转等,有了更多的认识,对开展全区含BSR特征研究有借鉴意义。     

黔东南那哥铜铅多金属矿床的矿化时空结构

黔东南那哥铜铅多金属矿床位于扬子陆块与华夏陆块的过渡带上,该区经历了自四堡期以来的多期构造活动,岩浆活动频繁,变形-变质强烈,构造形迹复杂;通过深入剖析矿床地质特征,结合区域地质演化史,从铜铅矿化的时空结构分析入手,系统研究了矿体空间定位规律。研究结果表明,在时间结构上,成矿与重大地质事件关系密切,具有多阶段成矿的特点;在空间结构上,矿体主要受控于尾硐溪断裂,赋存于断裂带走向上的弧形转弯处、断裂面的凹凸变化部位,矿体具膨大狭缩、尖灭再现特点,在空间上具有向W侧伏的趋势。     

华南东南沿海地区岩石圈电性结构

为了研究华南东南沿海地区的壳幔电性结构及其动力学背景,布设了4条大地电磁测深剖面,获得了相应的二维地电模型,并结合相关地质和地球化学信息对地电模型进行了研究。结果表明:研究区西部地壳由于碰撞汇聚作用变厚,东部地壳由于太平洋板块的俯冲作用剧烈减薄。华南东南沿海地区的岩石圈并不是简单的呈现"西厚东薄"的特征,研究区东西两端岩石圈厚度超过100km,推测西段岩石圈增厚主要形成于陆内挤压造山或陆内碰撞汇聚造山作用,而东端岩石圈增厚可能由于大洋板块俯冲时洋壳残留物叠置在岩石圈的下部所形成,而中部岩石圈的减薄与软流圈物质上侵有关,造成此区域大规模软流圈物质上侵的动力来自于太平洋板块俯冲产生的深部热扰动。     

川东南下寒武统牛蹄塘组烃源岩特征及有效性分析

通过地球化学分析、储层沥青薄片镜下鉴定,对川东南下寒武统牛蹄塘组烃源岩宏观特征以及微观地球化学特征进行深入研究,并以震旦系灯影组古油藏为例分析了烃源岩的有效性。结果表明,牛蹄塘组烃源岩厚度稳定,底部暗色泥页岩分别厚约25m-43m,平均有机碳含量介于0．5％-1．0％,现今已达过成熟阶段,为中等烃源岩。牛蹄塘组泥页岩是灯影组古油藏的主要烃源岩,古油藏原油裂解气是灯影组气藏成藏的物质基础。     

滇东南洒西白钨矿床稀土元素地球化学特征及其成因指示意义

洒西白钨矿床位于滇东南老君山矿集区内,呈层状、似层状产出。矿区围岩为一套中深变质岩,其稀土元素组成特征为:矿区围岩LREE/HREE比值为4.37~6.87,δEu为0.67~1.49,δCe值为0.62~0.98;外围混合片麻岩LREE/HREE比值为4.51~5.58,δEu平均为0.14。矿石Eu正异常与Ce负异常同时存在说明矿石沉淀时相对高温的热水流体和较低温的海水在海底发生了对流混合,部分样品中Eu负异常的形成可能与后期岩浆热液叠加改造作用有关。结合矿床地质特征,洒西白钨矿床成因为喷流沉积-后期岩浆热液改造型。     

贵州东南部含金刚石钾镁煌斑岩找矿远景区预测

[摘 要]钾镁煌斑岩是金刚石的成矿母岩、组成岩筒的基本物质。基于区内区域重磁异常分布特征,以北部镇远马坪及周边县域(施秉、三穗、雷山、剑河、麻江)出露的钾镁煌斑岩和南部从江一带镶嵌的基性-超基性岩为线索及岩体露头上的重磁场异常特征响应值为标尺,与地表出现的金刚石原生矿、砂矿、指示矿物、重砂异常分布为依据,圈定了数个基性-超基性岩体(带),结合物探资料推断的岩浆岩带、火山机构、板块结合带、深大断裂带以及地质矿产资料,共划分了6 个金刚石找矿远景区。预测在台江-剑河-锦屏-黎平一线,出现的1 处大型重磁(航磁环状异常)正异常分布区为区内金刚石找矿的重要靶区和找到具有工业价值金刚石原生矿的重点突破口,这里(G3 异常区)极有可能是破解贵州原生金刚石找矿瓶颈的福地,是揭示金刚石矿床赋矿岩筒神秘面纱的有利地段。     

Types,features, and prospecting potential for Mesozoic metal ore deposits in Zhejiang Province,southeast China

The geotectonic units of Zhejiang Province include the Yangtze Plate in the northwest juxtaposed against the South China fold system in the southeast along the Jiangshan–Shaoxing fault. The South China fold system is further divided into the Chencai–Suichang uplift belt and the Wenzhou–Linhai geotectogene belt, whose boundary is the Yuyao–Lishui fault. The corresponding metallogenic belts are the Mo–Au(–Pb–Zn–Cu) metallogenic belt in northwest Zhejiang, the Chencai–Suichang Au–Ag–Pb–Zn–Mo metallogenic belt, and the coastal Ag–Pb–Zn–Mo–Au metallogenic belt. The main Mesozoic metal ore deposits include epithermal Au–Ag(Ag), hydrothermal vein-type Ag–Pb–Zn(Cu), and porphyry–skarn-type Mo and vein-type Mo deposits. These ore bodies are related to the Mesozoic volcanic-intrusive structure: the epithermal Au–Ag(Ag) deposits are represented by the Zhilingtou Au–Ag deposit and Houan Ag deposit and their veins are controlled by volcanic structure; the hydrothermal vein-type Ag–Pb–Zn deposits are represented by the Dalingkou Ag–Pb–Zn deposit and also controlled by volcanic structure; and the porphyry–skarn-type Mo deposits are represented by the Tongcun Mo deposit and the vein-type Mo deposits are represented by the Shipingchuan Mo deposit, all of which are related to granite porphyries. These metal ore deposits have close spatio-temporal relationships with each other; both the epithermal Au–Ag(Ag) deposits and the hydrothermal vein-type Ag–Pb–Zn deposits exhibit vertical zonations of the metallic elements and form a Mo–Pb–Zn–Au–Ag metallogenetic system. These Jurassic–Cretaceous deposits may be products of tectonic-volcanic-intrusive magmatic activities during the westward subduction of the Pacific Plate. Favourable metallogenetic conditions and breakthroughs in the recent prospecting show that there is great resource potential for porphyry-type deposits (Mo, Cu) in Zhejiang Province.     

黔东南凯里生物群研究现状综述

产于黔东南剑河八郎的凯里生物群是一个含有10个大门类120多属动物化石的布尔吉斯页岩型的生物群,是全球寒武纪第3世生物多样化、生态复杂化的窗口,对早期后生生物研究具有十分重要的科学意义。丹寨南皋和镇远竹坪等新产地的发现,将凯里生物群产地扩大至整个黔东南地区,其研究取得了突破性的进展,也为凯里生物群进一步研究提供了新材料。