滇东南富宁地区基性侵入岩及喷出岩时代

在滇东南富宁地区基性侵入岩、喷出岩较发育,前人将其划分为"半瓦型"侵入岩、"安定型"侵入岩和"龙康型"喷出岩3类,3类岩石普遍缺乏可靠的同位素年代学资料。在对富宁地区基性侵入岩、喷出岩进行区域地质调查的基础上,应用LAICP-MS技术对其进行锆石U-Pb测年,在半瓦型侵入岩和安定型侵入岩中分别获得了254.0±2.0Ma和244.2±4.4Ma的加权平均年龄,在龙康型喷出岩中获得251.9±3.0Ma和255.92±0.72Ma加权平均年龄。结合野外调查和综合研究,将富宁地区"安定型"侵入岩的时代界定于中三叠世,将"半瓦型"侵入岩和"龙康型"喷出岩的时代界定于晚二叠世。     

Evaluating igneous sources of the Taveyannaz formation in the Central Alps by detrital zircon U–Pb age dating and geochemistry

Late Palaeogene syn-tectonic volcanic products have been found in the Northern Alpine foreland basin and in the South Alpine hemipelagic basin. The source of abundant volcanic fragments is still in debate. We analyzed the geochronology and geochemistry of detrital zircons, and evaluated their temporal and genetic relationships with potential volcanic sources. The study shows that the detrital zircon U–Pb age patterns have two major age groups: a dominance (ca. 90%) of pre-Alpine zircons was found, as commonly observed in other Alpine flysch formations. These zircons apparently derived from erosion of the early Alpine nappe stack in South Alpine and Austroalpine units. Furthermore, a few Neo-Alpine zircons (ca. 10%) have ages ranging from Late Eocene to Early Oligocene (~ 41–29 Ma). Both source materials were mixed during long riverine transport to the basin margins before being re-deposited by gravity flows. These Palaeogene ages match with the activity of Peri-Adriatic magmatism, including the Biella volcanic suite as well as the Northern Adamello and Bergell intrusions. The values of REE and ¹⁷⁶Hf/¹⁷⁷Hf_(t) ratios of the Alpine detrital zircons are in line with the magmatic signatures. We observe an in time and space variable supply of syn-sedimentary zircons. From late Middle Eocene to Late Eocene, basin influx into the South Alpine and Glarus (A) basins from the Northern Adamello source is documented. At about 34 Ma, a complete reorganisation is recorded by (1) input of Bergell sources into the later Glarus (B) basin, and (2) the coeval volcaniclastic supply of the Haute-Savoie basin from the Biella magmatic system. The Adamello source vanished in the foreland basin. The marked modification of the basin sources at ~ 34 Ma is interpreted to be initiated by a northwestern shift of the early Alpine drainage divide into the position of the modern Insubric Line.     

内蒙古巴拉格歹地区构造混杂岩带中浊积岩、震积岩特征及意义——以内蒙古哈拉黑等八幅1:5万区域地质调查为例

浊积岩为具有鲍马序列的古海沟沉积,其部分沉积物与古海沟地震密切相关,由于岛弧外弧海沟地质构造复杂,洋板块俯冲及火山岩的喷发,地震活动强烈、频繁,沉积岩在成岩过程不断受到地震扰动,形成具有地震活动特点的震积岩。通过对巴拉格歹地区构造混杂岩带中浊积岩、震积岩的研究,识别出浊积岩系的具递变层理的槽模、沟模等冲刷铸模,包卷层理构造及最顶部黑色粉砂质泥岩段;识别出震积岩系的液化脉、地震震碎角砾岩、滑塌角砾岩、震褶岩-卷曲、纹层状、阶梯状断层构造等,建立并确认浊积岩、地震岩识别标志,恢复古地理构造环境,认为原划分的大石寨组应该解体,应为一套弧前盆地古海沟浊积岩沉积。结合浊积岩中的火山岩、基性岩及区域上化石山发现的超基性岩,初步确认,在测区浊积岩与岛弧火山岩、洋壳沉积物受板块碰撞拼接作用,由一系列逆冲断裂将上述各种块体构造就位在一起,形成构造混杂岩,为二连-贺根山缝合带在本区东延问题提供了资料。     

A simple approach to evaluating leakage through thin impervious element of high embankment dams

Internal erosion is the most common reason which induces failure of embankment dams besides overtopping. Relatively large leakage is frequently concentrated at defects of impervious element, and this will lead to eventual failure. The amount of leakage depends not only on integrity of impervious element, but also on dam height, shape of valley, shape of impervious element and water level in reservoir. The integrity of impervious element, which represents the relative level of seepage safety, is not easy to be determined quantitatively. A simple method for generalization of steady seepage state of embankment dams with thin impervious element is proposed in this paper. The apparent overall value of permeability coefficient for impervious element can be obtained by this method with reasonable accuracy and efficiency. A defect parameter of impervious element is defined as an index to characterize seepage safety of embankment dams. It equals the ratio of the apparent overall value of permeability coefficient to the measured value in laboratory for intact materials. Subsequently, seepage safety of three dams is evaluated and the evolution of defect level of impervious element of dams is investigated. It is proved that the newly proposed method in this paper is feasible in the evaluation of relative seepage safety level of embankment dams with thin impervious element.     

余姚—丽水断裂带嵊州地区燕山期主要构造特征

余姚—丽水断裂带是浙东南地区活动时间长、延伸远、发育比较宽的一条NE—NNE展布的断裂构造带,在浙江嵊州地区上火山岩系磨石山群和下火山岩系永康群中构造形迹表现十分明显。余姚—丽水断裂带由一系列NE—NNE向控制区内白垩纪盆地形成与发展的正断层,以及NE—NNE走向、自北西向南东逆冲的叠瓦状断层和轴迹呈NE—NNE向的褶皱组成。通过对其构造活动特征及控制新老地层的时序关系研究,结合区域构造活动规律和时空演化关系等综合分析认为: 正断层形成时间较早,控制白垩纪盆地的形成和发展,与早白垩世岩石圈伸展减薄形成的拉张作用密切相关; 叠瓦状逆冲断层及斜歪褶皱、紧闭同斜褶皱等褶、断构造组合形成于晚白垩世之后,其动力学机制可能与古太平洋构造域向太平洋构造域的转换效应有关。研究成果为深入探讨浙东地区燕山期构造演化提供了新的素材和资料。     

In situ investigation into fracture and subsidence of overburden strata for solid backfill mining

Controlling the subsidence of overburden strata is the main objective for backfill mining technology. In order to understand the controlling effect of filling body, a detection scheme with three direction boreholes was designed in the tailgate of T₃290 mining face in Tangshan Coal Mine to monitor the fracture developing process of overburden strata. In addition, a few displacement and stress sensors used for monitoring the roof subsidence and filling body stress were arranged behind the longwall face to monitor and record the force and deformation of gangue. The field investigation shows that the solid backfill mining technology can effectively reduce the fracture of overburden strata, i.e., the fracture height and the damage degree. The subsidence of overburden strata is mainly caused by the subsidence of roof which is divided into four stages: roof subsidence stage of mining face, rapid subsidence stage of gob roof, relatively stable stage, and long-term rheological stage. The gauge plays an essential role in slowing down the subsidence in each stage of the overburden subsidence, especially the relatively stable stage.     

扬子地台东南缘下寒武统清虚洞组风暴沉积特征及其重要意义

在扬子地台东南缘,下寒武统龙王庙阶清虚洞组主要由浅水碳酸盐岩组成。在野外露头剖面实测和室内镜下薄片观察的基础上,大量风暴沉积被发现于不同剖面清虚洞组的不同层位中,同时大量风暴诱发形成的沉积构造被识别出来,包括侵蚀基底、粗粒滞留沉积、粒序层理、平行层理、丘状交错层理(少见并且值得怀疑)以及沙纹层理,组成了多种类型的风暴沉积序列。结合更靠扬子东南缘的深水剖面中重力流沉积的缺乏,可以推断早寒武世龙王庙期扬子地台的沉积模式为碳酸盐缓坡。结合风暴的形成机制以及清虚洞组风暴沉积的发育特征(尤其是粗粒滞留砾屑的定向排列和典型丘状交错层理的缺乏),可以推断研究区风暴沉积形成于强烈的冬季风暴作用,并且早寒武世龙王庙期华南的古地理位置应当位于中纬度地区,这一结论对一些著名的全球古地理重建方案提出了质疑。同时中纬度地区大规模发育蒸发岩和碳酸盐岩还佐证了寒武纪地球处于热室(Hothouse)时期。     

安徽省凤阳江山金矿床赋矿地层和相关岩浆岩锆石年代学研究及其意义

安徽省北部蚌埠隆起区被认为是山东胶东招远金成矿带以西的延伸部分,但蚌埠隆起区内之前一直未发现成规模的金矿床。江山金矿床是最近新发现的中型金矿床,区内成矿作用的时代、赋矿地层的归属仍缺乏系统的年代学证据。文章对蚌埠隆起区内江山金矿床的赋矿地层和相关岩浆岩开展系统的年代学研究,明确了赋矿地层时代归属,并限定了成矿时代的上限和下限。矿床赋矿围岩浅粒岩的结晶年龄为(2496±19)Ma,变质年龄为(2452±47)Ma;斜长角闪岩的变质年龄为(1824±11)Ma,对比区域地层岩性和时代,确定矿床的赋矿围岩为新太古代五河群西堌堆组,而非过去认为的庄子里组。矿床中穿切矿体的脉岩花岗闪长斑岩的结晶年龄为(121.2±1.4)Ma,代表成矿时代的下限;赋矿岩体巨斑花岗斑岩的结晶年龄为(128.3±1.7)Ma,代表了成矿时代的上限。通过与胶东金成矿带的对比,认为蚌埠隆起区与胶东地区的前寒武纪变质基底演化历史相似,江山金矿床的成矿作用类型属于胶东焦家式金矿,在此基础上,推测蚌埠隆起区西芦山岩体和淮光岩体有较大的成矿潜力。     

安徽省东源斑岩型钨矿床白钨矿原位微量元素特征及其指示意义

新兴的白钨矿面扫描技术对于解释矿物微量元素特征具有重要的指示意义。文章选择皖南地区东源斑岩型钨矿床中白钨矿为研究对象,利用面扫描和阴极发光图像技术对矿物微区结构和原位微量元素特征进行系统研究。分析结果显示,白钨矿具有核边结构且微量元素特征具有明显的分带性,同一白钨矿颗粒核部亏损Mo、Nb、Ta元素,富集REEs,而边部相反。在此基础上,文章通过系统的白钨矿单点微量元素分析,反演了成矿流体性质和演化过程,提出东源钨矿床成矿流体氧逸度逐渐增高,成矿流体富集F挥发分且F含量逐渐增加,成矿物质很可能有幔源组分加入。通过白钨矿面扫描和阴极发光图像查明矿物微区结构,进而开展了白钨矿微区微量元素单点分析,有可能对成矿流体和矿质来源作出合理的解释。     

赣南淘锡坑石英脉型钨矿床成矿机制探讨:来自流体包裹体的证据

赣南地区淘锡坑钨矿床是典型的大型石英脉型钨锡多金属矿床。矿体赋存于震旦系浅变质砂(板)岩,并延伸至深部花岗岩内,按空间产出位置分为内带矿体和外带矿体,包括宝山、西山、烂埂子、枫岭坑4大脉组,矿体产出各不相同,矿物组合也具有明显分带特征。在详细的岩相学研究基础上,文章选择淘锡坑主成矿期石英为研究对象,并与共生黑钨矿作对比,从空间角度开展不同脉组、不同矿体或中段的流体包裹体的对比研究。根据流体包裹体岩相学,石英包裹体类型有H_2O-NaCl型包裹体(Ⅰ型)、H_2O-NaCl-CO_2型包裹体(Ⅱ型)和纯CO_2体系裹体(Ⅲ型)及少量含石盐子晶的多相包裹体,并同时捕获贫CO_2的盐水溶液包裹体和纯CO-2气相包裹体。包裹体显微测温结果显示:内、外带石英脉气液两相的包裹体均具有较宽温度和盐度范围,外带均一温度和盐度w(NaCl_(eq))分别集中于200～220℃、1%～6%,内带均一温度和盐度w(NaCleq)分别集中于100～220℃、3%～7%,流体为中-低盐度、富含CO_2的H_2O-CO_2-NaCl体系,不同脉组不同矿脉之间对比结果均显示出多期成矿的特征。在矿脉形成过程中,流体的成分和温度在内外接触带有明显变化,表明岩体与围岩接触界面是造成淘锡坑矿床内带矿体和外带矿体的成矿条件改变的转折位置,成矿流体在此附近发生CO_2逸失引起相分离的不混溶作用是成矿的主要因素。