从藏南陆-陆碰撞带深部结构构造演化探讨斑岩铜矿的成岩成矿问题

本文以INDEPTH项目对印度大陆与欧亚大陆碰撞带深部成像结果为基础,从构造演化角度探讨藏南陆-陆碰撞带冈底斯斑岩铜矿带的成矿作用问题。深部探测给出的碰撞带深部结构与侯增谦等地质学家提出的深部结构有较大的异同,如何协调起来以深化对藏南陆-陆碰撞条件下成矿作用的认识,这是本文讨论的中心。藏南碰撞带成矿实际上是在新特提斯大洋岩石圈俯冲形成的冈底斯岩浆弧成矿作用的基础上,再经过陆-陆碰撞挤压强烈改造后的再成矿。碰撞带的深部结构构造演化的特点是:(1)新特提斯大洋岩石圈板块向北连续俯冲了约120 Ma,形成的冈底斯陆缘火山岩浆弧带,这导致了陆缘带地壳增厚并含有大量的地幔岩浆流体物质(如南美安第斯成矿带那样);(2)在印度大陆与冈底斯陆缘弧接近碰撞时,在对挤中新特提斯大洋洋壳与大洋岩石圈地幔发生向上挤出与向下拆沉,并使部分洋壳残片和大洋岩石圈物质保存在中上地壳内;(3)两大陆岩石圈碰撞对接后,印度岩石圈地幔加深达70~80 km并沿地壳底部向北推进,并将加厚地壳内大量的成矿物质、钙碱性岩浆,洋壳及新生的下地壳,以及部分地幔物质从地壳底部将其围限起来,成为后期再成矿的物质基础;(4)查明了碰撞带深部壳/幔间产生了一层中间速度层(相当于MASH层),在中上地壳部位出现一层巨大的部分熔融层;(5)在碰撞挤压下冈底斯带内产生多组断裂构造,大型逆冲断裂系与背冲断裂,并引发了含矿岩浆的再活动,并在浮力(下地壳内)和挤压力作用下多次活动上升生成斑岩型铜矿床;(6)成矿后地表遭受过强烈的风化剥蚀作用,使矿床出露地表。     

河南义马地区页岩气储层孔隙非均质性

运用高压压汞、液氮吸附及渗透率测试等实验,利用极差、突进系数、变异系数等参数,表征煤系页岩孔渗特征及孔隙层间非均质性,分析孔隙层间非均质性主控因素。结果表明:河南义马地区上、下石盒子组泥页岩微孔与小孔较为发育,山西组大孔较为发育,分别提供了气体吸附附着面积和储存运移空间;上石盒子组孔容与孔径相对偏差最小,孔隙分布均匀,山西组比表面积相对偏差最小,表面积分布均匀;随围压增大,渗透率不断降低,且满足负指数相关关系;渗透率级差、突进系数和变异系数显示下石盒子组渗透率非均质性较弱,山西组渗透率非均质性很弱,更易于压裂开发。非均质性宏观上主要受沉积物质组成和构造改造作用影响,微观上受成岩演化影响。     

辽中凹陷反转构造及其对郯庐断裂带走滑活动的响应

辽中凹陷发育多种样式的反转构造,其形成演化与郯庐断裂带辽东湾段新生代的脉动式活动有直接关系。通过最新的地震剖面、相干体切片等资料以及平衡剖面恢复等方法,对辽中凹陷反转构造的几何学形态、演化过程和反转期次进行研究,并结合区域板块活动背景,分析反转构造演化过程及其对郯庐断裂带新生代活动的响应。结果表明:辽中凹陷发育反转断裂、反转背斜、泥底辟、隐伏凸起等多种类型的反转构造,且沿郯庐断裂带呈带状展布。辽中凹陷在新生代主要曾经历了三期构造反转,分别发生在沙三段沉积末期、东营组沉积末期和明化镇组沉积末期。三期构造反转均与郯庐断裂带的走滑压扭活动有关,从根本上受控于周边板块活动背景的变化:第一期反转是由于太平洋板块俯冲方向和速率发生变化,导致郯庐断裂带由左旋走滑转为右旋走滑,由走滑张扭转为走滑压扭,形成反转构造的雏形;第二期反转的动力主要来源于太平洋板块对中国大陆向西的推挤作用,导致渤海湾地区受到整体挤压以及郯庐断裂带发生走滑压扭,使反转构造定型;第三期反转是由于太平洋板块的加速俯冲促使郯庐断裂带晚期再次发生走滑压扭活动,对早期反转构造进行改造。其中沙三段和明化镇组沉积末期的反转为局部反转,强度较弱,东营组沉积末期的反转为区域反转,强度最高。     

云南建水煌斑岩年代学和地球化学及其构造意义

华南大陆内部燕山期的岩浆事件可分为2期:燕山早期180~150 Ma,燕山晚期140~80 Ma。而处于扬子板块西南缘的滇黔贵等地,仅见有第二期晚白垩世中酸性侵入岩与相关成矿作用,缺乏第一期岩浆活动的时间记录。本文在滇东建水地区首次发现了麦地村煌斑岩,对其进行高精度LA-ICP-MS锆石U-Pb定年和主微量元素测试分析。结果显示煌斑岩的锆石U-Pb年龄为(158.4±2.4)Ma(MSWD=4.2),为晚侏罗世的产物,补充了该区较为空白的第一期岩浆热事件。麦地村煌斑岩不相容元素明显高于原始地幔,表现出不同程度的富集,大离子亲石元素Rb、Ba、Ce等富集程度不明显,高场强元素中U、Ta、Pb等表现出一定程度富集,LREE相对富集,HREE相对亏损,不具有Nb-Ta-Ti负异常的俯冲型配分曲线特征,具有明显的OIB型洋岛玄武岩稀土元素配分特征,为板内伸展环境下的产物。滇东地区发育中生代时期的NNE构造,早期NNE向褶皱叠加有后期同方向正断层。早期褶皱表现为SEE-NWW挤压应力作用下的构造特征,后期断层表现出同方向张应力作用下的特征。煌斑岩正是由于该区发生挤压之后伴随着一期应力松弛调整,伸展减压作用诱发地幔物质部分融熔,来自于深处的软流圈地幔流体与岩石圈地幔发生交代作用,形成富集型地幔,交代富集的岩石圈地幔局部受热、部分熔融,发生上升侵位。煌斑岩的侵位时间即是滇东地区中生代从挤压向伸展转换的起始时间。     

晋中至太原城际铁路沿线地质条件分析

晋中至太原城际铁路位于山西断陷带次级构造单元太原断陷盆地内,盆地内部新构造运动复杂,城际铁路沿线跨越多条第四纪隐伏活动断裂,并穿过榆次地裂缝发育地带及砂土液化区域,这些地质问题极大地影响着晋中至太原城际铁路的前期勘测选线。本文从地质构造、地层岩性、浅层地震勘探等方面对穿越城际铁路的三条活动断裂的危险性进行了分析评价,以查明断裂错动对城际铁路的影响。结合前人对榆次地裂缝的研究成果,对城际铁路附近的地裂缝发育情况进行了调查验证,以查明榆次地裂缝对城际铁路的影响。通过在城际铁路车站及车辆段布置地质钻孔,进行标贯试验、剪切波速测试,以查明城际铁路沿线工程地质条件,对沿线车站及车辆段场地进行液化判定及场地类别判定。针对城际铁路沿线存在的上述地质问题,给出了相应的工程建议,对城际铁路前期勘测设计具有重要的指导意义。     

扎龙湿地藻类植物群落结构特征及水质初步评价

扎龙湿地是我国北方同纬度地区保留最完整、最原始、最开阔的湿地生态系统,地处中温带,属大陆性季风气候。为了探究其藻类植物群落的变化特征及其与水环境的关系,本文于2011年春、夏、秋季对扎龙湿地的藻类植物群落进行调查分析,共发现藻类植物349个分类单位(包括变种、变型),隶属于8门105属,藻类植物群落全年均以绿藻为主导,其组成呈绿藻-硅藻型。优势种中绿藻门主要以镰形纤维藻(Ankistrodesmus falcatus)和四尾栅藻(Scenedesmus quadricauda)为主,硅藻门以弯棒杆藻(Rhopalodia gibba)和隐头舟形藻(Navicula cryptocephala)为主,优势种组成具有明显的季节演替现象。藻类植物细胞密度呈现明显的单峰型,夏季最高,平均为10.74×10~4ind./L。湿地研究区域分为开阔型水域、小型封闭水域、湿地型水域和湖泊型水域四个生态类型,不同水域藻类植物群落结构特征明显不同。经聚类和多维尺度分析,将不同采样点的藻类植物群落分为四组,多样性指数表明湿地水体处于轻度污染或无污染状态。综合研究结果可以认为扎龙湿地的水体基本处于贫营养-中营养状态,只有极少数水域处于富营养状态。     

Experimental and theoretical study of a cylindrical oscillating water column device with a quadratic power take-off model

The wave power extraction by a cylindrical oscillating water column (OWC) device with a quadratic power take-off (PTO) model was studied experimentally and theoretically. In the experiment, a scaled model OWC was tested in a wave flume, with an orifice being used to simulate a quadratic PTO mechanism. In the theoretical analysis, the quadratic PTO model was linearized based on Lorenz's principle of equivalent work, which allows us to perform a frequency domain analysis using an eigen-function matching method. The effects of higher harmonic components and the spatial non-uniformity of the surface velocity inside the chamber were discussed. A semi-analytical model was proposed to understand the viscous loss affecting the measured capture length. Our treatment of the quadratic PTO model was validated by comparing quasi-linear theoretical capture length and the laboratory measurement. Our results also showed that the effects of spatial non-uniformity and viscous loss could be noticeable for shorter waves.     

Anthropogenic factors and habitat complexity influence biodiversity but wave exposure drives species turnover of a subtropical rocky inter‐tidal metacommunity

Coastal ecosystems are complex and species rich, but are vulnerable to degradation from a variety of anthropogenic activities. Nevertheless, information on inter‐tidal community composition in the Caribbean Basin and at other oceanic sites is lacking. Such information is essential to developing a more comprehensive understanding of rocky inter‐tidal systems and their responses to global change. The goals of this study were to determine the relative importance of environmental (wave power density, wave height), habitat (e.g. algal cover, slope, complexity of rock surfaces) and anthropogenic (distance to roads, population density) factors associated with the structure of local assemblages at multiple shore heights and the regional metacommunity of mobile invertebrates on oceanic rocky inter‐tidal habitats. Environmental characteristics associated with habitat complexity (algal cover, rock surface complexity) and human population density were most strongly associated with abundance and biodiversity of invertebrates. Species richness was positively correlated with surface complexity, but abundance was negatively correlated with both surface complexity and per cent algal cover. By contrast, abundance of invertebrates was positively correlated with human population density, and diversity was negatively correlated with human population density. Abundance of invertebrates was greatest in the mid inter‐tidal zone, whereas diversity was greatest in the lower inter‐tidal zone. Metacommunity structure was Gleasonian, but the gradient along which species turnover occurred was correlated with measures of wave exposure, rather than anthropogenic activity. Unlike in previous studies, mostly at mainland sites, human activity primarily altered dominance patterns of communities, while having relatively little effect on species richness or composition.     

Reefs at the edge: coral community structure around Rapa,southernmost French Polynesia

Rapa (27°36′ S, 144°20′ W) is a small (~40 km²) volcanic island isolated in the Southern Austral Archipelago, where direct anthropogenic stressors are extremely limited. Here, we present the results of the first quantitative survey of coral community structure across habitats and depths around the island. Despite its geographical isolation in the depauperate South Central Pacific, its small size and unfavourable environmental conditions (competition with macroalgae, low sea surface temperatures, reduced reef accretion), the diversity of scleractinian corals at Rapa is particularly high (112 species from 32 genera, including 37 species of Acropora) in comparison to other French Polynesian islands and subtropical Pacific locations. Our results indicate that the abundance (>100 colonies per 10 m² recorded at nine of the 17 sampling stations) and cover (>40% at four stations) of corals are relatively high for a marginal reef location. Strong spatial heterogeneity was found, with high variation in diversity, abundance, cover and community composition among stations. Variation in community composition was related to habitat types, with distinct assemblages among fringing reefs within bays, reef formations at bay entrances, and those on the submerged platform surrounding the island. On the platform, a depth gradient was detected, with generic richness, abundance and cover generally greater at deeper stations (18–20 m depth) compared with medium‐depth (10–12 m) and shallow (1–3 m) stations. A gradient was also recorded along bays, with increasing coral diversity and abundance from the bay heads to the bay entrances. The coral community at Rapa was characterized by the presence of several taxa not found in other French Polynesian archipelagos and the rarity of others that are common and abundant in the Society and the Tuamotu islands. Another distinctive feature of reef communities at Rapa is the high cover and dominance of macroalgae, particularly in the shallower parts of the surrounding platform, which probably explains the lower densities of coral colonies recorded there. These characteristics of the diversity and biogeographical composition of coral assemblages at Rapa provide considerable ecological grounds for its conservation.     

Limited differences among habitats in deep‐sea macro‐infaunal communities off New Zealand: implications for their vulnerability to anthropogenic disturbance

The spread of human activities into the deep sea may pose a high risk to benthic communities and affect ecosystem integrity. The deep sea is characterized by physical and biological heterogeneity and different habitat types are likely to differ in their vulnerability to anthropogenic impacts. However, across‐habitat comparisons are rare, and no comprehensive ecological risk assessment has yet been developed. To address this gap in our knowledge, we compared macro‐infaunal community structure in four habitats (slope, canyons, seamounts and methane seeps) at depths between 700 and 1500 m in the Hikurangi Margin and Bay of Plenty regions off New Zealand. The most striking contrast in community structure was between the two study regions, due to an order of magnitude difference in macro‐infaunal abundance that we believe was caused by differences in surface productivity and food availability at the sea bed. We found differences in structural and functional attributes of macro‐infaunal communities among some habitats in the Hikurangi Margin (slope, canyon and seep), but not in the Bay of Plenty. We posit that differences between canyon and slope communities on the Hikurangi Margin are due to enhanced food availability inside canyons compared with adjacent slope habitats. Seep communities were characterized by elevated abundance of both symbiont‐bearing and heterotrophic taxa, and were the most distinct, and variable, among the habitats that we considered on the Hikurangi Margin. Communities of seamounts were not distinct from slope or canyon communities on the Hikurangi Margin, probably reflecting similar environmental conditions in these habitats. The communities of deep‐sea canyon and seep habitats on the Hikurangi Margin were sufficiently dissimilar from each other and from slope habitats to warrant separate management consideration. By contrast, the low dissimilarity between communities of canyon and slope habitats in the Bay of Plenty suggests that habitat‐based management is not required in this region, for macro‐infauna at least. Although the two study regions share similar species pools, populations of the Hikurangi Margin region may be less vulnerable than the sparser populations of the Bay of Plenty due to the higher availability of potential colonizers and faster population growth. Thus regions, and habitats in some regions, should be subject to separate ecological risk assessment to help identify the key risks and consequences of human activities, and to inform options for reducing or mitigating impacts.