Caractérisation géométrique et cinématique des structures liées aux phases compressives de l'Éocène au Quaternaire inférieur en Tunisie : exemple de la Tunisie nord-orientale

During Eocene to Early Quaternary period, three compressive tectonic phases are recognized in Northeast Tunisia: a NW–SE to north–south phase during the Late Eocene, a N120-to-N140 phase in the Late Miocene, and a NW–SE to north–south phase in the Plio-Early Quaternary. The first Eocene phase has built NE–SW folds and remobilised east–west-to-N120 and NE–SW faults with a reverse component. The second Miocene phase is characterized by east–west-to-N120 faults with a normal component and NE–SW folds. The third phase occurred during the Plio-Early Quaternary has edified NE–SW folds associated with east–west-to-N120 dextral reverse strike-slip faults and NE–SW faults with a reverse component. To cite this article: H. Mzali, H. Zouari, C. R. Geoscience 338 (2006).     

北天山山前乌鲁木齐—乌苏地区的构造变形特征

北天山山前乌鲁木齐—乌苏地区的构造变形,是在挤压兼左行剪切作用下形成的.根据皱皱构造的排列组合、地层组成、变形强度及构造线等特征,将本区划分为五个构造带,分属于两个构造系.其中小渠子构造带的成因与博格达山活动相关,属于另一个构造系.其四余个构造带组成独立的玛纳斯构造系,叠加在燕山期构造之上.     

华北北部古生代大陆地壳增生过程中的岩浆作用与成矿效应

包括前寒武纪克拉通与显生宙造山带两大构造单元的华北北部,古生代时期板块构造体制下古亚洲洋的裂解-扩展-消亡与汇聚大陆边缘的俯冲-碰撞-伸展循环构成了其大陆地壳增生与再造演化的基本图景,并形成了一系列记录这些因果演变连续过程的岩浆侵入与喷发事件。这些物质记录无疑是研究汇聚大陆边缘壳-幔作用和物质交换、大陆地壳演化与大规模成矿作用耦合关系的绝佳窗口。本文在系统总结最近几年积累的年代学和岩石地球化学资料的基础上,以一些带有特定过程印记的标志性岩浆事件为纲领,表征这些古生代岩浆作用形成过程中的地球动力学演变,揭示其所记录的华北北部大陆地壳的多阶段增生与再造演化机制,并初步探讨了有利地球动力学过程制约下的岩浆行为引起的成矿物质聚集效应。     

胶东—苏北石榴石二辉橄榄岩形成条件及年代

在胶东—苏北地区,由石榴石二辉橄榄岩、尖晶石二辉橄榄岩、石榴石辉石岩、榴辉岩、斜辉辉橄岩和纯橄岩组成的杂岩成群和成带分布,延长590km。该岩带越过郯庐断裂带延伸至大别山,全长约1200km。岩带内石榴石二辉橄榄岩与尖晶石橄榄岩伴生,组成较大的岩块,并且与榴辉岩伴生,曾被作者确定为一种有层序的岩套。石榴石二辉橄榄岩的Sm-Nd同位素年龄为925±53Ma,矿物地质温度计和压力计表明其形成于115—160km深部,温度为800—1371℃。该石榴石二辉橄榄岩平衡温度和压力符合大陆地温线,而不同于中国东部沿海地区玄武岩中包体石榴石二辉橄榄岩,后者的平衡温度压力符合于大洋地温线。     

The Role of Data Processing and Uncertainty Management in Seismic Hazard Evaluations: Insights from Estimates in the Garfagnana–Lunigiana Area (Northern Italy)

Significantly different estimates of seismic hazard may result for the same site as aneffect of different methodological choices underlying the adopted procedures. In orderto explore this aspect, two approaches devoted to probabilistic seismic hazard assessment are considered for the evaluation of hazard in a seismic area in Northern Italy. In particular, results of a standard procedure are compared with those obtained by an innovative approach. Fundamental features of this last methodology are the extensive use of intensity data relative to seismic effects observed at the site of interest during past earthquakes and the basic role attributed to the parameterisation of uncertainty which affects the considered pieces ofinformation. The analysis indicates that the new approach supplies results significantlydifferent from those obtained from standard methodology and that these differences strongly depend on strategies adopted for data processing and for the management of uncertainties which affect input parameters.     

青藏高原北部查保马组火山岩的锆石SHRIMP U-Pb定年和地球化学特点及其成因意义

查保马组火山岩位于青藏高原北缘、可可西里东部,为一钾质C型埃达克岩,形成于新近纪中新世(Nt)时期,锆石SHRIMP U-Pb谐和年龄为13.2±0.6～18.3±1.1Ms.火山岩具有SiO2为59.48%～64.63%,富碱(Na2O k2O=7.52%～8.30%),高K2O(4.21%～4.62%),高MgO(0.76%～2.48%)和高Mg#值(0.26～0.51),以及钾玄岩系列的岩石地球化学特征.稀土总量非常高(∑REE=482.26×10-6～592.11×10-6),轻稀土强烈富集(LREE=466.47×10-6～571.69×10-6),重稀土显著亏损(HREE=14.00×10-6～20.43×10-6),Y含量(13.29×10-6～19.87×10-6,平均16.27×10-6)和Yb含量(1.11×10-6～1.66×10-6,平均1.37×10-6)普遍偏低.稀土元素配分模式呈轻稀土强烈富集的右倾斜型,(La/Yb)N值为61.02～91.67,负铕异常不明显(Eu/Eu*=0.74～0.86).Sr含量及Sr/Y比值高,分别为949×10-6～1497×10-6和54～108.微量元素比值蛛网图上强烈地表现出Nb、Ta、P、Ti、Y的负异常.查保马组(N1c)钾质C型埃达克岩是青藏高原北部在中新世时期因大陆地壳巨量增厚(75～80km)引起榴辉岩相的下地壳物质发生部分熔融的岩浆产物.     

Distribution and storage of sediment-associated heavy metals downstream of the remediated Rum Jungle Mine on the East Branch of the Finniss River,Northern Territory,Australia

Instream, overbank and cut riverbank exposures along the East Branch of the Finniss River downstream of Rum Jungle Mine, Northern Territory have been analysed for their total metal concentrations using instrumental neutron activation analysis (INAA). Concentration values for the < 62.5 μm and bulk sample fractions are compared to Australian sediment quality guidelines values (ANZECC/ARMCANZ, 2000). The results reveal that channel and overbank environments are contaminated with heavy metals, with many samples exceeding the low and high sediment guidelines values. The < 62.5 μm fraction is consistently more contaminated than bulk samples as are instream environments compared to adjacent overbank environments. Metal concentrations are strongly correlated to sediment pH and Fe values, suggesting that these variables are significant in controlling the spatial distribution of sediment-associated metals. The strong positive correlation between sediment-associated metals and Fe is probably related to the process of metal sequestration by Fe (and Mn) oxyhydroxides. The spatial distribution of sediment-associated metals downstream of the Rum Jungle Mine site does not display a simple distance–metal concentration decay pattern. It is suggested that the non-uniform spatial distribution of sediment-associated metals is a function of local, reach-scale variations in channel geometry and geomorphology, which control sediment storage and transfer patterns. In cut riverbank exposures the vertical of metals distribution is non-uniform and probably reflects differential metal mobility. Despite rehabilitation of the mine site in the 1980s, the elevated sediment-associated metal concentrations that remain within the East Branch of the Finniss River system are likely to render the system contaminated for the foreseeable future and limit the potential for the full recovery of aquatic and terrestrial flora and fauna.     

新疆东天山红石岗北铜镍矿化镁铁质岩体岩石成因及成矿潜力分析

红石岗北岩体是新疆有色地质勘查局704队于2014年新发现的,产于东天山康古尔—黄山韧性剪切带内。岩体地表主要岩性为闪长岩、角闪辉长岩和橄榄辉长岩,硫化物主要由磁黄铁矿、镍黄铁矿和黄铜矿组成。为准确评价岩体深部找矿潜力,本文在对该岩体开展系统的锆石U-Pb年代学、矿物晶体化学、岩石地球化学及Sr-Nd同位素研究基础上,结合其地球物理特征,将其与东天山已知典型铜镍矿床进行了系统对比研究。结果表明红石岗北岩体锆石U-Pb谐和年龄为276.1±5.4Ma,表明其形成于早二叠世。橄榄石Fo值为69.9~72.6,属贵橄榄石,Ni含量变化范围为101×10~(-6)~1326×10~(-6);单斜辉石主要为顽透辉石—透辉石;斜方辉石主要为古铜辉石。MgO与SiO_2、CaO和Al_2O_3之间呈明显的负相关性,与FeO~T呈明显的正相关性。在稀土元素球粒陨石标准化图解上,所有样品均呈轻稀土略富集的右倾型,相对富集大离子亲石元素(Cs、Sr、Ba),具有明显的Nb、Ta负异常。样品(~(87)Sr/~(86)Sr)_i=0.70342~0.70349,ε_(Nd)(t)=+7.51~+8.25(t=276Ma),Sr、Nd同位素模拟计算表明母岩浆上升过程中遭受了约5%的地壳物质混染。与东天山地区已知典型铜镍矿床相比,红石岗北岩体中橄榄石Fo值及主量元素含量明显偏低,且变化范围较小,但其形成时代、微量元素和Sr-Nd同位素特征和同化混染程度均相似,表明红石岗北岩体与黄山东、黄山等矿床的岩浆源区性质、构造背景、母岩浆成分及演化过程具有相似性,暗示红石岗北岩体深部应存在超镁铁质岩石。红石岗北岩体地表磁异常、剩余重力异常和视电阻率均与东天山已知铜镍矿床具有相似性,表明其深部可能存在赋矿的超镁铁质岩体。综上所述,我们认为红石岗北岩体深部具有较大的铜镍找矿潜力。     

西藏北冈底斯巴尔达地区岩浆作用的成因:地球化学、年代学及Sr-Nd-Hf同位素约束

前人对西藏冈底斯中北部白垩纪岩浆岩的岩石成因和地球动力学背景仍然存在很多解释。本文报道了位于北冈底斯(拉萨地块北部)东段巴尔达地区的岩浆岩锆石U-Pb定年、元素地球化学和Sr-Nd-Hf同位素数据,以对这一问题进行约束。巴尔达岩浆岩包括花岗闪长斑岩和安山玢岩。锆石U-Pb定年结果表明,巴尔达岩浆岩侵位于～114Ma,是北冈底斯早白垩世岩浆岩的典型代表之一。巴尔达岩浆岩两种岩石均为高钾钙碱性系列,其中花岗闪长斑岩的SiO2为64.45%～67.52%,全碱(K2O+Na2O)含量为6.23%～7.47%,铝饱和指数(A/CNK)为0.98～1.22,为兼具I型特点的S型花岗岩;安山玢岩SiO2为57.50%～62.15%,K2O含量为2.30%～3.60%,MgO含量为2.27%～4.40%。两种岩石均富集大离子亲石元素和Pb,亏损高场强元素和Ba等。与冈底斯成熟大陆地壳相比,巴尔达岩浆岩具有更高的εNd(t)值(-7.8～-6.8)和相对低的(87Sr/86Sr)t值(0.7094～0.7105),并且具有不均一的锆石εHf(t)值(-4.2～+3.3)和相对年轻的Hf模式年龄(639～975Ma)。锆石Hf同位素数据和锆石饱和温度(768～818℃)均显示幔源物质在巴尔达岩浆岩形成过程中发挥了重要作用。巴尔达岩浆岩可能是在南向俯冲的班公湖-怒江洋岩石圈断离背景下,由上涌的软流圈提供热量诱发岩石圈地幔熔融产生幔源基性熔体侵位到上部地壳,并引发周围酸性物质的熔融混合,混合过程中幔源组分的输入使S型熔体向I型熔体转化。     

塔中北斜坡走滑断裂断距对碳酸盐岩油气藏的影响

塔中北斜坡奥陶系碳酸盐岩的储层改造和油气分布,都受到走滑断裂的影响。由于区域内较大规模的走滑断裂均表现为北东向,水平断距较小,使得利用地震资料直接计算断距时存在着较大的困难。实际上,走滑断裂还普遍表现出北西向拉张特征,并沿断裂走向形成了宽度不同的拉分区域。断裂多沿北东向平直延伸,表明这些拉分区域的宽度和高度主要是受局部应力作用而形成的。这些拉分区域的宽度和高度在三维地震资料中较容易识别。根据断裂的拉分特征,提出通过计算拉分区域的宽度和高度间接识别走滑断裂的断距的方法。断距计算结果符合走滑断裂发育的地质规律,断距较大处是走滑断裂活动性较强的区域,同时也是储层改造作用强烈和油气分布较好的区域。