L'aspidolite fluorée : rôle des évaporites dans la genèse du rubis des marbres de Nangimali (Azad-Kashmir,Pakistan)

Ruby-bearing marbles from Nangimali, in the Azad-Kashmir, Pakistan, contain, besides phengite, different mica intergrowths: paragonite, phlogopite and aspidolite (sodium phlogopite). Both phlogopites, intimately linked and coexisting with paragonite, are fluorine rich, contrary to phengite and paragonite. F-enriched aspidolite is described for the first time. Phengite is either associated with phlogopite or could be isolated. The presence of aspidolite in the ruby-bearing marbles, together with other arguments such as salt solid inclusions and presence of anhydrite, suggest the implication of evaporites in the genesis of gem corundums. To cite this article: V. Garnier et al., C. R. Geoscience 336 (2004).     

Petrogenesis of the Late Cretaceous Tholeiitic Volcanism and Oceanic Island Arc Affinity of the Chagai Arc, Western Pakistan

The Late Cretaceous Chagai arc outcrops in western Pakistan, southern Afghanistan and eastern Iran. It is in the Tethyan convergence zone, formed by northward subduction of the Arabian oceanic plate beneath the Afghan block. The oldest unit of the Chagai arc is the Late Cretaceous Sinjrani Volcanic Group. This is composed of porphyritic lava flows and volcaniclastic rocks, and subordinate shale, sandstone, limestone and chert. The flows are fractionated low-K tholeiitic basalts, basaltic-andesites, and andesites. Relative enrichment in their LILE and depletion in HFSE, and negative Nb and Ta and positive K, Ba and Sr anomalies point to a subduction-related origin. Compared to MORB, the least fractionated Chagai basalts have low Na2O, Fe2O3T, CaO, Ti, Zr, Y and 87Sr/86Sr. Rather than an Andean setting, these results suggest derivation from a highly depleted mantle in an intraoceanic arc formed by Late Cretaceous convergence in the Ceno-Tethys. The segmented subduction zone formed between Gondwana and a collage of small continental blocks (Iran, Afghan, Karakoram, Lhasa and Burma) was accompanied by a chain of oceanic island arcs and suprasubduction ophiolites including Semail, Zagros, Chagai-Raskoh, Kandahar, Muslim Bagh, Waziristan and Kohistan-Ladakh, Nidar, Nagaland and Manipur. These complexes accreted to the southern margin of Eurasia in the Late Cretaceous.     

Lithospheric scale folding: numerical modelling and application to the Himalayan syntaxes

 We describe the eastern and western Himalayan syntaxes, which are large-scale antiforms situated at geodynamically similar locations and the metamorphic evolution of which is coeval in the India–Asia collisional history. To understand the mechanical plausibility of the structural interpretation, we present two-dimensional finite-element modelling of lithospheric folding. The models reveal the coeval development of adjacent synformal basins, analogous to the Peshawar and Kashmir basins on both sides of the western syntaxis. Similarities between geological data and calculated models indicate that lithospheric buckling is a basic response to large-scale continental shortening and an efficient mountain building process. Received: 26 November 1998 / Accepted: 27 November 1998     

A PETROLOGICAL OVERVIEW OF THE KOHISTAN MAGMATIC ARC, NW HIMALAYA, N. PAKISTAN

A PETROLOGICAL OVERVIEW OF THE KOHISTAN MAGMATIC ARC, NW HIMALAYA, N. PAKISTAN1　TahirkheliRAK ,MattauerM .ProustF ,etal.1979.In :GeodynamicsofPakistan[C].FarahA ,DeJongKA ,eds.GeolSurvPakistan ,Quetta ,1979.12 5～ 130 . 2　CowardMP ,WindleyBF ,BroughtonRD ,etal.In :CollisionTectonics[C]..CowardMP ,RiesAC ,eds.GeolSoc,London ,SpecPub ,1986 ,19:2 0 3～ 2 19. 3　BardJP ,MaluskiH ,MattePh ,etal.GeolBull ,PeshawarUniversity ,1980 ,13:87～ 93. …     

Observations of damage due to the Kashmir earthquake of October 8, 2005 and study of current seismic provisions for buildings in Pakistan

On October 8, 2005 an earthquake of magnitude 7.6 (M _w) struck the Kashmir region of Pakistan causing widespread damage to buildings and infrastructure. This paper summarizes field observations of building damage made by the Earthquake Engineering Field Investigation Team (EEFIT) after the event, where the performance of residential, commercial and government buildings was investigated. A study of the seismic design provisions currently in place in Pakistan is presented and compared with seismic provisions of EC8 (1998) and UBC (1997). Several problems are identified for the implementation of the Pakistan seismic code in its current form and recommendations are made for its improvement in order to be used for the reconstruction of affected areas.     

巴基斯坦7.8级地震前新疆独山子台跨断层位移变化初析

2005年10月8日巴基斯坦发生7.8级强烈地震, 震前新疆独山子台横向位移测量仪(GDW)记录到了较大变化。 根据独山子台记录到的断层形变资料, 结合区域内其他观测资料及区域地震活动进行了初步分析, 结果表明: ① 独山子-安集海断裂现今活动是以右旋逆冲运动为主, 其断层垂直向活动速率为0.12 mm/a, 水平向活动速率为0.25 mm/a。 巴基斯坦7.8级地震前横向位移观测结果显示断层右旋滑动速率增强, 其日平均速率达1.79 mm/d, 是正常日平均活动速率的12.8倍。 ② 独山子台MD系列数字化跨断层形变观测资料, 对独山子台300 km范围内的M_S≥5.0地震, 震前均有明显的地震前兆异常显示; 对1000 km范围内的M_S≥7.5地震, 亦有孕震过程显示。 ③ 巴基斯坦7.8级地震后约15分钟, 独山子台的MD系列数字化跨断层形变测量仪先后记录到了同震变化, 这也进一步说明该测量仪具有高精度、 宽量程、 抗干扰能力强的特点。     

Characteristics of major and trace elements in surface sediments of the Makran Accretionary Prism,Pakistan and their implications for natural gas hydrates

To accurately identify the natural gas hydrates (NGH) in the sea area of the Makran Accretionary Prism, Pakistan, this paper presents the testing and analysis of major and trace elements in sediment samples taken from two stations (S₂ and S₃) in the area by the China Geological Survey. As shown by testing results, all major elements are slightly different in content between the two stations except SiO₂ and CaO. This also applies to the trace elements that include Sr and Ba primarily and Cr, Ni and Zn secondarily. It can be concluded in this study that the tectonic setting of the Makran Accretionary Prism is dominated by oceanic island arc and that provenance of the Makran Accretionary Prism is dominated by felsic igneous provenance, which is at the initial weathering stage and mainly consists of granodiorite. Besides terrigenous detritus, there are sediments possibly originating from Makran-Bela Ophiolite from the northwestern part and Murray Ridge igneous rocks from the southeastern part. The V/Cr, Ni/Co, and V/(V+Ni) ratios indicate that sediments of the two stations are in an oxidation-suboxidation environment. However, the authors infer that the sedimentary environment of the sediments 3.0 m below the seafloor tends to be gradually transformed into a reduction environment by comparison with the Qiongdongnan Basin in the South China Sea where NGH has been discovered. The sediments in the Makran Accretionary Prism are rich in organic matter, with total organic carbon (TOC) content greater than 1%. According to comprehensive research, the organic matter in the sediments mainly originates from marine algae and has high TOC content, which is favorable for the formation of NGH.     

基于Landsat 8光学影像的巴基斯坦Awaran M_w7.7地震形变监测及参数反演研究

2013年9月24日巴基斯坦俾路支省(Balochistan)境内的阿瓦兰县(Awaran)发生了Mw7.7级地震.本文利用覆盖该地区的Landsat 8数据,基于影像配准的方法获取了该次地震的同震形变场,并运用地统计的方法对形变结果进行精度评定.针对传统四叉树算法中近场和远场中采样密度的不均匀性,以及噪音区域对数据降采样和反演结果收敛性的影响,本文提出了改进的四叉树算法对点的密度和形变梯度进行合理兼顾.最后利用光学影像获取的形变结果和数据的精度水平,基于Okada弹性半空间形变模型反演了该地震的震源参数和断层滑动分布.结果表明,地震断层北倾47°,滑动以左旋走滑为主,断层的西南部兼具少量的倾滑运动分量,断层滑动主要集中分布在断层面0~15km深度范围,最大滑动量达10m.反演获得的地震标量矩为4.68×1020 N·m,震级约为Mw7.75级.本文的研究结果可以为该地区的地壳应力变化研究和地震灾害评估提供依据,同时为Landsat 8光学影像应用于地震的形变研究提供参考.     

巴基斯坦穆斯林巴赫铬铁矿床成矿环境、 地质特征及控矿因素

巴基斯坦境内蛇绿岩广泛分布,且大多发育铬铁矿化。穆斯林巴赫铬铁矿床位于巴基斯坦中部,是新特提斯缝合带中大型豆荚状铬铁矿床之一,目前已经发现数百个矿体,储量超过4000 kt,是巴基斯坦境内最重要的铬铁矿产地。张洪瑞等（2013）总结了中部瓦济里斯坦-贝拉蛇绿岩带的地质特征和穆斯林巴赫铬铁矿床的产出特征,认为穆斯林巴赫铬铁矿床成因仍存在争议,其形成构造环境、控矿因素有待于进一步研究。本文论述穆斯林巴赫矿床的地质特征,通过矿床地球化学和铬尖晶石矿物化学等研究,结合我国典型的罗布莎豆荚状铬铁矿研究成果,分析了主要控矿因素,为巴基斯坦境内相同类型矿床的找矿勘查提供依据。