The crystalline complexes of Hamadan (Sanandaj–Sirjan zone, western Iran): metasedimentary Mesozoic sequences affected by Late Cretaceous tectono-metamorphic and plutonic events

The Hamadan area is characterised by various metamorphic rocks where the slates yielded Jurassic fossils. The entire column, representing the Mesozoic from at least the Jurassic to the Mid-Cretaceous, has been affected by tectono-metamorphic events and the emplacement of Late Cretaceous granitic rocks. A timing of these events is based on the ⁴⁰K–⁴⁰Ar ages carried mainly on separated amphiboles, biotites and muscovites, and interpreted as the ages of their isotopic closure. Results are ranging between 91 and 70 Ma. To cite this article: A. Baharifar et al., C. R. Geoscience 336 (2004).

Résumé

La région de Hamadan expose des roches métamorphiques dont les termes les moins transformés contiennent des fossiles jurassiques. Au cours du Crétacé supérieur, elle a été affectée par un événement tectono-métamorphique régional et elle a été le siège d'une activité plutonique. Les résultats des datations ⁴⁰K–⁴⁰Ar des amphiboles et des micas séparés des roches métamorphiques et plutoniques qui s'étagent entre 91 et 70 Ma montrent l'importance de ces événements et leur étalement au cours du Crétacé supérieur. Pour citer cet article : A. Baharifar et al., C. R. Geoscience 336 (2004).     

滇西金满脉状铜矿床成矿年龄讨论

对滇西兰坪盆地内金满脉状铜矿床成矿主阶段的石英样品进行了40Ar 39Ar快中子活化测定,谱线特征为马鞍型,其坪年龄为(58 05±0 54)Ma,最小视年龄为(56 76±0 81)Ma,等时线年龄为(54 30±0 15)Ma,三者均十分接近,说明所测石英样品的年龄可靠。而石英的流体包裹体Rb Sr同位素分析数据因线性关系不太好,导致等时线年龄(68±76)Ma误差大,因而仅具参考意义。砂岩及矿化砂页岩中磷灰石的裂变径迹年龄为58 7～61 7Ma,反映了兰坪盆地内一期构造热演化事件的发生时间,其与40Ar 39Ar分析的年龄基本一致,说明金满脉状铜矿床的形成时代相当于喜马拉雅早期。结合滇西大区域内铜及其他矿种的成矿主要集中在喜马拉雅早期这一现象,认为滇西在此时期必定存在着诱发某种大规模成矿作用的关键因素,并在区域内统一制约着矿床的形成。     

Devonian to Triassic Successions of the Changning-Menglian Belt, Western Yunnan, China

Phanerozoic strata are distributed in several north-south trending zones in the central part of the Changning-Menglian Belt. Four types of Devonian to Triassic stratigraphic successions can be identified: (1) elastics with limestone lenses in the mid-section, changing up-section into alternations of fine elastics and cherts; (2) elastics with chert intercalations and limestone lenses, and topped by Permian basic volcanics; (3) elastics-basic volcanics-carbonates-clastics; and (4) limestones, dolomitic limestones-dark gray thin-bedded limestones, argillaceous limestones, mudstones and siliceous mudstones. Devonian to Triassic cherts occur in different horizons and different zones from east to west. These cherts are usually transitional to their neighboring elastics. There is no continuous Devonian to Middle Triassic chert sequence in the central zone of the Changning-Menglian Belt as Liu et al. (1991,1993) reported. Volcanics and the overlying carbonates described by some workers as "seamount" sequences     

广东交通建设占用耕地的特征及其趋势预测

1990～2000年是广东省交通建设大发展时期和耕地减少的高峰期。通过对这一时段的分析,发现交通建设占用耕地已成为广东省非农建设占用耕地的主要成分和耕地减少的一大因素。在空间分布特征上,利用土地扩展集中指数和扩展强度两个指标进行计算分析,结果是广东省交通占用耕地分布区域不均匀,扩展区域主要集中于清远、广州等市;而占用最为严重的地区是深圳和汕头两市。根据广东交通发展的需要,预测到2030年,全省由于交通建设还需占用土地118295.26hm2。     

Facies and basin architecture of the Late Carboniferous Salvan-Dorénaz continental basin (Western Alps, Switzerland/France)

The Salvan‐Dorénaz Basin formed during the Late Palaeozoic within the Aiguilles‐Rouges crystalline basement (Western Alps) as an asymmetric, intramontane graben elongated in a NE–SW direction and bounded by active faults. At least 1700 m of fluvial, alluvial fan and volcanic deposits provide evidence for a strong tectonic influence on deposition with long‐term, average subsidence rates of > 0·2 mm yr^?1. The early basin fill was associated with coarse‐grained alluvial fans that were dominated by braided channels (unit I). These issued from the south‐western margin of the basin. The fans then retreated to a marginal position and were overlain by muddy floodplain deposits of an anastomosed fluvial system (unit II) that drained towards the NE. Deposition of thick muds resulted from a reduction in the axial fluvial gradient caused by accelerated tectonic subsidence. Overlying sand‐rich meandering river deposits (unit III) document a reversal in the drainage direction from the NE to the SW caused by synsedimentary tectonism, reflecting large‐scale topographic reorganization in this part of the Variscides with subsidence now preferentially in the W and SW and uplift in the E and NE. Coarse‐grained alluvial fan deposits (unit IV) repeatedly prograded into, and retreated from, the basin as documented by coarsening‐upward cycles tens of metres thick reflecting smaller scale tectonic cycles. Volcanism was active throughout the evolution of the basin, and U/Pb isotopic dating of the volcanic deposits restricts the time of basin development to the Late Carboniferous (308–295 Ma). ⁴⁰Ar/³⁹Ar ages of detrital white mica indicate rapid tectonic movements and exhumation of the nearby basement. In unit I, youngest ages are close to that of the host sediment, but the age spectrum is wide. In unit II, high subsidence and/or sedimentation rates coincide with very narrow age spectra, indicating small, homogeneous catchment areas. In unit III, age spectra became wider again and indicate growing catchment areas.     

Thermobaric structure of a traverse across western Dabieshan: implications for collision tectonics between the Sino-Korean and Yangtze cratons

As the best preserved high‐ and ultrahigh‐pressure (HP and UHP) metamorphic terrane in the Qinling‐Dabieshan‐Sulu orogen, western Dabieshan is divided into six lithotectonic units along a traverse across the orogen, i.e. from north to south, the Nanwan, Balifan, Huwan, Xinxian, Hong'an and Mulanshan units. In this terrane five eclogite‐bearing zones (I–V) are developed. The garnet and clinopyroxene in eclogites from these zones exhibit chemical zoning, suggesting that the rims record general peak temperature and pressure. Thermobarometric study indicates that the peak P–T conditions of eclogite are 550–570°C and 21 kbar for Zone I, 470–500°C and 14–17 kbar for Zone II, 620–670°C and 26–29 kbar for Zone III, 530–560°C and 20–22 kbar for Zone IV, and 490–510°C and 19–20 kbar for Zone V. The symmetrical thermobaric pattern, in conjunction with structural and geochronological data, demonstrates that the Huwan and Hong'an units belong to the same HP slice overlying the UHP slice. This pattern, together with the Mulanshan LT/HP blueschist–greenschist belt in the south, roughly constitutes a ‘normal’ metamorphic zonation. However, clear metamorphic gaps occur between different slices. It is inferred that the LT/HP, HP and UHP slices were broken up from the downgoing slab during subduction and reached different depths along different geothermal gradients. The successive subduction of underlying slices leads to a nearly concomitant uplift of overlying slices, whereas exhumation of the deepest UHP slice was effected by underthrusting of the lower crust of the Yangtze craton.     

西部山区交通线路的泥石流灾害及减灾对策

全面总结了西部山区交通线路的泥石流问题,探讨了交通线路泥石流的特点、分布及其危害现状。在掌握了泥石流特征的基础上,进一步探讨了既有线路、在建线路和拟建线路所采取的不同防灾减灾对策,并提出了山区交通线路泥石流防灾工程建设应该进一步深入研究的问题,为西部山区线路建设中的防灾、减灾工作指明了方向。     

An Early Holocene Palaeoenvironmental Record from Two Mile Lake,South‐Western Australia

This research is part of an integrated study investigating the Cainozoic development of the Proteaceae in south‐western Australia and this study documents the pollen and geochemical record from Two Mile Lake, south‐western Australia, to determine the environment of this area during the late Quaternary. The vegetation record from Two Mile Lake is consistently dominated by Casuarina and Chenopodiaceae species, with a variety of other pollen types. Geochemical analysis indicates that the environment was low in magnetic minerals, organics, carbonates, nitrogen and phosphorus. Geochemical and palynological results indicate that the vegetation and environment of south‐western Australia were unresponsive and/or unaffected by climatic changes of the early Holocene. The sedimentation rates are unclear and represent an important constraint to this study. It is possible that there was either rapid sedimentation in this area during the early Holocene and/or a lack of environmental change as a result of complex environmental processes.     

四川盆地西部侏罗纪沉积相及油气分布

四川盆地西部侏罗纪为内陆盆地，除其北缘早侏罗世有湖沼相外，主要为河流相与湖泊相，邻龙门山区发育冲积扇，其余地区发育冲积平原相和泛滥平原相。依据湖泊积水状况，将湖泊相细分为时令湖相、间歇湖相和长年湖相。印支期，甘孜-阿坝造山带形成，四川盆地由湿热气候演变为干燥、炎热气候；并使早侏罗世-中侏罗世早期成为长年湖泊环境。受燕山早中期构造运动影响，河流相、时令湖相与间歇湖相发育。长年湖相形成了侏罗系重要的生储油层系。河流相的粗碎屑岩成为储层，时令湖相与间歇湖相的泥质岩成为盖层，组成了侏罗系中上统多个储盖组合。     

Preliminary analysis on characteristics of coseismic deformation associated with M_S=8.1 western Kunlunshan Pass earthquake in 2001

IntroductionOnNovember14,2001,aMS=8.1earthquakeoccurredonthewestofKunlunshanPassintheborderareaofQinghaiandXinjiang,whichwasthestrongestearthquakeinChinesemainlandsincetheMS=8.0earthquakeoccurredinDangxiongdistrictofXizangAutonomousRegiononNovember18,1951.TheearthquakeoccurredontheEasternKunlunTectonicZone,whichwasapalaeoplatejunctionzoneinsideTibetanPlateau.ItdividedTibetanPlateauintothesouthandnorthparts.ThezoneplayedaveryimportantroleinTibetanPlateausdeformationprocessanddynamicev…