Ophiolites of the Central Asian Orogenic Belt:Geochemical and petrological characterization and tectonic settings

We present a compilation of published data(field,petrography,ages and geochemistry)from 73 ophiolitic complexes of the Central Asian Orogenic Belt.The ophiolitic complexes,ranging in age from Neoproterozoic to Triassic.have been geochemically classified as subduction-related and subductionunrelated categories applying recent,well-established discrimination diagrams.The subductionunrelated category is further subdivided into Mid-Ocean Ridge type(MOR),a common rift-drift stage and Plume type,and the subduction-related category is subdivided into Backarc(BA),Forearc(FA).Backarc to Forearc(BA-FA)and Volcanic Arc(VA)types.The four subduction-related types define highly different geochemical features,with the BA and FA types defining end members showing subduction influence of 10%-100%and 90%-100%subduction influence,respectively,and the two other types(BAFA and VA)define values between the two end members.The subduction-related category comprises79%of the examined ophiolites,of which the BA type ophiolites is by far the dominant group,followed by the BA-FA type,and with FA and VA types as subordinate groups.The Neoproterozoic and Ordovician complexes exhibit the highest,whereas those of Silurian age exhibit the lowest subduction-influence.Of the remaining 21%subduction-unrelated ophiolites,the MOR type dominates.Both the subductionrelated and subduction-unrelated types,in particular the latter,are commonly associated with alkaline basalts taken to represent ocean island magmatism.Harzburgite,dunite,gabbro and basalt are the common lithologies in all ophiolite types,whereas the BA-FA,FA and VA types generally contain intermediate to felsic rocks,and in the FA type boninites occur.The subduction-related ophiolites types generally show low metamorphic grade,whereas greenschist.amphibolite and blueschist grades occur in the subduction-unrelated and BA types.The highly different subduction contribution(from 0 to 100%in the MOR and FA,respectively),attest to variable dips of the subducting slab,as well as variable flux of subduction-related elements into the mantle above subducting slabs,from where the ophiolite magmas got their geochemical fingerprints.As most MOR ophiolites get subducted to the deep mantle,the subduction-related ophiolites have become a dominant ophiolitic type on Earth’s surface through all times supporting the idea about the early start of Plate Tectonics.     

秦岭地区成矿单元划分

成矿单元是成矿意义上的地质单元。笔者在继承全国矿产资源潜力评价项目发布的中国成矿单元Ⅰ级(成矿域)、Ⅱ级(成矿省)、Ⅲ级(成矿区带)最新划分方案的基础上,对秦岭地区5个Ⅲ级成矿单元(成矿区带)界线进行修正,以较明显的地层、构造和岩浆带特征及相关的主成矿作用为标志,划分15个Ⅳ级成矿单元(成矿亚区带),并概述各Ⅳ级成矿单元的地质矿产特征。     

河南省赋煤单元划分及控煤构造模式分析

河南省在大地构造位置上跨越华北板块、秦岭-大别造山带两个重要构造单元,是华北聚煤域的重要组成部分,由于特殊的构造位置,使得河南省煤田构造格局具有南北分带、东西分区的基本特征。结合地层（含煤地层）沉积特征和煤层赋存状况分析,将河南省赋煤单元划分为太行赋煤构造带、嵩箕赋煤构造带、崤熊赋煤构造带和秦大赋煤构造带,各赋煤构造带可进一步划分为2个赋煤构造亚带。根据区内构造发育特征,控煤构造模式可分为5大类17小类,其中滑动构造、逆冲叠瓦构造、伸展构造及同沉积构造4种控煤构造样式为河南省煤田典型控煤构造模式。     

事件地层单位的理论及实践——以中扬子台地震旦-寒武纪界线事件集群为例

根据事件地层学的发展现状,首次提出了一套系统的事件地层单位,由小到大大致上为事件面、事件层、事件带、事件组合和事件集群,并界定了各事件地层单位的含义和特征。在此基础上,将该套事件地层理论应用于中扬子台地震旦—寒武系界线事件地层的研究,并划分出2个事件面即生物灭绝事件面和海泛事件面,1个事件层即粘土事件层,4个事件带即海平面下降事件带、浊流事件带以及海平面上升事件带和缺氧事件带,3个事件组合即海平面下降—浊流事件组合、外星撞击—生物灭绝事件组合和海平面上升—缺氧事件组合,共同构成了1个事件集群即震旦—寒武系界线事件集群。事件地层含油性分析表明,研究区海平面上升—缺氧事件组合是有利的烃源岩,海平面下降—浊流事件组合具有一定的储集意义。     

Sharp‐based marine sandstone bodies in the Mulichinco Formation (Lower Cretaceous), Neuquén Basin,Argentina: remnants of transgressive offshore sand ridges

The interpretation of sharp‐based shallow‐marine sandstone bodies encased in offshore mudstones, particularly transgressive units, has been a subject of recent debate. This contribution provides a multiple‐dataset approach and new identification criteria which could help in the recognition of transgressive offshore sandstone bodies worldwide. This study integrates sedimentology, ichnology, taphonomy and palaeoecology of Mulichinco Formation strata in the central Neuquén Basin (Argentina) in order to describe and interpret sharp‐based sandstone bodies developed in ramp‐type marine settings. These bodies are sandwiched between finer‐grained siliciclastics beneath and thin carbonates above. The underlying sediments comprise progradational successions from offshore mudstones to offshore transition muddy sandstones, grading occasionally into lower shoreface sandstones. The surfaces capping the regressive siliciclastics are flat and regionally extensive, and are demarcated by skeletal concentrations and a Glossifungites suite; they are also marked by sandstone rip‐up clasts, with encrustations and borings on all sides. These surfaces are interpreted as composite discontinuities, cut during a relative sea‐level fall and remodelled during the initial transgression. The overlying transgressive sandstone bodies are 3 to 7 m thick, >4 km long and about three times longer than wide; they are composed of fine‐grained sandstones with little lateral change in grain size. Cross‐stratification and/or cross‐lamination are common, typically with smaller‐scale structures and finer grain size towards the top. Large‐scale, low‐angle (5° to 8°) inclined stratification is also common, dipping at ca 30° with respect to body elongation and dominant currents. These sandstone bodies are interpreted as offshore sand ridges, probably developed under the influence of tidal currents. Intense burrowing is typical at the top of each unit, suggesting an abandonment stage. Final deactivation favoured colonization by epibenthic‐dominated communities and the formation of skeletal‐rich limestones during the latest transgressive conditions. As partial reworking of pre‐existing ridges occurred during this stage, the Mulichinco sandstone bodies are considered the remnants of transgressive offshore sand units.     

Tectono-sedimentary evolution of the External Liguride units (Northern Apennines,Italy): insights in the pre-collisional history of a fossil ocean-continent transition zone

Abstract

In the Northern Apennines, the External Liguride (EL) units are interpreted as derived from the domain that joined the Ligure–Piemontese oceanic basin to the Adriatic plate continental margin. The EL units can be divided into two different groups according to the lithostratigraphic features of the basal complexes underlying the Upper Cretaceous–Lower Tertiary carbonate flysch (e.g. Helminthoid flysch). The first group includes the western successions characterized by Santonian–Campanian sedimentary melanges where slide blocks of lherzolitic mantle, gabbros, basalts, granulites, continental granitoids are represented. The second group is represented by the eastern successions where the Cenomanian–Campanian basal complexes mainly consist of sandstones and conglomerates where the mafic and ultramafic rocks are scarce or completely lacking. Their original substrate is represented by the Middle Triassic to Lower Cretaceous, mainly platform carbonate deposits, found as slices at the base of the eastern successions.

The stratigraphic features shown by the basal complexes allow the reconstruction of their source area that is assumed to be also representative for the pre-Upper Cretaceous setting. The proposed reconstruction suggests the occurrence in the EL domain of two distinct domains. The eastern domain was characterized by a thinned and faulted continental crust belonging to the Adriatic continental margin. The western domain was instead floored by subcontinental mantle associated with lower and upper continental crust, representing the ocean–continent transition. This setting is interpreted as the result of the opening of the Ligure–Piemontese oceanic basin by passive rifting, mainly developed by simple shear, asymmetric extension of the continental crust. © 2001 Éditions scientifiques et médicales Elsevier SAS     

Evaluation of digital elevation models for delineation of hydrological response units in a Himalayan watershed

This study reports results from evaluation of the quality of digital elevation model (DEM) from four sources viz. topographic map (1:50,000), Shuttle Radar Topographic Mission (SRTM) (90 m), optical stereo pair from ASTER (15 m) and CARTOSAT (2.5 m) and their use in derivation of hydrological response units (HRUs) in Sitla Rao watershed (North India). The HRUs were derived using water storage capacity and slope to produce surface runoff zones. The DEMs were evaluated on elevation accuracy and representation of morphometric features. The DEM derived from optical stereo pairs (ASTER and CARTOSAT) provided higher vertical accuracies than the SRTM and topographic map-based DEM. The SRTM with a coarse resolution of 90 m provided vertical accuracy but better morphometry compared to topographic map. The HRU maps derived from the fine resolution DEM (ASTER and CARTOSAT) were more detailed but did not provide much advantage for hydrological studies at the scale of Sitla Rao watershed (5800 ha).     

地震传感器的量值溯源方法

地震传感器在地震学研究与防震减灾领域应用广泛,数量众多,将其测量量值溯源到国际单位,能够保证测量结果准确和统一。文中对地震传感器测量量值进行量值溯源的必要性进行了叙述,说明了地震传感器的量值单位与国际标准单位的关系。对地震传感器量值溯源的途径以及与校准之间的联系进行了阐述。以力平衡加速度计为例对地震传感器的工作原理进行了说明。参照有关的国际标准,研究了基于正弦逼近法的地震传感器绝对法校准的技术要求,并给出了量值溯源框图,为建立地震传感器的量值溯源体系提供了技术依据。最后对低频振动校准的技术发展方向也作了阐述。     

切莫再用"滴定度"这一术语

化学分析中,表示标准溶液浓度的法定计量单位是"物质的量浓度","滴定度"作为标准溶液浓度的非法定计量单位目前仍在大量使用,本文通过讨论非法定计量单位"滴定度"与法定计量单位"物质的量浓度"之间的换算关系,指出"滴定度"的缺陷,结合对相关法律法规的学习理解,阐述了使用"滴定度"既不合理,更不合法,在计量单位法制化、标准化...