辽东湾周边河流沉积物碎屑矿物组成及其物源意义

对辽东湾周边七条河流下游段河漫滩沉积物的碎屑矿物进行了鉴定,分析了轻重矿物组分的差异、流域基岩类型和沉积物粒度对碎屑矿物组成的影响。轻矿物组成以石英和长石占绝对优势。由于辽东湾西侧河流（六股河、小凌河和大凌河）和东侧河流（双台子河、大辽河、复州河）位于两个构造块体之上,不同的基岩类型导致重矿物组合差别很大。湾西河流普通角闪石含量低、金属矿物含量高,湾东河流则相反,这两种组分能有效区分辽东湾东西两侧的河流,同时也可将滦河与上述河流区分开。石榴子石和普通辉石含量特征可区分湾西三条河流,特征为大凌河前者含量高,小凌河后者含量高,六股河两者含量都很低。绿帘石和阳起石的含量在湾东河流沉积物中差别较大,特征为双台子河前者含量高,大辽河后者含量高,复州河两者含量都很低。七条河流片状矿物和碳酸盐矿物含量低的特征有别于黄河沉积物。     

Non-combustible suspended matter in surface waters off eastern Asia*

A total of about 1100 well-distributed samples of suspended matter in surface waters off the length of eastern Asia are available. From these samples, 180 were selected for detailed examination of the non-combustible fraction using optical and electron microscopy along with computer methods of particle measurement and counting. The results showed that, generally, all major components of the suspended matter are most abundant in the nearshore belt (combustible fraction, mineral grains of silt size, skeletal debris, and clay minerals), the result of mechanical transport of detrital sediment and chemical transport of nutrients from the land. Mineral grains of silt size average about 2%, skeletal debris plus clay minerals—23%, and combustible organic matter—75% of total sample weights, but the last two categories vary over a wide range depending upon geographical positions of the samples. Most evident is an oceanward decrease in percentage and concentration of the total noncombustible fraction and an oceanward increase in median diameter of the mineral grains.     

Eastern Ancient Terrane of the North China Craton

Based on the spatial distribution of ancient rocks and zircons, three ancient terranes older than ca. 2.6 Ga have recently been identified in the North China Craton, namely the Eastern, Southern, and Central Ancient Terranes. The Eastern Ancient Terrane is the best studied and understood of the three ancient terranes. It has a long geological history back to ca. 3.8 Ga ago and includes the areas of Anshan-Benxi, eastern Hebei, eastern Shandong and western Shandong. In Anshan-Benxi, several different types of 3.8 Ga rocks were discovered together with 3.1-3.7 Ga rocks, whereas 2.9-3.0 Ga K-rich granites and 2.5 Ga syenogranite occur on larger scales. In eastern Hebei, 3.0-3.4 Ga rocks and older detrital and xenocrystic zircons were identified. In eastern Shandong, there are a large volumes of 2.7 Ga and 2.9 Ga rocks. In western Shandong, early Neoarchean(2.6-2.7 Ga) intrusive and supracrustal rocks are widely distributed. Whole-rock Nd and zircon Hf isotope data suggest that both mantle additions and crustal recycling played important roles within the Eastern Ancient Terrane during almost every tectono-magmatic event. Most BIFs in the North China Craton are late Neoarchean in age and are distributed on continental crust along the western margin of the Eastern Ancient Terrane, probably suggesting that a stable environment was one of the key factors for the formation of large-scale BIFs.     

酒西盆地中新生代碎屑组分特征及指示意义

通过岩石碎屑成分分析,研究酒西盆地砂砾岩储集层沉积碎屑成分特征对物源属性、盆-山格局演化及油气成藏特征的指示意义。研究表明,酒西盆地下白垩统下沟组砂岩成分成熟度低,物源构造属性以再旋回造山带和部分岩浆弧为特征,物源岩石类型主要为中酸性岩浆岩和变质岩(沉积岩碎屑极少),岩石成分及其组合显示盆地东、西部的物源差异明显;古近系白杨河组在岩石成分、岩屑组成上与下白垩统下沟组砂岩有较大不同,显示物源属性的明显改变。物源属性的改变在一定程度上反映构造格局分异、盆-山格局的演变历程,控制了酒西盆地内油气富集和晚期成藏特征。碎屑成分特征在一定程度上决定了储集层的储集空间类型及裂缝发育规律,值得进一步深入研究。     

Tectonic delamination of the Pacific lithosphere

This paper presents data on the structure of some segments of the Pacific lithosphere that bear signs of its tectonic delamination. This tectonic phenomenon is inherent not only to the young slow-spreading Atlantic and Indian oceans but also to the ancient fast-spreading Pacific Ocean, where tectonic delamination of the lithosphere has been established beneath seamounts, in fault zones and between them, immediately beneath the East Pacific Rise, within small separate plates in the eastern part of the ocean, in the Northwest Pacific Basin, and beneath marginal swells that border deep trenches along the western periphery of the Pacific.     

Early Carboniferous paleogeography of the northern Verkhoyansk passive margin as derived from U–Pb dating of detrital zircons: role of erosion products of the Central Asian and Taimyr–Severnaya Zemlya fold belts

The first U–Pb dating of detrital zircons from the Lower Carboniferous sandstones in the frontal part of the northern Verkhoyansk fold-and-thrust belt showed that detrital zircon age spectra for the Lower Visean (Krestyakh Formation) and the Upper Visean–Serpukhovian (Tiksi Formation) rocks are quite different. The Early Visean sandstones contain up to 95% detrital zircons of Precambrian age, while those of Late Visean–Serpukhovian age, only 55%. The shape of age distribution plots of Precambrian zircons for both samples is similar, indicating that reworking of terrigenous sediments of the Krestyakh Formation or the same sources dominated in Early Visean time (crystalline basement of the craton, eroded Meso- and Neoproterozoic sedimentary complexes, and igneous rocks of Central Taimyr) contributed significantly to the accumulation of the Late Visean–Serpukhovian deposits. In the rocks of the Tiksi Formation, 45% of detrital zircons are of Paleozoic age, while 24% are Early Paleozoic, with prevailing Cambrian and Ordovician ages. Possible provenance areas with abundant igneous rocks of this age could be the Taimyr–Severnaya Zemlya and Central Asian fold belts extending along the northern, western or southwestern margins of the Siberia. The presence of Middle–Late Devonian zircons is thought to be related to the erosion of granitoids of the Yenisei Ridge and the Altai–Sayan region. Early Carboniferous detrital zircons probably had a provenance in igneous rocks of the Taimyr–Severnaya Zemlya fold belt, on the assumption that collision between the Kara block and the northern margin of the Siberian continent had already occurred by that time. In Early Visean time, sedimentation occurred in small deltaic fans, likely along steep fault scarps that formed as a result of Middle Paleozoic (Devonian–Carboniferous) rifting. The clastic material came from small rivers that eroded the nearby area. Late Visean–Serpukhovian time was marked by a sharp increase in the amount of clastic material and by the appearance of detrital zircons coming from new provenance regions, such as fold belts extending along the northern and southwestern margins of the Siberian continent. A large river system, which was able to transport clastic material over large distances to deposit it in submarine fans on the northern Verkhoyansk passive continental margin, had already existed by that time.     

Origin and significance of high nickel and chromium concentrations in Pliocene lignite of the Kosovo Basin, Serbia

Trace element data from 59 Pliocene lignite cores from the lignite field in the Kosovo Basin, southern Serbia, show localized enrichment of Ni and Cr (33–304 ppm and 8–176 ppm, respectively, whole-coal basis). Concentrations of both elements decrease from the western and southern boundaries of the lignite field. Low-temperature ash and polished coal pellets of selected bench and whole-coal samples were analyzed by X-ray diffraction and scanning electron microscopy with energy-dispersive X-ray analyses. These analyses show that most of the Ni and Cr are incorporated in detrital and, to a lesser degree, in authigenic minerals. The Ni- and Cr-bearing detrital minerals include oxides, chromites, serpentine-group minerals and rare mixed-layer clays. Possible authigenic minerals include Ni---Fe sulfates and sulfides. Analyses of three lignite samples by a supercritical fluid extraction technique indicate that some (1–11%) of the Ni is organically bound. Ni- and Cr-bearing oxides, mixed-layer clays, chromites and serpentine-group minerals were also identified in weathered and fresh samples of laterite developed on serpentinized Paleozoic peridotite at the nearby Glavica and ikatovo Ni mines. These mines are located along the western and northwestern rim, respectively, of the Kosovo Basin, where Ni contents are highest. The detrital Ni- and Cr-bearing minerals identified in lignite samples from the western part of the Kosovo Basin may have been transported into the paleoswamp by rivers that drained the two Paleocene laterites. Some Ni may have been transported directly into the paleoswamp in solution or, alternatively, Ni may have been leached from detrital minerals by acidic peat water and adsorbed onto organic matter and included into authigenic mineral phases. No minable source of Ni and Cr is known in the southern part of the lignite field; however, the mineral and chemical data from the lignite and associated rocks suggest that such a source area may exist.     

U-Pb SHRIMP ages of detrital zircons from Hiriyur Formation in Chitradurga greenstone belt and its implication to the Neoarchean evolution of Dharwar craton,south India

We report newly obtained U-Pb SHRIMP ages of detrital zircons from metagreywackes in the Hiriyur Formation (Chitradurga Group, Dharwar Supergroup) from the central eastern part of the Chitradurga greenstone belt. U-Pb analyses yield three major Neoarchean age populations ranging from 2.70–2.54 Ga with some minor age population of Mesoarchean. The maximum age of deposition is constrained by the youngest detrital zircon population at 2546 Ma. This is the first report of the occurrence of supracrustal rocks less than 2.58 Ga in the central part of Chitradurga greenstone belt. Close evaluation of detrital ages with the published ages of surrounding igneous rocks suggest that the youngest detrital zircons might be derived from rocks of the Eastern Dharwar craton and the inferred docking of the western and eastern Dharwar cratons happened prior to the deposition of the Hiriyur Formation. The Chitradurga shear zone, dividing the Dharwar craton into western and eastern blocks, probably developed after the deposition. Furthermore, the lower intercept is interpreted as evidence for the Pan-African overprints in the study area.     

http://www.sciencedirect.com/science/article/pii/S1674987115001280

The East African Rift system(EARS)provides a unique system with the juxtaposition of two contrasting yet simultaneously formed rift branches,the eastern,magma-rich,and the western,magma-poor,on either sides of the old thick Tanzanian craton embedded in a younger lithosphere.Data on the pre-rift,syn-rift and post-rift far-field volcanic and tectonic activity show that the EARS formed in the context of the interaction between a deep mantle plume and a horizontally and vertically heterogeneous lithosphere under far-field tectonic extension.We bring quantitative insights into this evolution by implementing high-resolution 3D thermo-mechanical numerical deformation models of a lithosphere of realistic rheology.The models focus on the central part of the EARS.We explore scenarios of plumelithosphere interaction with plumes of various size and initial position rising beneath a tectonically pre-stretched lithosphere.We test the impact of the inherited rheological discontinuities(suture zones)along the craton borders,of the rheological structure,of lithosphere plate thickness variations,and of physical and mechanical contrasts between the craton and the embedding lithosphere.Our experiments indicate that the ascending plume material is deflected by the cratonic keel and preferentially channeled along one of its sides,leading to the formation of a large rift zone along the eastern side of the craton,with significant magmatic activity and substantial melt amount derived from the mantle plume material.We show that the observed asymmetry of the central EARS,with coeval amagmatic(western)and magmatic(eastern)branches,can be explained by the splitting of warm material rising from a broad plume head whose initial position is slightly shifted to the eastern side of the craton.In that case,neither a mechanical weakness of the contact between the craton and the embedding lithosphere nor the presence of second plume are required to produce simulations that match observations.This result reconciles the passive and active rift models and demonstrates the possibility of development of both magmatic and amagmatic rifts in identical geotectonic environments.     

Authigenic transition elements in Pacific pelagic clays

The concentrations of Sc, Ti, Fe, Mn, Co, Ni, Cu, La, Th and U have been measured in several Pacific pelagic clays having widely different accumulation rates, 0.4–9.0 mm/10³ yr. The authigenic fractions and deposition rates of these elements have been estimated from the measured concentrations using various models. The results show that in Pacific clays about 90% Mn, 80% Co and Ni and 50% Cu are authigenic whereas the major fraction (?90%) of Sc, Ti, Fe, La, Th and U are of detrital origin.Anticorrelation between the clay accumulation rates and the concentrations of Mn, Co, Ni and Cu is observed. This suggests a uniform authigenic deposition of these elements superimposed on varying amounts of detrital materials. The concentrations of Sc, Ti and Th are almost independent of sedimentation rates, indicating that their authigenic deposition is small compared to their detrital contribution.Comparison of the authigenic deposition and river input rates shows that Mn, Co and Ni are accumulating in excess of their supply by factors of 2–10, whereas the converse is true for Cu and U. Additional sources to account for the budgetary discrepancies of Mn, Co and Ni are discussed, with particular reference to in situ leaching of detrital phases transported to the oceans via rivers.     

A preliminary inventory of periglacial landforms in the Andes of La Rioja and San Juan, Argentina, at about 28°S

The Cerro El Potro and nearby mountain chains belong to the Andean Frontal Cordillera (28°S). Cerro El Potro is a glaciated mountain that is surrounded by huge valleys both on its Chilean and Argentinean flanks. Its southern limit is a steep rock wall towards the trough-shaped Río Blanco valley in Argentina, with a wide valley floor. The other sides of the mountain are characterized by well-developed Pleistocene cirques. The predominant landforms in this area have been shaped in a periglacial environment superimposed on an earlier glacial landscape. It is a region with abundant rock glaciers, a noteworthy rock glacier zone, but nevertheless, it is a relatively little known area in South America. In this preliminary inventory, the landforms surveyed were mainly gravitational in origin, including valley rock glaciers, talus rock glaciers, debris cones, landforms originated by solifluction processes and talus detrital sheets on mountain sides. Ancient moraine deposits have been found on the sides of the main rivers that cross the area form west to east, including the Blanco and Bermejo rivers. Present day fluvial activity is limited, and restricted to these main rivers. In this area of glacial valleys and small cirques, there are small lakes and other water bodies, grass covered patches and zones with high mountain vegetation. Present day glacial activity is restricted to the highest part of the area, above 5500 m a.s.l., mainly in the Cerro El Potro (5879 m) where a permanent ice field exists, as well as small mountain glaciers.     

彰武盆地东、西物源—沉积体系差异:来自沙海组(K_1s)岩芯的证据

利用钻井取芯的岩石组成、碎屑粒度特征及岩性-岩相的差异分析,研究彰武盆地下白垩统沙海组东、西物源物质组成和沉积体系特征。结果表明,东部物源火山碎屑占45%～85%,其中原生火山碎屑占70%,风化火山碎屑占30%,空落碎屑占杂基的10%～25%;西部物源火山碎屑占25%,风化碎屑占75%,空落碎屑占杂基5%～10%。CVL图解显示,东部物源的火山岩屑(L)和玻屑(V)含量均高于西部物源,而晶屑(C)含量低于西部物源。东部为受大型断裂控制的火山斜坡-扇三角洲环境。西部为缓坡区,发育辨状河三角洲环境,接受部分来自于东部的空落火山物质。Dickson图解显示,物源均来自火山弧和造山带物源区。区域早白垩世地壳拉张、火山喷发和同期盆地沉积,是形成不同物源-沉积体系的主要原因。     

REE geochemistry of the recent playa sediments from the Thar Desert, India: An implication to playa sediment provenance

The playas (saline lakes) situated in the Thar Desert, north-west India, provide prominent examples of alkaline brine and varying assemblages of detrital and evaporite mineralogy. The eastern margin of the desert is relatively semi-arid, whereas the central to western region is arid to hyper-arid in nature. Rare earth elements (REEs) systematics in the sediments of nine different playas of the Thar Desert were studied to understand the provenance of the sediments and the intensity of chemical weathering in the region. Based on the REE patterns, fractionation of light REE (LREE) (La/Sm)_N and heavy REE (HREE) (Gd/Yb)_N, and Eu anomaly (Eu/Eu*), the upper continental crust normalised playa sediments are divided into two different groups. The eastern margin playa sediments show homogeneous REE contents, relatively positive Eu anomaly and depleted HREE values, whereas the western arid core playa sediments have highly variable REE contents, relatively negative Eu anomaly and similarly fractioned LREE and HREE patterns. The dissimilarity in the degree of HREE fractionations both in the eastern and western playa sediments is attributed to the differential distribution of minerals, depending upon their resistance to chemical weathering. It is believed that the relatively higher abundance of REE bearing heavy minerals and the presence of higher amounts of evaporites influence the large variation of REE distribution and enriched HREE in the western playa sediments. Apart from the relatively higher abundance of heavy minerals, the presence of rock fragments of variable petrographic character and roundness mirror the lower rock–water interaction in the arid western region. The presence of well-rounded metamorphic rock fragments and minerals, sourced from the eastern margin Aravalli mountains, indicates that the playas of the entire desert get the detrital and dissolved material mainly from the Aravalli mountains. Additionally, the western playas receive sediments from their surrounding Proterozoic and Mesozoic formations. This interpretation is supported by the presence of angular rock fragments of basalt, rhyolite and limestone in the western playas.     

晚中新世以来孟加拉-尼科巴扇跷跷板式沉积转换及其源-汇成因机制

利用沉积转换事件再造关键变革期的构造活动和气候演变是源-汇系统研究的新动向和切入点。新生代以来,印度大陆与亚洲大陆的汇聚隆升以及喜马拉雅-青藏高原的剥蚀、向孟加拉湾的物质输入,形成了当今世界上最大的源-汇系统(喜马拉雅-孟加拉湾源-汇系统)。利用3D地震数据和IODP 354与362航次获取的碎屑锆石数据揭示了晚中新世以来孟加拉-尼科巴扇沉积转换事件及其源-汇成因机制。研究认为尼科巴扇和孟加拉扇经历了此消彼长的沉积建造过程:尼科巴扇经历了“晚中新世快速进积→上新世缓慢建造→第四纪相对静止”的建造过程;而孟加拉扇经历了“晚中新世相对静止→上新世缓慢建造→第四纪快速进积”的沉积建造过程。喜马拉雅-孟加拉湾源-汇系统碎屑锆石年龄核密度统计结果显示:晚中新世以来,指示古布拉马普特拉河迁移演化路径的60~0 Ma碎屑锆石在若开-尼科巴扇呈现出逐渐减少的变化趋势,而在孟加拉扇呈现出逐渐增多的变化趋势。这一碎屑锆石年龄核密度变化特征表明:(1)在晚中新世,古布拉马普特拉河主沉积物分散路径靠近孟加拉湾东部一侧发育且大量碎屑颗粒向尼科巴扇搬运分散,形成“快速进积的尼科巴扇和相对静止的孟加拉扇”;(2)在上新世初,青藏高原隆升所诱发的西隆高原抬升使古布拉马普特拉河向西迁移分流,在古西隆高原北缘Mikir山附近分流为东西两支,东支向尼科巴扇搬运分散的碎屑颗粒开始减少,而西支向孟加拉扇搬运分散的碎屑颗粒开始增多,形成“以缓慢建造为演化特征的尼科巴-孟加拉扇”;(3)在第四纪初,印度板块-亚洲板块最强碰撞造成青藏高原最强隆升并达到最大海拔高度,古布拉马普特拉河东支袭夺废弃,向尼科巴扇卸载的沉积物相应显著减少,而古布拉马普特拉河西支与恒河并流后向孟加拉扇卸载的沉积物亦相应显著增加,形成“相对静止的尼科巴扇和快速进积的孟加拉扇”。由此可见,尼科巴-孟加拉扇“此消彼长的跷跷板式沉积转换事件”是古布拉马普特拉河沉积物分散路径迁移演化的源-汇响应;其在上新世-第四纪之交发生了一起最为显著的沉积转换事件,其是上新世晚期印度板块-亚洲板块碰撞的源-汇响应。     

天山两侧山前新生代构造变形特征及其成因刍议

摘要：天山两侧山前新生代构造变形强烈,是研究盆山耦合动力学机制的理想场所。文中在综合分析前人资料基础上,结合作者的野外观测和分析,综述了天山两侧盆山转换部位不同段的新生代构造变形特征,并进行对比分析。结果显示,新生代构造变形在天山南北山前相似性和差异性共存:变形由山体向盆地扩展,时间逐渐变新;但是南侧比北侧变形起始时间早,地壳缩短量和缩短率大。在东西方向上新生代构造变形也存在明显的分段相似性特征,整体上显示出斜方对称的变形图像:东天山博格达山前为基底式逆冲推覆,南侧为走滑变形;中天山南北两侧为多排子的褶皱 逆冲推覆构造,西天山南侧也为基底式的逆冲推覆,北侧为走滑变形。综合前人研究,认为印度和亚洲大陆的碰撞及其随后陆陆汇聚作用的远程效应,是形成天山两侧山前新生代构造变形在南北方向上相似性和差异性的主要原因;而天山山体内部先存的相对刚性地块和大型断裂,则导致了新生代构造变形的东西向分段差异性和斜方对称的特征。     

Sedimentary conditions and deposits of Akimiski Strait,James Bay,Canada

Akimiski Strait is a wide (17–20 km), shallow, emergent (0.70 cm per century) waterway in James Bay. It is localized in a saddle of a Paleozoic reef track, which has been enhanced and molded by Pleistocene glaciers. Drumlinoid ridges form the till cores of shoals and islets of the strait. The boundary conditions of the strait change throughout the year, as it is covered by ice for six months. During spring break-up the strait remains clogged with ice at its northern approach for several weeks, and acts as a large tidal inlet. It is during this period that most of the fluvial sediments are carried to sea. Other sediments are obtained by erosion of the Pleistocene tills and Holocene subtidal clays and silts exposed in nearshore areas. Resuspension of nearshore material is achieved through the action of wind-driven, short choppy waves and ice scour. Tides are the most important process for the redistribution of sediments along the coast, both flooding onshore and flooding and ebbing into and out from the strait generating locally powerful (2 m s^?1) reversing currents. Ice rafting and ice pushing are important processes in this frigid environment, particularly in upwind sides of shaols, and at/or near river mouths.Different intertidal sedimentary sequences develop as functions of sediment supply and exposure of the environments to ice, currents and waves. The eastern shores and the southern shoals of the strait develop pebble lags over till, covered by thin (5–20 cm) drapes of silty sand trapped and protected from erosion by algae. In these shores and in emerging small islands significant sedimentation (1–1.5 m thick) occurs in the marshes where the suspended load of tidal waters is trapped by vegetation. The western shores of the strait receive considerable amounts of sediment from large rivers and are affected by strong tidal longshore currents. Thick (3–4 m) and narrow tidal flats and marshes develop on the maincoast. The shoals of the northern part of the strait have characteristic sediments. Those near the western shore have thin (up to 80 cm) tidal silty sand deposits, locally heavily burrowed by Macoma balthica. Those strung across the northern approach to the strait have well-developed, thin, coarse sand dune fields, indicating a prevalent ebb flow out of the strait.     

石臼坨凸起西南陡坡带扇三角洲锆石定年与源汇示踪

为了示踪渤海湾盆地石臼坨凸起西南陡坡带扇三角洲源汇体系,对其东三段层序（Ed₃）的6个砂岩样品进行碎屑锆石U-Pb定年分析.西部扇体（C6-4-4井）富含白垩纪（K）锆石并具有110 Ma峰值,母岩以白垩系义县组火成岩为主;中部（C6-4-3、C6-4-6D井）、东部扇体（C6-4-5D）富含侏罗纪（J）锆石并具有152 Ma或168 Ma峰值,母岩以侏罗系蓝旗组火成岩为主,古生代（Pz）锆石则来自中生界碎屑岩.所有样品都含有太古代（Ar）、元古代（Pt）锆石,母岩为花岗岩基底.研究表明,除古生界碳酸盐岩外,源区的母岩地层均可通过碎屑锆石U-Pb年龄示踪,各扇体物源的差异性是由母岩地层倾向控制的,由于中生界向西北倾斜,白垩系主控西部扇体沉积,侏罗系则是中部、东部扇体的主要物源区.      

鞍山-本溪地区鞍山群含BIF表壳岩形成时代新证据:锆石SHRIMP U-Pb定年

鞍本是华北克拉通最为重要的BIF铁矿集中区之一,BIF赋存于鞍山群表壳岩中.通过对广泛分布的鞍山群表壳岩的12个样品进行锆石SHRIMP U-Pb定年,大都获得2.50~2.55 Ga岩浆锆石年龄,一些岩石中存在2.7~3.5 Ga碎屑锆石或外来锆石.一些东北部（东部）岩石记录了新太古代晚期-古元古代早期变质锆石年龄.结合前人研究成果,可得出如下结论:（1）鞍本地区广泛分布的鞍山群含BIF表壳岩形成时代为新太古代晚期;（2）鞍山群表壳岩形成于陆壳基底之上.该研究进一步支持了已有认识:鞍本为东部古陆块西缘新太古代晚期巨型BIF成矿带的重要组成部分,稳定的构造环境有利于大规模BIF形成.      

Identifying Laurentian and SW Gondwana sources in the Neoproterozoic to Early Paleozoic metasedimentary rocks of the Sierras Pampeanas: Paleogeographic and tectonic implications

The provenance of Neoproterozoic to Early Paleozoic sedimentary rocks in the Sierras Pampeanas has been established using U–Pb SHRIMP age determination of detrital zircons in twelve metasedimentary samples, with supplementary Hf and O isotope analyses of selected samples. The detrital zircon age patterns show that the western and eastern sectors of the Sierras Pampeanas are derived from different sources, and were juxtaposed during the Early Cambrian ‘Pampean’ collision orogeny, thus defining initiation of the supercontinent stage of southwestern Gondwana. The Western Sierras Pampeanas (WSP), which extend northwards to the southern Puna (Antofalla) and the Arequipa Massif (Peru), constitute a single large continental basement of Paleoproterozoic age — the MARA block — that was reworked during the Grenvillian orogeny. The MARA block probably extends eastwards to include the Río Apa block (southern Brazil), but in this case without a Mesoproterozoic overprint. Detrital zircons from the WSP and Antofalla yield age peaks between 1330 and 1030 Ma, remarkably similar to the range of ages in the Grenville province of eastern Laurentia. The WSP Neoproterozoic sedimentary cover to this basement shows the same 1330–1030 component, but also includes important 1430–1380 Ma zircons whose juvenile Hf and O isotopic signatures strongly suggest derivation from the Grenville and the Southern Granite–Rhyolite provinces of eastern Laurentia. In contrast the Eastern Sierras Pampeanas metasedimentary rocks have a typically bimodal detrital zircon pattern with peaks at ca. 1000 and 600 Ma, which respectively indicate sources in the Natal–Namaqua belt and the East African orogen and/or the Dom Feliciano belt of SE Brazil and Uruguay. Sedimentary rocks in the Eastern Sierras Pampeanas and Patagonia deposited during the Late Early Cambrian–Early Ordovician interval, after the Pampean orogeny, have detrital patterns common to many sectors along the Terra Australis orogen, reflecting increasingly dominant input to the Paleozoic basins from the Neoproterozoic to Early Cambrian orogenic belts of the Gondwana margin.     

Polychlorinated biphenyls residues in surface sediments of the eutrophic Chaohu Lake (China): characteristics, risk, and correlation with trophic status

Twenty-eight polychlorinated biphenyls (PCB) congeners were measured in surface sediments from Chaohu Lake to assess their characteristics, potential risk, and the correlation with lake trophic status. PCB levels ranged from 11.074 to 42.712 ng g^?1 dry weight (d.w.) in the western lake and 2.017 to 20.189 ng g^?1 d.w. in the eastern lake. The highest concentrations were found at the sites near the inlets of western lake tributary rivers where big cities and industrial centers are located. Congeners concentrations showed decreasing order of tetra-CB > tri-CB > deca-CB (PCB-209 detected) > penta-CB > hexa-CB > di-CB > hepta-CB > Octa-CB. It indicated that light and heavy Aroclor mixtures were simultaneously used surrounding the lake basin. PCB levels in the western lake are potentially dangerous to humans and the local fauna. There was a significant positive relationship between tetra-CB (one abundant PCB congener) concentration distribution and sediment grain size in the 16–64 μm fraction, whereas a negative correlation was found in the 4–8 μm fraction. Furthermore, PCB distributions were positively correlated with the total organic carbon of sediments and lake trophic status, especially in the more seriously polluted western lake zone. However, the correlation completely disappeared in eastern lake zone. It suggested that PCB contamination might be attributed to industrial wastewaters and domestic sewages from western lake basin, reaching the lake through rivers, rains and floods.