松嫩地块及其研究意义

块体拼贴是东北大地构造格架的基本特征,文中拟从这一构造背景出发,在区域地质研究基础上,选择目前研究相对薄弱的松嫩地块进行讨论。通过地层建造、古生物地理分区、构造岩浆组合及年代学的资料,揭示松嫩地块与东北其他地质体拼贴的历史。松嫩地块西侧通过嫩江中古生代造山带与兴安褶皱带相接;南侧通过吉中晚古生代造山带和华北地台北缘的西拉木伦早古生代褶皱带相接;东侧通过张广才岭中生代造山带与佳木斯地块拼贴;北侧是蒙古-鄂霍茨克中生代造山带。此外,结合前人关于全球构造格局变迁的研究,讨论了东北地块的来源,并认为松嫩地块东界的张广才岭造山带是古亚洲洋构造域向太平洋构造域转折的标志。     

Middle–Late Triassic sedimentation in the Helanshan tectonic belt: Constrain on the tectono-sedimentary evolution of the Ordos Basin,North China

The Helanshan tectonic belt is located to the west of the Ordos Basin, and separates the Alxa (or Yinshan) Massif to the west from the Ordos block to the east. Triassic sedimentation in the Helanshan tectonic belt records important information about tectono-sedimentary process between the Alxa Massif and the Ordos block. Detailed geological mapping and investigation on the lithological package, sedimentary facies and paleocurrent orientation have been conducted on the Middle to Upper Triassic clastic rocks in the Helanshan tectonic belt. The succession is characterized by upward-fining sequence and comprises coarse grained alluvial-fluvial facies in the lower part as well as deltaic-lacustrine facies in the upper part. Based on detailed study and comparisons on the sedimentary sequence along various sections, the Middle to Upper Triassic strata have been revealed that show clear southeastward-deepening sedimentary differentiation and transgression from southwest to northeast, which are consistent with the southeastward flowing paleocurrent. These features indicate a southeastward-dipping paleogeography in the Helanshan tectonic belt, which was original western part of southeastward orientated fluvial-lacustrine system in the northwestern proto-Ordos Basin. Further to the east, the Triassic succession in the Ordos Basin displays gradually thickening and alluvial-fluvial system flowed from southeast to northwest, showing a huge thick sedimentary wedge in the western basin margin. Together with the Late Permian–Early Triassic closure of the Paleo-Asian Ocean to the north, the Late Triassic extensional structures and diabase dykes in the Helanshan tectonic belt, all the above sedimentary features could be mostly interpreted as records of an extensional basin correlated to post-collisional collapse of the Central Asian Orogenic Belt.     

Early Paleoproterozoic magmatism in the Quanji Massif, northeastern margin of the Qinghai-Tibet Plateau and its tectonic significance: LA-ICPMS U-Pb zircon geochronology and geochemistry

The Quanji Massif is located on the north side of the Qaidam Block and is interpreted as an ancient cratonic remnant that was detached from the Tarim Craton. There are regionally exposed granitic gneisses in the basement of the Quanji Massif whose protoliths were granitic intrusive rocks. Previous studies obtained intrusion ages for some of these granitic gneiss protoliths. The intrusion ages span a wide range from ~ 2.2 Ga to ~ 2.47 Ga. This study has determined the U-Pb zircon age of four granitic gneiss samples from the eastern, central and western parts of the Quanji Massif. CL images and trace elements show that the zircons from these four granitic gneisses have typical magmatic origins, and experienced different degrees of Pb loss due to strong metamorphism and deformation. LA-ICPMS zircon dating yields an upper intercept age of 2381 ± 41 (2σ) Ma from monzo-granitic gneiss in the Hudesheng area and 2392 ± 25 (2σ) Ma from granodioritic gneiss in the Mohe area, eastern Quanji Massif, and 2367 ± 12 (2σ) Ma from monzo-granitic gneiss in the Delingha area, central Quanji Massif, and 2372 ± 22 (2σ) Ma from monzo-granitic gneiss in the Quanjishan area, western Quanji Massif. These results reveal that the intrusive age of the protoliths of the widespread granitic gneisses in the Quanji Massif basement was restricted between 2.37 and 2.39 Ga, indicating regional granitic magmatism in the early Paleoproterozoic, perhaps related to the fragmentation stage of the Kenorland supercontinent. Geochemical results from the granodioritic gneiss from the Mohe area indicate that the protolith of this gneiss is characterized by adakitic rocks derived from partial melting of garnet-amphibolite beneath a thickened lower crust in a rifting regime after continent-continent collision and crustal thickening, genetically similar to the TTG gneisses in the North China Craton. This suggests that the Quanji Massif had a tectonic history similar to the Archean Central Orogenic Belt of North China Craton during the early Paleoproterozoic. We tentatively suggest that the Quanji Massif and the parental Tarim Craton and the North China Craton experienced rifting in the early Paleoproterozoic, after amalgamation at the end of the Archean. The Tarim Craton and North China Craton might have had close interaction from the late Neoarchean to the early Paleoproterozoic.     

东北牡丹江地区"黑龙江群"中斜长角闪岩与花岗岩的锆石SHRIMP U-Pb定年及其地质学意义

佳木斯地块南缘牡丹江地区的岩石学和地球化学研究表明,"黑龙江群"中存在洋壳残片,为形成于古大陆边缘环境的一套造山建造.牡丹江地区东北部的"麻山群"为佳木斯地块南缘的陆壳基底;其南侧的"黑龙江群"属造山建造,包括阿尔卑斯型超基性岩和具有MORB特征的斜长角闪片岩等.对"黑龙江群"中的斜长角闪片岩以及其南边具有同碰撞特征的钾长花岗岩进行了锆石SHRIMP U-Pb定年.结果表明:斜长角闪片岩具有777±18Ma的结晶年龄,并受到437±7Ma的变质作用的影响;同碰撞的钾长花岗岩形成年龄为461±6Ma.据此指出佳木斯地块南缘的黑龙江群中存在新元古代的洋壳残片并推断牡丹江地区存在早古生代的碰撞事件.     

汞型活性碳纸富集—XRF法测定地质试样中痕量碘

本文用特制的汞型活性碳纸富集地质样品中痕量碘并用X-射线荧光光谱进行测定。方法操作简便,样品测定限为0.25ppm,测定含I~-量25μg薄试样片(n=10),其相对标准偏差为3％。经地质标准样品验证,结果与推荐值符合。     

鱼腥藻对某些金属离子的吸附效应研究（Ⅰ）

初步探讨了鱼腥藻对Mn~(2+)、Co~(2+)、Ni~(2+)、Cu~(2+)、Cd~(2+)和Pb~(2+)的生物吸附特性;研究了金属离子浓度与溶液pH值对吸附行为的影响;展示了某些藻类在分离富集中的应用前景。     

Probable anticlockwise P,–T evolution in extending crust: Hlinsko region, Bohemian Massif

ABSTRACT In the Hlinsko region (Variscan Bohemian Massif, Czech Republic) a major extensional shear zone separates low-grade metasedimentary series (Hlinsko schists) and high-grade rocks of the Moldanubian terrane (Svratka Crystalline Unit). During late-Variscan extension, a tonalite intruded syntectonically into the normal ductile shear zone, and caused contact metamorphism of the overlying schists. Concurrent syntectonic sedimentation of a flysch series took place at the top of the hangingwall schists. In order to decipher the detailed petrological evolution of the Hlinsko unit situated in the hangingwall of this tectonic contact, a phase diagram approach and petrogenetic grids, calculated with the thermocalc computer program, were used. The crystallization/deformation relationships and the paragenetic analysis of the Hlinsko schists define a P–T path with an initial minor increase in pressure followed by cooling. Calculated pseudosections constrain this anticlockwise P-T evolution to the upper part of the andalusite field between 0.36 and 0.40 GPa for temperatures ranging from 570 to 530°C. A low a_H2O is required to explain the presence of andalusite-biotite-bearing assemblages, and could be related to the presence of abundant graphite. In contrast, the footwall rocks of the Svratka Crystalline Unit record decompression from around 0.8 GPa at a relatively constant temperature, followed by cooling. Thus, the footwall and the hangingwall units display opposite, but convergent P–T histories. Decompression in the footwall rocks is related to a rapid exhumation. We propose that the inverse, anticlockwise P–T path recorded in the hangingwall pelites is related to the rapid, extension-controlled sedimentation of the overlying flysch series.     

Polyphase wrench tectonics in the southern french Massif Central: kinematic inferences from pre- and syntectonic granitoids

In the Variscan French Massif Central, the South Limousin area consists of low- to medium-grade metamorphic rocks intruded by two granitic bodies. The structural and textural analyses of these plutons undertaken in parallel with the structural analysis of their host rocks allow us to characterize and to date different stages in the tectonic evolution of this area. This study shows that the South Limousin area experienced successivelly two strike-slip events along two geographically distinct shear zones, from north to south the left-lateral Estivaux and the right-lateral South Limousin strike-slip faults, respectively. These ductile faults subdivide the South Limousin into three structural units, from north to south they are the Upper Gneiss unit, Thiviers-Payzac unit .and Génis unit. The two granitic bodies intrude the Thiviers-Payzac unit only. The younger Estivaux granite is a syntectonic pluton which emplaced during left-lateral wrenching. ⁴⁰Ar/³⁹Ar dates from biotites indicate an Early Carboniferous age (346 ± 3 Ma). The older granite is a pretectonic body. It is the Ordovician Saut du Saumon augen orthogneiss in which detailed structural analyses show the polyphase nature of the solid-state deformation. Our microtectonic data indicate that the right-lateral motions overprint the left-lateral ones and produce apparently symmetrical fabrics.     

Natural and anthropogenic budgets of a small watershed in the massif central (France): Chemical and strontium isotopic characterization of water and sediments

A small watershed (160 km²) located in the Massif Central (France) has been chemically, isotopically and hydrologically studied through its dissolved load, bed sediments and soils. This watershed is underlain by basaltic bedrock and associated soils in which the vegetation is dominated mainly by meadows.Dissolved concentrations of major ions (Cl, SO₄, NO₃, HCO₃, Ca, Na, Mg, K, Al and Si), trace elements (Rb and Sr) and strontium isotopes have been determined for two different hydrologic periods on the main stream of the Allanche river and its tributaries.The major objectives of this study were to characterize the chemical and isotopic signatures of each reservoir occurring in the watershed. Changes in chemical and isotopic signatures are interpreted in terms of fluctuations of the different components inputs: rainwater, weathering products, anthropogenic addition.Water quality may be influenced by natural inputs (rainwater, weathering processes) and anthropogenic additions (fertilizers, road salts, etc.). Precipitation serves as a major vehicle for dissolved chemical species in addition to the hydrosystem and, in order to constrain rain inputs, a systematic study of rainwaters is carried out over a one year period using an automatic collector. Corrections of rainwater addition using chloride as an atmospheric input reference were computed for selected elements and the Sr/Sr ratio. After such corrections, the geochemical budget of the watershed was determined and the role of anthropogenic additions evaluated through the relationship between strontium isotopes and major and trace element ratios. Thus, 10% of Ca and Na originate in rainwater input, 40 to 80% in fertilizer additions and 15 to 50% in rock weatheringThe cationic denudation rates for this watershed are around 0.3 g s^–1 km² during low water discharge and 0.6 g s^–1 km² in high water stage. This led to a chemical denudation rate of 5.3 mm/1000 years.For solid matter, the normalization of chemical species relative to parent rocks shows the depletion or enrichment in soils and sediments. The use of K and Ca as mobile reference illustrates the weathering state of soils and sediments relative to parent rocks. This weathering state for bed sediments range from 15 to 45% for the K normalization and from 2 to 50% for the Ca normalization. For the soils, the weathering state ranges from 15 to 57% for the K normalization and from 17 to 90% for the Ca normalization.     

Seismic stratigraphy of the Mesozoic and Cenozoic in northern Belgium: main results of a high-resolution reflection seismic survey along rivers and canals

This paper presents the results of high-resolution reflection seismic surveys carried out between 1989 and 1996 along rivers and canals in northern Belgium. The seismic data penetrate down to 900 m in the sedimentary cover or to the Paleozoic basement. The reflection response of the acoustic basement provides clear indications with regard to the top of the Paleozoic: crystalline basement and Lower Paleozoic metasediments and volcanics of the London-Brabant Massif and NE-dipping Devonian and Carboniferous strata. The subhorizontal Mesozoic and Cenozoic sedimentary cover comprises 20 unconformity-bound seismic units: 5 in the Cretaceous and 15 in the Cenozoic. Based on borehole information, these units are correlated with lithostratigraphically defined formations or groups. Some of the unit-bounding unconformities are of regional importance. They are attributed i) to eustatic sea-level changes causing regional flooding during the Late Cretaceous or incision of deep valleys during the Late Oligocene and Late Miocene, ii) to regional tectonic tilting between Late Eocene and Early Oligocene, or iii) to a combination of eustasy and tectonics causing valley incisions during the Lutetian. Faults of the Roer Valley Graben have offset different stratigraphic levels by sometimes considerable amounts (up to 230 m in the Oligocene to Quaternary succession). Although the main tectonic phase took place during the Miocene, the activity has varied considerably through time, and also from fault to fault. Most faults seem to have a 10 to 30-m displacement since the Late Pliocene.