九江下蜀黄土的常量元素组成及其物源指示          下载免费PDF全文

曾方明 《盐湖研究》2018,26(3)

长江中下游地区下蜀黄土的物质来源一直是个热点问题。本文对江西九江下蜀黄土和甘肃临洮晚更新世以来黄土的常量元素组成进行了研究,并与末次间冰期以来黄土高原其它点位的黄土、长江中下游其它地点的下蜀黄土和长江沉积物的元素组成进行对比,以期探讨九江下蜀黄土的物质来源。结果表明：（1）九江下蜀黄土的地球化学元素以SiO2、Al2O3、Fe2O3为主。与临洮黄土的元素组成相比,九江下蜀黄土具有较高的SiO2、Al2O3、Fe2O3、TiO2含量和较低的CaO、MgO含量。（2）在空间上,下蜀黄土的SiO2/Al2O3比值未表现出黄土高原黄土（北方黄土）的SiO2/Al2O3比值随纬度规律性变化的特点,揭示下蜀黄土的主要源区可能不是北方的内陆荒漠或黄土高原。（3）TiO2/Al2O3-K2O/Al2O3和TiO2/Al2O3-Fe2O3/Al2O3图解显示下蜀黄土与北方黄土存在显著差异,进一步表明下蜀黄土与北方黄土的主要源区可能不同。  相似文献   

Provenance, diagenesis, tectonic setting and geochemistry of Tawil Sandstone (Lower Devonian) in Central Saudi Arabia     

Omar A. Al-Harbi  M. Mujtaba Khan 《Journal of Asian Earth Sciences》2008,33(3-4):278-287

The Tawil Sandstone (Lower Devonian) in Central Saudi Arabia overlies the Sharwara Member of the Tayyarat Formation (Silurian) and succeeded conformly by the Shaiba Member of the Jauf Formation. Petrographical data reveal that the Tawil Sandstone comprises 96% quartz, 3% feldspar, and 1% rock fragments and all samples are classified as quartz arenites. The presence of well sorted, altered to fresh feldspar, and discriminate function analysis suggests that the sediments have been subjected to substartial reworking resulting in a high level of maturity. Modal analysis data (Q–F–L) suggest a stable cratonic provenance for the sediments and accumulation in a passive margin basin is indicated (binary plot of SiO₂ vs K₂O/Na₂O). Diagenetic features include dissolution of feldspar and rock fragments, compaction, reduction of the existing pore space through rearrangements, and rotation and fragmentation of grains resulting in dissolution of quartz grains and cementation.  相似文献   

Geochemistry of Renuka Lake and wetland sediments,Lesser Himalaya (India): implications for source-area weathering,provenance, and tectonic setting     

Brijraj K. Das  Birgit-Gaye  Parkash Kaur 《Environmental Geology》2008,54(1):147-163

The geochemical investigation of sediments deposited in the Renuka Lake basin and its adjoining wetland has shown variation in the distribution and concentration of major, trace and REEs. The major elements are depleted in the lake in relation to wetland and that of Post Archaean Australian, Shale (PAAS), except for CaO which is strikingly in excess and has a dilution effect on SiO₂ and other oxides and trace elements. The Wetland sediments, on the other hand, are enriched in Al₂O₃, Fe₂O₃, K₂O and TiO₂ and the latter three show a positive correlation with Al₂O₃ in both wetland and lake sediments suggesting their association with phyllosilicates and similar source rocks. The enrichment of Y, Zr, Ni, Th, U and Nb in wetland compared to lake and their similarity with PAAS in the former, suggests more clay fractions in the wetland. A high Zr/Hf ratio in wetland and lake sediments and a positive correlation of Zr with Y and HREE indicate Zr control on HREEs. However, higher Zr/Yb and Zr/Th ratios in wetland compared to lake indicate mineral sorting during the process of lighter particles (clays) being trapped in wetland soil. This is also reflected from negative correlation of Gd_N/Yb_N with Al₂O₃ and a strong positive correlation with SiO₂ in wetland sediments. The wetland in this context has a control on lake sediment chemistry. The chondrite normalized REE patterns are essentially the same for lake as well as wetland sediments but abundance decreases in the former. The similarity of pattern with that of PAAS and negative Eu anomaly indicates a cratonic source of sediments. In a plot of the individual samples, wetland samples cluster while lake samples are separated indicating fractionation of lake sediments. A strong positive correlation of La_N/Yb_N with Al₂O₃ and a positive correlation of Zr-∑LREE and Zr-La_N/Yb_N suggest that LREEs are controlled by both phyllosilicates and zircon. The chemical index of alteration (CIA) indices in lake sediments and in wetland are higher than PAAS indicating moderate chemical weathering in the source area. The petrography, lack of felsic magmatic rock fragments, and negative correlation between Zr-(Gd/Yb)_C indicate sedimentary source rocks for the detritus. This is in conformity with the Lesser Himalayan sedimentary sequence belonging to neo-Proterozoic–Proterozoic age and constituting lake catchment of Renuka. The tectonic delineation and discriminant function plots of lake and wetland sediments indicate their cratonic and/or quartzose sedimentary orogenic terrain source that has been deposited in a passive margin setting.  相似文献   

Late Jurassic-Cretaceous fluvial evolution of central Africa: Insights from the Kasai-Congo Basin,Democratic Republic Congo     

《Cretaceous Research》2016

The Congo Basin in central Africa is one of the largest intracratonic sedimentary basins in the world. The geological knowledge of Congo Basin is mainly based on studies from the central part of the basin (“Cuvette Centrale”). We present the results of sedimentary provenance investigations of the Jurassic–Cretaceous strata from the southwestern part of the basin, called the Kasai region. This study combines sandstone petrography with U-Pb and Lu-Hf analyses of detrital zircons to assess the stratigraphy, sedimentary provenance and drainage history of the Upper Jurassic-Cretaceous strata in the Kasai region. The stratigraphy is subdivided into a single Upper Jurassic unit (J1) and four Cretaceous units (C1–C4). Petrographically, sandstones from all units except the conglomeratic C3 are texturally and compositionally mature, dominated by quartzarenite and subarkosic compositions. These characteristics can be attributed to considerable recycling of older sedimentary strata and crustal sources, along with long distance fluvial and aeolian processes. The analyses of fifteen detrital zircon samples from the Upper Jurassic–Cretaceous strata yielded mainly Archean and Proterozoic zircons. This result suggests that sandstones are likely sourced from the underlying Archean-Paleoproterozoic Congo–Kasai Craton and from nearby Proterozoic mobile belts, particularly the Irumide and Lufilian Belts to the south of the basin. The dominance of Archean and Proterozoic detrital zircons in Upper Jurassic–Cretaceous strata suggests that the Kasai portion of the Congo Basin experienced exhumation and erosion, which is possibly associated with far-field reactivation of Archean and Proterozoic structures during and following Gondwana rifting in the late Mesozoic. A large fluvial drainage network sourced from the south of the basin, is interpreted to have developed across central Africa during the Late Jurassic–Cretaceous. This fluvial system is believed to have flowed northward across the Congo Basin and ultimately drained into a wrench fault system called the Central African Shear Zone, which extends in an ENE direction from the Gulf of Guinea through Cameroon into Sudan and Kenya.  相似文献   

共和盆地西缘柔起岗地区变质岩系LA-ICP-MS锆石U-Pb年龄 —原岩最大沉积时代及物源研究     

李瑞保  裴先治  杨栓海  王伟峰  魏立勇  孙雨  李飞  刘满年  赵长存  李佐臣  杨高学  陈力子 《地质学报》2016,90(1):93-114

共和盆地西缘原划古元古代金水口岩群中发育一套低级变质的灰色绢云石英片岩、绢云石英岩及黑云石英片岩组合,该套变质岩系原岩沉积时代及变质基底构造属性存在争议。本文对采自青海省兴海县柔起岗地区的两件片岩样品开展了系统的岩石学及LA-ICP-MS锆石 U-Pb年代学研究,对其原岩沉积时代、沉积物源及基底构造亲缘性进行了探讨。结果表明,该套片岩两件样品的碎屑锆石U-Pb年龄谱可明显分为新元古代和古元古代两个主年龄谱以及中元古代的两个次年龄谱,新元古代主年龄谱分别为688-908 Ma和711-841 Ma,峰值年龄为788 Ma和780 Ma,古元古代主年龄谱分别为1871-2174 Ma和1832-2194 Ma,峰值年龄为2140 Ma和2072 Ma,中元古代两个次年龄谱分别为1520-1638 Ma和1271-1276 Ma,峰值年龄为1635 Ma和1275 Ma。片岩最小碎屑锆石年龄值688 Ma限定了其原岩的最大沉积时代。塔洞片岩碎屑锆石U-Pb年龄谱特征表明其碎屑物质来源较为复杂,物源主体来自周邻造山带的西秦岭、东昆仑和柴达木盆地北缘构造带的前寒武纪块体,扬子板块对其沉积物源亦有部分贡献,而华北板块没有对其提供沉积物源。更为重要的是,该套片岩锆石U-Pb年龄谱突出显示新元古代早期的构造-岩浆-热事件年龄信息,而没有华北板块典型的1850 Ma 和2500 Ma左右的特征,结合区域资料认为西秦岭源区基底与东昆仑地块、柴达木盆地北缘、祁连地块等一样表现出扬子板块的构造亲缘性,源区基底固结时代为新元古代早期。  相似文献   

Provenance of Clay Minerals in the Amami Sankaku Basin and Their Paleoclimate Implications Since Late Pleistocene     

Liu Huahua  Jiang Fuqing  Zhou Ye  Li Anchun 《地球科学进展》2016,31(3):286-297

We analyzed the clay mineral assemblages, content and mineralogical characteristics of Hole U1438A sediment recovered from Amami Sankaku Basin during International Ocean Discovery Program (IODP) expedition 351. The results show that the clay minerals are mainly composed of illite (average 57%), smectite (average 26%), chlorite (average 14%) and minor kaolinite(average 3%). The crystallinity of illite in all samples are good (<0.4 Δ° 2θ), and the chemical indexes of illite in all samples are low (<0.4). Both indicate that illite in Hole U1438A formed in cold and dry climate. By comparing clay mineral assemblages of hole U1438A and the potential sediment sources, we suggest that smectite be mainly derived from the volcanic materials around Amami Sankaku Basin. Illite, chlorite and kaolinite are mainly derived from the Asian dust. The ratios of (illite+chlorite)/smectite show a phased increase over the last 350 ka, which is consistent with the cold and drying trend of the Asian continent since late Pleistocene. The high ratios of (illite+chlorite)/smectite and (illite+chlorite)/kaolinite during glacial period indicate that much more Asian dust was input into the Amami Sankaku Basin, which are responded to the aridity of Asian continent and strengthened east Asian Monsoon during glacial period.  相似文献   

Provenance of Triassic sandstones on the southwest Barents Shelf and the implication for sediment dispersal patterns in northwest Pangaea     

《Marine and Petroleum Geology》2016

Thick Triassic siliciclastic units form major reservoir targets for hydrocarbon exploration on the Barents Shelf; however, poor reservoir quality, possibly associated with variation in provenance, remains a key risk factor in the area. In this study, sandstone dispersal patterns on the southwest Barents Shelf are investigated through petrographic and heavy mineral analysis, garnet and rutile geochemistry and zircon U-Pb geochronology. The results show that until the Early Norian Maximum Flooding Surface, two contrasting sand types were present: (i) a Caledonian Sand Type, characterised by a high compositional maturity, a heavy mineral assemblage dominated by garnet and low chrome-spinel:zircon (CZi) values, predominantly metapelitic rutiles and mostly Proterozoic and Archaean detrital zircon ages, interpreted to be sourced from the Caledonides, and (ii) a Uralian Sand Type, characterised by a low compositional maturity, high CZi values, predominantly metamafic rutiles and Carboniferous zircon ages, sourced from the Uralian Orogeny. In addition, disparity in detrital zircon ages of the Uralian Sand Type with contiguous strata on the northern Barents Shelf reveals the presence of a Northern Uraloid Sand Type, interpreted to have been sourced from Taimyr and Severnaya Zemlya. As such, a coincidental system is inferred which delivered sand to the Northern Barents Shelf in the late Carnian/early Norian. Following the Early Norian Maximum Flooding Surface, a significant provenance change occurs. In response to Late Triassic/Early Jurassic hinterland rejuvenation, supply from the Uralian Orogen ceased and the northern Scandinavian (Caledonian) source became dominant, extending northwards out on to the southwest Barents Shelf. The data reveal a link between reservoir quality and sand type and illustrate how provenance played an important role in the development of clastic reservoirs within the Triassic of the Barents Shelf.  相似文献   

北秦岭二郎坪杂岩变沉积岩碎屑锆石年代学及其构造地质意义   总被引：6，自引：4，他引：2  

杨敏  刘良  王亚伟  廖小莹  康磊  盖永升 《岩石学报》2016,32(5):1452-1466

碎屑锆石为沉积岩中最稳定的矿物,其年龄谱系不仅可限定沉积物的最大沉积年龄与物源性质,而且能够为探讨其形成构造环境提供关键约束。作为北秦岭构造带主要构造岩石地层单元之一,二郎坪杂岩由北、中、南三个构造岩片——北部碎屑岩片、中部蛇绿岩片和南部变碎屑岩片组成。本文对二郎坪杂岩南部变碎屑岩片中的碎屑锆石进行了LA-ICP-MS U-Pb年龄测试研究,获得样品锆石谐和年龄值分布在500±7Ma~3894±5Ma之间,1个年龄高频集中区为0.9~1.0Ga,6个次要年龄集中区分别为500~600Ma、750~850Ma、1.35~1.48Ga、1.6~1.75Ga、2.6~2.7Ga和3.0~3.4Ga。研究结果表明:1)最小峰值年龄限定二郎坪杂岩南部碎屑岩片原岩的最大沉积时代为500Ma,结合西庄河花岗闪长岩侵入南部岩片的地质事实,南部岩片的形成时代应为早古生代寒武-奥陶纪(500~475Ma),明显早于中部蛇绿岩片中的火山岩的形成时代(463~475Ma);2)通过与邻区地质事件年龄谱峰及其锆石阴极发光图像特征的对比,二郎坪杂岩变碎屑岩原岩的物源分别主要来自南部秦岭杂岩中的早新元古代花岗岩和北部华北南缘熊耳群中元古代火山岩,其物源具有双源性,暗示其形成于与伸展作用相关的裂谷或弧后盆地构造背景,而二郎坪蛇绿岩片所代表的古洋盆可能正是在此基础上发育产生的;3)结合区域地质背景资料分析,二郎坪杂岩中的沉积碎屑岩片可能形成于商丹洋向北俯冲期间所产生的弧后伸展盆地构造环境;4)通过与宽坪岩群沉积岩中的碎屑锆石年龄数据的对比,揭示二者碎屑锆石具有相似的年龄谱峰,结合宽坪群变沉积岩中发现大量疑源类、几丁虫和虫颚等早-中奥陶世化石组合以及二郎坪杂岩蛇绿岩片中的火山岩夹层硅质岩中发现早-中奥陶世牙形石和放射虫的研究,分析认为二者沉积物的沉积时代相近,沉积物源几乎完全一致,暗示它们形成的构造环境可能具有一致性;5)二郎坪蛇绿岩片中的典型的与洋壳俯冲有成因联系的弧火山岩的形成时代(463~475Ma)明显迟后于区内高压-超高压岩石的峰期变质时代(514~484Ma)约20~30Myr,清楚地表明二郎坪洋壳拖曳秦岭杂岩发生陆壳俯冲-深俯冲作用的可能性不大;6)二郎坪杂岩南部碎屑岩片和宽坪岩群碎屑沉积物中碎屑锆石中最主要的年龄集中区(0.9~1.0Ga)的物源来自秦岭杂岩中的早新元古代花岗质岩石,而缺少秦岭杂岩中的早古生代岩浆岩和HP/UHP变质岩石锆石的年龄信息,明确指示二郎坪与宽坪盆地沉积时,秦岭杂岩重要组成的早新元古代花岗质岩石已出露于地表接受剥蚀,而秦岭杂岩中出露的HP/UHP岩石和早古生代岩浆岩未抬升出露地表,即秦岭杂岩现今出露的前早古生代陆壳物质不是整体而是部分经历了陆壳俯冲-深俯冲作用。  相似文献   

苏鲁地体折返与郯庐断裂活动:莱阳盆地中生界碎屑锆石年代学的制约   总被引：1，自引：0，他引：1  

周建波  韩伟  宋明春 《岩石学报》2016,32(4):1171-1181

胶莱盆地位于苏鲁造山带的北缘,其莱阳群沉积对反演郯庐断裂和苏鲁造山带中生代的折返过程具有重要的制约作用。本文利用LA-ICP-MS方法对莱阳盆地的莱阳群碎屑岩和青山群火山岩进行锆石U-Pb年龄测定,分析其年龄谱特征,探讨其沉积物源区,进而为苏鲁造山带的折返机制提供依据。(1)莱阳盆地发育莱阳群和青山群为代表的中生代沉积岩,锆石年龄测试得到莱阳群形成时代为125±0.6Ma;青山群形成时代为119±1Ma,表明两者都是早白垩世中-晚期的沉积产物;(2)超高压带北缘莱阳盆地与合肥盆地的碎屑锆石年龄谱对比表明,莱阳盆地的沉积物无论沉积时代还是物源区均明显不同与郯庐断裂西侧的合肥盆地,表明郯庐断裂应该形成于两个盆地形成之前,可能为三叠纪-早侏罗世之间;(3)莱阳盆地内发育大量的华北型碎屑物质,进一步表明在扬子大陆板块俯冲过程中华北板块曾经仰冲到扬子板块之上;(4)莱阳盆地发育少量的新元古代岩浆和印支期变质锆石的年龄,表明早白垩世苏鲁超高压变质岩已经折返到地表;(5)超高压变质岩与中生代岩浆岩同时作为莱阳盆地的物源,结合五莲拆离断层的同期活动和莱阳盆地的同时代沉积,说明苏鲁超高压带中生代的折返具有与变质核杂岩类似的大型伸展构造背景。  相似文献   

The Orosirian-Statherian banded iron formation-bearing sequences of the southern border of the Espinhaço Range,Southeast Brazil     

《Journal of South American Earth Sciences》2016

The Serra da Serpentina and the Serra de São José groups are two distinct banded iron formation-bearing metasedimentary sequences along the eastern border of the southern Espinhaço Range that were deposited on the boundary between the Orosirian and Statherian periods.The Serra da Serpentina Group (SSG) has an Orosirian maximum depositional age (youngest detrital zircon grain age = 1990 ± 16 Ma) and consists of fine clastic metasediments at the base and chemical sediments, including banded iron formations (BIFs), on the top, corresponding to the Meloso and Serra do Sapo formations, respectively, and correlating with the pre-Espinhaço Costa Sena Group. The SSG represents sedimentary deposition on an epicontinental-epeiric, slow downwarping sag basin with little tectonic activity.The younger Serra de São José Group (SJG) is separated from the older SSG by an erosional unconformity and was deposited in a tectonically active continental rift-basin in the early stages of the opening of the Espinhaço Trough. The Serra do São José sediments stretch along the north-south axis of the rift and comprise a complete cycle of transgressive sedimentary deposits, which were subdivided, from base to top, into the Lapão, Itapanhoacanga, Jacém and Canjica formations. The Itapanhoacanga Formation has a maximum depositional age of 1666 ± 32 Ma (Statherian), which coincides with the maximum depositional age (i.e., 1683 ± 11 Ma) of the São João da Chapada Formation, one of the Espinhaço Supergroup's basal units. The Serra de São José Rift and the Espinhaço Rift likely represent the same system, with basal units that are facies variations of the same sequence.The supracrustal rocks have undergone two stages of deformation during the west-verging Brasiliano orogeny that affected the eastern margin of the São Francisco Craton and generated a regional-scale, foreland N–S trending fold-thrust belt, which partially involved the crystalline basement. Thrust faults have segmented the terrain into a large number of tectonic blocks, where the stratigraphic sequence was nevertheless well preserved.  相似文献