Marine Ingressive Events Recorded in Epicontinental Sequences:Example from the Cretaceous Songliao Basin of NE China in Comparison with the Triassic Central Europe Basin of SW Germany     

WANG Pujun  LIU Wanzhu  YIN Xiuzhen 《东北亚地学研究》2002,(1)

Songliao Basin is filled predominantly with continental facies sediments including alluvial fan, fluvial plain, fan delta , lacustrine delta, shore ?shallow lacustrine, beach salty flat, semi - deep to deep lacustrine, subaqueous gravity flow, lacustrine swamp and pyroclastic sediments. However, some event units were formed during lake - marine linking periods of the Mid - Cretaceous in the basin, which include black shales with high values for salinity ( Sr/Ba) , alkalinity (Ca Mg)/ (Si Al) , reducibility ( Ni Zn)/Ga and sulfide sulfur as well as heavy isotopes. The Breitenholz ?section to be represen-ted for facies comparison with the Cretaceous evaporitic series in Northeast China is localized in Southwest Germany. Stratig-raphically it belongs to the Crabfeld Formation of Keuper of the Germanic Triassic corresponding to Ladinian - Camian of the international reference scale, and is generally called Lower Gipskeuper. The Germanic Triassic was deposited in the epiconti-nental(cratonic) central Euro  相似文献   

Lithospheric Origin of Oligocene-Miocene Magmatism in Central Chile: U-Pb Ages and Sr-Pb-Hf Isotope Composition of Minerals     

Montecinos  P.; Scharer  U.; Vergara  M.; Aguirre  L. 《Journal of Petrology》2008,49(3):555-580

Establishing the petrogenesis of volcanic and plutonic rocksis a key issue in unraveling the evolution of distinct subduction-relatedtectonic phases occurring along the South American margin. Thisis particularly true for Cenozoic times when large volumes ofmagma were produced in the Andean belt. In this study we havefocused on Oligo-Miocene magmatism in central Chile at 33°S.Our data include field and petrographic observations, whole-rockmajor and trace element analyses, U–Pb zircon dating,and Pb, Sr, and Hf isotope analyses of plagioclase, clinopyroxene,and zircon mineral separates. Combined with earlier dating resultsthe new zircon ages define a 28·8–5·2 Maperiod of plutonic and volcanic activity that ceased as a consequenceof flattening subduction of the Nazca–Farallon plate.Rare earth elements patterns are variable, with up to 92 timeschondrite concentrations for light rare earth elements yielding(La/Yb)_N between 3·6 and 7·0, and an absence ofEu anomalies. Initial Pb isotope signatures are in the rangeof 18·358–19·023 for ²⁰⁶Pb/ ²⁰⁴Pb, 15·567–15·700for ²⁰⁷Pb/ ²⁰⁴Pb and 38·249–39·084 for ²⁰⁸Pb/²⁰⁴Pb. Initial ⁸⁷Sr/ ⁸⁶Sr are mostly in the range of 0·70369–0·70505,with two more radiogenic values at 0·7066. Initial Hfisotopic compositions of zircons yield exclusively positiveHf_i ranging between + 6·9 and + 9·6. The newlydetermined initial isotope characteristics of the Oligo-Miocenemagmas suggest that the mantle source lithologies are differentfrom both those of Pacific mid-ocean ridge basalt and oceanisland basalt, plotting in the field of reference values forsubcontinental lithospheric mantle, characterized by moderatelarge ion lithophile element–high field strengh elementdepletion and high ²³⁸U/ ²⁰⁴Pb. A Hf model age of 2 Ga is estimatedfor the formation of the subcontinental mantle–continentalcrust assemblage in the region, suggesting that the initialSr and Pb isotope ratios inferred for the source of the Oligo-Mioceneparental magmas are the result of later Rb and U enrichmentcaused by mantle metasomatism. A time-integrated model Rb/Srof 0·039 and µ 16 are estimated for the sourceof the parental magmas, consistent with ratios measured in peridotitexenoliths from continental areas. Evolution from predominant(>90%) basaltic–gabbroic to andesitic–dioriticmagmas seems to involve a combination of (1) original traceelement differences in the metasomatized subcontinental mantle,(2) different degrees of partial melting and (3) fractionalcrystallization in the garnet- and spinel-peridotite stabilityfields. The genesis of more differentiated magmas reaching rhyolitic–graniticcompositions most probably also includes additional crystalfractionation at both shallow mantle depths and within the crust,possibly leading to some very minor assimilation of crustalmaterial. KEY WORDS: calc-alkaline magmatism; Oligo-Miocene; U–Pb dating; Sr–Pb–Hf isotopes; central Chile  相似文献   

Phase Relations and Melting of Anhydrous K-bearing Eclogite from 1200 to 1600{degrees}C and 3 to 5 GPa     

Spandler  Carl; Yaxley  Greg; Green  David H.; Rosenthal  Anja 《Journal of Petrology》2008,49(4):771-795

To investigate eclogite melting under mantle conditions, wehave performed a series of piston-cylinder experiments usinga homogeneous synthetic starting material (GA2) that is representativeof altered mid-ocean ridge basalt. Experiments were conductedat pressures of 3·0, 4·0 and 5·0 GPa andover a temperature range of 1200–1600°C. The subsolidusmineralogy of GA2 consists of garnet and clinopyroxene withminor quartz–coesite, rutile and feldspar. Solidus temperaturesare located at 1230°C at 3·0 GPa and 1300°C at5·0 GPa, giving a steep solidus slope of 30–40°C/GPa.Melting intervals are in excess of 200°C and increase withpressure up to 5·0 GPa. At 3·0 GPa feldspar, rutileand quartz are residual phases up to 40°C above the solidus,whereas at higher pressures feldspar and rutile are rapidlymelted out above the solidus. Garnet and clinopyroxene are theonly residual phases once melt fractions exceed 20% and garnetis the sole liquidus phase over the investigated pressure range.With increasing melt fraction garnet and clinopyroxene becomeprogressively more Mg-rich, whereas coexisting melts vary fromK-rich dacites at low degrees of melting to basaltic andesitesat high melt fractions. Increasing pressure tends to increasethe jadeite and Ca-eskolaite components in clinopyroxene andenhance the modal proportion of garnet at low melt fractions,which effects a marked reduction in the Al₂O₃ and Na₂O contentof the melt with pressure. In contrast, the TiO₂ and K₂O contentsof the low-degree melts increase with increasing pressure; thusNa₂O and K₂O behave in a contrasted manner as a function ofpressure. Altered oceanic basalt is an important component ofcrust returned to the mantle via plate subduction, so GA2 maybe representative of one of many different mafic lithologiespresent in the upper mantle. During upwelling of heterogeneousmantle domains, these mafic rock-types may undergo extensivemelting at great depths, because of their low solidus temperaturescompared with mantle peridotite. Melt batches may be highlyvariable in composition depending on the composition and degreeof melting of the source, the depth of melting, and the degreeof magma mixing. Some of the eclogite-derived melts may alsoreact with and refertilize surrounding peridotite, which itselfmay partially melt with further upwelling. Such complex magma-genesisconditions may partly explain the wide spectrum of primitivemagma compositions found within oceanic basalt suites. KEY WORDS: eclogite; experimental petrology; mafic magmatism; mantle melting; oceanic basalts  相似文献   

Geochronology of Pliocene volcanism in the Dzhavakheti Highland (the Lesser Caucasus). Part 1: Western part of the Dzhavakheti Highland     

V. A. Lebedev  S. N. Bubnov  O. Z. Dudauri  G. T. Vashakidze 《Stratigraphy and Geological Correlation》2008,16(2):204-224

Isotopic-geochronological study of the Pliocene magmatic activity in western part of the Dzhavakheti Highland (northwestern region of the Lesser Caucasus) is carried out. The results obtained imply that the Pliocene magmatic activity lasted in this part of the highland approximately 2 million years from 3.75 to 1.75–1.55 Ma. As is established, the studied volcanic rocks correspond in composition mostly to K-Na subalkaline and more abundant normal basalts. Time constraints of main phases in development of basic volcanism within the study region are figured out. We assume that individual pulses of silicic to moderately silicic volcanism presumably took place in the Dzhavakheti Highland about 3.2 and 2.5 Ma ago.  相似文献   

Oligocene sequence stratigraphy and basin development in the Danish North Sea sector based on log interpretations     

Mette Danielsen  Olaf Michelsen  Ole Rn Clausen 《Marine and Petroleum Geology》1997,14(7-8)

Five sequences are defined in the Oligocene succession of the Danish North Sea sector. Two of the sequences, 4.1a and 4.3, have been identified onshore Denmark.Two types of prograding lowstand deposits are recognized. Sand-dominated deposits occur proximally, comprising sharp-based forced regressive deposits covered with prograding low-stand deposits. Clay-dominated prograding lowstand deposits occur distally in the sequences. The highstand deposits are proximally represented by thick prograding sandy deposits and distally by thin and condensed intervals.The main sediment input direction was from the north and the northeast. A succession oif lithofacies, from shallow marine facies dominated by sand to outer shelf facies dominated by clay, is mapped in each of the sequences. An overall southward progradation of the shoreline took place during the Oligocene, interrupted only by minor shoreline retreats.  相似文献   

High-resolution sediment echosounding off Peru: Late Quaternary depositional sequences and sedimentary structures of a current-dominated shelf     

Reinhardt  L.  Kudrass  H.-R.  Lückge  A.  Wiedicke  M.  Wunderlich  J.  Wendt  G. 《Marine Geophysical Researches》2002,23(4):335-351

About 6000 km of both bathymetric and high-resolution acoustic profiles were acquired on the shelf and upper slope offshore Peru between 9° S and 14° S. Two new sediment echosounder systems – SEL-96 and SES-2000DS – provided details of the sedimentary structures of the Quaternary sequences within the Sechura-Salaverry, Huacho and Pisco Basins. To a great extent, the poleward undercurrent determines the distribution of sediments. The undercurrent has generated numerous erosional unconformities, it has winnowed hardgrounds and has created mudwaves common between 250 m and 400 m water depth. Distinct subbottom reflectors within sedimentary units represent hiatuses due to periods of intensified winnowing or non-deposition. Erosional unconformities usually marked by pronounced reflectors suggest shifts of the undercurrent system related to climatic changes and eustatic variations of sea level. On a larger scale, the stacked prograding depositional sequences reflect the sea-level cycles of the Middle Pleistocene to the Holocene. Based on the stratigraphy of our piston cores and that of Ocean Drilling Program (ODP) Site 680, the depositional sequences limited by extended unconformities were assigned to oxygen isotope stages 1 to 7. Other sedimentary structures are small straight channels that were conduits for downslope sediment transport. Deformed sediments associated with synsedimentary normal faults result from creep movements indicating beginning slope failure.  相似文献   

A genetic assessment of the taxonomic status of New Zealand mussels of the genus Xenostrobus Wilson, 1967     

Donald J. Colgan  Richard C. Willan  Lisa A. Kirkendale 《新西兰海洋与淡水研究杂志》2020,54(2):271-285

ABSTRACT

The genus Xenostrobus consists of small, marine and estuarine mussels that all appear similar externally. One of its estuarine species, Xenostrobus securis, with a native range in New Zealand and Australia, has become invasive in the Northern Hemisphere. No genetic data are available to determine if X. securis populations from the two countries are conspecific. Additionally, marine Xenostrobus from New Zealand have often been regarded as a species, X. neozelanicus, distinct fromthe marine Australian species X. pulex. We combined new DNA sequences with published data to assess the taxonomic status of New Zealand Xenostrobus. The data comprised 658 aligned bases of mitochondrial cytochrome c oxidase subunit I (COI) gene and 331 bases of nuclear histone H3. There was no evidence that X. securis populations from Australia and New Zealand are specifically distinct. Northern Hemisphere specimens of X. securis belonged to Australian, not New Zealand, clades in phylogenetic analyses of COI data, suggesting the former country as their more likely original source. The results confirm that X. neozelanicus and X. pulex are distinct species and for nomenclatural completeness for this taxonomic decision a lectotype is designated for Mytilus ater Zelebor in Dunker and Zelebor, 1866 DunkerW, ZeleborJ. 1866. Bericht über die von der Novara-expedition mitgebrachten Mollusken. Verhandlungen der Kaiserlich-Königlichen Zoologisch-Botanischen Gesellschaft in Wien. 16:909–916. [Google Scholar] [?=?Modiolus neozelanicus Iredale, 1915 IredaleT. 1915. A commentary on Suter’s ‘Manual of New Zealand Mollusca’. Transactions of the New Zealand Institute. 47:417–497. [Google Scholar]].  相似文献   

Post-Miocene stratigraphy and depositional environments of valley-fill sequences at the mouth of Tampa Bay, Florida     

Thomas W. Ferguson  Richard A. Davis  Jr.   《Marine Geology》2003,200(1-4):157-170

Post-Miocene sea-level low stands allowed rivers and karst processes to incise the exposed carbonate platform along the Gulf Coast of Florida. Few Miocene to mid-Pleistocene deposits survived erosion along the present coast except within incised valleys. Since their formation, these valleys have been filled and incised multiple times in response to sea-level changes. The thick sedimentary sequences underlying the mouth of Tampa Bay have been recorded as a range of depositional environments and multiple sea-level incursions and excursions during pre-Holocene time and subsequent to the accumulation of the Miocene carbonate sequences. Sediment analysis of cores collected from a north–south transect across the mouth of Tampa Bay has enabled the identification of lithofacies, ranging from well-sorted, quartz sand to dense, fossiliferous, phosphatic grainstone. These facies were deposited in freshwater, estuarine, and shallow, open marine environments. As a result of channel development and migration within the paleovalley, and cut-and-fill associated with individual transgressions and regressions, correlation of the lithofacies does not extend across the entire transect. Fining-upward sequences truncated by tidal ravinement surfaces that extend throughout the paleovalley can, however, be identified. Age determinations based on 14-C analysis, amino-acid racemization, and strontium isotope analysis dating of numerous samples yield ages of Miocene, Pliocene, early Pleistocene, and late Pleistocene, as well as Holocene for sequences that accumulated and were preserved in this valley-fill complex. Numerous inconsistencies in the stratigraphic organization of the age determinations indicate that there are bad dates, considerable reworking of shells that were dated, or both. For this reason as well as the lack of detailed correlation among the three relatively complete cores, it is not possible to place these strata in a sequence stratigraphic framework.  相似文献   

太平洋板块俯冲与中国东部中生代地质事件   总被引：44，自引：0，他引：44  

孙卫东  凌明星  汪方跃  丁兴  胡艳华  周继彬  杨晓勇 《矿物岩石地球化学通报》2008,27(3)

中国东部至少自侏罗纪开始就一直处于俯冲大洋板块之上,但是有关俯冲板块对其影响程度一直有不同的认识。最近的研究表明,太平洋海山岛链的时空分布显示太平洋板块的漂移方向曾发生多次转折,这些转折与白垩纪中国东部的构造演化和岩浆事件有着密切的时空耦合关系。从时代和力学性质上看,太平洋板块俯冲方向的改变在很大程度上控制着中国东部中生代的盆地演化和郯庐断裂活动等重要地质事件。这些认识为理解中国东部构造演化提供了新的视角,包括岩石圈减薄的机制、郯庐断裂的演化,以及燕山期大规模岩浆活动等。本文重点分析了太平洋板块俯冲与中国东部中生代岩浆活动的对应关系。在125～140Ma太平洋板块向南西方向俯冲,造成中国东部岩石圈减薄,软流圈卸载上涌,发生减压部分熔融;约125Ma,太平洋板块漂移方向发生了大幅度转折,形成安第斯式的俯冲挤压,岩石圈停止减薄和减压部分熔融,出现岩浆宁静期。随着俯冲的深入,到110Ma前后俯冲板块后撤,形成弧后拉张,岩浆活动又重新开始。  相似文献   

西藏冈底斯带侏罗纪岩浆作用的时空分布 及构造环境   总被引：40，自引：6，他引：34  

朱弟成  潘桂棠  王立全  莫宣学  赵志丹  周长勇  廖忠礼  董国臣  袁四化 《地质通报》2008,27(4):458-468

在新近完成的1：25万区域地质调查资料和相关研究成果的基础上,初步研究了西藏冈底斯带侏罗纪岩浆作用的分布特点及其年代学,并利用已有的地球化学数据重点分析了早期关注程度较低的侏罗纪花岗岩类岩浆作用的性质。目前在冈底斯弧背断隆带未发现侏罗纪火山岩;在冈底斯东部地区,早侏罗世岩浆活动几乎同时发生于南冈底斯（叶巴组火山岩和鸟郁、尼木花岗岩类）、冈底斯弧背断隆带（宁中、金达、布久花岗岩类）和北冈底斯（聂荣花岗岩类）,中晚侏罗世接奴群和拉贡塘组火山岩断续分布于北冈底斯,晚侏罗世岩浆活动零星分布于沙莫勒一麦拉一洛巴堆～米拉山断裂以北。将冈底斯侏罗纪岩浆活动置于时空框架内分析发现,南冈底斯和北冈底斯在侏罗纪时主要受俯冲作用的影响．而冈底斯弧背断隆带和中冈底斯自早侏罗世以来除了受到俯冲作用的影响外,还受到自东向西逐步扩展的碰撞作用的影响。结合古地磁重建资料和其他新发现．认为冈底斯带侏罗纪这种岩浆活动的特点可用班公湖一怒江洋壳向南、新特提斯洋壳向北的双向剪刀式（剪刀口向西张开）俯冲模式来解释。  相似文献