'Breaks' in grain-size distributions and applications of the suspension criterion to turbidites     

PAUL D. KOMAR 《Sedimentology》1986,33(3):438-440

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Polybaric Evolution of Calc-alkaline Magmas from Nisyros, Southeastern Hellenic Arc, Greece   总被引：4，自引：0，他引：4  

WYERS  G. PAUL; BARTON  MICHAEL 《Journal of Petrology》1989,30(1):1-37

The lavas of Nisyros were erupted between about 0?2 m.y B.P.and 1422 A.D., and range in composition from basaltic andesiteto rhyodacite. Most were erupted prior to caldera collapse (exactdate unknown), and the post-caldera lavas are petrographically(presence of strongly resorbed phenocrysts) and chemically (lowerTiO₂ K₂O, P₂O₅, and LIL elements) distinct from the pre-calderalavas. The pre-caldera lavas do not form a continuous seriessince lavas with SiO₂ contents between 60 and 66 wt.% are absent.Nevertheless, major element variations demonstrate that fractionalcrystalliz ation (involving removal of olivine, dinopyroxene,plagioclase, and Fe-Ti oxide from the basaltic andesites andandesites and plagioclase, clinopyroxene, hypersthene, Ti-magnetite,ilmenite, apatite, and zircon from the dacites and rhyodacites)played a major role in the evolution of the pre-caldera lavas.Several lines of evidence indicate that other processes werealso important in magma evolution: (1) Quantitative modelingof major element data shows that phenocryst phases of unlikelycomposi tion or unrealistic assemblages of phenocryst phasesare required to relate the dacites and rhyodacites to the basalticandesites and andesites; (2) The proportions of olivine andclinopyroxene required in quantitative models for the initialstages of evolution differ from those observed petrographicallyand this is not likely to reflect either differential ratesof crystal settling or the curvature of cotectics along whichliquids of basaltic andesite to andesite composition lie; (3)The concentrations of Rb, Cs, Ba, La, Sm, Eu, and Th in therhyod.acites are too high for these lavas to be related to thedacites by fractional crystallization alone; and (4) ⁸⁷Sr/⁸⁶Srratios for the andesites and rhyodacites are higher than thosefor the basaltic andesites and dacites, respectively. It isshown that fractional crystallization was accompanied by assimilation,and that magma mixing played a minor role (if any) in the evolutionof the pre-caldera lavas. Trace element and isotopic data indicatethat the andesites evolved from the basaltic andesites by AFCinvolving average crust or upper crust, whereas the rhyodacitesevolved from the dacites by AFC involving lower crust. Additionalevidence for polybaric evolution is provided by the occurrenceof distinct Ab-rich cores of plagioclase phenocrysts in thedacites and rhyodacites, which record a period of high pressurecrystallization, and by the occurrence of both normal and reverse-zonedphenocrysts in the basaltic andesites and andesites. Furthermore,calculated pressures of crystallization are {small tilde}8 kbfor the dacites and rhyodacites and 3?5–4 kb for the basalticandesites and andesites. It is concluded that the dacites andrhyodacites evolved via AFC from basaltic andesites and andesiteslargely in chambers sited near the base of the crust whereasthe basaltic andesites and andesites mostly evolved in chamberssited at mid-crustal levels. Eruption from different chambersexplains the compositional gap in the chemistry of the pre-calderalavas since eruptive products represent a more or less randomsampling of residual liquids which separate (via filter pressing)from bodies of crystallizing magma at various depths. Magmamixing was important in the evolution of the post-caldera lavas,but geochemical data require that these magmas evolved fromparental magmas which were derived from a more refractory sourcethan the parental magmas to the pre-caldera lavas. ^*Present address: Netherlands Energy Research Foundation (ECN), P.O. Box 1, 1755 ZG Petten, The Netherlands  相似文献   

High-Temperature Fluid-Rock Interaction and Scapolitization in an Extension-Related Hydrothermal System, Mary Kathleen, Australia   总被引：1，自引：0，他引：1  

OLIVER  NICHOLAS H. S.; RAWLING  TIMOTHY J.; CARTWRIGHT  IAN; PEARSON  PAUL J. 《Journal of Petrology》1994,35(6):1455-1491

In the polymetamorphic Mary Kathleen Fold Belt, at the centreof the Proterozoic Mount Isa Inlier, Queensland, an early phaseof extension (1760–1730 Ma) resulted in intrusion of voluminousgranitic and doleritic magmas into the carbonate-evaporite-dominatedCorella Formation at 5–10 km depths. Widespread high-temperaturemetasomatism ensued, involving scapolitization in dolerite,formation of albite-scapolite shear zones in granite, exo- andendoskarn formation, and a zone of K–Na–Ca alterationin the lowermost Corella Formation. Granites and dolerites werealtered to an unusual Na–Ca-rich bulk composition, reflectinghigh-temperature infiltration of highly saline, chemically reactiveexternally derived fluid. The alteration products and theirdistribution suggest not only reaction of magmatic/aqueous fluidswith the country rocks but also extensive halite dissolutionand recirculation of saline fluids back into the intrusive bodies.The bulk of fluid flow occurred at high temperatures (500–700C), and major element and isotopic fronts were generally notsmoothed out by the effects of temperature gradients, with theexception of one part of the system which shows evidence forup-temperature fluid flow. Analysis of oxygen isotopic dataand the position of isotopic and geochemical fronts revealstime-integrated fluid fluxes of up to 2 10⁴ m³/m² for themetasomatism. Although very high salinities (up to 50 mol% NaCl)were attained by evaporite dissolution, ¹⁸O values of most alterationproducts are in the range 7–12%, reflecting a predominanceof oxygen derived from an igneous fluid. The position and interrelationshipsof metasomatic and isotopic fronts indicate an earlier stageof infiltration dominated by fluid released from crystallizinggranite (with ¹⁸O 10–12%), and a later stage (¹⁸O 7–9%)in which fluid had already interacted with halite and a mixedmafic-felsic igneous source or was repeatedly circulated betweenthese rock types during alteration. The data reflect only aminimal contribution from fluids produced by devolatilizationof the abundant carbonate-bearing rocks in the Corella Formation,and there are substantial areas of Corella Formation rocks thathave escaped metasomatism during this phase of intrusion-relatedhydrothermal activity and during the subsequent regional metamorphicoverprint. Along with the requirement that the fluids dissolvedlarge amounts of halite from the same sequence, and the structuralobservations, we favour a model where fluid was preferentiallychannelled along specific permeable conduits, including formerevaporite layers, before interaction with the now exposed alteredrocks. Fluid was probably driven by both convective circulationand dilatancy-related deformation accompanying emplacement ofmagmas into a major crustal extensional dcollement.  相似文献   

Lower Silurian transgressive barrier islands, southwest Wales     

PAUL H. BRIDGES 《Sedimentology》1976,23(3):347-362

Barrier islands developed on the southeastern flanks of a volcanic terrain during the Lower Silurian transgression of southwest Wales. The barriers are preserved in transgressive sequences overlying basalts and comprising from base upwards: lagoon→barrier island→offshore marine sediments. The thickness of the barrier island sediments varies from 5 m to 28 m. Comparison with modern barriers suggests that the thin sequences result from narrow (<2 km), steadily transgressing barrier islands, whereas the thicker sequences represent broad (2–4 km), slowly transgressing forms. In one case the barrier became narrower as the rate of migration accelerated in response to decreased fluviatile sediment supply caused by rising sea-level. Despite the high preservation potential of inlet fill deposits, the latter are generally absent in these Silurian barriers because inlet migration was slow compared with the rate of barrier retreat. Possibly much shell material was dissolved during early diagenesis.  相似文献   

Cenozoic Volcanism in Tibet: Evidence for a Transition from Oceanic to Continental Subduction   总被引：93，自引：2，他引：93  

DING  LIN; KAPP  PAUL; ZHONG  DALAI; DENG  WANMING 《Journal of Petrology》2003,44(10):1833-1865

Geochronological (K–Ar or ⁴⁰Ar/³⁹Ar), major and traceelement, Sr–Nd–Pb isotopic and mineral chemicaldata are presented for newly discovered Cenozoic volcanic rocksin the western Qiangtang and central Lhasa terranes of Tibet.Alkali basalts of 65–45 Ma occur in the western Qiangtangterrane and represent primitive mantle melts as indicated byhigh mg-numbers [100 x Mg/(Mg + Fe)] (54–65), Cr (204–839ppm) and Ni (94–218 ppm) contents, and relatively lowratios of ⁸⁷Sr/⁸⁶Sr (0·7046–0·7061), ²⁰⁶Pb/²⁰⁴Pb(18·21–18·89), ²⁰⁷Pb/²⁰⁴Pb (15·49–15·61)and ²⁰⁸Pb/²⁰⁴Pb (38·42–38·89), and highratios of ¹⁴³Nd/¹⁴⁴Nd (0·5124–0·5127). Incontrast, younger volcanic rocks in the western Qiangtang terrane(  相似文献   

THE SOVIET WAR MEMORIAL IN TREPTOW,BERLIN*     

PAUL STANGL 《Geographical review》2003,93(2):213-236

ABSTRACT. The Soviet War Memorial in Treptow, Berlin, was an important emblem of political power and ideology during and after the cold war. Designed as the Soviet Union's premiere extraterritorial battlefield shrine, the site combines a veterans' cemetery with a large‐scale memorial complex celebrating the Soviet victory in World War II. The monument was intended for use in Soviet military commemorative activity and became a key sacred space in the Cult of the Soviet War Dead, but its location in Berlin meant that it served other political purposes. By avoiding definitive statements on key issues the memorial attained a semantic flexibility that enabled it to remain a focal point of commemorative activity for decades. The memorial continues to play a part in contemporary Berlin, though the political overtones are now overshadowed by its role as a shrine to the war dead.  相似文献   

EVOLVING FACTOR ANALYSIS APPLIED TO FLOW INJECTION ANALYSIS DATA     

PAULJ.GEMPERLINE  J.CRAIGHAMILTON 《地理学报(英文版)》1989,(2)

Evolving factor analysis is used to estimate the concentration profiles and spectra of Bi~(3 )and the bismuthchloride complexes BiCl~(2 )through BiCl_6~(3-)formed by injection of bismuth percblorate into a flowingstream of 1.0 mol l~(-1) HCl.The estimated spectra compare favorably with previously published spectraof the complexes.  相似文献   

Log Evaluation of Shaly Sandstones: A Practical Guide     

PAUL F. Worthington 《Basin Research》1989,2(3):203-203

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Paleo-oceanography of the Norwegian Sea during the past 130,000 years: coccolithophorid and foraminferal data     

PAUL E. BELANGER 《Boreas: An International Journal of Quaternary Research》1982,11(1):29-36

Faunal, floral and sedimentological properties of Norwegian Sea core V27-86 were examined in order to reconstruct the paleo-oceanographic history of this region. Downcore variations in the relative abundance of three microfossil groups and several sediment properties exhibit three different climate response patterns (CRP). Each pattern is judged to represent the response of a different part of the climate system. The covariance patterns among coccoliths, henthic foraminifera, and other properties suggest that the Norwegian Sea has been ice-free and productive during the present interhlacial. the penultimate interglacial (isotopic-stage se) and at least partially ice-free during an intermediate climatic regime (stages sa-d). A maximum change in these measures occurs at the boundary between isotopic stage 5a (an intermediate climatic regime)and isotopic stage 4 (a glacial climatic regime). In contrast, planktic foraminiferal assemblages and oxygen isotope measurements on planktic foraminifera show a major change at the end of stage 5e (the penultimate interglacial). The contrasting behavior of these two sets of observations is explained by a model which postulates a low-salinity surface layer 115,000 to 75,000 years ago (stages 5a-d).  相似文献   

Neotectonics     

PAUL L. HANCOCK 《Geology Today》1988,4(2):57-61

Neotectonics is the study of Earth movements of late Cenozoic age, especially those in harmony with contemporary horizontal and vertical crustal motions. Precise information about the character, frequency and rate of recent movements is an essential part of planning how to reduce earthquake hazard, and it also allows tectonicians to devise realistic models of crustal behaviour.  相似文献