The Belize margin revisited. 2. Origin of Holocene antecedent topography     

Edward G. Purdy  Eberhard Gischler  Anthony J. Lomando 《International Journal of Earth Sciences》2003,92(4):552-572

The importance of antecedent topography in dictating Holocene facies patterns has been generally recognized. There is, however, disagreement as to origin or lithology of the antecedent topography, particularly with respect to the siliciclastic or carbonate nature of the underlying topography and structural patterns. To help resolve these problems, published and unpublished information have been compiled to produce a structural fabric map of onshore and offshore Belize that includes a new geologic map of the country. The map, along with illustrated seismic lines, demonstrates the occurrence of a number of NNE-trending transpressional faults in which landward directed thrusting is consistently displayed along with tectonic inversion. Offshore wells in conjunction with the seismic lines document the inversion as post-Eocene, suggesting a similar age for transpressional fault movement. Presumably, the landward-directed thrusting reflects the opposing force of eastward-directed subduction along the western margin of Central America relative to the westward seafloor spreading of the Caribbean Cayman Ridge. The Belize faults show little current seismicity, but, nevertheless, the resulting structures have affected Quaternary carbonate deposition as evidenced on an illustrated seismic line by both seaward and landward (bi-directional) progradation of the reef margin from an underlying structural high. The structural influence on the development of Holocene antecedent topography is further suggested by the occurrence of a Bouguer gravity plateau in the same shelf area that marks the occurrence of the Belize lagoon rhomboid shelf atolls. The youngest documented lithology of 12 illustrated offshore exploration wells is Miocene carbonate. In some wells, the carbonate is interpreted as extending into the Pliocene and Holocene although no age diagnostic criteria are in evidence. In other wells, siliciclastics of unknown age and thickness are identified as overlying Neogene carbonates. The regional distribution and age of onshore limestones suggests that unroofing of the Cretaceous carbonate cap of the Maya Mountains siliciclastic sediment source did not occur until late in Neogene time, perhaps no earlier than late Pliocene. Consequently, the Maya Mountains could not have been a major offshore source of siliciclastics until the Quaternary. Information on the lithology of the immediately underlying pre-Holocene is provided by limited penetration core data and shallow resolution seismic lines. These show that antecedent Pleistocene limestones beneath the Holocene reefs were deposited around 130,000 b.p. (isotope stage 5e). The thickness of the overlying Holocene, shelf margin, reef-capped carbonates increases along depositional strike from a few meters in the north to more than 25 m in the south. In contrast, piston cores and seismic data from the southern shelf lagoon collectively document the occurrence of antecedent siliciclastic topography. The southward dip of both carbonate and siliciclastic antecedent surfaces is presumably a reflection of increasing southerly subsidence. Increasing antecedent erosional relief in the same direction reflects the pronounced southerly increase in paleo-rainfall that presumably paralleled that of present-day rainfall.  相似文献   

DNAPL to LNAPL Transitions During Horizontal Cosolvent Flooding   总被引：1，自引：0，他引：1  

Eberhard Roeder  Ronald W. Falta Jr.    Cindy M. Lee  John T. Coates 《Ground Water Monitoring & Remediation》2001,21(1):77-88

Cosolvent flooding is a technology with the potential to remove nonaqueous phase liquid (NAPL) sources from the subsurface. It can be used to initiate separate phase mobilization, which allows removal of NAPL within very few pore volumes. Mobilization may result in a sinking DNAPL bank during horizontal flooding of NAPLs denser than water. Reversal of phase density difference between aqueous and DNAPL phases could potentially avoid this downward migration of mobilized DNAPLs. We achieved phase density difference reversal and made DNAPLs float using two components in the cosolvent flooding solution. A low-density cosolvent partitions preferentially into the DNAPL and swells it, which causes a reduction in density of the DNAPL and reversal of the density difference between the NAPL and aqueous phases. A highdensity additive that remains in the aqueous phase allows the cosolvent flooding solution overall to have a density greater than that of water and permits control of the flooding instability. This study focused on tert-butanol as the swelling cosolvent and tetrachloroethylene as the contaminant. In batch tests with sucrose and glycerol as dense additives, phase density difference reversal occurred. To investigate the applicability of phase density difference reversal as a remediation technology, horizontal column and sandbox experiments were performed. These experiments demonstrated the occurrence of phase density difference reversal and effective remediation in horizontal cosolvent floods.  相似文献   

Origin and Evolution of the Kerguelen Plateau, Broken Ridge and Kerguelen Archipelago: Editorial     

WALLACE  PAUL J.; FREY  FREDERICK A.; WEIS  DOMINIQUE; COFFIN  MILLARD F. 《Journal of Petrology》2002,43(7):1105-1108

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DISCUSSION OF "Geochemical and Kinetic Evolution of a Karst Flow System: Laurel Creek, West Virginia," by Christopher G. Groves     

Eberhard Werner 《Ground water》1993,31(1):146-147

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Recent Volcanism in the Puyehue--Cordon Caulle Region, Southern Andes, Chile (40?5?S): Petrogenesis of Evolved Lavas     

GERLACH  DAVID C.; FREY  FREDERICK A.; MORENO-ROA  HUGO; LOPEZ-ESCOBAR  LEOPOLDO 《Journal of Petrology》1988,29(2):333-382

Puyehue Volcano (40?5?S) in the southern volcanic zone (33?–46?)of the Andes is a largely basaltic stratovolcano constructedon a highly eroded, dominantly andesitic volcanic center. Duringgrowth of Puyehue Volcano there was a trend from basaltic tomore siliceous lavas, and the most recent eruptions (1921–22,1960) are Cordon Caulle rhyodacites and rhyolites erupted fromfissures northwest of the volcano. These basaltic through rhyoliticlavas define a medium-K₂O suite of tholeiitic affinity withtrace element and Pb-isotopic signatures typical of volcanicrocks associated with subduction zones. Most of the evolved lavas, ranging from andesite to rhyolite,formed by low to moderate pressure ( 5 kb) fractional crystallizationof a plagioclase-dominated anhydrous assemblage. Magma mixingproduced aphyric basaltic andesites with anomalously high incompatibleelement contents and latestage andesites with disequilibriumphenocryst assemblages. The age progression from abundant basaltto younger, less voluminous, more silicic lavas reflects increasinglygreater degrees of fractional crystallization which caused theapparent compositional gap between mixing end members to widen. There is no evidence in the silicic lavas for assimilation ofgeochemically distinctive continental crust. Puyehue basaltsare surprisingly more heterogeneous in ⁸⁷Sr/⁸⁶Sr (0?70378–0?70416)and incompatible element abundance ratios (e.g., La/Sm, Ba/Nb)than the more evolved lavas. This geochemical variability mayreflect subcrustal source heterogeneities or contamination bylower crust. The older basaltic andesites and andesites underlyingthe Puyehue edifice have Sr and Nd isotopic ratios and incompatibleelement abundance ratios within the range of Puyehue basalts.Apparently, similar sources and processes were involved in theirgenesis.  相似文献   

Grundwasser der Zentralsahara: Fossile Vorräte     

Prof. Dr. Eberhard Klitzsch  Dr. Christian Sonntag  Dipl.-Geol. Klaus Weistroffer  Prof. Dr. E. M. El Shazly 《International Journal of Earth Sciences》1976,65(1):264-287

Zusammenfassung Aufgrund von¹⁴C-Datierungen, die an mehr als 40 Grundwasserproben aus Südlibyen vorgenommen wurden, wird nachgewiesen, daß die Grundwasservorräte des Murzuk-Beckens weitgehend fossil sind. Sie werden unter den gegenwärtigen klimatischen Bedingungen kaum ergänzt, was sehr wahrscheinlich ebenso auf den Hauptteil der Grundwasservorräte anderer Becken der Sahara zutrifft. Für die frühere Vorstellung, das Grundwasser werde in regenreicheren Gebirgen etwa der südlichen Sahara ausreichend ergänzt und fließe im Unterbau großflächig nach Norden, gibt es keine Hinweise. In Abhängigkeit vom ursprünglichen Ablagerungsmilieu und vom Speichergestein haben die Grundwässer der verschiedenen hydrogeologischen Teilprovinzen des Murzuk-Beckens jeweils spezifische hydrochemische Eigenschaften, und sie sind unterschiedlich alt. Als Ursache hierfür ist anzusehen, daß die Regenerationsmöglichkeiten innerhalb der verschiedenen Einzugsgebiete nicht immer einheitlich waren, außerdem kam es stellenweise zur Vermischung älterer mit jüngeren Grundwässern. Von erklärbaren Ausnahmen abgesehen entstammen die untersuchten Wässer dem letzten Pluvial, einige gehören nachpluvialen Feuchtphasen an. Das¹⁴C-Alter der meisten Wasserproben liegt zwischen 20 000 und 40 000 Jahren.

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¹⁴C-dating of more than 40 samples of groundwater proves, that exploited ground-water in the Murzuk Basin area of southern Libya is mainly between 20 000 and 40 000 years old. This water, as probably most of the large groundwater reserves in other Saharian basins, has to be considered mainly fossil water without noteworthy recharge under present climatical conditions. The supposition, that Saharian groundwaters are recharged at mountainous areas in the south, as was postulated by several authors previously, has to be denied, at least as respects the central Sahara.Waters of all groundwater subprovinces investigated in southern Libya show reservoir specific chemical characteristics. Differences in age are partly depending on differing recharge possibilities at the recharge areas and partly they are the result of mixture between younger and older waters. The water mainly results from precipitations of the last pluvial period of the Sahara, some from rainfalls of later subpluvial periods.

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Résumé Des datations par la méthode¹⁴C, effectuées sur plus de quarante échantillons d'eau provenant des nappes souterraines du Sud de la Libye, prouvent que les réserves des nappes souterraines du Bassin de Mourzouk sont essentiellement fossiles. Dans les conditions climatiques actuelles, elles ne peuvent pratiquement pas être complétées. Cette constatation concerne aussi, très vraisemblablement, la partie principale des réserves des nappes souterraines des autres bassins du Sahara. Aucune indication ne semble capable d'étayer les concepts antérieurs traitant d'une alimentation, encore suffisante aujourd'hui, de la nappe souterraine, coulant vers le Nord sur de grandes surfaces dans le sous-sol du Sahara, par les montagnes riches en pluies à peu près au Sud du Sahara.Les nappes souterraines des différentes parties des provinces hydrogéologiques du Bassin de Mourzouk possèdent, respectivement, des propriétés hydrochimiques spécifiques, dépendant du milieu de dépôt primitif et de la roche réservoir. Leurs distances variables jusqu'à l'ancienne aire d'alimentation et aussi sûrement, par endroit, le mélange imaginable d'eaux plus jeunes et plus vieilles causent, en partie, leurs différences d'âge.Les eaux étudiées, sauf quelques exceptions insignifiantes et faciles à expliquer, proviennent, d'une part des dernières grandes pluies, et d'autre part, pour quelques unes, des phases humides (post-pluviales). Elles ont, en grande partie, 20 000 à 40 000 ans.

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Eo-Alpine Metamorphism in the Uppermost Unit of the Cretan Nappe System — Petrology and Geochronology     

Eberhard Seidel  Martin Okrusch  Hans Kreuzer  Helmut Raschka  Wilhelm Harre 《Contributions to Mineralogy and Petrology》1976,57(3):259-275

Judging from relevant experimental data for the gneiss assemblage including the Fe/Mg distribution on coexisting garnet and cordierite, the P-T conditions of metamorphism are estimated at about 700° C and 5 kb water vapour pressure.K/Ar determinations on hornblendes from three amphibolites yielded cooling ages of 71.3, 71.2, and 71.1 (±1.7) m.y. respectively; biotites from three paragneisses gave 70.2 ± 1.4, 69.7 ± 1.2, and 67.9 ± 1.4 m.y. respectively. Assuming a sealing temperature against argon diffusion of 300° C, for biotite, and 500° C, for hornblende, a cooling rate of 100–200° C/m.y. is calculated. Thus a late Cretaceous (eo-Alpine) metamorphic event is established in the post-Cretaceous nappes of Crete.  相似文献   

Ein verbessertes Strukturmodell für die Ostalpen,abgeleitet aus refraktions-seismischen Daten unter Berücksichtigung des Alpen-Längsprofils     

Dr Heinz Miller  Dr Helmut Gebrande  Dr Eberhard Schmedes 《International Journal of Earth Sciences》1977,66(1):289-308

Zusammenfassung Die Vermessung des Alpen-Längsprofils 1975 lieferte unter anderem Daten zur verbesserten Bestimmung der Geschwindigkeits-Tiefen-Verteilung unter dem Alpen-Hauptkamm. Diese Geschwindigkeits-Tiefen-Verteilung ist charakterisiert durch eine mächtige Inversionszone im Tiefenbereich zwischen 20 und 30 km — sie liegt somit tiefer als bei früheren Modellen — sowie eine weitere weniger ausgeprägte Inversionszone in der Unterkruste. Eine mit diesen Ergebnissen konsistente Reinterpretation des EschenloheSüdost-Profils ermöglichte die Konstruktion eines zweidimensionalen Krustenmodells längs der Linie Eschenlohe-Triest. Dieses Modell ist auch in guter Übereinstimmung mit Ergebnissen der Refraktionsprofile Eschenlohe-Ost und Lago Lagorai-Ost. Darüber hinaus befriedigt es Laufzeitbeobachtungen von Nachbeben aus der Region Friaul.

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Refraction seismic measurements along the Alpine Longitudinal Profile 1975 yielded among other things data for a reliable determination of the velocity-depth distribution beneath the crest of the Alps. This velocity-depth distribution is characterized by a rather thick inversion zone in the depth range between 20 and 30 km — which is deeper than with earlier models — as well as another less pronounced one in the lower crust. A reinterpretation of the Eschenlohe-Southeast profile consistent with these new data allowed the development of a two-dimensional crustal model along the line Eschenlohe-Trieste. This model is in excellent agreement with results from refraction profiles Eschenlohe-East and Lago Lagorai-East. It furthermore satisfies travel time observations from aftershocks of the Friulian earthquake.

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Résumé La campagne ALP 1975 a permis entre autres de donner une meilleure détermination de la répartition de la vitesse en profondeur v(z) sous la crête principale des Alpes. Celle-ci est caractérisée par une épaisse zone d'inversion de vitesse (LVZ) entre 20 et 30 km, donc plus profonde que les modèles antérieurs, et une seconde zone d'inversion moins prononcée dans la croûte inférieure. Tenant compte de ces résultats nous avons fait une réinterprétation du profil Eschenlohe-Sud-Est, ce qui nous permet de construire une coupe structurale de la croûte le long de la ligne Eschenlohe-Trieste. Ce modèle est en bon accord avec les résultats des profils Eschenlohe-Est et Lago Lagorai-Est et avec des durées de propagation déterminées pour des répliques du séïsme du Frioul.

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A Lithospheric Seismic Profile Along the Axis of the Alps; paper No. II.  相似文献   

Petrology and Trace Element Geochemistry of the Honolulu Volcanics, Oahu: Implications for the Oceanic Mantle below Hawaii   总被引：7，自引：9，他引：7  

CLAGUE  DAVID A.; FREY  FREDERICK A. 《Journal of Petrology》1982,23(3):447-504

The Honolulu Volcanics comprises small volume, late-stage (post-erosional)vents along rifts cutting the older massive Koolau tholeüticshield on Oahu, Hawaii. Most of these lavas and tuff of theHonolulu Volcanics have geochemical features expected of near-primarymagmas derived from a peridotite source containing Fo_87–89olivine; e. g. 100 Mg/(Mg + Fe²⁺) >65, >250 p. p. m. Ni,and presence of ultramafic mantle xenoliths at 18 of the 37vents. Consequently, the geochemistry of the alkali olivinebasalt, basanite, nephelinite and nepheline melilitite lavasand tuff of the Honolulu Volcanics have been used to deducethe composition of their mantle source and the conditions underwhich they were generated by partial melting in the mantle. Compositional trends in 30 samples establish that the magmaswere derived by partial melting of a garnet (<10 per cent)Iherzolite source, which we infer to have been carbon-bearing,from analogy with experimental results. This source was isotopicallyhomogeneous (Sr, Lanphere & Dalrymple, 1980; Pb, Sun, 1980;Nd, Roden et al., 1981), and we infer that the source was compositionallyuniform in all major-element oxides except TiO₂, in compatibletrace elements (Sc, V, Cr, Mn, Co and Ni), and in highly incompatibletrace elements (P, Th, La, Ce). However, the source appearsto have been heterogeneous in TiO₂, Zr, Hf, Nb, and Ta, elementsthat were not strongly incompatible during partial melting.Some nepheline melilitite samples may be derived from a sourcewith distinct Sc and heavy-rare-earth-elements (REE) abundances,or which had a phase or phases controlling the distributionof these elements. The relatively limited abundance range for several elements,such as Ti, Zr, Nb, is partly a consequence of the low degreesof melting inferred for the series (2 per cent for nephelinemelilitite, 11 per cent for alkali olivine basalt), which failedto exhaust the source in minor residual phases. We infer thatthese residual phases probably included phlogopite, amphibole,and another Ti-rich phase (an oxide?), but not apatite. In comparison with estimates of a primordial mantle compositionand the mantle source of mid-oceanic-ridge basalt the garnetperidotite source of the Honolulu Volcanics was increasinglyenriched in the sequence heavy REEs, Y, Tb, Ti, Sm, Zr, andHf all <P <Nd <Sr Ce <La <Nb Ta. A multi-stagehistory for the source of the Honolulu Volcanics is requiredbecause this enrichment was superimposed on a mantle that hadbeen previously depleted in incompatible elements, as indicatedby the relatively low ⁸⁷Sr/⁸⁶Sr ratio, high ¹⁴³Nd/¹⁴⁴Nd ratioand low contents of K, Rb, Ba, and Th. The composition of thesource of the Honolulu Volcanics differs from the source ofthe previously erupted tholeiitic shield. The modal mineralogyof the source of the Honolulu Volcanics is not represented inthe upper-mantle xenoliths, e. g. the garnet pyroxenite andolivine-poor garnet Iherzolite included within the lavas andtuff of the unit.  相似文献   

Chloritoid-bearing metapelites associated with glaucophane rocks in western Crete,Greece     

Eberhard Seidel  Martin Okrusch  Wolfgang Schubert 《Contributions to Mineralogy and Petrology》1975,49(2):105-115

In western Crete, Greece, a widespread occurrence of chloritoid-bearing metapelites with the main mineral assemblage chloritoid-phengitic white mica-Fe-rich chlorite-quartz was recorded to form the country rock of glaucophane-bearing metabasalts. Six bulk rock analyses of the metapelites conform to the compositional restrictions evaluated by Hoschek (1967) for the formation of chloritoid. Three microprobe analyses revealed chloritoid compositions low in Mg and Mn, and, consequently, high in Fe. The metamorphic grade documented in the metapelites is obviously related to a subsequent prograde metamorphism by which, in the adjacent meta-basalts, epidote is formed at the expense of lawsonite. No relict of a high-P, low-T assemblage, in part well preserved in the meta-basalts, was recognized in the chloritoid schists. The significance of the metamorphic history is briefly discussed.  相似文献