Das albanische Erdbeben Ende 1930     

Ernst Nowack 《International Journal of Earth Sciences》1931,22(1):25-28

Ohne Zusammenfassung  相似文献   

Ultrahigh-pressure metamorphism and tectonics   总被引：11，自引：0，他引：11  

J. G. Liou  S. Banno  W. G. Ernst 《Island Arc》1995,4(4):233-239

Abstract Recognition of several ultrahigh-pressure (UHP) metamorphic terranes in continental collision belts has revolutionized the concept of geodynamic processes. In order to facilitate better communication and focus among active investigators, the Task Group III-6 of the International Lithosphere Program'Ultrahigh-Pressure Metamorphism and Geodynamics in Collision-type Orogenic Belts'held the first two day workshop at Stanford University in December, 1994. Petrotectonic settings, mineral paragenesis, geochronoldgy, and geochemical characteristics of UHP rocks from several recognized and suspected UHP terranes were addressed. This special issue presents 11 papers from the more than 50 contributions from the 88 participants representing 15 countries. Many challenging petrotectonic and petrochemical problems remain to be investigated. These include detailed P-T time paths for both the UHP unit and adjacent units, the role of fluids at mantle depths, deep seismic profiles and mechanisms and rate of exhumation of the UHP unit.  相似文献   

Geotectonic evolution of diamondiferous paragneisses, Kokchetav Complex, northern Kazakhstan: The geologic enigma of ultrahigh-pressure crustal rocks within a Paleozoic foldbelt   总被引：2，自引：0，他引：2  

N. L. Dobretsov  N. V. Sobolev  V. S. Shatsky  R. G. Coleman  W. G. Ernst 《Island Arc》1995,4(4):267-279

Abstract The Kokchetav Complex is a tectonic mega-melange consisting of seven pre-Ordovician units (units I-VII) of contrasting lithologies and P–T conditions of metamorphism, overlain and/or intruded by four post-recrystallization entities. Most of the constituent rock types display affinities with continental crust; paraschists and paragneisses, which carry biogenically produced carbon, clearly were laid down near the surface of the Earth. Microdiamond (and rare coesite) inclusions are contained in strong, refractory garnet, zircon, clinopyroxene, and kyanite, some of the constituent neoblastic phases of this metasedimentary unit. Systematic mineral parageneses and textural relationships support the hypothesis that the metamorphic assemblages represent a close approach to chemical equilibrium at the time of formation. Metamorphism of diamond-bearing paragneisses and schists transpired at 535 ± 5 Ma; physical conditions included minimum pressures of 40 kbar and temperatures exceeding 900 °C. Other associated units contain mineralogic evidence of somewhat lower to considerably lower pressures and temperatures: observed magnesite + diopside pairs, coesite, grossular-pyropic garnet, potassic clinopyroxene, Si-rich phengite, barroisite-crossite(?), aluminous titanite and/or Al-rutile, and the assemblage talc + kyanite + garnet all testify to relatively elevated pressures of formation. The metamorphosed lithotectonic units represent individual, discrete stages in what initially may have been a continuous P-T series, but intense post-metamorphic dislocation has resulted in the preservation of a chaotically mixed sequence rather than an unbroken gradation in preserved conditions of metamorphism. Only units I-III, and probably VIb may represent portions of a dismembered subduction zone lithologie assemblage. The uplift to mid-crustal levels and cooling of the mega-melange took place by about 515–517 Ma, at which time the complex was stabilized as a part of the Kazakhstan microcontinental collage. An hypothesized Late Vendian-Early Cambrian subduction of the Kazakhstan-North Tianshan(?) microcontinental salient to depths exceeding 125 km, followed by decoupling from the descending oceanic crust-capped lithospheric plate is held responsible for the ultrahigh-pressure metamorphism of the Kokchetav Complex. Inasmuch as vestiges of a calc-alkaline volcanic/plutonic arc of approximately Early Cambrian age are preserved as only scattered relics in the general region, the plate-tectonic setting may have involved an intra-oceanic, Marianas-type, incipient arc which was subsequently removed through transform faulting or erosion.  相似文献   

High-pressure Eo-Alpine parageneses developed in magnesian metagabbros,Gruppo di Voltri,Western Liguria,Italy     

B. Messiga  G. B. Piccardo  W. G. Ernst 《Contributions to Mineralogy and Petrology》1983,83(1-2):1-15

Aluminous, magnesian metagabbroic layers and pods occur in the Beigua serpentinite of Western Liguria, where they are associated with more voluminous (Fe+Ti)-rich lithologies. Both types were subjected to localized early rodingitization. All rocks show the effects of a pervasive, essentially isochemical, high-pressure Early Alpine metamorphism for which a sequence of mineral assemblages is partially preserved: eclogite → glaucophanic eclogite → Na+Al actinolitic amphibolite → greenschist. The nature of the eo-Alpine high-pressure recrystallization, and the origin of the protoliths are the subjects of this paper. Eighteen new bulk rock XRF analyses for the magnesian metagabbros, combined with previously published major element analytical data for the ferroan metagabbros, demonstrate that a spectrum of compositions exist in the Gruppo di Voltri. This chemical range is comparable to differentiated oceanic tholeiites and to plutonic ophiolite suites cropping out elsewhere in the Northern Apennines and Western Alps. Both (Al+Mg)- and (Fe+Ti)-rich protoliths are regarded as the products of crystal fractionation of an original basaltic melt which intruded the Beigua mantle during the opening of Mesozoic Tethys. Textural observations show that local reactions along grain boundaries produced the garnet+sodic clinopyroxene assemblages from low-grade precursor phase compatibilities. Garnet coronas and zoned blue → blue-green → green amphiboles attest to the prevalence of domain equilibrium. Summarization of approximately 170 new mineral analyses documents this paragenesis. Assuming an attendant load pressure of about 10 Kb during formation of the eclogites, nominal temperatures of Fe-Mg partitioning between garnet and omphacite range from 483 to 544° C and average 508° C, in good agreement with petrologic constraints provided by the regional metamorphic assemblages in the enclosing antigoritic serpentinite and in adjacent parts of Western Liguria. The early stage of rodingitization and serpentinization is thought to reflect metasomatism and hydration in the vicinity of a Tethyan spreading center or fracture zone near the surface of the sea floor. In contrast, the subsequent high-pressure production of eclogites probably was a consequence of the profound subduction of oceanic crust and its mantle underpinnings during eo-Alpine convergence. Only the culmination of this prograde event has been preserved in the Gruppo di Voltri, but buoyant return towards upper crustal levels following decoupling is recorded in the eclogitized magnesian metagabbros by a decompression paragenetic series, successive stages of which are represented by glaucophanic eclogite, Na+Al actinolitic amphibolite and prasinite, respectively.  相似文献   

Systematics of modal phenocryst assemblages in submarine basalts: Petrologic implications     

W. B. Bryan 《Contributions to Mineralogy and Petrology》1983,83(1-2):62-74

Phenocryst assemblages in ocean-ridge basalts generally show an increasing proportion of plagioclase as the total amount of phenocrysts increases. The variations in phase assemblages, as well as most crystal-liquid K_d's, are similar to variations (equimodal trends) predicted by low-pressure laboratory experiments, suggesting that many of these basalts have experienced varying degrees of low-pressure cyrstallization prior to quenching, with little sorting of crystals and liquid. Important exceptions include moderately to highly phyric basalts enriched either in plagioclase or olivine which lie well off the experimental trends. In these basalts, megacrysts and xenocrysts usually cited as evidence for magma mixing commonly represent a small proportion of the total crystalline phase assemblage. However, phase proportions for many of these basalts lie well outside the range that could be produced by simple mixing; selective gravitative sorting either prior or subsequent to mixing appears to be the likely explanation for these phyric basalts. A relation between spreading rate and phase proportions is neither supported nor refuted by the data, which as yet do not adequately represent fast-spreading ridges. Pyroxene-phyric varieties are especially common among LIL-element enriched (Group 2) basalts, and these basalts also show the greatest abundance of olivine-enriched (picritic) samples. Selective enrichment in plagioclase is more common among LIL-element depleted (Group 1) basalts, and pyroxene appears in Group 1 basalts only at relatively high degrees of crystallinity. These differences are consistent with expected compositional effects (including volatiles) on phase boundaries, as well as likely differences in depth (pressure) of mantle melting and magma fractionation. Sparsely to moderately phyric basalts tend to contain only olivine (±spinel) as phenocrysts, and lie in the olivine field in the projection from plagioclase in the CMAS tetrahedron. This is consistent with the concept that these magmas approach low-pressure equilibrium by olivine fractionation from a more picritic parent. The origin of these basalts, and relationships between them, remains an important fundamental problem. Phenocryst phase assemblages are consistent with the low-pressure phase saturation indicated by the projected positions of the associated glasses in CMAS. It is suggested that, in contrast to the classical practice of classifying basalts according to phase proportions, a classification based on presence and/or first appearance of each crystalline phase is both practical and petrogenetically significant for water-quenched submarine basalts.  相似文献   

Scavenging of heavy metals from particulates by brown seaweed     

S.N. Luoma  G.W. Bryan  W.J. Langston 《Marine pollution bulletin》1982,13(11):394-396

Concentrations of Cu, As, Pb, Zn and Ag (but not Cd, Co, Fe, Mn and Hg) in the tissues of benthic algae (Fucus vesiculosus) correlate significantly with concentrations in sediment. Metals which complex most strongly with algal tissues show the strongest correlations of algal tissue and sediment. Scavenging these metals from particulates may be an important source of uptake by the algae. If so, concentrations of Cu, As, Pb, Zn and Ag in algal tissues may not be good indicators of concentrations of these metals in solution.  相似文献   

Fish stocks under pressure from nylon monofilament gill-nets     

Victor Lilygreen  Bryan Meade 《Marine pollution bulletin》1982,13(8):263-266

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Heavy carbon in individual oxide grains from the Murchison meteorite     

Ernst Zinner  Samuel Epstein 《Earth and Planetary Science Letters》1987,84(4)

The carbon isotopic composition of individual oxide grains from Murchison HF—HCl acid residue CFOc has been measured in the ion microprobe. Many grains (Mg-spinel, Cr-spinel, and Fe-oxide) contain carbon with large¹³C excesses ranging to 7000‰ (corresponding to¹²C/¹³C= 11). In most cases the carbon is present as micron-sized subgrains. The association of silicon with the anomalous carbon points towards SiC as carrier. If this tentative identification is correct then the SiC grains most likely originated in the circumstellar atmospheres of red giants. Oxide grains in which the ¹⁸O/¹⁶O ratio has also been measured show variable¹⁶O excesses which are not correlated with the¹³C excesses. This indicates that the sources of the anomalous carbon and oxygen isotopic compositions of the oxide grains are unrelated.  相似文献   

The innovation of greenhouse crops in the Mediterranean area: The Turkish case     

Dr. Ernst Struck 《GeoJournal》1986,13(1):37-46

The cultivation of early vegetables has altered the agrarian regions of the Mediterranean coast. Even if this restructuring process has already been completed in many countries, it can still be observed in Turkey. The development on the S coast of Turkey, where in 1985 a total of 113 villages with winter vegetable cultivation were studied, serves as an example. Hot-house cultivation was introduced here in glass greenhouses near Antalya around 1940 and spread only slowly along the S coast. An accelerated increase in the land used for early season vegetables was triggered off by the technical innovation of under-plastic cultivation (plastic greenhouses, plastic tunnels) around 1965. The partial innovations glass greenhouse — plastic greenhouse — plastic tunnel were, because of their different capital intensity, adopted by different agrarian social groups. Today glass greenhouse-, plastic greenhouse-and plastic tunnel-regions have formed which have recently undergone a considerable degree of intermingling. The diffusion process of early vegetables in total, like that of the partial innovations, did not happen continuously, rather the changes were carried erratically over wide distances; the process of intermingling also showed such a form of spreading. A sociopsychological motive can be offered as a basis for this type of spreading, for which the term spasmodic diffusion is suggested: the comparatively high degree of isolation of the Turkish village communities from the outside world and their strong orientation inwards lead inevitably to isolation of innovations. Derived from this is the thesis that other spontaneous innovations in similarly structured agrarian regions also always spread erratically (spasmodic).  相似文献   

Sensitivity of cool-temperate forests and their fossil pollen record to rapid temperature change   总被引：1，自引：0，他引：1  

Margaret Bryan Davis  Daniel B. Botkin   《Quaternary Research》1985,23(3):327-340

Simulations of cool-temperate forest growth in response to climatic change using the JABOWA computer model show that a decrease of 600 growing degree-days (equivalent to a 2°C decrease in mean annual temperature) causes red spruce (Picea rubens) to replace sugar maple (Acer saccharum) as the dominant tree. These changes are delayed 100–200 yr after the climatic cooling, producing gradual forest changes in response to abrupt temperature changes, and reducing the amplitude of response to brief climatic events. Soils and disturbances affect the speed and magnitude of forest response. The delayed responses are caused by the difference in sensitivity of adult trees and younger stages. The length of the delay depends on the life history characteristics of the dominant species. Delayed responses imply that fossil pollen deposits, even if they faithfully record the abundances of trees in forests, may not be able to resolve climatic changes within 100–200 yr, or to record very brief climatic events. This explains why pollen deposits do not as yet show responses to climatic changes during the past 100 yr. Only the Little Ice Age, which lasted several centuries, caused sufficient forest change to be recorded in fossil pollen, and only at certain sites.  相似文献