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1.
D.K. Paul P. Kresten T. Ray Barman R.H. McNutt A.O. Brunfelt 《Journal of Volcanology and Geothermal Research》1984,21(1-2)
Petrographic and geochemical data are given for some basaltic rocks from the Koynaghat, Ambaghat and Panvel sections of the western Deccan volcanic province. This study confirms geochemical features established earlier for the Deccan basalts but brings out minor additional characters. Mineralogical and major-element compositions of the basaltic flows from the Koyna and Panvel sections indicate tholeiitic affinity; the Ambaghat flows exhibit a slight affinity towards alkali basalt. Rare earth element (REE) distribution patterns and trace-element abundances suggest minor fractionation of olivine and plagioclase during the evolution of the flows. The general similarity of chemical and mineralogical features over a wide area and the lack of conspicuous inter-element relationships suggest that the flows reflect the combined effects of partial melting, minor mineral fractionation and selective crustal contamination. 相似文献
2.
Peter Kresten Erik åhman Arild O. Brunfelt 《International Journal of Earth Sciences》1981,70(3):1215-1231
Alkahne ultramafic lamprophyres and associated carbonatite dykes form north-south trending dyke swarms. The lamprophyres are sub-divided into micaceous, picritic and breccia varieties. Carbonatites sensu stricto (beforsites) occur very subordinate.The dykes of the Kalix area show great similarities to petrographically related rocks from other Scandinavian occurrences (Sokli, Alnö and Fen). Major differences are found in their tectonic setting (regularly striking dyke swarms) and the REE-pattern (distinctly negative cerium anomalies).The following petrogenetic model is advanced for the Kalix dykes: (1) partial melting of upper mantle material, (2) Intrusion into a crustal magma chamber, fractional crystallization, (3) Interactions between crystallized material and the volatile phase (light REE depletion, oxidation of cerium), (4) Intrusion in fracture zones under horizontal tension.
Zusammenfassung Alkalin-ultrabasiscbe Lamprophyre und begleitende KarbonatitgÄnge bilden nordsüdlidi streichende GangschwÄrme. Die Lamprophyre zeigen gewisse Ähnlichkeiten zu alnöitischen und kimberlitischen Gesteinen; sie wurden unterteilt in glimmerreiche und pikritische Lamprophyre sowie Brekzien. Karbonatite im engeren Sinn treten nur sehr untergeordnet auf; sie sind als Beforsite charakterisiert.Die Ganggesteine des Kalix-Gebiets weisen gro\e Ähnlichkeiten mit petrographiscb verwandten Gesteinen von anderen skandinavischen Vorkommen (Sokli, Alnö und Fen) auf. GrundsÄtzliche Unterschiede finden sich vor allem im tektonischen Auftreten (ziemlich konstant streichende GangschwÄrme) und im Verteilungsmuster der seltenen Erden (deutlich negative Cer-Anomalien).Die Bildung der Kalix-GÄnge wird folgenderweise erklÄrt: (1) Partielle Aufschmelzung des oberen Mantels, (2) Intrusion der Schmelze in eine krustale Magmakammer, gefolgt von fraktionierter Kristallisation, (3) Reaktion zwischen vorzugsweise kristallisiertem Material und der volatilen Phase (Entarmung an leichten seltenen Erden, Oxidation des Cers), (4) Intrusion in Bruchzonen, die horizonteller Dehnung ausgesetzt sind.
Résumé Des lamprophyres alcalins ultrabasiques accompagnés de carbonatites forment des essaims de dykes de direction nord-sud. Les lamprophyres se subdivisent en variétés micacée, picritique ainsi que brÊchique. Les carbonatites sensu stricto sont rares et sont plutÔ des beforsites.Les dykes de la région de Kalix présentent de grandes similitudes avec des roches pétrographiquement apparentées d'autres localités Scandinaves (Sokli, Alnö et Fen). Les différences essentielles sont dues à leur situation tectonique (essaims de dykes de direction régulière) ainsi qu'à la distribution des Terres Rares (anomalie négative distincte de cérium).Le modèle pétrogénétique suivant est proposé pour les dykes de Kalix: (1) fusion partielle de matériau du manteau supérieur, (2) intrusion dans une chambre magmatique de l'écorce et cristallisation fractionnée, (3) interaction entre le material déjà cristallisé et la phase volatile (appauvrissement des éléments légers des Terres Rares, oxydation du cérium), (4) intrusion le long de zones de fracture dans des conditions d'extension horizontale.
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3.
P. Kresten 《Lithos》1980,13(2):153-158
The model of dyke emplacement proposed by v. Eckermann could not be confirmed by the present study. A new model is suggested, involving up-doming of the wall-rock due to the intrusion of magma (accompanied by the formation of radial dykes and two sets of cone sheets), followed by subsidence (formation of sövite ring dykes and two other sets of cone sheets). 相似文献
4.
Dr. Peter Kresten 《International Journal of Earth Sciences》1983,72(1):389-395
Based upon the composition of carbonatites of the Fen Complex in Norway and the Alnö Complex in Sweden, the following nomenclature of carbonatitic rocks is suggested: Carbonatites (> 70 % carbonate minerals), sub-divided into the calcitic sövites and alvikites, the dolomitic to ankeritic rauhaugites and beforsites and the alkali-carbonatitic lengaite. Silico-carbonatites are rocks with 50–70 % carbonate minerals. They are subdivided into silico-sövites, silico-alvikites, silico-rauhaugite and silico-beforsite. 相似文献
5.
Physical behaviour of Cretaceous calcareous nannofossil ooze: Insight from flume studies of disaggregated chalk 
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下载免费PDF全文 Toms Buls Kresten Anderskouv Patrick L. Friend Charlotte E. L. Thompson Lars Stemmerik 《Sedimentology》2017,64(2):478-507
Geomorphic features such as drifts, sediment waves and channels have been documented in the Upper Cretaceous of north‐west Europe. These features are interpreted to result from bottom currents and have been used to refine chalk depositional models and quantify palaeocirculation patterns. Chalk was first deposited as calcareous nannofossil ooze and geomorphic features are the result of sediment reworking after deposition. There is limited knowledge on the processes that govern nannofossil ooze mobility, thus forcing uncertainty onto numerical models based on sedimentological observations. This article provides an extensive view of the erosional and depositional behaviour of calcareous nannofossil ooze based on experimental work using annular flumes. A fundamental observation of this study is the significant decrease of nannofossil ooze mobility with decreasing bed porosity. Erosion characteristics, labelled as erosion types, vary with total bed porosity (φ) and applied shear stress (τ0). High‐porosity ooze (φ >80%) is characterized by constant erosion rates (Em). At φ <77%, however, erosion characteristics showed greater variance. Surface erosion was typically followed by transitional erosion (with asymptotically decreasing Em), and stages of erosion with constant, and exponential erosion rates. The estimated erosion thresholds (τc) vary from ca 0·05 to 0·08 Pa for the onset of surface erosion and up to ca 0·19 Pa for the onset of constant erosion (φ of 60 to 85%). Variability of deposition thresholds (τcd) from ca 0·04 to 0·13 Pa reflects the influence of variable suspended sediment concentration and τ0 on settling particle size due to the identified potential for chalk ooze aggregation and flocculation. Additionally, deposition thresholds seem to be affected by the size of eroded aggregates whose size correlates with bed porosity. Lastly, slow sediment transport without resuspension occurred in high‐porosity ooze as surface creep, forming low‐relief sedimentary features resembling ripples. This process represents a previously undescribed mode of fine‐grained nannofossil ooze transport. 相似文献
6.
The first occurrence of a discrete diopside nodule in alnöite from Alnö Island is reported. The diopside differs from all other Alnö clinopyroxenes by its subcalcic composition, low titanium content (0.5% TiO2) and elevated chromium content (0.2% Cr2O2). An upper mantle origin for the diopside is suggested. The conditions of equilibration are estimated to 975°C at 15–20 kb. Pressure estimates have been deduced from the geotherm obtained for the Fen (Norway) lherzolites. This geotherm (oceanic type) is regarded as a maximum geotherm for the Alnö intrusion. 相似文献
7.
An assemblage of geoduck clam shells from the marine environment of coastal British Columbia was studied. Shells were cut
and the widths of internal shell growth increments, annuli, were measured from the hinge plate. The largest shells showed
more than one hundred annual increments. Shell growth exhibited juvenile maxima at ontogenetic ages 3–6 years. The growth
maximum was followed by a distinct decline that continued until the death of each individual. Further, this ontogenetic growth
trend was mathematically removed from the data in order to examine growth variations other than ageing. The longest growth
records from the oldest shells were compared to monthly indices of the Pacific Decadal Oscillation (PDO). It was found that
the PDO exerts the strongest influence on the shell growth during the very start of the growing season, in February and March.
We also detected increased magnitude of growth variations towards the end of the 20th century. Similar trends were apparent
in the PDO record. Moreover, the shell specimen displaying the strongest trend of increasing variance had the strongest PDO-linked
regional growth signal. Our results support the view that PDO exerts a governing influence on the biological and ecological
system along Northeast Pacific coastal areas. Incorporation of geoduck shell growth increment analyses into multi-disciplinary
studies dealing with palaeoceanography and archaeology is suggested as a promising future approach. 相似文献
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9.
Kimberlitic zircons from 16 intrusions in Lesotho, the Republic of South Africa, and Tanzania have been investigated. The following characteristics distinguish the kimberlitic zircons from the zircons derived from most other sources: 1. Rounded to subrounded grains predominate; euhedral zircons are very rare. 2. Perfect parting in several directions, mainly (100) and (111). 3. Lattice distortions occur (decreasing molar volume). 4. High abundancy of fluid inclusions, occupying healed fractures. 5. Uranium contents less than 30 ppm U. Low contents of Th, Y, P, REE. 6. Whitish alteration rims composed of monoclinic and tetragonal zirconia in varying proportions are common. — The use of zircons in order to identify and trace kimberlite intrusives is discussed, as there may be a possible connection between some properties of the kimberlitic zircons and the diamond grade of their host rocks. 相似文献
10.
Myriam Boussaha Nicolas Thibault Kresten Anderskouv Julien Moreau Lars Stemmerik 《Sedimentology》2017,64(7):1998-2030
Detailed facies analysis of a 350 m long core of upper Campanian–Maastrichtian chalk at Stevns Peninsula, eastern Denmark, shows that four mudstone and wackestone chalk facies account for close to 95% of the succession, and that bioturbated mudstone chalk alone accounts for nearly 55% of the sediment. Sedimentation took place in deep water, below the photic zone and storm‐wave base, and is characterized by decimetre to metre‐scale variations in facies and trace fossil assemblages indicating repeated shifts in depositional environment. Integration of facies with published data on sea‐surface temperature and accumulation rates suggests that sea‐surface temperature is the most important parameter in controlling stratification of the water column and thereby, indirectly, the observed variations in depositional facies. However, bioturbated mudstone chalk occurs in all stratigraphic levels independent of accumulation rates and sea temperatures and is interpreted to represent a very broad set of deep water environmental conditions with an ample supply of calcareous nannofossil debris and intense bioturbation. Longer term shifts in deposition are best expressed by distribution of clay, flint and bioturbated micro‐wackestone, bioturbated wackestone and laminated mudstone chalk facies, whereas the trace fossil assemblages appear less useful. The data set indicates overall shallowing over time with two distinctive events of clay influx to the basin during the late Campanian–earliest Maastrichtian and late Maastrichtian. 相似文献