摘要:

Ultramafic dykes associated with dolerites and rhomb porphyries along the northern Skagerrak coast of Sweden seem closely related with the igneous activity in the Oslo Rift zone. On the basis of field evidence, petrography and geochemistry, a cumulus origin of the ultramafic dykes is suggested.

ISSN:0016-786X    

DOI:10.1080/11035898209453698

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898209453699

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Åreskutan is a type locality for the complex of Seve nappes, which covers vast areas in the Swedish Caledonides. Here, an upper tectonic unit, the Åreskutan Nappe, composed of migmatitic gneisses and metabasites metamorphosed in granulite facies, is separated by a thrust from a lower Seve unit. Various rocks in the Åreskutan Nappe have been investigated using Rb-Sr and U-Pb techniques. Conventional Rb-Sr whole-rock analyses fail to yield isochrons but show that the rocks are clearly Precambrian. Small-scale whole-rock samples from the neosome part of a 2 kg migmatized metabasite specimen define an isochron with the age 414 ± 27 Ma, while paleosome samples from the same specimen scatter about this isochron. The age is considered to date the migmatization. A late, cross-cutting pegmatite gives an age of 395 ± 40 Ma, and minerals separated from a gneissic granite give 390 ± 45 Ma. Zircon from gneissic granite and from metabasite give a discordia line with lower and upper intercept ages of 386 ± 12 and 1570 ± 25 Ma, respectively. All zircons plot closer to the lower than to the upper intercept. The old Pb component present in the zircon is situated in cores, the overgrowth of which took place during the high-grade Caledonian metamorphism. This conclusion is supported by the result of a stepwise dissolving experiment carried out on a core-bearing zircon sample. The lower intercept age, which dates this overgrowth, is somewhat low due to later, minor Pb-loss. Monazite from garnet-sillimanite gneiss has almost concordant U-Pb ages conforming to a lower intercept age of 402 Ma.

ISSN:0016-786X    

DOI:10.1080/11035898209453700

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Greenschist facies semipelitic metamorphic rocks of Lower Palaeozoic age in Sunnhordland region, SW Norway contain a well-developed crenulation cleavage of the second generation. In the generation of the crenulation cleavage from a pre-existing fabric, gradations exist between discrete crenulation cleavage to zonal crenulation cleavage. The orientation of phyllosilicates within the cleavage septa is controlled primarily by the relative dominance of solution transfer of materials in discrete cleavage and by microfolding mechanism in zonal cleavage. In the former, new phyllosilicates may lie sub-parallel to the cleavage, but in the latter, phyllosilicate orientation may be variable, usually bimodal. The sites of discrete (solution) planes in variably tight folds, and the degree of development of zonal cleavage are dependent on the flattening strain. The secondary dominal character of the rock is a feature related to compositional differentiation through microfolding and essentially, solution transfer.

ISSN:0016-786X    

DOI:10.1080/11035898209453701

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Some of the intrusion and metamorphic episodes in the Svecokarelian (early Proterozoic) orogenic development of northern Norrbotten County are discussed on the basis of U-Pb zircon and Rb-Sr whole-rock analyses. Prior to the main Svecokarelian folding, the mafic volcanic rocks of the Vittangi-Soppero-Karesuando belt were penetrated by hypabyssal sills, of which an albite-diabase has yielded a zircon age of about 1874 Ma. According to zircon data, intermediate to acid plutonic rocks were emplaced in close connection with the hypabyssal sills and in an early-orogenic stage at about 1880–1860 Ma. Corresponding Rb-Sr whole-rock systems have been more or less disturbed, however, indicating metamorphic-metasomatic conditions until at least 1700 Ma ago. A large granite massif south of Vittangi was emplaced, according to zircon data, at about 1795 Ma, while the 40 Ma younger Rb-Sr whole-rock isochron age is due to uplift or a delayed cooling process. Another granite dome, outcropping to the west of the above, has migmatized members of the Porphyry Group. The calculated Rb-Sr age of 1688 Ma for this granite, not an isochron agesensu stricto, is considered to be a minimum age of rock intrusion. It is thus conceivable that these dome-like granite massifs are contemporaneous late-orogenic (about 1800 Ma old) intrusions, which would position the extrusion of the volcanic rocks of the Porphyry Group within an early stage of the Svecokarelian orogenic development.

ISSN:0016-786X    

DOI:10.1080/11035898209453702

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

ISSN:0016-786X    

DOI:10.1080/11035898209453703

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Lead isotope composition of the secondary uranium minerals kasolite and wölsendorfite has been examined in a masspectrometer. The material originates from uranium mineralizations, radioactive pegmatites and a site with no known primary uranium mineral source. The lead of the secondaries consists of varying proportions of common lead (rock lead) and radiogenic lead formed by decay of uranium and thorium. Uranogenic lead dominates in all but one of the samples examined. The mineralization age is approximated by examining secondary uranium minerals. The secondaries are usually depleted in uranium in relation to lead, but the reverse relation also exists. The examined minerals, with one possible exception, seem to have been formed within recent geological time.

ISSN:0016-786X    

DOI:10.1080/11035898209453704

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

An integrated computer program system has been developed for flexible handling of X-ray powder diffraction data for minerals. Powder data from various sources may be processed, and crystallographic unit cell dimensions for all symmetries can be refined. A program which permits interactive search-match through an X-ray powder diffraction data file for minerals is also included. The mineral data have been extracted from the JCPDS(ASTM) files and the recent mineralogical literature. Illustrative test examples are given. All programs are written in Fortran IV for a NOVA 4/X computer, but may easily be modified for a similar computer.

ISSN:0016-786X    

DOI:10.1080/11035898209453705

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

The thermal conductivity of compact limestones was measured by means of the transient needle-probe method in the field and in the laboratory as well, A comparison of the two procedures indicates that the laboratory measurements are the most representative ones because of a better control of the influence from the surroundings. The water-saturated limestone samples measured under laboratory conditions have thermal conductivities of 2.52–3.34 W m−1K−1and densities of 2520–2690 kg/m3, which are in agreement with standard values. The thermal conductivities were found to increase with increasing density, and a linear correlation ofKw= 4.18 · 10−3ρ −7.97 (W m−1K−1) was obtained as a first approximation by the least squares method.

ISSN:0016-786X    

DOI:10.1080/11035898209453706

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor

摘要:

Three bore-hole cores (30–200 m long) from the latest Cretaceous chalk of southern Sweden (Limhamn area, Skåne) have been analyzed for planktic Foraminifera. The sequences are referable to the Upper Maastrichtian (Nephrolithus frequenscoccolith Zone). Planktic foraminiferal assemblages, mostly dominated byHeterohelix striataandGlobigerinelloides multispina, are of a typical high-latitude (Boreal) character.Rugoglobigerina rugosaand thePseudotextularia elegans-Racemiguembelina fructicosacomplex are occasionally abundant. TheP. elegans-R. fructicosacomplex is abundant in the uppermost parts of the sequences; this increase has been suggested by other workers to represent a climatically related migration from the Tethys. Other taxa are all rare (Hedbergella monmouthensis, Praeglobotruncana havanensis, Guembelitria cretacea, Heterohelix glabrans, Globigerinelloidessp., andGlobotruncanasp.). The proportions between the two dominating species,G. multispinaandH. striata, change systematically with time (towards increase inH. striata), and it is suggested that this represents a response to the shallowing of the Danish Embayment at the end of the Cretaceous reported by other workers. Four subzones are established within theH. striata-G. multispinaZone spanning the entire sequences: theR. rugosaSubzone II (lowermost), theR. rugosa-R. rugosaInterval-Subzone, theR. rugosaSubzone I, and theP. elegans-R. fructicosaSubzone (uppermost). TheR. rugosasubzones are distinguished by differentG. multispinal H. striataratios (> 1 in Subzone II and < 1 in Subzone I). TheP. elegans-R. fructicosaSubzone can be correlated with the latest MaastrichtianBelemnella casimirovensisbelemnite Zone, but the other subzones may be local.

ISSN:0016-786X    

DOI:10.1080/11035898209453707

出版商:Taylor & Francis Group    

年代:1982

数据来源: Taylor