摘要:

AbstractThe Svalbard Platform, in middle Carboniferous time, was dominated by a series of NNW‐SSE oriented, asymmetric rift basins. The Landnørdingsvika Formation represents the infill of one such basin in the Bjørnøya (Bear Island) area and consists of red beds deposited during a regional rise of sea level. The basin was filled mainly from the west and southwest across a Carboniferous fault zone, the West Bjørnøya. Fault, which bounded the deep edge of the basin.The basin succession is dominated by floodplain and coastal plain deposits in its lower part and fanglomerates interbedded with shallow marine clastics and carbonates in its upper part. The marine facies gradually increase in volume upwards and culminate in the overlying, carbonate‐dominated Kapp Kåre Formation (Moscovian). This continental‐marine transition, which has also been identified in the other Svalbard basins, thus reflects an important middie‐late Palaeozoic transgression. Analysis of the facies sequences shows that there are repeated submergence‐emergence events which are superimposed on the longer term transition. These are interpreted in terms of repeated basin floor tilting and sinking against t

ISSN:0072-1050    

DOI:10.1002/gj.3350180102

出版商:John Wiley&Sons Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractIn the Mona Complex of Llŷn, a narrow, steep belt of fine grained schists known as the Penmynydd Zone of Metamorphism lies between a deformed melange (Gwna Group) and a unit of gneisses and plutonic rocks (Sarn Complex). Rocks within and adjacent to this Zone are characterized by mylonitic textures. The highest grade Penmynydd rocks on Llŷn reached greenschist and, locally, glaucophanitic greenschist fades conditions. The schist belt is interpreted as a major shear zone formed as the Sarn Complex moved up against the lower grade Gwna Group. A previous interpretation of the schists (Shackleton 1956) as being the result of a prograde metamorphism from sub‐greenschist facies Gwna Group to anatectic granitic and gneissic rocks of the Sarn Complex is rejec

ISSN:0072-1050    

DOI:10.1002/gj.3350180103

出版商:John Wiley&Sons Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractA section of hornfelsed Skiddaw Slate adjacent to the margin of the Grainsgill Greisen is described and chemical analyses of the various rock types presented. The results confirm that hydrothermal fluids liberated K and Na from the granite to produce the greisen. This gave rise to K metasomatism of the adjacent hornfels and to retrogressive metamorphism over a radius of 200m from the intrusion. Na leached from the hornfels near the intrusion and that liberated during the formation of the greisen are probably the sources of the Na in the brines recorded in fluid inclusions within the nearby quartz‐tungsten vein

ISSN:0072-1050    

DOI:10.1002/gj.3350180104

出版商:John Wiley&Sons Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractNepheline syenite gneiss is exposed in three localities near the village of Boca Nova (47·04′W, 1°51′S) in northeastern Pará, Brazil. Isotopic and chemical evidence for an igneous premetamorphic history include: (1) bulk compositions which plot in the Q–Ne–Ks system on a peralkaline fractionation curve; (2) bulk compositions which fall on the Hviddal igneous trend in the SiO2–Al2O3–Na2O + K2O molecular diagram; (3) an average K/Rb ratio identical to the average for nepheline syenites of the Khibina massif; (4) K/Rb ratios which lie on the ideal igneous fractionation curve; (5) Nb(Ta) contents far in excess of average crustal abundance; and (6) a low Sr87/Sr86value (0·7034) characteristic of mantle derivation.Post‐kinematic lit‐par‐lit injections, discordant veins, and concordant pods of leucocratic nepheline–alkali feldspar pegmatite partially replaced the metamorphic assemblage and destroyed any microscopic equilibrium texture that may have been present. The final disequilibrium assemblage consists of Fe‐rich biotite and two generations each of sodic plagioclase, microcline, and nepheline. Some minor metasomatic chemical effects may be present in the rocks but a case for nephelinization of crustal rocks cannot be documented. Field, petrographic, and chemical constraints indicate that the Boca Nova gneiss is an early‐stage migmatite formed by anatexis of metamorphosed igneous nepheline syenite or its volcanic equivalent. Regional metamorphism and partial melting opened the Rb‐Sr system so that the whole‐rock Rb/Sr isochron age of 724 m.y. has no unambiguous interpretation. A K/Ar age of 580 ± 10 m.y. from biotite denning the metamorphic foliation is regarded as a minimum date for the regional metamorphism and anatexis. No other alkaline rocks of comparable age

ISSN:0072-1050    

DOI:10.1002/gj.3350180105

出版商:John Wiley&Sons Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractRelict discordant relationships between thec.3000–2800 Ma old Nǔk granitic (s.l.) gneisses and thec.3700 Ma old Amǐtsoq gneisses of Ivisǎrtoq clearly indicate that the Nǔk gneisses originated as intrusive sheets and bosses. The older gneisses are preserved as continuous banded units which are injected by thin granitic dykes and sills and become progressively disrupted by increasing proportions of intrusive Nǔk granitic material until they occur merely as discrete xenoliths and enclaves dissemminated within a younger gneiss matrix. The Nǔk granites were emplaced into the cores of developing large scale folds within intercalated oceanic and ancient continental portions of the Archaean crust, previously interleaved by th

ISSN:0072-1050    

DOI:10.1002/gj.3350180106

出版商:John Wiley&Sons Ltd    

年代:1983

数据来源: WILEY

摘要:

AbstractBrachiopod‐dominated assemblages from the Allt y Clych conglomerate near Llanafan Fawr provide good evidence for a Silurian (Lower Llandovery) age. The conglomerates are interpreted as mass flow deposits and are related to the revised stratigraphy of Davies (1980) by emendation of some of the author's previous interpretation

ISSN:0072-1050    

DOI:10.1002/gj.3350180107

出版商:John Wiley&Sons Ltd    

年代:1983

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350180108

出版商:John Wiley&Sons Ltd    

年代:1983

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350180110

出版商:John Wiley&Sons Ltd    

年代:1983

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350180111

出版商:John Wiley&Sons Ltd    

年代:1983

数据来源: WILEY

ISSN:0072-1050    

DOI:10.1002/gj.3350180101

出版商:John Wiley&Sons Ltd    

年代:1983

数据来源: WILEY