Plume-Related Alkaline Basic Magmatism of the Kuznetsk Alatau: The Kia-Shaltyr Complex

ABSTRACTThe Souter Head sub-volcanic complex (Aberdeenshire, Scotland) intruded the high-grade metamorphic core of the Grampian Orogen at 469.1 ± 0.6 Ma (uranium-238–lead-206 (238U–206Pb) zircon). It follows closely peak metamorphism and deformation in the Grampian Terrane and tightly constrains the end of the Grampian Event of the Caledonian Orogeny. Temporally coincident U–Pb and argon/argon (40Ar/39Ar) data show the complex cooled quickly with temperatures decreasing from ca.800 °C to less than 200 °C within 1 Ma. Younger rhenium–osmium (Re–Os) ages are due to post-emplacement alteration of molybdenite to powellite. The U–Pb and Ar/Ar data combined with existing geochronological data show that D2/D3 deformation, peak metamorphism (Barrovian and Buchan style) and basic magmatism in NE Scotland were synchronous at ca.470 Ma and are associated with rapid uplift (5–10 km Ma−1) of the orogen, which, by ca.469 Ma, had removed the cover to the metamorphic pile. Rapid uplift resulted in decompressional melting and the generation of mafic and felsic magmatism. Shallow slab break-off (50–100 km) is invoked to explain the synchroneity of these events. This interpretation implies that peak metamorphism and D2/D3 ductile deformation were associated with extension. Similarities in the nature and timing of orogenic events in Connemara, western Ireland, with NE Scotland suggest that shallow slab break-off occurred in both localities.

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The Mesozoic-Tertiary evolution of the Aquitaine Basin

Philosophical Transactions of the Royal Society of London. Series A, Mathematical and Physical Sciences ◽

10.1098/rsta.1982.0026 ◽

1982 ◽

Vol 305 (1489) ◽

pp. 63-84 ◽

Cited By ~ 28

Keyword(s):

Upper Cretaceous ◽

Oil Fields ◽

Upper Eocene ◽

The South ◽

Gas Field ◽

Massif Central ◽

Tectonic Plates ◽

The North ◽

Basic Magmatism ◽

Aquitaine Basin

The Aquitaine Basin, situated in southwest France, with an area of about 60 000 km 2 , has the form of a triangle which opens towards the Atlantic (Bay of Biscay) and is limited to the north by the Hercynian basement of Brittany and the Massif Central, and to the south by the Pyrenean Tertiary orogenic belt. Beneath the Tertiary sequence (2 km thick, and which outcrops over much of the basin) a Mesozoic series, up to 10 km thick, rests generally on a tectonized Hercynian basement but locally it covers narrow (NW-SE-trending) post-orogenic trenches of Stephano-Permian age. The Mesozoic history can be subdivided into four major structural-sedimentary episodes: (1) during a Triassic taphrogenic phase a continental-evaporitic complex developed with associated basic magmatism; (2) throughout the Jurassic, a vast lagoonal platform developed, initially (Lower Lias) as a thick evaporitic sequence followed by a uniform shale-carbonate unit, indicating a relative structural stability; (3) the end of the Jurassic and the Lower Cretaceous saw a fragmentation of this platform, due to an interplay between the Iberian and European tectonic plates, resulting in an ensemble of strongly subsident sub-basins; (4) during the Upper Cretaceous and until the end of the Neogene, the evolution of the Aquitaine Basin was influenced by the Pyrenean orogenic phase, with the development, towards the south, of a trench infilled by flysch which, from the Upper Eocene, is succeeded by a thick post-orogenic molasse complex. The main hydrocarbon objectives in the basin are situated in the Jurassic platform (e.g. the Lacq giant gas field) and the Cretaceous sub-basins (e.g. the Cazaux and Parentis oil fields). To date, production has been about 4 x 10 7 m 3 of oil, and about 15 x 10 10 m 3 of gas since the first gas discovery (St Marcet) in 1939.

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A review of the geochronology of the Precambrian of Saskatchewan—some clues to uranium mineralization

Mineralogical Magazine ◽

10.1180/minmag.1981.044.336.02 ◽

1981 ◽

Vol 44 (336) ◽

pp. 371-378 ◽

Cited By ~ 9

Author(s):

Keith Bell

Keyword(s):

Hydrothermal Activity ◽

Uranium Mineralization ◽

Dyke Swarm ◽

Thermal Activity ◽

Late Proterozoic ◽

Vein Type ◽

Close Relationship ◽

Basic Magmatism ◽

Granitoid Rocks ◽

Depositional Age

AbstractAssessment of available geochronological information, as well as new whole-rock Rb-Sr data from several granitoid rocks of Saskatchewan, shows a close relationship between magmatic-metamorphic events in the Hudsonian orogen and uranium mineralization. Most uranium deposits lie to the west of the Needle Falls Shear Zone and occur as either: (i) vein-type deposits or (ii) unconformity-type deposits close to the contact between the Athabasca sediments and their basement. At least two metamorphisms have affected the pre-Athabasca rocks: the Kenoran at about 2500 Ma ago, and the more pervasive ‘main’ Hudsonian event at 1740 Ma. A much younger thermal event (perhaps associated with uplift and cooling) at 1540 Ma is also indicated. The post-Kenoran K-Ar dates suggest prolonged thermal activity from about 1900 Ma through to about 1500 Ma ago. Granitoid events at 1870 Ma and 1740 Ma ago are outlined by both U-Pb zircon and Rb-Sr whole-rock isochron data. Whole-rock Rb-Sr data from the unmetamorphosed Athabasca sediments suggest an approximate depositional age of 1450±50 Ma, a figure that is consistent with the age of the underlying Hudsonian basement and the truncation of the sediments by the Cree Lake diabase dyke swarm at about 1200–1300 Ma ago. Although several episodes of uranium deposition have been documented, the main ones seem to have occurred at 1860 Ma (syngenetic uraninite in pegmatites), 1740 Ma (the Beaverlodge vein-type deposits) and between 1300 and 800 Ma (the epigenetic uranium of the unconformity-type deposits). Whereas the two earlier episodes can be correlated with periods of either magmatic or metamorphic activity, the late Proterozoic episodes cannot. The close agreement between the age of the Cree Lake dyke swarm and the late Proterozoic mineralization suggests that at about 1300 Ma ago possible hydrothermal activity from relatively deep-seated fractures may have been responsible for the solution and transportation of the uranium of the unconformity-type deposits. The period 1300 Ma to about 900 Ma, in other parts of the Canadian Shield, was a time of crustal rifting, basic magmatism, carbonatite activity, and intense deformation. Prior to the deposition of the Athabasca sediments uranium was concentrated by Hudsonian magmatic and metamorphic processes whereas subsequently, transportation and intermittent deposition of the unconformity-type deposits were related to fairly long-lived, low-temperature hydrothermal activity.

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Early basic magmatism in the evolution of Archaean high-grade gneiss terrains: an example from the Lewisian of NW Scotland

Mineralogical Magazine ◽

10.1180/minmag.1987.051.361.02 ◽

1987 ◽

Vol 51 (361) ◽

pp. 345-355 ◽

Cited By ~ 9

Author(s):

H. R. Rollinson

Keyword(s):

Trace Element ◽

Source Region ◽

High Grade ◽

Ocean Ridges ◽

Layered Gabbro ◽

Basic Magmatism ◽

Melting Regime ◽

High Grade Metamorphism ◽

Tonalitic Gneiss ◽

Common Parent

AbstractAmphibolite blocks from an Archaean (2.9 Ga) trondhjemite-agmatite complex in the Lewisian at Gruinard Bay have a varied trace element and REE content. Whilst some of the variability is attributable to element mobility during high-grade metamorphism and subsequent trondhjemite magmatism, it is for the main part considered to be a primary feature of the amphibolites. The observed trace element and REE chemistry is best explained in terms of source region heterogeneity and suggests a melting regime comparable with that beneath certain types of mid-ocean ridge. There are geochemical similarities between the amphibolites and the Lewisian layered gabbro-ultramafic complexes, and the two may represent the derivative liquid and associated cumulates respectively from a common parent magma. Thus there is a parallel between the processes which generated some Archaean amphibolites and layered gabbro complexes and those operating beneath modern ocean ridges. Hornblendite and amphibolite pods enclosed within tonalitic gneiss, also found as blocks in the agmatite complex, are geochemically distinct from the main group of amphibolites and are probably of calc-alkaline parentage.

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