Compositions of the Neoproterozoic Basement Rocks in Northern Vietnam and its Tectonic Significance

Petrology and the Western Rift of Central Africa

Geological Magazine ◽

10.1017/s0016756800098265 ◽

1932 ◽

Vol 69 (11) ◽

pp. 497-510 ◽

Cited By ~ 2

Author(s):

A. W. Groves

Keyword(s):

Rift Valley ◽

Volcanic Rocks ◽

Central Africa ◽

Volcanic Field ◽

Thin Sections ◽

Basement Rocks ◽

Geochemical Study ◽

Northern Half ◽

Tectonic Significance ◽

Near Future

IN the course of several journeys between Masindi and Butiaba, and one from Butiaba to Hoima (via Waki Camp), specimens of the various gneisses were collected from roadside exposures. Thin sections of these were subsequently studied by the writer in England with the result that they were found to yield evidence of tectonic significance. In addition, the writer has, during the last three years, examined petrographically a large number of other rocks from those parts of Uganda bordering the Lake Albert Depression. In particular he has made a special study of the Charnockite Series, which are widely spread over the northern half of the Protectorate, with the result that it has been possible to observe the effects of the rift valley movements on these rocks in the regions adjacent to Lake Albert. It is hoped to publish a petrological and geochemical study of the Charnockite Series of Uganda in the near future. In the following pages it is proposed in Part I to present petrological evidence from the basement rocks of various districts in the hinterland of the Lake Albert scarps and then in Part II to point out the tectonic significance of this evidence in the light of the various theories of rift valley formation. In Part III the relation between the petrological characters of the volcanic rocks and the rift valley tectonics will be briefly reviewed. In the case of the basement rocks the remarks will be confined to the Lake Albert Depression, but in the case of the volcanic rocks the discussion will extend also to Lakes George and Edward and the Birunga volcanic field.

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Geochemistry and tectonic significance of augen gneisses from the southern Menderes Massif (West Turkey)

Geological Magazine ◽

10.1017/s0016756800013613 ◽

1995 ◽

Vol 132 (3) ◽

pp. 287-301 ◽

Cited By ~ 33

Author(s):

E. Bozkurt ◽

J. A. Winchester ◽

R. G. Park

Keyword(s):

Lower Crust ◽

Early Eocene ◽

Late Oligocene ◽

Calc Alkaline ◽

Menderes Massif ◽

Early Oligocene ◽

Basement Rocks ◽

Metamorphic Basement ◽

Tectonic Significance ◽

Water Saturated

AbstractThe protoliths of mylonitized augen gneisses exposed in the southern sector of the Menderes Massif (West Turkey) are calc-alkaline, peraluminous, S-type, late- to post-tectonic tourmaline- and garnet-bearing, two-mica leucogranites. They cut and post-date the fabrics of the ‘main Menderes metamorphism’ which took place between the early Eocene and early Oligocene and intrude metamorphic basement rocks comprising the so-called ‘Palaeozoic schist envelope’ of the massif. They are themselves cut by an extensive network of tourmaline-rich dykes. Chemical, mineralogical, isotopic and field relations suggest that the granitic protolith crystallized from a boron-rich, water-saturated melt, derived from partial melting of metagreywacke in the lower crust during peak Barrovian-type metamorphism. The protolith was probably emplaced during lateorogenic extensional collapse of the thickened crust in west Turkey during late Oligocene time.

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Cld-St-And-Bearing Assemblages in the Central Southalpine Basement: Markers of an Evolving Thermal Regime during Variscan Convergence

Minerals ◽

10.3390/min11101124 ◽

2021 ◽

Vol 11 (10) ◽

pp. 1124

Author(s):

Marco Filippi ◽

Maria Iole Spalla ◽

Nicola Pigazzini ◽

Valeria Diella ◽

Jean-Marc Lardeaux ◽

...

Keyword(s):

High Temperature ◽

Structural Analysis ◽

Thermal Regime ◽

Intermediate Pressure ◽

Tectonic Events ◽

Basement Rocks ◽

Southalpine Basement ◽

Tectonic Significance ◽

The Alps ◽

Variscan Basement

Multiscale structural analysis was carried out to explore the sequence of superposed pre-Alpine chloritoid–staurolite–andalusite metamorphic assemblages in the polydeformed Variscan basement of the upper Val Camonica, in the central Southalpine domain. The dominant fabric in the upper Val Camonica basement is the late-Variscan S2 foliation, marked by greenschist facies minerals and truncated by the base of Permian siliciclastic sequences. The intersection with the sedimentary strata defines a Permianage limit on the pre-Alpine tectonometamorphic evolution and exhumation of the Variscan basement. The detailed structural survey revealed that the older S1 foliation was locally preserved in low-strained domains. S1 is a composite fabric resulting from combining S1a and S1b: in the metapelites, S1a was supported by chloritoid, garnet, and biotite and developed before S1b, which was marked by staurolite, garnet, and biotite. S1a and S1b developed at intermediate pressure amphibolite facies conditions during the Variscan convergence, S1a at T = 520–550 °C and P ≃ 0.8 GPa, S1b at T = 550–650 °C and P = 0.4–0.7 GPa. The special feature of the upper Val Camonica metapelites is andalusite, which formed between the late D1b and early D2 tectonic events. Andalusite developed at T = 520–580 °C and P = 0.2–0.4 GPa in pre-Permian times, after the peak of the Variscan collision and before the exhumation of the Variscan basement and the subsequent deposition of the Permian covers. It follows that the upper Val Camonica andalusite has a different age and tectonic significance as compared to that of other pre-Alpine andalusite occurrences in the Alps, where andalusite mostly developed during exhumation of high-temperature basement rocks in Permian–Triassic times.

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Petrochemistry and tectonic significance of Carboniferous volcanic rocks in New Brunswick

Canadian Journal of Earth Sciences ◽

10.1139/e86-121 ◽

1986 ◽

Vol 23 (9) ◽

pp. 1243-1256 ◽

Cited By ~ 14

Author(s):

L. R. Fyffe ◽

S. M. Barr

Keyword(s):

New Brunswick ◽

Tectonic Setting ◽

Volcanic Rocks ◽

Age Groups ◽

Late Paleozoic ◽

Basement Rocks ◽

Basaltic Composition ◽

Tectonic Significance ◽

Maritimes Basin ◽

Alkalic Basalts

Carboniferous volcanic rocks from the New Brunswick Platform in the Maritimes Basin are divided into three age groups. Late Tournaisian to early Visean volcanic rocks are tholeiitic basalts and andesites that, in southern New Brunswick, are inter-bedded with abundant calc-alkalic rhyolite. Late Visean to Namurian volcanic rocks consist of an interbedded sequence of alkalic basalts and trachyandesites. Late Westphalian volcanic rocks change in composition up section from trachyte to peralkalic rhyolite. All three age groups display petrochemical features indicative of an intraplate tectonic setting. The volcanic geochemistry is consistent with the development of the Maritimes Basin either as a failed rift formed along the margin of a late Paleozoic ocean or as a rhomb graben formed within a transcurrent zone; the former model is preferred. The change in basaltic composition from tholeiitic to alkalic apparently coincided with a decrease in rate of extension between the Tournaisian and Namurian. Local peralkalic volcanism occurred during regional sagging of the basin as extension ceased and basement rocks cooled in the Late Carboniferous.

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Geochemical characteristics of Precambrian Basement rocks from southeastern Nigeria: an approach to their petrogenesis and tectonic setting.

Geologica Acta ◽

10.1344/geologicaacta2020.18.19 ◽

2020 ◽

Vol 18 ◽

pp. 1-13

Author(s):

CHINEDU UDUMA IBE

Keyword(s):

Partial Melting ◽

Tectonic Setting ◽

Southeastern Nigeria ◽

Eu Anomaly ◽

Basement Rocks ◽

Geochemical Study ◽

Tectonic Significance ◽

Granitic Intrusions ◽

Ree Patterns

Trace and Rare-Earth element geochemical study of twenty samples of migmatitic banded gneisses, garnet biotite schists, dolerites, granites and rhyolites was carried out in a bid to determine their petrogenetic and tectonic significance in the evolution of the southeastern Basement complex of Nigeria. The data shows that partial melting (crustal anatexis) of migmatitic gneisses and schists played a significant role in the evolution of the granitic intrusions. This is supported by the high incompatible (Rb/Sr = 0.16 to 1.31 and Ba/Sr = 0.75 to 6.21) elements ratio in the granitic intrusions than that of the migmatitic gneisses and schists (Rb/Sr, 0.051 to 0.824; Ba/Sr, 0.7 to 5). High ratios of Ba/Sr and Rb/Sr and lesser values of Ba/Rb ratios in some granitic intrusions than in others suggests increasing fractionation during the anatexis. The role of partial melting is also evident in the smooth REE patterns shown by most of these rocks and the negative Eu anomaly as indicated by the values of Eu/Eu* (0.097 to 0.7). LREE enrichment is evident in the high values of Ce/YbN (12.08-174.5), La/YbN (15.2-228.4) and La/SmN (2.6-7.2) in the granitic intrusions. Tectonic discrimination diagrams of the rocks indicate that the basement rocks were most probably formed in a post-collision orogenic setting while the dolerite and the rhyolite were formed in within-plate anorogenic setting.

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