REE systematics and Nd model age of Upper Vendian argillites of the Shkapovo-Shikhan Depression

2006 ◽  
Vol 411 (1) ◽  
pp. 1267-1271
Author(s):  
A. V. Maslov ◽  
Yu. L. Ronkin ◽  
M. V. Isherskaya ◽  
O. P. Lepikhina
Keyword(s):  
Upper Vendian ◽  
Nd Model Age

Chapter 4 The Loch Maree Group

2002 ◽  
Vol 26 (1) ◽  
pp. 29-44
Keyword(s):  
Cross Section ◽  
Detrital Zircon ◽  
Main Part ◽  
Close Association ◽  
Volcanic Origin ◽  
Metasedimentary Rocks ◽  
Rock Types ◽  
Depositional Age ◽  
Nd Model Age ◽  
Narrow Bands

The supracrustal rocks of the Loch Maree Group (LMG) consist of a variety of metasedimentary rocks interbanded with amphibolites considered to be of volcanic origin. The metasedimentary rocks fall into two distinct categories: a) schistose semipelites, which form the main part of the outcrop; and b) narrow bands of different rock types, including siliceous, carbonate-bearing and graphitic rocks, occurring in close association with the metavolcanic amphibolites. Both the compositional banding and the dominant foliation throughout the LMG outcrop are steeply dipping and trend uniformly NW-SE.The sequence of lithotectonic rock units from SW to NE (structurally upwards) is shown in the cross-section (Fig. 4.1) and briefly described in Table 4.1. The original names of the lithotectonic units (Park 1964) are retained for convenience. The depositional age of the LMG is presumed to be around 2.0 Ga, based on a Sm-Nd model age (O'Nions et al. 1983) and detrital zircon dates (Whitehouse et al. 1991 a, 2001) (see below).Semipelites form several distinct NW-trending belts separated by amphibolite sheets. The most prominent belt comprises the Flowerdale schist unit (see map) which occupies a broad belt about 700 m in width, extending in a northwesterly direction across the Gairloch district, but ending north of the mapped area, where the two amphibolites from either side converge, 3.5 km north of the Gairloch-Poolewe road. This belt is offset in the centre of the area by the Flowerdale fault, and has a total exposed length of about 15 km. Southwest of this belt is the

scholarly journals Lithostratigraphy and geochemistry of Upper Vendian‒Lower Cambrian deposits in the northeastern Baltic monocline

2017 ◽  
Vol 25 (1) ◽  
pp. 1-20 ◽  
Author(s):  
V. N. Podkovyrov ◽  
A. V. Maslov ◽  
A. B. Kuznetsov ◽  
V. B. Ershova
Keyword(s):  
Lower Cambrian ◽  
Upper Vendian

scholarly journals Distribution of Microfossils in the Vendian Deposits of the Orsha Depression of the East European Platform, Belarus

2021 ◽  
Vol 29 (6) ◽  
pp. 627-640
Author(s):  
E. Yu. Golubkova ◽  
O. F. Kuzmenkova ◽  
E. A. Kushim ◽  
A. G. Laptsevich ◽  
S. S. Mankievič ◽  
...  
Keyword(s):  
East European Platform ◽  
Taxonomic Composition ◽  
Northwestern Part ◽  
East European ◽  
The Third ◽  
The North ◽  
Upper Vendian

Abstract— The complete sections of the Lower and Upper Vendian of the East European Platform were opened in the boreholes of Belarus. This allows us to consider this region as a stratotype area. In order to update the paleontological characteristics of the Vendian, organic-walled microfossils from the Bogushevsk-1, Bogushevsk-2 (Liozno), and Lepel-1 reference boreholes drilled in the north of the Orsha Depression were studied. The transitive assemblage I with Leiosphaeridia minutissima–Leiosphaeridia tenuissima was recognized in the Lower Vendian Liozno Formation of the Volyn Series and the Upper Vendian Kotlin Formation. The Redkino microfossil assemblages were identified at three stratigraphic levels in the Nizy, Selyava, and Chernitsa formations: assemblage II with Morania zinkovi, assemblage III with Morania zinkovi–Tynnia precambrica, and assemblage IV with Morania zinkovi–Tynnia precambrica–Striatella coriacea, respectively. The Kotlin assemblage V with Vendotaenia antiqua–Primoflagella speciosa was distinguished in the upper part of the Kotlin Formation (Bogushevsk-1 borehole). On the basis of the taxonomic composition, assemblages III and IV are correlated with the first Redkino biota of the Starorusskaya Formation; assemblage V is correlated with the third Kotlin biota of the Vasileostrovskaya Formation of the northwestern part of Russia. Our data show a high biostratigraphic potential of organic-walled microfossils, which should be used to substantiate regional stratigraphic units of the Upper Vendian in the updated stratigraphic scheme of the East European Platform.

Fossil Organisms of the Redkino Regional Stage of the Upper Vendian of the Northwestern Russian Platform (Leningrad Region)

2021 ◽  
Vol 55 (5) ◽  
pp. 579-587
Author(s):  
E. Yu. Golubkova ◽  
I. M. Bobrovskiy ◽  
E. A. Kushim ◽  
Yu. V. Plotkina
Keyword(s):  
Russian Platform ◽  
Leningrad Region ◽  
Regional Stage ◽  
Upper Vendian

Age and petrogenesis of the Qassiarsuk carbonatite-alkaline silicate volcanic complex in the Gardar rift, South Greenland

1997 ◽  
Vol 61 (407) ◽  
pp. 499-513 ◽  
Author(s):  
Tom Andersen
Keyword(s):  
Volcanic Rocks ◽  
Single Stage ◽  
Volcanic Complex ◽  
Crustal Material ◽  
Crustal Component ◽  
Depleted Mantle ◽  
Common Parent ◽  
Nd Model Age ◽  
Extrusive Carbonatite ◽  
Age Estimates

AbstractThe Qassiarsuk (formerly spelled Qagssiarssuk) complex is located in a roughly E–W trending graben structure between Qassiarsuk village and Tasiusaq settlement in the northern part of the Precambrian Gardar rift, South Greenland. The complex comprises a sequence of alkaline silicate tuffs and extrusive carbonatites interlayered with sandstones, and their subvolcanic equivalents, which represent possible feeders for the extrusive rocks. The Rb-Sr, Sm-Nd and Pb isotopic characteristics of 65 samples of extrusive carbonatite- and silicate tuffs and carbonatite diatremes have been determined by mass spectrometry. The Qassiarsuk complex can be dated to c. 1.2 Ga by Rb-Sr and Pb-Pb isochrons on whole-rocks and mineral separates, agreeing with previous isotopic ages for the volcanic rocks of the Eriksfjord formation in the Eriksfjord area of the Gardar rift, but not with previous, indirect age estimates of >1.31 Ga for assumed Eriksfjord equivalents in the Motzfeldt area further east. Recalculated isotopic compositions at 1.2 Ga indicate that the Qassiarsuk carbonatite- and alkaline-silicate magmas were comagmatic and derived from a depleted mantle source (εNd>4, εSr<−13, time-integrated, single- stage 238U/204Pb ≤ 7.4). The mantle-derived magmas were contaminated with crustal material, equivalent to the local, pre-Gardar granites and gneisses and sediments derived from these. The crustal component has a depleted mantle Nd model age of 2.1-2.6 Ga; at 1.2 Ga it was characterized by εSr = +76, εNd = −8.4, time-integrated, single- stage 238U/204Pb = 8.2−8.3. Strong decoupling of the Pb from the Sr and Nd isotopic systems suggests that the contamination happened only after carbonatitic and alkaline-silicate magmas had evolved from a common parent, by processes such as liquid immisicibility and/or fractional crystallization. Post-magmatic hydrothermal alteration (oxidation, hydration of mafic silicates, carbonatization of melilite) may have contributed further to the contamination of the carbonatite and alkaline silicate rocks of the Qassiarsuk complex.

Upper Vendian-lowest Ordovician sequences of the western Gondwana margin, NE Spain

2009 ◽  
Vol 326 (1) ◽  
pp. 231-244 ◽  
Author(s):  
José A. Gámez Vintaned ◽  
Ulrich Schmitz ◽  
Eladio Liñán
Keyword(s):  
Upper Vendian ◽  
Gondwana Margin ◽  
Ne Spain

First report of Pan-African Sm—Nd and Rb—Sr mineral isochron ages from regional charnockites of southern India

1995 ◽  
Vol 132 (3) ◽  
pp. 253-260 ◽  
Author(s):  
C. Unnikrishnan-Warrier ◽  
M. Santosh ◽  
M. Yoshida
Keyword(s):  
Sri Lanka ◽  
Shear Zone ◽  
East Antarctica ◽  
Southern India ◽  
Peninsular India ◽  
Pan African ◽  
Mineral Isochron ◽  
Nd Model Age ◽  
Tectonothermal Event ◽  
Good Agreement

AbstractMineral and whole-rock isotope data for a massive charnockite from Kottaram in the Nagercoil Block at the southern tip of Peninsular India yield Sm—Nd and Rb—Sr ages of 517 ± 26 Ma and 484 ± 15 Ma respectively. The Nd model age calculated for the charnockite is c. 2100 Ma. Our study reports the first Pan-African mineral isochron ages from regional charnockites of Peninsular India, which are in good agreement with the recently obtained ages of incipient charnockites in the adjacent blocks, as well as alkaline plutons within the same block. Our results indicate that the Pan-African tectonothermal event in the granulite blocks south of the Palghat—Cauvery shear zone was regional, with terrain-wide rejuvenation. These results correlate with similar Pan-African tectono-thermal events reported from Sri Lanka and East Antarctica, and have an important bearing on Gondwana reconstructions.

scholarly journals LITHOLOGICAL AND FACIAL FEATURES, COMPOSITION, AND SEDIMENTATION CONDITIONS OF TERRIGENOUS-CARBONATE ROCKS OF THE MOTY GROUP (SHAMAN CLIFF, IRKUTSK REGION)

2021 ◽  
Vol 12 (3) ◽  
pp. 628-644
Author(s):  
Z. L. Motova ◽  
A. V. Plyusnin ◽  
E. V. Nikulin
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Siberian Platform ◽  
Carbonate Rocks ◽  
Facial Features ◽  
Upper Vendian ◽  
Terrigenous Rocks ◽  
Irkutsk Region ◽  
The Cross ◽  
Sedimentation Conditions

We have studied terrigenous-carbonate rocks in the area near the Sayan mountains in the Irkutsk Region (Russia), specifically at the Shaman Cliff, being the stratotype area of rocks that belong to the Moty group. The cliff’s lower part is composed of sandstones, which fragments gradually decrease in size upward the cross-section. The middle and upper parts are composed of sandy dolomites and dolomites, respectively. In terms of material characteristics, the terrigenous rocks correspond to arkoses. According to the genetic typification, the arkoses are composed of destructed primary igneous rocks. The terrigenous-carbonate rocks contain a carbonate component that gradually increases in the upper part of the cross-section. In the Shaman Cliff cross-section, we distinguish 32 lithological units and eight lithologicalgenetic types of deposits. Paleogeodynamic conditions are reconstructed for the formation of the sedimentation basin. Our study of the Shaman formation reveals specific features of the lithological facies, which suggest that these rocks accumulated in a coastal environment affected by tides. In the study area, clastic materials were mainly removed from an orogen that formed due to the Vendian accretion-collision events in the southern folded frame of the Siberian platform. Dolomites composing the upper part of the cliff are attributed to the Irkutsk formation of the Moty group. Their lithological features give evidence of shallow-marine conditions of their formation, without any supply of clastic material, which contributed to mass dispersal of the Cambrian biota described in [Marusin et al., 2021]. It is our first initiative to draw a boundary between the Shaman and Irkutsk formations of the Moty Group along the base of the carbonate eluvial breccia unit that marks the stratigraphic break. In the cross-section, this boundary represents the border between the Upper Vendian and Lower Cambrian.Our conclusions are generally consistent with the ideas of most researchers about the Late Vendian evolution of the southern margin of the Siberian platform. The results of our study can be used in further investigation of this area and provide a basis for correlating the studied strata with the same-age reference cross-sections of other regions in Siberia.

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