Geochemistry of gold weathering crusts of the crystalline basement of the Ukrainian Shield (Brusilovsk suture zone and surrounding areas)

Crustal and uppermost mantle structure along the Teisseyre-Tornquist Zone (TTZ)&#160; was explored along the ~550 km long, NW-SE-trending TTZ-South profile, using seismic wide-angle reflection/refraction (WARR) method. The profile line was intended to follow the border between the East European Craton (EEC) and the so called Palaeozoic Platform (PP) of north-central Europe, believed to contain a number of crustal blocks that were accreted to the craton during pre-late Carboniferous times, defining the Trans-European Suture Zone (TESZ).The seismic velocity model of the TTZ-South profile shows lateral variations in crustal structure. Its Ukrainian segment crosses the interior of the Sarmatian segment of the EEC, where the crystalline basement gradually dips from ~2 km depth in the SE to ~12 km at the Ukrainian-Polish border. This part of the model shows a four-layered crustal structure, with an up to 15 km-thick sedimentary cover, an underlying crystalline upper crust, a 10-15 km-thick middle crust and a ~15 km thick lower crust. In Poland, the profile passes along the TESZ/EEC transition zone of complex crustal structure. The crystalline basement, whose top occurs at depths of 10-17 km, separates the sedimentary cover from the ~10 km thick mid-crustal layer (Vp=6.5-6.6 km/s), which, in turn, overlies a block of 10-15 km thickness with upper crustal velocities (Vp~6.2 km/s). The latter is underlain by a ~10-15 km-thick lower crust. Along most of the model one can see conspicuous velocity inversion zones occuring at various depths. At intersections of the TTZ-South profile with some previous deep seismic profiles (e.g. CEL02, CEL05, CEL14, PANCAKE) such inversions document complex wedging relationships between the EEC and PP crustal units. These may have resulted from tectonic compression and thick-skinned thrusting due to either Neoproterozoic EEC collision with accreting terranes or intense Variscan orogenic events. Five high velocity bodies (HVB; Vp = 6.85-7.2 km/s) were detected in the middle and lower crust at 15-37 km depth. The Moho depth varies substantially along the profile. It is at ~42 km depth in the NW and deepens SE-ward to ~50 km at ~685 km. Subsequently, it rises abruptly to ~43 km at the border of the Sarmatian segment of the EEC and sinks again to ~50 km beneath the Lviv Paleozoic trough at ~785 km. From this point until the SE end of the profile, the Moho gently shallows, up to a depth of ~37 km, including a step-like jump of 2 km at ~875 km. Such abrupt Moho steps may be related to crust-scale strike-slip faults. Along the whole profile, sub-Moho velocities are ~8.05-8.1 km/s, and at depths of 57-63 km Vp values reach 8.2-8.25 km/s. Four reflectors/refractors were modelled in the upper mantle at ~57-65 km and ~80 km depths.

Download Full-text

Geochemistry, zircon U-Pb geochronology and Sr-Nd-Hf isotopic composition of the Cha Val plutonic rocks in central Vietnam: Implications for Permian-Triassic Paleo-Tethys subduction-related magmatism

Vietnam Journal of Earth Sciences ◽

10.15625/2615-9783/16842 ◽

2021 ◽

Author(s):

Minh Pham ◽

Hieu ◽

Kenta Kawaguchi ◽

Anh ◽

Phuc

Keyword(s):

Suture Zone ◽

Early Triassic ◽

Late Permian ◽

Magmatic Complex ◽

High K ◽

Plutonic Rocks ◽

Surrounding Areas ◽

A Minor ◽

Hf Isotopic Composition ◽

T Values

together with abundant Permian-Triassic magmatic rocks. This magmatic complex provides important information to reconstruct the tectonic evolution of the Indochina block and surrounding areas. The Cha Val plutonic rocks mainly comprise diorite, quartz diorite, and granodiorite. Geochemically, they are metaluminous with low A/CNK (0.49 to 1.16 with an average of 0.85), medium to high K, low to medium SiO2, and Na2O/K2O>1. Trace and rare earth element compositions display enrichment in Cs, U, Pb, and Nd, but depletion in Ba, Nb, Ta, P, Eu, and Ti, similar to those of continental arc-related magmas. Rock-forming minerals of the Cha Val plutonic rocks are characterized by abundant hornblende. All observed petrographical and geochemical characteristics suggest that the Cha Val plutonic rocks are typical for I-type affinity generated from a subduction regime. LA-ICP-MS U-Pb zircon analyses of three representative samples yielded their crystallization ages between 258.0 Ma and 248.9 Ma, temporally coeval with Late Permian-Early Triassic magmatism previously reported in the Truong Son belt. The (87Sr/86Sr)i ratios (0.7081 to 0.7244), negative whole-rock εNd(t) values (-4.5 to -2.9), zircon εHf(t) values (-1.04 to 2.71), and whole-rock Nd and zircon Hf model ages (TDM2) (1394 Ma to 1111 Ma) indicate that the Cha Val plutonic rocks are derived from melting of Mesoproterozoic crustal materials with a minor contribution of mantle-derived melt. Together with other Permian-Triassic magmatic complexes along the Song Ma suture zone and the Truong Son Belt, the Cha Val plutonic rocks are a representative of magmatism associated with the subduction-collision that amalgamated the South China and Indochina blocks after the closure of a branch of Paleo-Tethys along the Song Ma suture zone during the Late Permian-Early Triassic Indosinian orogeny.

Download Full-text

THE TECTONIC STRUCTURE OF THE CRYSTALLINE BASEMENT IN THE BUG-ROSS MEGABLOCK OF THE UKRAINIAN SHIELD

Geological Journal ◽

10.30836/igs.1025-6814.2010.4.216413 ◽

2010 ◽

Vol 0 (4) ◽

pp. 48-57

Author(s):

M. M. Kostenko

Keyword(s):

Crystalline Basement ◽

Ukrainian Shield ◽

Tectonic Structure

Download Full-text

Stratigraphic basement and correlation of the precambrian central part cuts of the Ukrainian shield

Мінеральні ресурси України ◽

10.31996/mru.2019.4.11-16 ◽

2020 ◽

pp. 11-16

Author(s):

M. M. Kostenko

Keyword(s):

Suture Zone ◽

Ukrainian Shield ◽

Structural Elements ◽

The West ◽

Early Precambrian ◽

Carbonate Carbon

In the central part of the Ukrainian Shield are allocated two independent structural elements: Inhul block and Inhulets-Kryvyi Rih suture zone, instead of the Inhul-Inhulets region, according to the current tectonic zoning in “Correlation Chronostratigraphic Scheme of the Early Precambrian of the Ukrainian Shield”. The stratigraphic dividing of this territory has not undergone any changes. The article suggests existing Inhul-Inhulets Series in this scheme to divided into two: the Inhul (Inhul block) and the Inhulets (Inhulets-Kryvyi Rih suture zone) and several independent strattons in the Suites rank. As part of the Inhul Series, the upper part of the Inhul-Inhulets Series remains as part of the Kamianokostuvatska and Roshсhakhivska (Bratskа SFZ) and Spasivska and Checheliivska (Inhul SFZ) Suites. In the lower part of the section, there is an independent Rodionivska Suite. The West Inhulets and Kryvyi Rih-Kremenchuk SFZ stratigraphic sections of the Inhulets-Kryvyi Rih suture zone are identical and completely correlate with each other: lower Mesoarchean metaterigenic Lativska Suite is basal for both, Mesoarchean metavolcanogenic Nyzhnozelenorichanska Suite of the West-Inhulets SFZ is correlated with the Novokryvorizka Suite of the Kryvyi Rih-Kremenchuk SFZ, Paleoproterozoic Inhulez Series – respectively, with the Kryvyi Rih Series (metavolcanogenic-sedimentary Verkhnozelenorichanska Suite – with the Skeliuvatska Suite, and the metaterigenic-ferrous Artemivska Suite – with the Saksaganska), carbonate-carbon-terigenic Rodionivska Suite – with Hdantsivska. These stratigraphic units represent by themselves their own suture formations of the Inhulets-Kryvyi Rih suture zone.

Download Full-text