Lithofacies and petrochemical characterization of volcano-sedimentary sequence of Chandil Formation around Kharidih-Bareda area, Seraikela-Kharsawan District, Jharkhand: implications for uranium mineralization

Mesoproterozoic Chandil Formation (ca. 1600 Ma) of North Singhbhum Mobile Belt record numerous features of felsic volcaniclastics and felsic to intermediate volcanics preserved in the central sector of the fold belt around Kharidih-Bareda area, Seraikela-Kharsawan district, Jharkhand. The felsic volcanic rocks exhibit flow bands, autoclasts and layering of crystal mushes revealing viscous nature of eruptives. The volcaniclastic sediments comprise of significant proportion of volcanic epiclasts and accidental lithic fragments. These volcaniclastics have been categorized into five prominent lithofacies viz, stratified lapilli tuff, banded tuff, tuff with penecontemporaneous deformation, welded lapilli stones, vitric tuff and volcanic bombs by field and petrographic studies of outcrops and subsurface borehole cores. The welded lapilli tuffs display fiamme and eutaxitic texture. Interlayering of the volcaniclastics, which are most often pyrite-rich, with psamo-pelitic lithology like carbonaceous phyllite, variegated phyllite, quartzite and minor limestone is suggestive of marine euxenic depositional environment. Petrographic study of the volcaniclastics indicated presence of glass shards, garnet phenocrysts, spherules of tremolite, ovoid to lenticular accretionary lapilli along with devitrified glassy material. Compositionally these felsic volcanics and volcaniclastics are rhyodacitic to andesitic in nature with peraluminous to meta aluminous in character. A/CNK values vary from 0.52 to 2.42 in felsic volcanics and from 0.12 to 1.63 in volcaniclastics. Signatures of arc magmatism is indicated by low concentration of HFS elements such as Nb (5-17 ppm), Ga (11-17 ppm) and Y (5-28 ppm). Elevated intrinsic content of uranium (3-8 ppm), Th/U ratio ranging from 1.2 to 13.2, presence of metamict allanite and zircon in volcanics and volcaniclastics reveal their suitability as a prospective source for search of uranium mineralization. The volcanic-volcaniclastic-clastic association of the Chandil Formation provides an ideal situation where provenance and province both are available. Thus, suitable litho-structural locales such as the concealed shear zones sympathetic to the Dalma thrust and South Purulia Shear Zone within the volcano-sedimentary package of Chandil Formation may be targeted as preferable sites for locating concealed uranium mineralization.

Geology of the Tinui district

<p>The Tinui District is assumed to be typical of the more deformed part of the New Zealand Mobile Belt. It contains an unusually complete stratigraphic record, rocks representing most stages from Upper Jurassic to Recent being present. Although the rocks are strongly deformed, the complex diapiric structures that occur in the northeast of the mobile belt are absent. The stratigraphy is described in terms of formations which are then used to infer the paleogeography for eight periods of time. An attempt is made to treat the structure according to its development with time. The main conclusion is that there was a change in the strike of the fold axes and in the sense of movement of the faults. Strong folds, striking approximately northeast, are Paleocene in age and weak folds, striking approximately north, are post-Miocene. There are two fault trends, one NNE and the other ENE. The ENE striking faults were dominant in the Early Cenozoic and the NNE striking faults were dominant in the Late Cenozoic. The sense of movement on the NNE faults changed from sinistral to dextral. The change in the direction of the axes and in the sense of movement on the faults can be expressed as a change in the direction of maximum horizontal shortening, which is inferred to have changed with time. It is also found that the rates of tilting, and probably faulting, have not been constant with time, but occurred as bursts (disturbances) in the Paleocene, Early Miocene Late Pliocene, and Late Quaternary. The Mesozoic part of the geological history of the Tinui District is scrappy and far less complete than the Cenozoic part. In order to place the Tinui District in a broader setting, the central part of the New Zealand landmass in the Cenozoic, called the New Zealand Mobile Belt, is discussed in some detail. The mobile belt consists of fault blocks which form a geanticline along the New Zealand landmass and a geosynclinal trough between the east coast and the Hikurangi Trench. It is shown that a clear distinction has to be made between tilting and uplift. A main feature of the New Zealand Mobile Belt is the dextral faulting, on major NNE striking faults, in the Late Cenozoic. A major reversal in the direction of maximum horizontal shortening was found in the Tinui District to have taken place at the beginning of the Miocene or in the Oligocene. The reversal indicates that the dextral faulting of the New Zealand Mobile Belt may have started at that time, and that earlier strike-slip movement had been sinistral. This conclusion contradicts existing reconstructions of the New Zealand landmass with time, and a more complex reconstruction is required to satisfy the tectonics of the Tinui District.</p>

Geology of the Tinui district

<p>The Tinui District is assumed to be typical of the more deformed part of the New Zealand Mobile Belt. It contains an unusually complete stratigraphic record, rocks representing most stages from Upper Jurassic to Recent being present. Although the rocks are strongly deformed, the complex diapiric structures that occur in the northeast of the mobile belt are absent. The stratigraphy is described in terms of formations which are then used to infer the paleogeography for eight periods of time. An attempt is made to treat the structure according to its development with time. The main conclusion is that there was a change in the strike of the fold axes and in the sense of movement of the faults. Strong folds, striking approximately northeast, are Paleocene in age and weak folds, striking approximately north, are post-Miocene. There are two fault trends, one NNE and the other ENE. The ENE striking faults were dominant in the Early Cenozoic and the NNE striking faults were dominant in the Late Cenozoic. The sense of movement on the NNE faults changed from sinistral to dextral. The change in the direction of the axes and in the sense of movement on the faults can be expressed as a change in the direction of maximum horizontal shortening, which is inferred to have changed with time. It is also found that the rates of tilting, and probably faulting, have not been constant with time, but occurred as bursts (disturbances) in the Paleocene, Early Miocene Late Pliocene, and Late Quaternary. The Mesozoic part of the geological history of the Tinui District is scrappy and far less complete than the Cenozoic part. In order to place the Tinui District in a broader setting, the central part of the New Zealand landmass in the Cenozoic, called the New Zealand Mobile Belt, is discussed in some detail. The mobile belt consists of fault blocks which form a geanticline along the New Zealand landmass and a geosynclinal trough between the east coast and the Hikurangi Trench. It is shown that a clear distinction has to be made between tilting and uplift. A main feature of the New Zealand Mobile Belt is the dextral faulting, on major NNE striking faults, in the Late Cenozoic. A major reversal in the direction of maximum horizontal shortening was found in the Tinui District to have taken place at the beginning of the Miocene or in the Oligocene. The reversal indicates that the dextral faulting of the New Zealand Mobile Belt may have started at that time, and that earlier strike-slip movement had been sinistral. This conclusion contradicts existing reconstructions of the New Zealand landmass with time, and a more complex reconstruction is required to satisfy the tectonics of the Tinui District.</p>

COMMENTS ON THE ARTICLE AUTHORED BY M.V. MINTS AND K.A. DOKUKINA – THE BELOMORIAN ECLOGITE PROVINCE (EASTERN FENNOSCANDIAN SHIELD, RUSSIA): MESO-NEOARCHEAN OR LATE PALEOPROTEROZOIC?

The comments are given on the article authored by M.V. Mints and K.A. Dokukina – The Belomorian Eclogite Province (Eastern Fennoscandian Shield, Russia): Meso-Neoarchean or Late Paleoproterozoic? (Geodynamics & Tectonophysics 2020, 11 (1), 151–200). The Belomorian (White Sea) province of the Fennoscandia Shield is a key site for studying the tectonics of the early periods because numerous Precambrian eclogites have been found there. It was not anticipated, but the problem of age determinations of the eclogite metamorphism of gabbroids in the White Sea mobile belt has turned out to be extremely relevant not only for this region, but also for the Precambrian geology in general. The reason is that a number of authors determine the age of eclogites as Archean (2.7–2.8 Ga), which makes the White Sea mobile belt the only example of the Archean eclogite metamorphism in the world and, therefore, the only dated evidence in support of the plate tectonic model of the evolution of the Earth’s crust at the earliest stage of its formation. The article consistently provides a critical analysis of the arguments put forward by the supporters of the Archean age of the eclogites of the White Sea mobile belt. Special emphasis is made on the isotope geochronological and geochemical features of the composition of zircons from eclogite samples, as well as on the phase and chemical compositions and distribution patterns of mineral inclusions. Considering the age of eclogite metamorphism that led to the formation of eclogites in the White Sea mobile belt, we propose our interpretation based on a set of independent isotope geochemical dating methods, including the local U- Pb method for heterogeneous zircons with magmatic cores and eclogite rims, the Lu-Hf and Sm-Nd methods for the minerals of eclogite paragenesis (garnet and omphacite). And this age interpretation is fundamentally different from the one described in the commented article: all the three methods independently determine the eclogite metamorphism as Paleoproterozoic and yield the same age of circa 1.9 Ga. According to our data, the eclogites of the White Sea mobile belt are among the most ancient high-pressure rocks, their reliably established age of metamorphism is circa 1.9 Ga, and the age of the magmatic protolith is the range of 2.2–2.9 Ga.

New Insights into Pre-to-Post Ediacaran Zircon Fingerprinting of the Mamfe PanAfrican Basement, SW Cameroon: A Possible Link with Rocks in SE Nigeria and the Borborema Province of NE Brazil

The pre- to post-Late Neoproterozoic geological histories in the south to southwestern part of Mamfe Basin (SW Cameroon) were reported following analysis of the zircon crystals from their host rocks. A genetic model was developed for the zircon host rocks’ formation conditions, and the registered post-emplacement events were presented. The obtained ages were correlated with the data available for rocks in the Cameroon Mobile Belt, SE Nigeria, and the Borborema Province of NE Brazil. Separated zircons from Araru black to whitish gneiss, Araru whitish-grey gneiss, and Mboifong migmatite were analyzed for their morphology and texture U-Th-Pb composition, and U-Pb ages. Published U-Pb zircon ages for Otu granitic pegmatite, Babi mica schist, and Nkogho I-type anatectic granite were updated. Zircon ages in Araru black to whitish gneiss; Araru whitish-grey, Mboifong migmatite, Babi mica schist, Nkogho I-type anatectic granite, and Otu granitic pegmatite date the Eburnean tectono-magmatic/metamorphic event in Cameroon and SE Nigeria. The Late Paleoproterozoic to Early Mesoproterozoic ages record extensional (continental rift) settings and anorogenic magmatism in the Borborema Province in the NE of Brazil. These ages date collisional phases between the São Francisco–Congo and West African cratons and the Saharan metacraton with metamorphism and magmatism in Cameroon. They also date the Kibarian tectono-magmatic/metamorphism and PanAfrican tectono-magmatic/metamorphism in SE Nigeria. The Late Paleoproterozoic to Early Mesoproterozoic ages date the Cariris Velhos orogeny in the Borborema Province in NE Brazil, with Early Tonian crustal rifting, magmatism, and metamorphism and the collisional phase of the Brasiliano orogeny with syn-collisional plutons and extensive shear zoning and post-collisional granite intrusions.

PALEOZOIC GRANITOID MAGMATISM OF THE URALS: THE REFLECTION OF THE STAGES OF THE GEODYNAMIC AND GEOCHEMICAL EVOLUTION OF A COLLISIONAL OROGEN

The Ural mobile belt is an intracontinental epioceanic orogen that has already gone through all stages of the geodynamic development. Igneous rocks formed during each stage are important indicators for understanding the evolution of this belt and determining potential ore contents of its segments. We consolidated large datasets on petrogeochemistry and isotope geochronology of the Paleozoic (490–250 Ma) granitoids associated with the opening and evolution of the Ural paleoocean and the subsequent formation of the collisional orogen. Using these data, we have revised the ages of several tectono-magmatic events, clarified the paleogeodynamic settings for the generation of granitoids of different compositions, and described the roles of mantle-crust interactions and the plume factor in the formation of the mature continental crust in the study area. The results can be useful for geological mapping and improving the assessment of the potential ore contents in granitoid complexes that differ in origin and composition.