Mobile Belt Research Articles

Lithospheric Deformation of Far‐Field Terranes in Response to the India–Asia Collision

ABSTRACTThe influence of the India–Asia collision is far‐reaching on the Cenozoic continental deformation in East Asia. Several cratonic lithospheres surrounding Tibet exhibit distinct lithospheric morphologies. However, the mechanisms driving these diverse responses of strong terranes remain incompletely understood. Here, we conduct thermo‐mechanical models to explore the effects of the width of the mobile belts, lithospheric properties and convergence rate on the deformation of the strong terranes. The model results reveal three different deformation modes. Far‐field strong terranes are vulnerable to delamination or underthrusting when the mobile belt is narrow and detached, whereas they remain largely undeformed when it is wide and strong. These deformation patterns align with the observed lithospheric structures around the Tibetan Plateau and are primarily influenced by the convergence rate and proximity to the collision front. Our findings provide new insights into the lithospheric deformation mechanisms of cratonic terranes in response to continental collision.

The South Purulia Shear Zone, eastern India: Its anatomy and implication for timing the Rodinia-age collision in the eastern part of the Central Indian Tectonic Zone

The Proterozoic Central Indian Tectonic Zone (CITZ) is an ~1500-km-long collision zone between the North India and the South India blocks. The age of collision is debated, but constraining the age of collision is crucial for reconstructing the paleogeographic position of India in the Precambrian. In this study, mesoscale structures, metamorphic pressure-temperature path, U-Pb zircon dates, and monazite chemical dates are combined to constrain the collision age. In the eastern part of the CITZ, the North Singhbhum Mobile Belt (NSMB) comprising 1.5–1.3 Ga low-grade phyllites and schists and the 1.88 Ga Ranibandh granitoid are juxtaposed with the Chottanagpur Gneiss Complex (CGC; eastern CITZ) dominated by 1.76 Ga anatectic basement gneisses intruded by 1.67 Ga, 1.57 Ga, and pre-collisional 1.02 Ga felsic intrusives. The juxtaposition of the disparately evolved crustal domains along the South Purulia Shear Zone (SPSZ) involved top-to-the-south thrusting consistent with amphibolite facies loading. Continued oblique N-S shortening of the thickened crust led to nucleation of ESE-striking, steeply dipping left-lateral transpressional shear zones tens of kilometers wide that obliterated pre-collisional structures in the rheologically weak NSMB phyllites and schists but are weakly developed in the rheologically strong CGC rocks. The 1.02–0.91 Ga oblique collision between the North India and South India blocks along the SPSZ suggests the paleopole data pre-dating the collision are unlikely to ascertain the paleogeographic position of the Indian landmass because the landmass did not exist in its entirety before 1.02–0.91 Ga. But the paleopole data may help locate the North India and South India blocks independent of each other.

Mineralogy and geochemical controls on the distribution of REY-Ga-Se-Nb enrichment in the No. 6 Coal Seam, Soutpansberg Coalfield, South Africa

Coal is being explored as a potential alternative source for rare earth elements (REY + Sc), which are critical for advancing modern technology. Previous research has mainly focused on assessing the concentration and distribution of REY + Sc in coals from South Africa. However, the modes occurrence of these elements in coal is yet to be investigated. This study offers new insights on the mineralogy and inorganic geochemistry of the No. 6 Seam coal from the Soutpansberg Coalfield (South Africa). The objective is to investigate the distribution, enrichment, and modes of occurrence of critical elements such as Ga, Se, Nb, and REY + Sc within this coal. The No. 6 Seam is a medium rank-B, moderate vitrinite (avg. 41.5 vol%) coal, and contains major minerals such as kaolinite, quartz, and minor minerals including muscovite, siderite, dolomite, pyrite, and calcite. The total REY + Sc concentrations in the coal samples range from 79.9 to 332.1 mg/kg (avg. 213.2 mg/kg; whole-coal/rock basis), higher than global averages for hard coal. The upper continental crust (UCC) normalized concentration coefficients (CC) of the coal shows enrichment of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Yb, and Y. Distinct REY + Sc enrichment patterns are observed across different coal horizons, divided into two categories: light-REY (LREY) and medium-REY (MREY) in the bottom horizon coal [bottom-upper (BU) and bottom-lower (BL)], whereas the middle horizon coal [middle-upper (MU) and middle-lower (ML)] are enriched in medium-REY (MREY) and heavy-REY (HREY). The BU and BL samples show greater REY + Sc enrichment relative to the MU and ML samples. The samples also contain elevated concentrations of Ga (max. 106.1 mg/kg), Se (max. 50.9 mg/kg), and Nb (max. 14.8 mg/kg), exceeding the average values reported for Chinese coals.When considering the correlations between REY + Sc and major oxide elements, minerals, and organic petrographic assemblages, REY + Sc appears to be more closely associated with inorganic fraction, particularly aluminosilicate (such as kaolinite) and carbonate minerals (like dolomite), rather than with the organic fraction. The kaolinite and dolomite represent mostly detrital input and epigenesis, respectively. Gallium in the coal is primarily associated with aluminium oxide-hydroxide, Nb with minerals such as clay, rutile/anatase, and zircon; and Se with pyrite. Redox-sensitive elemental ratios of Al2O3/TiO2 andTiO2/Zr suggest that the detrital components of the No. 6 Seam coals were predominantly derived from a source consisting of felsic-intermediate rocks. These materials likely represent the weathering products of magmatic rocks from the passive-continental margin tectonic framework of the Limpopo Mobile Belt. Paleoclimatic conditions are inferred to be warm-humid to hot, with the peat deposited under suboxic-to-oxic environments. High values of critical REY percentage (REYdef,rel%: 29.85 to 39.75 %) and an outlook coefficient ≥ 0.7 suggest these Soutpansberg coal samples to be promising for REY + Sc recovery along with Ga.

Evidence of a Proterozoic suture along the southern part of Eastern Ghats Mobile Belt: Implications for the Nuna supercontinent

Evidence of a Proterozoic suture along the southern part of Eastern Ghats Mobile Belt: Implications for the Nuna supercontinent

Anisotropy of magnetic susceptibility and rock magnetism of high-grade rocks from Eastern Ghats Mobile Belt, India: Constraints to tectonics

Anisotropy of magnetic susceptibility and rock magnetism of high-grade rocks from Eastern Ghats Mobile Belt, India: Constraints to tectonics

Pulsating orogenesis and Neoproterozoic crustal architecture in the western part of Aravalli-Delhi Mobile belt, India: new evidence from structural, metamorphic, and U-Pb zircon geochronological data

ABSTRACT Structural, metamorphic, and geochronological study of the Delhi Supergroup rocks near the western margin of the Aravalli-Delhi Mobile Belt (ADMB) elucidate the Neoproterozoic tectonics of the South Delhi Fold Belt (SDFB) and its implication for the evolution of the Greater Indian Landmass (GIL). In this study, we establish three deformational events in the SDFB. While the D1 event produced isoclinal, reclined F1 folds synchronous with prograde amphibolite facies metamorphism (~5 kbar, 650°C), D2 formed outcrop to map-scale upright F2 folds. D3 comprised ‘partitioned transpression’ along two subvertical shear zones. Oblique dextral-reverse movement (D3a) along one shear zone formed an outcrop-scale positive flower structure, while sinistral-reverse movement along the other rotated and steepened the hinges of the F2 folds (D3b). U-Pb zircon dating of post-tectonic (post-D2, but pre-D3) and syntectonic (syn-D3) granite intrusives suggests >844 Ma age for D2 and ca. 820 Ma for D3. An older magmatic event (ca. 990 Ma) is recorded from sheared pink granites (pre- to syn-D1 intrusion). We suggest that the amalgamation of the ADMB and the Marwar Craton was initiated by the Grenville-age (ca. 1000 Ma) subduction-collision, while the younger events (ca. 844 Ma and 820 Ma) mark the final stitching of the ADMB – Marwar Craton along the Phulad-Ranakpur palaeo-suture zone to form the GIL. The distribution of early (ca. 1000–900 Ma) and late (ca. 800–700 Ma) Tonian magmatic and metamorphic ages in the SDFB suggest that the final growth of the GIL took place through multiple stages of oblique collision in a pulsating orogenesis through the Early Neoproterozoic.

Subsurface structural trends in Central-Western India: Inferences from magnetotelluric data using the complex MT apparent resistivity tensor

The central-western part of the Indian subcontinent exhibits significant geological diversity and possesses a rich record of different tectonothermal events in the earth's evolutionary history, spanning from the Archean to the present. Precambrian geology in the region is mostly obscured by Cretaceous-Tertiary/Paleocene volcanic eruptions and Proterozoic to Quaternary/recent sedimentary cover. Magnetotelluric (MT) impedance and tipper responses from 146 stations, covering central-western India in a grid fashion with a spacing of ∼55 km, were analyzed to evaluate the subsurface structural trends, dimensionalities, and qualitative characteristics of the electric lithosphere in the region. An advanced Complex Apparent Resistivity Tensor (CART) approach, along with the popular Phase Tensor (PT) approach and induction arrows are utilized to achieve the above goals. The analysis revealed a high degree of 3D induction effects in the data at almost every station and period. The directionality information retrieved from the tensor properties showed that the structural trends in the deep crust and upper mantle of the major geologic domains correlate with the known surface tectonic trend of the respective geologic domain. This study provides vital evidence to support the suspected bifurcation of the Precambrian Aravalli-Delhi Mobile Belt (ADMB) tectonic trend and its extensions into neighboring Kutch, Saurashtra, and Central Indian Tectonic Zone (CITZ) domains. The analysis results indicate a lithospheric scale enhanced conductivity beneath the Malwa plateau, which marks the first major phase of the Reunion mantle plume eruption in India. A critical finding of this study is that the Resistivity Phase Tensor better defines the subsurface resistivity structure and provides much clearer structural information than the conventional Phase Tensor.

Neotectonic evolution of the Caucasus: recent vertical movements and mechanism of crustal deformation

It is generally recognized that the formation of the fold-and-thrust tectonic structures of mobile belts on continents is associated with crushing and narrowing of the Earth’s crust as a result of collision of lithospheric plates. The deformation of the Caucasian lithosphere in the neotectonic time is generally consistent with these ideas. However, the block differentiation of the Caucasian lithosphere introduces specific features in the directivity of modern vertical and horizontal movements. In this paper, we analyze vertical movements of the Caucasus estimated by means of high-precision leveling over more than a century and consider their spatial correlation with tectonics, seismicity, stress-strain state, and geophysical fields. A clear relationship indicating the deep tectonic nature of the long-term uplifting of the Caucasus crust is revealed. Due to the differentiation of the Arabian plate movement, the territory of the Caucasus is divided into provinces that differ from each other in the pattern of modern movements, in the orientation of faults, and in the stress-strain state. The seismic regime in these provinces also has differences in the number of seismic events and focal mechanisms of the earthquakes. We propose a model of the deformation mechanism of the Greater Caucasus, which takes into account the long-term trend of the Caucasus uplifting in the conditions of general shortening of the Earth’s crust. The results of the analysis are used as a basis for discussion of a probable mechanism of tectonic evolution of the Greater Caucasus in the neotectonic time, which can be used in the assessment of seismic hazard in the North Caucasus.

Visible-Near Infrared–Short-Wave Infrared Spectroscopy and Mineral Mapping of Hydrothermal Alteration Zones at the Brejuí W-Mo Skarn Deposit, Seridó Mobile Belt, Borborema Province, Brazil

Abstract The Brejuí W-Mo skarn deposit is the main scheelite deposit of the Seridó tungsten province (Borborema province, NE Brazil). It constitutes the largest Brazilian W ore reserve. The orebodies are hosted in the metasedimentary Jucurutu Formation of the Seridó Group (650–610 Ma), close to the margin of the Neoproterozoic Acari pluton (Brasiliano orogeny). Skarns include prograde and retrograde mineral assemblages. Infrared spectral analysis shows that the skarns mainly reflect retrograde mineral assemblages, formed in three different hydrothermal alteration stages with overprinting. Mineral phases spectrally detected include (1) vesuvianite, actinolite, and phlogopite (alteration stage 1), (2) epidote, prehnite, and illite (alteration stage 2), and (3) laumontite, montmorillonite, chlorite, and gypsum (alteration stage 3; main ore zone). Phlogopite chloritization and actinolite recrystallization were observed in the main W-Mo skarn orebodies. Chloritization is marked by a displacement in the Fe-OH–related absorption wavelength (2,246.5–2,250.5 nm). A spectral index using spectral mixtures of laumontite + montmorillonite + actinolite is proposed here to map mineralized skarn layers (WO3 + Mo ≥ 0.1%) in drill cores. It was used to vector to richer mineralized bodies of the Brejuí deposit successfully and may be applied to similar skarn deposits with the same aim.

T-t Evolution of the Early Proterozoic Rocks in the Northern Ladoga Region from the Data on U-Pb, Rb-Sr and Sm-Nd Systems in Minerals

This paper presents the results of a study of isotopic systems in minerals and rocks in southern margin of the epi-Archean Karelian craton in the zone of its junction with the Svecofennian mobile belt. U-Pb, Sm-Nd and Rb-Sr mineral ages of metamorphic rocks allowed reconstructing a T-t trend during ~1.88–1.61 Ga, which reflects a wide-ranging cooling history of metamorphic rocks from the peak values of about 650–700 °C at 1.88–1.79 Ga (U-Pb age of monazites and apparent oldest Sm-Nd age of amphiboles) to 300–400 °C at 1.61 Ga (model Rb-Sr age of biotites) in zones of low- and medium-temperature metamorphism. The specificity of removal of deep-seated rocks to the present-day erosion surface and the reconstructed T-t trend comply with the development of thrust-nappe structures during the exhumation of the Svecofennids. It is also assumed that differential vertical block movements played a significant role during the post-orogenic extensional collapse and neorifting.

Characteristics and control of gold mineralisation of Sindurpur Area, North Singhbhum Mobile Belt, Eastern India: Evidence from petrography and mineral chemistry

Characteristics and control of gold mineralisation of Sindurpur Area, North Singhbhum Mobile Belt, Eastern India: Evidence from petrography and mineral chemistry

The influence of geology on the quality of groundwater for domestic use: a Kenyan review.

Kenya's population, akin to other Sub-Saharan countries, is rapidly growing. With the increasing unreliability of surface water, groundwater resources are becoming highly relied on for domestic and industrial use. Despite several known contaminants reported in different parts of the country, no study has attempted to correlate groundwater quality in the different geological provinces. This review critically synthesizes the influence of Kenya's diverse geology on groundwater quality for human consumption. This was achieved through a review of published journal articles and other research material through research and government databases. Groundwater was categorised based on the major geological provinces including the Archaean volcanic Nyanzian Craton, the Proterozoic metamorphic Mozambique Mobile Belt (MMB) and volcanic Kisii Group, the Palaeozoic and Mesozoic sediments, and Tertiary volcanic Rift Valley. Groundwater quality in these regions showed a characteristic high concentration of fluoride (F-) in volcanic aquifers of the Rift Valley and Nyazian Craton and metamorphic aquifers of the MMB, where mineral dissolution was the main process of F- release. High salinity was common in metamorphic aquifers in the MMB and the Palaeozoic and Mesozoic sedimentary aquifers where mineral dissolution and seawater intrusion were the common contributors to salinity. Other contaminants such as lead and iron were reported in localised areas in the sedimentary and metamorphic aquifers, respectively. Anthropogenic contaminants such as Escherichia coli (E.coli), NO3 -, and NO2 - were common in shallow groundwater resources in most informal settlements in urban areas. Due to the presence of health implications, of the highlighted contaminants, such as fluorosis, high blood pressure and diarrhoea (due to high F- and salinity) in affected regions, this review highlights the need for an active water resource management program in any country relying on groundwater resources to determine the presence of all region-specific potentially harmful chemical elements and mitigation measures in all its water resources.

Apatite-hosted REE mineralization in the Eastern Ghats Mobile Belt: A future prospect for REE

The growing need of rare earth elements in different sectors of the modern-day world has led to their increasing demand, which is in accordance with their limited supply. In such a scenario, investigations related to search for potential zones of rare earths have become the need of the hour. In one such investigation, undertaken by Geological Survey of India, the authors report profuse intrusion of the apatite veins into the syenite-pyroxenite suite in the eastern part of the Eastern Ghats Mobile Belt (EGMB) in Nayagarh area of eastern Odisha. These apatite veins are anomalously rich in REEs, particularly LREEs, which on average ranges between 37,000 to 53,000 ppm. Rare earths and apatite are generally directly proportional, where apatites tend to carry sufficient REE budget, depending on the phosphorous fugacity and other ambient conditions inducing their genesis. The major-oxide chemistry of apatite veins indicates that apatites in the study area can be divided into two types based on SiO2 wt.% and their inverse relationship with P2O5 and CaO wt.%. Mineral chemistry data shows overall SiO2 depletion, with dominance of CaO, followed by P2O5. Apatite veins, as per mineral chemistry, contain numerous veinlets (identified microscopically), where one type is REE-bearing and another type is REE-free. The REE-bearing phases are rich in Ce, Nd, La and Pr and are represented by allanite, monazite, and bastnaesite. Thorite and zircon are prevalent. Earlier instances of apatite intrusions into granulite have been reported from parts of south India. On the contrary, in this area, the intrusion is typically restricted to the younger intrusive units of the EGMB, represented by syenite-pyroxenite suite. The intrusives also show moderately high values of REEs. In this paper, an attempt has been made to characterize the apatite veins and the syenite-pyroxenite suite, they have intruded, in respect to their mineralogy and tectonics and to elucidate the potentiality of the area in terms of future REE exploration.

Provenance of low-grossular–high-pyrope detrital garnets from beach sands of East Coast of India between Gosthani and Vamsadhara rivers

Major element compositional spectrum, formation in diverse magmatic and metamorphic rocks, and relative stability during sediment transport, burial, and diagenesis make garnet an important indicator of sedimentary provenances. However, a fundamental question yet to be answered is whether the low-grossular–high-pyrope detrital garnets reflect source characteristics or record sedimentary processes. To address this problem, we have analysed garnets from the beach sands of the East Coast of India and in the source lithologies of the catchment area within the Eastern Ghats Mobile Belt. Investigated garnets show a broad compositional spectrum; most garnets are dominated by almandine49–86% with variable contents of pyrope9–47%, minor grossular0.8–15%, and low spessartine0.5–4%. Using multiple proxies, including a state-of-the-art machine-learning-based garnet discrimination scheme, we found that 96 % of analysed beach sand garnets are of metamorphic origin and 4 % igneous. Amongst the metamorphic garnets, 85 % were derived from granulite facies, 5 % from eclogite/ultrahigh-pressure facies, 5 % from amphibolite facies, and 1 % from blueschist/greenschist facies rocks. Concerning host-rock bulk composition, 93 % of garnets belong to intermediate–felsic/meta-sedimentary class and 7 % belong to the mafic category. The chemistries of the beach sand detrital garnets of the East Coast of India are readily coupled with the compositions of the garnets from source rock lithologies of the Eastern Ghats Mobile Belt. Very low-grossular garnets are derived from meta-pelitic rocks (khondalites) and mafic granulites, whereas slightly grossular-rich garnets are derived from charnockites. The present study indicates that the low-grossular–high-pyrope detrital garnets are vital signposts of sedimentary provenances. We advocate that the high P-T granulite facies mobile belts are distinctive sources for the low-grossular–high-pyrope detrital garnets.

Sedimentation tempo in an Early Jurassic erg system: Refined chronostratigraphy and provenance of the Clarens Formation of southern Africa

AbstractThe Clarens Formation is a widespread aeolianite deposited over southern Gondwana and represents the final phase of erg evolution in the main Karoo Basin during the Early Jurassic. Previous age assessments of the formation hinge on limited detrital zircon data, supplemented by relative ages from the biostratigraphy and geochronology of the adjacent Karoo units. This study refines the depositional history of the Clarens Formation, including its sediment source dynamics as well as basin‐wide geochronological framework, based on U–Pb dating of detrital zircon grains, together with petrographic and sedimentological characterization. The abundant presence of heavy minerals like zircon, tourmaline and rutile suggests large‐scale detritus recycling, while the uniform sandstone composition on a regional scale is an indication of sediment homogenisation across the basin. Based on the prominent detrital zircon age fractions, the sediments are interpreted as having been reworked from pre‐existing rocks of the Karoo Supergroup (Permian), the Damara and Saldania Orogenic belts (650–490 Ma), whereas minor sources can be assigned to the Namaqua‐Natal Mobile Belt (1.35–1.1 Ga) and the western Sierras Pampeanas (1.30–1.33 Ga). Unstable minerals (hornblende, garnet, titanite, feldspar) provide evidence for a nearby granitic source east and southeast of the basin, related to likely Grenvillian rocks (1.0–1.3 Ga). An Early Jurassic zircon age fraction is linked to volcanic activity in the Chon Aike Magmatic Province that, at the time, was situated south and southwest of the study area. Maximum depositional ages derived from these detrital zircon dates suggest that the sedimentation of the Clarens Formation spanned an interval of ~10 Ma during the Pliensbachian and early Toarcian. More specifically, the lower part of the formation is of early Pliensbachian age or younger (~191–192), while the upper part is of early Toarcian age or younger (~181–183 Ma). These age patterns are particularly prominent in the south of the basin that was situated closer to the volcanic source.

Paleozoic to Mesozoic paleotectonic reconstructions of Gondwana assembly: Insights from petrography, heavy mineral chemistry and detrital U–Th–total Pb monazite geochronology of sandstones in the Pranhita-Godavari Basin (SE India)

The provenance study of Paleo-Mesozoic sediments of the Pranhita-Godavari (P-G) Basin, located in the southeastern India is crucial for the reconstruction of the eastern Gondwanaland, including the India-Antarctica connection. This study examines petrography, heavy mineral chemistry and detrital monazite geochronology of the Permo-Carboniferous to Cretaceous, predominantly fluviatile sandstones in the P-G Basin to track the possible sediment sources in East Antarctica and Eastern India. The sandstones show a gradual shift in composition from feldspatho-quartzose to quartzose arenite from older to younger succession, accompanied by a change in source terranes in a changing setting from transitional continental to the cratonic interior. The heavy minerals of the sandstones are dominated by garnet, rutile, ilmenite, monazite and zircon in order of decreasing abundance. The mineral chemistry of garnet and rutile indicates the predominance of sources from amphibolite to granulite facies rocks with minor inputs from metapelitic sources. The increase in textural and mineralogical maturity of sandstones accompanied by a gradual increase in ilmenite alteration from the bottom to the top of the succession indicates the attainment of tectonic stability with time. U–Th–total Pb dating of detrital monazites yielded three distinct major clusters at (1) 2556–2125 Ma, (2) 969–715 Ma, and (3) 581–418 Ma. Based on the correlation of source composition and monazite geochronology and paleocurrent data, the source of sediments is traced to the orogens of the Eastern Ghats mobile belt, East Antarctica (including Rayner and Napier complex), Karimnagar granulite belt, Khammam schist belt, and Bhopalpatnam granulite belt, situated to the west, south, and southeast of the present outcrops of the P-G Gondwana succession. The younger age populations possibly represent the sediment input from Kuunga Orogen, which represents the youngest orogenic event (635–488 Ma) in the Gondwana assembly. The rocks of Kuunga orogeny, occurring to the south of the basin, was a minor contributor to the P-G Gondwana sediments of this basin. The new data supports that the Eastern Ghats Mobile Belt of India and East Antarctica were conjugate to each other till the Late Triassic Period, both of which contributed major sediments to the P-G Gondwana Basin.

EARLY NEOPROTEROZOIC GRANITOIDS IN THE RYAZANOVSKY MASSIF OF THE YENISEI RIDGE AS INDICATORS OF THE GRENVILLE OROGENY AT THE WESTERN MARGIN OF THE SIBERIAN CRATON

Studies of the geological history of the Yenisei Ridge are important not only for understanding the tectonic evolution of mobile belts at the boundaries of ancient cratons but also for problem solving whether the Siberian craton was a part of the Rodinia supercontinent. The mineralogical-petrological, geochemical and isotope-geochronological studies yielded new data on the petrogeochemical composition, petrogenesis features, U-Pb age of zircon, and Sr and 147Sm-143Nd isotopic parameters for the rocks of the Ryazanovsky granitoid massif located near the Yenisei fault zone of the Yenisei Ridge. These rocks are represented by high-ferruginous peraluminous varieties and are comparable to A-granites or highly differentiated I-granites. Their composition evolves from normal to subalkaline granites and leucogranites, characterized by increased concentrations of highly charged and radioactive elements. Isotopic (Sr, Nd) characteristics of the rocks indicate generation from an ancient crustal substrate, the average age of which corresponds to the Paleoproterozoic. The formation of these granites at the Meso-Neoproterozoic boundary (1013±9.9 Ma) corresponds to the early stage of the Grenville orogeny and the formation time of the structure of the Rodinia supercontinent. This episode of regional crustal evolution is correlated with the synchronous successions and similar style of tectonothermal events on the periphery of large Precambrian cratons (Laurentia and Baltica), thus confirming the reliability of the proposed paleocontinental reconstructions of incorporation of the Siberian craton into the Rodinia.

Presence of Ecandrewsite and Zincian-ilmenite in Auriferous Quartz Veins of North Singhbhum Mobile Belt, Jharkhand

Presence of Ecandrewsite and Zincian-ilmenite in Auriferous Quartz Veins of North Singhbhum Mobile Belt, Jharkhand

Metamorphic turnover at 2 Ga related to two-stage assembly of Columbia

Understanding the stabilization of cratons and how this is related to the onset of plate-tectonics is among the most important questions in geoscience. The assembly of Earth’s first supercontinent Columbia represents the first lines of evidence for a global subduction network, when the oldest, deep subduction-related rocks have been reported. We combine the low-, intermediate- and high-T/P global metamorphic record with the two-stage assembly of the Nuna-Columbia supercontinent to address the significance of the oldest “cold” rocks (low-T/P) and the related emergence of bimodal metamorphic belts. For this purpose, we analyse two examples from Laurentia (including Greenland) and Australia between 2.0–1.8 Ga and 1.8–1.6 Ga. Two main observations are: (i) a first-stage (2.0–1.8 Ga) amalgamation of the megacontinent Nuna (precursor to Columbia) is characterized by bimodal metamorphism along major mobile belts suturing the megacontinent’s center. In contrast, a second-stage (1.8–1.6 Ga) is dominated by the formation of soft collisional orogens during the final Columbia supercontinent assembly, recording intermediate- to high-T/P metamorphism; (ii) the metamorphic signature of the two assembly stages, featuring low- and intermediate-T/P rocks during Nuna assembly followed by their near absence during Columbia amalgamation, contrasts with the thermobaric ratios recorded by the Phanerozoic Gondwana-Pangea assembly, where intermediate and low-T/P rocks dominated the final stage of Pangea amalgamation. This discrepancy may signify substantial changes in intraplate metamorphism and minor rearrangements during Columbia assembly compared to major continent–continent collisions, such as the Appalachian-Variscan Orogen as well as production and fast exhumation of high- to ultra-high-pressure rocks during the assembly of the supercontinent Pangea. Furthermore, the variation of thermobaric ratios aligns with the concept of a two-stage mega-supercontinent formation, emphasizing differences between the potentially oldest and youngest supercontinent cycles.

Magmatic and Geochemical Studies of Early Neoproterozoic Koraput Anorthosite Massif, Eastern Ghats Mobile Belt and their Implications for Rodinia Assembly

Abstract This paper reports new mineralogical and geochemical information on the Neoproterozoic Koraput Anorthosite pluton in domain-2 of the Eastern Ghats Mobile Belt. The lenticular-shaped, NE-SW trending small Koraput Anorthosite Pluton is dominated by gabbro-anorthosite, anorthosite sensu-stricto, and norite-diorite. Isolated patches of ferrodiorite (residual melt following crystallization of anorthosite) occur at the pluton margin. The estimated magmatic P-T conditions for anorthosite emplacement are ~1000°C and ~1.1GPa. In addition, the intermediate Anorthite (48-52 mole %) presence in plagioclase of gabbro-anorthosite and anorthosite indicates plagioclase crystallisation and accumulation at 30-40 km (circa 1 GPa) depth near the crust-mantle boundary. Furthermore, the geochemical traces suggest Koraput anorthosite pluton crystallized from a less fractionated basaltic magma. The REE and trace element systematics of anorthosite and norite-diorite exhibit enriched LILEs over depleted HFSE with negative Nb, Ta, Th, and Zr anomalies. Gabbro-anorthosite and ferrodiorite, on the other hand, exhibit positive Nb, Ti, and negative Zr and Th anomalies. Nb/Th versus Nb/La diagram implies lithodemic units in Koraput Anorthosite pluton are variably contaminated by crustal sources. Integration of geochemical data with available monazite age suggests that the Koraput anorthosite pluton in isotopic domain-2 of the Eastern Ghats Mobile Belt was emplaced during the collision between proto-India and Antarctica during the Rodinia assembly.