Proterozoic Mobile Belts Research Articles

Structure and geodynamic evolution of the lithosphere below Northwest Indian Shield: Constraints from geological, geochronological and multi-scale potential field modelling

The Northwest Indian shield (NWIS) comprises of Archean cratons such as the Bundelkhand (Bh.C), Marwar (MC) and Dharwar (DC), the intervening Proterozoic mobile belts, the Aravalli Delhi Fold Belt (ADFB), Narmada-Son Lineament (NSL) and the Vindhyan basin (VB), the Mesozoic Cambay (CR) and Kutch rift basin (KB) basins and the Saurashtra Continental Block (SCB). The region is covered by thick traps of Deccan Volcanic Province (DVP) thereby masking the geological structures. In this study, we carry out a seismically constrained multi-scale geopotential field interpretation along two long corridors that cut across major Precambrian terrains of the NWIS. The models reveal the Moho varying between 30 and 45 km and LAB between 120 and 180 km. The derived crustal architecture shows that i) the ADFB and NSL are bounded by deep crustal faults having denser crustal rocks, ii) shallow Moho below DVP and CR, iii) presence of thick underplated layer at the base of lower crust in the entire region indicating a strong magmatic imprint. Correlation of modelled lithosphere structure with the structural geological and geochronological data across different terrains of the region suggests that the localized thickening of lithosphere below the ADFB and NSL could be the imprint of paleo-subduction during Proterozoic period, whereas, the thin lithosphere observed below NWIS as a whole represents lithosphere delamination caused by two major LIP events such as 800 Ma Malani and 65 Ma Deccan events. Hence, the proposed evolutionary models across the Precambrian terranes adequately explain the geopotential observations with linkages to present-day lithosphere below NWIS.

Petrology, geochemistry and U–Pb zircon geochronology of Fe–Ti oxide ore‐bearing mafic sill from Saltora‐Mejia area of Chotanagpur Granite Gneissic Complex, eastern India: Implication for late tectonic emplacement of mafic rock of E‐MORB nature in an orogenic belt

An east–west‐trending medium‐grained mafic sill containing co‐genetic Fe–Ti oxide ore lenses is found disposed within granite gneisses around Saltora‐Mejia area in the eastern part of the Chotanagpur Granite Gneissic Complex (CGGC) of eastern India. CGGC is considered as a Proterozoic mobile belt as it witnessed multiple phases of deformation and high‐ grade metamorphism during 1.8–0.8 Ga. Occurrence of such Fe–Ti oxide ore‐bearing mafic sill is unique in the entire CGGC which is a vast Proterozoic orogenic belt and has witnessed many phases of voluminous mafic and felsic magmatisms. The mafic rock is of gabbronorite composition which contains plagioclase, clinopyroxene, orthopyroxene as major constituent primary minerals and amphibole as late magmatic mineral. The rock shows sub‐ophitic, intergranular, mosaic and poikilitic texture (defined by larger pargasitic grain). The gabbronorite shows iron enriched tholeiitic character, low Mg#, low abundances of Ni and Cr, slight enrichment in LILE, LREE and slight depletion in HFSE like Nb and Ti. The computed melt in equilibrium with the studied gabbronorite shows transitional orogenic to anorogenic, within‐plate and E‐MORB‐like geochemical character. In this study, the U–Pb zircon crystallization age (~960 Ma) of the Saltora‐Mejia gabbronorite is reported for the first time which coincides with the late tectonic stage of the most pervasive orogenic activity in the CGGC around 1.2–0.9 Ga. Transitional orogenic to anorogenic geochemical character, late tectonic evolution and other field and laboratory evidences together suggest evolution of the Saltora‐Mejia gabbronorite sill in a late tectonic extensional environment which might have been facilitated by delamination of a subducted plate and upwelling of asthenospheric mantle during the waning stage of a major orogeny in the CGGC.

Crustal and lithospheric mantle structure below the Indian shield based on 3-D constrained gravity inversion and Deep Neural Network approach: Geological implications

The Indian shield region comprises of several Archean cratons, Proterozoic mobile belts, Proterozoic-Phanerozoic rift basins, and volcanic provinces and has been significantly modified by various tectono-thermal events and the supercontinental cycles. These overprinting processes and evolution can be understood, to some extent by characterizing the lithosphere structure. In this study, we carried out seismically constrained 3-D nonlinear gravity inversion using tesseroids in the spherical coordinate system to delineate the Moho geometry for the Indian shield. Further, the supervised machine learning approach using Deep Neural Network (DNN) is implemented on the geopotential data to obtain Lithosphere-Asthenosphere Boundary (LAB) across the Indian shield. The inversion results show that the Moho depth varies between 33 and 60 km below the Indian shield with a mean difference of ∼ −0.3 km and a standard deviation of ∼4.9 km relative to the Moho from receiver function data. For the DNN model, the estimated LAB depth values range between 95 and 280 km below the Indian shield. The model gave rise to the coefficient of determination R2 of 0.93, Mean Absolute Error of ∼14 km, and Root Mean Square Error of ∼22 km between the observed and predicted LAB depths. Apart from the general agreement of Moho and LAB depth estimates with previous seismological studies, the present study provides better resolved information of lithosphere structure across the Indian shield. The modelled lithosphere structure therefore will be useful to integrate with the geochronological data in order to to understand the Proterozoic tectonic evolution of the Indian Shield.

Timing of shear deformation in the Singhbhum Shear Zone, India: implications for shear zone-hosted polymetallic mineralization

AbstractThe Singhbhum Shear Zone in eastern India hosts several Fe oxide–Cu–Au (IOCG)-type polymetallic deposits, mined primarily for U, Cu and apatite, with elevated concentrations of rare earth elements, Ni, Co, Mo, Te and Au in association with low-Ti magnetite. Although the main stages of hydrothermal U, Cu and rare earth element mineralization are known to be Palaeoproterozoic in age, the age of shear deformation in the host shear zone has hitherto not been constrained. Here, we report Re–Os ages of syn-shearing massive molybdenite occurring along shear surfaces transecting the uranium ores in the Jaduguda uranium deposit. Integrating the obtained Re–Os age of c. 1.64–1.59 Ga of molybdenite, the known ages of mineralization and the known tectonothermal events in the adjoining Proterozoic Mobile Belt, we propose that the main stages of polymetallic hydrothermal mineralization pre-dated the pervasive shear deformation event in the Singhbhum Shear Zone. We further suggest that the shear zone was not the principal foci of the hydrothermal mineralization of the main stages. Instead, the shear zone was localized during the Palaeoproterozoic to Mesoproterozoic transition (c. 1.64–1.59 Ga) along pre-existing crustal-scale extensional faults which had earlier been the foci of hydrothermal alteration and mineralization in Palaeoproterozoic time (c. 1.9–1.8 Ga). Shear deformation and metamorphism have reconstituted/redistributed existing mineral/metal inventories with/without neo-mineralization.

Neoproterozoic reworking of a Mesoproterozoic magmatic arc from the north-eastern part of the Central Indian Tectonic Zone: Implication for the growth and disintegration of the Indian shield in the Proterozoic supercontinental cycles

Thermotectonic evolution of the rocks of the Central Indian Tectonic Zone (CITZ) is crucial to understand the growth of the Indian shield and its response to the supercontinental cycles of the Earth. In this study we present field, petrology, geochemistry, in-situ U-Pb zircon and Th-U-total Pb monazite dates from a suite of felsic orthogneisses from the least studied Makrohar Granulite Belt (MKGB) of the CITZ. Petrology and geochemical data identify two rock groups: charnockitic orthogneiss (COG) and garnet orthogneiss (GOG). Geochemical fingerprints suggest that the magmatic protoliths of the gneisses are S-type granitoids, formed in a continental arc setting. In situ U-Pb zircon dates yield the time of arc magmatism at ca. 1400–1350 Ma. This is the first report of mid-Mesoproterozoic arc magmatism in the CITZ. These arc granites were subsequently metamorphosed at granulite facies condition that culminated at ∼800–850 °C, 7–7.5 kbar. A prominent gneissic (migmatitic) fabric was formed with garnet ± orthopyroxene + plagioclase + K-feldspar + quartz as peak metamorphic assemblages. After reaching the recorded P-T maxima, the studied rocks followed a decompression and cooling path to 4 kbar and 500 °C. The inferred clockwise P-T path is consistent with reworking of the Mesoproterozoic arc granites in a continent–continent collisional setting. In-situ Th-U-total Pb monazite and in-situ U-Pb ages of zircon overgrowth constrain the age of deformation and metamorphism in the span of ca. 974–913 Ma. In combination with the published information, the results of this study are consistent with the views that (a) the Indian shield participated as a coherent block in the Columbia supercontinent since ca. 1450 Ma (or before), (b) the ca. 1400–1350 Ma arc magmatism is presumably linked to collapse or closure of a basin (either north or south of the MKGB) in the CITZ in response to the prolonged accretionary phase of the Columbia supercontinent and (c) during the assembly of the Rodinia supercontinent, localized dismembered fragments of the Columbia got re-amalgamated during late Mesoproterozoic to early Neoproterozoic. Archean cratons got fused along the Proterozoic mobile belts (such as Central Indian Tectonic Zone, Eastern Ghats Mobile Belt). Different units within these mobile belts also experienced local compression during this time frame of the Grenvillian orogeny in the Indian subcontinent.

Comment on “EPMA geochemistry and LA-ICPMS dating of allanite, epidote, monazite, florencite and titanite from the Jaduguda uranium deposit, Singhbhum Shear Zone, eastern India: Implications for REE mineralisation vis-a-vis tectonothermal events in the Proterozoic Mobile Belt” by Sinha. [(PR 359, 2021), 1–15

Comment on “EPMA geochemistry and LA-ICPMS dating of allanite, epidote, monazite, florencite and titanite from the Jaduguda uranium deposit, Singhbhum Shear Zone, eastern India: Implications for REE mineralisation vis-a-vis tectonothermal events in the Proterozoic Mobile Belt” by Sinha. [(PR 359, 2021), 1–15

Reply to the comments of D.K. Sinha on “EPMA geochemisty and LA-ICPMS dating of allanite, epidote, monazite, florencite and titanite from the Jaduguda uranium deposit, Singhbum Shear Zone, Eastern India:Implications for REE mineralisation vis-a-vis tectonothermal events in the Proterozoic Mobile Belt”

Reply to the comments of D.K. Sinha on “EPMA geochemisty and LA-ICPMS dating of allanite, epidote, monazite, florencite and titanite from the Jaduguda uranium deposit, Singhbum Shear Zone, Eastern India:Implications for REE mineralisation vis-a-vis tectonothermal events in the Proterozoic Mobile Belt”

Insights Into the Source of Magmatic Hot-Lines: Forty Years of Geophysical Studies of the Cameroon Volcanic Line

The Cameroon Volcanic Line (CVL) of west Africa poses many challenges to common models of mantle processes and volcanic system genesis. Although the CVL superficially resembles the hot-spot trace of a mantle plume, there is no evidence for age progression of initiation or cessation of volcanic activity, making the CVL one of several hot-lines observed on Earth, which exhibit asynchronous volcanism along each line. This unusual form of volcanic system, together with the complexity of the surrounding geology, which includes a Mesozoic rift, an Archean Craton, a Proterozoic mobile belt, and a major continental-scale shear zone, have fueled numerous geophysical investigations of the crust and upper mantle structure within the region. This review highlights major findings from geophysical studies, including controlled source and passive source seismic studies and gravimetric modeling, conducted in the late 20th and early 21st centuries. Potential geodynamic models for the formation of the CVL are examined and evaluated based on the body of geophysical evidence. Finally, several key outstanding questions about the structure and formation of the CVL are highlighted, potentially guiding future studies of this region.

Crustal shear wave velocity and radial anisotropy beneath Southern Africa from ambient noise tomography

Southern Africa is an amalgamation of a distinct Archean core, several Proterozoic mobile belts, and large igneous provinces, making it an ideal natural laboratory for studying Precambrian crustal evolution and deformation. Here we present a new radially anisotropic shear-velocity model of the crust and uppermost mantle beneath Southern Africa using Rayleigh- and Love-wave ambient noise tomography from multiple seismic networks. In the upper and middle crust, the distribution of the isotropic shear velocity correlates well with known surface geology. However, in the lower crust there is no systematic lateral variation of shear velocity between the Archean and Proterozoic terranes, which is likely due to the intensive modifications of Precambrian crust by several later thermo-tectonic events through processes such as lower crustal flow. The strong positive radial anisotropy (VSH > VSV) in the lower crust, when combined with weak azimuthal anisotropy imaged previously, suggests a complex flow pattern, the directions of which likely varied on local-scale due to inhomogeneous shortening or extension during the multiple post-cratonization thermo-tectonic events.

Tectonics of the Greater India Proterozoic Fold Belt, with emphasis on the nature of curvature of the belt in west-central India

The Greater India Proterozoic Fold Belt (GIPFOB) is a curved highly tectonized zone dominated by Early Paleoproterozoic to Early Neoproterozoic magmatic and metamorphic rocks extending from NW India (Aravalli Delhi Fold Belt, ADFB) through central India (the Satpura Mobile Belt, SMB) to eastern India (the Chottanagpur Gneiss Complex, CGC). The continuity of the crustal domains within GIPFOB is obscured by the Gondwana Formation, the Mesozoic Deccan basalts, the intertrappean Bagh Beds and the infratrappean Lameta Formations, and younger alluvium. In supercontinent reconstructions the GIPFOB is speculated to be continuous with Proterozoic mobile belts in Western Australia and the Trans North China Orogen. The NNE-striking western arm (ADFB) of the GIPFOB is flanked by the North India Block (NIB) in the east and the Marwar Craton in the west, whereas the E-striking southern arm (CGC-SMB) is sandwiched between the South India Block (SIB) and the NIB. In the Godhra-Chhota Udepur sector (west-central India) the two arms converge. We synthesize and compare existing data on mesoscale structures, U-Pb (zircon) and monazite chemical ages, and magmatic and metamorphic histories in the Precambrian crystalline rocks in the three crustal blocks to constrain the accretion dynamics in the GIPFOB with an emphasis on the origin of the curvature in the Godhra-Chhota Udepur sector. The CGC and the central and southern domains of the SMB share considerable homogeneity in chronology and regional structures. In the CGC, the early, N-striking steep-dipping tectonic fabrics in ~1.6 Ga anatectic gneisses with ~1.45 Ga and 1.05–0.9 Ga granitoids are modified into a carapace of shallowly-dipping tectonic mélange of recumbently folded basement gneisses and granitoid mylonites thurst over by allochthonous supracrustal rocks at ~0.95 Ga. The central and southern domains within SMB also exhibit the shallowly-dipping foliations and the emplacement of 1.05–0.9 Ga granitoids. The unmodified basement and the overlying tectonic mélange in the CGC-SMB are traversed by 1.0–0.9 Ga E-striking steep-dipping sinistral (dominant) and dextral (uncommon) shear zones that accommodated the Early Neoproterozoic transpressive deformation induced by the NIB-SIB oblique collision. The mesoscale structures in the rocks of the Godhra-Chhota Udepur sector intruded by Early Neoproterozoic granitoids and followed by oblique collision are similar to CGC-SMB. In the ADFB, by contrast, the basement rocks are older (Archean to Early Paleoproterozoic), high-grade metamorphism and felsic magmatism are older (1.8–1.7 Ga), the expansive ~1.45 Ga granitoids are absent, nappe structures are locally present, and expansive domains of the shallowly-dipping foliations are lacking. Overall, the tectonic evolution of the ADFB is incoherent with those in CGC-SMB and the GC sector. We suggest that the structures in the N/NNE-striking western accretion arm terminate against the E-striking southern arm. The Early Neoproterozoic (1.0−0.9 Ga) integration of the crustal domains within the GIPFOB resulted due to broadly contemporaneous convergence of the NIB, the SIB and the Marwar Craton (?) during the Rodinia supercontinent assembly, but the accretion along the southern arm post-dated the accretion in the western arm. [482 words]

Geodynamic processes inferred from Moho and Curie depths in Central and Southern African Archean Cratons

Central and Southern Africa is home to major Archean Cratons, flanked by Proterozoic mobile belts. The region is characterized by anomalously high topography and shallow Curie depth (Zb). Factors controlling topography and Zb anomalies in old continental crusts remain poorly understood. In this study, we present high-resolution Moho undulation (Zm) derived with gravity spectral technique. Archean Cratons and Proterozoic belts are mostly characterized by deep Moho (>36 km), whereas the Moho depths in Mozambique belts is mostly shallow (~26 to 41 km). Extremely shallow Zb (<10 km) is dominant in Archean Cratons, whereas intermediate Zb (10–25 km) is prevalent in the mobile belts. The Curie points are mostly above the Moho. Low surface heat flow (Qs) in Archean Cratons indicate that Zb is not correlated with thermal perturbation. Shallow Zb are mostly found in areas with low Vp/Vs ratio, predominantly felsic lower crust and sharp Moho. Shallow Zb also correlate with intense metasomatism and mineral enrichment, as well as depletion in basaltic components and geochemical overprinting by multiple episodes of melt and fluid infiltration. Crustal composition is the main factor that controls shallow Zb in Central and Southern Africa Archean Cratons. The regional elevated topography is not due to thermal perturbation as mostly argued by mantle plume hypothesis, but may be caused by regional thermo-chemical mantle upwelling dominated by composition.

EPMA geochemistry and LA-ICPMS dating of allanite, epidote, monazite, florencite and titanite from the Jaduguda uranium deposit, Singhbhum Shear Zone, eastern India: Implications for REE mineralization vis-à-vis tectonothermal events in the Proterozoic Mobile Belt

The Singhbhum shear zone (SSZ), eastern India, located close to the boundary between the Proterozoic North Singhbhum Mobile Belt and the Archaean Singhbhum craton, is the best known uranium province and one of the most important copper districts in India. The uranium ores and associated rocks are enriched in rare earth elements (REEs). This study integrates texture, composition and in situ LA-ICPMS dating of allanite, epidote, monazite, florencite and titanite from the Jaduguda uranium deposit in the SSZ. The earliest LREE-rich allanite (Allanite-Ce) formed at 1883 ± 14 Ma and was subsequently replaced and overgrown respectively by LREE-depleted allanite and epidote at 1637 ± 11 Ma and 1107 ± 18 Ma. The earliest monazite (Monazite-Ce) formed at ca. 1809 ± 9 Ma, while a new generation of monazite and florencite are dated at 952.2 ± 7.9 Ma and 959 ± 83 Ma respectively. Titanite, discordant to the pervasive foliation, records ancient Pb-loss and probably new titanite growth at 978 ± 17 Ma.The SSZ witnessed protracted evolutionary history with accompanying multi-stages REE mineralization and mobilization, spanning over ca. 900 Ma. The Paleoproterozoic LREE-mineralization occurred in two different pulses at ca. 1.88 Ga and ca. 1.80 Ga predating the known ages of metamorphism. It is envisaged that extension-related faults developed at the present location of the SSZ acted as fluid conduits and localized the earliest ca. 1.88 Ga hydrothermal REE mineralization. It is unclear whether the ca 1.80 event is the continuation of the ca 1.88 Ga event or represents a separate and discrete pulse of mineralization in the same locale under different geotectonic environment. The ca. 1.64 Ga event associated with LREE-removal is related to either reactivation of the existing faults or partial closure of the mobile belt with concomitant shear deformation and metamorphism in the shear zone when the rocks in the northern mobile belt were thrust southwards along existing mineralized faults. The status of the ca. 1.11 Ga event is ambiguous. The 950 ± 50 Ma event, which primarily redistributed REEs from existing mineralization is related to the final closure of the mobile belt and reactivation of the SSZ associated with the formation of the greater Indian land mass in Peninsular India.

Thermochemical Modification of the Upper Mantle Beneath the Northern Malawi Rift Constrained From Shear Velocity Imaging

AbstractTo investigate the controls on continental rifting in the western branch of the East Africa Rift System, we conduct shear velocity imaging of the crust and uppermost mantle beneath the weakly extended Malawi Rift and the Rungwe Volcanic Province (RVP). We use local‐scale measurements of Rayleigh wave phase velocities between 9‐ and 100‐s periods combined with constraints on basin architecture and crustal thickness to invert for shear velocity from the surface to ~135 km. Our resulting 3‐D model reveals a localized low‐velocity anomaly associated with the RVP extending from the crust and through the upper mantle, which can be explained with modestly elevated temperatures. Away from the RVP, velocities within mantle flanking the rift are fast (&gt;4.6 ± 0.1 km/s), suggesting depleted lithospheric mantle to depths of ~100 and &gt;135 km to the west and east of the rift, respectively. The upper mantle beneath the rift axis is characterized by thinned lithosphere with slower velocities than the surrounding plateau, suggestive of thermal and/or chemical modification by the rifting process. Slowest velocities are mildly asymmetric about the rift axis, with the lowest velocities observed beneath the rift and adjacent footwall escarpments. The underlying asthenosphere is only moderately slow (~4.25 ± 0.1 km/s), including beneath the RVP, precluding the presence of significant volumes of partial melt. The positions of localized lithospheric modification and basin‐bounding border faults correlate with the location of Proterozoic mobile belts, suggesting that these sutures provide lithospheric‐scale weakening mechanisms necessary for localizing strain and allowing extension to occur in the Malawi Rift.

Spatiotemporal Variations in Upper Crustal Extension Across the Different Basement Terranes of the Lake Tanganyika Rift, East Africa

AbstractPreexisting crustal heterogeneities are shown to influence rift process at a variety of scales. However, our understanding of how crustal inheritance influences rift‐scale spatiotemporal kinematics of faulting in magma‐poor rift environments is still very limited. Studies of active continental rifts can provide high‐fidelity assessments of extensional processes and structures that are not possible through examination of ancient rifts that have undergone subsequent deformation events or are buried deeply beneath passive margins. We examine the influence of crustal inheritance on active rifting through balancing and restoring a series of regional cross sections across the Lake Tanganyika Rift in the Western Branch of the East African Rift System. The cross sections are produced using legacy seismic reflection data, reprocessed through prestack depth migration. This type example of a young, magma‐poor continental rift transects several different basement terranes, including an Archean/Paleoproterozoic craton, and Proterozoic mobile belts. The Lake Tanganyika Rift exhibits two classic bell‐shaped profiles of extension along strike, reaching a maximum of 7.15 km. A spatiotemporal integration of the extension data, and comparison with the various basement terranes the rift transects, reveals that extension in cratonic blocks is more widely distributed compared to mobile belt terranes, where strain rapidly localizes onto border faults by later rift stages. These results reveal how crustal inheritance exerts a fundamental control on the evolution of extension localization, ultimately impacting the geometry and structural architecture of rift basins.

Recurrent seismicity in Rajasthan State in the tectonically stable NW Indian Craton

Indian peninsular region comprises several Archean cratonic blocks (Dharwar, Bastar, Singhbhum, Aravalli – Bundelkhand), bordered by Proterozoic mobile belts. Therefore, this region is considered as tectonically stable and designated as the least vulnerable region to earthquake hazard except the still active Central Indian Tectonic Zone (CITZ). The latter is a major suture between southern and northern Indian blocks. Seismicity in India is common along its northern and northeastern (Himalayan) region defining the Indian Plate margin, in collision with the Eurasian (Tibetan) Plate. Being tectonically active, this region has a documented record of frequent earthquakes including some high magnitude and devastating ones. The northwestern Indian block is amongst the relatively stable Precambrian regions of India and categorized under Zone – II by the Indian Meteorology Department, one of the seismically least vulnerable regions. However, the region has been a site of recurring low to moderate magnitude earthquakes. Compilation of the earthquake data from the Rajasthan State in NW India documents at least 45 earthquakes in this region during the last one and a half decades. Several of these have remained unnoticed because of their low magnitude. The NE –SW trending Aravalli Mountain Region (AMR), running across the eastern half of Rajasthan State represents the most significant tectonomorphic feature of NW India. The AMR is an ensemble of Proterozoic age Aravalli and Delhi Supergroup rocks (metasediments, volcanics and intrusives) that overlie an Archean basement (Banded Gneissic Complex – BGC). These Proterozoic mobile belts have evolved through several episodes of deformation that have shaped its present day geomorphology. The western part of the State, the Marwar Block, is relatively younger in age and was accreted to the AMR during the 1 Ga subduction event. The western margin of AMR, also called as the Western Margin Fault, represents a major suture between the two terranes. However, the entire region was cratonized by end Proterozoic and has remained tectonically stable during the Phanerozoic Eon. The Archean basement and overlying Proterozoic cover rocks are infested with several major and minor faults and shear zones. The most prominent ones are the NE-SW trending major lineaments corresponding with the regional tectonic grain and several minor ones across. The earthquake epicenter distribution pattern shows a close spatial association with these lineaments. In the absence of any significant tectonic activity in the region and rise in pore pressure either due to magmatism or excessive rainfall, we attribute recurrence of earthquakes in the region to reactivation of such old sutures/weaker zones as a response to stress build-up along the northern margin of the Indian Plate resulting from ongoing northward convergence of the Indian Plate. Some of the faults in western part are traceable into the Cambay Basin active faults in the south that may have triggered seismic activity in western Rajasthan.

Depositional history and provenance of cratonic “Purana” basins in southern India: A multipronged geochronology approach to the Proterozoic Kaladgi and Bhima basins

Peninsular India is a collage of Archaean cratonic domains separated by Proterozoic mobile belts. A number of cratonic basins, known as “Purana basins” in the Indian literature, formed in different parts of the Indian Peninsula during extensional tectonic events, from Paleoproterozoic through Neoproterozoic times. In this contribution, we present a diversity of new geochronological data for different units within the Kaladgi and the Bhima basins, which overlie the western and eastern Dharwar cratons, respectively. The new geochronology data are discussed in terms of depositional history and provenance of these poorly understood Proterozoic intracratonic basins. For the Kaladgi Group, a U–Pb baddeleyite age of 1,861 ± 4 Ma obtained for a dolerite dyke intruding the Yendigere Formation is used to constrain the minimum age of deposition of the lower Kaladgi Group. This result demonstrates that this part of the succession is comparable in age to the Papaghni Group of the Cuddapah Basin, heralding onset of Purana sedimentation at ~1,900 Ma. The detrital zircon populations from the clastic rocks of the Kaladgi and Bhima basins show unique and distinct age patterns indicating different source of sediments for these two basins. Palaeocurrent analysis indicates a change in provenance from south or southeast to west or northwest between the Kaladgi and Bhima clastic sedimentation. New U–Th–Pb and Rb–Sr radiometric dates of limestones and glauconite‐bearing sandstones of the Bhima Group (Bhima Basin) and the Badami Group (Kaladgi Basin) indicate deposition at around 800–900 Ma, suggesting contemporaneity for the two successions. Thus, the unconformity between the Kaladgi Group and the overlying Badami Group represents a time gap of up to 1,000 Myr. These new results demonstrate the complex multistage burial and unroofing history of the Archaean Dharwar Craton throughout the Proterozoic, with important implications for exploration of metal deposits and diamonds in Peninsular India.

НОВЫЙ ЗОЛОТОРУДНЫЙ РАЙОН В ТАНЗАНИИ

Tanzania is one of the leading gold mining countries in the world and the discovery of new gold resources on its territory is an actual task. Known gold deposits are concentrated mainly in the northwest of the country, in the metallogenic zone of Lake Victoria, where they are associated with the Archean greenstone belts, and to a lesser extent – in the southwest, in the ore regions of Lupa and Mpanda, confined to the Ubendian Paleoproterozoic mobile belt. With regard to the eastern regions of Tanzania, where the Proterozoic structures of the Uzagaran mobile belt are developed, until recently in this region any significant manifestations of gold mineralization were not known. As a result of our research in the northern part of the Morogoro province of the Republic of Tanzania, a new previously unknown gold deposit Mananila was discovered. It is represented by a large volume, up to 400–450 m long, up to 60–80 m thick, mineralized shear zone over intensely leached and schistosed migmatites, gneisses, amphibolites, penetrated by echelon systems of quartz veins and veinlet, steeply dipping bodies of quartz breccia up to 1.0–1.5 m thick. Gold contents range from 0.61 to 8.11 g/t, the average zone content is 2.5–3.0 g/t. Parallel to the main zone, similar structures are developed on the site, although they are of lower thickness. The forecast resources of the deposit are estimated at 20 tons of gold. 2.8 km to the east from the Mananila field, the recently discovered Mazizi gold deposit is located, and a number of small occurrences of gold are also known in the region. All these objects are located within a large shear zone of the northeastern strike, up to 4–5 km width, over 20 km in length. This serves as the basis for the identification of a new gold ore region in the northern part of the Morogoro province of the United Republic of Tanzania, within the Proterozoic mobile belt of Usagaran, the possible gold content of which has never been previously discussed in geological literature.

About this title ‐ Crustal Evolution of India and Antarctica: The Supercontinent Connection

The Proterozoic aeon involved at least three major continental readjustments. India and Antarctica appear in most models of supercontinent reconstructions, but their relative position has been the subject of debate. High-resolution petrological and geochronological data, especially from the Proterozoic mobile belts, provide the principal means of resolving this issue. The ice-covered nature of Antarctica allows only limited access to the rocks, and then only in coastal tracts, so detailed studies in more accessible Proterozoic terrains in India assume added significance. This volume, a follow-up to the XII International Symposium on Antarctic Earth Science, Goa (a SCAR symposium), provides new data from selected locations in east Antarctica (Enderby Land and Dronning Maud Land) and from India, including the Eastern Ghats Mobile Belt (EGMB), Chota Nagpur Gneissic Complex, the Khasi Hills and the Aravalli–Delhi Mobile Belt. The presented geochronological data, constrained by petrological studies, are expected to provide new insights, especially into the EGMB–east Antarctica connection and the rate of continental readjustments in the post-Rodinia break-up.

Proterozoic Tectonics and Trans-Indian Mobile Belts: A Status Report

The Archean cratonic nuclei in India are hemmed by Proterozoic mobile belts or fold belts. These mobile belts reveal the tectonic processes that shaped the then craton margin magmatism, sedimentation, metamorphism and deformation of crustal segments, and suturing of the cratonic blocks embedded within the peninsular Indian shield that remained more or less stable since the Cambrian. A loose spatial connection of the Eastern Ghats belt (EGB) along southeastern margin of India, through Chotanagpur granite gneiss terrain and adjoining North Singhbhum fold belt in eastern India, Central Indian tectonic zone, to Aravalli-Delhi mobile belt in northwestern India constitute the trans-Indian mobile belts with tectonic episodes apparently linked to assembly and dispersal of two major supercontinents in the Proterozoic. Beyond southern extremity of the EGB (Ongole domain), the Nellore schist belt and tectonically juxtaposed Nallamalai fold belt in southern India abuts further south against the Southern granulite terrain (SGT) with remnants of Neoarchean inheritance and Neoproterozic remobilization. SGT is a key element in unravelling trans-continental connections of India during the late Neoproterozoic marked by assembly of the Gondwana supercontinent. Despite the apparent first order connection of these belts developed under largely similar global tectonic framework, individual mobile belts show diverse rock association, metamorphic grade and geologic antiquity. In this status report we briefly review these Indian Proterozoic mobile belts and associated fold belts in the light of recently published work bearing on tectonomagmatic, structural, metamorphic and geochronological data and interpretation.

Late Jurassic-Cretaceous fluvial evolution of central Africa: Insights from the Kasai-Congo Basin, Democratic Republic Congo

The Congo Basin in central Africa is one of the largest intracratonic sedimentary basins in the world. The geological knowledge of Congo Basin is mainly based on studies from the central part of the basin (“Cuvette Centrale”). We present the results of sedimentary provenance investigations of the Jurassic–Cretaceous strata from the southwestern part of the basin, called the Kasai region. This study combines sandstone petrography with U-Pb and Lu-Hf analyses of detrital zircons to assess the stratigraphy, sedimentary provenance and drainage history of the Upper Jurassic-Cretaceous strata in the Kasai region. The stratigraphy is subdivided into a single Upper Jurassic unit (J1) and four Cretaceous units (C1–C4). Petrographically, sandstones from all units except the conglomeratic C3 are texturally and compositionally mature, dominated by quartzarenite and subarkosic compositions. These characteristics can be attributed to considerable recycling of older sedimentary strata and crustal sources, along with long distance fluvial and aeolian processes. The analyses of fifteen detrital zircon samples from the Upper Jurassic–Cretaceous strata yielded mainly Archean and Proterozoic zircons. This result suggests that sandstones are likely sourced from the underlying Archean-Paleoproterozoic Congo–Kasai Craton and from nearby Proterozoic mobile belts, particularly the Irumide and Lufilian Belts to the south of the basin. The dominance of Archean and Proterozoic detrital zircons in Upper Jurassic–Cretaceous strata suggests that the Kasai portion of the Congo Basin experienced exhumation and erosion, which is possibly associated with far-field reactivation of Archean and Proterozoic structures during and following Gondwana rifting in the late Mesozoic. A large fluvial drainage network sourced from the south of the basin, is interpreted to have developed across central Africa during the Late Jurassic–Cretaceous. This fluvial system is believed to have flowed northward across the Congo Basin and ultimately drained into a wrench fault system called the Central African Shear Zone, which extends in an ENE direction from the Gulf of Guinea through Cameroon into Sudan and Kenya.