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[Display omitted] • U-Pb and REE analysis of Ediacaran Zirku Fm. Reveal its c. 550 Ma Cadomian origin. • The UAE Neoproterozoic basement is part of the Omani tectonic domain. • Application of apatite as petrochronological tool can help tracking orogenic cycle. The thick Phanerozoic sedimentary cover lying above the Arabian Platform conceals extensive basement between the western Neoproterozoic domains of the Arabian Nubian Shield (ANS) and of the eastern Omani basement. The Neoproterozoic rocks entrained within salt domes that crop out within the United Arab Emirates (UAE) and Qatar are the only direct samples that allow us to investigate the tectonic history of the concealed Arabian basement domains before c. 550 Ma. This study focuses on the U-Pb geochronological and REE geochemical analysis of detrital zircon, apatite, titanite and rutile grains from the Zirku turbidites brought to the surface by halokinetic movements offshore UAE. These data are compared with new U-Pb and REE data from detrital heavy minerals of three metasedimentary members of the Omani Neoproterozoic Hatat Formation collected in the Saih Hatat window. The Omani metasedimentary units yield detrital titanite, zircon and apatite U–Pb ages that span from c. 2500 to 690 Ma, with an age maxima at c. 850 Ma, while the UAE unit yield ages from c. 2550 to 550 Ma with major age peaks at c. 1000, 820, 650 Ma. The analysis of the Omani stratigraphic sequence in the Saih Hatat window revealed that the rocks of the Neoproterozoic Hatat Formation yield similar age distributions of the Abu Mahara Group (lower Huqf Supergroup, exposed in central and southern Oman), and that the REE geochemical composition of the Hatat detrital apatite grains shares akin REE signature with the c. 550 detrital apatite of the Zirku Formation, with both being sourced from volcanic-arcs. These new geochronological and geochemical data, together with recent geophysical evidences, suggest that the basement of the UAE is originally part of the Oman tectonic domain and evolved as part of a volcanic-arc in an active margin at c. 550 Ma, which we interpret as part of the retro -arc of the Cadomian collision in between the Arabian and the Cadomian Taurides, Iran and Afghanistan terranes. [ABSTRACT FROM AUTHOR]

Madagascar is a key area for unraveling the geodynamic evolution of the transition between the Rodinia and Gondwana supercontinents as it contains several suites of c. 850–700 Ma magmatic rocks that have been postulated to correlate with other Rodinian terranes. The Bemarivo Domain of northern Madagascar contains the youngest of these units that date to c. 750–700 Ma. We present zircon Hf and O isotope data to understand northern Madagascar's place in the Neoproterozoic plate tectonic reconfiguration. We demonstrate that the northern component of the Bemarivo Domain is distinct from the southern part of the Bemarivo Domain and have therefore assigned new names—the Bobakindro Terrane and Marojejy Terrane, respectively. Magmatic rocks of the Marojejy Terrane and Anaboriana Belt are characterized by evolved εHf(t) signatures and a range of δ18O values, similar to the Imorona‐Itsindro Suite of central Madagascar. These magmatic suites likely formed together in the same long‐lived volcanic arc. In contrast, the Bobakindro Terrane contains juvenile εHf(t) and mantle‐like δ18O values, with no probable link to the rest of Madagascar. We propose that the Bobakindro Terrane formed in a juvenile arc system that included the Seychelles, the Malani Igneous Suite of northwest India, Oman, and the Yangtze Belt of south China, which at the time were all outboard from continental India and south China. The final assembly of northern Madagascar and amalgamation of the Bobakindro Terrane and Marojejy Terrane occurred along the Antsaba subduction zone, with collision occurring at c. 540 Ma. Key Points: New model links northern Madagascar, Seychelles, NW India, Oman, south China at c. 750 MaNew zircon Hf and O isotope data from northern Madagascar indicate that the Bobakindro Terrane (northern Bemarivo Domain) is juvenileThe Marojejy Terrane (southern Bemarivo Domain) has evolved Hf isotope signatures and likely links with central Madagascar magmatic suites [ABSTRACT FROM AUTHOR]

It has long been recognised that Madagascar was contiguous with India until the Late Cretaceous. However, the timing and nature of the amalgamation of these two regions remain highly contentious as is the location of Madagascar against India in Gondwana. Here we address these issues with new U-Pb and Lu-Hf zircon data from five metasedimentary samples from the Karwar Block of India and new Lu-Hf data from eight previously dated igneous rocks from central Madagascar and the Antongil-Masora domains of eastern Madagascar. New U-Pb data from Karwar-region detrital zircon grains yield two dominant age peaks at c. 3100 Ma and c. 2500 Ma. The c. 3100 Ma population has relatively juvenile ε Hf (t) values that trend toward an evolved signature at c. 2500 Ma. The c. 2500 Ma population shows a wide range of ε Hf (t) values reflecting mixing of an evolved source with a juvenile source at that time. These data, and the new Lu-Hf data from Madagascar, are compared with our new compilation of over 7000 U-Pb and 1000 Lu-Hf analyses from Madagascar and India. We have used multidimensional scaling to assess similarities in these data in a statistically robust way. We propose that the Karwar Block of western peninsular India is an extension of the western Dharwar Craton and not part of the Antananarivo Domain of Madagascar as has been suggested in some models. Based on ε Hf (t) signatures we also suggest that India (and the Antongil-Masora domains of Madagascar) were palaeogeographically isolated from central Madagascar (the Antananarivo Domain) during the Palaeoproterozoic. This supports a model where central Madagascar and India amalgamated during the Neoproterozoic along the Betsimisaraka Suture. [ABSTRACT FROM AUTHOR]

Neoproterozoic tectonic geography was dominated by the formation of the supercontinent Rodinia, its break-up and the subsequent amalgamation of Gondwana. The Neoproterozoic was a tumultuous time of Earth history, with large climatic variations, the emergence of complex life and a series of continent-building orogenies of a scale not repeated until the Cenozoic. Here we synthesise available geological and palaeomagnetic data and build the first full-plate, topological model of the Neoproterozoic that maps the evolution of the tectonic plate configurations during this time. Topological models trace evolving plate boundaries and facilitate the evaluation of “plate tectonic rules” such as subduction zone migration through time when building plate models. There is a rich history of subduction zone proxies preserved in the Neoproterozoic geological record, providing good evidence for the existence of continent-margin and intra-oceanic subduction zones through time. These are preserved either as volcanic arc protoliths accreted in continent-continent, or continent-arc collisions, or as the detritus of these volcanic arcs preserved in successor basins. Despite this, we find that the model presented here still predicts less subduction (ca. 90%) than on the modern earth, suggesting that we have produced a conservative model and are likely underestimating the amount of subduction, either due to a simplification of tectonically complex areas, or because of the absence of preservation in the geological record (e.g. ocean-ocean convergence). Furthermore, the reconstruction of plate boundary geometries provides constraints for global-scale earth system parameters, such as the role of volcanism or ridge production on the planet's icehouse climatic excursion during the Cryogenian. Besides modelling plate boundaries, our model presents some notable departures from previous Rodinia models. We omit India and South China from Rodinia completely, due to long-lived subduction preserved on margins of India and conflicting palaeomagnetic data for the Cryogenian, such that these two cratons act as ‘lonely wanderers’ for much of the Neoproterozoic. We also introduce a Tonian-Cryogenian aged rotation of the Congo-São Francisco Craton relative to Rodinia to better fit palaeomagnetic data and account for thick passive margin sediments along its southern margin during the Tonian. The GPlates files of the model are released to the public and it is our expectation that this model can act as a foundation for future model refinements, the testing of alternative models, as well as providing constraints for both geodynamic and palaeoclimate models. [ABSTRACT FROM AUTHOR]

Madagascar occupies an important location within the East African Orogen (EAO), which involves a collection of Neoproterozoic microcontinents and arc terranes lodged between older cratonic units during the final assembly of the supercontinent Gondwana. The detrital zircon record of Proterozoic metasedimentary rock packages within the Antananarivo Domain (the Ambatolampy, Manampotsy, Vondrozo, Itremo and Ikalamavony Groups) is used to identify pre-orogenic tectonic affiliations of the region—affiliations that control interpretations of the evolution of the Mozambique Ocean and the formation of this part of central Gondwana. Here we focus on the Ambatolampy Group, a previously poorly known group of high-grade siliciclastic metasedimentary rocks, and compare these data to similar data from the other sedimentary packages in central Madagascar (the Vondrozo, Sofia, Manampotsy, Itremo, Molo, Ikalamavony, Androyen, Ambodiriana, Iakora and Maha Groups). New U–Pb (SHRIMP) zircon data for the Ambatolampy Group yield detrital age maxima of ~ 3000 Ma, ~ 2800–2700 Ma, ~ 2500 Ma, ~ 2200–2100 Ma and ~ 1800 Ma. The youngest near-concordant detrital zircon age is 1836 ± 25 Ma, which we suggest represents the maximum depositional age of the Ambatolampy Group, in contrast to younger ages reported elsewhere. The detrital spectra are very similar to those from the Itremo Group and we suggest that they correlate with each other. Metamorphic zircons and zircon rims constrain the minimum depositional age to be ~ 540 Ma; the interpreted age of metamorphism. New δ 18 O data (SHRIMP-SI) and hafnium (MC-LA–ICP–MS) isotopic data complement the U–Pb data and provide new constraints on the age, geochemistry and provenance of the metasedimentary rocks. We suggest that central Madagascar contained a Mesoproterozoic (to possibly Tonian) siliciclastic sedimentary basin, within which the Ambatolampy Group, and the Itremo and Maha Groups (and possibly part of the Iakora Groups) were deposited. Later sedimentary systems are represented by the Ikalamavony, Ambodiriana, Manampotsy and Molo Groups. [ABSTRACT FROM AUTHOR]

Data from a migmatised metapelite raft enclosed within charnockite provide quantitative constraints on the pressure–temperature–time ( P – T – t ) evolution of the Nagercoil Block at the southernmost tip of peninsular India. An inferred peak metamorphic assemblage of garnet, K-feldspar, sillimanite, plagioclase, magnetite, ilmenite, spinel and melt is consistent with peak metamorphic pressures of 6–8 kbar and temperatures in excess of 900 °C. Subsequent growth of cordierite and biotite record high-temperature retrograde decompression to around 5 kbar and 800 °C. SHRIMP U–Pb dating of magmatic zircon cores suggests that the sedimentary protoliths were in part derived from felsic igneous rocks with Palaeoproterozoic crystallisation ages. New growth of metamorphic zircon on the rims of detrital grains constrains the onset of melt crystallisation, and the minimum age of the metamorphic peak, to around 560 Ma. The data suggest two stages of monazite growth. The first generation of REE-enriched monazite grew during partial melting along the prograde path at around 570 Ma via the incongruent breakdown of apatite. Relatively REE-depleted rims, which have a pronounced negative europium anomaly, grew during melt crystallisation along the retrograde path at around 535 Ma. Our data show the rocks remained at suprasolidus temperatures for at least 35 million years and probably much longer, supporting a long-lived high-grade metamorphic history. The metamorphic conditions, timing and duration of the implied clockwise P – T – t path are similar to that previously established for other regions in peninsular India during the Ediacaran to Cambrian assembly of that part of the Gondwanan supercontinent. [ABSTRACT FROM AUTHOR]

The Pranhita-Godavari Basin in central eastern India is one of the Proterozoic “Purāna” basins of cratonic India. New geochronology demonstrates that it has a vast depositional history of repeated basin reactivation from the Palaeoproterozoic to the Mesozoic. U-Pb laser ablation inductively coupled plasma mass spectrometry dating of detrital zircons from two samples of the Somanpalli Group—a member of the oldest sedimentary cycle in the valley—constrains its depositional age to ∼1620 Ma and demonstrates a tripartite age provenance with peaks at ∼3500 Ma, ∼2480 Ma and ∼1620 Ma, with minor age peaks in the Eoarchaean (∼3.8 Ga) and at ∼2750 Ma. These ages are consistent with palaeocurrent data suggesting a southerly source from the Krishna Province and Enderby Land in East Antarctica. The similarity in the maximum depositional age with previously published authigenic glauconite ages suggest that the origin of the Pranhita-Godvari Graben originated as a rift that formed at a high angle to the coeval evolving late Meosproterozoic Krishna Province as Enderby Land collided with the Dharwar craton of India. In contrast, detrital zircons from the Cycle III Sullavai Group red sandstones yielded a maximum depositional age of 970 ± 20 Ma and had age peaks of ∼2550 Ma, ∼1600 Ma and then a number of Mesoproterozoic detrital zircons terminating in three analyses at ∼970 Ma. The provenance of these is again consistent with a southerly source from the Eastern Ghats Orogen and Antarctica. Later cycles of deposition include the overlying Albaka/Usur Formations and finally the late Palaeozoic to Mesozoic Gondwana Supergroup. [ABSTRACT FROM AUTHOR]

Gondwana amalgamated along a suite of Himalayan-scale collisional orogens, the roots of which lace the continents of Africa, South America, and Antarctica. The Southern Granulite Terrane of India is a generally well-exposed, exhumed, Gondwana-forming orogen that preserves a record of the tectonic evolution of the eastern margin of the East African Orogen during the Ediacaran-Cambrian (circa 600-500 Ma) as central Gondwana formed. The deformation associated with the closure of the Mozambique Ocean and collision of the Indian and East African/Madagascan cratonic domains is believed to have taken place along the southern margin of the Salem Block (the Palghat-Cauvery Shear System, PCSS) in the Southern Granulite Terrane. Investigation of the structural fabrics and the geochronology of the high-grade shear zones within the PCSS system shows that the Moyar-Salem-Attur shear zone to the north of the PCSS system is early Paleoproterozoic in age and associated with dextral strike-slip motion, while the Cauvery shear zone (CSZ) to the south of the PCSS system can be loosely constrained to circa 740-550 Ma and is associated with dip-slip dextral transpression and north side-up motion. To the south of the proposed suture zone (the Cauvery shear zone), the structural fabrics of the Northern Madurai Block suggest four deformational events (D1-D4), some of which are likely to be contemporaneous. The timing of high pressure-ultrahigh temperature metamorphism and deformation (D1-D3) in the Madurai Block (here interpreted as the southern extension of Azania) is constrained to circa 550-500 Ma and interpreted as representing collisional orogeny and subsequent orogenic collapse of the eastern margin of the East African Orogen. The disparity in the nature of the structural fabrics and the timing of the deformation in the Salem and the Madurai Blocks suggest that the two experienced distinct tectonothermal events prior to their amalgamation along the Cauvery shear zone during the Ediacaran/Cambrian. [ABSTRACT FROM AUTHOR]

Abstract: Peninsular India forms a keystone in Gondwana, linking the East African and Malagasy orogens with Ediacaran–Cambrian orogenic belts in Sri Lanka and the Lützow Holm Bay region of Antarctica with similar aged belts in Mozambique, Malawi and Zambia. Ediacaran–Cambrian metamorphism and deformation in the Southern Granulite Terrane (SGT) reflect the past tectonic setting of this region as the leading vertex of Neoproterozoic India as it collided with Azania, the Congo–Tanzania–Bangweulu Block and Kalahari on one side and the Australia/Mawson continent on the other. The high-grade terranes of southern India are made up of four main tectonic units; from north to south these are a) the Salem Block, b) the Madurai Block, c) the Trivandrum Block, and d) the Nagercoil Block. The Salem Block is essentially the metamorphosed Dharwar craton and is bound to the south by the Palghat-Cauvery shear system — here interpreted as a terrane boundary and the Mozambique Ocean suture. The Madurai Block is interpreted as a continuation of the Antananarivo Block (and overlying Palaeoproterozoic sedimentary sequence — the Itremo Group) of Madagascar and a part of the Neoproterozoic microcontinent Azania. The boundary between this and the Trivandrum Block is the Achankovil Zone, that here is not interpreted as a terrane boundary, but may represent an Ediacaran rift zone reactivated in latest Ediacaran–Cambrian times. [Copyright &y& Elsevier]

Abstract: The Madurai Block of southern India is rich in granitic orthogneiss, much of which is orthopyroxene-bearing (charnockite). This study has identified that orthogneiss from the northwest of the Madurai Block (broadly defined as north and west of the Karur–Kambam–Painavu–Trichur lineament) has a very different origin from that in the south-eastern Madurai Block. To the north and north-west of the Madurai Block, charnockites record Neoarchaean (∼2.7–2.5Ga) crystallization ages with metamorphic overprinting at ∼535Ma. Their Archaean Nd depleted mantle model ages (2.51–3.01Ga), high ɛNd(T) values (between −3.28 and +4.55) and low to moderate initial 87Sr/86Sr ratios (0.7017–0.7106) indicate a primarily mantle-derived origin with variable involvement of Archaean crustal material. The south-east Madurai Block samples have much younger crystallization ages of 1007±23Ma and 784±18Ma and a range of Nd depleted mantle model ages between 1.38 and 1.69Ga, suggesting a significantly different isotopic evolution of this terrane. The isotopic signature of these charnockites (ɛNd(T) =+2.58 to −3.28, initial 87Sr/86Sr=0.7054–0.7084) suggests the involvement of a mantle source with variable input from the contemporary crust. All samples show subsequent zircon growth, or isotopic disturbance, due to Ediacaran–Cambrian metamorphism (∼535Ma). The sharply contrasting primary igneous U–Pb ages of orthogneisses identify two distinct terranes; an Archaean basement terrane to the north and west and a Proterozoic terrane dominated by metasedimentary rocks to the south and east of the Madurai Block. The isotopic boundary between the two is here defined as a broad zone south of the Karur–Kambam–Painavu–Trichur (KKPT) lineament and appears as a southerly dipping series of seismic reflectors. A correlation is made with central Madagascar where Proterozoic metsedimentary rocks are thrust over Neoarchaean orthogneisses of the Antananarivo Block. [Copyright &y& Elsevier]

Abstract: Southern Madagascar is the core of a >1million km2 Gondwanan metasedimentary belt that forms much of the southern East African Orogen of eastern Africa, Madagascar, southern India and Sri Lanka. Here the Vohibory Series yielded U–Pb isotopic data from detrital zircon cores that indicate that it was deposited in the latest Tonian to late Cryogenian (between ~900 and 640Ma). The deposition of the Graphite and Androyen Series protoliths is poorly constrained to between the late Palaeoproterozoic and the Cambrian (~1830–530Ma). The Vohibory Series protoliths were sourced from very restricted-aged sources with a maximum age range between 910 and 760Ma. The Androyen and Graphite Series protoliths were sourced from Palaeoproterozoic rocks ranging in age between 2300 and 1800Ma. The best evidence of the timing of metamorphism in the Vohibory Series is a weighted mean 206Pb/238U age of 642±8Ma from 3 analyses of zircon from sample M03-01. A considerably younger 206Pb/238U metamorphic age of 531±7Ma is produced from 10 analyses of zircon from sample M03-28 in the Androyen Series. This ~110Ma difference in age is correlated with the early East African Orogeny affecting the west of Madagascar along with its type area in East Africa, whereas the Cambrian Malagasy Orogeny affected the east of Madagascar and southern India during the final suturing of the Mozambique Ocean. [Copyright &y& Elsevier]

Abstract: The Ad Dawadimi Terrane is an Ediacaran basin of the Arabian Nubian Shield (ANS), Saudi Arabia. This basin terrane is situated in the far eastern part of the ANS and represents the youngest accretion event of the exposed ANS. Therefore, the timing of events within the basin is key to understanding both the closure of the Mozambique Ocean and the amalgamation of Gondwana along the northern East African Orogen. Here we present U/Pb detrital zircon data for the Abt Formation, the principle basin sediments of the Ad Dawadimi Terrane, along with 40Ar/39Ar ages on muscovite and whole rock Sm/Nd data. These data indicate that deep-water deposition in the Abt Basin did not end until after ca. 620Ma and that deformation and greenschist-facies metamorphism of the Abt Formation occurred at 620±3 (2σ) Ma along an active margin. This is the youngest terrane amalgamation event reported so far in the Arabian–Nubian Shield, but we suggest even younger sutures lie further east beneath the Phanerozoic cover of eastern Saudi Arabia. Our results suggest that the Ediacaran basins of the eastern ANS were not part of the Huqf basin in Oman, which was instead part of a passive margin of Neoproterozoic India, separated from the active margin of Africa by the Mozambique Ocean that probably did not close until the late Ediacaran or early Cambrian. [Copyright &y& Elsevier]

Abstract: The northern Madurai Block, southern India, lies directly south of, and partly deformed by, the Palghat–Cauvery Shear Zone System (PCSS) – a potential suture of the Neoproterozoic Mozambique Ocean. The Kadavur gabbro-anorthosite complex lies south of the PCSS, in the northern Madurai Block, and crystallized at 829±14Ma (LA-ICPMS zircon data) in a supra-subduction zone setting. The complex contains zircon ε Hf(t) values of −12.5 to −8.6 that represent Palaeoproterozoic T (DM) model ages (2.3–2.5Ga). These broadly agree with a whole rock neodymium T (DM) model age of 2287Ma. Oxygen isotope δ18O ratios range from 5.82‰ and 6.74‰. The parental magma for the gabbro-anorthosites are interpreted to be derived from a juvenile Neoproterozoic mantle contaminated by Mesoarchaean igneous infra-crustal sources. The gabbro-anorthosites intrude quartzites with dominantly Palaeoproterozoic detrital zircons that contain Neoarchaean and Mesoarchaean hafnium model ages. These quartzite zircons contain metamorphic rims that yield an age of 843±23Ma demonstrating the autochthonous nature of the gabbro-anorthosite complex. Later felsic magmatism is recorded by the 766±8Ma crystallisation age of the protolith of a felsic gneiss. Cryogenian magmatism in the Madurai Block is interpreted to form part of an extensive arc magmatic province within the southern East African Orogen that can be traced from central Madagascar, through southern India to the Wanni Complex of Sri Lanka. This province is interpreted to have formed above a south/west dipping subduction system as the Mozambique Ocean was subducted under the Neoproterozoic continent Azania. [Copyright &y& Elsevier]

Abstract: Understanding the relationship between accessory mineral growth and the evolution of silicate mineral assemblages along the entirety of a P-T-t path is a critical step in developing models for evolving tectonic systems. Here we combine U–Pb age data (for zircon and monazite), rare earth element (REE) data and compositionally specific phase diagrams (P-T pseudosections) for the rocks of the Palghat Cauvery shear system (PCSS), Southern Indian order to constrain the periodicity of heating/cooling and burial/exhumation events during the Ediacaran/Cambrian amalgamation of Gondwana. HREE data from zircon are consistent with zircon grow that 672–724°C during the breakdown of garnet in the kyanite stability field at 535.0±4.9Ma. This represents a cooling that punctuates the P-T-t path. Subsequent monazite growth and symplectite formation occurred at 920°C and 7.5kbar, ∼10Ma after zircon growth which reflects a period of reheating and decompression related to delamination and the collapse of the East African orogen. The REE chemistry of the monazite is consistent with the system having undergone partial melting prior to monazite growth, thereby altering the bulk rock chemistry. The periodicity of the heating and cooling cycles (∼10Ma) from this study is consistent with recently proposed tectonic switching models for the formation of granulite metamorphism in accretionary/collisional tectonic settings. The elevated heat flows required to generate the UHT metamorphism are achievable in the proposed back-arc setting for the PCSS during Gondwana amalgamation. [Copyright &y& Elsevier]

Abstract: In this paper, we present Sensitive High Resolution Ion Microprobe (SHRIMP) U and Pb isotope analyses of zircon from a charnockite and a charnockite-hosted leucosome in order to determine the age of magmatism and anatexis related to high-grade metamorphism immediately to the north of the Palghat Cauvery Shear System (PCSS), a proposed Neoproterozoic terrane boundary within Southern India. Weakly luminescent, oscillatory-zoned cores in I06–128 and analyses with high Th/U ratios in I06–129 yield weighted mean 207Pb–206Pb ages of 2538±6 Ma and 2529±7 Ma. These two ages are statistically indistinguishable and are interpreted to reflect the crystallisation age of the original magmatic protolith to the charnockite. Low Th, Th/U ratio and brightly luminescent overgrowths and complete zircon grains in I06–128 and I06–129 give weighted mean 207Pb–206Pb ages of 2473±8 Ma and 2482±15 Ma respectively. The two ages are statistically distinct and are interpreted to constrain the timing of post-crystallisation high-grade metamorphism and partial melting of the magmatic rocks that crystallised at ~2530 Ma. The new ages of the charnockites are consistent with the suggestion that this activity is related to accretionary processes on the margin of the Dharwar craton and may be related to a second stage of convergent tectonics and collision on the margin of Kenorland. There is no evidence of a pervasive Neoproterozoic high-grade metamorphic event associated with the amalgamation of Gondwana recorded in these rocks. However, the possibility that deformation was localised along discrete shear zones at this time cannot be discounted. The data from this study add weight to the hypothesis that the PCSS represents a Neoproterozoic suture zone along which the Dharwar Craton and the microcontinent Azania, with its constituent Madurai and Trivandrum Blocks in the Southern Granulite terrane, collided at ca. 530 Ma Ga during the closure of the Mozambique ocean. [Copyright &y& Elsevier]

Abstract: Southern India lies at a junction in the Gondwana-forming orogenic belts, between the East African Orogen and the Kuunga Orogen. It contains voluminous high-grade metasedimentary gneisses that make up an important component of the record of collision and amalgamation of Gondwana. Here we present U-Pb Secondary Ion Mass Spectrometry (SIMS) isotopic data from detrital zircon cores from throughout southern India that demonstrate dominant Neoarchaean to Palaeoproterozoic age components that are incompatible with the known ages of potential southern and central Indian source regions. The original sediments to the Trivandrum Block gneisses were deposited between ∼1900 and ∼515Ma, whereas a sample from the Achancovil Unit, and possible also a sample from the Madurai Block, were deposited in Neoproterozoic times. We speculate that these rocks broadly correlate with southern and western Malagasy metasedimentary rocks (including the Itremo and Molo Groups) and formed an extensive basin (or basins) that lay on the west side (present orientation) of the Neoproterozoic continent Azania. In addition, metamorphic zircon from four samples yielded an age of 513±6Ma that is interpreted as dating high-grade metamorphism throughout much of the Southern Granulite Terrane. [Copyright &y& Elsevier]

Abstract: Madagascar lay in an interesting position in Gondwana, straddling one of the largest orogens that formed as the supercontinent amalgamated. The Malagasy basement preserves a record of the timing and style of this amalgamation, and in addition contains much information as to the palaeogeography of the eastern Mozambique Ocean. Madagascar consists of a number of tectonic units that amalgamated in the Ediacaran–Cambrian. The tectonic units are: The Antongil Block; the Antananarivo Block; the Tsaratanana Sheet and the Bemarivo Belt. In addition to these, there are a number of regions dominated by Neoproterozoic metasedimentary rocks, including the Molo, Betsimisaraka, Vohibory and Androyen regions. In this review I outline these units, discuss their amalgamation history and implications for Neoproterozoic–Cambrian palaeogeography, and highlight a few key questions for future study. [Copyright &y& Elsevier]

The southern East African Orogen is a collisional belt where the identification of major suture zones has proved elusive. In this study, we apply U–Pb isotopic techniques to date detrital zircons from a key part of the East African Orogen, analyse their possible source region and discuss how this information can help in unravelling the orogen.U–Pb sensitive high-mass resolution ion microprobe (SHRIMP) and Pb evaporation analyses of detrital zircons from metasedimentary rocks in eastern Madagascar reveal that: (1) the protoliths of many of these rocks were deposited between ∼800 and 550 Ma; and (2) these rocks are sourced from regions with rocks that date back to over 3400 Ma, with dominant age populations of 3200–3000, ∼2650, ∼2500 and 800–700 Ma.The Dharwar Craton of southern India is a potential source region for these sediments, as here rocks date back to over 3400 Ma and include abundant gneissic rocks with protoliths older than 3000 Ma, sedimentary rocks deposited at 3000–2600 Ma and granitoids that crystallised at 2513–2552 Ma. The 800–700 Ma zircons could potentially be sourced from elsewhere in India or from the Antananarivo Block of central Madagascar in the latter stages of closure of the Mozambique Ocean. The region of East Africa adjacent to Madagascar in Gondwana reconstructions (the Tanzania craton) is rejected as a potential source as there are no known rocks here older than 3000 Ma, and no detrital grains in our samples sourced from Mesoproterozoic and early Neoproterozoic rocks that are common throughout central east Africa. In contrast, coeval sediments 200 km west, in the Itremo sheet of central Madagascar, have detrital zircon age profiles consistent with a central East African source, suggesting that two late Neoproterozoic provenance fronts pass through east Madagascar at approximately the position of the Betsimisaraka suture. These observations support an interpretation that the Betsimisaraka suture separates rocks that were derived from different locations within, or at the margins of, the Mozambique Ocean basin and therefore, that the suture is the site of subduction of a strand of Mozambique Ocean crust. [Copyright &y& Elsevier]

The 40Ar/39Ar age data on single detrital muscovite grains complement U-Pb zircon ages in provenance studies, as micas are mostly derived from proximal sources and record low-temperature processes. Ediacaran and Cambrian sedimentary rocks from northwest Iberia contain unmetamorphosed detrital micas whose 40Ar/39Ar age spectra suggest an Amazonian-Middle American provenance. The Ediacaran sample contained only Neoproterozoic micas (590-783 Ma), whereas the Cambrian sample contained three age groups: Neoproterozoic (550-640 Ma, Avalonian-Cadomian-Pan African), Mesoproterozoic-Neoproterozoic boundary (ca. 920-1060 Ma, Grenvillian-Sunsas), and late Paleoproterozoic (ca. 1580-1780 Ma, Rio Negro). Comparison of 40Ar/39Ar muscovite ages with published detrital zircon age data from the same formations supports the hypothesis that the Neoproterozoic basins of northwest Iberia were located in a peri-Amazonian realm, where the sedimentary input was dominated by local periarc sources. Tectonic slivering and strike-slip transport along the northern Gondwanan margin affected both the basins and fragments of basement that were transferred from Amazonian to northern African realms during the latest Neoproterozoic-earliest Cambrian. Exhumation and erosion of these basement sources caused shedding of detritus to the Cambrian basins, in addition to detritus sourced in the continental mainland. The apparent dominance of Rio Negro-aged micas in the Cambrian sandstone suggests the presence of unexposed basement of that age beneath the core of the Ibero-Armorican Arc. [ABSTRACT FROM AUTHOR]

Recent progress in plate tectonic reconstructions has seen models move beyond the classical idea of continental drift by attempting to reconstruct the full evolving configuration of tectonic plates and plate boundaries. A particular problem for the Neoproterozoic and Cambrian is that many existing interpretations of geological and palaeomagnetic data have remained disconnected from younger, better-constrained periods in Earth history. An important test of deep time reconstructions is therefore to demonstrate the continuous kinematic viability of tectonic motions across multiple supercontinent cycles. We present, for the first time, a continuous full-plate model spanning 1 Ga to the present-day, that includes a revised and improved model for the Neoproterozoic–Cambrian (1000–520 Ma) that connects with models of the Phanerozoic, thereby opening up pre-Gondwana times for quantitative analysis and further regional refinements. In this contribution, we first summarise methodological approaches to full-plate modelling and review the existing full-plate models in order to select appropriate models that produce a single continuous model. Our model is presented in a palaeomagnetic reference frame, with a newly-derived apparent polar wander path for Gondwana from 540 to 320 Ma, and a global apparent polar wander path from 320 to 0 Ma. We stress, though while we have used palaeomagnetic data when available, the model is also geologically constrained, based on preserved data from past-plate boundaries. This study is intended as a first step in the direction of a detailed and self-consistent tectonic reconstruction for the last billion years of Earth history, and our model files are released to facilitate community development. [ABSTRACT FROM AUTHOR]

Abstract The extent of continental rifts and subduction zones through deep geological time provides insights into the mechanisms behind supercontinent cycles and the long term evolution of the mantle. However, previous compilations have stopped short of mapping the locations of rifts and subduction zones continuously since the Neoproterozoic and within a self-consistent plate kinematic framework. Using recently published plate models with continuously closing boundaries for the Neoproterozoic and Phanerozoic, we estimate how rift and peri-continental subduction length vary from 1 Ga to present and test hypotheses pertaining to the supercontinent cycle and supercontinent breakup. We extract measures of continental perimeter-to-area ratio as a proxy for the existence of a supercontinent, where during times of supercontinent existence the perimeter-to-area ratio should be low, and during assembly and dispersal it should be high. The amalgamation of Gondwana is clearly represented by changes in the length of peri-continental subduction and the breakup of Rodinia and Pangea by changes in rift lengths. The assembly of Pangea is not clearly defined using plate boundary lengths, likely because its formation resulted from the collision of only two large continents. Instead the assembly of Gondwana (ca. 520 Ma) marks the most prominent change in arc length and perimeter-to-area ratio during the last billion years suggesting that Gondwana during the Early Palaeozoic could explicitly be considered part of a Phanerozoic supercontinent. Consequently, the traditional understanding of the supercontinent cycle, in terms of supercontinent existence for short periods of time before dispersal and re-accretion, may be inadequate to fully describe the cycle. Instead, either a two-stage supercontinent cycle could be a more appropriate concept, or alternatively the time period of 1 to 0 Ga has to be considered as being dominated by supercontinent existence, with brief periods of dispersal and amalgamation. Highlights • Compilation of rifting events in the Neoproterozoic • Analysis of continental arc, continental rift and connectedness of continental lithosphere for the last 1 Ga • Two stage supercontinent cycle may better explain changes in the connectedness of continental lithosphere • Extraversion and introversion models of successive supercontinents occur on different timescales [ABSTRACT FROM AUTHOR]

The Paraguay Belt in central South America developed in response to the collision between the Amazonian Craton, the Rio Apa Block, the São Francisco Craton and the Paranapanema Block and marks the final suture of western Gondwana. The traditional ‘Brasiliano’ age (∼620 Ma) of this belt has recently been questioned by evaluation of the geological record of sedimentation, deformation, metamorphism and magmatism, which indicate the closing stages of orogenesis occurred well into the Cambrian. Here we investigate the time of deposition and source areas for the metasedimentary rocks of the Jacadigo and Corumbá Groups overlying the Amazonian and Rio Apa cratons in the southern part of the Paraguay Belt. 1177 LA-ICPMS and 61 SHRIMP detrital zircon U-Pb ages were analysed from samples taken from both the basement and the sedimentary succession. A new maximum age constraint of 686 ± 10 Ma is presented for the Puga Formation to complement existing work in the region. The youngest ages from our samples are 566 ± 8 Ma and 543 ± 11 Ma. These maximum depositional ages indicate that final sedimentation began no earlier than 543 ± 11 Ma in the southern Paraguay Belt. Given that zircon inheritance in these rocks continues up until this age and that known Amazonian Craton ages are older than ∼950 Ma we discuss other potential sources for these sediments by integrating the U-Pb detrital zircon data with Hf isotopic data. Cumulative proportion analysis of our detrital U-Pb data set indicate a transition from a passive to a collisional setting. Our final conclusions are that sedimentation in the belt transitioned from a passive margin environment to a collisional setting, consistent with an ocean to the east of the present-day Amazonian Craton that did not close until the Cambrian. [ABSTRACT FROM AUTHOR]