East African Orogen Research Articles

Thick-skinned tectonics of the Achankovil Shear Zone, southern India, inferred from new deep seismic reflection image: Constraints on the East African Orogen

The East Gondwana was formed by the assembly of continental fragments, namely India, Madagascar, Sri Lanka, and Antarctica, with the evolution of 2000 km long East African Orogen around 550 Ma. Lack of knowledge on the subsurface structure of the orogen led to a wide range of evolutionary models. The present study attempts to resolve various models’ ambiguity by presenting new results of the first deep seismic reflection study across the Achankovil Shear Zone, Southern Granulite Terrain, India that was evolved during the East African Orogen. The seismic study is also the first of its kind among the east Gondwana fragments. The Common reflection surface stack images of the present study reveal hitherto unknown details along with a unique south-dipping reflection fabric extending from the surface to upper mantle depth. We interpret this fabric is formed due to subduction-accretion of Madurai and Trivandrum blocks during the East African Orogen and represents a suture zone. Two deep-seated shear zones, the Achankovil and Tenmalai were also developed at both ends of collision fabric with strike-slip characteristics. Orogenic collapse and post-orogenic extension are inferred from the subhorizontal lower-crustal reflection fabric, which is interpreted as an equilibrated younger Moho. The present study provided an opportunity to understand the formation and exhumation of granulites, which act as a window on the inaccessible lower continental crust. Gravity modelling is performed along the seismic profile. Integration of present results with the existing geological and geophysical data provided basic constraints on the structure and tectonics of east Gondwana fragments and the East African Orogen.

Four-dimensional thermal evolution of the East African Orogen: accessory phase petrochronology of crustal profiles through the Tanzanian Craton and Mozambique Belt, northeastern Tanzania

U–Pb petrochronology of deep crustal xenoliths and outcrops across northeastern Tanzania track the thermal evolution of the Mozambique Belt and Tanzanian Craton following the Neoproterozoic East African Orogeny (EAO) and subsequent Neogene rifting. At the craton margin, the upper–middle crust record thermal quiescence since the Archean (2.8–2.5 Ga zircon, rutile, and apatite in granite and amphibolite xenoliths). The lower crust of the craton documents thermal pulses associated with Neoarchean ultra-high temperature metamorphism (ca. 2.64 Ga, > 900 °C zircon), the EAO (600–500 Ma rutile), and fluid influx during rifting ( 650 °C (above Pb closure of rutile and apatite) at the time of eruption. Zoned titanite records growth during cooling of the lower crust at 550 Ma, followed by fluid influx during slow cooling and exhumation (0.1–1 °C/Myr after 450 Ma). Permissible lower-crustal temperatures for the craton and orogen suggest variable mantle heat flow through the crust and reflect differences in mantle lithosphere thickness rather than advective heating from rifting.

Petrogenesis of a rare Ediacaran tonalite–trondhjemite–granodiorite suite, Egypt, and implications for Neoproterozoic Gondwana assembly

AbstractMost tonalite–trondhjemite–granodiorite (TTG) suites are Archean–Palaeoproterozoic in age, but those of Neoproterozoic–Phanerozoic age are scarce. A rare Ediacaran high-Al TTG suite has been identified at the Fannani Igneous Complex (FIC) in the northern Arabian–Nubian Shield, which is essentially composed of amalgamated Neoproterozoic island-arc Pan-African composite terranes that contain several ophiolitic sutures. The FIC exhibits a wide range of SiO2, Al2O3, Sr and Zr, shows moderate rare earth element (REE) enrichment, and K, Ti, Nb, Y and heavy REE depletion. It is a subsolvus suite with clear orogenic affinities and strong arc-geochemical signatures. The precise U–Pb zircon thermal ionization mass spectrometry age obtained (607.4 ± 1.95 Ma) indicates oceanic subduction extended to late stages of the East African Orogeny. The FIC exhibits87Sr/86Sr compositions of 0.70346–0.71091 (Sr(i)ratio, 0.70284), and143Nd/144Nd of 0.51254–0.51270 (ϵNd(t) = +5.12 to +7.16), typical of modern oceanic-arc rocks (as Japan-arc basalts), and suggestive of mantle sources and island-arc settings. The FIC possesses low values of Yb (1.55 ppm), Nb (14 ppm) and Y (24 ppm), and high ratios of Sr/Y (27), Zr/Sm (46) and Nb/Ta (11.8), typical of magmas produced by anatexis of a basaltic slab. Partial melting models show that the FIC magma was generated by melting (F= 0.25–0.50) of a subducted oceanic crust transformed into eclogite, leaving 10–25% garnet in the residue. The FIC and similar complexes produced via slab melting during the closure of the Mozambique Ocean formed large juvenile belts along the East African Orogen that sutured East and West Gondwana together into a united supercontinent.

Post–east African Orogen dilation and magmatism: development of a conjugate-style of dolerite dike swarm in the northwestern Arabian shield

The Al Madinah area bimodal dike swarms underwent detailed field mapping, measurements of dikes’ attitudes, structural analyses, remote sensing data interpretation, and petrology study. The oldest rock unit is a greenish intermediate dioritic unit that varies in its petrologic composition between microdiorite and andesite porphyry which is intruded by alkali granite. The dioritic and alkali granite units have been cut by intermediate to mafic dikes, ranging in texture and composition from micromonzodiorite and micromonzonite to microgabbro, microdolerite, and basalt or basaltic andesite, as revealed by thin-section work. A stereographic projection and rose diagrams of the mafic dikes formed a regional conjugate dike system, following probably a typical andersonian style, consisting of three major sets, namely, the WNW set which trends between N295 and N330, E-W set between N265 and N270, and finally the ENE (N065) set. The WNW set has its own local system, but it is considered as a set in the overall regional conjugate dike system. The WNW and E-W sets are the conjugate pair of the WNW Najd fault system maximum horizontal shearing, where the ENE set reflects the minimum regional horizontal shearing stress of the Najd system. The interpretation of this dike system is a WNW-ESE sinistral faulting and NE-SW dilation that formed Wadi Al-Hamd Ediacaran continental basin, bounded by two Najd faults and Thurwah-Bir Um suture. The study area underwent final thrust faulting that tilted the dikes towards the east. For the consequent magmatisms during the Neoproterozoic period, followed by Cenozoic volcanism, the Al Madinah area is considered a large igneous province.

Detrital zircon provenance of north Gondwana Palaeozoic sandstones from Saudi Arabia

AbstractWe present the first comprehensive detrital zircon U–Pb age dataset from Palaeozoic sandstones of Saudi Arabia, which provides new insights into the erosion history of the East African Orogen and sediment recycling in northern Gondwana. Five main age populations are present in varying amounts in the zircon age spectra, with age peaks at 625 Ma, 775 Ma, 980 Ma, 1840 Ma and 2480 Ma. Mainly igneous rocks of the Arabian–Nubian Shield are suggested to be the most prominent sources for the Ediacaran to middle Tonian zircon grains. Palaeoproterozoic and Archaean grains may be xenocrystic zircons or they have been recycled from older terrigenous sediment. A primary derivation from Palaeoproterozoic and Archaean basement is also possible, as rocks of such age occur in the vicinity. Approximately 4 % of the detrital zircons show Palaeozoic (340–541 Ma) ages. These grains are likely derived from Palaeozoic post-orogenic and anorogenic igneous rocks of NE Africa and Arabia. A few single grains gave up to Eoarchaean (3.6–4.0 Ga) ages, which are the oldest zircons yet described from Arabia and its vicinity. Their origin, however, is yet unknown. Detrital zircons with U–Pb ages of 1.0 Ga are present in varying amounts in all of the samples and are a feature of terrigenous sediment belonging to the Gondwana super-fan system with an East African – Arabian zircon province.

Cadomian (ca. 550 Ma) magmatic and thermal imprint on the North Arabian-Nubian Shield (south and central Israel): New age and isotopic constraints

The Arabian-Nubian Shield (ANS) is a province of mostly juvenile Neoproterozoic continental crust in NE Africa and Arabia, forming the northern extension of the East-African orogen. Subsequent to widespread, mostly late- to post-orogenic early-Ediacaran calc-alkaline granitoid emplacement, the latest magmatic phase in the ANS saw the intrusion of alkaline shallow plutons alongside volcanic massifs and dikes of variable compositions. While some of these intrusions were dated to 550–530 Ma by Rb-Sr and Ar-Ar, U-Pb zircon data has mostly limited ANS magmatism to no younger than ca. 580 Ma. Here we report new age and isotopic data from latest Neoproterozoic intrusions along a N-S transect within the northern ANS and its periphery, substantiating the record of a ca. 550 Ma igneous-thermal event in the area. In the northern Negev of Israel, mafic igneous rocks intruded into the subsurface late Neoproterozoic clastic wedge of the Zenifim Formation produced apatite U-Pb isochron ages between 557 and 545 Ma. In the Amram alkaline massif, 150 km to the south, an alkali-granite was dated to 605 ± 2.5 Ma by zircon U-Pb, but apatite U-Pb ages from all rocks of the massif concentrate at ca. 550 Ma indicating thermal resetting. Apatites from the zircon dated 611 ± 5 Ma Roded quartz diorite in the Elat area, south of Amram, produced a 600 ± 4 Ma U-Pb age, demonstrating that southern segments were not thermally reset at ca. 550 Ma. Nd isotopes in apatite and whole rock show the ca. 550 Ma igneous rocks to be variable in their isotopic composition, ranging between εNd(t)=(-4) – (+2), far less juvenile than typical ANS magmas. The ca. 550 Ma intrusions resemble in their age and isotopic properties Cadomian granites and volcanic rocks that are known from southern Turkey, Iran and Europe. We interpret the ca. 550 Ma igneous overprint and thermal resetting documented in the northernmost ANS as related to the superposition of Cadomian orogeny on the ANS periphery. This can be related to the late Ediacaran subduction of proto-Tethys accompanying the accretion of the Cadomian basement of the Tauride block to NE Africa and Arabia, before the area was overstepped by Cambrian platform sedimentation.

Spatial analysis and GIS mapping of regional hotspots and potential health risk of fluoride concentrations in groundwater of northern Tanzania

Safe drinking water supply systems in naturally contaminated hydrogeological environments require precise geoinformation on contamination hotspots. Spatial statistical methods and GIS were used to study fluoride occurrence in groundwater and identify significant spatial patterns using fluoride concentrations. The global and local Morans I indices were used. While the significant positive global Morans I index indicated spatial structure in fluoride occurrence, the significant spatial clusters were identified using local Morans I index and mapped at p-value of 0.05. The spatial clusters demonstrated patterns of drinking water sources with fluoride concentrations below or above WHO guideline and Tanzania standard for drinking water and were considered as ‘regional fluoride cool spots’ and ‘regional fluoride contamination hotspots’, respectively. Two regional fluoride contamination hotspots were identified and mapped around the Stratovolcano Mountains in the north-east and south-west of the study area; and along the Neogene Quaternary volcanic formations and Palaeo-Neoproterozoic East African Orogen (Mozambique Belt). The two largest regional fluoride cool spots dominated the major and minor rift escarpments in the west and east of the study area respectively while the small ones emerged around the volcanic mountains in the north and south. Furthermore, significant spatial outliers emerged at the boundary of regional fluoride hotspots and cool spots as an indication of the spatial processes controlling the mobilization of fluoride in groundwater. While all water sources in the cool spots had fluoride concentrations below 1.5 mg/L, some had extremely low concentrations below 0.5 mg/L which is not safe for human consumption. For hotspots, 96% of water sources had fluoride concentrations above 1.5 mg/L. The probability of having safe source of drinking water varied from one geological unit to another with sources in the Neogene Quaternary volcanic formations having least probabilities.

40Ar/39Ar and U-Pb SIMS zircon ages of Ediacaran dikes from the Arabian-Nubian Shield of south Jordan

A spectacular feature of the Arabian-Nubian Shield (ANS) is the abundance of well-exposed and extensive Neoproterozoic dike swarms of variable compositions. Most of these dikes are late to post-orogenic with respect to the East African Orogen (EAO) and are unmetamorphosed. We dated a composite dike with latite margins and a rhyolite core (607 ± 6 Ma, U-Pb), a biotite rhyolite dike (600 ± 4 Ma, 40Ar/39Ar age of biotite), an andesite dike (594 ± 3, 40Ar/39Ar age of amphibole) and a dolerite dike (~579 Ma, 40Ar/39Ar whole rock total gas age). We propose that the first three dikes represent one generation that was emplaced at different episodes extending between 607 and 590 Ma. Time and composition equivalent dikes are common in the northern ANS. The dikes crosscut late collisional granitoids and geochemically display a subduction-related character as evidenced by a negative Nb-Ta anomaly. These dikes are absent in the alkali feldspar A-type Humrat Syenogranite dated at 586 ± 5 Ma in Jordan and equivalent rocks in the northern ANS, which are crosscut only by the (~579 Ma) dolerite dikes. The within-plate character of the dolerite dikes is supported by the absence of the Nb-Ta anomaly and high field strength element geochemistry. We propose that the dolerite dikes are a generation, distinct from the ~607–590 Ma dikes, that reflects a change in tectonic regime and represents the last magmatic activity of the Neoproterozoic in the northern ANS. The ages of the dikes dated in this study agree with the published age range of the transitional stage from late orogenic calc-alkaline to extensional alkaline tectono-magmatic setting for the ANS. We propose that the magmatic activity was terminated ~50 m.y. before the age of the Cambrian unconformity at ~530 Ma. Correlation with ages of dikes and magmatic rocks in the northern ANS favors this supposition. The dike geochemistry and geochronology are compatible with a tectonic model that involves mantle lithosphere delamination from below the northern ANS after a significant crust-mantle thickening caused by the EAO, followed by thermal relaxation, subsidence and gradual denudation until the age of the unconformity at ~530 Ma.

Structural evolution and medium-temperature thermochronology of central Madagascar: implications for Gondwana amalgamation

Madagascar occupied an important place in the amalgamation of Gondwana and preserves a record of several Neoproterozoic events that are linked to orogenesis of the East African Orogen. In this study, we integrate remote sensing, field data and thermochronology to unravel complex deformation in the Ikalamavony and Itremo domains of central Madagascar. The deformation sequence comprises a gneissic foliation (S 1 ), followed by south- to SW-directed, tight to isoclinal, recumbent folding (D 2 ). These are overprinted by north-trending upright folds that formed during an approximately east–west shortening event (D 3 ). Together these produced type 1 and type 2 fold interference patterns throughout the Itremo and Ikalamavony domains. We show that the Itremo and Ikalamavony domains were deformed together in the same orogenic system, which we interpret as the c . 630 Ma collision of Azania with Africa along the Vohibory Suture in southwestern Madagascar. In eastern Madagascar, deformation is syn- to post-550 Ma, and probably formed in response to final closure of the Mozambique Ocean along the Betsimisaraka Suture that amalgamated Madagascar with the Dharwar Craton of India. Apatite U–Pb and novel laser ablation triple quadrupole inductively coupled plasma mass spectrometry (LA-QQQ-ICP-MS) muscovite and biotite Rb–Sr thermochronology indicates that much of central Madagascar cooled through c . 500°C at c . 500 Ma. Supplementary material: A detailed geological map of central Madagascar (Supplementary A), detailed methods and geo- and thermochronology results (Supplementary B), isotopic data for geo- and thermochronology (Supplementary C) and Landsat images and structural interpretation examples (Supplementary D) are available at https://doi.org/10.6084/m9.figshare.c.4840575

Evolution of the Western Ethiopian Shield revealed through U-Pb geochronology, petrogenesis, and geochemistry of syn- and post-tectonic intrusive rocks

Ethiopian basement formed between 850 and 450 Ma during the East African Orogen and represents the junction of the two distinct basement types found in Africa and Saudi Arabia: the low-grade Arabian-Nubian Shield and the high-grade Mozambique Belt. While many other localities along the East African Orogenic belt are well studied and despite the huge potential insight it could grant to the orogen’s evolution, Ethiopian Basement is poorly understood. This study aims to understand the tectonic evolution of the East African Orogen in Ethiopia through the examination of the age, origin, and evolution of previously unmapped syn- and post-tectonic plutons intruded into the Western Ethiopian Shield’s eastern edge. Dabana granite pluton crystallization ages were determined through U-Pb geochronological dating, and structural history was revealed through field mapping and thin section petrographic analysis. Whole rock elemental composition was determined through XRF (X-ray fluorescence) and ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry) methods to investigate petrogenesis and chemical evolution of the plutonic rocks. Results indicate this pluton formed during three intrusive periods under distinct tectonic domains that represent an evolving convergent margin. The oldest granite dates to 797.6 Ma and is associated with hydrous melting during volcanic arc subduction, followed by post-subduction related anhydrous magmatism at 774.6 Ma. The youngest granites date to 635–639 Ma and are evidence of late-stage crustal thickening in the final stage of collision. Two metamorphic episodes are recorded in the structure and petrography, which formed gneiss during high-grade metamorphism at 775.22 Ma and low-grade deformation around 630 Ma. This study presents the first geochronological and geochemical data from plutonic rocks in the study area, and grants valuable insight into the dynamics and evolution of the East African Orogen in Ethiopia.

Neoproterozoic tectonic evolution and exhumation history of transpressional shear zones in the East African orogen: implications from kinematic analysis of Meatiq area, Central Eastern Desert of Egypt

The origin, structural history, and tectonic evolution of core complexes and associated shear zones in the East African orogen are fundamental issues in the recent geological studies. Meatiq dome is one of the best exposed complexes in the Arabian–Nubian shield. The dome is occupied by metamorphic rocks with amphibolite-facies grade, tectonites, and deformed granites which are structurally overlaid by low-grade metamorphosed ophiolitic and island-arc rock assemblage. This tectonic pile is intruded by several granite intrusions through their evolution history. Microstructural, strain, and vorticity data from deformed tectonites were used to investigate the kinematics of rock flow in the Meatiq and Atalla shear zones and to reconstruct their deformation and exhumation history. The strain and vorticity analyses of Atalla shear zone (ASZ) indicate that this zone experienced general shear transpression with a monoclinic symmetry. The mean vorticity number (Wm) estimated with the porphyroclast-based methods ranges from 0.65 to 0.72 which indicate a high pure shear contribution in the shear zone. The numerical estimates allow the kinematic modelling of ASZ which introduces valuable implication about the tectonic framework of the Central Eastern Desert during the collision of East and West Gondwana. The results of satellite image interpretation and structural analysis of Meatiq area reveal a poly-deformational structural history including five stages of deformation during the successive convergence and collision of East and West Gondwana continents at around 600 Ma. The first stage is represented by compressional structures and high-grade metamorphism in the amphibolite enclaves preserved in Um Baanib granite. The reconstructed structural history of the shear zones started with the second structural stage. It involves the initiation of Meatiq shear zone and associated ductile structures and fabrics. The third stage was related to the final oblique convergence and collision of East and West Gondwana and represented by the NW–SE thrust faults, NW–SE folds, and the initiation of Atalla shear zone. The fourth and fifth stages were evolved after the crustal thickening. They involve the initiation of the strike-slip faults and the NW–SE extensional structures. The tectonic and regional implications of the structural and kinematic analysis were discussed.

Wandering continents of the Indian Ocean

Wandering continents of the Indian Ocean

Emplacement and thermal effect of post-collisional Chewo Pluton (Arabian-Nubian Shield); implication for late East-African Orogeny

The Chewo pluton built by pyroxene-amphibole to amphibole-biotite monzodiorite and quartz monzonite is a typical post-collisional intrusive body emplaced into a low-grade Neoproterozoic Tambien Group belonging to the Tokar-Barka Terrane in the southern Arabian–Nubian Shield. The pluton shows a high-K calc-alkaline and metaluminous composition with significant enrichment in both LREE and LILE due to hybridization and magma mixing between crustal and mantle-derived melts. Estimated P-T conditions of quartz monzonite magma solidification at T: 703 ± 23 °C and P: 0.32 ± 0.08 GPa and thermal overprint in the pluton aureole at T: ̴200–755 °C and P: 0.28 ± 0.06 GPa indicate that the Chewo pluton intruded at a depth of between ca. 10–13 km. The Chewo Pluton was emplaced diapirically, which was driven by a local extension in the hinge of the large-scale asymmetric syncline during the last increments of regional deformation – orogen-perpendicular WNW(NW)-ESE(SE) compression. It indicates that the regional WNW(NW)-ESE(SE) shortening is the main geodynamic event of the East African Orogen in the upper-crustal Tokar-Barka Terrane resulting in the assembly of the eastern and western Gondwana continents. In concordance, the zircon U/Pb age of the Chewo pluton (618.1 ± 1.5 Ma) provides the upper limit for the regional deformation.

Provenance of Ordovician–Silurian and Carboniferous–Permian glaciogenic successions in Ethiopia revealed by detrital zircon U–Pb geochronology

Paleozoic sedimentary successions in northern Ethiopia contain evidence for two Gondwana glaciations during the Late Ordovician and Carboniferous–Permian. We compare the sediments of the two glaciations with respect to their detrital zircon U–Pb ages. The main age group for both formations is Pan-African ( c . 700–550 Ma). However, the remaining spectra are different. The Upper Ordovician–Lower Silurian Enticho Sandstone is characterized by a Stenian–Tonian ( c. 1 Ga) zircon population. The Carboniferous–Permian Edaga Arbi Glacials contain a prominent c. 800 Ma population. The Stenian–Tonian zircons are probably derived from the centre of the East African Orogen and were supplied via the Gondwana super-fan system. This material was transported by the Late Ordovician glaciers and formed the Enticho Sandstone. Tonian ( c. 800 Ma) zircons are abundant in the Ethiopian basement and represent the earliest formation stage of the southern Arabian–Nubian Shield. Glaciers of the Late Paleozoic Ice Age must have cut deeply into the basement for efficient erosion. No recycling of the Enticho Sandstone by the Edaga Arbi Glacials took place on a grand scale, probably because the sedimentation of the former was limited to northern Ethiopia, whereas the source area for the latter was to the south. Supplementary material: Laser ablation ICP-MS operation parameters and results are available at https://doi.org/10.6084/m9.figshare.c.4605548

Stenian A-type granitoids in the Namaqua-Natal Belt, southern Africa, Maud Belt, Antarctica and Nampula Terrane, Mozambique: Rodinia and Gondwana amalgamation implications

We carried out SHRIMP zircon U-Pb dating on A-type granitic intrusions from the Namaqua-Natal Province, South Africa, Sverdrupfjella, western Dronning Maud Land, Antarctica and the Nampula Province of northern Mozambique. Zircon grains in these granitic rocks are typically elongated and oscillatory zoned, suggesting magmatic origins. Zircons from the granitoid intrusions analyzed in this study suggest ∼1025–1100 Ma ages, which confirm widespread Mesoproterozoic A-type granitic magmatism in the Namaqua-Natal (South Africa), Maud (Antarctica) and Mozambique metamorphic terrains. No older inherited (e.g., ∼2500 Ma Achean basement or ∼1200 Ma island arc magmatism in northern Natal) zircon grains were seen. Four plutons from the Natal Belt (Mvoti Pluton, Glendale Pluton, Kwalembe Pluton, Ntimbankulu Pluton) display 1050–1040 Ma ages, whereas the Nthlimbitwa Pluton in northern Natal indicates older 1090–1080 Ma ages. A sample from Sverdrupfjella, Antarctica has ∼1091 Ma old zircons along with ∼530 Ma metamorphic rims. Similarly, four samples analysed from the Nampula Province of Mozambique suggest crystallization ages of ∼1060–1090 Ma but also show significant discordance with two samples showing younger ∼550 Ma overgrowths. None of the Natal samples show any younger overgrowths. A single sample from southwestern Namaqualand yielded an age of ∼1033 Ma.Currently available chronological data suggest magmatism took place in the Namaqua-Natal-Maud-Mozambique (NNMM) belt between ∼1025 Ma and ∼1100 Ma with two broad phases between ∼1060–1020 Ma and 1100–1070 Ma respectively, with peaks at between ∼1030–1040 Ma and ∼1070–1090 Ma. The age data from the granitic intrusions from Namaqualand, combined with those from Natal, Antarctica and Mozambique suggest a crude spatial-age relationship with the older >1070 Ma ages being largely restricted close to the eastern and western margins of the Kalahari Craton in northern Natal, Mozambique, Namaqualand and WDML Antarctica whereas the younger <1060 Ma ages dominate in southern Natal and western Namaqualand and are largely restricted to the southern and possibly the western margins of the Kalahari Craton. The older ages of magmatism partially overlap with or are marginally younger than the intracratonic Mkondo Large Igneous Province intruded into or extruded onto the Kalahari Craton, suggesting a tectonic relationship with the Maud Belt. Similar ages from granitic augen gneisses in Sri Lanka suggest a continuous belt stretching from Namaqualand to Sri Lanka in a reconstituted Gondwana, formed during the terminal stages of amalgamation of Rodinia and predating the East African Orogen. This contiguity contributes to defining the extent of Rodinia-age crustal blocks, subsequently fragmented by the dispersal of Rodinia and Gondwana.

The timing of migmatization in the northern Arabian–Nubian Shield: Evidence for a juvenile sedimentary component in collision‐related batholiths

AbstractCollision‐related granitoid batholiths, like those of the Hercynian and Himalayan orogens, are mostly fed by magma derived from metasedimentary sources. However, in the late Neoproterozoic calcalkaline (CA) batholiths of the Arabian–Nubian Shield (ANS), which constitutes the northern half of the East African orogen, any sedimentary contribution is obscured by the juvenile character of the crust and the scarcity of migmatites. Here, we use paired in situ LASS‐ICP‐MS measurements of U–Th–Pb isotope ratios and REE contents of monazite and xenotime and SHRIMP‐RG analyses of separated zircon to demonstrate direct linkage between migmatites and granites in the northernmost ANS. Our results indicate a single prolonged period of monazite growth at 640–600 Ma, in metapelites, migmatites and peraluminous granites of three metamorphic suites: Abu‐Barqa (SW Jordan), Roded (S Israel) and Taba–Nuweiba (Sinai, Egypt). The distribution of monazite dates and age zoning in single monazite grains in migmatites suggest that peak thermal conditions, involving partial melting, prevailed for c. 10 Ma, from 620 to 610 Ma. REE abundances in monazite are well correlated with age, recording garnet growth and garnet breakdown in association with the prograde and retrograde stages of the melting reactions, respectively. Xenotime dates cluster at 600–580 Ma, recording retrogression to greenschist facies conditions as garnet continued to destabilize. Phase equilibrium modelling and mineral thermobarometry yield P–T conditions of ~650–680°C and 5–7 kbar, consistent with either water‐fluxed or muscovite‐breakdown melting. The expected melt production is 8–10 vol.%, allowing a melt connectivity network to form leading to melt segregation and extraction. U–Pb ages of zircon rims from leucosomes indicate crystallization of melt at 610 ± 10 Ma, coinciding with the emplacement of a vast volume of CA granites throughout the northern ANS, which were previously considered post‐collisional. Similar monazite ages (c. 620 Ma) retrieved from the amphibolite facies Elat schist indicate that migmatites are the result of widespread regional rather than local contact metamorphism, representing the climax of the East African orogenesis.

Late Cryogenian magmatic activity in the North Lhasa terrane, Tibet: Implication of slab break-off process

The North Lhasa terrane in Tibet is generally interpreted to be paleotectonically unrelated to the East African Orogen (EAO) and is instead thought to have derived from northeastern India or northwestern Australia. In this study, we present petrogenetic and geochronological results pertaining to the analysis of gabbros (ca. 652 Ma), diorites (ca. 658 and 646 Ma), and tonalites (ca. 652 Ma) from the North Lhasa terrane. The gabbros are calc-alkaline and exhibit arc-like geochemical features. Low positive zircon εHf(t) values (+1.0 to +3.8), high zircon δ18O (6.25‰ to 7.94‰), and low negative whole-rock εNd(t) values (−3.5 to −1.4) indicate that the gabbros were derived from the lithospheric mantle, with geochemical modification by a subduction component. The diorite suite is characterized by a wide range of whole-rock chemistries (e.g., SiO2 = 51.33–61.98 wt%) and Hf–O–Sr isotopic compositions (εHf(t) = −10.8 to −0.1; δ18O = 5.17‰ to 7.11‰; ISr = 0.706 to 0.710), and negative whole-rock εNd(t) values (−7.0 to −4.7). These diorites are geochemically similar to OIB and are interpreted to be products of the partial melting of a relatively deep mantle source (>85 km) prior to extensive modification by continental crustal material. The tonalites are adakitic and have moderate Mg# values (47–54), low compatible element abundances, positive zircon εHf(t) values (+3.4 to +6.2), high ISr values (0.714 to 0.715), and small negative whole-rock εNd(t) values (−1.6 to −0.4). These tonalites most likely formed by the melting of thickened Mesoproterozoic continental crust. The generation of these ca. 650 Ma magmatic rocks was related to slab break-off in a collision zone. By integrating the findings of previous studies with the data of the present study, we suggest that the North Lhasa terrane was most likely located in the northern segment of the EAO in paleotectonic reconstructions of the Gondwana supercontinent.

High-grade metamorphism during Neoproterozoic to Early Palaeozoic Gondwana assembly, exemplified from the East African Orogen of northeastern Mozambique

Northeastern Mozambique exposes a deeply eroded high-grade segment of the East African Orogen, situated at the critical intersection of the Pan-African orogenic belts, showing widespread granulite facies lithologies. This study documents and characterizes metamorphism attributed to the multistage Neoproterozoic and Early Palaeozoic events, relating to a polyphase Pan-African history of outboard nappe stacking, nappe emplacement onto Mesoproterozoic crust, and compressional and extensional deformation along the Lurio belt: 1) A Neoproterozoic nappe stack (Cabo Delgado Nappe Complex) records high-pressure granulite facies: The highest peak conditions reach P = 1.45 GPa and T > 800 °C are in Grt-Cpx-Pl-bearing mafic granulites of the Xixano Complex. A post-peak isothermal decompressional P-T evolution is supported by garnet chemical zoning pattern, pseudsection modelling and garnet corona textures. 2) The underlying Mesoproterozoic gneiss complexes record amphibolite facies to intermediate-pressure granulite facies, the high-grade metamorphism is documented by Grt-Opx-Cpx-Pl-bearing mafic granulites and charnockitic gneisses in the southern part of the Unango and Marrupa complexes. This metamorphism is attributed to crustal thickening related to overriding of the nappe complex and shortening along the Lurio belt during the early Palaeozoic Kuunga orogeny. 3) The Ocua Complex coring the Lurio belt is a locus of Early Palaeozoic high-pressure metamorphism. A minimum of P = 0.79 ± 0.13 GPa at T = 760 ± 98 °C is constrained by Grt-Opx-Cpx-Pl-Qz assemblage in mafic granulite from the western limb while high-pressure granulite metamorphism was reached in the eastern part of the complex. The high-pressure granulite facies conditions is followed by isothermal decompression.

Geochronological systematics for the Chimoio-Macossa frontal nappe in central Mozambique: Implications for the tectonic evolution of the southern part of the Mozambique belt

This work aims to acquire a better understanding of the tectonic evolution of the Mozambique Belt, for the region located in the central-western part of Mozambique that corresponds to the southernmost part of the East African Orogen, in Africa. The main objective was to make a robust geochronological study, by means of a series of U-Pb zircon ages, in order to establish some precise magmatic crystallization and/or metamorphic recrystallization ages, as well as to estimate provenance and maximum ages for meta-sedimentary units. Limited zircon Lu-Hf analyses and some Sm-Nd ages on metamorphic garnets were also obtained.Two large nappes, Macossa-Chimoio and Mungari, are envisaged in the study area, tectonically juxtaposed to the Zimbabwe Craton. The Macossa-Chimoio nappe comprises the high-grade paragneisses, granulites and migmatites characteristic of the Macossa and Chimoio Groups, which occur in close association with the pre-existent mesoproterozoic granitic rocks of the Báruè Complex. The metamorphic P-T conditions, estimated between 4 and 6 kb and 700–800 °C, and the tectonic unit was exhumed at different crustal levels. A few granitoids of the Báruè Complex yielded mesoproterozoic U-Pb zircon cristallyzation ages near 1100 M, but detrital zircons of some paragneisses yielded neoproterozoic maximum ages of deposition of 700–800 Ma. In addition, the main age of the very young cambrian metamorphism event was set by means of U-Pb dating of zircon overgrowths and Sm-Nd garnet-whole rock isochron at 500 Ma.The boundary between the Macossa-Chimoio and Mungari nappes is a thrust zone with a NW trending tectonic transport. It disappears to the NE below a Karoo sedimentary cover, but most likely reappears at the NE side of the basin as a prolongation of a long-lived tectonic boundary, the Lurio mega-shear belt of northeastern Mozambique which separates the Nampula tectonic block in the south from a northern block comprising the Marrupa and Unango complexes. Therefore, the Macossa-Chimoio Nappe would correlate closely with the Nampula Block, which includes mesoproterozóic orthogneisses with about 1100 Ma age, reactivated in the Cambrian.On the light of the U-Pb ages of overgrowth rims on zircon crystals and corroborative Sm-Nd isochron ages, the southern end of the Mozambique Belt in Africa was affected by a strong orogenic episode in the Cambrian. This confirms that the amalgamation of Gondwana was diachronous along the EAO, starting earlier in the north and cease later in the south. In the south, the orogenic event was coeval to the Kuunga Orogeny between Australia and Antarctica, usually constrained between 530 and 490 Ma.

Early Neoproterozoic (ca. 900 Ma) rift sedimentation and mafic magmatism in the North Lhasa Terrane, Tibet: Paleogeographic and tectonic implications

The origin and evolution of the Precambrian North Lhasa Terrane in the central Tibetan Plateau remain enigmatic. Here we present UPb age and Hf isotopic data for detrital zircons from early Neoproterozoic quartzites in the North Lhasa Terrane, Tibet. An integrated petrological, geochronological, geochemical, and Sr–Nd–Hf isotopic study was also undertaken on amphibolites associated with the quartzites. The depositional age of the quartzites is constrained to be between ca. 931 Ma (youngest detrital igneous zircon core) and 869 Ma (oldest metamorphic zircon rim). The detrital zircons have a main age population from 1200 to 1000 Ma, and lack zircons with ages of 1000–900 Ma. Zircons from the amphibolites yield concordant ages of ca. 913–902 Ma, which are comparable to the depositional age of the quartzites. The amphibolites have N-MORB-like compositions and are characterized by high positive zircon εHf(t) (+7.2 to +14.0) and whole-rock εNd(t) (+5.5 to +6.0) values. Their compositions have been modified by crustal contamination. The formation of these quartzites and amphibolites was related to an early Neoproterozoic rift adjacent to the African side of the northern East African Orogen, followed by opening of part of the Mozambique Ocean.